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1.
Effect of pO(2) during Growth on the Gaseous Diffusional Properties of Nodules of Cowpea (Vigna unguiculata L. Walp.)
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Adaptations of nodules of cowpea (Vigna unguiculata L. Walp. cv Vita 3: Bradyrhizobium CB 756) to growth in pO2 ranging from 1 to 80% O2 (volume/volume) involved both readily reversible mechanisms of adjustment and more stable alterations which together resulted in nodules with widely ranging resistance to diffusion of gases. Those grown in subambient pO2 (1-5% O2 were altered such that rapid diffusional adjustment was unable to prevent irreversible loss of nitrogenase on their transfer to higher levels of O2. Those cultured in 80% had adapted to over-supply of O2 such that their transfer to lower levels of O2 limited both nitrogenase and respiratory CO2 release. There was also some evidence for `protective respiration.' Measurement of diffusional properties based on gas exchange kinetics indicated that gaseous permeability values for nodules from 5 to 40% O2 were relatively constant around 20 × 10−3 millimeters per second, while those for nodules from 1% O2 were as high as 67.7 × 10−3 millimeter per second and from 80% as low as 6.8 × 10−3 millimeters per second. Estimates of the thickness of the diffusion barrier ranged from 7.5 micrometers for nodules from 1% O2 to 71.9 micrometers in those from 80% O2. 相似文献
2.
Nodules of cowpea plants (Vigna unguiculata (L.) Walp. cv. Vita 3 :Bradyrhizobium CB756) cultured for periods of 23 d with their root systems maintained in atmospheres containing a range of partial pressures
of O2 (pO2; 1–80%, v/v, in N2) formed and exported ureides (allantoin and allantoic acid) as the major products of fixation at all pO2 tested. In sub-ambient pO2 (1 and 2.5%) nodules contained specific activities of uricase (urate: O2 oxidoreductase; EC 1.7.3.3) and allantoinase (allantoin hydrolyase; EC 3.5.2.5) as much as sevenfold higher than in those
from air. On a cell basis, uninfected cells in nodules from 1% O2 contained around five times the level of uricase. Except for NAD: glutamate synthase (EC 1.4.1.14), which was reduced in
sub-ambient O2, the activities of other enzymes of ureide synthesis were relatively unaffected by pO2. Short-term effects of pO2 on assimilation of fixed nitrogen were measured in nodules of air-grown plants exposed to subambient pO2 (1, 2.5 or 5%, v/v in N2) and15N2. Despite a fall in total15N2 fixation, ureide synthesis and export was maintained at a high level except in 1% O2 where formation was halved. The data indicate that in addition to the structural and diffusional adaptations of cowpea nodules
which allow the balance between O2 supply and demand to be maintained over a wide range of pO2, nodules also show evidence of biochemical adaptations which maintain and enhance normal pathways for the assimilation of
fixed nitrogen.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian Development Assistance
Bureau postgraduate fellowship (to F.D.D.). 相似文献
3.
Nodules of cowpea (Vigna unguiculata (L.) Walp. cv. Vita 3:Bradyrhizobium CB 756) from 28-d-old plants cultured for 23 d with their root systems maintained in O2 levels from 1 to 80% (v/v, in N2) in the external gas phase showed a range of structural changes which have been interpreted in relation to an over- or under-supply
of O2. A response to the partial pressure of O2 in the gas phase (pO2) was noted with respect to nodule size, lenticel development, the relative distributions of cortical and infected central
tissue, the differentiation of cortex, especially the inner cortex, the frequency and size of infected and uninfected interstitial
cells, the volume of extracellular spaces both in cortex and infected tissue, and in the frequency of bacteroids. As a consequence
of these changes the surface area of inner cortex relative to the nitrogenase-containing units of fixing tissue (infected
cells or bacteroids) was increased by as much as 20-fold. Effectiveness of bacteroid functioning increased from 0.10 ± 0.02
· 10-9 μmol acetylene reduced per bacteroid in air-grown nodules to 0.9 ± 0.16 · 10-9 (same units) per bacteroid in those cultured in 1% O2.
This work was supported by a grant from the Australian Research Council (to C.A.A.) and an Australian International Development
Assistance Bureau postgraduate fellowship (to F.D.D.). The authors wish to thank Dr. W.F.C. Blumer for his considerable help
with morphometric analysis, Dr. J. Kuo for guidance in the use of histological techniques, and to Dr. J.S. Pate for the suggestion
that lenticel development might be quantified by surface staining of nodules. 相似文献
4.
