Role of Plant Cell Conditioned Medium in the Phenotypic Expression of Nitrogenase Activity of Rhizobium trifolii Strain T1

Abstract

The influence of substances from a conditioned medium of cultured plant cells on nitrogenase activity, respiration and ATP synthesis was investigated in R. tri/olii strain Tl. Nitrogenase activity in strain Tl was dependent on the addition of the plant cell conditioned medium. Studies showed that the initial effects of the plant substances on rhizobial cells was to increase their respiration rate and ATP production. Mutants of strain Tl which were uncoupled in their oxidative phosphorylation, were also tested. However, the plant factors had no effect on respiration and ATP synthesis and also failed to elicit in vitro nitrogenase activity in these mutants. It is proposed that these plant factors act by increasing the efficiency of oxidative phosphorylation, making more ATP available, and thus stimulating nitrogenase activity of R. tri/olii cells.