Hydrogen Reactions of Nodulated Leguminous Plants: I. Effect of Rhizobial Strain and Plant Age 1

AUTOR(ES)

Schubert, Karel R.

RESUMO

The ATP-dependent evolution of H2 catalyzed by nitrogenase and the hydrogenase-catalyzed oxidation of H2 have been implicated as factors influencing the efficiency of energy utilization in the N2 fixation process. The effects of rhizobial strain and plant age on the H2-evolving and H2-utilizing activity of leguminous root nodules are described in this manuscript. Two classes of legume-Rhizobium combinations were observed in studies with soybeans (Glycine max L. Merr.) and cowpeas (Vigna unguiculata L. Walp.). One group evolved H2 in air; the other group did not exhibit net evolution of H2. The latter group metabolized H2 formed within the nodule through the action of a hydrogenase. The capacity to oxidize H2 was strongly linked to the strain of Rhizobium used to inoculate cowpeas and soybeans. Although the magnitude of H2 evolution in air changed during vegetative growth of a given symbiont, the ratio of H2 evolved in air to total nitrogenase activity was not appreciably altered during this period. No consistent difference in nitrogenase activity as measured by the C2H2 reduction assay was observed between symbionts with an active hydrogenase and those that apparently lack the enzyme and evolve H2. The effects of the two reactions of H2 on total N2 fixation and yield must now be established.

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