In vitro nitrogenase activity of Rhizobium japonicum affected by conditioned medium from cultured plant cells

Abstract

Soybean root cells grown in liquid suspension culture in a transfilter apparatus with Rhizobium japonicum elaborated materials which initiated the in vitro activity of rhizobial nitrogenase. This material, termed nitrogenase initiating factor(s) (NF), in the plant conditioned medium (PCM) was partially purified by gel filtration chromatography. The resulting gel-filtered column fractions showed differential effects on the nitrogenase activity of two Rhizobium japonicum strains 31-1b-138 and 61A76, and the cowpea Rhizobium strain 32H1. Strains 61A76 and 32H1 could reduce acetylene without NF added to the incubation media. Strain 31-1b-138 could not reduce acetylene without the addition of NF. Moreover, this effect of NF on strain 31-1b-138 nitrogenase activity could not be mimicked by the single additions of either different carbon and nitrogen sources or vitamins or hormones to the incubation media.