The cytosolic O-acetylserine(thiol)lyase gene is regulated by heavy metalsand can function in cadmium tolerance

Regulation of the expression of the cytosolic O-acetyl-serine(thiol)lyase g ene (Atcys-3A) from Arabidopsis thaliana under heavy metal stress condition s has been investigated. Northern blot analysis of Atcys-3A expression show s a 7-fold induction after 18 h of cadmium treatment. Addition of 50 muM Cd Cl2 to the irrigation medium of mature Arabidopsis plants induces a rapid a ccumulation of the mRNA throughout the leaf lamina, the root and stem corte x, and stem vascular tissues when compared with untreated plants, as observ ed by in situ hybridization. High pressure liquid chromatography analysis o f GSH content shows a transient increase after 18 h of metal treatment. Our results are compatible with a high cysteine biosynthesis rate under heavy metal stress required for the synthesis of GSH and phytochelatins, which ar e involved in the plant detoxification mechanism. Arabidopsis-transformed p lants overexpressing the Atcys-3A gene by up to g-fold show increased toler ance to cadmium when grown in medium containing 250 muM CdCl2, suggesting t hat increased cysteine availability is responsible for cadmium tolerance. I n agreement with these results, exogenous addition of cystine can, to some extent, also favor the growth of wild type plants in cadmium-containing med ium. Cadmium accumulates to higher levels in leaves of tolerant transformed lines than in wild-type plants.