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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Entomologia experimentalis et applicata 77 (1995), S. 315-321 
    ISSN: 1570-7458
    Keywords: Insecta ; Helicoverpa zea ; Zea mays ; resistance inheritance ; joint scaling test ; additive-dominance model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The corn earworm,Helicoverpa zea (Boddie), is a perennial economic pest of field crops in the United States. Maize,Zea mays L., is the major host crop promoting the build-up of devastating corn earworm populations that limit full production of cotton, soybean, peanut, and grain sorghum. Resistance to the corn earworm in maize and in particular sweet maize, would provide an environmentally safe, economical method of control for this pest insect. Antibiotic effects of corn silks on this insect are: small larvae, extended developmental period, and reduced fecundity. Silks from individual maize plants of resistant and susceptible lines and progeny in six generations consisting of parents (P1, P2), F1, F2, and backcrosses BC1.1 (F1 × P1) and BC1.2 (F1 × P2) from each of four crosses were used to determine the genetic basis of the antibiotic resistance of silks to the corn earworm. In the cross of Zapalote Chico × PI340856, genes controlling resistance in the silks to the corn earworm larvae are dominant in PI340856 to those in Zapalote Chico. The cross of Zapalote Chico × GT114 involves parents differing in degree of resistance, and possibly differing for the genetic mechanism by which the resistance is inherited. The inheritance of resistance may involve non-additive (dominance and epistasis) genetic variance. A digenic 6-parameter model indicated (1) the resistance in this cross is controlled by more than one pair of genes and (2) some or all of the genes interact to cause non-allelic interaction. Thus, the resistance in this cross may be controlled by both dominant and recessive genes. The resistance of Zapalote Chico × CI64, an intermediate inbred, is influenced by additive gene effects. The digenic model adequately predicts all generation means of the cross of GT3 × PI340856 except for the F1. Thus, it appears that the additive-dominance model is not satisfactory for this cross involving susceptible and resistant parents. Generation mean analysis indicates that resistance to silk-feeding by corn earworm larvae is under genetic control, but gene action differs from one type of cross to another.
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  • 2
    ISSN: 1432-1890
    Keywords: Glomus mosseae ; Zea mays ; Mineral uptake ; Root exudation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-μm nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterle soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shoot∶root ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, threeto sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.
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  • 3
    ISSN: 1432-1890
    Keywords: Key words Glomus mosseae ; Zea mays ; Mineral uptake ; Root exudation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Maize (Zea mays L. cv. Alize) plants were grown in a calcareous soil in pots divided by 30-μm nylon nets into three compartments, the central one for root growth and the outer ones for hyphal growth. Sterile soil was inoculated with either (1) rhizosphere microorganisms other than vesicular-arbuscular mycorrhizal (VAM) fungi, (2) rhizosphere microorganisms together with a VAM fungus [Glomus mosseae (Nicol. and Gerd.) Gerdemann and Trappel], or (3) with a gamma-irradiated inoculum as control. Plants were grown under controlled-climate conditions and harvested after 3 or 6 weeks. VAM plants had higher shoot : root ratios than non-VAM plants. After 6 weeks, the concentrations of P, Zn and Cu in roots and shoots had significantly increased with VAM colonization, whereas Mn concentrations had significantly decreased. Root exudates were collected on agar sheets placed on the interface between root and hyphal compartments. Six-week-old VAM and non-VAM plants had similar root exudate compositions of 72–73% reducing sugars, 17–18% phenolics, 7% organic acids and 3% amino acids. In another experiment in which root exudates were collected on agar sheets with or without antibiotics, the amounts of amino acids and carbohydrates recovered were similar in VAM and non-VAM plants. However, three- to sixfold higher amounts of carbohydrates, amino acids and phenolics were recovered when antibiotics were added to the agar sheets. Thus, the high microbial activity in the rhizosphere and on the rhizoplane limits the exudates recovered from roots.
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  • 4
    ISSN: 1432-0789
    Keywords: Arbuscular mycorrhiza ; Limed silty loam Heavy metals ; Pb-Zn smelter ; Root colonization Spore numbers ; Tolerance ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The bioavailability of heavy metals (Cd, Zn, Pb, Cu) and the abundance of arbuscular mycorrhiza (AM) were studied in two agricultural fields close to a Pb-Zn smelter and three fields outside the pollution zone all cultivated with maize (Zea mays L.). Metal extractability with ethylenediaminetetraacetic acid (EDTA)-NH4OAc and Ca(NO3)2, plant metal uptake, and mycorrhizal parameters (spore number, root colonization) were assessed at two growth stages (six-leaf and maturity). Despite regular liming, the availability of Cd, Zn, and Pb was markedly higher in the two metal-polluted fields than in the three uncontaminated fields. However, the AM abundance was not correlated with metal availability. Root colonization and spore numbers in the metal polluted fields were relatively high, though at plant maturity the former was significantly lower than in one of the uncontaminated fields. The very low AM abundance in the two other unpolluted fields was related to other factors, particular soil and plant P status and soil pH. AM root colonization did not substantially prevent plant metal accumulation, since the metal concentrations in maize grown on the polluted fields strongly exceeded normal values, and for Cd and Pb reached the limits of toxicity for animal feed.
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  • 5
    Electronic Resource
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    Springer
    Biology and fertility of soils 20 (1995), S. 57-62 
    ISSN: 1432-0789
    Keywords: Nitrogen use ; Nitrogen fertilizer recovery ; Zea mays ; Phaseolus vulgaris ; Vigna unguiculata ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Locally suitable cultivars of maize, beans, and cowpeas were grown in field experiments for four seasons in semi-arid Kenya. For three seasons, the dry matter production and grain yield of maize and beans were not increased by N fertilizer additions up to 120 kg N ha-1. Fertilizer recoveries measured by 15N isotope dilution techniques were low, less than 20%. Inoculated and uninoculated beans failed to fix N2. By contrast the cowpea derived 50% of its N from fixation, equivalent to 197 kg N ha-1. The N content of the grain generally exceeded 40 kg N ha-1, and the N content of the seeds from the grain legumes were greater than those from the cereals. Large inputs of N fertilizer or N by fixation are required if maize-grain legume cropping system in semiarid Kenya are to be sustained in the long term.
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  • 6
    Electronic Resource
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    Springer
    Mycopathologia 129 (1995), S. 117-125 
    ISSN: 1573-0832
    Keywords: Biological control ; Corn seedling disease ; Enterobacter cloacae ; Fusarium moniliforme ; Maize ; Seedling blight ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The bacteriumEnterobacter cloacae is presently used for biocontrol of postharvest diseases of fruits and vegetables and as a preplant seed treatment for suppression of damping-off. This bacterium has apparent affinities for several grass species, but it is not considered to be an endophyte. While screening corn for fungi and bacteria with potential for biocontrol of various corn diseases, the surface-sterilized kernels of one unknown Italian corn cultivar produced fungus-free corn seedlings with roots endophytically infected byE. cloacae. This paper describes the microscopic nature ofE. cloacae RRC 101 with corn, and the in vitro control ofFusarium moniliforme and other fungi with this bacterium. Light and electron microscopy determined that this isolate ofE. cloacae was biologically associated with corn seedling roots, where it was distributed intercellularly within the cortex and stele. This is a first report of a strain of this bacterium as an endophytic symbiont of roots. Following a topical application ofE. cloacae to kernels, and upon germination this bacterium readily infected roots of two other corn cultivars. The bacterium was observed within the endosperm of germinating corn seedling, but germination was not affected. Further, the bacterium was isolated from leaves and stems of 3- to 6-week-old seedlings indicating that the above ground portions of corn were also colonized. There was no evidence of damage to cells of the root during a three to four week observation period. This bacterium was antagonistic to several isolates of the corn pathogenFusarium moniliforme, and to two other species of fungi, all of which produce mycotoxins on corn.
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  • 7
    Electronic Resource
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    Springer
    Mycopathologia 132 (1995), S. 173-183 
    ISSN: 1573-0832
    Keywords: Deoxynivalenol ; Embryo ; Mature ; Ochratoxin ; Plantlet ; Zearalenone ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mature maize (Zea mays) embryos were exposed to 5, 10 and 25 µg ml−1 of deoxynivalenol (DON), zearalenone (ZEA), ochratoxin A (OA) and a mixture of zearalenone and deoxynivalenol (ZEA/DON) for 9 days. DON and the ZEA/DON combination were consistently more inhibitory of the measured parameters than either ZEA or OA. Based on the predicted additive values, it would appear that, in combination, ZEA and DON act synergistically to inhibit root and shoot growth. For ZEA alone, a concentration of 5 µg ml−1 ZEA was generally inhibitory of root and shoot elongation and fresh mass accumulation, while at 10 and 25 µg ml−1, this toxin had a stimulatory effect on these parameters. For OA, the measured effects on root and shoot growth at 5 and 25 µg ml−1 were stimulatory, while at 10 µg ml−1 OA, an inhibitory effect was observed. For all toxins, inhibitory/stimulatory effects were generally more marked for root parameters than for shoot elongation or mass.
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  • 8
    ISSN: 1432-2145
    Keywords: Embryo sac ; Zea mays ; Enzymatic isolation ; Zygotic embryogenesis ; Microinjection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The long-term viability of isolated embryo sacs was studied in maize. Fertilised embryo sacs were digested in order to remove most of the nucellus cells present on their surfaces and then transferred to culture. Experiments on 161 embryo sacs showed that isolation treatments using even minimal enzymatic digestion affected the further development of the embryo sacs. Few embryo sacs survived in culture and those produced only abnormal embryos; they produced no plants. We concluded that embryo sacs isolated through enzymatic digestion may offer limited prospects for long-term studies where normal embryogenic development is required. Alternative strategies are discussed for maize.
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  • 9
    ISSN: 1432-2145
    Keywords: Zea mays ; Calcium ; Cell integrity ; Cell viability ; Sperm cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Our previous studies showed that Brewbaker and Kwack salts, which have been widely used in pollen germination and sperm isolation, are not appropriate for the maintenance of isolated maize (Zea mays L.) sperm cells. In the present study, we have characterized the effects of each BKS component salt on the integrity of isolated sperm cells using hemacytometry. At 0.01 and 0.1 mM, there were no differences in cell number between control and any salt-treated cells except a 22% decrease with 0.1 mM MgSO4 at 48 h. At the 1 mM level, cell number decreased with time in the presence of Ca(NO3)2 and MgSO4, with loss of integrity of most cells at 48 h, while KNO3 and H3BO3 had little or no effect. Further characterization of calcium-induced reduction in cell integrity using flow cytometry showed that depletion of possible residual free calcium by addition of EGTA to the suspension medium improved cell longevity and viability. Exposure of isolated sperm cells to 1 mM calcium had no effect on cell integrity and viability in 5 h; however, only 12% of cells remained intact at 24 h. The reduction in cell integrity was hastened when cells were pretreated with the calcium ionophore A23187 prior to exposure to 1 mM calcium, with a 54% reduction in cell number at 1 h and complete cell lysis at 24 h. However, depletion of cytosolic free calcium by pretreatment of cells with the calcium ionophore followed by resuspension in the presence of EGTA resulted in rapid reduction of cell integrity as well. These results collectively suggest that maize sperm cells are sensitive to exogenous free calcium; however, a certain level of cytosolic free calcium is necessary for maintenance of integrity. Mechanisms of calcium-induced reduction in cell integrity are discussed along with possible roles of the sensitivity of sperm cells to calcium in fertilization.
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  • 10
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    Springer
    Water, air & soil pollution 85 (1995), S. 1461-1466 
    ISSN: 1573-2932
    Keywords: ozone ; wheat ; Triticum aestivum ; growth ; senescence ; biomass partitioning ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract In closed-chamber fumigation experiments dry matter partitioning and chlorophyll fluorescence of wheat were studied, analysing the effects of ozone during different stages of plant development. Ozone causes enhanced leaf senescence, leading to a loss of green leaf area and, consequently to a decreased supply of assimilates, affecting (in increasing order of severeness) stem, ear and grain productivity because of reduced storage pools for translocation. Leaves of plants before shooting stage were most sensitive but the lack of green leaf area after ear emergence had the most pronounced effects on grain yield. Measurements of photochemical capacity showed that evidence for negative ozone effects could be found in changes of chlorophyll fluorescence parameters in leaf sections not yet showing visible ozone injury. Negative effects on photosynthesis were more distinct with increasing accumulated ozone dose, with increasing age of leaf tissue and with increasing ozone sensitivity of the cultivar. The changes in chlorophyll fluorescence are most likely to be explained by a decreased pool size of plastoquinones caused by ozone.
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  • 11
    ISSN: 1573-5028
    Keywords: GTP binding ; ADP ribosylation ; Zea mays ; Escherichia coli ; fatty acid biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In an attempt to isolate a plant malonyl-coenzyme A:acyl carrier protein transacylase cDNA clone, by direct genetic selection in an Escherichia coli fabD mutant (LA2-89) with a maize cDNA expression library, a Zea mays cDNA clone encoding a GTP-binding protein of the ARF family was isolated. Complementation of a mutation affecting bacterial membrane lipid biosynthesis by a plant ARF protein, could indicate the existence of as yet unidentified bacterial equivalents of this ubiquitous eucaryotic GTP-binding protein.
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  • 12
    ISSN: 1573-5028
    Keywords: β-prolamin ; Coix lacryma-jobi ; different O2-binding sites ; Opaque 2 ; transcriptional regulation ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The maize opaque 2 (o2) mutation is known to have numerous pleiotropic effects. Some polypeptides have their expression depressed while others are enhanced. The best characterized effects of the o2 mutation are those exerted on endosperm genes encoding the storage protein class of the 22 kDa α-zeins and the ribosome inactivating protein b-32. The Opaque 2 (O2) locus encodes a basic domain-leucine zipper DNA-binding factor, O2, which transcriptionally regulates these genes. In the maize-related grass Coix lacryma-jobi, an O2-homologous protein regulates the 25 kDa α-coixin gene family. We show in this paper that O2 transcriptionally regulates the structurally and developmentally different class of the β-prolamins. A new O2-binding box was identified in β-prolamin genes from maize and Coix that, together with the boxes previously identified in other endosperm expressed genes, forms a curious collection of O2 cis elements. This may have regulatory implications on the role of O2 in the mechanism that controls coordinated gene expression in the developing endosperm. Considering that the O2 locus controls at least three distinct classes of genes in maize endosperm, we propose that the O2 protein may play a more general role in maize endosperm development than previously conceived.
