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

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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.