PRIMARY CARBON METABOLISM IN PHASEOLUS-VULGARIS PLANTS UNDER CD FE INTERACTION/

The influence of the Cd/Fe interaction on primary carbon metabolism in Phaseolus vulgaris L. cv. Slowianka plants was investigated. It was d ocumented earlier that Cd induced a decrease in the leaf Fe content, a nd increased levels of Fe may reduce Cd toxicity. The aim of the prese nt study was to check whether Cd is toxic to Calvin cycle enzymes and especially if different Fe levels can modify the Cd effect. Bush-bean seedlings were cultivated in the presence of different Cd concentratio ns (0, 10, 20, 50 mu M) and at different Fe doses (deficient: 0 mmol, normal: 0.25 mmol, excessive: 0.5 mmol). Leaf content of ATP, ADP, Cal vin cycle metabolites, activity of RUBISCO and carbonic anhydrase were measured. The influence of Cd/Fe interaction on the content of Calvin cycle metabolites seemed to be of both direct and indirect nature. Th e Cd-induced increase in ATP content, and in the ATP/ADP ratio, result ed from a decreased ATP consumption. At a higher Fe dose, the Cd/Fe in teraction resulted in a revitalisation of the adenylate pool and Calvi n cycle metabolites. The inhibition of RUBISCO carboxylase activity ma y be considered as the primary plant response to Cd-stress. The mechan isms of RUBISCO activation operate to overcome this limitation, althou gh their efficiency was decreased by high Cd concentrations, resulting in decreased RUBISCO activity. At a low Cd concentration, the increas e in RUBISCO activity was correlated with increased carbonic anhydrase activity.