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  • 1
    Electronic Resource
    Electronic Resource
    The acetylene reduction assay as a means of studying nitrogen fixation in white clover under sward and laboratory conditions (1976)
    Oxford, UK : Blackwell Publishing Ltd
    Grass and forage science 31 (1976), S. 0 
    Details
    ISSN: 1365-2494
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The acetylene reduction assay was used to follow seasonal changes in nitrogen fixation activity in a white clover-perennial ryegrass ley in Northern Ireland. The annual estimate for fixation by the ley was 268 kg ha−1 (239 lb/acre) nitrogen virtually all of which was fixed during March to October. Nitrogen fixation was curtailed drastically after the ley was cut but recovered as new foliage expanded on the clover. Glasshouse experiments described the effects of temperature, shading and defoliation on nitrogen fixation by white clover, and indicated that these factors might be important in modifying symbiosis under field conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2494.1976.tb01112.x
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  • 2
    Electronic Resource
    Electronic Resource
    Root xylem transport of amino acids in the root hemiparasitic shrub Olax phyllanthi (Labill) R.Br. (Olacaceaea) and its multiple hosts (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The amino acid compositions of the root xylem saps of Olax phyllanthi and a range of its common hosts were examined in native coastal heath in Western Australia and in pot cultures of Olax reliant on single hosts. When hosts specializing in the xylem transport of one major solute (asparagine, glutamine, histidine, arginine or proline) were exploited, the endophytic tissue of haustoria and the xylem sap of Olax showed much lower proportions of this than of other solutes, suggesting pronounced metabolic transformation prior to xylem loading by the parasite. However, the xylem sap of Olax did partly reflect the compositions of its hosts; for example, djenkolic acid and pipecolic acid were present when Olax was parasitic on species of Acacia, and levels of citrulline and aspartic acid were higher than normal when it exploited hosts transporting large amounts of these compounds. Back-flow of S-ethenyl cysteine, a novel amino acid specific to Olax, was observed to another root hemiparasite (Exocarpos sparteus) in native habitat and to certain non-parasitic hosts in water-stressed pot cultures. Haustoria exhibited high levels of glutamine synthetase but showed appreciable in vivo nitrate reductase activity only when on hosts with high xylem levels of nitrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb00528.x
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  • 3
    Electronic Resource
    Electronic Resource
    15N natural abundance of plant and soil components of a Banksia woodland ecosystem in relation to nitrate utilization, life form, mycorrhizal status and N2-fixing abilities of component species (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Studies of the variation in δ15N values for plants from a fire-prone Banksia woodland in South West Australia showed that pioneer herbaceous, non-mycorrhizal species which were active in nitrate reduction and storage, had the highest values (1.81%c). A detailed study of one such species Ptilotus polystachus demonstrated a close correspondence between the δ15N values of soil nitrate, xylem nitrate and leaf total nitrogen, suggesting an exclusive reliance on nitrate ions as nitrogen source. These pioneer species also showed a preponderance of the chloroplastic isoform of glutamine synthetase while woody species generally had higher activity associated with the cytosolic isoform. The group comprising monocotyledonous hemicryptophytes and geophytes contained species with slightly positive δ15N values and moderately active in nitrate reduction and storage. Nitrogen-fixing species had the lowest δ15N values (–0.36‰), irrespective of their apparent utilisation of nitrate. However, woody resprouter species which had low levels of nitrate reduction and storage had δ15N values which fell within the range of values obtained for the miscellaneous assemblage of N2-fixing species. Consequently, 15N abundance values failed to distinguish N2 fixing from non-fixing woody species, and therefore, could not be used in the ecosystem to determine the dependence of putative nitrogen fixing species on N2 fixation. The study demonstrated complex patterns of nitrogen utilization in the ecosystem in which exploitation of different nitrogen resources related to plant life form and the physiological attributes of nitrogen assimilation by component species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00882.x
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  • 4
    Electronic Resource
    Electronic Resource
