BIOLOGICAL-ACTIVITIES OF AN ABSCISIC-ACID ANALOG IN BARLEY, CRESS, AND RICE

Biological activities of an abscisic acid (ABA) analog, RCA-7a [1-(3-c arboxyl-5-methylphenyl)-1-hydroxy-2,6,6- trimethyl-4-oxo-2-cyclohexene ], carrying a phenyl group in the side chain are reported. (+)-RCA-7a was approximately 3-fold less active than (+)-ABA in the inhibition of alpha-amylase induction by gibberellic acid (GA(3)) in embryo-less ba rley grains. In aleurone layers, RCA-7a inhibited GA(3)-induced alpha- amylase mRNA accumulation and induced the accumulation of dehydrin mRN A, but less effectively than ABA. It also activated a dehydrin gene pr omoter in barley aleurone protoplast transient assays. A higher concen tration of RCA-7a than ABA was required for similar levels of inhibiti on of the growth of cress plants at 1 week after sowing; however, RCA- 7a remained effective for at least 3 weeks. In contrast, ABA rapidly l ost its effectiveness and became less effective than RCA-7a by 3 weeks . RCA-7a also significantly retarded the growth of rice plants. These greenhouse pot experiments showed that RCA-7a had more useful characte ristics than ABA for practical applications. These and our previous re sults indicate that RCA-7a has an ABA-like activity in various biologi cal processes in plants and has potential as a novel plant growth regu lator.