Abstract
Levels of endogenous ABA are changed dynamically in response to environmental conditions. We examined physiological roles of Arabidopsis CYP707As in the plant's response to the change in humidity. When wild-type plants were transferred to high humidity condition, CYP707A1 and CYP707A3 transcript levels increased, followed by reduction of ABA levels. cyp707a3 mutant exhibited high ABA levels even after transferring to high humidity conditions, whereas cyp707a1 mutant exhibited low ABA levels comparable to wild type. High humidity-induced expression of CYP707A1 and CYP707A3 occurred in guard cells and vascular tissues, respectively. Stomatal closure of cyp707a1 mutant, but not cyp707a3 mutant, was ABA-hypersensitive when epidermal peel was treated with exogenous ABA. These results implicate that CYP707A3 reduces the amount of mobile ABA in vascular tissues in response to high humidity, whereas CYP707A1 inactivates local ABA pools inside the guard cells.
