ALBERT

Notes: We have studied the stomatal response in relation to the xylem-derived abscisic acid (ABA) accumulation in sunflower leaves. When ABA was introduced into detached leaves of the sunflower through xylem flux, stomatal conductance was regulated, water flux was changed as a result and at the same time the xylem-derived ABA was metabolised in the leaves. We computed the xylem-derived ABA accumulation in the leaves as a function of time by taking into account the variation of ABA flux into the leaves (the product of water flux and ABA concentration) and a continuing ABA metabolism. We found that ABA accumulation was rapid during an initial lag phase, much slowed down during the decreasing phase of stomatal conductance, but still substantial when stomatal conductance reached a new stable state. The results show a poor link between the kinetics of ABA-induced stomatal closure and the xylem-derived ABA accumulation. Xylem-derived ABA was metabolised rapidly in the leaves. Tetcyclacis, as an inhibitor, substantially inhibited this process. Two hours after ABA was fed into a leaf, about 70% of the fed ABA was metabolised, but when tetcyclacis was added into the feeding solution, less than 30% of ABA was metabolised, even after 24 h of incubation. The inhibition of ABA metabolism by tetcyclacis did not lead to more stomatal closure, which was still concentration-dependent. Since the accumulation of xylem-derived ABA was enhanced substantially by the presence of tetcyclacis, these results strongly indicate that stomata mainly respond to the prevailing ABA concentration in the xylem stream, rather than to the accumulated amount of xylem-derived ABA in the leaves.

Notes: Enzymatic digestion of the cell wall of Brassica napus hypocotyls gave a heterogeneous suspension of protoplasts with the cortical microtubules (CMTs) randomly organised or CMTs organised in parallel. The effect of variable g-influences has been tested on CMT organisation. In contrast to the 1 g-protoplasts, which reorganised the CMTs into parallel arrays during the 96 h test period, the frequency of randomly-oriented CMTs in the protoplasts exposed to simulated weightlessness (0 g) on a 2-D clinostat increased significantly during the same period. The opposite effect was obtained when the protoplasts were exposed to hyper-g (7 or 10 g), where the reorganisation of the CMTs into parallel arrays was accelerated compared to the 1 and 0 g-protoplasts. These results indicate that a unidirectional gravity force is a necessity for the reorganisation of CMTs in protoplasts to parallel arrays and that CMTs act as responding elements that are able to sense different levels of gravity. Besides the inability of the protoplasts to reorganise the CMTs into parallel arrays, the quantity of CMTs in the individual protoplast decreased during 4 days of simulated weightlessness, both compared to the CMTs quantity in the protoplasts immediately after isolation and compared to the 1 g- and hyper-g-protoplasts after 24 and 48 h of g-exposure. The size of the protoplasts was also affected by the g-exposure. Protoplasts exposed to simulated 0 g increased significantly after 24 and 48 h, whereas the 1 g- and 10 g-protoplasts maintained the same size during the 48 h test period.

Notes: The role of mitochondrial respiration in optimizing photosynthesis was assessed in mesophyll protoplasts of pea (Pisum sativum L., cv. Arkel) by using low concentrations of oligomycin (an inhibitor of oxidative phosphorylation), antimycin A (inhibits cytochrome pathway of electron transport) and salicylhydroxamic acid (SHAM, an inhibitor of alternative oxidase). All three compounds decreased the rate of photosynthetic O2 evolution in mesophyll protoplasts, but did not affect chloroplast photosynthesis. The inhibition of photosynthesis by these mitochondrial inhibitors was stronger at optimal CO2 (1.0 mM NaHCO3) than that at limiting CO2 (0.1 mM NaHCO3). We conclude that mitochondrial metabolism through both cytochrome and alternative pathways is essential for optimizing photosynthesis at limiting as well as at optimal CO2. The ratios of ATP to ADP in whole protoplast extracts were hardly affected, despite the marked decrease in their photosynthetic rates by SHAM. Similarly, the decrease in the ATP/ADP ratio by oligomycin or antimycin A was more pronounced at limiting CO2 than at optimal CO2. The mitochondrial oxidative electron transport, through both cytochrome and alternative pathways, therefore akppears to be more important than oxidative phosphorylation in optimizing photosynthesis, particularly at limiting CO2 (when ATP demand is expected to be low). Our results also confirm that the alternative pathway has a significant role in contributing to the cellular ATP, when the cytochrome pathway is limited.

Notes: Recent studies have suggested that Ca2+/calmodulin (CaM) or CaM-like proteins may be involved in blue light (BL)-dependent proton pumping in guard cells. As the increase in cytosolic concentration of Ca2+ is required for the activation of CaM and CaM-like proteins, the origin of the Ca2+ was investigated by measuring BL-dependent proton pumping with various treatments using guard cell protoplasts (GCPs) from Vicia faba. BL-dependent proton pumping was affected neither by Ca2+ channel blockers nor by changes of Ca2+ concentration in the medium used for the GCPs. Addition of Ca2+ ionophores and an agonist to GCPs did not induce proton pumping. However, BL-dependent proton pumping was inhibited by 10 mM caffeine, which releases Ca2+ from the intracellular stores, and by 10 μM 2,5-di-(tert-butyl)-1,4-benzohydroquinone (BHQ) and 10 μM cyclopiazonic acid (CPA), inhibitors of Ca2+-ATPase in the sarcoplasmic and endoplasmic reticulum (ER). By contrast, the inhibitions were not observed by 10 μM thapsigargin, an inhibitor of animal ER-type Ca2+-ATPase. The inhibitions by caffeine and BHQ were reversible. Light-dependent stomatal opening in the epidermis of Vicia was inhibited by caffeine, BHQ, and CPA. From these results, we conclude that the Ca2+ thought to be required for BL-dependent proton pumping may originate from intracellular Ca2+ stores, most likely from ER in guard cells, and that this origin of Ca2+ may generate a stimulus-specific Ca2+ signal for stomatal opening.

Notes: Plant aspartic proteinases have been characterized from seeds, flowers and leaves of a number of different species. The enzymes are generally either monomeric or heterodimeric, containing two peptides processed from the same precursor protein. The plant enzymes, like their mammalian and microbial counterparts, are active at acidic pH and inhibited by a class specific inhibitor pepstatin A. Plant aspartic proteinases are generally either secreted or targeted to the vacuolar/protein storage body compartment. The primary sequences of many of these enzymes have been determined and are very homologous with each other as well as with enzymes from mammalian and microbial origins. Plant aspartic proteinases, however, have a very unique plant specific region, which is not found in mammalian, microbial, or viral aspartic proteinases. The function of this region has not been elucidated. A role for these plant enzymes in protein processing or degradation has been proposed, however, more studies are required to confirm their in vivo functions. Recent intriguing results suggest possible roles for these enzymes in programmed cell-death of tissues and in pathogen resistance.

Notes: In shoots of the garden pea (Pisum sativum L.), the main bioactive gibberellin (GA) is GA1, which is synthesised from GA20 by 3β-hydroxylation. Gibberellin A20 is produced from GA19, as part of the process known as GA 20-oxidation. Because these steps are thought to be negatively regulated by GA1, we compared the metabolism of labelled GA19 and GA20 in mutants deficient in GA1, with that observed in isogenic wild-type (WT) plants. There was a large and specific increase in the 3β-hydroxylation of labelled GA20 in the GA1-deficient (dwarf) mutants, compared with the WT. Metabolism experiments did not provide convincing evidence for feedback regulation of 20-oxidation, possibly because GA19 akppears to be metabolised rapidly, even in WT pea shoots. Both 3β-hydroxylase and 20-oxidase transcript levels were markedly higher in the mutants than in isogenic WT lines. The results sukpport previous suggestions that both biosynthetic steps are feedback-regulated by GA1 in pea.

Notes: An overview is given of electrical events that occur in plant chloroplasts in association with their energization and subsequent photosynthetic performance. Special emphasis is given to the measuring techniques, in particular application of patch-clamp methods, which enable comparison of light-induced photocurrent and -potential kinetics of the thylakoid with kinetics of changes in chlorophyll fluorescence yield.

Notes: Pyrophosphate: d-fructose-6-phosphate 1-phosphotransferase (PFP; EC 2.7.1.90) and ATP: d-fructose-6-phosphate 1-phosphotransferase (PFK; EC 2.7.1.11) activities were determined in sugarcane varieties differing in sucrose content. For this purpose, activities were measured in those internodes where the maximum rate of sucrose accumulation occurs. The specific activity of internodal PFP varied significantly between the sugarcane varieties and was inversely correlated with the sucrose content. There was also a highly significant inverse correlation between PFP and sucrose content in a segregating F1 population. PFK activity was comparable to, or lower than, PFP activity and no relationship was evident between PFK activity and sucrose content. In all tissues investigated, the fructose 2,6-bisphosphate levels were probably sufficient to ensure full activation of PFP. The levels of PFP activity appear to be controlled by the expression of the β-subunit of the protein. The molecular mass of the PFP subunit polypeptide(s) was approximately 63 kDa. There was an inverse correlation between sucrose content and the partitioning of radiolabel into respiration in internodal tissue slices labelled with [U-14C]glucose across 3 sugarcane lines. The estimated flux of carbon into respiration correlated directly with PFP activity.

Notes: Twenty-one durum wheat genotypes originating from different geographic areas were grown during 3 successive years. The trials were characterised by different precipitation regimes. Carbon isotope discrimination (Δ), carbon content (CC) and ash content (ma) were assessed in the flag leaf during anthesis, then in the kernel at full maturity. Differences between the 3 years, due to water availability, were noted for Δ, ma, CC and yield. Genotypic differences were also noted within each year for all the traits studied. Some genotypes from the Middle East exhibited higher flag leaf and kernel Δ than those originating from the West of the Mediterranean basin. The kernel Δ was strongly correlated with grain yield (GY). The leaf Δ correlated with GY only under strong water limitation and with biomass production (BP) in favourable water conditions. For the flag leaf, Δ was correlated with ma and with CC. Silicon content was then assessed in the flag leaf and in the kernel on a subset of 10 genotypes differing in their Δ values. Strong positive correlations were noted between silicon content and Δ and ma for the flag leaf. However, no clear relationship was found between silicon content and GY. The results obtained in this study confirm the validity of kernel Δ as a predictive criterion for GY under water stress and suggest the possible use of kernel ma as an alternative criterion to select genotypes with higher water stress tolerance.

Notes: In order to clarify the effect of abscisic acid (ABA) on anaerobic tolerance in alfalfa (Medicago sativa L.), the seedlings were subjected to anaerobic stress after pretreatment with ABA. At concentrations〉 1 μM, ABA pretreatment increased the root viability of the seedlings to anaerobic stress and the viability increased with increasing ABA doses. At 100 μM ABA, the viability was 2.5-fold greater as compared with that of control seedlings. Roots of the seedlings rapidly lost ATP under the anaerobic stress; however, the decrease in ATP was much slower in the ABA-pretreated seedlings than the control seedlings. At 12 h after onset of the stress, ATP concentrations in the roots of 100 and 10 μM ABA-pretreated seedlings were 2.7- and 2.0-fold that of the control seedlings, respectively. During the period of ABA pretreatment under aerobic condition, ABA increased alcohol dehydrogenase (ADH, EC 1.1.1.1) activity in the roots until 12 h and then leveled off. The maximum ADH activities were 4.3- and 2.8-fold that in the roots of the control seedlings for 100 and 10 μM ABA-pretreated seedlings, respectively. After being subjected to the anaerobic stress, both ADH activities in the roots of the ABA-pretreated and the control seedlings increased but the differences in their activity remained. These results suggest that ABA pretreatment may maintain ATP level due to induction of ADH activity, which may be one of the causes of increasing anaerobic tolerance in the seedlings.

Notes: To elucidate how plants adapt to overheating followed by water deficiency, experiments with two cotton (Gossypium hirsutum L.) cultivars (Ok-oltin and INEBR-85) were performed. Preliminary heat-shock (HS) treatment (45°C for 1.5 h) increased resistance of both cultivars to subsequent progressive soil drought [40 days without watering, with soil moisture gradually decreasing from 70 to 20% of field moisture capacity (FMC)]. HS induced accumulation of amino acids and amides and increased their contribution to the osmotic pressure (OP) of the leaf cell sap. HS also enhanced resistance to water deficiency and to overheating of the leaves, especially in cv. INEBR-85, the more drought resistant of the two cultivars. The results suggest the existence of common resistance systems to both stress factors, in particular, accumulation of amino acids and amides (mainly arginine, proline and asparagine) – their concentration in the cell sap increased up to 240-, 160- and 150-fold, respectively.

Notes: Messenger RNA translation is a tightly regulated event in maize axes during germination. To obtain a deeper understanding of this process, the present research was centered on the expression regulation of the translation initiation factor eIF-4E within this period. Two maize eIF-4E isoforms were isolated by mGTP-Sepharose affinity chromatography. The eIF-iso4E protein content remained at a constant level in the axes during the first 24 h of maize germination, whereas the eIF-4E level increased after 12 h of germination as indicated by western blot analysis. Fast in vivo eIF-iso4E, but not eIF-4E, de novo synthesis was found within 6–12 h of germination. Northern blot analysis of total RNA from ungerminated axes with cDNAs encoding either -iso4E or -4E indicated that both transcripts were present in the stored mRNA pool of maize axes. Transcription for any of these mRNAs was not detected before 12 h of germination. Northern blots of polysomal RNAs indicated that the eIF-iso4E stored transcript is selectively recruited into polysomes for translation as early as 6 h of germination, whereas this does not occur for the eIF-4E transcript. The above data demonstrate differential 4E isoform expression regulation during maize germination. Expression of the eIF-iso4E protein appears to be translationally controlled, whereas the expression of the eIF-4E protein might be regulated at the transcriptional level.

Notes: Callus derived from the roots of Inmil® cherry rootstock (Prunus incisa×serrula) proliferates in a hormone-free solid medium. When transferred to a hormone-free liquid medium, such callus forms somatic embryos. On the other hand, leaf-derived callus of P. incisa×serrula and leaf- and root-derived calli of P. domestica require exogenous auxin for sustained growth and never form embryos. Levels of free and esterified indole-3-acetic acid (IAA) were similar in both types of calli grown on a solid medium, whereas the amide-conjugated IAA was higher in the root-derived embryogenic one. Transfer to a liquid medium did not affect the level of both free and conjugated IAA in the nonembryogenic callus, but in the embryogenic callus it decreased the level of amide-conjugated IAA. Isotopic dilution of C-IAA taken up from a medium was faster in the embryoegenic than in the nonembryogenic calli, which shows that the rate of IAA metabolism was higher in embryogenic callus. Besides IAA, indole-3-ethanol and indole-3-acetyl-N-aspartate were detected in nonembryogenic calli and in in vitro-grown shoots of P. domestica, whereas in embryogenic callus and in in vitro-grown shoots of P. incisa×serrula indole-3-acetamide was detected.

Notes: The metabolism of the polyamine precursors arginine and ornithine was studied in maturing and vernalised seeds of Picea abies (L.) Karst. (Norway spruce) in feeding experiments. Incorporation of radioactivity from these C-labelled amino acids into liberated CO2, amino acids, polyamines, proteins and cell wall fractions, as well as polyamine levels were determined in embryos and megagametophytes. Ornithine and especially arginine decarboxylation was more active in the embryo than in the megagametophytic cells, and vernalisation increased arginine metabolism more than it increased ornithine metabolism. Both precursors were metabolised to each other, to other amino acids, and to polyamines. The only polyamine in which radioactivity incorporated was free putrescine, showing either a slow synthesis or a high degradation rate of spermidine and spermine in maturing spruce seeds. The putrescine level was approximately 10 times higher in the embryo than in the megagametophytic tissues, whereas spermidine and spermine levels were almost the same in both tissues. The label from arginine and ornithine was also incorporated into proteins as amino acids and post-translationally as polyamines. Higher radioactivity was seen in the small ≤14-kDa polypeptides. Protein hydrolysates of the embryo and the megagametophytic tissues contained spermidine and spermine and their degradation product 1,3-diaminopropane (DAP), suggesting that polyamines may play a role in the accumulation of seed storage protein and in the maturation of spruce seeds.

