Abstract
Abscisic acid (ABA) is a plant hormone that regulates many aspects of plant growth and development, including tolerance to a variety of environmental stresses. Our recent works dealing with the Arabidopsis aao3 mutant have shown that AAO3, a member of the aldehyde oxidase family, has important roles for ABA accumulation in leaves after drought stress. Here, we report (1) a rapid ABA biosynthesis in response to drought stress takes place mainly in leaves, and the accumulated ABA in leaves is transported to roots, and (2) the expression of AAO3 protein is observed in the vascular systems and in the root tips. Moreover, immunohistochemical analysis reveals significant signals of immuno-fluorescence in the leaf guard cells. These results suggest the possibility for inter-organ and inter-cellular transport of ABA precursors and/or ABA to the target sites. A possible source of ABA for rapid stomatal closure in response to water stress is also discussed.