    Characteristics of inorganic nitrogen assimilation of plants in fire-prone Mediterranean-type vegetation (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 16 (1993), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A range of approaches was used to investigate how species within a fire-prone Banksia woodland in South West Australia exploited inorganic soil nitrogen sources and how this changes through the development of the fire chronosequence. Nitrate and ammonium were present in soil solution throughout the chronosequence but nitrate predominated in recently burnt sites. Mean shoot nitrate reductase activities were high for all species in recently burnt sites and showed little increase when nitrate was supplied via the transpiration stream. Nitrate reductase of shoots of most species was low at sites not burnt for several years, but following transpirational induction with nitrate, developed activities similar to those at recently burnt sites. The principal amino compounds transported in the xylem were species specific, including asparagine, glutamine and citrulline-dominated species, and changed little in relative composition across the chronosequence. Species most active in leaf nitrate reduction transported the largest amounts of nitrate in their xylem sap and proportional amounts of nitrate in xylem tended to be greatest in recently burnt sites. Most of the species examined appeared to be shoot rather than root nitrate assimilators, but marked differences were recorded in potential of leafy shoots of different species to reduce nitrate. As a general rule, shallow-rooted herbaceous, non-mycorrhizal or VAM-positive species had the highest capacity to reduce nitrate, whereas woody species with ericoid mycorrhizae or combined vesicular arbuscular/ectomycorrhizal associations exhibited little capacity to reduce nitrate in roots or shoots. It seems likely that this latter group utilize ammonium or even organic forms of nitrogen rather than nitrate. Some putative nitrogen-fixing species were active in reducing and transporting nitrate, others were virtually inactive in these respects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1993.tb00881.x
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  • 5
    Electronic Resource
    Electronic Resource
    Selectivity in xylem to phloem transfer of amino acids in fruiting shoots of white lupin (Lupinus albus L.) (1975)
    Springer
    Planta 127 (1975), S. 251-262 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 14C-labelled amino compounds were fed singly to fruiting shoots of white lupin as a 15 min pulse through the transpiration stream. The time course of labelling of phloem was followed over a 6 h period by making successive collections of phloem sap from the cut tips of attached fruits. The distribution of 14C amongst solutes of phloem sap was examined. Seeds harvested at 6 h were analyzed for 14C content and 14C distribution amongst amino acid residues of protein. Certain amino compounds (valine, asparagine, threonine, serine, citrulline, glutamine) were transferred rapidly in unchanged form from xylem to phloem. Each labelled phloem sap intensely, and its 14C was transfrrred to fruit and seed with high efficiency. Other amino compounds (glycine, methionine, aspartic acid, homoserine, glutamic acid and γ-amino butyric acid) passed unchanged to phloem only in small amounts. The bulk of their 14C appeared in phloem sap attached to other substances, especially non-amino compounds and amino acids metabolically related to the one applied. The 14C from each of this second group of amino acids labelled phloem less intensely and was donated to fruit and seed with low efficiency. Selectivity in transfer of amino acids from xylem to phloem appeared to be an important element in determining the overall balance of nitrogenous solutes in the translocation stream. The significance of this and coupled loading of photosynthate was examined in relation to the seed's requirements for amino acids in protein synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380722
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  • 6
    Electronic Resource
    Electronic Resource
    Contrasting effects of supplementary feeding of insects or mineral nutrients on the growth and nitrogen and phosphorous economy of pygmy species of Drosera (1992)
    Springer
    Oecologia 92 (1992), S. 8-13 
    Details
    ISSN: 1432-1939