Notes: Soybean (Glycine max [L.] Merr. cv. Century) seedlings were germinated in vermiculite, sub-irrigated with a complete nutrient solution, without nitrogen or supplemented with 10 mM KNO3, 5 mM (NH4)2SO4, or 5 mM NH4NO3. After 14 days in the light, or 5 days in the dark, tissues from different organs were harvested separately. Similarly, tissues from different organs from 14- or 21-day-old nodulated or non-nodulated soybean seedlings, maintained in the absence of nitrogen, were harvested. Proteins and total RNA were isolated from the different plant organs and used for immunoblot and RNA blot analyses, respectively. Protein or RNA blots were separately incubated with antisera or hybridized with probes specific for either ferredoxin-dependent glutamate synthase (Fd-GOGAT) or NADH-dependent glutamate synthase (NADH-GOGAT). The specific activity and the abundance of the Fd-GOGAT peptide and transcript increased, approximately 3–10 times, in cotyledons and hypocotyls/stems in plants germinated in the light compared with those germinated in the dark. Fd-GOGAT activity, peptide, and transcript were highest in leaves. Except for increases in the specific activity of samples from roots treated with (NH4)2SO4 or NH4NO3, there were minor or no changes in Fd-GOGAT activity, peptide and transcript among organs of seedlings treated with different nitrogen sources or by nodulation. Low levels of NADH-GOGAT transcript were detected in all organs. NADH-GOGAT activity, peptide, and transcript increased in roots of seedlings treated with different nitrogen sources, but these changes were more apparent on RNA blots versus immunoblots. The highest NADH-GOGAT activity and most abundant amounts of the peptide and transcript were observed in nodules. Despite being induced by different environmental factors, both GOGAT activities are controlled, at least in part, by either gene expression or by RNA stability, because in most instances, both isoenzymes exhibited paralleled changes in specific activity and the abundance of their corresponding peptides and transcripts on immunoblot and RNA blots, respectively. However, there were some exceptions to the parallel increases in specific activities, peptides and transcripts which suggest that post-translational modification may also regulate the activties of the two GOGAT isoforms. Collectively, the results presented here suggest that the two GOGAT isoforms have distinct physiological functions in soybean.

Notes: Kiwifruit (Actinidia deliciosa) is a dioecious vine whose staminate and pistillate flowers nonetheless develop non-functional reproductive structures of the ompposite sex. Ubiquitin is a small, highly conserved protein found in all eucaryotes: a covalent ATP-dependent attachment of ubiquitin marks proteins for degradation. In the present paper, we used immunoblotting to investigate the presence of free ubiquitin and ubiquitin conjugates during pollen development in male (androfertile) and in female (androsterile) genotypes of kiwifruit. In the male, several high molecular mass protein conjugates were present throughout development. On the contrary, such a pattern characterized only early stages of pollen from the female genotype, where conjugates progressively disamppeared, until they were detectable only in trace amounts at anthesis. The highest content of conjugates in the male genotype was observed when microspores were ampproaching the first mitosis. Free ubiquitin increased continuously during development of the male microgametophyte so that mature pollen contained considerable amounts of the ubiquitin monomer at the time of its release from the anther. By contrast, only low levels were detectable in the degenerating microspores in the pistillate flowers. In vitro experiments using labeled ubiquitin indicated that early-uninucleate microspores of the female genotype had a much higher conjugation rate than those of the male genotype at the same stage. However, after feeding α-lactalbumin as exogenous substrate, the rate of ubiquitin conjugation strongly increased and was quite similar in both sexes. Nuclear features of pollen development in both genotypes are also described. The nucleus progressively degenerated in the microspores of the pistillate flowers starting from the early-uninucleate stage, in parallel with the progressive decrease in ubiquitin content and activity. At anthesis, the microspores in the pistillate flowers either had no nucleus or showed only traces of chromatin. Thus, the ubiquitin system seems to play an important role in protein turnover occurring during the normal developmental pathway of the kiwifruit microgametophyte, while it was mainly involved in regressive events related to microspore degeneration in the female genotype.

Notes: A growing body of evidence indicates that phenylpropanoid and flavonoid metabolism is catalyzed, not by free-floating ‘soluble’ enzymes, but via one or more membrane-associated multienzyme complexes. This type of macromolecular organization has important implications for the overall efficiency, specificity, and regulation of these pathways. Classical biochemical studies of phenylpropanoid and flavonoid metabolism have laid a solid foundation for this model, providing evidence of the channeling of intermediates between enzyme active sites and co-localization of enzymes in cell membranes. This work is now being extended using transgenic plants to determine how the partitioning of metabolites within these pathways is controlled, as well as applying sensitive methods to define specific interactions among the individual enzymes. Information from these studies promises to provide new insights into the structuring of biosynthetic pathways within cells, which should lead to more effective means for engineering the production of plant metabolites with nutritional and agronomic importance.

Notes: Tomato plants (Lycopersicon esculentum Mill. cv. Pera) were transformed via Agrobacterium tumefaciens with the binary vector pKYLX71 containing a tomato basic peroxidase (EC 1.11.1.7) gene, tpx1, under the control of the cauliflower mosaic virus (CaMV35S) promoter. Transgenic plants showed a 2–5-fold increase in the activity of the peroxidase ionically bound to the cell wall, whereas soluble peroxidase activity remained similar or even lower than wild-type plants. Isoelectric focusing showed the presence of a new isoperoxidase of pI ca 9 in the ionically bound extract. Western blot also showed the presence of a new band at 41 kDa that was absent in the wild-type extract. A 40–220% increment of lignin content of the leaf was found in transgenic plants. Shoot phenotype of transgenic plants was similar to wild type, although under stress, the plants appeared wilted and the new leaves had a reduced area and were thicker than wild-type or older transgenic leaves. The root system was underdeveloped in transgenic plants, but the rooting ability of the stem was not affected by the overexpression of peroxidase. Finally, the morphogenetic response of cotyledon and hypocotyl explants from transgenic plants was evaluated. In the case of cotyledons, the percentage of explants with shoot was not different from wild-type plants. For hypocotyl, one of the transgenic lines showed a 30% reduction in the percentage of shoot organogenesis. The results are discussed in relation to the role of tpx1 in lignin synthesis.

Notes: Levels of three major dehydrins of 65, 60, and 14 kDa have been observed to increase in blueberry (Vaccinium smpp.) floral buds during chill unit accumulation and cold acclimation and decrease during deacclimation and resumption of growth. Indeed, levels of the 65-, 60-, and 14-kDa dehydrins increase such that they become the most predominant proteins visible on sodium dodecyl sulfate (SDS)-polyacrylamide gels. The peptide sequence information from the 65- and 60-kDa dehydrins was used to synthesize degenerate DNA primers for amplification of a part of the gene(s) encoding the dehydrins. One pair of primers amplified a 174-bp fragment. The 174-bp fragment was used to screen a cDNA library (prepared from RNA from cold-acclimated blueberry floral buds) and resulted in the isolation of a clone with a 2.0-kb insert. The cDNA was sequenced and found to be a full-length clone encoding a K5-type dehydrin (5 K boxes). Five high-confidence peptide sequences, ranging from 9 to 25 amino acids long, obtained from the 60-kDa dehydrin exactly matched sequences encoded within the cDNA clone. Furthermore, amino acid composition of the 60-kDa dehydrin agreed well with the expected amino acid composition based on the cDNA sequence. However, the DNA sequence and coupled in vitro transcription/translation reactions of the cDNA clone indicated that it encodes a dehydrin with a native molecular mass of ∼40 kDa instead of 60 kDa. Experiments to determine if the dehydrins undergo post-translational modifications revealed that the 65- and 60-kDa dehydrins are glycosylated. Thus, our results indicate that the 2.0-kb dehydrin cDNA encodes the native version of the 60-kDa dehydrin. The dehydrin cDNA hybridized on RNA blots to two chilling/cold-responsive messages of 2.0 and 0.5 kb. Both the 2.0- and 0.5-kb messages increased to higher levels more quickly in the cold-hardy cultivar Bluecrop than in the less hardy cultivar Tifblue. In addition, the 0.5-kb message remained at a higher level longer in Bluecrop than in Tifblue.

Notes: Winter annual and perennial crop species grown in the northern boreal ecosystem must survive periods of protracted snow cover and low temperatures during the winter. In deep snow regions, plants are susceptible to winter stresses caused by both snow molds and low temperatures. Therefore, high levels of tolerance to freezing and snow molds are requisite for crops adapted to these regions. Accumulation of soluble carbohydrates in winter wheat during the autumn is linked to both hardening and resistance to attack by snow molds. Snow mold-resistant cultivars accumulate higher levels of carbohydrate and metabolize them at slower rates than susceptible cultivars. The quantity and quality of carbohydrates, particularly fructans, remaining in the spring after snow mold attack appear important for survival of winter wheat. However, the total accumulation of carbohydrates is dependent on the stage of development of the winter cereal plant at the beginning of the winter. Recent research findings have shown that sugars are pivotal metabolic activators of the sugar-sensing enzyme, hexokinase, which initiates signal transduction and activation of numerous metabolic genes including host defense genes. Thus, an understanding of the metabolism of soluble carbohydrates, particularly fructans, during plant growth, hardening, and snow mold infection, is essential to the elucidation of survival mechanisms in plants subjected to these winter stresses.

Notes: The involvement of the ascorbate-glutathione cycle in the defence against Cu-induced oxidative stress was studied in the roots of Phaseolus vulgaris L. cv. Limburgse vroege. All the enzymes of this cycle [ascorbate peroxidase (APOD), EC 1.11.1.11; monodehydroascorbate reductase (MDHAR), EC 1.6.5.4; dehydroascorbate reductase (DHAR), EC 1.8.5.1; glutathione reductase (GR), EC 1.6.4.2] were increased, and the total ascorbate and glutathione pools rose after a 15 μM root Cu treatment. In the first hours after the start of the experiment, the accumulation of dehydroascorbate (DHA), formed as a result of a Cu-mediated direct oxidation of ascorbate (AA), was limited by a non-enzymatic reduction using glutathione (GSH) as the reductant. At 24 h, the enzyme capacities of both DHAR and GR were increased to maintain the redox status of the AA and GSH pools. After 72 h of Cu application, the DHAR capacity was inhibited and MDHAR was responsible for maintaining the AA pool in its reduced form. Although the GR capacity was enhanced after 72 h in the treated plants, the GSSG/GSH ratio was increased. This could be due to direct participation of GSH in the detoxification of Cu through reduction and complexation.

Notes: In an effort to study regulation of starch synthesis in the source and sink tissues, a cDNA clone for starch granule-bound starch synthase (GBSSI), which encodes a 67-kDa protein, was isolated from a cDNA library prepared from tuberous roots of sweet potato (Ipomoea batatas Lam. cv. Tainong 62). This GBSSI protein contains a signal peptide of 77 amino acids, and the mature protein has a molecular mass of about 59 kDa. The mature protein shares 75–85% sequence identity with GBSSIs of dicotyledonous plants and about 70% identity with those of monocotyledons. The sequence of the signal peptide, on the other hand, differs substantially from those of the dicotyledons and monocotyledons studied, although their hydropathic profiles are all similar. This GBSSI gene was well expressed in tuberous roots, leaves, and stems, but not in roots. However, mechanisms involved in regulating the expression of this gene were different between tuberous roots and leaves. In tuberous roots, the synthesis of GBSSI transcript increased coordinately with tuberous root expansion; nevertheless, accumulation rates of GBSSI protein in starch granules remained constant regardless of tuberous root sizes, suggesting an involvement of post-transcriptional regulation for the synthesis of this protein. The levels of GBSSI transcript were investigated in photosynthetic tissues during diurnal cycles, and the results suggest that the transcription of the GBSSI gene in leaves is controlled by the endogenous circadian rhythm.

Notes: The early cellular events in leaf explants of Medicago sativa L. cultured on somatic embryogenesis- and callogenesis-inducing media (EIM and CIM, respectively) were correlated with the endogenous contents of polyamines (PAs) and aromatic monoamines (AMs). On the second day of culture, replication of DNA occurred in epidermal and subepidermal cells on the edges of explants on EIM and was a prerequisite for proembryonal mass and, later, globular proembryo formation. In explants cultured on CIM, replication occurred at least one day later and in fewer cells, which were randomly spread all over the explant. Transition of leaf explant cells to rapidly dividing meristematic-like cells on EIM or to enlarged, highly vacuolated cells on CIM was observed. The increase in total PA levels in cultured explants was primarily a consequence of increases in putrescine (Put) and spermidine (Spd) contents and was much more pronounced on EIM than on CIM. High Spd levels were characteristic of meristematic cells and might be essential for the development of globular structures. The higher amount of insoluble PA conjugates was determined in explant cells on EIM, as compared with CIM. Proembryogenic cell mass formation was positively correlated with free tyramine and negatively correlated with free phenylethylamine contents.

Notes: Immunofluorescent and immunogold labeling was used to study the localization of cytokinins in developing somatic and zygotic embryos of Tilia cordata Miller. Broad-specificity polyclonal antibodies active against dihydrozeatin riboside (DHZR)/zeatin riboside (ZR)-type and isopentenyladenosine (iPR)-type cytokinins were used for immunolabeling. Immunofluorescent microscopy showed that these cytokinins were concentrated in highly cytoplasmic cells showing meristematic character. Cotyledon initials and primary meristems of heart-stage somatic embryos, as well as heart-stage zygotic embryos, were labeled. During elongation of embryos, cytokinin immunoreactive material was concentrated to areas having meristematic character. Root apex, shoot meristem, and cotyledon cells of somatic and zygotic cotyledonary embryos, as well as epidermal and subepidermal cell layers of the hypocotyl, showed the strongest immunoreaction. The nucleoli, especially, had a very strong signal. Results at the ultrastructural level with gold-conjugated protein A supported these conclusions. Gold particles were distributed in the nuclei, especially in the nucleoli and throughout the ground cytoplasm. They were occasionally associated with plastids and mitochondria, but seldom with other organelles.

Notes: Leaf discs of Capsicum annuum L. were illuminated in air enriched with 1% CO2 in the absence or presence of lincomycin, an inhibitor of chloroplast-encoded protein synthesis. The loss of functional photosystem (PS) II complexes with increase in cumulative light dose (photon exposure), assessed by the O2 yield per single-turnover flash, was greater in leaves of plants grown in low light than those in high light; it was also exacerbated in the presence of lincomycin. A single exponential decay can describe the relationship between the loss of functional PSII and increase in cumulative photon exposure. From this relationship we obtained both the maximum quantum yield of photoinactivation of PSII at limiting photon exposures and the coefficient k, interpreted as the probability of photoinactivation of PSII per unit photon exposure. Parallel measurements of chlorophyll fluorescence after light treatment showed that 1/Fo−1/Fm was linearly correlated with the functionality of PSII, where Fo and Fm are the chlorophyll fluorescence yields corresponding to open and closed PSII reaction centers, respectively. Using 1/Fo−1/Fm as a convenient indicator of PSII functionality, it was found that PSII is present in excess; only after the loss of about 40% functional PSII complexes did PSII begin to limit photosynthetic capacity in capsicum leaves.

