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Summary

The relationship between metal tolerance and accumulation of organic acids has been investigated using zinc-cadmium tolerant and non-tolerant clones of Deschampsia caespitosa. Zinc significantly increased citrate and malate levels in the roots of the tolerant clone but had no significant effect on the levels of these acids in the roots of the non-tolerant clone. Cobalt, copper, mercury and nickel had no significant effect on the levels of these acids in either clone. A number of enzymes involved in organic metabolism were extracted from the roots of the two clones, but no difference in their sensitivities to zinc was found. Changing the citrate levels in the roots by growing plants under different iron regimes did not change tolerance indices. Grown in the presence of zinc, both clones contained enough citrate and malate to complex only approximately half of the zinc present in their roots.