Abstract
Suppression of seed germination by high temperature (thermoinhibition) during summer is crucial for winter annuals to establish vegetative growth in autumn. Abscisic acid (ABA) has been shown to have a decisive role in thermoinhibition of lettuce and many winter annual seeds including Arabidopsis. Germination of red-light pulse irradiated Arabidopsis seeds were almost completely inhibited at 30oC in the dark. In contrast to continuous light condition, the seeds of ABA deficient aba2-2 showed little thermoinhibition tolerance in the dark after the red-light treatment. The seeds of knockout mutant of PIL5, a light-labile germination suppressor, were thermoinhibition sensitive under the continuous light but were thermoinhibition tolerant in the dark after the red-light pulse. Preliminary results indicate high temperature represses the decrease of PIL5 protein induced by red-light. These results suggest that PIL5 works as a main suppressor of GA action in thermoinhibition of Arabidopsis seeds in the dark after the red-light pulse.