Notes: Characteristics of the cell cycle in cortical regions (0–0.6 mm from the root-cap junction) of the primary root of lentil (Lens culinaris L.) during germination in the vertical position on earth were determined by iododeoxyuridine labelling and image analysis. All cells were in the G1 phase at the beginning of germination and the duration of the first cell cycle was about 25 h. At 29 h, around 14% of the cortical nuclei were still in the G2 or M phases of the first cell cycle, whereas 53 and 33% of the nuclei were respectively in the G1 or S phase of the second cell cycle. In parallel, the cell cycle was analysed in root tips of lentil seedlings grown in space during the IML 2 mission (1994), (1) on the 1-g centrifuge for 29 h, (2) on the 1-g centrifuge for 25 h and placed in microgravity for 4 h, (3) in microgravity for 29 h, (4) in microgravity for 25 h and placed on the 1-g centrifuge for 4 h. The densitometric analysis of nuclear DNA content showed that in microgravity there were less cells in DNA synthesis and more cells in G1 than in the controls on the 1-g centrifuge (flight and ground). The comparison of the sample grown continuously on the 1-g centrifuge in space and of the sample grown first in 1-g and then in microgravity indicated that 4 h of microgravity modified cell cycle, increasing the percentage of cells in the G1 phase. On the contrary, the transfer from microgravity to the 1-g centrifuge (for 4 h) did not provoke any significant change in the distribution of the nuclear DNA content. Thus the effect of microgravity could not be reversed by a 4 h centrifugation. As the duration of the first cell cycle in the lentil root meristem is about 25 h, the results obtained are in agreement with the hypothesis that the first cell cycle and/or the second G1 phase was lengthened in absence of gravity. The difference observed in the distribution of the nuclear DNA content in the two controls could be due to the fact that the 1g control on board was subjected to a period of 15 min of microgravity for photography 25 h after the hydration of the seeds, which indicated an effect of short exposure to weightlessness. The mitotic index of cortical cells was greater on the 1-g centrifuge in space than in any other sample (flight and ground) which could show an effect of the centrifugation on the mitosis.

Notes: Olive trees are often subjected to low temperatures during winter. To quantify the effects of low temperatures on the water relations of olive trees, we studied the responses to low soil temperatures on winter days of variable evaporative demand (ET0) in 1-year-old potted olive (Oleo europaea L. cv. Picual) trees in 1996 and 1997. Low night (2.5 and 5.2°C) but ambient day soil temperatures (above 10°C) did not affect stomatal conductance (gs), leaf (Ψleaf) and stem (Ψstem) water potentials. Soil temperature levels inducing water stress in olive trees were determined for winter days with ET0 typical for southern Spain (ET0= 1.5 ± 0.3 mm day−1). Leaf and stem water potential decreased and root hydraulic resistance (rroot) increased when trees were exposed to night and day soil temperatures below 10°C. Stomatal conductance was not affected at soil temperatures between 6.4 and 10°C, but decreased at temperatures below 6.4°C. The soil temperature levels affecting the water uptake of olive trees remained relatively constant over the range of ET0 of 1-2 mm day−1 during winter and early spring months. However, the soil temperature influencing gs appeared to be more variable and was affected by ET0. Olive tree recovery from low soil temperature stress depended on stress duration and severity and interacted with ET0. Recovery of ψ started already during the stress period, probably induced by stomatal closure and high rroot, thus allowing tree rehydration overnight. Root hydraulic resistance contributed the major part of whole-tree hydraulic resistance in response to cold stress, accounting for 76 and 89% at 6.4 and 4.6°C, respectively; which indicates that rroot is the primary control of the water status in olive trees under low temperatures.

Notes: The effects of the ratio of Rubisco activase to Rubisco (activase/Rubisco ratio) on light dependent activation of CO2 assimilation were investigated during leaf aging of rice. Changes of photosynthetic CO2 gas exchange rates in relation to step increases of light intensity from two photon flux densities of 60 µmol m−2 s−1 (low initial PFD) and 500 µmol m−2 s−1 (high initial PFD) to saturated PFD of 1 800 µmol m−2 s−1 were measured. These photosynthetic activation processes were considered to be limited by the Rubisco activation rate when analyzed by the relaxation method. The relaxation time of low initial PFD gradually declined from 3 to 33 days after leaf emergence and showed high and negative correlation to the activase/Rubisco ratio. The initial rate of Rubisco activation under low initial PFD linearly correlated to the amounts of Rubisco activase, whereas these were almost constant from 3 to 23 days after leaf emergence. But these correlations could not be recognized in the case of high initial PFD. Moreover, the relaxation times were more sensitive to intercellular CO2 concentration (Ci) under high initial PFD than under low initial PFD, especially, at Ci below 300 µl l−1. These results suggest the involvement of the activase/Rubisco ratio in the photosynthetic activation under relatively low initial PFD, and the limitation of photosynthetic activation under relatively high initial PFD by Rubisco carbamylation during leaf aging of rice.

Notes: Peroxidase (EC 1.11.1.7) activity from homogenized tissue or in apoplastic fluid was analyzed along the developmental gradient of expanding B73 maize (Zea mays L.) leaf blades. Soluble plus ionically bound peroxidase activity from homogenized tissue was present in high levels at the leaf base, which includes the region of cell division, and decreased as tissue was displaced away from the base by growth. A different pattern of change in peroxidase activity was seen in apoplastic fluid extracted from segments of intact tissue, where an increase in peroxidase activity preceded a rapid decrease in leaf elongation rate. Similar patterns in peroxidase activity from homogenized and intact tissue have been found in leaf blades of tall fescue (Festuca arundinacea Schreb.), suggesting a common phenomenon. At the location within the elongation zone where the increase in apoplastic peroxidase activity occurred, the activities of neutral and acidic (pl 4.6) peroxidase isoforms were also elevated in both the homogenate and in apoplastic fluid. The coincidence of these isoforms with the decline in leaf elongation rate suggests they may contribute to cessation of growth. At the distal end of the elongation zone, the activities of other acidic peroxidases (pI 5.6 and 5.7) increased in the homogenate and in apoplastic fluid, and remained elevated as tissue was displaced into the maturation region. The location of their appearance and their relatively high activity in the maturation region suggest the involvement of these isoforms in lignification.

Notes: Hexanal and cis-3-hexenal are principal flavor volatiles in ripe tomato fruit, but whether they accumulate during ripening or are formed upon maceration of the tissue has not been clarified. This has been addressed by measuring levels of these aldehydes in green and ripe fruit with discrimination between intrinsic aldehyde content and aldehyde generation following tissue disruption. Volatile sampling of tomato fruit homogenates was accomplished by purge/trapping, followed by thermal desorption on a gas chromatograph equipped with a mass selective detector. Incubation of some samples with alcohol dehydrogenase to convert the aldehydes to their respective alcohols permitted positive identification of the isomeric form of hexenal as cis-3-hexenal. Red and green tomato fruit homogenized in buffer with saturated CaCl2 contained low (0.1-0.8 µg g−1 fresh weight) levels of hexanal and cis-3-hexenal; thus there is minimal endogenous volatile content in intact fruit. Volatile levels increased rapidly, up to 10-fold, following homogenization of ripe tomato fruit in the absence of CaCl2, and more modestly in corresponding green tomato fruit homogenates. Incubation with the appropriate lipoxygenase/hydroperoxide lyase substrate (linoleic acid for hexanal, linolenic acid for cis-3-hexenal) doubled the amount of volatile compound produced. Hexanal generation was suppressed in the presence of linolenic acid, suggesting that the enzyme complex has greater affinity for this substrate. As well, levels of cis-3-hexenal, but not hexanal, tended to decline within 30 min of homogenization, possibly reflecting a specific degradative process. The results collectively indicate that the contribution of six-carbon aldehydes to tomato fruit flavor is attributable to metabolism invoked following tissue disruption rather than within the intact fruit.

Notes: A protein kinase (PK-II), phosphorylating casein, was purified from ripening mango, Mangifera indica L., fruit tissue. The purification procedure consisted of ammonium sulphate fractionation and sequential anion exchange-, dye-ligand, and gel filtration chromatography. The enzyme was purified over 500-fold to near homogeneity with a recovery of 4%. The purified enzyme had a specific activity of ca 1 µmol mg−1 protein min−1 with ATP as phosphoryl donor. SDS-PAGE results indicated a monomeric enzyme with molecular mass of 35 kDa. The protein kinase phosphorylated the acidic substrates casein and phosvitin, but had a very low activity with histones and protamine sulphate. The optimum pH and temperature for catalysis were determined to be 9.6 and 35°C, respectively. Mn2+ could not substitute for the Mg2+ needed for activity and Ca2+ had a slight stimulatory effect. Phospholipids, cAMP, calmodulin and the calmodulin inhibitor, calmidazolium, did not have any significant effect on activity, but the enzyme was inhibited by heparin and the specific inhibitor, CKI-7, (N-[2-aminoethyl]-5-chloroisoquinoline-8-sulphonamide). Autoradiographic studies revealed the ability of the protein kinase to autophosphorylate as well as the presence of endogenous protein substrates in the crude extract. Initial velocity studies with casein as substrate and product inhibition studies with ADP indicated a Km (ATP) and Km (casein) of 14 µ M and 0.18 mg ml−1, respectively, with a Ki (ADP) of 3.2 µM. The enzyme can be classified as a casein kinase I type of protein kinase (EC 2.7.10).

Notes: Stem elongation can be suppressed by a temperature drop at the onset of the photoperiod (DROP) or with a cooler day than night temperature (DT and NT, respectively), commonly described as DIF (DT - NT). To test our hypothesis that phytochrome A (phyA) mediated the reduction of stem elongation caused by −DIF and DROP, we conducted experiments with photomorphogenic mutants of tomato (Solarium lycopersicon L.) and transgenic potato (Solarium tuberosum L.). The plants studied were tomato mutants fri1 (deficient in phyA) and tri3 (deficient in phytochrome B1 [phyBl]) and their isogenic wild-type (WT) cv. Moneymaker, nontransformed potato, and two lines each of antisense phyA (15-9 and 15-11) and overexpressed phyA (PS-2 and PS-4). Plants were placed in three temperature regimens with a daily mean of 20°C: a constant 20°C (0 DIF), an 8°C DROP for 3 h, and a - 8°C DIF. For all tomato genotypes, −DIF and DROP reduced intemode length by ≥ 21% and stem elongation by 30% compared to that of plants at 0 DIF. Interactions between temperature treatment and genotype were nonsignificant. For potato, −DIF, but not DROP, significantly reduced intemode length of WT (by 39%) and both antisense lines (by 36 or 48%) but only one of the two lines of overexpressed phyA plants (by 18%). The −DIF significantly reduced stem length for only antisense phyA (by 36 or 48%) and WT (by 35%) plants. Thus, at least for tomato and potato, it appears that phyA does not control stem extension in relation to cool-temperature treatments.

Notes: Purified preparations of NAD(H)-glutamate dehydrogenase (GDH, EC 1.4.1.2.) were assayed to determine the effects of mono- and divalent cations, nucleotides and select carbon compounds on NAD(H)-dependent GDH activity. The amination reaction was stimulated 2- to 17-fold by divalent cations (Ca2+ 〉 Cd2+ 〉 Co2+ 〉 Mg2+ 〉 Mn2+ 〉 Zn2+ between 1 and 1000 µM), but the reaction was unaffected by monovalent cations (Na + and K +). The amination reaction was most responsive to changes in Ca2+ in a NADH-dependent manner. The addition of EDTA or EGTA nullified the stimulatory effects of Ca2+. Calmodulin alone or in combination with calmodulin antagonists did not affect the amination reaction. Divalent cations (at 1 mM) inhibited the rate of the deamination reaction by 15 to 25%, while monovalent cations had no effect. ATP inhibited the amination reaction by 10 to 60%, while ADP had little or no effect. ATP or ADP decreased the rate of the deamination reaction 23 to 60 or 20 to 38%, respectively. Many tricarboxylic acid cycle intermediates inhibited the amination reaction, 20 to 50% of the inhibition could be attributed to the chelating capacity of intermediates. Conversely, most of the carbon sources tested did not affect the deamination reaction, the only appreciable differences were increases in activity with sucrose (21%) and glucose (41%) and a decrease in activity with pyruvate (34%). Inhibitors of sulfhydryl groups were used to examine the importance of reduced thiol groups in the amination or deamination reactions. The amination was not dependent on reduced thiol groups, whereas the deamination reaction was dependent on reduced thiol groups.

Notes: The mechanism of cobalt uptake was investigated using cells of the giant alga Chara corallina in which it is possible to resolve separately uptake by the cell wall and actual influx across the cell membrane. The absorption of 60Co by Chara cells appeared to saturate within 2 h, but this was mainly due to rapid uptake into the cell wall which accounted for 87–92% of the total activity. Even after prolonged desorption most of the cell-associated 60Co was found on the cell wall. The intracellular distribution of absorbed 60Co was investigated by fractionating the cell into cytoplasm and vacuole. It was shown that 60Co influx to the vacuole occurs simultaneously with influx to the cytoplasm. The transported species appears to be Co2+ rather than the less charged Co(OH)+ or Co(OH)2. 60Co influx is pH dependent (optimum pH 7–9), and is sensitive to some other divalent metals. Influx from solutions containing 1 µM60Co was inhibited by 5 µM Cd2+, Cu2+, and Zn2+, but Mn2+ and Ni2+ had no significant effect. The sensitivity of Co uptake to N-ethyl maleimide (NEM) and cysteine suggests that the transport system involves direct binding of CO2+ to -SH groups.

Notes: Experiments were carried out to evaluate the effects of exposure to nitric oxide on the ability by NADPH-dependent microsomal electron transfer to generate oxygen radicals. Such interactions could play a role in the potential antioxidant action of nitric oxide (NO). Isolated microsomes from soybean (Glycine max [L.] Merr. cv. Hood) embryonic axes were exposed to an exogenously added source of nitric oxide (NO) (S-nitrosoglutathione + dithiothreitol). The O2− generation rate by microsomes exposed to NO decreased significantly as compared to the rate measured in microsomes incubated in the absence of NO. The exposure of the microsomes to the NO donor did not alter the microsomal rate of hydroxyl radical generation. Preincubation of the microsomes with the NO donor affected neither iron reduction rate nor activity of cytochrome c reductase. However, cytochrome P450 activity was significantly inhibited after exposure to NO. This inhibition was completely prevented by hemoglobin. The data are consistent with the hypothesis that NO exhibits a potential antioxidant role in the plant cell by decreasing the rate of generation of superoxide anion. Since endogenous NO was detected in homogenates of soybean embryonic axes by EPR studies, this interaction between NO and cytochrome P450 in soybean embryonic axes could be a factor of relevance for the control of oxidative stress in vivo.

Notes: Three soluble invertase (EC 3.2.1.26) isoforms from Easter lily (Lilium longiflorum Thunb. cv. Nellie White) flower buds were purified to apparent homogeneity. Non-denaturing PAGE showed one band for all three invertases that corresponded to the invertase activity. SDS-PAGE of purified invertase I gave a single band at 78 kDa, whereas invertases II and III gave three bands at 54, 52 and 24 kDa. Antibodies against tomato fruit acid invertase and Urtica dioica leaf acid invertase recognized all three invertase isoforms, whereas antibodies against wheat coleoptile acid invertase recognized only 56- and 54-kDa bands of invertases II and III. Antibodies against wheat coleoptile invertase recognized the 54- and 52-kDa proteins from crude extracts of all flower organs, and a 72-kDa protein in both leaf and bulb scale extracts. All three invertases bound to Con-A peroxidase. Deglycosylation of invertase I with glycopeptidase F was complete and resulted in a peptide of 75 kDa. Invertases II and III were deglycosylated partially by glycopeptidase F and resulted in proteins of 53, 51, 50 and 22 kDa. Invertase I was localized only in anther and filament, whereas the other two isoforms were present in all flower organs.

