Ethylene Inhibits Abscisic Acid-Induced Stomatal Closure in Arabidopsis

To examine the cross talk between the abscisic acid (ABA) and ethylene signal transduction pathways, signaling events during ABA-induced stomatal closure were examined in Arabidopsis (Arabidopsis thaliana) wild-type plants, in an ethylene-overproducing mutant (eto1-1), and in two ethylene-insensitive mutants (etr1-1 and ein3-1). Using isolated epidermal peels, stomata of wild-type plants were found to close within a few minutes in response to ABA, whereas stomata of the eto1-1 mutant showed a similar but less sensitive ABA response. In addition, ABA-induced stomatal closure could be inhibited by application of ethylene or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). In contrast, stomata of the etr1-1 and ein3-1 mutants were able to close in response to concomitant ABA and ACC application, although to a lesser extent than in wild-type plants. Moreover, expression of the ABA-induced gene RAB18 was reduced following ACC application. These results indicate that ethylene delays stomatal closure by inhibiting the ABA signaling pathway. The same inhibitive effects of ethylene on stomatal closure were observed in ABA-irrigated plants and the plants in drought condition. Furthermore, upon drought stress, the rate of transpiration was greater in eto1-1 and wild-type plants exposed to ethylene than in untreated wild-type control plants, indicating that the inhibitive effects of ethylene on ABA-induced stomatal closure were also observed in planta.