Cytokinin Production by Rhizobium japonicum

Possible hormonal interactions between soybean roots and the Rhizobium initiating nodule proliferation in this genus were studied. A cytokinin has been isolated by column and paper chromatography from an effective strain of Rhizobium japonicum grown in pure culture. The substance promotes cell proliferation in a cytokinin-requiring soybean callus tissue. The bacteria are capable of conditioning a cylokinin-free soybean culture medium so that it is able to support the cytokinin-requiring tissue. It is concluded that the substance is a product of the bacteria rather than an artifact of purification. This unidentified cytokinin or a substance moving to a similar Rf value on the paper chromalogram produces polyploid divisions when tested on cultured pea root segments. Some of the division figures exhibit the diploclirornosomes typical of the root nodule primordium in pea.