Notes: Starch represents the major component of virtually all plant-derived foods consumed by man and animal. Hence, a thorough understanding of the starch biosynthetic pathway is critically important not only in understanding the biosynthesis of a major plant storage product, but also in allowing the genetic manipulation of both starch quality and quantity for human benefit. A major goal in these studies has been the identification of key steps in controlling starch levels. Evidence from a number of independent approaches clearly points to the enzyme adenosine diphosphate glucose pyrophosphorylase (AGPase) as a key regulatory step in starch synthesis. Here we highlight and summarize our understanding of this important enzyme.

Notes: In a chilling-sensitive plant, cucumber, chilling of leaves in the light results in irreversible damage to PSI. Recent in vitro studies suggested that hydroxyl radicals, which are formed in the presence of H2O2 and reduced Fe-S centers, are involved in the PSI inhibition. We therefore examined this possibility in vivo. Chilling of leaves at 5°C in the light caused a temporary increase in H2O2 concentration, which was probably due to the net H2O2 production in vivo. The activity, measured at 5°C, of the thylakoid ascorbate peroxidase (APX), a key enzyme of the H2O2-scavenging system, was about 20% of that measured at 25°C. The isolated thylakoids retaining high thylakoid APX activity did not show light-dependent net H2O2 production at 25°C. However, at 5°C, net production of H2O2 was observed. Since the rate of electron flow to molecular oxygen in the isolated thylakoids was ca 5 mmol e− mol−1 Chl s−1 at 5°C, the H2O2-scavenging capacity was below this level. When intact leaves were illuminated at 5°C at an irradiance of 100 µmol m−2 s−1, the rate of electron transport through PSII was ca 20 mmol e− mol−1 Chl s−1 and more than 80% of QA was in the reduced state. Since thylakoids are uncoupled in cucumber leaves at 5°C in the light. ATP is not formed and energy dissipation in the form of heat is suppressed. Therefore, the electron flow to molecular oxygen would be greater than 5 mmol e− mol−1 Chl s−1. Moreover, under such conditions, components in the electron transport chain, including Fe-S centers in PSI, were probably reduced. These features indicate that, when cucumber leaves are chilled in the light, hydroxyl radicals can be produced by the Fenton reaction and cause damage to PSI.

Notes: Prior work demonstrated that Heuchera americana, an evergreen herb inhabiting the deciduous forest understory in the southeastern United States, has a 3-4-fold greater photosynthetic capacity under the low-temperature, strong-light, open canopies of winter compared to the high-temperature, weak-light, closed canopies of summer. Moreover, despite the reductions in soil nitrogen, the chilling temperatures, and the increased quantum flux associated with winter, chronic photoinhibition was not observed in this species at this time of the year. We were interested in the photosynthetic acclimation and photoinhibition characteristics of this species when grown under contrasting light and nitrogen regimes. Newly expanded shade-acclimated leaves of forest-grown plants exposed to strong light varying in intensity and duration at 25°C showed a reduction in Fv/Fm (the ratio of variable to maximum room temperature chlorophyll fluorescence measured after dark adaptation), which was correlated with a decline in øa (the intrinsic quantum yield of CO2-saturated O2 evolution on an absorbed light basis). Plants grown in the glasshouse under contrasting light (high and low light; HL and LL, respectively) and nitrogen supply (high and low nitrogen; HN and LN, respectively) regimes showed that photosynthetic acclimation to HL was impaired in LN regimes. The HL-LN plants also had the lowest values of Fv/Fm and of ø on both incident and absorbed light bases and had 50% less chlorophyll (per unit area) compared to plants from other growth regimes. Controlled exposure to bright light at low temperatures (2-3°C) for 3 h resulted in a sharp decrease in Fv/Fm (and rise in Fo, the minimum fluorescence yield) in all plants. Shade-grown plants from both N regimes were highly susceptible to chronic photoinhibition, as indicated by a greater reduction in Fv/Fm and incomplete recovery after 18 h in weak light at 25°C. The HL-HN plants were the least susceptible to chronic photoinhibition, having the smallest decrease in Fv/Fm with near full recovery within 6 h. The decline in Fv/Fm in HL-LN plants was comparable to that of shade-acclimated plants, but recovered fully within 6 h. Low-N plants from both light regimes displayed greater increases in Fo which did not return to pretreatment levels after 18 h of recovery. These studies indicate that HL-LN plants were sensitive to chronic photoinhibition and, at the same time, had a high capacity for dynamic photoinhibition. Experimental garden studies showed that H. americana grown in an open field in summer were photoinhibited and did not fully recover overnight or during extended periods of weak light. These results are discussed in relation to the photosynthetic acclimation of H. americana under natural conditions.

Notes: Protoplasts isolated from pear fruit at the end of the cell-division stage, 30 days after flowering (DAF), had already formed a large central vacuole and the vacuole occupied most of the protoplast. The changes in protein composition and density of the tonoplast (vacuolar membrane) were investigated during fruit development. After a linear sucrose density gradient centrifugation, the distribution of tonoplasts at 30 and 48 DAF was broad and began to narrow with further fruit development. This suggests that the tonoplast of young fruit is heterogeneous and becomes homogeneous with fruit development. The apparent density of the tonoplast at 30 DAF was approximately 1.12 g ml−1; it decreased with fruit development and was finally 1.09 g ml−1 in mature fruit. The phospholipid amount on the basis of tonoplast protein was 0.80 mg mg−1 at 30 DAF. It increased with fruit development, and finally reached 7.49 mg mg−1. This result indicates that the decrease in the density of the tonoplast was caused by the increase in the ratio of phospholipid to membrane protein. The protein composition of the tonoplast at each stage was quite different. The level of polypeptides of 94, 70, 61, 52, 48 and 41 kDa was low in young fruit and high in the middle or later stages of fruit development. In contrast, the level of a 76-kDa polypeptide was high in young fruit and decreased with fruit development. Although their functions are still unclear, these tonoplast proteins may play important roles in fruit development.

Notes: Many plants accumulate organic osmolytes in response to the imposition of environmental stresses that cause cellular dehydration. Although an adaptive role for these compounds in mediating osmotic adjustment and protecting subcellular structure has become a central dogma in stress physiology, the evidence in favour of this hypothesis is largely correlative. Transgenic plants engineered to accumulate proline, mannitol, fructans, trehalose, glycine betaine or ononitol exhibit marginal improvements in salt and/or drought tolerance. While these studies do not dismiss causative relationships between osmolyte levels and stress tolerance, the absolute osmolyte concentrations in these plants are unlikely to mediate osmotic adjustment. Metabolic benefits of osmolyte accumulation may augment the classically accepted roles of these compounds. In re-assessing the functional significance of compatible solute accumulation, it is suggested that proline and glycine betaine synthesis may buffer cellular redox potential. Disturbances in hexose sensing in transgenic plants engineered to produce trehalose, fructans or mannitol may be an important contributory factor to the stress-tolerant phenotypes observed. Associated effects on photoassimilate allocation between root and shoot tissues may also be involved. Whether or not osmolyte transport between subcellular compartments or different organs represents a bottleneck that limits stress tolerance at the whole-plant level is presently unclear. None the less, if osmolyte metabolism impinges on hexose or redox signalling, then it may be important in long-range signal transmission throughout the plant.

Notes: The evergreen species Yucca glauca was characterized at the end of September and following exposure to low temperatures at the end of November. In November the diurnal pattern of xanthophyll cycle-dependent energy dissipation was altered such that this thermal dissipation process was engaged at a high level throughout the day, whereas in September it only became engaged when leaves received direct sunlight. An analysis of the diurnal partitioning of the absorbed excitation energy into photochemistry versus thermal dissipation suggested that a smaller fraction of that energy was utilized in photochemistry and a greater fraction was dissipated thermally at the end of November compared to September. Lower ratios of Chl a/b and β-carotene/xanthophylls both suggested a decrease in the ratio of reaction centre plus core antenna proteins compared to light-harvesting proteins, and a lower leaf chlorophyll content suggested a decrease in light-harvesting capacity in November versus September. Thus adjustments to the photosynthetic apparatus occurred on several levels in response to the increase in excess excitation energy that Y. glauca experienced during the onset of winter.

Notes: Variations in the water relations and stomatal response of Quercus ilex were analysed under field conditions by comparing trees at two locations in a Mediterranean environment during two consecutive summers (1993 and 1994). We used the heat-pulse velocity technique to estimate transpirational water use of trees during a 5 month period from June to November 1994. At the end of sap flow measurements, the trees were harvested, and the foliage and sapwood area measured. A distinct environmental gradient exists between the two sites with higher atmospheric CO2 concentrations in the proximity of a natural CO2 spring. Trees at the spring site have been growing for generations in elevated atmospheric CO2 concentrations. At both sites, maximum leaf conductance was related to predawn shoot water potential. The effects of water deficits on water relations and whole-plant transpiration during the summer drought were severe. Leaf conductance and water potential recovered after major rainfall in September to predrought values. Sap flow, leaf conductance and predawn water potential decreased in parallel with increases in hydraulic resistance, reaching a minimum in mid-summer. These relationships are in agreement with the hypothesis of the stomatal control of transpiration to prevent desiccation damage but also to avoid ‘runaway embolism’. Trees at the CO2 spring underwent less reduction in hydraulic resistance for a given value of predawn water potential. The decrease in leaf conductance caused by elevated CO2 was limited and tended to be less at high than at low atmospheric vapour pressure deficit. Mean (and diurnal) sap flux were consistently higher in the control site trees than in the CO2 spring trees. The degree of reduction in water use between the two sites varied among the summer periods. The control site trees had consistently higher sap flow at corresponding values of either sapwood cross-sectional area or foliage area. Larger trees displayed smaller differences than smaller trees, between the control and the CO2 spring trees. A strong association between foliage area and sapwood cross-sectional area was found in both the control and the CO2 spring trees, the latter supporting a smaller foliage area at the corresponding sapwood stem cross-sectional area. The specific leaf area (SLA) of the foliage was not influenced by site. The results are discussed in terms of the effects of elevated CO2 on plant water use at the organ and whole-tree scale.

Notes: Water relations of tomato fruit and the epidermal and pericarp activities of the putative cell wall loosening and tightening enzymes Xyloglucan endotransglycosylase (XET) and peroxidase were investigated, to determine whether tomato fruit growth is principally regulated in the epidermis or pericarp. Analysis of the fruit water relations and observation of the pattern of expansion of tomato fruit slices in vitro, has shown that the pericarp exerts tissue pressure on the epidermis in tomato fruit, suggesting that the rate of growth of tomato fruit is determined by the physical properties of the epidermal cell walls. The epidermal activities of XET and peroxidase were assayed throughout fruit development. Temporal changes in these enzyme activities were found to correspond well with putative cell wall loosening and stiffening during fruit development. XET activity was found to be proportional to the relative expansion rate of the fruit until growth ceased, and a peroxidase activity weakly bound to the epidermal cell wall appeared shortly before cessation of fruit expansion. No equivalent peroxidase activity was detected in pericarp tissue of any age. It is therefore plausible that the expansion of tomato fruit is regulated by the combined action of these enzyme activities in the fruit epidermis.

Notes: We explore the extent to which a simple mechanistic model of short-term plant carbon (C) dynamics can account for a number of generally observed plant phenomena. For an individual, fully expanded leaf, the model predicts that the fast-turnover labile C, starch and protein pools are driven into an approximate or moving steady state that is proportional to the average leaf absorbed irradiance on a time-scale of days to weeks, even under realistic variable light conditions, in qualitative agreement with general patterns of leaf acclimation to light observed both temporally within the growing season and spatially within plant canopies. When the fast-turnover pools throughout the whole plant (including stems and roots) also follow this moving steady state, the model predicts that the time-averaged whole-plant net primary productivity is proportional to the time-averaged canopy absorbed irradiance and to gross canopy photosynthesis, and thus suggests a mechanistic explanation of the observed approximate constancy of plant light-use efficiency (LUE) and carbon-use efficiency. Under variable light conditions, the fast-turnover pool sizes and the LUE are predicted to depend negatively on the coefficient of variation of irradiance. We also show that the LUE has a maximum with respect to the fraction of leaf labile C allocated to leaf protein synthesis (alp), reflecting a trade-off between leaf photosynthesis and leaf respiration. The optimal value of alp is predicted to decrease at elevated [CO2]a, suggesting an adaptive interpretation of leaf acclimation to CO2. The model therefore brings together a number of empirical observations within a common mechanistic framework.

Notes: To assess the possible physiological function of chlorogenic acid (CGA, 3-O-caffeoylquinic acid) in vivo, we characterized the free radical scavenging properties of pure phenylpropanoids and leaf extracts against two free radicals, superoxide and the 2,2’-azinobis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radical cation. CGA was found to be a highly efficient scavenger of these free radicals, surpassing the activity of all other phenylpropanoids tested, as well as the ‘classical’ antioxidant ascorbate. Seasonal differences in the leaf content of CGA were examined in field populations of the broadleaf evergreen Mahonia repens growing in different light environments. Leaves of fully sun-exposed plants contained significantly more (74 ± 10 mmol m–2) CGA in winter than leaves from plants growing under deeply shaded conditions (17 ± 2 mmol m–2). Sun-acclimated, but not shade-acclimated, leaves also produced high levels of anthocyanins in winter, suggesting a simultaneous increase in carbon flow through the phenylpropanoid and flavonoid pathways in response to high light and seasonal low temperature stress. In summer, high light-acclimated leaves contained ≈ 2-fold less CGA than in winter, whereas CGA levels were similar between seasons in shaded leaves. Consistent with the strong scavenging capacity of CGA measured in vitro, a linear correlation was observed between CGA content and the antioxidant activity of leaf extracts in both scavenging assays. On the basis of these results, we propose that CGA is a powerful hydrogen-donating antioxidant that may play an important role in mitigating the effects of oxidative stress in plants.

Notes: Pulses of blue light cause stimulation of red light saturated photosynthesis in Ectocarpus siliculosus, because blue light activates the operation of a pathway for inorganic carbon (Ci) acquisition by inducing the mobilization of CO2 from an intermediate metabolite. In the absence of exogenous Ci, photosynthetic rates roughly equal those of CO2 release by respiration. In seawater of pH 9·5 (2·3 mol m–3 total Ci, but concentrations of free CO2 below 0·2 mmol m–3), photosynthesis was clearly above these rates, although they were only ≈ 30% of those in normal seawater (≈ pH 8). The degree and the time course of the stimulations of photosynthesis by pulses of blue light were unaltered at high pH. Essentially the same characteristics were found after buffering or in the presence of acetazolamide, an inhibitor of extracellular carbonic anhydrase activity. Therefore, it is concluded that Ectocarpus is able to directly take up HCO3– in addition to CO2 (uptake of CO32– cannot be excluded). The dependence of photosynthesis on Ci at pH 9·5 was biphasic, with Ci below 0·2 mol m–3 having no effect at all. In Ci-free seawater, the shapes of the stimulations after blue light pulses differed for pH 6, pH 8 and pH 9·5. At low pH, only the fast peak (maximum ≈ 5 min after blue light) was detected, whereas at high pH mainly the slow peak (maximum ≈ 20 min after blue light) was observed. At the intermediate pH 8, both peaks were present. As inhibition of total carbonic anhydrase by ethoxyzolamide brought out the fast peak of the stimulations at pH 9·5 it is concluded that the fast component was due to a transient disequilibrium of an intracellular pool of Ci which, after blue light, was fed by CO2 released from the postulated storage intermediate.