Effects of elevated ultraviolet-B radiation on native and cultivated plants of southern Africa 总被引:1,自引:0,他引:1
Seventeen herb, shrub and tree species of commercial and ecological importance in southern Africa were exposed at one location to ultraviolet-B (UV-B, 280-315 nm) radiation approx. 35 % above clear-sky background (control). The aims were to assess how UV-B affects canopy area, dry mass, and some biochemical and morphological properties of leaves, and to investigate whether differences between species are related to growth form of the plants. There was no pattern of response to UV-B related to growth form. Leaves of trees had altered chlorophyll a and b, carotenoid and flavonoid concentrations, but those of shrubs or herbs did not. Non-structural carbohydrates were unaffected. Smaller canopy areas and dry masses were observed under enhanced UV-B, but these were not statistically different among growth forms. There was a general insensitivity of species to elevated UV-B. Only five species had significantly altered leaf biochemical and morphological properties, canopy area and dry mass, the changes differing in magnitude. There was no consistent pattern of change in leaf thickness or biochemical composition with increased UV-B. Correlation analyses did not support the view that growth is less negatively affected in species with thick leaves or in those where leaf thickness increases, or in species with naturally high leaf flavonoid contents or that are able to synthesize additional flavonoids in response to UV-B enhancement. The analyses did not support the hypothesis that growth was inhibited by starch accumulation in leaves under elevated UV-B. However, changes in leaf shape did correlate with canopy area and dry mass, showing the importance of photomorphogenetic changes caused by UV-B which affect species' performance. We conclude that generalizations on plant sensitivity to UV-B based on growth form and functional type could be misleading, and that the great majority of economically important species of the region are likely to be insensitive to future UV-B increases. Notable exceptions include the Colophospermum mopane tree ecotypes chota and leslie and the arable annual Vigna unguiculata, both of which are traditional sources of livelihood to rural African populations and of importance to African industry and agriculture. 相似文献
5.
Adaptation of Nodulated Soybean (Glycine max L. Merr.) to Growth in Rhizospheres Containing Nonambient pO(2)
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Nodulated soybean (Glycine max L. Merr. cv White Eye inoculated with Bradyrhizobium japonicum strain CB 1809) plants were cultured in the absence of combined N from 8 to 28 days with their root systems maintained continuously in 1, 2.5, 5, 10, 20, 40, 60, or 80% O2 (volume/volume) in N2. Plant dry matter yield was unaffected by partial pressure of oxygen (pO2) and N2 fixation showed a broad plateau of maximum activity from 2.5 to 40 or 60% O2. Slight inhibition of nitrogenase activity occurred at 1% O2 and as much as 50% inhibition occurred at 80% O2. Low pO2 (less than 10%) decreased nodule mass on plants, but this was compensated for by those nodules having higher specific nitrogenase activities. Synthesis and export of ureides in xylem was maintained at a high level (70-95% of total soluble N in exudate) over the range of pO2 used. Measurements of nitrogenase (EC 1.7.99.2) activity by acetylene reduction indicated that adaptation of nodules to low pO2 was largely due to changes in ventilation characteristics and involved increased permeability to gases in those grown in subambient pO2 and decreased permeability in those from plants cultured with their roots in pO2 greater than ambient. A range of structural alterations in nodules resulting from low pO2 were identified. These included increased frequency of lenticels, decreased nodule size, increased volume of cortex relative to the infected central tissue of the nodule, as well as changes in the size and frequency of extracellular voids in all tissues. In nodules grown in air, the inner cortex differentiated a layer of four or five cells which formed a band, 40 to 50 micrometers thick, lacking extracellular voids. This was reduced in nodules grown in low pO2 comprising one or two cell layers and being 10 to 20 micrometers thick in those from 1% O2. Long-term adaptation to different external pO2 involved changes which modify diffusive resistance and are additional to adjustments in the variable diffusion barrier. 相似文献
6.
* Root respiration, stomatal conductance, leaf transpiration and photosynthetic rates were measured in phytotron and field-grown plants following the application of 5 or 10 nM lumichrome, 10 nM ABA (abscisic acid) and 10 ml of 0.2 OD600 infective rhizobial cells. * Providing soybean and cowpea roots with their respective homologous rhizobia and/or purified lumichrome increased the concentration of this molecule in xylem sap and leaf extracts. Relative to control, rhizobial inoculation and lumichrome application significantly increased root respiration in maize, decreased it in lupin, but had no effect on the other test species. * Applying either lumichrome (10 nM), infective rhizobial cells or ABA to roots of plants for 44 h in growth chambers altered leaf stomatal conductance and transpiration in cowpea, lupin, soybean, Bambara groundnut and maize, but not in pea or sorghum. Where stomatal conductance was increased by lumichrome application or rhizobial inoculation, it resulted in increased leaf transpiration relative to control plants. Treating roots of field plants of cowpea with this metabolite up to 63 d after planting showed decreased stomatal conductance, which affected CO2 intake and reduction by Rubisco. * The effect of rhizobial inoculation closely mirrored that of lumichrome application to roots, indicating that rhizobial effects on these physiological activities were most likely due to lumichrome released into the rhizosphere. 相似文献
7.
