Cadmium Alters Mitochondrial Membrane Potential, Inhibits Electron Transport Chain Activity and Induces Callose Deposition in Rice Seedlings

In the present study, seedlings of indica rice (Oryza sativa L.) cultivars were subjected to 100 and 200 A mu M Cd(NO3)(2) treatment in hydroponics for 10 days which resulted in a marked decline in the growth of the seedlings compared to untreated controls. The integrity of the root cell plasma membrane was significantly decreased and high callose deposition in roots was observed. We observed that mitochondrial functioning was adversely affected in Cd-treated seedling marked by alteration of mitochondrial membrane potential and inhibition of electron transport chain activity. In particular, the activity of the electron transport chain Complex II was more inhibited with Cd treatment compared to the activities of Complex I and Complex IV. Transmission electron microscopic (TEM) analysis of rice leaves from control and Cd-treated seedlings showed significant alteration in membrane composition. Cd treatment at 100 and 200 A mu M resulted in partial to full disintegration of the mitochondrial membrane, respectively. The increased callose deposition might be a defense response against Cd toxicity. The findings indicate that Cd exposure to rice seedlings causes damage to mitochondria and inhibition of mitochondrial electron transport activity which would ultimately contribute to inhibited growth of rice plants in Cd-polluted soils.