    Keywords: Carnivorous plants ; Drosera ; Supplementary feeding ; Fertilizing ; Growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Growth responses and accumulation of N and P were studied in two pygmy south-west Australian species of Drosera following supplementary feeding of arthropods (collembolans, Hypogastrura vernalis and fruit flies, Drosophila melanogaster) and/or a balanced mineral nutrient supplement (N as nitrate) via the roots. One feeding experiment used glasshouse-raised germlings from vegetative propagules (gemmae) of the perennial Drosera closterostigma, the other three (two on D. closterostigma and one on the annual D. glanduligera) involved natural populations engaging in natural captures of indigenous prey. All experiments recorded highly significant increases in plant dry matter, N and P (all plant age groups) and in reproductive performance (adult plants only) from artificial feeding of arthropods, but no apparent benefits from minerals alone or additive effects of minerals above that due to insects. Unresponsiveness to mineral nutrients was suggested to relate to inability of the species to use nitrate, while up to three-fold growth and nutrient uptake response to insects indicated that growth of natural populations might be severely limited by inadequate catches of prey. It is concluded that the highly nutrient-poor conditions typical of the habitat of pygmy species of Drosera may have promoted marked specialization towards carnivory and an attendant decline in ability to utilize soil-derived sources of nutrients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317256
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  • 7
    Electronic Resource
    Electronic Resource
    The utilization of nitrogen from insect capture by different growth forms of Drosera from Southwest Australia (1991)
    Springer
    Oecologia 87 (1991), S. 240-246 
    Details
    ISSN: 1432-1939
    Keywords: Nitrogen isotope ratio ; Nutrition ; Insectivorous plants ; Drosera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plants of Drosera species, neighbouring noncarnivorous plants, and arthropods on or near each Drosera sp. were collected at 11 contrasting habitat locations in SW Australia. At three of the sites clones of the rare glandless mutant form of D. erythrorhiza were collected alongside fully glandular counterparts. The δ 15N value (15N/14N natural isotope composition) of insect-free leaf and stem fractions was measured, and the data then used to estimate proportional dependence on insect N (%NdI) for the respective species and growth forms of Drosera. The data indicated lower %NdI values for rosette than for self-supporting erect or for climbing vine species. The latter two groups showed an average %NdI value close to 50%. The %NdI increased with length and biomass of climbing but not erect forms of Drosera. δ 15N values of stems were positively correlated with corresponding values for leaves of Drosera. Leaf material was on average significantly more 15N enriched than stems, possibly due to delayed transport of recent insect-derived N, or to discrimination against 15N in transfer from leaf to the rest of the plant. The comparison of δ 15N values of insects and arthropod prey, glandless and glandular plants of D. erythrorhiza indicated %NdI values of 14.3, 12.2 and 32.2 at the respective sites, while matching comparisons based on δ 15N of insect, reference plants and glandular plants proved less definitive, with only one site recording a positive %NdI (value of 10.4%) despite evidence at all sites of feeding on insects by the glandular plants. The use of the δ 15N technique for studying nutrition of carnivorous species and the ecological significance of insect feeding of different growth forms of Drosera growing in a large range of habitats is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325262
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  • 8
    Electronic Resource
    Electronic Resource
    Xylem to phloem transfer of solutes in fruiting shoots of legumes, studied by a phloem bleeding technique (1975)
    Springer
    Planta 122 (1975), S. 11-26 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Comparisons were made of the levels of various solutes in xylem (tracheal) sap and fruit tip phloem sap of Lupinus albus (L.) and Spartium junceum (L.). Sucrose was present at high concentration (up to 220 mg ml-1) in phloem but was absent from xylem whereas nitrate was detected in xylem (up to 0.14 mg ml-1) but not in phloem. Total amino acids reached 0.5–2.5 mg ml-1 (in xylem) versus 16–40 mg ml-1 in phloem. Phloem: xylem concentration ratios for mineral nutrients (K, Na, Mg, Ca, Fe, Zn, Mn, Cu) spanned the range 0.7 to 20, the ratios generally reflecting an element's phloem mobility and its availability to the xylem from the roots. The accessibility of nitrate to xylem and phloem was studied in Lupinus. Increasing the nitrate supply to roots from 100 to 1000 mg NO3−Nl-1 increased nitrate spill over into xylem, but nitrate always failed to appear in phloem. However, phloem loading of small amounts of nitrate was induced by feeding 750 or 1000 mg NO3−Nl-1 directly to cut shoots via the transpiration stream. Transfer of reduced nitrogen to phloem was demonstrated by feeding 15NO3 to shoots and recovering 15N-enriched amides and amino acids in phloem sap. Increased nitrate supply to roots led to increased amino acid levels in xylem and phloem but did not alter markedly the balance between individual amino acids. The fate of xylem-fed 14C-labelled asparagine, glutamine and aspartic acid and of photosynthetically fed 14CO2 was studied in Spartium, with reference to phloem transport to seeds. Substantial fractions of the 14C of all sources appeared in non-amino compounds. [14C]asparagine passed largely in unchanged form to the phloem whereas the 14C from aspartic acid or glutamine appeared in phloem attached to other amino acids (e.g. asparagine and glutamic acid). Serine, asparagine and glutamine were the main amino compounds labelled in phloem sap after feeding 14CO2. The wide distribution of 14C amongst free and bound amino acids of seeds suggested that extensive metabolism of phloem-borne solutes occurred in the fruits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385400
