Biological Activity of Brassinosteroid Inhibitor KM-01 Produced by a Fungus Drechslera avenae.

The biological activity of KM-01, a fungal metabolite isolated from Drechslera avenae, was tested with various bioassays of known plant hormones, It inhibited the action of brassinosteroid dose dependently, whereas no activity was observed with auxin and cytokinin bioassays, Although a synergistic effect with GA(3) at low concentrations and an inhibitory effect on ABA were observed, we conclude that KM-01 is the first selective brassinosteroid inhibitor found in natural sources.