Studies on cytokinin production by Rhizobium.

Cytokinin was released into the medium by cultures of both Rhizobium japonicum and R. leguminosarum. Calculations show that the amount of cytokinin released during the logarithmic phase of growth by R. japonicum would be sufficient to initiate the cortical cell divisions necessary to form a root nodule. The substance released by R. japonicum was identified as a zeatin-like compound on the basis of paper chromatography in four solvent systems. Two solvents clearly separated the rhizobial product from N(6)-Delta(2)-isopentenyladenine and its ribonucleoside. The predominant intracellular cytokinin found in both enzymatic hydrolysates of sRNA and alkaline hydrolysates of total RNA also was similar to zeatin.