Contribution of gibberellin deactivation by AtGA2ox2 to the suppression of germination of dark-imbibed Arabidopsis thaliana seeds

Gibberellin levels in imbibed Arabidopsis thaliana seeds are regulated by light via phytochrome, presumably through regulation of gibberellin biosynthesis genes, AtGA3ox1 and AtGA3ox2, and a deactivation gene, AtGA2ox2. Here, we show that a loss-of-function ga2ox2 mutation causes an increase in GA4 levels and partly suppresses the germination inability during dark imbibition after inactivation of phytochrome. Experiments using 2,2-dimethylGA4, a GA4 analog resistant to gibberellin 2-oxidase, in combination with ga2ox2 mutant seeds suggest that the efficiency of deactivation of exogenous GA4 by AtGA2ox2 is dependent on light conditions, which partly explains phytochrome-mediated changes in gibberellin effectiveness (sensitivity) found in previous studies.