THE INHIBITION OF BRASSINOSTEROID-INDUCED ETHYLENE BIOSYNTHESIS IN ETIOLATED MUNG BEAN HYPOCOTYL SEGMENTS BY 2,3,5-TRIIODOBENZOIC ACID AND 2-(P-CHLOROPHENOXY)-2-METHYLPROPIONIC ACID

The effect of two auxin antagonists, 2,3,5-triiodobenzoic acid (TIBA) and 2-(p-chlorophenoxy)-2-methyl propionic acid (CMPA) on brassinosteroid (BR)-induced ethylene biosynthesis in etiolated mung bean hypocotyl (Vigna radiata L. R wilcz cv. Berken) segments was studied. The maximum inhibition of both ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC) biosynthesis by TIBA and CMPA was achieved at concentrations of 50-mu-M and 10-mu-M, respectively. With increasing concentrations of BR, there were significant increases in both ethylene and ACC production. When varying concentrations of BR were used in combination with 50/mu-M TIBA or 10-mu-M CMPA, there was a decrease in ethylene and ACC production at all BR concentrations tested, with the exception of the lowest. After 18 h, mung bean hypocotyl segments pre-incubated for 8 h with either 50-mu-M TIBA or 10-mu-M CMPA showed a maximum inhibition of BR-induced ethylene and ACC production. The results of treatment sequences showed that both TIBA and CMPA caused the same inhibitory effect whether applied before or after BR-treatment.