Overexpression of phytochelatin synthase in tobacco: distinctive effects of AtPCS1 and CePCS genes on plant response to cadmium.

Phytochelatins, heavy-metal-binding polypeptides, are synthesized by phytochelatin synthase (PCS) (EC 2.3.2.15). Previous studies on plants overexpressing PCS genes yielded contrasting phenotypes, ranging from enhanced cadmium tolerance and accumulation to cadmium hypersensitivity. This paper compares the effects of overexpression of AtPCS1 and CePCS in tobacco (Nicotiana tabacum var. Xanthi), and demonstrates how the introduction of single homologous genes affects to a different extent cellular metabolic pathways leading to the opposite of the desired effect. In contrast to WT and CePCS transformants, plants overexpressing AtPCS1 were Cd-hypersensitive although there was no substantial difference in cadmium accumulation between studied lines. Plants exposed to cadmium (5 and 25 μM CdC