Tomato plants (Lycopersicum esculentum Mill. cv. Moneymaker) grown on nutrient medium containing cadmium exhibit reduced net photosynthesis and reduced contents of chlorophyll and accessory pigments. In chloroplasts isolated from cadmiumtreated plants photosystem II activity, as measured by 2,6-dichlorophenolindophenol photoreduction, and photosystem II -(-I activity (H2O -> methyl viologen) were both inhibited to about 60%, When 1,5-diphenylcarbazide was used as artificial electron donor, no significant cadmium effect was observed. Photosystem I activity was not affected by cadmium. The fine structure of ehloroplasts in eadmium-treated plants was degenerated, similarly to senescence response. The principal symptom of cadmium action was the occurrence of large plastoglobules and a disorganization of the lamellar strueture, mainly grana stacks. Transfer of cadmium-treated plants into a medium with increased manganese level caused grana stacking and restoration of photosystem II activity.

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The effect of cadmium on growth parameters of seedlings of maize, rye and wheat as well as the role of phytochelatins in Cd detoxication in these species were studied. Cadmium was found to inhibit root growth and decrease fresh weight and water content in roots and shoots of the studied plants. Although a considerably lower Cd accumulation was shown in maize seedlings than in other species, they were characterized by the highest sensitivity to cadmium. Among 7-Glu-Cys peptides synthetized by plant species, phytochelatins -glutathione derivatives predominated. In maize they were synthetized in amounts sufficient for binding the total pool of the metal taken up, and the detoxication mechanism was localized in their roots. Larger amounts of cadmium were accumulated in roots of wheat and rye, but the quantity of the formed y-Glu-Cys peptides seems insufficient for detoxication of the metal.

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