Synergistic inhibition of the growth of suspension cultured tobacco cells by simultaneous treatment with cadmium and arsenic in relation to phytochelatin synthesis

Simultaneous treatments with Cd and arsenic (arsenite and arsenate) led to the synergistic growth inhibition of tobacco (Nicotiana tabacum cv. BY-2) c ells, Cd contents in cells increased by co-treatment with arsenic for 24 h, The amount of total phytochelatins (PCs) per unit of Cd in the cells treat ed with Cd and arsenate was lower than that in the cells treated with Cd al one, Simultaneous treatments with Cd and arsenic promoted the induction of the biosynthesis of (gamma-Glu-Cys)(2)-Gly and inhibited the induction of t he biosynthesis of (gamma-Glu-Cys)(3)-Gly and (gamma-Glu-Cys)(4)-Gly, compa red with the treatment with Cd alone. Consequently, since the inhibition of PC biosynthesis led to the increase of the cellular concentration of putat ive ionic (=toxic) Cd, cell growth was inhibited synergistically by simulta neous treatments with Cd and arsenic. In addition, based on the results sho wing that buthionine sulfoximine increased the sensitivity to arsenite and arsenate, and that PC biosynthesis was induced by treatment with arsenite o r arsenate, it is suggested that glutathione and/or its metabolic products such as PCs are involved in arsenic tolerance.