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 growinfi; tillers in nutrient solution without sulphur had no eftect 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. T'olerance of a copper-tolerant clone screened from seed of a non-tolerant population was unaffected by sulphur deficiency. Sulpl-iur deficiency reduced the amount of copper-inducible tliiol-ricli protein in roots of both the tolerant and non-tolerant clones exposed to excess copper. Roots of the tolerant clones fjrown in micronutrient copper solutions without sulphur for 26 d and then exposed to 1-61 //M copper for a further 4 d both produced 7S",, 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 tbe amount of tbiol-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 cloties produced coi-isiderably more thiol-rich protein when exposed to excess copper than did the tolerant clones.

Phytochelatins in Cadmium-Sensitive and Cadmium-Tolerant Silene vulgaris (Chain Length Distribution and Sulfide Incorporation)

“…This indicates that the amounts of PCs are also not responsible for Cu or Zn tolerance in S. vulgaris (de Vos et al, 1992;Schat and Kalff, 1992;Harmens, 1993). A similar result was obtained for Cu-tolerant Deschampsia cespitosa (Schultz and Hutchinson, 1988).…”

Are Phytochelatins Involved in Differential Metal Tolerance or Do They Merely Reflect Metal-Imposed Strain?

“…It is conceivable that both the production, which takes place in the cytoplasm, and the breakdown, which presumably occurs in the vacuole (21), as well as the transport of the copper-PC complex over the tonoplast, occur faster in tolerant plants. Moreover (15). BSO treatment of copper-tolerant Mimulus guttatus, however, seems to result in an enormous increase in copper sensitivity (13).…”

“…The literature does not provide conclusive evidence on this point. Moreover, in some studies, inhibition of PC synthesis through sulfur starvation increased the sensitivity in nontolerant plants but did not affect the sensitivity of tolerant ones (15).…”

Comparison of Metallothionein Gene Expression and Nonprotein Thiols in Ten Arabidopsis Ecotypes (Correlation with Copper Tolerance)

“…A second caveat is that different metal tolerance mechanisms may operate at different developmental stages. Schultz and Hutchinson (1988) utilized mature Deschampsia plants treated with copper for 30 d. In the present study with Arabidopsis, only seedlings were examined. Further studies are needed to confirm that MT production correlates with metal tolerance in mature plants as well as in seedlings.…”

“…Despite the strong circumstantial evidence, based on mRNA measurements, favoring a key role for MTs in plant metal tolerance, direct measurement of MT protein levels has proven difficult in the past, and specific antibodies against plant MTs for immunoblotting are not yet available. Schultz and Hutchinson (1988) measured total copper-inducible thiol-rich proteins in tolerant and nontolerant clones of Deschampsia. Nontolerant clones synthesized higher amounts of thiol-rich proteins than tolerant clones.…”