The effects of cadmium on photosynthesis of Phaseolus vulgaris – a fluorescence analysis

Abstract

Bean plants (Phaseolus vulgaris L. cv. Scarlett), germinated in darkness for I week, were transferred to light (200 μmol m⁻² s⁻¹) and cultivated for I week in a complete nutrient solution. After this period, cadmium ions in the form of CdSO₄ were added at the concentrations of 0.10.20 and 50 μM. The effects of this metal on the properties of photosystem II photochemistry were studied by means of modulated fluorescence analysis. Steady state photochemical quenching. non-photochemical quenching and terminal fluorescence were determined in control and cadmiumtreated plants. We postulate that, during short term exposure of plants to cadmium in the early stages of growth, the Calvin cycle reactions are more likely than photosystem II to be the primary target of the toxic influence of cadmium. The reduced demand for ATP and NADPH upon Calvin cycle inhibition causes a down-regulation of photosystem II photochemistry and of the yield of linear electron transport.