Cysteine synthase overexpression in tobacco confers tolerance to sulfur-containing environmental pollutants.

Cysteine (Cys) synthase [O-acetyl-L-Ser(thiol)-lyase, EC 4.2.99.8; CSase] is responsible for the final step in biosynthesis of Cys. Transgenic tobacco (Nicotiana tabacum; F(1)) plants with enhanced CSase activities in the cytosol and in the chloroplasts were generated by cross-fertilization of two transformants expressing cytosolic CSase or chloroplastic CSase. The F(1) transgenic plants were highly tolerant to toxic sulfur dioxide and sulfite. Upon fumigation with 0.1 microL L(-1) sulfur dioxide, the Cys and glutathione contents in leaves of F(1) plants were increased significantly, but not in leaves of non-transformed control plants. Furthermore, the leaves of F(1) plants exhibited the increased resistance to paraquat, a herbicide generating active oxygen species.