Transgenic Plants Absorbing Environmental Sulfur Pollutants

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Cysteine synthase [O-acetyl-L-serine(thiol)-lyase, EC 4.2.99.8] (CSase), which is responsible for the final step in biosynthesis of cysteine, catalyzes the formation of L- cysteine from O-acetyl-L-serine and hydrogen sulfide. Transgenic tobacco plants carrying either spinach cytosolic Csase A cDNA (3F) or chimeric CSase A cDNA fused with the sequence for chloroplast-targeting transit peptide of pea ribulose- 1,5- bisphosphate carboxylase small subunit (4F) driven by the cauliflower mosaic virus 35S promoter have already been constructed. The enhanced CSase activities of transgenic plants of 3F and 4F have been shown in cytosol and in chloroplasts, respectively (1). We crossed 3F transgenic tobacco with 4F transgenic tobacco, and generated F1 transgenic tobacco in which Csase activities were enhanced both in cytosol and chloroplasts. Both cysteine and reduced glutathione (GSH) contents in leaves of F1 transformants were higher than those of 3F, 4F transformants and control plants, indicating that high activities of CSase both in cytosol and chloroplasts caused an efficient assimilation of sulfur into cysteine and GSH.Furthermore, F1 transgenic tobacco showed more resistance to sulfur dioxide (SO2) gas and sodium sulfite than 3F, 4F transformants and control tobacco.