Transgenic Plants Absorbing Environmental Sulfur Pollutants

半胱氨酸合成酶[o -乙酰-L-丝氨酸（硫醇）裂解酶，EC 4.2.99.8] （CSase）负责半胱氨酸生物合成的最后一步，它催化o -乙酰-L-丝氨酸和硫化氢生成L-半胱氨酸。已经构建了携带菠菜胞质Csase A cDNA （3F）或与菜花花叶病毒35S启动子驱动的豌豆核酮糖- 1,5-二磷酸羧化酶小亚基（4F）叶绿体靶向转运肽序列融合的嵌合Csase A cDNA转基因烟草植株。3F和4F转基因植株的CSase活性分别在细胞质和叶绿体中得到增强(1)。我们将3F转基因烟草与4F转基因烟草杂交，得到了细胞质和叶绿体中Csase活性均增强的F1转基因烟草。F1转化体叶片中半胱氨酸和还原性谷胱甘肽（GSH）含量均高于3F、4F和对照植株，表明细胞质和叶绿体中CSase活性高，导致硫有效同化为半胱氨酸和GSH。此外，F1转基因烟草对二氧化硫（SO2）气体和亚硫酸钠的抗性高于3F、4F转基因烟草和对照烟草。

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.