Evidence against a key role for metallothionein‐like protein in the copper tolerance mechanism of Deschampsia cespitosa (L.) Beauv.

Abstract

SUMMARYThe role of sulphur and copper‐inducible thiol‐rich protein in the copper tolerance‐ of the grass Deschampsia cespitosa (L.) Beauv. was investigated. Sulphur deficiency, induced by growing tillers in nutrient solution without sulphur had no effect on the copper tolerance of two clones from a site contaminated with copper and nickel. In contrast sulphur deficiency increased the susceptibility of two non‐tolerant clones from an uncontaminated site‐to copper toxicity. Tolerance of a copper‐tolerant clone screened from seed of a non‐tolerant population was unaffected by sulphur deficiency. Sulphur deficiency reduced the amount of copper‐inducible thiol‐rich protein in roots of both the tolerant and non‐tolerant clones exposed to excess copper. Roots of the tolerant clones grown in micronutrient copper solutions without sulphur for 26 d and then exposed to 1.61 μM copper for a further 4 d both produced 75% less copper‐inducible thiol‐rich protein than those grown with sulphur. In an experiment with one of the tolerant clones, the amount of thiol‐rich protein did not increase between 4 and 30 d of exposure to excess copper despite a 43% increase in copper in the cell‐free extract. Sulphur deficiency reduced the amount of thiol‐rich protein to a lesser extent in the non‐tolerant clones, with a 57% decrease in one clone and a 31% decrease in the other. In the presence of sulphur both non‐tolerant clones produced considerably more thiol‐rich protein when exposed to excess copper than did the tolerant clones.