Abstract
When suspension cultures of actively growing soybean (Glycine max L.) root cells were separated by two or three membrane filters from suspension cultures of the bacteria, a synergetic (cooperative) activation of nitrogenase was observed in the Rhizobium japonicum used in the bacterial side. Either plant cells or plant cell-conditioned medium was needed for this activation to take place. Both acetylene reduction and hydrogen evolution by the activated R. japonicum persisted for several days after removal from the apparatus when (a) a suitable carbon source was provided, (b) oxygen supply was limited, and (c) growth of bacteria was suppressed by lowering of ammonia and nitrate concentrations. Activation could also take place when the bacteria were placed in media to which plant cell-conditioned medium was added. The advantages of this method for studies on symbiosis are discussed.