Hydrogen Reactions of Nodulated Leguminous Plants

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During the period examined from 12 to 63 days after planting, the ureides, allantoin and allantoic acid, were fixation (C2H2) from day 18 reaching a maximum value of 13.9 micromoles per plant per hour at day 49, and then both activities declined rapidly. During the period of active nitrogen fixation the ratio of PRPP synthesis estimated from measurements of PRPP synthetase activity in cell-free extracts to the apparent rate of ureide export was between 1 and 2. The activities of the enzymes of purne catabolism, xanthine dehydrogenase, uricase, and allantoinase, increased in parallel with the increases in nodule mass and the export of ureides with maximum activities of 13, 119, and 79 micromoles per plant per hour, corresponding with apparent rates of ureide export in the range of 9.5 to 11.9 micromoles per plant per hour. These results demonstrate that there is a ciose association between nitrogen fixation, PRPP synthetase activity, and ureide export in soybeans and support the proposal that recently-fixed nitrogen is utilzed in the de novo synthesis of purnes which are subsequently catabolized to produce the ureides.Based on in vitro measurements of the ATP requirement for the nitrogenase-catalyzed reduction of dinitrogen and whole plant studies of the effects of altering photosynthesis on the rates of N2 fixation in legumes, a number of researchers have suggested that the availability of photosynthetically reduced carbon is the major factor limiting symbiotic nitrogen fixation (9). An estimated 15 to 30%o of the net photosynthate of a plant may be required to

Section: Resultsmentioning

confidence: 99%

Enzymes of Purine Biosynthesis and Catabolism in Glycine max

Schubert¹

1981

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“…Using 3H2 incorporation as an assay for uptake hydrogenase, they suggested that changes in RE ofthat host-strain combination resulted from variations in both uptake hydrogenase activity and EAC (4). In other studies of a symbiosis between the Hup+ Rhizobium strain 176A28 and Vigna unguiculata (L.) Walp., where essentially no H2 was measured outside the nodule, plant age had no effect on RE (18).…”

mentioning

confidence: 99%

Effect of the Host Legume on Acetylene Reduction and Hydrogen Evolution by Rhizobium Nitrogenase

Edie

Phillips²

1983

The relative efficlency (RE) of N2 fxation (RE - uptake hydrogenase activity (Hup-phenotype), RE presumably is a measure of apparent EAC.The potential agronomic advantages postulated for Rhizobium phenotypes with uptake hydrogenase activity (19) led to studies of various factors that influence RE. Bethlenfalvay and Phillips (2,3) showed that RE was altered by plant age and irradiance in Pisum sativum L. cv 'Alaska' with the Hup+ R leguminosarum strain 128C53. Using 3H2 incorporation as an assay for uptake hydrogenase, they suggested that changes in RE ofthat host-strain combination resulted from variations in both uptake hydrogenase activity and EAC (4). In other studies of a symbiosis between the Hup+ Rhizobium strain 176A28 and Vigna unguiculata (L.) Walp., where essentially no H2 was measured outside the nodule, plant age had no effect on RE (18).Results with purified nitrogenase showed that the availability of MgATP and other factors influenced EAC (6,7,11). If such changes occur in vivo, they could have physiological significance. The present study was conducted to determine whether the RE, and thus presumably the apparent EAC, changed in the Hup-R leguminosarum strain 3740 (5) on Alaska peas during an extension of the normal dark period. The hypothesis underlying this experiment was that an extended dark treatment could affect carbohydrate supply within the root nodule and possibly alter energy available to the bacterial nitrogenase complex. MATERIALS AND METHODSBiological Materials. Alaska peas (Pisum sativum L.) were grown aseptically in vermiculite with N-free nutrient solution as described by DeJong and Phillips (8), except for the following modifications. Leonard jars were constructed from 1.5-liter wine bottles, and two plants were maintained in each jar. The normal conditions in environmental cabinets were a 16/8 h light/dark, 19/14°C day/night with a 550 ,uE m-2 s-1 (400-700 nm) photosynthetic photon flux density measured 25 cm above the jar surface with the LI-185B quantum sensor (Licor, Inc.). 'Woogenellup' subclover (Trifolium subterraneum L.) was grown under identical conditions with nine seeds in each Leonard jar. When the normal dark period was extended, the customary night temperature was maintained. Upon reillumination, the normal day temperature was established under various irradiance levels. Peas were inoculated with Rhizobium leguminosarum strain 3740; subclover was inoculated with R trifolii strain 162X99 (supplied originally by J. Burton, The Nitragin Co., Milwaukee, WI). Both strains 3740 and 162X99 show a Hup-phenotype in the 3H2 incorporation assay (5; S. S. Jue and D. A. Phillips, unpublished data). Bacterial stocks were maintained on agar, using TY medium (1) and LMB medium (14) for strains 3740 and 162X99, respectively.Physiological Analyses. Detached root systems were analyzed for HE, AR, and H2 evolution in 80% argon, 20% 02. Assays were conducted in 135 ml bottles sealed with rubber septa. Ethylene and H2 were quantified by GC using flame ionization and therm-