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  • 13
    ISSN: 1573-5028
    Keywords: Cell cycle ; circadian clock ; green alga ; GTP-binding proteins ; light regulation ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract ADP-ribosylation factor (ARF) is a highly conserved, low molecular mass (ca. 21 kDa) GTP-binding protein that has been implicated in vesicle trafficking and signal transduction in yeast and mammalian cells. However, little is known of ARF in plant systems. A putative ARF polypeptide was identifed in subcellular fractions of the green alga Chlamydomonas reinhardtii, based on [32P]GTP binding and immunoblot assays. A cDNA clone was isolated from Chlamydomonas (Arf1), which encodes a 20.7 kDa protein with 90% identity to human ARF1. Northern blot analyses showed that levels of Arf1 mRNA are highly regulated during 12 h/12 h light/dark (LD) cycles. A biphasic pattern of expression was observed: a transient peak of Arf1 mRNA occurred at the onset of the light period, which was followed ca. 12 h later by a more prominent peak in the early to mid-dark period. When LD-synchronized cells were shifted to continuous darkness, the dark-specific peak of Arf1 mRNA persisted, indicative of a circadian rhythm. The increase in Arf1 mRNA at the beginning of the light period, however, was shown to be light-dependent, and, moreover, dependent on photosynthesis, since it was prevented by DCMU. We conclude that the biphasic pattern of Arf1 mRNA accumulation during LD cycles is due to regulation by two different factors, light (which requires photosynthesis) and the circadian clock. Thus, these studies identify a novel pattern of expression for a GTP-binding protein gene.
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  • 14
    ISSN: 1573-5028
    Keywords: elongation factor 1α ; EF-1α ; Zea mays ; cDNA sequence ; gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A cDNA (zmEF1A) and the corresponding genomic clone (zmgEF1A) of a member of the gene family encoding the α subunit of translation elongation factor 1 (EF-1α) have been isolated from maize. The deduced amino acid sequence is 447 residues long interrupted by one intron. Southern blot analysis reveals that the cloned EF-1α gene is one member out of a family consisting of at least six genes. As shown by northern hybridizations in leaves the mRNA level increases at low temperature whereas time-course experiments over 24 h at 5°C show that in roots the overall mRNA level of EF-1α is transiently decreased. These results indicate that the expression of EF-1α is differently regulated in leaves and roots under cold stress.
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  • 15
    ISSN: 1573-5028
    Keywords: chloroplasts ; gene expression ; heat bleaching ; photosynthesis ; transcription
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A shift in the ratio of chlorophyll (Chl) a and Chl b is an early indicator of heat bleaching in Euglena gracilis. This observation prompted us to consider whether or not changes in steady-state levels of chloroplast transcripts and in transcriptional activity could limit the synthesis of Chl a-binding proteins in bleaching plastids. We found that the mature transcripts for CP47 and CP43, the Chl a-binding apoproteins of the proximal antenna of photosystem II, decline sharply very early during bleaching. Our study also shows that transcription of psbB and psbC, the chloroplast genes encoding CP47 and CP43, remains essentially unchanged during the same interval. We conclude that posttranscriptional events, such as mRNA stability, could play a major role in initiating an irreversible loss of chloroplast function in Euglena at a moderately elevated temperature. Lack of these transcripts would eventually impair the assembly of photosystem II in thylakoids.
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  • 16
    ISSN: 1573-5028
    Keywords: anaerobiosis ; BMS cells ; glyceraldehyde-3-phosphate dehydrogenase ; transient gene expression ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GapC) gene family of maize is differentially expressed in response to anaerobic stress. While GapC1 and GapC2 are downregulated, GapC3 and GapC4 are anaerobically induced. We have sequenced and analyzed a 3073 bp promoter fragment of GapC4. The promoter confers anaerobic induction of a reporter gene construct in a transient gene expression system in maize. Deletion analysis of the GapC4 promoter revealed a 270 bp long DNA region required for anaerobic induction. This region contains sequence motifs resembling the cis-acting sequences of the anaerobically induced maize Adh1 and Adh2 genes. Furthermore, the 3073 bp GapC4 promoter fragment displays homology to long terminal repeats of maize retrotransposons and to the 3′ region of the maize anthocyanin regulatory locus C1.
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  • 17
    ISSN: 1573-5028
    Keywords: carbon catabolite repression ; cDNA ; gene expression ; stress-induced genes ; glucose-starvation ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to isolate glucose-starvation-related cDNAs in maize (Zea mays L.) root tips, a cDNA library was constructed with poly(A)+ mRNA from 24 h starved root tips. After differential screening of the library, we isolated six different cDNAs (named pZSS2 and pZSS7) which were expressed during glucose starvation. Time course analysis revealed that maximum expression of five of these genes occurs 30 h after the onset of the starvation treatment. On the contrary, the expression of mRNAs corresponding to pZSS4 was maximal at an early stage of starvation and then dramatically decreased. The expression of this gene did not seem to be specific for glucose starvation. The pattern of induction of the genes corresponding to pZSS2, pZSS3, pZSS5, pZSS6 and pZSS7 revealed that non-metabolizable sugars such as L-glucose and mannitol induce mRNA transcription similarly to glucose starvation. When D-glucose or any other metabolizable sugar was supplied, the level of transcripts was reduced. Nucleotide sequence analyses of the six cDNAs allowed identification of five of them by comparison with sequence data bases. The protein encoded by clone pZSS2 is analogous to a wound-induced protein from barley. Clones pZSS4 to pZSS7 encode, respectively, a transmembrane protein, a cysteine protease, a metallothionein-like protein and a chymotrypsin/subtilisin-like protease inhibitor. Clone pZSS3 shares no significant homology with any known sequence.
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  • 18
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    Plant molecular biology 28 (1995), S. 667-676 
    ISSN: 1573-5028
    Keywords: gene expression ; promoter ; glyceraldehyde-3-phosphate dehydrogenase ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transient expression experiments show that the maize GapA1 promoter exhibits a requirement for sequences contained within intron 1 and surrounding exon border regions for expression in maize Black Mexican Sweet cells. Maize GapA1-promoter constructs lacking intron 1 are inactive. Intron 1 and its exon border sequences, when reintroduced into constructs lacking introns, restore gene activity whereas intron 2 and its exon borders to not. The minimal promoter so defined encompasses roughly 250 bp upstream of the in vivo transcription start and appears also to include intron 1. An octameric sequence was identified in intron 1 of maize GapA1 which is similar to sequence motifs found in other maize introns known to increase transient expression. Partial restoration of gene expression in GapA1 constructs lacking intron 1 was achieved through insertion of the identified octameric sequence.
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  • 19
    ISSN: 1573-5028
    Keywords: calmodulin ; cDNA library ; embryogenesis ; PCR ; transition stage ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract One hundred maize zygotic embryos microdissected at the transition stage were used to construct a cDNA library after non-selective PCR (NS-PCR) amplification of whole cDNA populations. The library contains 2.3 × 105 recombinants and two different calmodulin cDNAs were cloned using a heterologous probe from petunia. Calmodulin expression was confirmed throughout maize embryogenesis at the mRNA, amplified cDNA and protein levels. Sequence analysis suggests a maize origin for both clones and negligible nucleotide changes linked to PCR. This library is the first described for early plant embryos and represents a breakthrough to isolate genes involved in embryo differentiation.
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  • 20
    ISSN: 1573-5028
    Keywords: Cyanobacteria ; gene copy number ; light regulation ; photosynthesis ; photosystem II reaction center ; polymerase chain reaction ; psbA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract DNA sequence, copy number, expression and phylogenetic relevance of the psbA gene from the abundant marine prokaryote P. marinus CCMP 1375 was analyzed. The 7 amino acids near the C-terminus missing in higher plant and in Prochlorothrix hollandica D1 proteins are present in the derived amino acid sequence. P. marinus contains only a single psbA gene. Thus, this organism lacks the ability to adapt its photosystem II by replacement of one type of D1 by another, as several cyanobacteria do. Phylogenetic trees suggested the D1-1 iso-form from Synechococcus PCC 7942 as the next related D1 protein and place P. Marinus separately from Prochlorothrix hollandica among the cyanobacteria.
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  • 21
    ISSN: 1573-5028
    Keywords: Zea mays ; thiamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thiamine or vitamin B-1, is an essential constituent of all cells since it is a cofactor for two enzyme complexes involved in the citric acid cycle, pyruvate dehydrogenase and α-ketoglutarate dehydrogenase. Thiamine is synthesized by plants, but it is a dietary requirement for humans and other animals. The biosynthetic pathway for thiamine in plants has not been well characterized and none of the enzymes involved have been isolated. Here we report the cloning and characterization of two cDNAs representing members of the maize thi1 gene family encoding an enzyme of the thiamine biosynthetic pathway. This assignment was made based on sequence homology to a yeast thiamine biosynthetic gene and by functional complementation of a yeast strain in which the endogenous gene was inactivated. Using immunoblot analysis, the thi1 gene product was found to be located in a plastid membrane fraction. RNA gel blot analysis of various tissues and developmental stages indicated thi1 expression was differentially regulated in a manner consistent with what is known about thiamine synthesis in plants. This is the first report of cDNAs encoding proteins involved in thiamine biosynthesis for any plant species.
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  • 22
    ISSN: 1573-5028
    Keywords: chlorophyll synthesis ; cyanobacteria ; chlorophyl-binding proteins ; photosynthesis ; thylakoid membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Part of the chlL gene encoding a component involved in light-independent protochlorophyllide reduction was deleted in wild type and in a photosystem I-less strain of Synechocystis sp. PCC 6803. In resulting mutants, chlorophyll biosynthesis was fully light-dependent. When these mutants were propagated under light-activated heterotrophic growth conditions (in darkness except for 15 min of weak light a day) for several weeks, essentially no chlorophyll was detectable but protochlorophyllide accumulated. Upon return of the chlL - mutant cultures to continuous light, within the first 6 h chlorophyll was synthesized at the expense of protochlorophyllide at a rate independent of the presence of photosystem I. Chlorophyll biosynthesized during this time gave rise to a 685 nm fluorescence emission peak at 77 K in intact cells. This peak most likely originates from a component different from those known to be directly associated with photosystems II and I. Development of 695 and 725 nm peaks (indicative of intact photosystem II and photosystem I, respectively) required longer exposures to light. After 6 h of greening, the rate of chlorophyll synthesis slowed as protochlorophyllide was depleted. In the chlL - strain, greening occurred at the same rate at two different light intensities (5 and 50 μE m-2s-1), indicating that also at low light intensity the amount of light is not rate-limiting for protochlorophyllide reduction. Thus, in this system the rate of chlorophyll biosynthesis is limited neither by biosynthesis of photosystems nor by the light-dependent protochlorophyllide reduction. We suggest the presence of a chlorophyll-binding ‘chelator’ protein (with 77 K fluorescence emission at 685 nm) that binds newly synthesized chlorophyll and that provides chlorophyll for newly synthesized photosynthetic reaction centers and antennae.
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  • 23
    ISSN: 1432-2048
    Keywords: Anoxia ; Biochemical pH-stat ; Cytoplasmic pH ; Ethanol production ; Pyruvate decarboxylase ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ethanol production by maize (Zea mays L.) root tips, measured by an enzymic assay of the suspending medium, was correlated with changes in the cytoplasmic pH, determined by in-vivo 31P nuclear magnetic resonance (NMR) spectroscopy, following the onset of anoxia. Strong evidence for the role of the cytoplasmic pH in triggering the switch to ethanol production under anoxia was obtained by: (i) varying the pH of the suspending medium between pH 4 and pH 10; and (ii) using the permeant weak base methylamine to combat the acidification of the cytoplasm induced by the anoxic conditions. Experimentally, it proved to be much easier to manipulate the cytoplasmic pH under anoxia after the pH had stabilised, rather than during the initial rapid acidification that occurred following the onset of anoxia, and in the presence of methylamine, it was possible to impose a normal aerobic cytoplasmic pH value on tissue that was metabolising anaerobically. By this means it was possible to demonstrate the reversibility of the pH effect on ethanol production under anoxia and thus to provide good evidence in support of the biochemical pH-stat model of the anoxic response. The NMR measurement of the cytoplasmic pH in the presence of methylamine was achieved by using a manganese pretreatment technique to eliminate interference between the cytoplasmic and vacuolar Pi signals, and it seems likely that the experimental approach used here will have further applications in studies of the metabolic response to anoxia.
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  • 24
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    The journal of membrane biology 143 (1995), S. 19-28 
    ISSN: 1432-1424
    Keywords: Plant membrane ; Lipid domain ; Fluorescence photobleaching recovery ; Electron paramagnetic resonance ; Temperature stress ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Translational diffusion of a fluorescent sterol probe was measured in the plasma membranes of protoplasts isolated from cortical cells of the primary root of maize seedlings. The apparent lateral diffusion coefficient was typically observed to be nearly insensitive to temperature, while the mobile fraction increased with increasing temperature. These fluorescence photobleaching recovery (FPR) measurements were compared with the electron paramagnetic resonance (EPR) spectra of the methyl ester of 13-doxyl palmitic acid in membranes of corn root tissue in situ. The complex spectra observed with this probe were analyzed as weighted sums of simpler spectra of various order parameters and rotational correlation times. The reconstituted spectra calculated from the model show that EPR also detects a mobile (less ordered, fluid) fraction, distinguished by the order parameter S=0.1 to 0.2, which becomes more abundant as temperature increases and is qualitatively comparable to the mobile fraction determined by the FPR method. The observed results on the mobile fractions and the diffusion rates for translational (FPR) as well as rotational (EPR) motions are interpreted in terms of membrane organization, thus providing information on the population and structural patterns of the coexisting domains with a special emphasis on the response of the membrane to temperature changes.