Notes: The combined effects of carbon dioxide (CO2) enrichment and water deficits on nodulation and N2 fixation were analysed in soybean [Glycine max (L.) Merr.]. Two short-term experiments were conducted in greenhouses with plants subjected to soil drying, while exposed to CO2 atmospheres of either 360 or 700 μmol CO2 mol–1. Under drought-stressed conditions, elevated [CO2] resulted in a delay in the decrease in N2 fixation rates associated with drying of the soil used in these experiments. The elevated [CO2] also allowed the plants under drought to sustain significant increases in nodule number and mass relative to those under ambient [CO2]. The total non-structural carbohydrate (TNC) concentration was lower in the shoots of the plants exposed to drought; however, plants under elevated CO2 had much higher TNC levels than those under ambient CO2. For both [CO2] treatments, drought stress induced a substantial accumulation of TNC in the nodules that paralleled N2 fixation decline, which indicates that nodule activity under drought may not be carbon limited. Under drought stress, ureide concentration increased in all plant tissues. However, exposure to elevated [CO2] resulted in substantially less drought-induced ureide accumulation in leaf and petiole tissues. A strong negative correlation was found between ureide accumulation and TNC levels in the leaves. This relationship, together with the large effect of elevated [CO2] on the decrease of ureide accumulation in the leaves, indicated the importance of ureide breakdown in the response of N2 fixation to drought and of feedback inhibition by ureides on nodule activity. It is concluded that an important effect of CO2 enrichment on soybean under drought conditions is an enhancement of photoassimilation, an increased partitioning of carbon to nodules and a decrease of leaf ureide levels, which is associated with sustained nodule growth and N2 rates under soil water deficits. We suggest that future [CO2] increases are likely to benefit soybean production by increasing the drought tolerance of N2 fixation.

Notes: The aim of the present study was to test the four commonly used models to predict the dates of flowering of temperate-zone trees, the spring warming, sequential, parallel and alternating models. Previous studies concerning the performance of these models have shown that they were unable to make accurate predictions based on external data. One of the reasons for such inaccuracy may be wrong estimations of the parameters of each model due to the non-convergence of the optimization algorithm towards their maximum likelihood. We proposed to fit these four models using a simulated annealing method which is known to avoid local extrema of any kind of function, and thus is particularly well adapted to fit budburst models, as their likelihood function presents many local maxima. We tested this method using a phenological dataset deduced from aeropalynological data. Annual pollen spectra were used to estimate the dates of flowering of the populations around the sampling station. The results show that simulated annealing provides a better fit than traditional methods. Despite this improvement, classical models still failed to predict external data. We expect the simulated annealing method to allow reliable comparisons among models, leading to a selection of biologically relevant ones.

Notes: Carbon isotope composition (δ13C) was measured in a glasshouse experiment with N2-fixing and NO3–- or NH4+-fed Casuarina equisetifolia Forst. & Forst plants, both under well-watered and drought conditions. The abundance of 13C was higher (more positive δ13C) for NH4+- than for NO3– -grown plants and was lowest for N2-fixing plants. NH4+-fed plants had more leaf area and dry weight and higher water use efficiency (on a biomass basis) than N2- and NO3–-grown plants and had lower water consumption than plants supplied with NO3–, either with high or low water supply. Specific leaf areas and leaf area ratios were higher with NH4+ than with NO3– or N2 as the N source. The difference observed in δ13C between plants grown with different N sources was higher than that predicted by theory and was not in the right direction (NH4+-grown plants with a more negative δ13C) to be explained by differences in plant composition and engagement of the various carboxylation reactions. The more positive δ13C in NH4+- than in NO3–-grown plants is probably due to a decreased ratio of stomatal to carboxylation conductances, which accounts for the lower water cost of C assimilation in NH4+-grown plants.

Notes: Growth under elevated [CO2] promoted spring frost damage in field grown seedlings of snow gum (Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO2] (– 5·7 °C versus – 4·3 °C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO2 fertilization and may affect predictions of vegetation change based on increasing temperature.

Notes: The objective of this investigation was to examine the effect of an elevated atmospheric CO2 partial pressure (pCO2) on the N-sink strength and performance of symbiotic N2 fixation in Trifolium repens L. cv. Milkanova. After initial growth under ambient pCO2 in a nitrogen-free nutrient solution, T. repens in the exponential growth stage was exposed to ambient and elevated pCO2 (35 and 60 Pa) and two levels of mineral N (N-free and 7·5 mol m–3 N) for 36 d in single pots filled with silica sand in growth chambers. Elevated pCO2 evoked a significant increase in biomass production from day 12 after the start of CO2 enrichment. For plants supplied with 7·5 mol m–3 N, the relative contribution of symbiotically fixed N (%Nsym) as opposed to N assimilated from mineral sources (15N-isotope-dilution method), dropped to 40%. However, in the presence of this high level of mineral N, %Nsym was unaffected by atmospheric pCO2 over the entire experimental period. In plants fully dependent on N2 fixation, the increase in N yield reflects a stimulation of symbiotic N2 fixation that was the result of the formation of more nodules rather than of higher specific N2 fixation. These results are discussed with regard to physiological processes governing symbiotic N2 fixation and to the response of symbiotic N2 fixation to elevated pCO2 in field-grown T. repens.

Notes: Tobacco seedlings were grown in nutrient agar at a range of ammonium nitrate concentrations either without added sucrose, or with 100 mol m–3 sucrose. In the absence of added sucrose, nitrogen-limited plants had increased levels of glucose, fructose and sucrose, decreased chlorophyll, decreased protein, and decreased Rubisco activity, but the level of the transcript for the small subunit of Rubisco (RbcS) did not decrease compared with nitrogen-sufficient plants. When sucrose was added to nitrogen-sufficient seedlings, there was an increase of sucrose, glucose and fructose in the leaves, growth was increased, and the chlorophyll and protein content, Rubisco activity, and the RbcS transcript level did not change. When sucrose was added to nitrogen-limited seedlings, there was a further increase of sucrose, glucose and fructose, growth was not increased, and there was a further decrease of chlorophyll, protein and Rubisco activity, and a marked decrease of the RbcS transcript level. To check that the decrease of the RbcS transcript level was not an indirect effect due to changes of nitrogen metabolites after adding sugars, glucose was added to Chenopodium cells in the presence and absence of glutamine or azaserine. Changes of glutamine that suffice to increase and decrease the level of the transcript for nitrate reductase (Nia) do not affect the RbcS transcript concentration, and glucose addition still led to a decrease of the RbcS transcript level when the internal glutamine concentration was high. Tobacco seedlings were also grown in nutrient agar at a range of phosphate concentrations either without added sucrose, or with 100 mol m–3 sucrose. Phosphate-limited seedlings did not show a decrease of chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript, compared with phosphate-sufficient seedlings. The addition of sucrose to phosphate-limited plants led to a similar increase of sugars to that seen after adding sucrose to nitrogen-limited seedlings, but did not alter chlorophyll, protein, Rubisco activity, or the level of the RbcS transcript. The addition of sucrose to phosphate-limited plants led to a slight increase of the level of the transcript for nitrate reductase (Nia), increased nitrate reductase activity, and a marked increase of the amino acid content. Phosphate limitation led to an increased level of the transcript for the regulatory subunit of ADP glucose pyrophosphorylase (AgpS2), and this response was strengthened when sucrose was added. The regulation of AgpS2 expression by phosphate and sucrose was further investigated by feeding sucrose and phosphate to detached source leaves via the transpiration stream. The level of the AgpS2 transcript decreased after feeding phosphate and increased after feeding sucrose, and the effect of sucrose was antagonised by phosphate. It is concluded that the response to sugar signalling is modulated by nitrogen and phosphate in a gene-specific manner. The significance of these results for understanding the visual phenotype of nitrogen- and phosphate-limited plants, and the response of photosynthesis and starch synthesis to the plant nutrient status is discussed.

Notes: In many woody plants a short photoperiod triggers the onset of cold acclimation, but the nature of this process has remained obscure. We aimed to establish which physiological and genetic factors have a role in short-day-induced acclimation by comparing two types of birch, Betula pubescens Ehrh. and B. pubescens f. hibernifolia Ulv., the latter being unable to increase its abscisic acid (ABA) levels. In the wild type, short-day or natural autumn conditions in the field appeared to elevate the ABA levels before acclimation, which was accompanied by tissue desiccation, osmotic adjustments and accumulation of Group 2 LEA proteins [responsive to ABA (RAB) 16-like; 24, 30 and 33 kDa] and Group 4 LEA proteins [late embryogenesis abundant (LEA) 14-like; 19 kDa]. Under similar conditions the ABA-deficient birch showed reduced water loss, defective osmoregulation, absence of inducible Group 2 LEA proteins, and delayed or reduced tolerance to freezing. In contrast, both birch genotypes showed similar seasonal production patterns of Group 4 LEA proteins. Our results demonstrate that onset of cold acclimation in birch is based on multiple mechanisms, including molecular pathways that are typical of stress responses. ABA may be important for the accurate timing of cold acclimation in trees that are sensitive to photoperiod.

Notes: Tadmor is a Syrian barley landrace that has adapted to semi-arid environments. Its leaves are pale green because of a 30% decrease in the chlorophyll and the carotenoid content of the chloroplasts (leading to a 7·5% decrease in light absorption) compared with barley genotypes that are not adapted to harsh Mediterranean climatic conditions (e.g. Plaisant). This difference in pigment content was attenuated during growth of the plants in strong light, but was strongly amplified when strong light was combined with a high growth temperature. The low pigment content of Tadmor leaves was not associated with significant changes in the pigment distribution between the photosystems or between the reaction centres of the photosystems and their associated chlorophyll antennae. No significant difference in the photosynthetic activity (O2 production per unit absorbed light) was observed between Tadmor and Plaisant. The conversion of violaxanthin to zeaxanthin in strong light and its reversal in darkness were much faster and operated at a higher capacity in Tadmor leaves compared with Plaisant leaves, resulting in an increased photostability of photosystem II in the former leaves. The accelerated xanthophylls interconversion in the Syrian landrace was associated with, and possibly related to, an increased fluidity of the thylakoid membranes. The lipid peroxide level was lower in Tadmor compared with Plaisant. In contrast, no difference was found in the non-photochemical quenching of chlorophyll fluorescence between the two barley genotypes. The data indicate that the pale green Syrian landrace is equipped to survive excessive irradiance through a passive reduction of the light absorptance of its leaves, which mitigates the heating effects of strong light, and through the active protection of its photochemical apparatus by a rapid xanthophyll cycling.

Notes: A mechanistic model has been used to examine the environmental regulation of photosynthetic gas exchange in moss. The effects of water content on conductance to CO2 and on photosynthetic capacity during desiccation were calculated from the carbon isotope discrimination data of Williams & Flanagan (1996, Oecologia 108, pp. 38–46) and combined with the biochemical model of Farquhar et al. (1980, Planta 149, pp. 78–90). The model includes a simple light attenuation function that imparts curvature to the light response curve for net assimilation, enabling the use of physiologically realistic values for the biochemical parameters. Measurements of gas exchange for Sphagnum and Pleurozium were made in an old black spruce ecosystem over a growing season in order to assign values to parameters in the model. The calculated maximum rates of carboxylation by Rubisco (Vmax) were 5, 14 and 6μmol m–2 s–1 for Sphagnum during the spring, summer and autumn seasons of 1996, respectively. The increase in Vmax during the summer was consistent with an increased allocation of resources to the photosynthetic apparatus. In contrast, no seasonal variation in Vmax was observed in Pleurozium with average values of 7, 5 and 7 μmol m–2 s–1 during the spring, summer and autumn, respectively.

Notes: We investigated variation in intrinsic water-use efficiency during the past century by analysing δ13C in tree rings of beech growing in north-eastern France. Two different silvicultural systems were studied: high forest and coppice-with-standards. We studied separately effects related to the age of the tree at the time the ring was formed and effects attributable to environmental changes. At young ages, δ13C shows an increase of more than 1‰. However, age-related trends differ in high forest and coppice-with-standards. Changes in microenvironmental variables during stand maturation, and physiological changes related to structural development of the trees with ageing, could explain these results. During the past century, δ13C in tree rings shows a pattern of decline that is not paralleled by air δ13C changes. Isotopic discrimination has significantly decreased from 18·1 to 16·4‰ in high forest and varied insignificantly between 17·4 and 16·9‰ in coppice-with-standards. As a consequence, intrinsic water-use efficiency has increased by 44% in high forest and 23% in coppice-with-standards during the past century. These results accord with the increased water-use efficiency observed in controlled experiments under a CO2-enriched atmosphere. However, other environmental changes, such as nitrogen deposition, may be responsible for such trends.

Notes: We investigated (1) the effect of constant and altered inorganic phosphate (Pi) supply (1–100 mmol m–3) on proteoid root production by white lupin (Lupinus albus L.); and (2) the variation in citrate efflux, enzyme activity and phosphate uptake along the proteoid root axis in solution culture. Proteoid root formation was greatest at Pi solution concentrations of 1–10 mmol m–3 and was suppressed at 25 mmol m–3 Pi and higher. Except at 1 mmol m–3 Pi, the formation of proteoid roots did not affect plant dry matter yields or shoot to root dry matter ratios, indicating that proteoid roots can form under conditions of adequate P supply and not at the expense of dry matter production. Plants with over 50% of the root system as proteoid roots had tissue P concentrations considered adequate for maximum growth, providing additional evidence that proteoid roots can form on P-sufficient plants. There was an inverse relationship between the Pi concentration in the youngest mature leaf and proteoid root formation. Citrate efflux and the activities of enzymes associated with citric acid synthesis (phosphoenolpyruvate carboxylase and malate dehydrogenase) varied along the proteoid root axis, being greatest in young proteoid rootlets of the 1–3 cm region from the root tip. Citrate release from the 0–1 and 5–9 cm regions of the proteoid root was only 7% (per unit root length) of that from the 1–3 cm segment. Electrical potential and 32Pi uptake measurements showed that Pi uptake was more uniform along the proteoid root than citrate efflux.

Notes: The boring activity of microendolithic organisms such as cyanobacteria, chlorophytes, rhodophytes and fungi, represents a major destructive process affecting sediment preservation within reef environments. This study demonstrates the presence of two distinct assemblages of microborers within sediments collected from the fringing reefs of north Jamaica, correlating to the upper (〈18 m depth) and lower (〉18 m depth) photic zones. The upper photic zone assemblage is dominated by cyanobacteria and chlorophytes, whilst rhodophytes and fungi become more abundant with increasing water depth. Most significant from a grain preservation perspective is the variable nature of grain infestation observed between different reef sites and different carbonate grain types. The highest degree of grain infestation occurs within shallow, low-energy back-reef environments and the most susceptible grains (at all sites) are corals, molluscs and foraminifera. Coralline algae, Halimeda and echinoid fragments are rarely heavily infested. High rates of infestation at back-reef sites result in rapid diminution of the most susceptible grains, especially coral, which are either underrepresented, or contribute only to the finer sediment fractions, in the subsurface. Fore-reef grain assemblages undergo relatively little alteration. Microboring therefore has potential to bias the fossil record by removing the most susceptible skeletal grains. The impact of microboring upon back-reef grain assemblages must be considered when attempting to model depositional processes within both modern and ancient reef environments.

