Abstract
A nitrogen-fixing association can be readily established in vitro between Rhizobium and cultured soybean root cells. Plant cells are grown as a thin callus on the surface of solid defined medium containing low levels of inorganic nitrogen and inoculated with bacteria during the active phase of growth. Acetylene reduction activities up to 275 nmoles ethylene/hr.g dry weight of cells have been recorded.The system is compact, uses inexpensive glassware, and facilitates multiple replication of samples. The use of a single medium throughout the experiments avoids unnecessary disturbance to the cells. The development of nitrogenase activity is relatively rapid and its activity can be recorded within a 3-week period.