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  • 25
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    Theoretical and applied genetics 90 (1995), S. 1198-1203 
    ISSN: 1432-2242
    Keywords: Diplospory ; RFLP ; Bulk-segregant analysis ; Genome similarity ; Intergeneric hybrids ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Polyploid plants in the genus Tripsacum, a wild relative of maize, reproduce through gametophytic apomixis of the diplosporous type, an asexual mode of reproduction through seed. Moving gene(s) responsible for the apomictic trait into crop plants would open new areas in plant breeding and agriculture. Efforts to transfer apomixis from Tripsacum into maize at CIMMYT resulted in numerou intergeneric F1 hybrids obtained from various Tripsacum species. A bulk-segregant analysis was carried out to identify molecular markers linked to diplospory in T. dactyloides. This was possible because of numerous genome similarities among related species in the Andropogoneae. On the basis of maize RFLP probes, three restriction fragments co-segregating with diplospory were identified in one maize-Tripsacum dactyloides F1 population that segregated 1∶1 for the mode of reproduction. The markers were also found to be linked in the maize RFLP map, on the distal end of the long arm of chromosome 6. These results support a simple inheritance of diplospory in Tripsacum. Manipulation of the mode of reproduction in maize-Tripsacum backcross generations, and implications for the transfer of apomixis into maize, are discussed.
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  • 26
    ISSN: 1615-6102
    Keywords: Drosera rotundifolia ; Embryogenic callus ; Extracellular matrix ; Scanning electron microscopy ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Primary embryogenic callus ofDrosera rotundifolia and long-term cultured embryogenic callus ofZea mays possess a conspicuous extracellular matrix (ECM) around and between embryogenic cells. The structural arrangement of ECM depends on the developmental stage of the embryogenic cells. Single embryoid cells were covered with, and connected by net-like material. However, surface cells of young globular embryoids were covered with a coherent layer of ECM which forms bridges with net-like material between the cells which was gradually reduced to coarse strands. When protodermis was formed on the surface of globular embryoids, the ECM disappeared completely. The ECM network was never observed on the surface of heart- and torpedo-shaped embryoids. Safranine (especially 0.1%) stabilized the structure of ECM. Digestion with pronase E and proteinase K indicated that the ECM contains proteinaceous components. Similar developmental patterns of ECM were observed in dicotyledonous and monocotyledonous examples. The ECM represents a stable morphological structure even during long-term embryogenic culture in maize.
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  • 27
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    Protoplasma 187 (1995), S. 3-12 
    ISSN: 1615-6102
    Keywords: Gamete protoplasts ; In vitro fertilization ; Early embryogenesis ; Developmental mutations ; Polymerase chain reaction ; cDNA libraries ; Gene cloning ; Angiosperm ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The development of in vitro fertilization methods in plants, the characterization of developmental mutants, and the adaptation of molecular biology techniques to construct cDNA libraries from minute samples, all represent important recent technical break-throughs. They allow the study of fertilization and early embryogenesis at a molecular level and considerable improvement in the under-standing of higher plant reproduction can be predicted over the next few years. Important biological questions, such as polyspermy, gamete fusion physiology, asymmetrical cell division, embryo axis formation, can now be addressed experimentally in maize, which appears as a major study model in this area.
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  • 28
    ISSN: 1615-6102
    Keywords: Biolistics ; Microspores ; GUS-expression ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The ability to recover male gametophyte derived plants, which is necessary to get transformed haploid plants, was verified for a hybrid of maize. Using the isolated microspore culture technique, a 9 × 10−5 plant regeneration frequency was obtained. Maize microspores were bombarded with tungsten particles using a PDS He/1000 apparatus. GUS expression in the microspores was maximum with 1.1 μm diameter tungsten microprojectiles for 1100 and 1350 psi helium pressures at a 6 cm distance between the launch point and the target cells. Increasing the amount of DNA coated on the microparticles from 1.66 to 4 μg DNA/mg of particles allowed a two-fold and four-fold increase of the GUS-expressing microspore frequency for 1100 and 1350 psi helium pressure bombardment, respectively. Optimal concentration of solidifying agent in the bombardment support culture medium was found to be 1%. Cell density ranging from 25000 microspores/bombardment to 100000 microspores/bombardment did not affect the frequency of GUS-expressing microspores. Using these optimal conditions, the maximum frequency of GUS-expressing microspores was found to be about 9 × 10−4, while maintaining an embryo formation frequency about 5 × 10−4.
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  • 29
    ISSN: 1615-6102
    Keywords: Auxin ; Cell wall ; Coleoptile ; Pectin ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Aiming to elucidate the possible involvement of pectins in auxin-mediated elongation growth the distribution of pectins in cell walls of maize coleoptiles was investigated. Antibodies against defined epitopes of pectin were used: JIM 5 recognizing pectin with a low degree of esterification, JIM 7 recognizing highly esterified pectin and 2F4 recognizing a pectin epitope induced by Ca2+. JIM 5 weakly labeled the outer third of the outer epidermal wall and the center of filled cell corners in the parenchyma. A similar labeling pattern was obtained with 2F4. In contrast, JIM 7 densely labeled the whole outer epidermal wall except the innermost layer, the middle lamellae, and the inner edges of open cell corners in the parenchyma. Enzymatic de-esterification with pectin methylesterase increased the labeling by JIM 5 and 2F4 substantially. A further increase of the labeling density by JIM 5 and 2F4 and an extension of the labeling over the whole outer epidermal wall could be observed after chemical de-esterification with alkali. This indicates that both methyl- and other esters exist in maize outer epidermal walls. Thus, in the growth-controlling outer epidermal wall a clear zonation of pectin fractions was observed: the outermost layer (about one third to one half of wall thickness) contains unesterified pectin epitopes, presumably cross-linked by Ca2+ extract. Tracer experiments with3H-myo-inositol showed rapid accumulation of tracer in all extractable pectin fractions and in a fraction tightly bound to the cell wall. A stimulatory effect of IAA on tracer incorporation could not be detected in any fraction. Summarizing the data a model of the pectin distribution in the cell walls of maize coleoptiles was developed and its implications for the mechanism of auxin-induced wall loosening are discussed.
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  • 30
    ISSN: 1615-6102
    Keywords: Chromosome endoreduplication ; Endosperm ; Protein accumulation ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Chromosome endoreduplication is a very common process in higher plants but its function and genetic control are still to be clarified. In our experiments we analyzed, by Feulgen cytophotometry, chromosome endoreduplication in endosperm cells of two maize genotypes, IHP and ILP, having high and low protein content in their seed, respectively. Chromosome endoreduplication occurs in both lines within 24 days after pollination, attaining a maximum ploidy level of 384C (7 DNA replication rounds) in IHP and of 192C (6 replication rounds) in ILP. In the mature seed, endosperms of the two lines show different mean ploidy level. In reciprocal crosses between IHP and ILP the f1 endosperms have mean ploidy levels analogous to that of the maternal parent, showing that the difference in ploidy level between the two genotypes is maintained. After selfing of the f1 plants, the difference in ploidy level between the two F2 populations is reduced. In F2 the mean ploidy level is as variable as in f1, indicating the absence of genetic segregation. From our data, it is apparent that both the genetic constitution (cytoplasmic and nuclear) of the maternal parent and the genotype of the individual endosperms influence the ploidy level. An analysis of the protein content in endosperms carried out on the same seed sample as analyzed cytophotometrically showed that the protein content increases, during seed development, parallel to chromosome endoreduplication and varies, in the two lines, in reciprocal crosses and their progeny, according to the same trend as mean ploidy level, suggesting a correlation between the two parameters.
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  • 31
    ISSN: 1615-6102
    Keywords: Avena sativa ; Elongation growth ; Glycine max ; Hexacyanoferrate III (ferricyanide) ; Indole-3-acetic acid ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influence of exogenous potassium hexacyanoferrate (III) (HCF III) on elongation of maize (Zea mays L.) coleoptile segments was investigated. Addition of HCF III led to a strong stimulation of growth both in the presence and absence of indole-3-acetic acid (IAA). The magnitude of growth stimulation was dependent on the presence of IAA, HCF III concentration, incubation time, and phase growth. The reduced form, potassium hexacyanoferrate (II), was without effect on growth. In the presence of HCF III, elongation was suppressed when coleoptile segments were treated with N,N′-dicyclohexylcarbodiimide, cycloheximide or atebrine (quinacrine). The addition of HCF III stimulated the IAA-induced proton extrusion, and the e−/H+ ratio decreased with incubation time. HCF III also strongly stimulated elongation ofAvena saliva L. coleoptile segments andGlycine max L. hypocotyl segments. These results suggested that a plasma membrane redox system (NADH oxidase type I) may be involved in the regulation of growth through the activity of the plasma membrane-bound ATPase.
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  • 32
    ISSN: 1615-6102
    Keywords: Zea mays ; Plasma membrane ; Proton microprobe ; Copper ; Iron ; Zinc
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plasma membranes of maize (Zea mays L., cv. Sil Anjou 18) roots were isolated by aqueous two-phase partitioning. Multi elemental analysis by proton induced X-ray emission (PIXE) was used for the investigation of elemental composition of plasma membranes. Fe, Cu, and Zn as well as P, S, and Ca were identified. We did not find significant amounts of V, Mn, Se, Mo, or W.
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  • 33
    ISSN: 1615-6102
    Keywords: Glutathione ; Plasma membrane redox acitvity ; Electron transfer ; Zea mays ; Diamide ; Buthionine-D,L-suIfoximine ; Hexacyanoferrate III ; Hexabromoiridate IV
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We investigated changes of thiols (GSH, GSSG, and cysteine) induced by transplasma membrane electron transport after addition of artificial electron acceptors and the influence of the thiol level on redox activity. GSH, GSSG, and cysteine content of maize (Zea mays L. cv. Golden Bantam) roots and coleoptile segments was determined by high performance liquid chromatography with a fluorescence detector. GSSG increased after treatment with 0.8 mM diamide, an SH-group oxidizer. GSH level of roots increased after treatment with diamide, while GSH levels of coleoptiles decreased. Incubation of roots with the GSH biosynthesis inhibitor buthionine-D,L-sulfoximine for 6 days lowered the glutathione level up to 80%. However, the GSH/GSSG ratio of maize roots remained constant after treatment with both effectors. The GSH/GSSG ratio and the glutathione level were changed by addition of artificial electron acceptors like hexacyanoferrate (III) or hexabromoiridate (IV), which do not permeate the plasma membrane. Hexacyanoferrate (III) reduction was inhibited up to 25% after the cellular glutathione level was lowered by treatment with diamide or buthionine-D,L-sulfoximine. Proton secretion induced by reduction of the electron acceptors was not affected by both modulators. The change in glutathione level is different for roots and coleoptiles. Our data are discussed with regard to the role of GSH in electron donation for a plasma membrane bound electron transport system.
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  • 34
    ISSN: 1573-5176
    Keywords: cell-wall polysaccharides ; chlorophylla ; Gelidium sesquipedale ; internal C and N ; light quality ; photosynthesis ; phycobiliproteins ; respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of different light qualities on the photosynthetic rate, dark respiration, intracellular carbon and nitrogen content, and accumulation of photosynthetic pigments and cell-wall polysaccharides during short-term incubation (5 h) of the red algaGelidium sesquipedale was investigated. The same photon irradiance of 50μmol m−2 s−2 below the light saturation point of photosynthesis was applied in each case. Blue light stimulated photosynthesis, dark respiration and the accumulation of chlorophyll and biliproteins, phycoerythrin in particular. The accumulation of internal carbon and nitrogen was greater under blue light than under the other light qualities. In contrast, the percentage of cell-wall polysaccharides was higher in red light. The content of cell-wall polysaccharides decreased during the time of incubation in all light treatments except in red light. The action of a non-photosynthetic photoreceptor in the control of cell-wall polysaccharide synthesis is suggested because the accumulation of cell-wall polysaccharides was not correlated with net photosynthesis in contrast to what occurred with carbon, chlorophyll and phycoerythrin accumulation.
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  • 35
    ISSN: 1573-5117
    Keywords: gas exchange ; mangrove ; photosynthesis ; salinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Continuous measurements of gas exchange characteristics were made on two to nine year old hydroponically grown Avicennia germinans (L.) Stearn, Aegialitis annulata R. Br. and Aegiceras corniculatum (L.) Blanco maintained at 50 or 500 mol m−3 NaCl. In Avicennia germinans and Aegialitis annulata, CO2 assimilation rates were initially higher at 500 mol m−3 NaCl and decreased gradually towards the end of the photoperiod when rates were similar to those at the lower salinity. In Aegiceras corniculatum, assimilation rates were higher at 50 mol m−3 NaCl and about 55% lower at the higher salinity. In all three species, leaf conductance and transpiration exhibited trends similar to those for CO2 assimilation. Intercellular CO2 concentrations were similar at both salinities in Avicennia germinans and Aegialitis annulata, but considerably higher at the lower salinity in Aegiceras corniculatum. Water use efficiencies (WUE), although similar between salinity treatments in Avicennia germinans and Aegialitis annulata, were greater at the higher salinity in Aegiceras corniculatum. Data obtained from CO2 response curves indicated that assimilation at high salinity in Aegiceras corniculatum was limited by conductance, and to a lesser extent, by photosynthetic capacity. In Avicennia germinans and Aegialitis annulata, assimilation was greater at the higher salinity as indicated by increase in both the initial slope and the upper plateau of the CO2 response data. Greater assimilation at high salinity in Avicennia germinans and Aegialitis annulata may be attributed to lower carbon losses via photorespiration and to efficient salt excretion and sequestration.
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  • 36
    ISSN: 1573-5117
    Keywords: photon flux density ; intracellular metabolic pools ; proteins ; carbohydrates ; lipids ; polysaccharides ; photosynthesis ; phytoplankton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of photon flux density (PFD) on the partitioning of photosynthetically fixed 14CO2-C into major intracellular end products was investigated for three species of freshwater planktonic algae (Nitzschia palea, Monoraphidium minutum and Synechococcus elongatus belonging to three different classes. This study was designed to investigate the phenomenon of polysaccharide synthesis associated with the saturation of protein synthesis and to test if this process is common to all three phytoplankton species. Protein synthesis was saturated at low PFD in all three species of algae studied. However, fixed carbon was differentially stored, namely in lipids in Nitzschia palea (Bacillariophyceae), in polysaccharides in Monoraphidium minutum (Chlorophyceae), and in low molecular weight metabolites (LMW) in Synechococcus elongatus (Cyanophyceae). The results of this transient state study indicate that the metabolic pathways of algae can easily be controlled by different irradiance. Furthermore, it appears that the difference in the patterns of synthesis is taxonomy dependent.
