THE OCCURRENCE IN PLANTS OF THE GROWTH-INHIBITORS, THE RAPHANUSANINS

The growth inhibitors, cis- and trans-raphanusanins are widespread in the genus Raphanus. However, no raphanusanins were detected in the other plant species tested. Effects of raphanusanins on the action of plant hormones, indole-3-acetic acid (IAA), gibberellic acid (GA3) and benzyladenine (BA) were also studied using various bioassays. Raphanusanins significantly inhibited IAA activity in the Avena curvature test but h ad no effect in the Avena section test. BA activity was strongly inhibited by raphanusanins in both the radish cotyledon and the Amaranthus betacyanin bioassays. In contrast, GA activity was not influenced in the range of concentrations of raphanusanins tested either in the leaf-sheath bioassay of dwarf rice endosperm bioassay. The present results suggest that raphanusanins cause growth inhibition through suppressing the action of auxin and/or cytokinin.