Abstract
Seed germination is controlled by multiple environmental and endogenous factors. We have previously shown that red-light upregulates the gibberellin (GA) biosynthesis gene AtGA3ox1 and AtGA3ox2, and downregulates GA deactivation gene AtGA2ox2. In situ RNA analysis showed that mRNA of these genes are mainly detected in the cortex of embryonic axis. This suggests that the cortex may function as the major cell type that regulates endogenous GA levels. Recently, we have identified new 2-oxidases, AtGA2ox9-10, both of which catalyze the conversion of GA12, an intermediate of bioactive GAs, into GA110, an inactive GA. We found that AtGA2ox9 and AtGA2ox2 were both downregulated, while AtGA3ox1 was upregulated, during cold treatment after imbibition. These results indicate that multiple GA-metabolic steps regulate endogenous levels of bioactive GAs, which in turn control seed germination, in response to environmental signals.