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  • 37
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    Molecular genetics and genomics 246 (1995), S. 716-722 
    ISSN: 1617-4623
    Keywords: α-tubulin gene ; DNA methylation ; Endosperm ; Parental imprinting ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have investigated the methylation status of the α-tubulin genes, and the degree of accumulation of their mRNAs in endosperm, embryo and seedling tissues of Zea mays L. We have found that many of the α-tubulin genes are differentially demethylated in the endosperm relative to the embryo and seedling. However, only for tubα2 and tubα4 could a correlation between DNA demethylation and increased RNA accumulation be detected. By analyzing the inbred lines W64A and A69Y and their reciprocal crosses, we have also identified in the endosperm two α-tubulin genes, tubα3 and tubα4, that are differentially demethylated if transmitted by the maternal germline, but that remain hypermethylated when transmitted by the paternal germline.
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  • 38
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    Molecular genetics and genomics 247 (1995), S. 255-263 
    ISSN: 1617-4623
    Keywords: Zea mays ; Mitochondrial genome ; Pulsed-field gel electrophoresis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pulsed-field gel electrophoresis (PFGE) in combination with infrequently cutting restriction enzymes was used to investigate the structure of the mitochondrial (mt) genome of the maize variety Black Mexican Sweet (BMS). The mt genome of this variety was found to resemble that of the closely related B37N variety, with one recombination and five insertion/deletion events being sufficient to account for the differences observed between the two genomes. The majority of the BMS genome is organized as a number of subgenomic chromosomes with circular restriction maps. Several large repeated sequences are found in the BMS mt genome, but not all appear to be in recombinational equilibrium. No molecules large enough to contain the entire mt genome were discernible using these techniques. The mapping approach described here provides a means of quickly analyzing the large and complex rut genomes of plants.
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  • 39
    ISSN: 1617-4623
    Keywords: Zea mays ; Transposable elements ; Unstable mutation ; Variegation pattern ; Modifier gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Ac elements present in the unstable wxm7 and wx-m9 alleles of maize trigger different patterns of Ds excision in trans. To determine whether this differential regulation is a feature of the Ac alleles themselves or is mediated by genetically distinct factors, maize plants heterozygous for the wx-m7 and wx-m9 alleles were crossed to tester strains homozygous for Ds reporter alleles. Kernels showing the variegation pattern characteristic for the Ac elements carried in the wx-m7 and wx-m9 alleles were found to be present in the ratios expected from the genetic constitution of the strains. The aleurone variegation caused by excision of the Ds reporter element and the endosperm variegation caused by excision of Ac from the wx-m7 and wx-m9 alleles themselves segregated with the original wx-m alleles. In addition, stable Wx and wx derivatives of wx-m9 that have lost Ac no longer exert any trans effect on the wx-m7 allele (and vice versa). Therefore it is concluded that the observed variegation patterns are autonomously determined by specific trans effects of the particular Ac element.
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  • 40
    ISSN: 1573-5036
    Keywords: nitrogen ; nutrient availability ; photosynthesis ; Scots pine ; seasonal change ; site quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The relationship between light saturated net photosynthesis (Amax) and nitrogen concentration (N) was studied in needles of both Scots pine seedlings, grown at three relative growth rates (2,6 and 8%) controlled by nutrient addition rate, and Scots pine shoots collected from four sites with different fertility. In the seedlings, Amax was measured on 14 different dates starting at the beginning of the second growing season and ending when growth of the new shoot and the secondary needles had finished. In shoots from the natural stands Amax of the previous-year shoots was measured on 6 dates throughout the growing season. Both in seedlings and shoots, the correlation between Amax and N was poor, when data from all sampling dates were taken together. However, Amax was correlated with N in most instances when the age of the needles was considered and the data were examined either at weekly intervals (seedlings) or separately for each sampling date (shoots). The slope of the Amax vs N relationship varied greatly between sampling dates. In the seedlings the correlation between Amax and N was strongest by the time when the new needles were developing. In the shoots the correlation was significant from mid June until mid August, while no correlation was found in the beginning and at the end of the growing season. Our data indicate that in pine needles the photosynthesis-nitrogen relationship is more complex than in broadleaved species. Contrary to the broadleaved species, where the correlation is independent of sampling time, in this conifer the time of the year affects the correlation and there are phases during the growing season when the correlation is poor or nonexistent.
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  • 41
    ISSN: 1573-5036
    Keywords: carbon budget ; growth analysis ; interspecific variation ; nitrogen supply ; photosynthesis ; respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In previous experiments systematic differences have been found in the morphology, carbon economy and chemical composition of seedlings of inherently fast- and slow-growing plant species, grown at a non-limiting nutrient supply. In the present experiment it was investigated whether these differences persist when plants are grown at suboptimal nutrient supply rates. To this end, plants of the inherently fast-growing Holcus lanatus L. and the inherently slow-growing Deschampsia flexuosa (L.) Trin. were grown in sand at two levels of nitrate supply. Growth, photosynthesis, respiration and carbon and nitrogen content were studied over a period of 4 to 7 weeks. At low N-supply, the potentially fast-growing species still grew faster than the potentially slow-growing one. Similarly, differences in leaf area ratio (leaf area:total dry weight), specific leaf area (leaf area:leaf dry weight) and leaf weight ratio (leaf dry weight:total dry weight), as observed at high N-supply persisted at low N-availability. The only growth parameter for which a substantial Species × N-supply interaction was found was the net assimilation rate (increase in dry weight per unit leaf area and time). Rates of photosynthesis, shoot respiration and root respiration, expressed per unit leaf, shoot and root weight, respectively, were lower for the plants at low N-availability and higher for the fast-growing species. Species-specific variation in the daily carbon budget was mainly due to variation in carbon fixation. Lower values at low N were largely determined by both a lower C-gain of the leaves and a higher proportion of the daily gain spent in root respiration. Interspecific variation in C-content and dry weight:fresh weight ratio were similar at low and high N-supply. Total plant organic N decreased with decreasing N-supply, without differences between species. It is concluded that most of the parameters related to growth, C-economy and chemical composition differ between species and/or are affected by N-supply, but that differences between the two species at high N-availability persist at low N-supply.
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  • 42
    ISSN: 1573-5036
    Keywords: cadmium ; root distribution ; root methods ; soil pollution ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cadmium uptake by maize from polluted river sediments covered with a clean top layer of variable thickness is discussed in relation to root distribution. Two pathways for uptake are distinguished: roots penetrating the contaminated layer or contaminants moving into the root zone. Relative Cd uptake proved to be roughly proportional to the fraction of total root length found in the contaminated layer. A deeper water table induced a deeper root development and more Cd uptake for a given thickness of clean topsoil. A model based on exponential decrease of root length density with depth is acceptable as first approximation only. Little or no evidence was found for contaminants moving into the root zone during the ten years of the experiment.
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  • 43
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    Euphytica 82 (1995), S. 157-164 
    ISSN: 1573-5060
    Keywords: EPSP synthase ; glyphosate ; herbicide tolerance ; natural variation ; Zea mays ; maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Variation in susceptibility to the safe broad-spectrum herbicide glyphosate was investigated in maize. Eleven inbred lines, grown in a growth chamber, were evaluated for their tolerance to the herbicide at 2.4 mM (0.2 kg a.i. in 400 I ha-1 of water). Following treatment with glyphosate at the three-leaf stage, significant variation in damage, expressed as visual injury ratings scored 7, 14 and 21 days after the application of the herbicide, was found. Effects on dry weight and shoot height were consistent with visual scores and the carbon-exchange rate was found to be a sensitive index of differential injury. Biochemical characterization of 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase, the main target of the herbicide, ruled out the possibility that this differential susceptibility was due to variations in the sensitivity of the enzyme. On the contrary, a positive correlation was found between in vivo tolerance and EPSP synthase levels, measured at different stages during seedling growth. This result suggests that a naturally occurring difference in EPSP synthase levels in the tissues may contribute to the differential response observed in vivo in maize inbreds.
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  • 44
    ISSN: 1573-5060
    Keywords: barley landraces ; drought ; Hordeum vulgare ; leaf colour ; photosynthesis ; photosystem I and II ; thylakoid chlorophyll-proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Barley breeders at ICARDA have observed that genotypes adapted to dry regions have leaves which are lighter in colour than those of unadapted ones. We measured photosynthesis, chlorophyll content and chlorophyll a:b ratios in two sets of genotypes which had previously been observed to have either light green or dark green leaves when grown in the field. Thylakoid membranes were also extracted and the proteins analysed on SDS-PAGE gels. The light leaf colour was associated with a higher chlorophyll a:b ratio. This was a measure of a reduction in the amount of antenna chlorophyll compared to that in the core complex of PSII. Genotypes with light green leaves had consistently less chlorophyll per unit leaf area and lower photosynthetic rates per unit area than those with dark green leaves. It is suggested that these features of light green leaves may confer the ability to adapt to high levels of irradiance under drought conditions. This ability may result from a high rate of photosynthetic electron transport through each PSII reaction centre, thus reducing the risk of damage from the overexcitation of these centres.
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  • 45
    ISSN: 1573-5060
    Keywords: Zea mays ; maize, subtropical white germplasm ; S3 recurrent selection ; inbreeding depression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In maize (Zea mays L.) source germplasm having tolerance to inbreeding is needed for the derivation of productive inbred lines. The germplasm with non-temperature adaptation, generally suffer from large inbreeding depression (ID). the objective of the present study was to improve four white subtropical populations for tolerance to ID through S3 recurrent selection. Two cycles of selection were conducted and the effect of selection was evaluated in the first selfed (S1) and random0mated (Synthetic-2=Syn-2) generations. To complete each cycle. 200 to 250 S3 progenies were evaluated and 15 to 20 superior ones selected for recombination in each population. Selection was practiced for high grain yield, vigour and other agronomie traits. The S1 and Syn-2 generations of the original (C0) and improved (C1, C2) populations were evaluated in a split-split plot design, with populations in main plots, generations in subplots and cycles in sub-subplots. In all populations, S1 and Syn-2 generations of C2 were significantly higher yielding than the C0 and the linear gain per cycle varied from 16.3 to 28.8% in S1 generation and 5.5 to 10.7% in Syn-2 generation. Selection reduced the anthesis-silking interval but slightly increased plant height, grain moisture and days to silk. An increase in plant height was expected because of emphasis on vigour during selection. For grain yield. ID decreased from 48.4% in C0 populations to 37.9% in C2, indicating an improved tolerance to inbreeding. Further, the selection accumulated favourable alleles; and Pop. 42 seemed to be the best source populations for deriving high yielding inbred lines. It may be concluded that S3 recurrent selection was effective in improving grain yield and the improved populations would provide better germplasm sources for the derivation of productive inbred lines.
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  • 46
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    Photosynthesis research 45 (1995), S. 157-168 
    ISSN: 1573-5079
    Keywords: chloroplast movement ; photosynthesis ; photothermal deflection spectroscopy ; Vallisneria americana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In a study of photosynthetic energy storage efficiency (ES), the adaxial surface of the leaves of Vallisneria americana exhibited the highest ES values (22%) of the four aquatic plants examined. V. americana leaves have a dispersed structure and it was possible to measure the energy storage properties of the epidermal cells independently of the rest of the leaf. The abaxial epidermis had a higher value of ES at zero light fluence than the adaxial epidermis but ES in the abaxial epidermis declined much more rapidly with light fluence. Thus the abaxial epidermis is more suited to lower light fluences than the adaxial epidermis. ES declined as the pH rose from 4.0 to 8.0 at a constant dissolved inorganic carbon concentration. This paralleled the change from carbon dioxide to bicarbonate and suggests that these leaves utilise CO2 more efficiently than bicarbonate. ES increased by about 50% at pH 8.0 as leaf sections further from the leaf tip were examined which demonstrates that the older epidermal cells are less well able to use bicarbonate. Exposure to 30 min of a saturating light fluence caused the epidermal chloroplasts to move from the periclinal walls to the anticlinal walls. This decreased the photothermal signal by increasing the thermal diffusion distance and lowering the light fluence due to greater chloroplast shading. The latter effect increased ES. It appears that chloroplast movement could assist the epidermis to survive harmful light fluences.
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  • 47
    ISSN: 1573-5036
    Keywords: aluminium toxicity ; Eucalyptus camaldulensis ; fulvic acid ; humic acid ; root elongation ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Complexes of aluminium (Al) with organic ligands are believed to represent an important detoxification mechanism in acid soils. However, relatively little is known about the particular ligands produced by decomposing vegetation or about their effects on plant growth in the presence or absence of toxic Al. This paper reports an experiment on the effects of decomposition products of Eucalyptus camaldulensis leaves on the root elongation of maize (Zea mays) cv. DK687 in the presence or absence of Al. The static solution culture experiment used fulvic acid (FA) and humic acid (HA), extracted from E. camaldulensis leaves, at three nominal concentrations, viz. 40, 120 and 360 mg C L-1, replicated 4 times in the presence and absence of 30 µM Al. In the absence of Al, root elongation was increased by 30% by HA at 40 mg C L-1 and by 36% by FA at 120 mg C L-1. In the presence of 30 µM Al, the effects of toxic Al on root elongation were negated by FA and HA at all concentrations. Aluminium was totally complexed in all treatments except FA at 40 mg C L-1 in which treatment only 2.7 µM Al was present in the monomeric form. The E. camaldulensis FA and HA at concentrations of 40 and 120 mg C L-1, either in the presence or absence of Al, stimulated maize root elongation. Aluminium was strongly complexed by the E. camaldulensis FA and HA. The present results, in which FA and HA alleviated Al toxicity limitations on root elongation of maize, are relevant to the protection afforded to plant growth in acid soils amended with organic materials. They highlight the need to focus more on the role of FA and HA.
