Salt-specific regulation of the cytosolic O-acetylserine(thiol)lyase gene from Arabidopsis thaliana is dependent on abscisic acid

The expression of Atcys-3A gene coding for cytosolic O-acetylserine(thiol)l yase, a key enzyme in cysteine biosynthesis, from Arabidopsis thaliana is s ignificantly induced by exposure to salt and heavy-metal stresses. Addition of NaCl to mature plants induced a rapid accumulation of the mRNA througho ut the leaf lamina and roots, and later on in stems, being mainly restricte d to vascular tissues. The salt-specific regulation of Atcys-3A was also me diated by abscisic acid (ABA) since: (1) exogenous addition of ABA to the c ulture medium mimicked the salt-induced plant response by raising the level of Atcys-3A transcript, and (2) Arabidopsis mutants aba-1 and abi2-1 were not able to respond to NaCl. Our results suggest that a high rate of cystei ne biosynthesis is required in Arabidopsis under salt stress necessary for a plant protection or adaptation mechanism. This hypothesis was supported b y the observation that intracellular levels of cysteine and glutathione inc reased up to 3-fold after salt treatment.