85 種子発芽過程における低温処理によるジベレリンの生合成の制御

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Seed germination is regulated by various environmental factors such as water, light and temperature. In Arabidopsis seeds, gibberellin (GA) plays an important role in promoting germination because its biosynthesis mutants are defective in germination. We have previously shown that light regulates expression of GA biosynthesis genes. Cold treatment is known to be effective to break seed dormancy in Arabidopsis, however the role of GA in this process has not been clarified. To examine the effect of cold treatment on GA biosynthesis, we determined mRNA levels of GA biosynthesis genes using DNA microarray and quantitative RT-PCR analysis. Among GA biosynthesis genes that we tested, AtGA3ox1 and AtGA20ox1-3 genes were up-regulated after cold treatment. In addition, the mRNA levels of some GA up-regulated genes were increased during cold treatment in wild-type seeds. The elevated expression of GA-upregulated genes by cold treatment was partially abolished in the GA biosynthesis mutant seeds. This indicated that the induction of GA-upregulated genes is at least partially due to an increase in the amount of bioactive GAs by cold treatment. Our previous work showed that the AtGA3ox1 mRNA after light treatment was localized in the cortex and endodermis of embryonic axis. Interestingly, in situ analysis demonstrated that AtGA3ox1 mRNA was detectable in additional cell types. The different localization patterns of AtGA3ox1 mRNA suggest that light and cold treatment result in different distributions of bioactive GAs in imbibed seeds. The regulation of GA 3-oxidase genes by environmental factors may be a key step for determining seed germination.
2002-10-31

85 種子発芽過程における低温処理によるジベレリンの生合成の制御

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