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  • 48
    ISSN: 1573-5036
    Keywords: calcium ; Coffea arabica ; fluorescence analysis ; nutrient relations ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Calcium deficiency was induced in hydroponically grown 1.5-years-old coffee plants with 12–14 pairs of leaves. Calcium was given in the form of Ca(NO3)2: 5, 2.5, 0.1, 0.01 and 0 mM. After 71 days of Ca-treatment root and shoot as well as total biomass were decreased by severe Ca-deficiency. However, a stronger decrease was observed for shoot growth as revealed by the increase in the root/shoot ratio. New leaves were affected showing decreases in the total leaf area and in Leaf Area Duration (LAD). After 91 days of deficiency, leaf protein concentration decreased (by about 45%) in the top leaves while nitrate reductase activity (NRA) and NO3 content showed no significant changes. Total nitrogen and mineral concentrations (P, K, Ca, Mg and Na) were also determined in leaves and roots. With the decrease in calcium concentration in Ca-deficiency conditions, we observed concomitant increases in the concentrations of K+, Mg2+ and Na+ in leaves (maximal changes of 32% for K+, 96% for Mg2+ and 438% for Na+) and in roots (108% for K+, 86% for Mg2+ and 38% for Na+). Accordingly, the ratio between elements changed, including the ratio N/P, showing a non-equilibrium in the balance of nutrients. Significant correlations were obtained between Ca2+ concentration and some photosynthetic parameters. Ca-deficiency conditions would increase the loss of energy as expressed by the rise in aE and decrease the photochemical efficiency, which confirms the importance of this element in the stabilization of chlorophyll and in the maintenance of good photochemical efficiency at PS II level.
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  • 49
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    Plant and soil 175 (1995), S. 233-238 
    ISSN: 1573-5036
    Keywords: arbuscular mycorrhiza (AM) ; Cd ; Glomus mosseae ; phytotoxicity ; tolerance ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A Cd-tolerant arbuscular mycorrhizal fungus, Glomus mosseae, isolated from a polluted soil (P2 culture), was compared with a Cd-sensitive reference Glomus mosseae (Gm) for its capacity to colonize maize (Zea mays L.) roots and to affect plant growth and Cd uptake in sand culture at increasing exposure to Cd added with the nutrient solution (0, 0.1, 1, 5 and 10 mg L-1). After eight weeks, mycorrhizal colonization by P2 culture was relatively high (50% of the control without Cd added) up to 5 mg L-1 Cd, whereas colonization by Gm was almost totally suppressed at that Cd level. However, even mycorrhizal colonization by the Cd-tolerant P2 culture appeared more sensitive to Cd than plant growth and was completely suppressed at 10 mg L-1 Cd. AM colonization did not alleviate the negative effect of Cd on plant growth compared to the non-mycorrhizal treatment. On the contrary, at the 5 mg L-1 Cd level non-mycorrhizal plants were greater than mycorrhizal plants with lower Cd concentration.
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  • 50
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    Plant and soil 176 (1995), S. 219-227 
    ISSN: 1573-5036
    Keywords: calcium ; chloride ; cotton ; photosynthesis ; potassium ; sodium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The optimum Ca2+ concentration for growth of cotton (Gossypium hirsutum cv. Acala SJ-2) was in the range 1 to 15 mol m−3 for plants growing in hydroponic culture with 100–150 mol m−3 NaCl. Most saline (but not sodic) soils contain higher Ca2+ concentrations. CaCl2 was inhibitory to the growth of cotton above 20–50 mol m−3. Increasing concentrations of Ca2+ in the range 0–2 mol m−2 drastically reduced Na+ accumulation in the leaves. As CaCl2 concentrations were increased above the optimum for growth there was a further reduction in leaf Na+ accumulation, but this was more than offset by increased leaf Ca2+ and Cl− concentrations. Leaf K+ concentrations were not much affected by changes in external CaCl2 concentrations. The response of Mg2+ varied from an increase to a decrease with increasing external CaCl2 and was influenced by nutritional status. There was no evidence that high Ca2+ caused a deficiency of Mg2+ in cotton. Except for Cl−, whose concentrations tended to decrease initially and then increase as the CaCl2 concentration increased, the anions were largely unaffected by changes in external CaCl2.
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  • 51
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    Plant and soil 168-169 (1995), S. 255-261 
    ISSN: 1573-5036
    Keywords: magnesium deficiency ; Norway spruce ; photosynthesis ; Picea abies (L.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In order to investigate the influence of different magnesium nutrition on photosynthesis, one hundred 6-year-old spruce trees derived from one clone were planted in October 1990 into a special out-door experimental construction, where they were cultivated in sand culture with an optimal supply of nutrients, except magnesium, via circulating nutrient solutions. Magnesium was added to the nutrient solutions in three different concentrations, varying from optimal to severe deficient supplies. During the first vegetative period in 1991, photosynthetic performance and carboxylation efficiency were measured under saturating light, controlled CO2 conditions, optimal temperature and humidity, using a minicuvette system. During summer, the trees under moderate magnesium deficiency developed tip yellowing symptoms on older needles, while the youngest needles remained green with unchanged chlorophyll contents. Trees under severe magnesium deficiency showed yellowing symptoms on all needle age classes combined with decreased chlorophyll contents in the youngest needles as well. In comparison with the controls, the photosynthetic performance of the 1-year-old needles was significantly lower in both deficiency treatments. The same was observed in the youngest needles of the trees under severe deficiency. Trees under moderate deficiency treatment decreased in photosynthetic performance during the summer without reduction of chlorophyll contents. The reduction of photosynthetic rates corresponded to a decrease in carboxylation efficiency, which is taken as a measure of the activity of the enzyme ribulose-1,5-bisphosphate carboxylase. This reduction, together with the observed increase of carbohydrate contents in needles of trees growing under magnesium deficiency, led to the assumption that the photosynthetic carbonfixation is reduced as a consequence of the accumulation of carbohydrates.
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  • 52
    ISSN: 1573-5036
    Keywords: ammonium toxicity ; buffered nutrient solution ; eggplant ; flowers ; fruit yield ; nitrate ; photosynthesis ; Solanum melongena ; starch ; sucrose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Eggplants (Solanum melongena L. cv. Bonica) were grown in a glasshouse during summer under natural light with one unbranched shoot or one shoot with 3 to 4 branches and with or without fruit in quartz sand buffered and not buffered with 0.5% CaCO3 (w : v), respectively. Nutrient solutions supplied contained nitrate or ammonium as the sole nitrogen source. Compared with nutrient solutions containing nitrate (10 mM), solutions containing ammonium (10 mM) caused a decrease in net photosynthesis of eggplants during early stages of vegetative growth when grown in quartz sand not buffered with CaCO3. The decrease was not observed before leaves showed interveinal chlorosis. In contrast, net photosynthesis after bloom at first increased more rapidly in eggplants supplied with ammonium than with nitrate nitrogen. However, even in this case, net photosynthesis decreased four weeks later when ammonium nutrition was continued. The decrease was accompanied by epinasty and interveinal chlorosis on the lower leaves and later by severe wilting, leaf drop, stem lesions, and hampered growth of stems, roots, and fruits. These symptoms appeared later on plants not bearing fruits than on plants bearing fruits. If nutrient solutions containing increasing concentrations of ammonium (0.5–30 mM) were supplied after the time of first fruit ripening, shoot growth and set of later flowers and fruits were promoted. In contrast, vegetative growth and reproduction was only slightly affected by increasing the concentration of nitrate in the nutrient solutions. In quartz sand buffered with CaCO3 ammonium nutrition caused deleterious effects only under low light conditions (shade) and on young plants during rapid fruit growth. If eggplants were supplied with ammonium nitrogen before bloom, vegetative growth was promoted, and set of flowers and fruit occurred earlier than on plants supplied with nitrate. Furthermore, the number of flowers and fruit yield increased. These effects of ammonium nutrition were more pronounced when plants were grown with branched shoots than with unbranched shoots. The results indicate that vegetative and reproductive growth of eggplants may be manipulated without causing injury to the plants by supplying ammonium nitrogen as long as the age of the plants, carbohydrate reserves of the roots, quantity of ammonium nitrogen supplied, and pH of the growth medium are favourable. T W Rufty Section editor
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  • 53
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    Plant cell, tissue and organ culture 43 (1995), S. 123-126 
    ISSN: 1573-5044
    Keywords: bioreactor ; dissolved oxygen ; haploid cell suspension ; pH ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Maize (Zea mays L.) haploid cells were cultivated in a 1500 ml aerated and stirred batch bioreactor using modified BM medium. Cell growth was highly affected by pH and dissolved oxygen, and we observed two fairly distinct growth phases. During the first two days after inoculation at pH 5.8, oxygen consumption was high and the cells lowered the pH to a value around 4.3. After this period the pH stabilized at 4.5 and the dissolved oxygen reached a steady level. Decreasing dissolved oxygen concentration leads to lower growth rate and to higher pH. Both events mean stress conditions for the cell culture and probably result in increased genetic variability, and the loss of regeneration capacity. The stress condition during the adaptation phase can be eliminated by decreasing the pH of the medium to 4.7 before inoculation and by keeping dissolved oxygen above 40%. These conditions provide prolonged exponential growth dynamics and the cell suspensions could be the basis of large scale cultures also.
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  • 54
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    Photosynthesis research 44 (1995), S. 23-40 
    ISSN: 1573-5079
    Keywords: chloroplasts ; cyanobacteria ; ferredoxin ; photosynthesis ; plastocyanin ; thylakoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photosystem I functions as a plastocyanin:ferredoxin oxidoreductase in the thylakoid membranes of chloroplasts and cyanobacteria. The PS I complex contains the photosynthetic pigments, the reaction center P700, and five electron transfer centers (A0, A1, FX, FA, and FB) that are bound to the PsaA, PsaB, and PsaC proteins. In addition, PS I complex contains at least eight other polypeptides that are accessory in their functions. Recent use of cyanobacterial molecular genetics has revealed functions of the accessory subunits of PS I. Site-directed mutagenesis is now being used to explore structure-function relations in PS I. The overall architecture of PSI complex has been revealed by X-ray crystallography, electron microscopy, and biochemical methods. The information obtained by different techniques can be used to propose a model for the organization of PS I. Spectroscopic and molecular genetic techniques have deciphered interaction of PS I proteins with the soluble electron transfer partners. This review focuses on the recent structural, biochemical and molecular genetic studies that decipher topology and functions of PS I proteins, and their interactions with soluble electron carriers.
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  • 55
    ISSN: 1573-5079
    Keywords: diadinoxanthin ; dinoflagellate ; light-harvesting-complex ; peridinin ; photoacclimation ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have isolated Chl a-Chl c-carotenoid binding proteins from the dinoflagellates Prorocentrum minimum and Heterocapsa pygmaea grown under high (500 μmol m−2 s−1, HL) and low (35 μmol m−2 s−1, LL) light conditions. We compared various isolation procedures of membrane bound light harvesting complexes (LHCs) and assayed the functionality of the solubilized proteins by determining the energy transfer efficiency from the accessory pigments to Chl a by means of fluorescence excitation spectra. The identity of the newly isolated protein-complexes were confirmed by immunological cross-reactions with antibodies raised against the previously described membrane bound Chl a-c proteins (Boczar et al. (1980) FEBS Lett 120: 243–247). Spectroscopic analysis demonstrated the relatedness of these proteins with the recently described Chl-a-c 2-peridinin (ACP) binding protein (Hiller et al. (1993) Photochem Photobiol 57: 125–131; Iglesias Prieto et al. (1993) Phil Trans R Soc London B 338: 381–392). The water-soluble peridinin-Chl a binding-protein (PCP) was not detectable in P. minimum. Two functional forms of ACP with different pigmentation were isolated. A variant of ACP which was isolated from high-light grown cells, that specifically binds increased amounts of diadinoxanthin was compared to the previously described ACPs that bind proportionately more peridinin.
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  • 56
    ISSN: 1573-5079
    Keywords: glycine betaine ; osmolyte ; oxygen-evolving complex ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Natural osmoregulatory substances (osmolytes) allow a wide variety of organisms to adjust to environments with high salt and/or low water content. In addition to their role in osmoregulation, some osmolytes protect proteins from denaturation and deactivation by, for example, elevated temperature and chaotropic compounds. A ubiquitous protein-stabilizing osmolyte is glycine betaine (N-trimethyl glycine). Its presence has been reported in bacteria, in particular cyanobacteria, in animals and in plants from higher plants to algae. In the present review we describe the experimental evidence related to the ability of glycine betaine to enhance and stabilize the oxygen-evolving activity of the Photosystem II protein complexes of higher plants and cyanobacteria. The osmolyte protects the Photosystem II complex against dissociation of the regulatory extrinsic proteins (the 18 kD, 23 kD and 33 kD proteins of higher plants and the 9 kD protein of cyanobacteria) from the intrinsic components of the Photosystem II complex, and it also stabilizes the coordination of the Mn cluster to the protein cleft. By contrast, glycine betaine has no stabilizing effect on partial photosynthetic processes that do not involve the oxygen-evolving site of the Photosystem II complex. It is suggested that glycine betaine might act, in part, as a solute that is excluded from charged surface domains of proteins and also as a contact solute at hydrophobic surface domains.
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  • 57
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    Photosynthesis research 44 (1995), S. 117-125 
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; chlorophyll-protein complex ; maize mutant ; photosynthesis ; thylakoid membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Chl-protein complexes of three maize (Zea mays L.) mutants and one barley (Hordeum vulgare L.) mutant were analyzed using low temperature Chl fluorescence emissions spectroscopy and LDS-polyacrylamide gel electrophoresis. The maize mutants hcf-3, hcf-19, and hcf-114 all exhibited a high Chl fluorescence (hcf) phenotype indicating a disruption of the energy transfer within the photosynthetic apparatus. The mutations in each of these maize mutants affects Photosystem II. The barley mutant analyzed was the well characterized Chl b-less mutant chlorina-f2, which did not exhibit the hcf phenotype. Chlorina-f2 was used because no complete Chl b-less mutant of maize is available. Analysis of hcf-3, hcf-19, and hcf-114 revealed that in the absence of CP43, LHC II can still transfer excitation energy to CP47. These results suggest that in mutant membranes LHC II can interact with CP47 as well as CP43. This functional interaction of LHC II with CP47 may only occur in the absence of CP43, however, it is possible that LHC II is positioned in the thylakoid membranes in a manner which allows association with both CP43 and CP47.
