INCREASED ZINC TOLERANCE IN SILENE-VULGARIS (MOENCH) GARCKE IS NOT DUE TO INCREASED PRODUCTION OF PHYTOCHELATINS

The concentration of acid-soluble thiols other than reduced glutathion e (SH - GSH) increases in the roots of zinc-sensitive and zinc-toleran t Silene vulgaris (Moench) Garcke after exposure to zinc for 1 to 3 d. The concentration of SH - GSH in the roots is higher in the sensitive plants than in the tolerant ones, both at equal external zinc concent rations and at zinc concentrations causing the same level of root-leng th growth inhibition. High performance liquid chromatography analyses show that the increase in the concentration of SH - GSH is not only du e to the production of phytochelatins, but is also due to an increase in the concentration of cysteine and the production of nonidentified t hiols. The cysteine concentration increases equally in the roots of se nsitive and tolerant plants. The accumulation of phytochelatins is hig her in the roots of the sensitive plants, whereas the chain length dis tribution of phytochelatins is the same in sensitive and tolerant plan ts. It is concluded that increased zinc tolerance in S. vulgaris is no t due to increased production of phytochelatins.