“…However, symbiotic characteristics with these nonhomologous hosts have been investigated in detail with only few strains of A japonicum. Strain-dependent hydrogen evolution and hydrogenase activity by R. japonicum in symbiosis with soybean has been reported (18,19), but these characters have not been studied with other legumes as hosts. Our objectives were to investigate the legume host-A japonicum strain interactions for nodulation, effectiveness, acetylene reduction, hydrogen evolution, and hydrogenase activity in soybean, cowpea, and siratro.…”

Section: Introductionmentioning

confidence: 99%

A Comparative Study of the Physiology of Symbioses Formed by Rhizobium japonicum with Glycine max, Vigna unguiculata, and Macroptilium atropurpurem

Keyser¹,

Berkum²,

Weber³

1982

Although Rhizobisum japoniewn nodulates Viga --g icula an Macroptium arpwpwem , little is known about the physiology of these symbioses. In this study, strains of R. japonicum of varying effectiveness on soybean were examined. The nonhomologous hosts were nodulated by all the strains tested, but effectiveness was not related to that of the homologous host. On siratro, compared to soybean, many strains reversed their relative effectiveness ranking. Both siratro and cowpea produced more dry matter with standard cowpea rhizobia CB756 and 176A22 than with the strains of R. japonum. Strains USDA33 and USDA74 were more effective with siratro and cowpea than with soybean. The strain USDA122 expressed high rates of hydrogenase activity in symbiosis with the cowpea as well as the soybean host. The strains USDA61 and USDA74 expressed low levels of hydrogenase activty in symbiosis with cowpea, but no activity was found with soybean. Our results indicate host influence for the expression of hydrogenase activity, and suggest the possibility of host influence of nitrogenase for the allocation of electrons to N2 and H+.Rhizobium japonicum forms a N2-fixing symbiosis with Glycine max L. Merr. (soybean), but these bacteria also nodulate Vigna unguiculata (cowpea) and Macroptilium atropurpurem (siratro) (12,20,22). However, symbiotic characteristics with these nonhomologous hosts have been investigated in detail with only few strains of A japonicum. Strain-dependent hydrogen evolution and hydrogenase activity by R. japonicum in symbiosis with soybean has been reported (18,19), but these characters have not been studied with other legumes as hosts. Our objectives were to investigate the legume host-A japonicum strain interactions for nodulation, effectiveness, acetylene reduction, hydrogen evolution, and hydrogenase activity in soybean, cowpea, and siratro. MATERIALS AND METHODSPlant Material. Seed of soybean (Glycine max L. Merr.) cv 'Bragg', 'Clark', 'Hood', 'Kent', 'Lee', and 'Roanoke'; cowpea (Vigna unguiculata) cv 'Cardinal', 'Black Eye-5', 'Pinkeye Purple Hull', 'Queen Anne', and 'Suneto'; and siratro (Macroptilium atropurpurem) were surface sterilized with acidified 0.1% (w/v) HgC12 (24) for 3 min and washed 10 times with sterile distilled H20. Surface sterile seed was sown in sand or vermiculite moistened with 100 ml of a N-free nutrient solution (14) in modified Leonard jars (12) sterilized with steam for 4 h. Each jar was inoculated with approximately 109 cells of Rhizobium, which had been grown in yeast-mannitol-salts broth (24) for 7 d. The strains of R japonicum used were obtained from the USDA Rhizobium Collection at Beltsville. These strains were originally isolated from soybean root nodules and have been described (1 1). These strains were chosen for their wide range in effectiveness on soybean. Strains of Rhizobium 'cowpea miscellany' CB756 and 176A22 were used as controls with siratro and cowpea. Soybean and cowpea (four per jar) and siratro (six per jar) were grown in a greenhouse without artificial ligh...