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  • 58
    ISSN: 1573-5079
    Keywords: circular dichroism (CD) ; cyanobacteria ; energy transfer ; fluorescence ; light-harvesting antennae ; photosynthesis ; core particle ; allophycocyanin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have constructed a mutant Synechococcus sp. PCC 7942, termed R2HECAT, in which the entire phycobilisome rod operon has been deleted. In the whole cell absorption spectra of R2HECAT, the peak corresponding to phycocyanin (PC), λmax≈620 nm, could not be detected. However, a single pigment-protein fraction with λmax=654 nm could be isolated on sucrose gradients from R2HECAT. Analysis of this pigment-protein fraction by non-denaturing PAGE indicates an apparent molecular mass of about 1200–1300 kDa. On exposure to low temperature, the isolated pigment-protein complex dissociated to a protein complex with a molecular mass of about 560 kDa. When analysed by SDS-PAGE, the pigment-protein fraction was found to consist of the core polypeptides but lacked PC, 27, 33, 30, and the 9 kDa polypeptides which are a part of the rods. All the chromophore bearing polypeptides of the core were found to be chromophorylated. CD as well as absorption spectra showed the expected maxima around 652 and 675 nm from allophycocyanin (APC) and allophycocyanin B (APC-B) chromophores. Low temperature fluorescence and excitation spectra also showed that the core particles were fully functional with respect to the energy transfer between the APC chromophores. We conclude that PC and therefore the rods are dispensable for the survival of Synechococcus sp. PCC 7942. The results indicate that stable and functional core can assemble in absence of the rods. These rod-less phycobilisome core is able to transfer energy to Photosystem II.
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  • 59
    ISSN: 1573-5079
    Keywords: chlorophyll radicals ; cyanobacteria ; photosynthesis ; photoinhibition ; protein degradation ; thylakoids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Photosystem II reaction center is rapidly inactivated by light, particularly at higher light intensity. One of the possible factors causing this phenomenon is the oxidized primary donor, P680+, which may be harmful to Photosystem II because of its highly oxidizing nature. However, no direct evidence specificially implicating P680+ in photoinhibition has been obtained yet. To investigate whether P680+ is harmful to Photosystem II, turnover of the D1 protein and of the Photosystem II reaction center complex were measured in vivo in a mutant of the cyanobacterium Synechocystis sp. PCC 6803, in which the physiological donor to P680+, Tyrz, was genetically deleted. In this mutant, D1 degradation in the light is an order of magnitude faster than in wild type. The most straightforward explanation of this phenomenon is that accumulation of P680+ leads to an increased rate of turnover of the Photosystem II reaction center complex, which is compatible with the hypothesis of destructive oxidation by P680+ that is damaging to the Photosystem II complex.
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  • 60
    ISSN: 1573-5079
    Keywords: chlorophyll-a-fluorescence ; imaging ; oscillations ; photosynthesis ; minor veins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Images of chlorophyll-a-fluorescence oscillations were recorded using a camera-based fluorescence imaging system. Oscillations with frequencies around 1 per min were initiated by a transient decrease in light intensity during assimilation at an elevated CO2-concentration. The oscillation was inhomogenously distributed over the leaf. In cells adjacent to minor veins, frequency and damping rate was high, if there was any oscillation. In contrast, the amplitude was highest in cells most distant from phloem elements (maximal distance about 300 μm). The appearance of minor veins in oscillation images is explained by a gradient in the metabolic control in the mesophyll between minor veins and by transport of sugar from distant cells to phloem elements. The potential of fluorescence imaging to visualize ‘microscopic’ source-sink interactions and metabolic domains in the mesophyll is discussed.
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  • 61
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    Photosynthesis research 46 (1995), S. 87-91 
    ISSN: 1573-5079
    Keywords: bioenergetics ; photosynthesis ; chromatophores ; energy coupling ; evolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This minireview in memory of Daniel I. Arnon, pioneer in photosynthesis research, concerns properties of the first and still only known alternative photophosphorylation system, with respect to the primary phosphorylated end product formed. The alternative to adenosine triphosphate (ATP), inorganic pyrophosphate (PPi), was produced in light, in chromatophores from the photosynthetic bacterium Rhodospirillum rubrum, when no adenosine diphosphate (ADP) had been added to the reaction mixture (Baltscheffsky H et al. (1966) Science 153: 1120–1122). This production of PPi and its capability to drive energy requiring reactions depend on the activity of a membrane bound inorganic pyrophosphatase (PPase) (Baltscheffsky M et al. (1966) Brookhaven Symposia in Biology, No. 19, pp 246–253); (Baltscheffsky M (1967) Nature 216: 241–243), which pumps protons (Moyle J et al. (1972) FEBS Lett 23: 233–236). Both enzyme and substrate in the PPase (PPi synthase) are much less complex than in the case of the corresponding adenosine triphosphatase (ATPase, ATP synthase). Whereas an artificially induced proton gradient alone can drive the synthesis of PPi, both a proton gradient and a membrane potential are required for obtaining ATP. The photobacterial, integrally membrane bound PPi synthase shows immunological cross reaction with membrane bound PPases from plant vacuoles (Nore BF et al. (1991) Biochem Biophys Res Commun 181: 962–967). With antibodies against the purified PPi synthase clones of its gene have been obtained and are currently being sequenced. Further structural information about the PPi synthase may serve to elucidate also fundamental mechanisms of electron transport coupled phosphorylation. The existence of the PPi synthase is in line with the assumption that PPi may have preceded ATP as energy carrier between energy yielding and energy requiring reactions.
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  • 62
    ISSN: 1573-5079
    Keywords: photosynthesis ; photoinhibition ; Photosystem II ; reaction center ; damage and repair cycle ; Dunaliella salina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition in the green alga Dunaliella salina is accompanied by the formation of inactive Photosystem II reaction centers. In SDS-PAGE analysis, the latter appear as 160 kD complexes. These complexes are structurally stable, enough to withstand re-electrophoresis of excised gel slices from the 160 kD region. Western blot analyses with specific polyclonal antibodies raised against the D1 or D2 reaction center proteins provided evidence for the presence of both of these polypeptides in the re-electrophoresed 160 kD complex. Incubation of excised gel slices from the 160 kD region, under aerobic conditions at 4°C for a prolonged period of time, caused a break-up of the 160 kD complex into a ∽52 kD D1-containing and ∽80 and ∽26 kD D2-containing pieces. Western blot analysis with polyclonal antibodies raised against the apoproteins of CPI (reaction center proteins of PS I) did not show cross-reaction either with the 160 kD complex or with the ∽52, ∽80 and ∽26 kD pieces. The results show the presence of both D1 and D2 in the 160 kD complex and strengthen the notion of a higher molecular weight D1- and D2-containing complex that forms upon disassembly of photodamaged PS II units.
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  • 63
    ISSN: 1573-5079
    Keywords: Chlamydomonas ; mutation ; photosynthesis ; Photosystem 1 ; PsaA ; reaction center
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The psaA and psaB genes of the chloroplast genome in oxygenic photosynthetic organisms code for the major peptides of the Photosystem 1 reaction center. A heterodimer of the two polypeptides PsaA and PsaB is thought to bind the reaction center chlorophyll, P700, and the early electron acceptors A0, A1 and Fe-SX. Fe-SX is a 4Fe4S center requiring 4 cysteine residues as ligands from the protein. As PsaA and PsaB have only three and two conserved cysteine residues respectively, it has been proposed by several groups that Fe-SX is an unusual inter-peptide center liganded by two cysteines from each peptide. This hypothesis has been tested by site directed mutagenesis of PsaA residue C575 and the adjacent D576. The C575D mutant does not assemble Photosystem 1. The C575H mutant contains a photoxidisable chlorophyll with EPR properties of P700, but no other Photosystem 1 function has been detected. The D576L mutant assembles a modified Photosystem 1 in which the EPR properties of the Fe-SA/B centers are altered. The results confirm the importance of the conserved cysteine motif region in Photosystem 1 structure.
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  • 64
    ISSN: 1573-5079
    Keywords: 9-aminoacridine fluorescence ; chlorophyll fluorescence ; cyclic electron transport ; light scattering ; photosynthesis ; transthylakoid proton gradient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transthylakoid proton transport based on Photosystem I-dependent cyclic electron transport has been demonstrated in isolated intact spinach chloroplasts already at very low photon flux densities when the acceptor side of Photosystem I (PS I) was largely closed. It was under strict redox control. In spinach leaves, high intensity flashes given every 50 s on top of far-red, but not on top of red background light decreased the activity of Photosystem II (PS II) in the absence of appreciable linear electron transport even when excitation of PS II by the background light was extremely weak. Downregulation of PS II was a consequence of cyclic electron transport as shown by differences in the redox state of P700 in the absence and the presence of CO2 which drained electrons from the cyclic pathway eliminating control of PS II. In the presence of CO2, cyclic electron transport comes into play only at higher photon flux densities. At H+/e=3 in linear electron transport, it does not appear to contribute much ATP for carbon reduction in C3 plants. Rather, its function is to control the activity of PS II. Control is necessary to prevent excessive reduction of the electron transport chain. This helps to protect the photosynthetic apparatus of leaves against photoinactivation under light stress.
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  • 65
    ISSN: 1573-5095
    Keywords: Key words ; Water relations ; photosynthesis ; chlorophyll a fluorescence ; artificial forest regeneration ; cold storage ; frost hardiness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Logistic problems of large-scale reforestation necessitate freezer-storage of conifer seedlings. Frozen stock is typically thawed slowly at low temperatures for up to several weeks before shipping to the plantation site, but the necessity of this practice is questionable. Experiments were conducted to study effects of different thawing regimes on photosynthetic recovery, frost hardiness, water relations and growth initiation in “interior spruce” (white spruce (Picea glauca (Moench) Voss) and Engelmann spruce (Picea engelmannii Parry) hybrid complex). One year-old container-grown seedlings were planted after 9 days post-storage thawing at 5–15 °C or still frozen, directly from the freezer. During a 29 day observation period after planting, both groups showed changes in xylem water potential (Ψw), carbon fixation (A), stomatal conductance (g s ), chlorophyll a fluorescence and xanthophyll cycle pigments. Treatment differences in fluorescence and pigments peaked within one hour after planting. All differences in Ψw, A, g s , ratio of internal to external CO2 concentration (Ci/Ca), fluorescence, pigments and root number disappeared after 5 to 8 days. Terminal bud burst occurred 2.6 days earlier in the pre-thawed seedlings. When seedlings were rapidly thawed in the dark at 21 °C they achieved maximum Ψw (−0.2 MPa) in 3–4 hour. When evaluated 45 min after planting, A, g s , Ci/Ca and fluorescence values of rapidly thawed seedlings were intermediate between those for seedlings planted frozen or after 9 days slow thawing, showing that the recovery process was well underway a few hours after removal from the freezer. These results suggested that a suitable on-site operational protocol for rapid thawing might be to lay frozen bundles on the ground at ambient temperature overnight. In field trials of this method, rapidly thawed seedlings broke bud 3.3 days later than slowly thawed stock and also had greater frost hardiness at time of planting. Height, shoot and root mass did not differ after 3 months growth.
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  • 66
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    New forests 10 (1995), S. 79-98 
    ISSN: 1573-5095
    Keywords: Abies, acclimation ; photosynthesis ; shade tolerance ; Tsuga
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Successful regeneration of coastal montane sites harvested using alternative silvicultural systems may depend on the degree to which tree species can acclimate morphologically and physiologically to a variety of light environments. In a study to determine shade acclimation in montane conifers, one-year-old amabilis fir (Abies amabilis (Dougl.) Forbes) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings were grown in a nursery under four shade treatments: full sunlight (0% shade), 60% and 30% shade using shade cloth, and 30% shade using lath slats. Shading influenced shoot development, foliar physiology and morphological characteristics of both amabilis fir and western hemlock but in general, the effects were small. Shade levels of 60% were required to induce significant acclimation, and western hemlock appeared to respond more positively than amabilis fir and therefore was considered more shade tolerant than amabilis fir. Light quality had little influence on growth and development, as indicated by a lack of significant differences in physiology or morphology between seedlings grown under shade cloth or lath slats. There were indications that adequate nutrition levels may mitigate the effects of shade on seedling morphology and physiology.
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  • 67
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    Photosynthesis research 44 (1995), S. 55-65 
    ISSN: 1573-5079
    Keywords: asymmetry ; bacteriopheophytins ; electron transfer ; pigment replacement ; photosynthesis ; plant-type pheophytins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The native bacteriopheophytin a in reaction centers of Rb. sphaeroides R26 has been exchanged with modified bacteriopheophytins (bacteriochlorins), as well as with plant-type pheophytins (chlorins). Emphasis is on four pigments, which differ by their C-3 substituents (vinyl or acetyl) or their state of oxidation (chlorin or bacteriochlorin). The native BPhe a, which is a member of this group, can be replaced by the other three at both binding sites, HA and HB. However, exchange at HB proceeds more readily. Optical spectra (absorption, cd) show characteristic shifts, and the cd spectra indicate induced interactions between HA,B and BA,B and possibly also with P. Upon flash illumination, all modified reaction centers show reversible electron transfer to QB with recombination times comparable to native reaction centers. Forward rates and electron-transfer yields are also reported for some of the pigments.
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  • 68
    ISSN: 1573-5079
    Keywords: photosynthesis ; specific mutagenesis ; chloroplast DNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chloroplast transformation of Chlamydomonas reinhardtii has developed into a powerful tool for studying the structure, function and assembly of thylakoid protein complexes in a eukaryotic organism. In this article we review the progress that is being made in the development of procedures for efficient chloroplast transformation. This focuses on the development of selectable markers and the use of Chlamydomonas mutants, individually lacking thylakoid protein complexes, as recipients. Chloroplast transformation has now been used to engineer all four major thylakoid protein complexes, photosystem II, photosystem I, cytochrome b 6/f and ATP synthase. These results are discussed with an emphasis on new insights into assembly and function of these complexes in chloroplasts as compared with their prokaryotic counterparts.
