Activation and induction of phvtochelatin synthase by heavy metal ions in tomato cells.

植物螯合素（PC）在植物重金属耐性中的作用已被广泛研究。PC合成酶的性质和功能还有待进一步研究。在本研究中，我们分离了几个同工酶的PC合酶的镉适应番茄细胞，并发现其酶活性的重金属离子的具体影响。它们的各种动力学参数，生产和细胞响应金属离子的关系也进行了表征。基于这些结果，我们得出结论，番茄细胞的重金属耐受性是由金属离子激活的PC2合酶组成型表达，并且通过PC3或PC4合酶同工酶的适应性合成而更加增强或稳定。这一思路可应用于其他植物系统，以评价PC合成酶在PC形成和重金属耐性中的一般作用。方法学的改进将为进一步研究植物中与PC途径和金属耐性相关的功能同工酶和基因提供重要的基础。

Role of phytochelatin (PC) in heavy-metal tolerance in plants has been well investigated by many workers. Properties and functions of PC synthase howeverremained to be established. In the present study, we isolated several isoenzymes of PC synthase from Cd-adapted tomato cells and found specific effects of heavy metal ions on their enzymic activities. Their various kinetic parameters, productions and relationships to cell responses to metal ions were also characterized. Based upon these results, we concluded that heavy-metal tolerance of tomato cells is constitutively expressed by the metal ion-activated PC2 synthase, and more enhanced or stabilized by an adaptational synthesis of PC3 or PC4 synthase isozymes. This idea can be applied to the other plant systems to evaluate general roles of PC synthase in PC formation and heavy metal tolerance. Methodological upgrades will allow the further important findings for functional isozymes and genes related to the PC pathway and metal-tolerance in higher plants.