ABSTRACT 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 µM) 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.

中文翻译：

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镉胁迫下玉米植株体外解毒机制

摘要 了解作物用来解毒重金属 (HMs) 的过程对作物生产和环境管理至关重要。有机酸 (OAs) 渗出作为玉米植物解毒镉 (Cd) 毒性的外部机制的作用在水培实验中进行了检查。处理包括四种水平的 Cd 浓度（0、10、25 和 40 µM）和四个暴露于 Cd 压力的时间段（2、4、8 和 16 天）。增加的 Cd 浓度增加了 OAs 的释放速率，即草酸、柠檬酸和乙酸。草酸是植物释放的主要 OA（≥ 80% 测量的总 OA）。释放 OA 可通过络合营养液中的 Cd 离子增加植物对 Cd 的吸收。OAs 渗出率随着暴露于镉胁迫的时间增加而降低。降低的渗出率最大限度地减少了镉胁迫对植物生长的不利影响。因此，随着玉米植株暴露于 Cd 胁迫的时间增加，干物质产量减少率的百分比降低。总之，结果表明，玉米根部 OAs 渗出率通过络合 Cd 离子并在根液泡中积累以保护细胞代谢和植物生长，在解毒 Cd 毒性方面发挥重要作用。