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  • 69
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    World journal of microbiology and biotechnology 11 (1995), S. 649-653 
    ISSN: 1573-0972
    Keywords: Anacystis nidulans ; gibberellic acid ; glycollate dehydrogenase ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Gibberellic acid at 10-4 Mxxx was optimal for enhancement of growth, O2 evolution, photosystem II and I and the activity of glycollate dehydrogenase of Anacystis nidulans. A stimulatory effect was observed on photosystem II. Other concentrations of gibberellic acid were inhibitory to O2 evolution and photosystem I. Syntheses of phycocyanin, phycoerythrin and β-carotene were significantly enhanced after 48 h incubation with gibberellic acid at 10-3 Mxxx but the chlorophyll content began to increase 3 h after adding 10-4 Mxxx gibberellic acid.
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  • 70
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    Plant cell, tissue and organ culture 42 (1995), S. 147-152 
    ISSN: 1573-5044
    Keywords: corn ; kernel culture ; light quality ; phytochrome ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Growth and development of plants are known to be affected by exposure to red and blue light. Mechanisms by which light quality influences gene expression in maize (Zea mays L.) embryos have not been explored. Maize kernels can be cultured in vitro allowing experimental manipulation of environmental factors during seed development. We used the in vitro kernel culture system to investigate the response of developing maize seeds, which normally develop without exposure to light, to controlled light quality. Kernels grown under red light accumulated more dry weight than those grown in darkness, whereas kernels grown under blue light accumulated less. Reciprocal color shift experiments showed that light quality during the first week in culture had more influence on kernel weight than during the subsequent three weeks in culture. Soluble sugars were higher in both light treatments than in darkness. Blue-grown kernels had higher amino acid and lower lipid levels than red-or dark-grown kernels. Embryo morphology was markedly affected by red light, under which the upper shoot axis was longer than under blue light or in darkness. Embryo morphology was influenced by light quality during the later stages of development rather than the first week. We suggest, based on these results, that gene expression in the embryo and endosperm of developing maize seeds is sensitive to light quality, and the mechanism and time dependence of this effect warrant further study. In vitro maize kernel culture affords a convenient system for such light quality experiments.
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  • 71
    ISSN: 1573-5060
    Keywords: maize ; climatic factor ; genotype x environment interaction ; root trait ; statistical model ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The efficiency of genotopic and climatic characteristics in accounting for the interaction between genotypes and environments has been assessed in a three-year trial involving a set of genotypes presenting a range of root morphology characteristics (number and size). Climatic information on rainfall and temperature was recorded during the experiments, together with extra data on the growth and development of the genotypes. Their effects have been tested in factorial regression models. Climatic covariates were very powerful in accounting for the genotype by year interaction as well as the year main effect alone. For the number of adventitious roots on internode 7, the main effect of year could be described as a linear function of the average temperature and precipitation that occurred during the period of root initiation and growth. For internode 6, no clear conclusion was possible. For the root traits studied, 74 to 98% of the interaction could be explained by one climatic covariate. The regression coefficients can be considered as measures of genotypic stability. The genotypic covariates describing aerial development performed rather poorly, compared with environmental ones, even though the physiological and functional relationships between root and shoot are well known. Neither genotype main effect nor genotype by year interaction could be described sufficiently by factorial regression. Still, the genotypic covariates performing best clearly differed between root counts and size. Also the best genotypic covariates differed for main effect and interaction.
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  • 72
    ISSN: 1573-5060
    Keywords: germplasm registration ; maize ; Zea mays ; Isozyme ; markers ; morphological traits ; morphological variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Genetic markers (isozymes), in addition to the traits recommended by the UPOV convention, have been used in France since 1989 to characterize the maize inbred lines submitted to registration. In the years 1989. 1990 and 1991, a total of 974 inbreds has been described according to this procedure. Relationships between genetic markers were investigated and underlined the occurrence of linkage disequilibria within the tested germplasm. These disequilibria appeared to depend strongly on the breeding history of the germplasm. In some cases, these disequilibria could be related to a major progenitor (foundation effect). Relationships between genetic markers and quantitative traits were also pointed out. High coefficients of determination (up to 60%) were in some cases observed at the within group level, and also appeared to be very dependent on the major progenitors of the group of interest. The consequences of these results for breeding and distinctiveness studies are discussed.
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  • 73
    ISSN: 1573-5060
    Keywords: diallel cross ; qualitative interactions ; recurrent selection ; stability analysis ; maize ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A 10×10 diallel cross experiment involving white modified opaque-2 maize inbred lines was grown at four sites. A stability analysis, based on both a combining ability and a heterotic pattern model, was developed. The stability analysis provided valuable information on the genotype x environment interaction properties of the 10 inbred lines. The Gail & Simon (1985) test for qualitative interactions provided a means of determining the nature of these interactions. The inbred, SO507W(M), is shown to have the best potential for use in a hybrid breeding programme, in terms of having the highest weighted general combining ability and line heterosis, and the best general adaptability to all four sites. The single cross, SO713W(P) x PO558W(F), has been identified as one of the genotypes to be used in a recurrent selection programme that favours specific combining ability.
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  • 74
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    Photosynthesis research 44 (1995), S. 253-260 
    ISSN: 1573-5079
    Keywords: CO2 conductance ; CO2 recycling ; membrane ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 μL L−1 near the leaf base to below atmospheric (〈350 μL L−1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 μmol m−2 s−1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by 14CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 μL L−1 of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L−1 O2 compared to 20 mL L−1 O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.
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  • 75
    ISSN: 1573-5079
    Keywords: absorption cross-section ; cyanobacterium ; 77 K fluorescence ; fluorescence decay ; iron-stress ; photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43′, which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43′ apoprotein (designated isiA −) and (ii) flavodoxin (designated isiB −). The function of CP 43′ was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA − and isiB − strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43′ and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43′ is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB − strain grown under iron-deficient conditions, CP 43′ was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (Fo) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.
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  • 76
    ISSN: 1573-5079
    Keywords: cytochrome b 559 ; electron transport ; pH ; pheophytin ; photosynthesis ; Photosystem II ; reaction center ; redox potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A series of experiments have been conducted with isolated reaction centers of photosystem two (PS II) with the aim to elucidate the functional role of cytochrome (Cyt b 559). At pH 6.5 it was found that Cyt b 559 was reversibly photoreduced by red actinic light when Mn2+ was present as an electron donor while at pH 8.5 a photo-oxidation was observed under the same lighting conditions, which was dark reversible in the presence of hydroquinone. These pH dependent light induced changes were measured under anaerobic conditions and correlated with changes in the relative levels of high (HP) and low (LP) potential forms of the cytochrome. At pH 6.5 the cytochrome was mainly in its LP form while at pH 8.5 a significant proportion was converted to the HP form as detected by dark titrations with hydroquinone. This pH dependent difference in the levels of HP and LP Cyt b 559 was also detected when bright white light was used to monitor the level of the LP form using a novel reaction involving direct electron donation from the flavin of glucose oxidase (present in the medium and used together with glucose and catalase as an oxygen trap). The results suggest that PS II directly oxidises and reduces the HP and LP forms, respectively and that the extent of these photo-reactions is dependent on the relative levels of the two forms, which are in turn governed by the pH. This conclusion is interpreted in terms of the model presented previously (Barber J and De Las Rivas J (1993) Proc Natl Acad Sci USA 90: 10942–10946) whereby the pH induced effect is considered as a possible mechanism by which interconversion of LP and HP forms of Cyt b 559 is achieved. In agreement with this was the finding that as the extent of photo-oxidisable HPCyt b 559 increases, with increasing pH, the rate of irreversible photo-oxidation of β-carotene decreases, a result expected if the HP form protects against donor side photoinhibition.
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  • 77
    ISSN: 1573-5036
    Keywords: acclimation ; ecosystem carbon balance ; elevated CO2 ; global change ; photosynthesis ; respiration ; soil carbon ; soil organic matter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Acclimation of photosynthesis and respiration in shoots and ecosystem carbon dioxide fluxes to rising atmospheric carbon dioxide concentration (C a ) was studied in a brackish wetland. Open top chambers were used to create test atmospheres of normal ambient and elevated C a (=normal ambient + 34 Pa CO2) over mono-specific stands of the C3 sedge Scirpus olneyi, the dominant C3 species in the wetland ecosystem, throughout each growing season since April of 1987. Acclimation of photosynthesis and respiration were evaluated by measurements of gas exchange in excised shoots. The impact of elevated C a on the accumulation of carbon in the ecosystem was determined by ecosystem gas exchange measurements made using the open top chamber as a cuvette. Elevated C a increased carbohydrate and reduced Rubisco and soluble protein concentrations as well as photosynthetic capacity(A) and dark respiration (R d ; dry weight basis) in excised shoots and canopies (leaf area area basis) of Scirpus olneyi. Nevertheless, the rate of photosynthesis was stimulated 53% in shoots and 30% in canopies growing in elevated C a compared to normal ambient concentration. Elevated C a inhibited R d measured in excised shoots (−19 to −40%) and in seasonally integrated ecosystem respiration (R e ; −36 to −57%). Growth of shoots in elevated C a was stimulated 14–21%, but this effect was not statistically significant at peak standing biomass in midseason. Although the effect of elevated C a on growth of shoots was relatively small, the combined effect of increased number of shoots and stimulation of photosynthesis produced a 30% stimulation in seasonally integrated gross primary production (GPP). The stimulation of photosynthesis and inhibition of respiration by elevated C a increased net ecosystem production (NEP=GPP−R e ) 59% in 1993 and 50% in 1994. While this study consistently showed that elevated C a produced a significant increase in NEP, we have not identified a correspondingly large pool of carbon below ground.
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  • 78
    ISSN: 1573-5060
    Keywords: genetic control ; maize streak virus ; major genes ; minor genes ; resistance ; Zea mays ; maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary S1 to S5 inbred lines, derived from a maize population bred for its overall resistance to three tropical viruses, were screened for resistance to maize streak virus (MSV) by artificial plant infection using viruliferous leafhoppers. Symptoms were rated and intra-line frequency distributions studied for all pedigree inbred lines. Mortality due to MSV was very low among these inbreds. Symptoms appeared later, developed slower and were less severe than in the susceptible control hybrid. Results of a study of 500 S1 and 93 S2 lines suggested that resistance is under genetic control via a system involving loci with major genes (with dominance for resistance) controlling high to complete resistance, associated with a genetic system involving loci with minor genes controlling partial resistance. Lines expressing complete resistance to MSV were developed from 5 cycles of inbreeding and selection. The relevance of such complete and partial resistance is discussed.
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  • 79
    ISSN: 1573-5060
    Keywords: glyphosate ; herbicide tolerance ; non-target effects ; somaclonal variation ; Zea mays ; maize
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The progeny of 104 regenerated maize plants were screened for tolerance to the safe broad-spectrum herbicide glyphosate during seed germination and early growth. Seven somaclones showed varying degrees of resistance to the application of the herbicide at 1.2 mM (0.1 kg a.i. in 400 1 ha-1 of water). Plants capable of a normal growth following treatment with 2.4 mM (0.2 kg ha-1) glyphosate at the three leaf stage were selfed, and their progeny analyzed. A family able to tolerate the exposure to glyphosate at 2.4 mM was isolated and shown to maintain a photosynthetic rate comparable with control after the application of the herbicide. The selfed progeny of the tolerant somaclone was characterized as to the properties of two targets of glyphosate, the shikimate pathway enzymes 5-enol-pyruvyl-shikimate-3-phosphate (EPSP) synthase and 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase. In vitro tests ruled out the possibility that the tolerance was due to altered forms of these enzymes. Families showed significant variability with regard to EPSP and DAHP synthase levels, measured at different stages during seedling growth; however, not even these traits were correlated with in vivo response to glyphosate. The possible role of other physiological processes in determining the increased tolerance to the herbicide is discussed.
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  • 80
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    Euphytica 82 (1995), S. 175-184 
    ISSN: 1573-5060
    Keywords: digestibility ; feeding value ; forage maize ; selection ; combining ability ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Variations in feeding value characteristics were studied on a factorial mating design, within a multilocal network. The in vitro digestibility of dry matter (IVDDM), neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), starch, soluble carbohydrate, protein and ash contents were evaluated on whole plant samples. The in vitro digestibility of the non-starch and non-soluble carbohydrate plant part (IVDNSC) was also computed from near infra-red reflectance spectroscopy estimations of IVDDM, starch and soluble carbohydrate contents. Variations due to general combining ability (GCA) were more important, for all traits, than variations due to specific combining ability (SCA). Variations due to the GCA × environment interaction were also sizeable and were partly explained by the earliness of the lines. IVDDM was primarily influenced by the relative proportions of cell walls and starch in the whole plant, which were particularly susceptible to the development stage of the plants, at harvest. When adjusted for earliness, there was generally no significant relation between the line per se value and GCA performance in the biochemical constituent contents of the plant. On the contrary, IVDNSC seemed to be a feeding value trait worth evaluating at the inbred line level. It was also almost independent of the ripening stage and could be easily computed from whole plant samples. IVDNSC, with a simultaneous control of starch content, might be a good selection criterion for evaluating and improving the nutritive value of forage maize.
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  • 81
    ISSN: 1573-5060
    Keywords: Zea mays ; insect vectors ; resistance ; maize ; maize streak virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Settling, probing and oviposition behaviour ofCicadulina mbila, the main vector of maize streak virus (MSV) disease were studied on four maize genotypes, 100MSR, HASR, Reunion and H512. Of the four, only H512 was completely susceptible to MSV while the other three genotypes were all known to have some resistance to MSV. Generally,C. mbila settled in higher numbers on the MSV susceptible genotype compared to the three virus resistant ones. However, the number of probing marks left on H512 and 100MSR were similar while more marks were made on Reunion and HASR in increasing order. The oviposition patterns were similar to those observed for probing behaviour. The results suggest the existence of potentially useful resistance mechanisms against the vector. The possible implications of these results are discussed.
