COMPARATIVE ROOT-GROWTH INHIBITORY ACTIVITY OF 4 BRASSINOSTEROIDS

The effects of four brassinosteroids (brassinolide, 24-epibrassinolide , 22, 23, 24-trisepibrassinolide and 28-homobrassinolide) which differ in side chain structure were examined on the growth of excised tomato roots in aseptic culture at concentrations from 10(-6) to 10(-15) M a nd also at 10(-20) M. NO growth alterations were observed at 10(-11) M or less, but all compounds caused some inhibition at one or more of t he higher concentrations. Inhibitory activity occurred in the order br assinolide > 24-epibrassinolide > 22, 23, 24-trisepibrassinolide > 28- homobrassinolide. Brassinolide first inhibited at 10(-10) M; 28-homobr assinolide at 10(-6) M. The structural features associated with this d ifferential activity are discussed.