Activity of brassinosteroids in the dwarf rice lamina inclination bioassay

Biological activities of brassinolide, its biosynthetic intermediates and some biosynthetically related brassinosteroids were evaluated using modified dwarf rice lamina inclination bioassay. A very strong synergistic effect was observed when IAA was applied together with brassinosteroid. In particular co-application of brassinosteroid and 5 mu g IAA was ca. 300 times more active than a single application of brassinosteroid. Under co-application of 5 mu g IAA, the minimum detectable amount of brassinolide was less than 0.01 ng/rice plant. Biological activity increased according to the order of the biosynthetic pathway. Brassinosteroids in the early C-6 oxidation pathway (6-oxobrassinosteroids) were more active than corresponding brassinosteroids in the late C-6 oxidation pathway (6-deoxobrassinosteroids). Even very early biosynthetic intermediates such as campestanol showed some activity in our modified bioassay. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.