Abstract
Like other winter annual species, germination of Arabidopsis seed is inhibited by high temperature (thermoinhibition). We have found that de novo ABA biosynthesis during imbibition is responsible for thermoinhibition of Arabidopsis seeds. We also found that three 9-cis-epoxycarotenoid dioxygenase genes, NCED2, NCED5 and NCED9, were up-regulated by supraoptimal temperatures. To reveal contribution of each NCED gene on thermoinhibition, we selected and produced their T-DNA insertion mutants. The seeds of nced9 mutant showed considerable tolerance to thermoinhibition, but those of nced2 and nced5 showed no apparent phenotypes. The seeds of nced5nced9 double mutant showed higher thermoinhibition tolerance than nced9, but nced2nced9 and nced2nced5 double mutants showed similar germination to nced9 and their parents, respectively. The seeds of nced2nced5nced9 triple mutant showed similar tolerance to nced5nced9. These results suggest that NCED9 and NCED5 genes are unequally redundant and their up-regulation by high temperature is critical for thermoinhibition of Arabidopsis seeds.
