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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T. 1993. Inhibition of electron flow around photosystem I in chloroplasts of Cd-treated maize plants is due to Cd-indueed iron deficiency. Photosystem I activity of ehloroplasts isolated from 21 days old maize seedlings {Zeu mays L. ev. Hidosil) cultivated in a nutrient solution containing different concentrations of Cd (10, 20, 30 \i.M) was investigated. Cd markedly decreased ferredoxin(Fd)dependent NADP* photoreduetion, while it had no effect on electron transport from 2,6-diehlorophenolindophenol to methyl viologen, indicating that the metal interferred with electron transport on the reducing side of photosystem I. The decrease in electron transport correlated with a low Fd content, which in turn was correlated with a low Fe concentration, suggesting Cd-indueed Fe deficiency. In in vitro experiments direet Cd inhibition of Fd-dependent NADP* photoreduetion required much higher Cd coneentrations than those observed in Cd-treated plants.

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