title: Abscisic acid regulation of heterophylly in Marsilea quadrifolia L.: effects of R-(-) and S-(+) isomers.
abstract: The plant hormone abscisic acid (ABA) induces a developmental switch in the aquatic fern Marsilea quadrifolia, causing the formation of aerial type characteristics, including the elongation of petioles and roots, a change in leaf morphology, the expansion of leaf surface area, and the shortening of the internodes. A number of ABA-responsive heterophylly (ABRH) genes are induced early during the transition. Using optically pure isomers of ABA, it was found that both the natural S-(+)-ABA and the unnatural R-(-)-ABA are capable of inducing a heterophyllous switch and regulating ABRH gene expression. When dose responses are compared, the unnatural ABA gives stronger morphogenic effects than the natural ABA at the same concentration, it is effective at lower concentrations, and its optimal concentration is also lower compared with the natural ABA. Deuterium-labelled ABA enantiomers were used to trace the fate of applied ABA and to distinguish the applied compound and its metabolites from the endogenous counterparts. In tissues, the supplied (+)-ABA was metabolized principally to dihydrophaseic acid, while the supplied (-)-ABA was converted at a slower rate to 7'-hydroxy abscisic acid. Treatment with either enantiomer resulted in increased biosynthesis of ABA, as reflected in the accumulation of endogenous dihydrophaseic acid. Taken together, these results suggest two distinct mechanisms of action for (-)-ABA: either (-)-ABA is intrinsically active, or its activity is due to the stimulation of ABA biosynthesis.
authors.affiliation: Molecular and Cell Biology Division, Development Center for Biotechnology, 101 Lane 169 Konning Street, Hsichih 22143, Taiwan.
authors.forename: Bai-Ling
authors.initials: BL
authors.lastname: Lin
authors.forename: Huei-Jen
authors.initials: HJ
authors.lastname: Wang
authors.forename: Jang-Shiun
authors.initials: JS
authors.lastname: Wang
authors.forename: L Irina
authors.initials: LI
authors.lastname: Zaharia
authors.forename: Suzanne R
authors.initials: SR
authors.lastname: Abrams
mesh_terms: D000040:Abscisic Acid / Q000737:chemistry* / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D007536:Isomerism; D043964:Marsileaceae / Q000737:chemistry / Q000187:drug effects* / Q000254:growth & development*; D015394:Molecular Structure; D010937:Plant Growth Regulators / Q000737:chemistry* / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D015398:Signal Transduction
chemical_list: D010937:Plant Growth Regulators; D000040:Abscisic Acid