Abstract
Temperature is one of the critical environmental factors for seed germination. Like other winter annual species, germination of A. thaliana seeds is inhibited in high temperature conditions (thermoinhibition). We have found that thermoinhibition of Arabidopsis seeds required de novo synthesis of abscisic acid (ABA) during imbibition. Quantitative PCR analyses showed that three 9-cis-epoxycarotenoid dioxygenase genes, NCED2, NCED5 and NCED9, were up-regulated by supraoptimal temperatures. To reveal contribution of NCED genes on thermoinhibition, we analyzed seed germination of each NCED gene knockout (T-DNA insertion) lines. The seeds of NCED9 knockout line showed high germination percentage (ca.70%) at 32oC, while almost no germination was observed with the seeds of wild type (Col) and NCED2 knockout line. In wild type seeds, NCED9 gene transcript was most abundant among the three NCED genes when imbibed at 34oC. These results suggest NCED9 gene plays a primary role on ABA accumulation and thermionhibition in Arabidopsis.