Summary Provision of silicon (0, 0.048, 0.096, 0.24, 0.48, and 0.96 g/1) in the form of silicic acid (H4SiO4) to nodulated cowpea plants(Vignia unguiculata [L.] Walp.) grown in liquid culture resulted in considerable changes in the internal organization of nodule structure. Compared
to the control plants which received no added silicate, bacteroid numbers increased significantly (P ≤ 0.05) at silicate concentrations
of both 0.096 and 0.48 g/1. The number of symbiosomes also increased by 3.2-fold at the silicate concentration of 0.96 g/1
compared to the control. In contrast, the size of bacteroids and symbiosomes decreased significantly (P ≤ 0.05) inside nodules
of silicate-treated plants. The peribacteroid space was also decreased considerably (P ≤ 0.05) with the application of 0.096
and 0.96 g of silicate per liter to plants. However, the size of intercellular spaces adjacent to infected and uninfected
interstitial cells within the nodule medulla increased significantly (P ≤ 0.05) at 0.096 g of silicate per liter followed
by a sharply marked (P ≤ 0.05) decrease with each subsequent increase in silicate application. The result was a large decrease
(P≤0.05) in the area of bacteria-infected tissue occupied by intercellular space at the highest silicate concentration, which
was caused by a significant (P ≤ 0.05) increase in cell wall thickness. Our findings show that the positive effects of silicon
on N2 fixation might actually be due to an increased number of bacteroids and symbiosomes. 相似文献
8.
9.
In this study, the response of N2 fixation to elevated CO2 was measured in Scirpus olneyi, a C3 sedge, and Spartina patens, a C4 grass, using acetylene reduction assay and 15N2 gas feeding. Field plants grown in PVC tubes (25 cm long, 10 cm internal diameter) were used. Exposure to elevated CO2 significantly (P < 0·05) caused a 35% increase in nitrogenase activity and 73% increase in 15N incorporated by Scirpus olneyi. In Spartina patens, elevated CO2 (660 ± 1 μ mol mol − 1) increased nitrogenase activity and 15N incorporation by 13 and 23%, respectively. Estimates showed that the rate of N2 fixation in Scirpus olneyi under elevated CO2 was 611 ± 75 ng 15N fixed plant − 1 h − 1 compared with 367 ± 46 ng 15N fixed plant − 1 h − 1 in ambient CO2 plants. In Spartina patens, however, the rate of N2 fixation was 12·5 ± 1·1 versus 9·8 ± 1·3 ng 15N fixed plant − 1 h − 1 for elevated and ambient CO2, respectively. Heterotrophic non-symbiotic N2 fixation in plant-free marsh sediment also increased significantly (P < 0·05) with elevated CO2. The proportional increase in 15N2 fixation correlated with the relative stimulation of photosynthesis, in that N2 fixation was high in the C3 plant in which photosynthesis was also high, and lower in the C4 plant in which photosynthesis was relatively less stimulated by growth in elevated CO2. These results are consistent with the hypothesis that carbon fixation in C3 species, stimulated by rising CO2, is likely to provide additional carbon to endophytic and below-ground microbial processes. 相似文献
10.
Cynthia Gyogluu Sanjay K. Jaiswal Stephen Kyei-Boahen Felix D. Dakora 《Systematic and applied microbiology》2018,41(5):506-515
Indigenous soybean rhizobial strains were isolated from root nodules sampled from farmers’ fields in Mozambique to determine their identity, distribution and symbiotic relationships. Plant infection assays revealed variable nodulation and symbiotic effectiveness among the 43 bacterial isolates tested. Strains from Ruace generally promoted greater whole-plant growth than the others. 16S rRNA-RFLP analysis of genomic DNA extracted from the rhizobial isolates produced different banding patterns, a clear indication of high bacterial diversity. However, the multilocus sequence analysis (MLSA) data showed alignment of the isolates with B. elkanii species. The 16S rRNA sequences of representative soybean isolates selected from each 16S rRNA-RFLP cluster showed their relatedness to B. elkanii, as well as to other Bradyrhizobium species. But a concatenated phylogeny of two housekeeping genes (glnII and gyrB) identified the soybean nodulating isolates as Bradyrhizobium, with very close relatedness to B. elkanii. The nifH and nodC sequences also showed that the majority of the test soybean isolates were closely related to B. elkanii, albeit the inconsistency with some isolates. Taken together, these findings suggest that the B. elkanii group are the preferred dominant microsymbiont of soybean grown in Mozambican soils. Furthermore, the distribution of soybean rhizobia in the agricultural soils of Mozambique was found to be markedly influenced by soil pH, followed by the concentrations of plant-available P and Mn. This study suggested that the identified isolates TUTMJM5, TUTMIITA5A and TUTLBC2B can be used as inoculants for increased soybean production in Mozambique. 相似文献