PISUM-SATIVUM CULTIVAR EFFECTS ON HYDROGEN METABOLISM IN RHIZOBIUM

Data from 14 P. sativum L. cultivars establish that 3 pea genotypes, which were previously reported to affect net H2 evolution from root nodules in air and uptake hydrogenase activity of R. leguminosarum 128C53, are not unique. Two pea lines, ''JI1205'' and ''Green Arrow'', produced very active uptake hydrogenase activity in strain 128C53, and essentially no H2 was evolved in air from root nodules capable of reducing 20 .mu.mol C2H2 .cntdot. plant-1 .cntdot. h-1. Five other cultivars produced significantly lower uptake hydrogenase activities in the same bacterial strain and had much higher rates of net H2 evolution with similar C2H2-reduction capabilities. Parallel experiments with the same cultivars nodulated by R. leguminosarum 300, an organism with no convincing uptake hydrogenase activity in any pea line, showed that ''JI1205'' and ''Green Arrow'' had a significantly lower relative efficiency (RE) of N2 fixation (I-(H2 evolved in air/C2H2 reduced)) than the other 5 cultivars. Developmental differences among the pea lines prevented any conclusion about the advantages or disadvantages of uptake hydrogenase activity for plant growth, but in general, cultivars with high uptake hydrogenase activity and low net H2 evolution grew more slowly than those evolving large amounts of H2.