Role of Abscisic Acid in the Regulation of Root and Shoot Growth at Low Water Potentials

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Root growth is frequently less inhibited than shoot growth in water stressed plants. Despite the importance of this response to plant performance under drought, the physiological mechanisms regulating the differential growth sensitivities are not known and little studied. This proposal will examine in detail the role of the plant hormone abscisic acid (ABA) in the growth responses of maize to water stress. Preliminary results suggest that naturally-occurring ABA maintains root growth while inhibiting shoot growth of water stressed maize seedlings. Additionally, the PI has shown that large differences in the growth response to water stress exist among closely related tissues within the growing zone of the root and shoot. In the proposed work, internal levels of ABA will be manipulated in the growing zones of roots and shoots using a mutant deficient in ABA synthesis as well an inhibitor of ABA synthesis. High resolution techniques will be used to determine growth rate, ABA levels and molecular indicators of tissue response to ABA in one-millimeter sections of the growing zones. Results will greatly assist in determining the biochemical and biophysical processes regulated by the hormone and will set the stage for breeding strategies to improve maize performance drought-prone environments.