A Transmissible Plant Shoot Factor Promotes Uptake Hydrogenase Activity in Rhizobium Symbionts

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Abstract
Shoot/root grafting studies showed organ and host cultivar effects on net H2 evolution from Pisum sativum L. root nodules. Net H2 evolution from those nodules represents the sum of H2 formed by Rhizobium nitrogenase and H2 oxidized by any uptake hydrogenase present in the bacteria. Grafts between pea cultivars `JI1205' or `Alaska' and `Feltham First' in symbioses with R. leguminosarum 128C53 showed that shoots of both JI1205 and Alaska increased H2 uptake significantly (P ≤ 0.05) in Feltham First root nodules. The same plants also had less net H2 evolution at similar rates of C2H2 reduction than plants formed by grafting Feltham First shoots on Feltham First roots. Although JI1205 and Alaska shoots increased H2-uptake activity of Feltham First root nodules 28 days after the graft was made, intermediate to high levels of H2 uptake activity were still present in nodules on roots of both JI1205 and Alaska grafted to Feltham First shoots. These results indicate the presence of a transmissible shoot factor(s) which can increase uptake hydrogenase activity in a Rhizobium symbiont and show that root genotype also can influence that parameter.