Gibberellic acid of Arabidopsis regulates the abscisic acid-induced inhibition of stomatal opening in response to light

Gibberellic acid (GA3) has often known to affect stomatal movement; however, the physiological role of GA3 in stomatal guard cells has not been defined. In this study, we show that abscisic acid (ABA) is regulated by gibberellic acid via a mechanism opposing that of the ABA-induced inhibition of stomatal opening in response to light in Arabidopsis leaves. GA3 modulated ABA-induced stomatal closing in response to light in a dose-dependent manner. We found that there did no affect on stomatal opening in response to light in the presence of the gibberellin (GA) biosynthesis inhibitor prohexadione-calcium (BX-112). However, the effects of GA3 on the ABA-induced inhibition of stomatal opening in response to light were blocked by BX-112. In RT-PCR studies, the expression of the RD22 gene was decreased by the addition of GA3. The expression of the GA-inducible genes, GASA4 and AtExp1, was reduced by ABA treatment. Our results strongly suggest that GA3 regulates the ABA-induced inhibition of stomatal opening in response to light.