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 documented earlier that Cd induced a decrease in the leaf Fe content, and increased levels of Fe may reduce Cd toxicity. The aim of the present 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 concentrations (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, Calvin 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. The Cd-induced increase in ATP content, and in the ATP/ADP ratio, resulted from a decreased ATP consumption. At a higher Fe dose, the Cd/Fe interaction resulted in a revitalisation of the adenylate pool and Calvin cycle metabolites. The inhibition of RUBISCO carboxylase activity may be considered as the primary plant response to Cd-stress. The mechanisms of RUBISCO activation operate to overcome this limitation, although their efficiency was decreased by high Cd concentrations, resulting in decreased RUBISCO activity. At a low Cd concentration, the increase in RUBISCO activity was correlated with increased carbonic anhydrase activity.

Nyckelord

activation

adenylates

carbonic anhydrase

carboxylation

Cd/Fe interaction

metabolites

RUBISCO

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