Notes: Hueneme and Dume submarine fans in Santa Monica Basin consist of sandy channel and muddy levee facies on the upper fan, lenticular sand sheets on the middle fan, and thinly bedded turbidite and hemipelagic facies elsewhere. Fifteen widely correlatable key seismic reflections in high-resolution airgun and deep-towed boomer profiles subdivide the fan and basin deposits into time-slices that show different thickness and seismic-facies distributions, inferred to result from changes in Quaternary sea level and sediment supply. At times of low sea level, highly efficient turbidity currents generated by hyperpycnal flows or sediment failures at river deltas carry sand well out onto the middle-fan area. Thick, muddy flows formed rapidly prograding high levees mainly on the western (right-hand) side of three valleys that fed Hueneme fan at different times; the most recently active of the lowstand fan valleys, Hueneme fan valley, now heads in Hueneme Canyon. At times of high sea level, fans receive sand from submarine canyons that intercept littoral-drift cells and mixed sediment from earthquake-triggered slumps. Turbidity currents are confined to ‘underfit’ talweg channels in fan valleys and to steep, small, basin-margin fans like Dume fan. Mud is effectively separated from sand at high sea level and moves basinward across the shelf in plumes and in storm-generated lutite flows, contributing to a basin-floor blanket that is locally thicker than contemporary fan deposits and that onlaps older fans at the basin margin. The infilling of Santa Monica Basin has involved both fan and basin-floor aggradation accompanied by landward and basinward facies shifts. Progradation was restricted to the downslope growth of high muddy levees and the periodic basinward advance of the toe of the steeper and sandier Dume fan. Although the region is tectonically active, major sedimentation changes can be related to eustatic sea-level changes. The primary controls on facies shifts and fan growth appear to be an interplay of texture of source sediment, the efficiency with which turbidity currents transport sand, and the effects of delta distributary switching, all of which reflect sea-level changes.

Notes: Analysis of a large data base of ground-penetrating-radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid- to high-latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment-source areas are characterized by chaotic, parallel, and tangential-oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection-free, and bounding-surface configurations. Back-barrier sediments may yield basin-fill configurations, but generally include abundant signal-attenuating units.The GPR data, calibrated with information from cores, were collected across swash-aligned and drift-aligned barriers in a variety of wave- and tidal-energy settings. Application of a 120-MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m.The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt-marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.

Notes: The Pliocene Loreto basin is an asymmetrical half graben located on the eastern margin of Baja California Sur, Mexico, which formed by rapid subsidence along the dextral-normal Loreto fault. The southern Loreto basin contains numerous, well exposed coarse-grained Gilbert-type fan deltas that were derived from the footwall of the Loreto fault. Detailed sedimentological study of individual foreset beds provides information about down-slope flow transformations of cohesionless sediment gravity flows in shallow water. Deposits of Gilbert-delta foresets consist of ungraded, normal-graded, inverse- to normal-graded, and bipartite conglomerate and sandstone. Lateral transitions in sorting, grading style and internal structure are commonly observed within individual beds, both across and down slope, suggesting heterogeneity within flows and a close relationship between high-density turbidity currents and gravel traction carpets. A conceptual model for flow transformation and deposition of high-density turbidity currents on Gilbert-delta foreset slopes is developed for Pliocene strata in the Loreto basin. In this model, ungraded cohesionless debris flows evolved rapidly down-slope into normal-graded gravelly turbidity currents. With continued down-slope transport, the gravel fraction collapses and becomes concentrated into a basal traction carpet undergoing laminar shear, and is over-ridden by a sandy turbulent suspension. The short distances (10–20 m) over which lateral transitions within single beds are observed indicate very rapid flow transformations (10–20 s) and rapid deposition of gravel traction carpets by frictional freezing on and near the base of the foreset slope.

Notes: 1. Aquatic insects were quantitatively surveyed at five sites along the tidally influenced section of a river-dominated estuary in North Wales. Site 1 was the furthest upstream and was established as a reference site as it was never inundated by salt water. Site 5 was the furthest downstream and was inundated by all incoming tides. Numerically, insects made up 32% of the estuarine invertebrate fauna.2. Although the densities of most insect taxa decreased towards the estuary mouth, there were significant numbers present downstream for much of the year; for example, in April at site 4 (which was inundated by 81% of all high tides), a mean of 3514 chironomid larvae were recorded per m2 of estuary bed. Even at site 5, which was inundated twice daily, there were 747 larvae per m2. Among the larger aquatic insects, caddisfly and elmid beetle larvae, together with stonefly nymphs, were consistently taken at site 4 (e.g. maxima of forty-eight caddisfly larvae m–2 in December and seventy elmids m–2 in April), although their densities were lower than upstream.3. There were seasonal shifts in the longitudinal distribution of several taxa, most notably the extension of chironomids down the estuary in April and July, and the concentration of simuliid larvae and mayfly nymphs at site 2 in July. The total freshwater benthos showed a downstream shift between September and December, which was maintained through April and into the summer. The latter was despite peak saltwater inundation (highest tides) in October, November and April. In June and July, when saltwater intrusion was lowest, the ranges of many aquatic insects had contracted to sites 1 and 2.4. Laboratory experiments showed that virtually all individuals of nineteen species of insects collected from site 1 (freshwater) survived a 4-h immersion in 8.75‰ saltwater (25% strength seawater). Immersion in progressively more saline solutions reduced the survivorship of first the mayflies, followed by the caddisflies Glossosoma conformis and Hydropsyche instabilis. After 4 h in full strength seawater, all specimens of the stonefly Dinocras cephalotes, over half of the Perla bipunctata, and some individuals of nine species of caddisfly were alive. Four species of caddisfly (Sericostoma personatum, Odontocerum albicorne, Potamophylax cingulatus and Adicella reducta) survived a 24-h simulated tidal cycle of immersion. With the exception of P. cingulatus, a few individuals of these caddisfly species survived immersion in full-strength seawater for 24 h. For some individual species there was good agreement between their observed longitudinal distribution in the estuary and laboratory-measured salinity tolerance; however, there was no significant correlation, overall, for the fauna.

Notes: 1. This study presents a qualitative and quantitative survey of epibionts infesting two populations of the freshwater isopod Asellus aquaticus (L.). Using scanning electron microscopy, the prevalence, mean intensity, abundance, spatial preferences and distribution of organisms on various external surfaces were ascertained.2. A diverse community, consisting primarily of protozoa and rotifers, utilised A. aquaticus as a substrate organism. Every individual A. aquaticus supported some form of epizoic life. Peritrich species comprised 89.2% of all epibionts. Carchesium polypinum, Pseudocarchesium aselli, Pseudocarchesium asellicola, Pseudocarchesium simulans and Opercularia hebes dominated the epifauna.3. Highest epibiont burdens occurred on the mouthparts, the first few ventral segments and the gills and largely comprised the above peritrich species. Most epibionts exhibited some degree of site preference on the host. A distinct gill epifauna existed. Apart from Acineta tuberosa and Vorticella rotunda, which had equal prevalences on dorsal and ventral surfaces in one culture, most species largely avoided the dorsal surface.4. Epibionts exhibited varying degrees of adaptation to life on a living substrate. They ranged from facultative species such as A. tuberosa, which are capable of colonising abiotic substrata, to Gymnodinoides aselli whose life cycle relies on interaction with A. aquaticus. Highly specialised species tended to exhibit the most pronounced and consistent site restriction.5. Asellus aquaticus offers a highly tractable system for further study of substrate species–epibiont relationships.

Notes: 1. The assemblage of suspension-feeding microcrustaceans in lakes changes along a habitat gradient from nearshore to offshore. This gradient of microcrustaceans was explored in relation to differences in macrophytes and the associated changes in water chemistry, food resources and types of predators.2. Some microcrustacean species were littoral or limnetic specialists, while others changed their distribution along this horizontal habitat gradient on a diel or seasonal basis. Distribution patterns were similar in a lake and a pond which differed in extent of macrophyte habitat.3. There was a large shift in the composition of sestonic food, indicating heterotrophic seston nearshore and more autotrophic seston offshore. Sit-and-wait predators of microcrustaceans (e.g. Enallagma spp.) dominated nearshore and cruising predators (e.g. Leptodora kindtii Focke) were more common offshore.4. A reciprocal transplant experiment revealed that littoral specialists could survive equally well when fed littoral or limnetic seston, while limnetic specialists performed poorly when fed littoral seston. Food resources may be important in determining where some microcrustacean species live along this horizontal habitat gradient.

Notes: 1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method.2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short-lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer-lived, temperate species, the signal crayfish, Pacifastacus leniusculus.3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P. leniusculus from several known year-classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age (r2 = 92.4%) and produced much more accurate age estimates than conventional body size-based procedures.4. A model derived from the crayfish of known-age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin-estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P. leniusculus to approximately 16 years.5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish, with probable further potential both within and outside the Crustacea.

Notes: 1. The nutritional value of detrital aggregate, which refers to the mixture of plant debris (i.e. organic detritus) and microorganisms, in the diets of fathead minnows (Pimephales promelas Rafinesque) was assessed in experiments using surface benthic samples from three sites in Clear Lake (Houghton County, Michigan, U.S.A.).2. In the first experiment, fish were fed small (〈250 μm) and large (250–1000 μm) particle detritus from one profundal and two littoral sites. Fish in all treatments lost weight. However, fish fed detritus from the littoral erosional site, where wild fish forage intensively, had significantly lower weight loss.3. In the second experiment, fish were fed various quantities of Artemia with or without ad libitum erosional site detritus. Growth was proportional to the mass of Artemia consumed, yet minnows showed increased growth with the detritus supplement at low invertebrate rations.4. This study shows that detrital aggregate produced by decompositional processes at the erosional site could be nutritionally valuable to minnows. It appears that a feeding strategy of consuming detritus with a higher nutritional quality (i.e. detrital aggregate) as a dietary supplement benefits fishes in temperate as well as tropical systems.

Notes: 1. A survey was made of denitrification and nitrous oxide (N2O) production in river sediments at fifty sites in north-east England during one season in order to investigate the relationship between rates and environmental factors likely to influence these processes. The sites were chosen to represent a wide range of physical and chemical conditions. Denitrification rate and N2O production were measured within 5 h of sampling using the slurry acetylene blockage technique.2. Denitrification rate ranged from less than 0.005–260 nmol N g–1 DW h–1, tending to increase in a downstream direction. N2O production ranged from negative values (net consumption) to 13 nmol N2O-N g–1 DW h–1 and accounted for 0–115% of the N gases produced.3. Denitrification rate and N2O concentration in the sediment were correlated positively with nitrate concentration in the water column, water content of the sediment and percentage of fine (〈 100 μm) particles in the sediment.4. The variation in denitrification rate was satisfactorily explained (64% total variance) by a model employing measurements of water nitrate and water content of sediments. No simple or multiple relationship was found for N2O production.

Notes: 1. A novel method was used to determine if the statutory regulation of drift-netting at the mouth of the River Usk in Wales was associated with a significant improvement in the stock and rod catch of salmon in the river upstream.2. A linear regression model was constructed, in which the annual rod catch of salmon declared from the Usk between 1977 and 1988 was the dependent variable and the simultaneous annual catch declared from the nearby River Wye was the independent variable. The model was extrapolated to project the annual rod catches of salmon on the Usk, relative to the Wye, between 1989 and 1995.3. The model accurately projected the actual rod catches declared from the Usk in 1989, 1990 and 1991. However, between 1992 and 1995 the declared catches deviated significantly (P≤ 0.05) from those projected by the model. The upsurge in rod catches declared after 1992 from the Usk, relative to the Wye was concomitant with the regulation of estuarine drift-netting.4. It was concluded that diminished estuarine exploitation had a beneficial impact on salmon angling success on the Usk. However, the utility of the model was restricted by inconsistencies in the methods used to generate the data, by changes in fishery management policies and by a lack of essential information on the interrelationships between catch, effort, stock and environmental conditions.

Notes: 1. The algae and sedentary macroinvertebrates on the upper surface of stones from the littoral of Crosemere were investigated over 13 months. This lake is one of a series of eutrophic meres of glacial origin in the English Midlands.2. Stones were taken from shallow and deep areas in the littoral and from areas shaded by bankside trees and those away from trees. This gave four habitat types: open/shallow; open/deep; shade/shallow; shade/deep. Epilithic algae and sedentary macroinvertebrates from the upper surfaces of the stones were quantified monthly for each habitat type.3. Chlorophyll a and ash-free dry mass both showed a strong seasonal pattern common to all habitat types, with a spring peak declining to a summer minimum, followed by a small autumn recovery, and a winter minimum.4. In terms of percentage cover, Cladophora glomerata showed a markedly different pattern. There were strong differences between habitat types, with shaded stones from the shallows, in particular, having very sparse Cladophora cover. In the open, Cladophora cover was high in summer and low at other times.5. The invertebrate community was dominated by retreat-dwelling larvae of the psychomyiid caddis, Tinodes waeneri, and four species of chironomids with tube-building larvae, Cricotopus sylvestris, Microtendipes pedellus, Glyptotendipes pallens and Endochironomus albipennis. For Tinodes, Cricotopus and Microtendipes, peaks of density occurred chiefly beneath trees in spring and summer.6. The seasonal pattern of algal abundance showed little relationship with that of invertebrate biomass. The ratio of chlorophyll a to ash-free dry mass also declined in summer, despite the higher invertebrate biomass. This indicated that grazing was not the dominant factor diminishing algal abundance seasonally. It seems likely that algae were limited chiefly by physical factors, such as light and temperature, and by nutrients, particularly nitrates, which decline in summer in the epilimnion of the lake.7. Grazing may have contributed to spatial patchiness of algae in summer, however, particularly that of Cladophora. The scarcity of Cladophora on shallow, shaded stones coincided with a high abundance of Tinodes on these stones in early summer. Riparian trees could thus have affected epilithic algae, not only by shading but also indirectly through the supply of grazers.

Notes: 1. By the aid of a computer technique, the in situ variations in heart rate and locomotor activity were recorded continuously for 7 days in sixteen individuals of the crayfish, Astacus astacus (Linnaeus 1758), in association with natural changes in water temperature and light intensity.2. All sixteen crayfish investigated were found to express circadian rhythmicity in heart rate with a periodicity of ≈ 24 h. For 88% of the animals investigated, rhythmicity was significant (P 〈 0.05). Ninety-three per cent of the crayfish showed circadian rhythmicity in locomotor activity with a 24 ± 2 h periodicity and, for 67% of the animals, this rhythmicity was significant (P 〈 0.05). In general, the expression of circadian rhythms was associated with nocturnal behaviour, heart rates and locomotor activity levels being higher at night than by day.3. A positive correlation was observed between heart rate and locomotor activity. Temperature and light intensity exerted positive and negative influences on heart rate in A. astacus, respectively.4. In the first experiment, 84% of the variation in heart rate could be explained by the changes in locomotor activity, temperature and light intensity. In the second experiment 35% of the variation in the heart rate was explained using these parameters.

