A Comparative Study on the Organic Acid Content and Exudation in Maize (Zea mays L.) Seedlings under Conditions of Copper and Cadmium Stress

This study focuses on the comparative effects of copper and cadmium on the organic acid content and exudation in maize (Zea mays L.). We have also discussed the role of organic acids in copper and cadmium tolerance. The maize seedlings were grown in hydroponics for 8 days and then treated with 100 μM copper or cadmium for 4 days. The copper reduced more than cadmium root fresh wt and shoot dry wt, while Cd had more decreasing effect on root dry wt. Analysis of organic acids in root exudates showed that citrate exudation was not affected by both metals, suggesting that root exudation was not involved in copper or cadmium tolerance in maize. This prompted us to investigate the role of organic acids in internal tolerance mechanism. Total organic acids were decreased in roots but remained unchanged in shoots of Cu and Cd-treated plants. However, malate content decreased substantially in roots by 68 and 53%, respectively with Cu and Cd. The marked increase in the content of citrate with both metals in roots, as well as in those of malate with Cu and citrate with Cd in shoots, underlined the main role of these organic acids in Cu and Cd tolerance in maize.