Abstract
Plant regulates transpiration by controlling the stomatal conductance. In addition to such rapid responses, stomatal development is also regulated by environmental factors. The phytohormone abscisic acid (ABA) is known to regulate stomatal closure in response to the changing water status. We previously reported that the density of stomata was increased in both ABA-insensitive abi1-1 and ABA-deficient aba2-2 mutants and suggested that ABA regulates stomatal differentiation. In the present study, we investigated the effect of exogenous ABA application on the defect in stomatal development of the aba2-2 mutant. The suppressed stomatal density of aba2-2 was restored by ABA application. This is possibly due to both enlargement of the pavement cell size and decreased formation of stomatal meristemoids. Moreover, we found the up-regulation of the genes for stomatal development in the aba2-2 and abi1-1 mutants. Taken together, we conclude that ABA regulates developmental programs of stomatal formation.