Notes: 1. The rate of grazing damage experienced by submersed and floating leaves of water lilies (Nuphar variegata and Nymphaea odorata) was monitored in lakes in the Upper Peninsula of Michigan, U.S.A. Herbivores damaged 0.2–1.7% of the leaf surface of water lilies per day. These grazing rates differed between plant species, between submersed and floating leaves, and between lakes. Some leaves had more than 60% of their surface damaged and an overall mean of 16% damage occurred during the 2–3 week monitoring period of this study.2. Snapshot measurements of grazing damage on randomly collected submersed and floating leaves of Nuphar showed that submersed leaves were more damaged (11.0 ± 1.6%, n = 84) than floating leaves (3.8 ± 0.6%, n = 92). Overall, these 176 Nuphar leaves had 7.2% of their area damaged.3. Five species of herbivorous insects were commonly found on water lilies (Nymphaeacea). One primarily aquatic insect (sensuNewman 1991), a caddisfly larva (Trichoptera: Limniphilidae), had a generalized diet of water lilies, other macrophytes, algae, and detritus. Four of the five insects were from primarily terrestrial insect groups (Coleoptera and Diptera;‘secondary invaders’, sensuNewman 1991) and consumed only water lilies in food preference experiments.4. The feeding preferences of the generalist trichopteran were altered when the macrophytes were freeze-dried, ground into a powder, and reconstituted in an alginate gel. This suggests that plant structure may be an important feeding determinant for this insect. In contrast, a specialist weevil preferred its host plant in choice assays, regardless of whether fresh tissue or reconstituted macrophytes were used, suggesting this insect cued on a unique, non-structural property of its host plant.5. These results suggest that herbivory on freshwater macrophytes is of a similar magnitude to that on terrestrial plants. The findings of this study are consistent with the hypothesis that herbivorous insects of primarily terrestrial groups have a narrower diet breadth than insects of primarily aquatic groups.

Notes: 1. Phosphorus (P) uptake by macrophytes and epiphytes from the LaPlatte River (VT) was examined in the laboratory by adding 32PO4-P to recirculating stream microcosms.2. Water, plugs of sediment and plants were removed from the river and placed into the microcosms. 32PO4-P was then added either to the water or the sediment, and its incorporation into plants and epiphytes was monitored over 3 days. Uptake was examined at both ambient (5 μg L–1) and increased (50 μg L–1) soluble reactive phosphorus (SRP) concentrations. A computer program was developed to fit curves to the radiotracer data and calculate rate constants for the simultaneous transfer of 32P among compartments.3. Both macrophytes and epiphytes removed P from the water, but epiphyte uptake of P was more rapid. Phosphate enrichment stimulated P uptake by both macrophytes and epiphytes. Macrophytes also obtained P from the sediment. The relative contribution of P to macrophytes from the water vs. that from the sediment appeared to vary with SRP in the overlying water. Accurate estimates of rates of P uptake from sediments by macrophytes were difficult to obtain however, due to very low and highly variable unit rate constants for P uptake and uncertainty about the magnitude of the phosphate pool available for uptake.4. SRP concentrations were greater in the overlying water than in the sediment pore water of stream microcosms in the present study. Numerous reports in the literature have suggested that this condition favours uptake by macrophyte stems and leaves rather than by roots.5. Phosphate uptake from the water by macrophytes in shallow streams may be more common than for macrophytes in lakes.

Notes: 1. The feeding methods and intensity of predation by larvae of the damselfly Erythromma najas on leaf-mining larvae of the chironomid Glyptotendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimuli from the predator, light and the concentration of suspended food on the feeding activity of G. gripekoveni inside and outside of the mine.2. Erythromma najas preyed upon G. gripekoveni as the latter grazed outside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey.3. When the food concentration for the chironomid was high, it significantly reduced both filtering activity and activity outside mines in response to the kairomone produced by E. najas. Feeding activity did not change when food was scarce.4. The induced reduction in filter-feeding and deposit-feeding activity probably reduced predator success by reducing the probability of long-distance detection of a mine and location of the chironomid’s hole.5. The predator can detect and catch mining prey in either the light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey activity.6. Reduced feeding activity of mining larvae in the chemically simulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade-off between feeding demands and predation risk in a poorly known link of the littoral foodweb.

Notes: 1. To investigate direct effects of zebra mussel (Dreissena polymorpha) feeding activities on phytoplankton community composition, short-term microcosm experiments were performed in natural water with complex phytoplankton communities. Both gross effects (without resuspension of mussel excretions) and net effects (with resuspension) were studied.2. Gross clearance rates were not selective; essentially all taxa were removed at similar rates ranging from 24 to 63 mL mussel–1 h–1. Net clearance rates were highly selective; different plankton taxa were removed at very different rates, ranging from 12 to 83% of the gross rates, leading to consistent changes in the phytoplankton community composition. Thus, although zebra mussels can cause most phytoplankton to decline, there is considerable variation among taxa in either pre-digestive selection or post-digestive survival.3. The direct, short-term effects of zebra mussels on phytoplankton community composition are consistent with some of the major changes observed in the Hudson River since establishment of zebra mussels.4. We show, with simple calculations, how zebra mussel filtration rate, its selective efficiency on various taxa, and phytoplankton growth rates interact to produce changes in the phytoplankton composition.

Notes: 1. Cosmarium abbreviatum var. planctonicum, a desmid from oligo-mesotrophic lakes, had a higher maximum alkaline phosphatase activity (APA) and affinity constant under both continuous and pulsed inorganic phosphorus (Pi) limitation than Staurastrum chaetoceras, a desmid predominantly encountered in eutrophic lakes.2. APA of both species increased when measured in starved cells subjected to pulsed Pi conditions when compared to continuous Pi limitation.3. The portion of extracellular relative to cellular APA was higher in S. chaetoceras than in C. abbreviatum, indicating that S. chaetoceras secreted the enzymes more readily into its environment.4. The difference in APA could explain the dominance of C. abbreviatum during competition between these two species under conditions of continuous organic P (Po) limitation, but not the outcome under a pulsed Po shortage. The dominance of S. chaetoceras in the latter experiment can, however, be explained by species-specific Pi-uptake characteristics.5. After a saturating pulse of Pi, no increase in Pi in the extracellular mucus layer of C. abbreviatum was found and it was therefore concluded that the mucilage sheath does not store P. However, the sheath could have a main function as an accumulation site of cellular APA, providing the cell with Pi.

Notes: 1. The macroinvertebrate fauna living on stones in the exposed stony littorals of thirty-nine Danish lakes were examined by multivariate numerical methods. The data were derived from 125 semi-quantitative samples and a species list of 126 taxa. The mean number of individuals per sample was 960, and among the most common taxa were Asellus aquaticus, Gammarus, Oulimnius, Tinodes, Cricotopus and Dicrotendipes.2. The total number of species and fourteen individual taxa were positively correlated to mean depth of the lakes and eleven taxa were correlated to the total phosphorus concentration. The Shannon diversity was negatively correlated to the chlorophyll a concentration ([Chl a]).3. Community patterns were examined by detrended correspondence analysis (DCA), and the relationship between species data and selected environmental variables was analysed by canonical correspondence analysis (CCA). Mean lake depth was found to be the strongest environmental variable in explaining the species data. The [Chl a] and Secchi depth also explained significant variation in the distribution of the stony littoral invertebrates. Wind fetch and relative exposure did not explain any variation in the faunal composition among sites.4. The abilities of the macroinvertebrates to predict the lake trophic state, expressed as log ([Chl a]), were explored by means of weighted averaging (WA) regression and calibration. Two tolerance-weighted WA models using inverse and classical regression for deshrinking are presented. The models were assessed by the root mean square error (RMSE) of prediction, using bootstrapping as cross validation, and by the correlation between observed and inferred log ([Chl a]). The model using inverse deshrinking had a RMSEboot = 0.41 and r2 = 0.63. By using classical regression, the predictability in the ends of the gradient was improved but the RMSE increased: RMSEboot = 0.46.5. Although the factors determining faunal distribution patterns in the Danish lowland lakes were highly multivariate and difficult to disentangle, it seems reasonable to use the WA estimated species optima and tolerances to [Chl a] in a bio-assessment model.

Notes: 1. The hypothesis that body storage is used by daphniids as a physiological cue for adaptively adjusting egg size and number to food availability was tested.2. Egg size and number were examined to see whether they are related to individual variation in body storage independent of maternal size, genotype and food level. Egg mass and brood size (number of eggs in a brood) were compared to somatic mass, all adjusted to maternal body length, at two food levels in two parthenogenetic clones of Daphnia magna.3. The prediction that adjusted brood size should increase with body storage, whereas adjusted egg mass should decrease with increasing body storage, was not fulfilled as seven of eight comparisons failed to fit the expectation.4. It is concluded that body storage is probably not the food-availability cue used by daphniids to control intrabrood resource allocation. Other possibilities, such as chemical cues emitted by food organisms and by coexisting cladocerans, are briefly discussed.

Notes: 1. The total phosphorus–algal biomass relationship from a set of turbid tropical ponds in Kenya was compared with predictions derived from surveys of temperate and subtropical lakes. Despite high concentrations of total phosphorus (TP) (up to 797 μg L–1) and inorganic turbidity (up to 800 mg L–1), the log–log relationship between algal biomass and TP was steeper than expected.2. No evidence of nitrogen limitation was found at high TP, and total nitrogen (TN):TP ratios were higher than in lakes with similar TP levels studied previously. High TN:TP ratios may be a consequence of excretion by cattle into the ponds, a nutrient source characterized by a high ratio of available N to available P.3. Despite extremely high turbidity, the ratio of mixed layer depth to euphotic depth was generally low because these ponds are shallow (≤ 2 m), and was not related to algal yield. A positive relationship was also found between TP and zooplankton biomass, and between TP and the density of the zooplanktivorous bug, Anisops. In contrast, no relationship was found between fish biomass and TP, algal biomass or zooplankton biomass.

Notes: 1. Hydrological exchange between the surface stream and the hyporheic zone is well documented in the main channel of rivers, especially at the reach scale. Hydrological processes of advection/convection occur at different scales, and in secondary channels of large rivers little is known about these exchanges in the hyporheic zone on a broad scale (i.e. kilometres). This work studied exchanges of water and biota in a secondary channel on a large scale (4 km), using a three-dimensional framework.2. The exchanges of water were described using physicochemical indicators of surface and groundwaters. Samples of water and biota were taken in three dimensions: (i) vertically from benthic (i.e. 0.20 m below the surface of the substratum) to hyporheic (0.50 m) and deep interstitial (1.0 m) zones; (ii) laterally from the right to the left bank (i.e. right, middle and left positions); and (iii) longitudinally from upstream to downstream (seven stations regularly distributed along the channel).3. The physicochemical indicators clearly revealed hydrological heterogeneity in the longitudinal and vertical dimensions, whereas lateral variability was not significant.4. Spatial distribution of biota exhibited strong longitudinal variations that were not gradual as predicted by an upstream/downstream continuum, but patchy and discontinuous. No significant differences were found between the three positions across the channel.5. Analyses of both physicochemical and faunal data sets produced matched ordination of samples and stations, indicating that interstitial–surface flow relationships appear to be an important governing factor in the distribution of interstitial biota at this broad scale.6. Results are discussed in relation to the hypothetical three-dimensional models of the hyporheic zone in rivers. Contrasting with other observations on the main channel (where advection/convection patterns are dominated by morphological changes of the river-bed morphology), it is proposed that water exchanges in backwaters are more likely to be related to local modifications of stream-bed porosity.

Notes: 1. Diadromy is a dominating behavioural characteristic of fish faunas in New Zealand rivers, with amphidromy and catadromy being the most common strategies.2. Juvenile life stages of amphidromous and catadromous species migrate from the sea, through river systems, to find habitats for feeding, growth, maturation and reproduction.3. Studies of fish distributions in rivers of the West Coast of the South Island of New Zealand show that, in most species, these migrations result in more or less continuous distributions from the lower reaches to the upstream limits of each species’ range.4. Upstream penetration of rivers varies widely between species and this generates downstream–upstream trajectories of declining species richness.5. Parallel trajectories of declining downstream–upstream abundance are likely in each species.6. These patterns demonstrate the presence of downstream–upstream linkages in the community ecology of freshwater fishes in New Zealand rivers.

Notes: 1. Oligotrophic ‘Lobelia-lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years.2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today.3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species.4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long-term changes in nutrient concentration have been difficult to detect.

Notes: 1. In this field study, diatom-specific and bacteria-specific fatty acids were used as biomarkers to evaluate the differences in diet between Chironomus plumosus (a spring-emerging cohort) and C. anthracinus (an autumn-emerging cohort), and Procladius spp. Furthermore, total lipid content of Chironomus larvae was analysed.2. Individual dry mass of the spring cohort of C. plumosus rapidly increased during spring and early summer. Surprisingly, the autumn-emerging cohort showed remarkably little growth over the same time interval. The individual dry mass of C. anthracinus initially declined in early spring, but then increased during April and May.3. Accumulation of the diatom-specific fatty acid palmitoleic acid (16 : 1ω7) during spring was much higher in C. plumosus (〉 3-fold increase) than in C. anthracinus (1.5-fold). Conversely, the bacterial indicating iso form of septadecanoic acid (17 : 0i) was higher in C. anthracinus than in the spring-emerging cohort of C. plumosus. This shows that C. plumosus assimilates energy from the spring diatom bloom to a greater degree, whereas C. anthracinus feeds more exclusively on detritus in the sediment.4. Concentrations of 17 : 0i in Procladius larvae were 0.54 ± 0.13 mg g–1, i.e. consistently higher than for both Chironomus taxa, indicating that this predator gains a relatively high fraction of its energy through detrital pathways (from bacteria).5. These results show that fatty acid biomarkers can be an appropriate tool to detect differences in larval diet between coexisting chironomid species, between two closely related Chironomus species and between different cohorts.6. The different feeding modes of both Chironomus species may be important for among-lake distribution patterns, with filter-feeding C. plumosus being dominant in relatively shallow lakes and deposit-feeding C. anthracinus more common in deeper lakes with stable stratifications. This conjecture was supported by a compilation of data from Lake Mälaren.

Notes: 1. The effects of woody debris on stream habitat of juvenile masu salmon (Oncorhynchus masou) were examined at two spatial scales, stream reach and channel unit, for first- to third-order tributaries of the Teshio River in northern Hokkaido, Japan. The forty-eight study reaches were classified into three distinct types: coarse-substrate step-pool (CSP), coarse-substrate pool–riffle (CPR) and fine-substrate pool–riffle (FPR) reaches. Each reach type included reaches with different riparian settings, broadly classified as forest (relatively undisturbed forest and secondary forest after fires) or grassland (bamboo bushland and pasture).2. The reach-scale analyses showed that neither total pool volume nor pool-to-pool spacing was correlated with woody debris abundance in any of the three reach types. Masu salmon density was positively correlated with both woody-debris cover area and total cover area, but not with total pool volume in the reaches.3. Channel-unit-scale analyses revealed that woody debris reduced non-pool velocity, increased pool depth and retained fine sediment in pools in FPR reaches, where the size of woody debris was very large relative to the substrate material size. However, woody debris did not influence any of the hydraulic variables (depth, velocity, substrate) in either non-pools or pools of CSP and CPR reaches. Habitat use by masu salmon in non-pools or pools was affected by woody-debris cover area or total cover area rather than by hydraulic variables in any of the reach types.4. The effects of woody debris on habitat at the reach- and channel-unit scales in the study area were less than those indicated by previous work in the Pacific Northwest, North America, owing to the relatively small size of the riparian trees. However, the overall results suggested that woody debris in the study area contributed to masu salmon habitat by providing cover at the smaller, microhabitat scale.