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  • 82
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    Euphytica 84 (1995), S. 57-65 
    ISSN: 1573-5060
    Keywords: bush bean ; Phaseolus vulgaris ; intercropping ; maize ; sole cropping ; Zea mays ; quality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The intereropping of common bean (Phaseolus vulgaris L.) and maize (Zea mays L.) is a common practice in the Northwest of the Iberian Peninsula. In this experiment, 25 populations of bush bean were evaluated for nutritional and culinary traits of dry seed and immature pod in sole crop and in intercrop in two years and in two locations, in order to determine whether selection of bush bean in sole crop can result in genetic progress for intercrop. There were no differences in the population means between cropping systems. Significant differences were detected among populations for all traits tudied except starch content, crude ash, water absorption and coat proportion. Population x environment interaction was significant for pod thickness. Bean populations did not interact with cropping systems for any trait, although there were differences between cropping systems for crude protein. These results suggest that a sole crop system provides sufficient information to select bean populations efficiently for the bush bean-maize intercropping system, although the advanced generations of the breeding program should be tested for quantitative traits such as protein content in the appropriate cropping system (intercropping) to know the competitive ability with the associated species. This would permit to choose bush bean populations which complement more efficiently and would be less competitive with the maize population.
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    Photosynthesis research 46 (1995), S. 45-46 
    ISSN: 1573-5079
    Keywords: phosphoenolpyruvate carboxylase ; photophosphorylation ; photosynthesis ; respiration ; sugar biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 84
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    Photosynthesis research 46 (1995), S. 141-149 
    ISSN: 1573-5079
    Keywords: photosynthesis ; chloroplast thylakoid ; Photosystem I ; Photosystem II ; linear and cyclic electron transport ; plastocyanin ; plastoquinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Recent work on the domain organization of the thylakoid is reviewed and a model for the thylakoid of higher plants is presented. According to this model the thylakoid membrane is divided into three main domains: the stroma lamellae, the grana margins and the grana core (partitions). These have different biochemical compositions and have specialized functions. Linear electron transport occurs in the grana while cyclic electron transport is restricted to the stroma lamellae. This model is based on the following results and considerations. (1) There is no good candidate for a long-range mobile redox carrier between PS II in the grana and PS I in the stroma lamellae. The lateral diffusion of plastoquinone and plastocyanin is severely restricted by macromolecular crowding in the membrane and the lumen respectively. (2) There is an excess of 14±18% chlorophyll associated with PS I over that of PS II. This excess is assumed to be localized in the stroma lamellae where PS I drives cyclic electron transport. (3) For several plant species, the stroma lamellae account for 20±3% of the thylakoid membrane and the grana (including the appressed regions, margins and end membranes) for the remaining 80%. The amount of stroma lamellae (20%) corresponds to the excess (14–18%) of chlorophyll associated with PS I. (4) The model predicts a quantum requirement of about 10 quanta per oxygen molecule evolved, which is in good agreement with experimentally observed values. (5) There are at least two pools of each of the following components: PS I, PS II, cytochrome bf complex, plastocyanin, ATP synthase and plastoquinone. One pool is in the grana and the other in the stroma compartments. So far, it has been demonstrated that the PS I, PS II and cytochrome bf complexes each differ in their respective pools.
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  • 85
    ISSN: 1573-5079
    Keywords: iron-sulfur cluster FA ; iron-sulfur cluster FB ; midpoint potential ; photosynthesis ; Photosystem I ; PsaC ; Synechococcus sp. PCC 6301
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The FB iron-sulfur cluster is destroyed preferentially by treating Photosystem I complexes with HgCl2(Kojima Y, Niinomi Y, Tsuboi S, Hiyama T and Sakurai H (1987) Bot Mag 100: 243–53). When FB is 95% depleted but FAis quantitatively retained in cyanobacterial PS I complexes, the reduction potential of FA remains highly electronegative (Em=−530 mV, n=1), the EPR spectral and spin relaxation properties of FA and FXremain unchanged, but NADP+ photoreduction rates decline from 552 to 72 μmol mg Chl−1 h−1.When FB is reconstituted with FeCl3, Na2S and β-mercaptoethanol, NADP+photoreduction rates recover to 528 μmol mg Chl−1 h−1. The correlation between the presence of FBand NADP+ photoreduction provides direct experimental evidence that this iron-sulfur cluster is required for electron throughput from cytochromec 6 to flavodoxin or ferredoxin in Photosystem I.
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  • 86
    ISSN: 1573-5079
    Keywords: photosynthesis ; photosystem I ; psaD ; reaction center ; subunit ; sequence ; thermophilic cyanobacterium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nucleotide sequence was determined for the psaD gene of a thermophilic cyanobacterium, Synechococcus vulcanus, which encoded the PsaD subunit (Subunit II) of the Photosystem I reaction center complex. Except for some differences in the peripherals, the nucleotide sequence of the gene encoding PsaD was identical to that of another thermophilic cyanobacterium Synechococcus elongatus reported previously. Relationship between these primary structures and thermostability was also discussed.
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  • 87
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    Photosynthesis research 43 (1995), S. 1-9 
    ISSN: 1573-5079
    Keywords: Zea mays ; C4-photosynthesis ; decarboxylation ; NADP-ME type ; reaction mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetic mechanism of NADP-dependent malic enzyme purified from maize leaves was studied in the physiological direction. Product inhibition and substrate analogues studies with 3′ aminopyridine dinucleotide phosphate and tartrate indicate that the enzyme reaction follows a sequential ordered Bi-Ter kinetic mechanism. NADP is the leading substrate followed by l-malate and the products are released in the order of CO2, pyruvate and NADPH. The enzyme also catalyzes a slow, magnesium-dependent decarboxylation of oxaloacetate and reduction of pyruvate and oxaloacetate in the presence of NADPH to produce l-lactate and l-malate, respectively.
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  • 88
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    Photosynthesis research 46 (1995), S. 393-397 
    ISSN: 1573-5079
    Keywords: photosynthesis ; down-regulation ; variable fluorescence ; dark recovery ; Artabotrys hexapetatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Using variable to maximum fluorescence (Fv/Fm) as the criterion, the down regulation of photosynthesis by high light stress was characterized in the detached leaves of Artabotrys hexapetatus. The decrease in Fv/Fm was corelated with the decrease in oxygen evolution by thylakoids isolated from high light exposed leaves. The decrease in Fv/Fm was linear with increasing time of exposure to high light. A comparison of recovery measured as Fv/Fm, in low light versus dark, revealed that the recovery in darkness was as significant as in low light. Since the relaxation of fluorescence was a rapid response after exposure to high light and the fact that the recovery occurs in total darkness, it is concluded that photoinhibition and down regulation of photosynthesis by high light are independent events.
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  • 89
    ISSN: 1573-5087
    Keywords: chlormequat chloride ; flag leaf ; grain filling ; imazaquin ; photosynthesis ; Triticum aestivum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In West-Europe, intensive cereal management uses plant growth regulators (PGRs) especially for wheat. A green-house experiment compared the effects of two PGRs on flag leaf characteristics and yield of winter wheat. Chlormequat chloride + choline chloride (CCC) and chlormequat chloride + choline chloride + imazaquin (CCC+I) were applied to winter wheat at growth stage 5 (Feekes Large scale). CCC and CCC+I significantly increased flag leaf surface area at anthesis. Both treatments also enhanced chlorophyll content of the main stem flag leaf. The grain filling period was extended with PGR application by 2 days. CCC and CCC+I significantly increased net CO2 assimilation rates during the flag leaf life. No effects of PGR spraying were observed on the pattern of 14C labelled assimilate distribution. Increased grain yield was due to the increase in average grain weight. The results indicate that PGR treatments increased flag leaf contribution to grain filling. The addition of imazaquin (I) to chlormequat (CCC) improved the effects of CCC.
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  • 90
    ISSN: 1573-2932
    Keywords: Age classes ; branch cuvette ; chamber design ; CO2 ; gas exchange ; ozone ; Picea abies ; photosynthesis ; transpiration ; twigs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The gas exchange system is computer controlled and is designed to measure and control 14 temperature regulated chambers enclosing spruce twigs for several months with minimum ozone absorption. The system is mounted on sun exposed single year classes of a Norway spruce stand in western Jutland, Denmark. Since July 1994 the temperature control system has been in function. Results show that 95% of the temperature measurements inside the cuvettes are within the range −2 to +3 °C of the ambient temperature. Gas exchange measurements show that the current year shoots have a higher net photosynthesis than the older shoots. The net photosynthesis in current year needles on sunny days is significantly reduced by the 6 h daily 30–40 ppb ozone addition.
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  • 91
    ISSN: 1572-9788
    Keywords: DNA markers ; heterotic breeding groups ; polymorphism ; popcorn ; simple sequence repeats ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Popcorn (Zea mays L.) hybrids grown in the United States are derived from narrow-based germplasm, and standard RFLP analysis detects relatively little polymorphism. Inter-simple sequence repeat (ISSR) amplification, a novel technique based on PCR amplification of inter-microsatellite sequences to target multiple loci in the genome, was employed to investigate its potential for detection of polymorphism among nineteen popcorn and eight dent corn inbred lines. ISSR yielded an average of 54 bands/primer/inbred line, with over 98% of the bands repeatable across DNA extractions and separate PCR runs. Ten primers based on di- and tri-nucleotide tandem repeats revealed 73% and 87% polymorphism among popcorn and dent corn lines, respectively, with an overall 95% polymorphism rate. Principal component and cluster analyses resulted in grouping of dent and popcorn lines corresponding to their heterotic breeding pools. ISSR amplification, in addition to being both simple and cost and time efficient, provides for rapid production of highly polymorphic markers which appear to correspond to known pedigree information. Therefore, the ISSR technique may have great potential for identifying polymorphism in species with narrow-based germplasm, and for use in DNA marker-assisted breeding approaches.
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  • 92
    ISSN: 1573-1561
    Keywords: Infochemicals ; Zea mays ; stem borer ; Chilo partellus ; parasitoid ; Cotesia flavipes ; host searching ; herbivore-induced synomones ; systemic effect ; exogenous elicitor ; caterpillar regurgitate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The origin of olfactory stimuli involved in the host microhabitat location inCotesia flavipes, a parasitoid of stem-borer larvae, was investigated in a Y-tube olfactometer. The response of femaleC. flavipes towards different components of the plant-host complex, consisting of a maize plant infested with two or more larvae of the stem borerChilo partellus, was tested in dualchoice tests. The concealed lifestyle of the stem-borer larvae did not limit the emission of volatiles attractive to a parasitoid. A major source of the attractive volatiles from the plant-host complex was the stem-borer-injured stem, including the frass produced by the feeding larvae. Moreover, the production of volatiles attractive to a parasitoid was not restricted to the infested stem part but occurs systemically throughout the plant. The uninfested leaves of a stem-borer-infested plant were found to emit volatiles that attract femaleC. flavipes. We further demonstrate that an exogenous elicitor of this systemic plant response is situated in the regurgitate of a stem-borer larva. When a minor amount of regurgitate is inoculated into the stem of an uninfested plant, the leaves of the treated plant emit volatiles that attract femaleC. flavipes.
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  • 93
    ISSN: 1573-2932
    Keywords: air pollution ; SO2 ; photosynthesis ; Quercus pubescens ; Quercus cerris ; oaks
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Young oak plants (Quercus pubescens Willd. and Q. cerris L.) were exposed for 23 weeks to a gradient of sulphur dioxide concentrations (28, 61, 93 ppb in vol., compared with charcoal filtered-air ventilated controls) in fumigation chambers. Foliar gas exchange was analyzed by an IRGA methodology after 11 weeks and chlorophyll was assessed in a non-destructive way. At the end, foliar biomass produced during the experimental period was determined and its total sulphur and carbohydrate content analyzed. Visible foliar injury, as well as reduction in chlorophyll content was not observed. Carbon dioxide assimilation was linearly depressed by sulphur dioxide in both the species, with a maximum depression of 25% in Q. pubescens and 44% in Q. cerris. Stomatal conductance and transpiration were negatively affected only in Q. pubescens, with a linear trend. The two species showed a similar behaviour in water use efficiency, this parameter being reduced in a linear fashion. The intracellular/ambient carbon dioxide concentration ratio was affected in a differential way: while in Q. pubescens no alteration was evident, a linear increase was shown by Q. cerris. Total foliar sulphur content was dramatically increased in both the species. Average leaf area was unaffected in both the species. Reduction in foliar dry weight was only observed in Q. cerris (−30% at the highest sulphur dioxide concentration). We speculate that in Q. pubescens photosynthetic limitations are mainly of stomatal nature, and in Q. cerris the major constraints are probably associated with mesophyll disturbances. Foliar starch content was linearly increased by the pollutant.
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  • 94
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    European journal of plant pathology 101 (1995), S. 301-310 
    ISSN: 1573-8469
    Keywords: Bipolaris zeicola ; maize ; multilocus haplotypes ; Northern Corn Leaf Spot ; sexual reproduction ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Over 3 years 15 samples ofC. carbonum were collected from 11 corn fields in North Carolina and Tennessee. Among 514 isolates of race 2 and 319 isolates of race 3, five phenotypic characters (mating type, production of pseudothecia, production of asci and ascospores, tolerance to cycloheximide and carboxin, respectively) that are controlled by single genes at unlinked loci (Mat, Psu, Asc, Cyh, Crb) were examined. Gametic phase disequilibrium (GPD) was analyzed by three methods. First, observed and expected four-locus haplotype frequencies were compared inG-tests for goodness of fit (method 1) and second, four-locus disequilibrium was calculated using an index of association which is based on the variance of the number of loci at which two isolates in a given population differ (method 2). Third, observed and expected frequencies of allele pairs were compared in 2×2 contingency tables (method 3). Each test was performed on individual and pooled samples which also allowed assessment of heterogeneity among samples. In general this heterogeneity was low, i.e. the consistency of associations among samples was high. Four-locus disequilibrium was significant in race 2 with method 1 but not with method 2. In race 3 we found no disequilibrium with any of the two methods. Method 3 indicated that several allele pairs were significantly associated in race 2 but not race 3. Thus GPD was significant in race 2 but not in race 3. Mating type frequencies were close to 0.50 in race 2 and race 3. This and the non-significant index of association indicate that the sexual stage ofC. carbonum is operating within each of the two race populations. It is suggested that selection favours different haplotypes in the asexual than in the sexual stage of the pathogen. Such disruptive selection may have maintained polymorphisms of genes related to sexual fertility and stabilized gene frequencies inC. carbonum over a period of 15 years (1972–1987).
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