Abscisic acid regulates hydrotropism through tissue-specific signaling in Arabidopsis roots

Roots respond to different environment signals and reorientate the direction of growth accordingly. It is known that under water stress, abscisic acid (ABA), a plant hormone required for stress tolerance, is synthesized to mediate the growth of roots relative to moisture. Due to the dominating effect of gravitational force, it is believed that the root respond to moisture by suppressing the gravitational response. Preliminary data had shown that the ABA biosynthesis enzyme, 9-cis-epoxydioxygenase (NCED) is expressed on the side of root cap that is exposed to dryness. This suggests that ABA is synthesized at the relative dry side of the root cap during water deficit. To investigate the site of action of ABA after its synthesis, ABA signaling in certain root tissue layers was inhibited by enhancer trap transgenic Arabidopsis lines that express ABA-insensitive 1-1 (abi1-1) mutant protein in certain root tissue layers. Using a simplified hydrotropism assay, ABA signaling in the lateral root cap, quiescent center and endodermis was found to play a significant role in suppressing root response to gravity. We concluded that accumulation of ABA in the relative dry side of the lateral root cap suppressed root response to gravity and thus enables bending of the roots away from dryness.Bachelor of Science in Biomedical Science