External detoxification mechanism of corn plants exposed to cadmium stress

Understanding the processes crops use to detoxify heavy metals (HMs), are critical in crops production and environmental management. The role of organic acids (OAs) exudation as an external mechanism of corn plants to detoxify cadmium (Cd) toxicity was examined in a hydroponic experiment. Treatments consisted of four levels of Cd concentrations (0, 10, 25 and 40 mu M) and four exposure time periods (2, 4, 8 and 16 days) to Cd stress. The increased Cd concentration increased the release rates of OAs, namely oxalic, citric and acetic acids. Oxalic acid was the dominate OA (>= 80% of the total OAs measured) released by the plants. Releasing OAs increased Cd uptake by plants via complexing Cd ions in nutrient solution. OAs exudation rate decreased by increasing exposure time periods to Cd stress. The decreased exudation rate minimised the adverse effect of Cd stress on plant growth. As a result, the percentage of dry matter yield reduction rates decreased by increasing corn plants exposure time periods to Cd stress. In conclusion, results indicated that corn roots OAs exudation rates play an important role in detoxifying Cd toxicity by complexing Cd ions and accumulate it in root vacuoles to protect cell metabolism and plant growth.