Inhibition of electron flow around photosystem I in chloroplasts of Cd‐treated maize plants is due to Cd‐induced iron deficiency

Photosystem I activity of chloroplasts isolated from 21 days old maize seedlings ( Zea mays L. cv. Hidosil) cultivated in a nutrient solution containing different concentrations of Cd (10,20,30μM) was investigated. Cd markedly decreased ferredoxin(Fd)‐dependent NADP + photoreduction, while it had no effect on electron transport from 2. 6‐dichlorophenolindophenol 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‐induced Fe deficiency. In in vitro experiments direct Cd inhibition of Fd‐dependent NADP + photoreduction required much higher Cd concentrations than those observed in Cd‐treated plants.