XVI International Botanical Congess

Phytochelatins and their precursor glutathione play an important role in sequestrating and detoxifying xenobiotics including heavy metals. With the goal to identify limiting factors for heavy metal accumulation and tolerance, and to develop transgenic plants with an increased capacity to accumulate and/or tolerate heavy metals, the Escherichia coli gshI gene encoding g-glutamyl-cysteine synthetase (ECS) was overexpressed in the chloroplasts of Brassica juncea (Indian mustard). The transgenic ECS plants accumulated significantly more cadmium than wildtype plants: shoot cadmium concentrations were up to 40-90 % higher, and total cadmium accumulation plant was up to 2-fold higher. Moreover, the ECS plants showed enhanced tolerance to cadmium, both at the seedling and mature plant stage. The ECS plants had higher concentrations of glutathione, phytochelatins, non-protein thiol, total sulfur and calcium than wildtype plants. We conclude that ECS enzyme is rate-limiting for the biosynthesis of glutathion and phytochelatins, and that overexpression of ECS offers a promising strategy for the production of plants with superior heavy metal phytoremediation capacity.