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  • 9
    Electronic Resource
    Electronic Resource
    Translocation from leaves to fruits of a legume, studied by a phloem bleeding technique: Diurnal changes and effects of continuous darkness (1976)
    Springer
    Planta 128 (1976), S. 63-72 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Diurnal changes in the carbohydrates of leaf laminae and fruits and in the bleeding of sugar and amino acids from fruit phloem were followed by successive sampling from a population of Lupinus albus L. plants. Phloem sap was collected for a standard 5 min period from cut distal tips of attached fruits. Daily fluctuations in leaf dry matter resulted largely from changes in starch and sugar. Leaf sugar rose to a maximum in the afternoon, starch to a maximum at, or shortly after, dusk. Leaves lost sugar and starch from dusk to dawn. Phloem bleeding rate varied little over a daily cycle but sucrose levels fluctuated from a noon maximum of 12–13% (w/v) to a dawn minimum of 9–10%. The rhythm of phloem sugar levels matched closely those of fruit and leaf. Phloem amino acid levels fluctuated in phase with that of sucrose: the relative composition of the amino fraction did not vary significantly over the daily cycle. Pulse feeding of source leaves with 14CO2 at different times in the photoperiod allowed study of the pattern of release of labelled photosynthate to the fruit phloem and the build up and depletion of 14C starch in leaves. Plants transferred to continuous darkness showed a rapid decline in output and concentration of phloem sap solutes, and translocated nitrogen to their fruits at only one quarter of the rate of control plants retained in natural daylight. The combined data from the experiments showed that the rate of output of sugar from cut phloem of a fruit was directly related to the current level of sugar in leaves. When leaf sugar levels were low (5–10 mg ml tissue water-1) sugar in phloem was 10–11 times more concentrated than in source leaves, but at high leaf sugar levels (25–30 mg ml-1) this concentration difference was only 3–4 fold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397180
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of NO3 on N2 fixation and nitrogenous solutes of xylem in two nodulated West African geocarpic legumes, Kersting's bean (Macrotyloma geocarpum L.) and Bambara groundnut (Vigna subterranea L.) (1992)
    Springer
    Plant and soil 140 (1992), S. 255-262 
    Details
    ISSN: 1573-5036
    Keywords: effect of combined N ; geocarpic legumes ; nitrogen fixation ; Rhizobium ; root nodule ; ureide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nodulation, nitrogen (N2) fixation and xylem sap composition were examined in sand cultured plants of Bambara groundnut (Vigna subterranea L.) and Kersting's bean (Macrotyloma geocarpum L.) inoculated with Bradyrhizobium strain CB756 and supplied via the roots for a 4 week period from the third week onwards with different levels of (15N)-nitrate (0–15 mM). The separate contributions of nitrate and N2 to plant nitrogen were measured by isotope dilution. Increasing levels of nitrate inhibited nodule growth (measured as dry matter or nodule N) of both species parallel with decreased dependence on symbiotically-fixed N. Specific nodule activity (N2 fixed g nodule dry−1 d−1 of nodules) was reduced progressively with time in V. subterranea at higher (5 or 15 mM) levels of NO3, but this was not so for M. geocarpum. Root xylem bleeding sap of both species showed ureides (allantoin and allantoic acid) as predominant (〉90%) solutes of nitrogen when plants were relying solely on atmospheric N. Levels of ureide and glutamine decreased and those of asparagine and nitrate in xylem increased with increasing level of applied nitrate. Relative levels of xylem ureide-N were positively correlated (R2=0.842 for M. geocarpum and 0.556 for V. subterranea), and the ratio of asparagine to glutamine in xylem exudate negatively correlated (R2=0.955 for M. geocarpum and 0.736 for V. subterranea) with plant reliance on nitrogen fixation. The data indicate that xylem sap analyses might be useful for indirect field assays of nitrogen fixation by the species and that Kersting's bean might offer some potential as a symbiosis in which N2 fixation is relatively tolerant of soil N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010602
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