Notes: 1. A new marking technique was developed and used to track individual water flea behaviour. A single clone of Ceriodaphnia reticulata exhibited no significant differences in mean depth, mean activity (antennae beats used in swimming), and mean travel (total vertical displacement) for fast-green dyed and control animals (n = 30, each treatment).2. Individual and group antipredator responses were recorded in three vertebrate predator densities (three odour concentrations of green sunfish Lepomis cyanellus; 0.00, 0.03 and 0.10 fish L–1) and four water flea group sizes (1, 5, 15 and 25), with n = 18 for each of the twelve treatment combinations. Water flea groups were probably mixtures of clones. Differences in behaviour after addition of predator odour showed that increasing predator density increased mean depth of marked individuals and mean proportion of water fleas descending. Additionally, increasing prey density decreased both mean depth of marked individuals and mean proportion of water fleas descending.3. Predator density and prey density had opposing affects on activity and travel for marked individuals. Higher predator density decreased mean activity (antennae beats), yet increased mean travel. Higher prey density increased mean activity, but decreased mean travel. Descending animals altered their swimming pattern by using fewer swimming beats to travel greater vertical distances in the presence of predator odour.

Notes: 1. An experimental field study examined the aggregation of stream macroinvertebrates associated with leaf packs over different spatial scales (several metres–km) (extent), at different patch sizes (grain) and temporal scales (2 and 4 weeks).2. Standardized leaf packs were constructed and set in eighteen blocks of nine equally spaced packs in glide areas over a 2 km stretch of a wooded stream. The distribution of macroinvertebrates colonizing the artificial leaf packs was investigated to examine the extent of both intraspecific and interspecific aggregation across leaf packs.3. All major colonizing taxa were intraspecifically aggregated across the leaf packs. Aggregation decreased with increasing patch size (grain) (from pack to block), and also decreased with decreasing spatial extent (from 2 km stretch to within-block scale) with patch size held constant. Interspecific associations among all major taxa were not common on most occasions at the short temporal scale, although the proportion of significant associations tended to increase somewhat over time and with spatial scale, but did not exceed 42% of all possible associations. The vast majority of significant associations were positive rather than negative.4. The influence of heterogeneity in a number of environmental variables measured for each leaf pack (accumulated detritus and sediment, leaf mass, flow and depth) on the distribution of invertebrates was considered, but this could only partially explain the variation in macroinvertebrate abundance across leaf packs.5. The roles of intrinsic aggregation and stochastic processes were examined as alternative explanations for the distribution patterns observed. It is apparent from this study that intrinsic aggregation, in concert with resource partitioning, influences the community structure of stream macroinvertebrates associated with leaf packs. These findings may also have implications for the distribution of taxa in the benthos as a whole.

Notes: 1. The role of sediment phosphorus (P) and nitrogen (N) in regulating growth of rooted macrophytes in a Canadian prairie river was investigated by means of in situ observations and artificial stream fertilization experiments.2. Biomass and percentage cover of rooted macrophytes in the South Saskatchewan River increased downstream of a municipal sewage treatment plant, with maximum abundance occurring between 25 and 100 km downstream of the outfall. Biomass in the river was related to sediment P but not N concentration, although sites of maximum biomass did not coincide with sites of maximum sediment P concentration.3. Artificial stream experiments revealed that while biomass was unaffected by addition of N to the sediment, it was enhanced by the addition of P to sediments, and further enhanced with the addition of N and P together, indicating a primarily P-limited system, with secondary N limitation when P is in excess.4. Macrophyte biomass increased linearly with increasing sediment P concentration in the artificial streams, and tissue P concentration peaked at ≈ 400 μg g–1. Biomass did not respond to increasing sediment N concentration, and only a weak relationship was observed between tissue N and sediment N, with maximum tissue N corresponding to ≈ 140 μg g–1 sediment exchangeable N.5. A lack of concurrence between the sediment P concentration producing maximum biomass and tissue P concentration in situ vs. under experimental conditions indicates that other environmental factors have an important role in regulating macrophyte growth in rivers. Thus, while nutrient control may be one element in a river macrophyte control programme, a holistic ecosystem approach should be adopted to account for the other factors that may affect the growth of rooted plants.

Notes: 1. Few studies have assessed the effects of macroconsumers, such as fishes and shrimps, on detritus and detritivores.2. We used an underwater electric field to prevent macroconsumers from feeding in and on leaf packs in a lowland stream in Costa Rica and thus to determine their effects on the density of insect detritivores and decay rates of leaves.3. Exclusion of macroconsumers resulted in significantly higher densities of small invertebrates inhabiting leaf packs. Most of these were collector–gatherers, none were shredders.4. Despite the increase in invertebrate density, decay rates of leaves were not statistically different. These findings contrast with results from temperate streams showing that increases in the density of invertebrates in leaf packs typically result in an increased rate of decay.5. Leaf decay rates and invertebrate densities were also compared between leaf packs placed in electric exclusion treatments and those placed in coarse (2 cm) plastic net bags (as used in many previous studies). Our results suggest that using such netting in tropical streams may deter macroconsumers, which can affect insect density and, potentially, decay rates of organic matter.

Notes: 1. The rate of microbial respiration on fine-grained stream sediments was measured at 196 first- to third-order sites in the mid-Atlantic region of the United States.2. Sample collection took place between April and July in 1993, 1994 and 1995.3. Study streams were randomly selected from the United States Environmental Protection Agency’s (USEPA) River Reach File (RF3) using the sample design developed by USEPAs Environmental Monitoring and Assessment Programme (EMAP).4. Respiration rate ranged from 0 to 0.622 g O2 g–1 ash-free dry mass (AFDM) h–1, and was significantly correlated with stream temperature, water chemistry and physical habitat.5. Respiration rate was significantly higher in streams from the Chesapeake drainage area compared to those from the Ohio drainage area, and in streams from the Northern Appalachian Plateau and Uplands and Central Appalachian Valleys ecoregions compared with streams from the Blue Ridge and Central Appalachian Plateau ecoregions.6. Respiration was not significantly different among stream orders or between years.

Notes: 1. At two organically polluted sites in the River Nethravathi, banyan and eucalypt leaves were colonized by one or two species of aquatic hyphomycetes. A total of three or four species were identified at the two sites in samples of water and naturally occurring leaves.2. Spore production from stream-exposed leaves by aquatic hyphomycetes was lower by a factor of up to 1 million compared with an earlier study in geographically close but unpolluted streams.3. Exponential decay rates and loss rates of phosphorus and calcium, were not statistically different from an earlier study in unpolluted streams. Nitrogen increased during decomposition more slowly in the current study.4. The microbial community on both leaves released enzymes active against starch, pectin, cellulose and xylan.5. Banyan leaves conditioned for 12 weeks were more palatable to the gastropod Notopala sp. than unconditioned leaves.6. Together with earlier data from unpolluted streams, the study provides evidence that organic pollution severely restricts diversity of aquatic hyphomycetes and their reproductive output, but does not have an equally strong effect on ecological functions generally associated with this group.

Notes: 1. A sample of adult signal crayfish were taken from a pond with a hepatotoxic bloom of the benthic cyanobacterium Oscillatoria sancta. Cyanobacteria were found in the stomachs of thirty-one out of thirty-two crayfish examined.2. To examine the effect of hepatotoxic cyanobacteria on crayfish a 14-day feeding trial was carried out with thirty-six animals. There were three treatments: (i) hepatotoxic and (ii) non-toxic Planktothrix agardhii; and (iii) crayfish pellets as a control.3. High-performance liquid chromatography (HPLC) showed that microcystins (the toxins of P. agardhii) had accumulated in the hepatopancreas of 50% of the animals in the toxic treatment.4. The cyanobacteria did not appear to have any negative impact on the crayfish. All crayfish survived, remained motile and ate throughout the experiment.5. During the experiment blood samples were taken and the total number of haemocytes counted. At the end of the experiment glucose concentration and relative wet weight of the hepatopancreas were measured. No differences between crayfish fed on toxic and non-toxic P. agardhii and the controls were found.6. The fact that microcystin accumulates in the crayfish hepatopancreas indicates that the toxin may be transferred further up the food chain.

Notes: 1. A method for quantifying interstitial water velocity based on the dissolution rate of plaster of Paris standards was developed as part of a study of vertical, longitudinal (1–4 order sites) and seasonal variation in the biotic and physical characteristics of the shallow hyporheic zone (0–30 cm) of a headwater stream system in West Virginia, U.S.A.2. A calibration model was developed using a water velocity simulation tank to relate mass loss of plaster standards to water velocity and temperature. The model was then used to calculate water velocity through artificial substrata embedded in the shallow hyporheic zone of four stream reaches based on in situ mass loss of plaster standards.3. Water velocity in the hyporheic zone increased with stream order, was highest in early spring and winter during high stream base flows, and decreased with depth into the substratum. There was a strong interaction between depth and season: during periods of high stream discharge, water velocity through the upper level of the shallow hyporheic zone (0–10 cm into the substrate) increased disproportionately more than velocity at greater depths. Mean interstitial velocity in March ranged from 0 cm s–1 in the lowest level (20–30 cm) to 3.5 cm s–1 at the upper level (0–10 cm) at the first-order site, and from 2.5 cm s–1 (20–30 cm) to 9.5 cm s–1 (0–10 cm s–1) at the fourth-order site. Gradients in stream discharge and sediment permeability accounted for treatment effects.4. Use of calibrated data improved the ability to resolve among-season differences in interstitial water movement over the use of uncalibrated mass loss data. For some applications of the plaster standard method, empirical calibration may not be necessary.

Notes: 1. A model developed over 20 years ago has been used to estimate daily food intake in brown trout living in streams and lakes over a wide geographical range. The chief disadvantages of this early model are that it is not continuous and requires twelve parameters, not all of which can be interpreted biologically. A new model, using a larger data set, was therefore developed to overcome these problems and estimate the mean daily energy intake.2. The two data sets used to develop the original model were also used to develop the general form of the new one, but a third data set was used to specify the model more precisely and to estimate the parameters. This third data set originated from experiments in which 185 trout (live weight range 1–350 g) were kept individually at 19 constant temperatures (range 3.8–21.7 °C) usually for 5–6 weeks. They were fed freshly killed shrimps (Gammarus pulex) and their food consumption was recorded throughout each experiment.3. Five, six and eight parameter versions of the new model were all excellent fits to the data (P 〈 0.001, R2 〉 0.99), with the eight parameter version being slightly the best. All parameters can be interpreted in biological terms; three define threshold temperatures, three define the curvilinear slopes in the model over different temperature ranges, one is a weight exponent and one is the maximum daily energy intake of a 1 g trout. The simpler six parameter model was adequate at temperatures above 7 °C.4. An additional experiment with twenty-eight trout feeding on six different invertebrate foods provided estimates of energy intake that were very similar to those predicted from the model. However, when daily intake was converted to dry weight, agreement with values from the model (also as dry weight) was poor. Possible reasons for this are discussed, as are other studies using the earlier model, and it is shown that different conclusions can be reached depending upon whether comparisons are based on units of energy, dry weight or wet weight.

Notes: 1. Temporal variation in the spatial aggregation of the freshwater bivalve Elliptio complanata was studied at a sandy site in an oligotrophic lake over three years.2. Epibenthic populations varied in aggregation over the season bringing animals closer together during spawning. The complex link between movements of mussels and aggregation dynamics suggested a functional reproductive role for horizontal locomotion of unionid mussels in lentic systems.3. The rate of locomotion did not differ systematically among males, females or hermaphrodites, and was independent of gravidity, whether compared during spawning, after spawning or throughout the ice-free season.4. In spite of the high reproductive output of mussels and the energetic cost of locomotion, no relationship was found between the rate of movement of spawning gravid mussels and reproductive output.

Notes: 1. Two sampling techniques were used to characterize invertebrate communities in eight, low-order streams along an altitudinal gradient in Costa Rica that represents the last continuous tract of primary forest spanning such extremes in elevation (i.e. near sea level to 2900 m a.s.l.) along the Caribbean Slope of Central America. A standard Surber sampler was used to sample invertebrates on the stream bottom, and drift sampling nets were used to sample invertebrates drifting in the stream flow.2. Sites were established at 30, 50, 700 1800 and 2700 m a.s.l. In one to two streams per site, six Surber samples were collected, and drift was sampled every 3 h over one 24-h period between April and August 1994. All sites were in primary forest, with the exception of the lowest elevation site (30 m) which was located in banana plantations.3. Both sampling techniques indicated that Diptera (Chironomidae) and Ephemeroptera were the dominant insect groups at all sites. Disturbed streams draining banana plantations were dominated by Chironomidae and had lower taxon richness and diversity than other sites.4. While data from benthic samples indicated that insects were the major faunal component (〉 90%) at all sites, drift samples were dominated by larval shrimps (〉 50%) at the 30 m and 50 m sites.5. Drift periodicity of invertebrates was observed at those sites characterized by predaceous fishes: nocturnal drift densities were higher than diurnal densities at 30, 50 and 700 m a.s.l., however, no periodicity was observed at 1800 and 2700 m a.s.l. where fish were absent.6. This study shows the importance of measuring invertebrate drift, in addition to directly sampling the benthos. Drift sampling provided data on a major community component (shrimps) of lowland tropical streams, that would have been overlooked using traditional benthic sampling techniques, and in some cases provided additional information on taxon richness.7. Based on results of the present study, it is recommended that drift sampling be included as a standard complementary tool to benthic sampling in biological assessments (e.g. bioassessment protocols) of tropical streams, which are often characterized by migratory invertebrate species such as shrimps. Drift samples provide critical information on the presence or absence of shrimps and also on the timing and magnitude of their migration which is an important link between many tropical rivers and their estuaries.

Notes: 1. Lough Neagh is a large eutrophic lake covering 387 km2 with a mean depth of 8.9 m. It is an important natural resource, being the largest single source of potable water for Belfast, Northern Ireland.2. This report examines the causes of the year-to-year variation in the April–June (spring) algal biomass, measured as chlorophyll a, for the period 1974–92.3. The spring chlorophyll a declined following the introduction of a phosphorus (P) reduction programme at major sewage treatment works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased.4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spring chlorophyll a concentrations.5. The independent variables used in the multiple regression model were the previous year’s spring chlorophyll a concentration, soluble reactive P inputs for April–June and the particulate P concentration in the Lough during the previous summer.

Notes: 1. Variations in the relative biovolumes of dominant cyanobacterial taxa were evaluated in the context of environmental conditions using canonical correlation analysis (CCorrA) and Redundancy Analysis (RDA). The objective was to test a conceptual model in which underwater irradiance determines dominance by bloom-forming (high light adapted) or non-blooming (low light adapted) taxa.2. The data set consisted of 404 contiguous observations, collected over a 3-year period at eight pelagic sites, in shallow Lake Okeechobee, Florida, U.S.A. Data included species biovolumes, total phosphorus (TP), total nitrogen (TN), dissolved oxygen (DO) and chlorophyll a concentrations, as well as two indices: underwater irradiance (Secchi depth) and the ratio of Secchi:total depth.3. The first environmental canonical variable was strongly correlated with the two light-related indices, and negatively correlated with TP. This reflects the predominant role of resuspended P-rich lake sediments in controlling underwater irradiance in the shallow lake. The first species canonical variable displayed a strong negative correlation with Lyngbya limnetica and L. contorta, and positive correlations with Anabaena circinalis, Aphanizomenon flos aquae and Microcystis spp. The results support the conceptual model; the first pair of canonical variables explained 55% of the variation in the species–environmental data set. RDA results provided further support for the hypothesis that irradiance was the major force controlling community structure.4. One unexpected result was a positive association between Oscillatoria spp. dominance and indicators of high irradiance. This conflicts with past research indicating that Oscillatoria is a low light adapted taxon, and the finding that it is the most abundant taxon in Lake Okeechobee. This may reflect the fact that the two Lyngbya taxa were more strongly associated with low light conditions than Oscillatoria. CCorrA results indicated that Oscillatoria densities are strongly controlled by water temperature. There is a need for more detailed studies of cyanobacteria ecophysiology in order to explain fully the seasonality of phytoplankton in this and other shallow subtropical lakes.