High temperature-induced abscisic acid biosynthesis and its role in the inhibition of gibberellin action in Arabidopsis seeds.

Abstract

Suppression of seed germination by environmental high temperature (thermoinhibition) during summer is crucial for Arabidopsis (Arabidopsis thaliana (L.) Heynh.) to establish vegetative growth in autumn. We have reported that high temperature enhances abscisic acid (ABA) level by up-regulation of ABA biosynthesis genes, and suppresses gibberellin (GA) action by down-regulation of its biosynthesis genes in conjunction with up-regulation of a GA negative regulator gene, SPINDLY (SPY). To observe the hormone interaction in thermoinhibition, we used ABA deficient mutant, aba2, and found that the expression of GA 3-oxydase genes are not suppressed and the expression of SPY gene is down-regulated even at high temperature. In addition, thermoinhibition resistant germination phenotype of aba2 seeds is suppressed by GA boisynthesis inhibitor, paclobutrazole. These results suggest that suppression of GA synthesis and signaling in thermoinhibited Arabidopsis seeds is mediated by ABA.