title: Characterization of an Arabidopsis thaliana mutant that has a defect in ABA accumulation: ABA-dependent and ABA-independent accumulation of free amino acids during dehydration.
abstract: In an attempt to elucidate the physiological role of ABA in seed dormancy and the adaptive response to dehydration, we isolated an ABA-deficient mutant of Arabidopsis thaliana (L.) Heynh. which germinated in the presence of a gibberellin biosynthetic inhibitor. Genetic analysis showed this mutation is a new allele of a recently reported locus aba2, and therefore has been designated aba2-2. The levels of endogenous ABA in fresh and dehydrated tissues of the aba2-2 mutant were highly reduced compared to those of wild-type plants. As a consequence, aba2-2 plants wilt and produce seeds with reduced dormancy. Dark germinated seedlings of the aba2-2 mutant showed true leaves, which were not observed in those of the wild type, indicating that aba2-2 embryos grew precociously during seed maturation. In the dehydrated tissues of the wild-type plants, the levels of free proline, isoleucine and leucine were elevated to a content approximately 100-fold higher than those in fresh tissues. In contrast to the wild-type plants, dehydration-induced accumulation of proline was highly suppressed in the aba2-2 mutant plants while that of leucine and isoleucine accumulated. Furthermore, exogenous application of ABA to wild-type plants promoted accumulation of free proline, but not leucine nor isoleucine. These results suggest that dehydration-induced accumulation of free leucine and isoleucine is achieved independent of ABA.
authors.affiliation: Department of Applied Bioscience, Faculty of Agriculture, Hokkaido University, Sapporo, Japan.
authors.forename: E
authors.initials: E
authors.lastname: Nambara
authors.forename: H
authors.initials: H
authors.lastname: Kawaide
authors.forename: Y
authors.initials: Y
authors.lastname: Kamiya
authors.forename: S
authors.initials: S
authors.lastname: Naito
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D000597:Amino Acids, Branched-Chain / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D016296:Mutagenesis; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D000597:Amino Acids, Branched-Chain; D010937:Plant Growth Regulators; D000040:Abscisic Acid