Growth and Physiological Response of Lettuce, Radish and Chinese Cabbage Exposed to As.

Understanding the physiological response of plants to As accumulated in tissue is crucial for As phytotoxicity studies. The current study was conducted to determine the physiological toxicity and tolerance response of As sensitive plants, including lettuce (Lactuca sativa), radish (Raphanus sativus) and Chinese cabbage (Brassica campestris ssp. pekinensis), to As stress together with growth response. Plant seedlings were grown in hydroponic solution containing a wide range of As concentrations and the physiochemical responses to As exposure recorded. Lipid peroxidation and H₂O₂ accumulation were used as indicators of oxidative damage, while expression of glutathione (GSH) and antioxidative enzymes were used as indicators of As tolerance mechanisms. Among the plant species studied, Chinese cabbage appeared to be more As tolerant than both lettuce and radish, exhibiting less inhibition of root elongation despite accumulating higher levels of As in the roots than other two species. The tolerance of Chinese cabbage was related to elevated GSH synthesis resulting in reduced lipid peroxidation, while increases in lipid peroxidaiton was the main reason for stunted root growth in lettuce and radish. At high concentrations of solution As (50 and 100 μM), Chinese cabbage also showed declines in root growth which was mainly due to H₂O₂ accumulation. In contrast, H₂O₂ accumulation was not detected in lettuce and radish. Activation of antioxidative enzymes varied among plant species with increases of superoxide dismutase (SOD) and guaiacol peroxidase (GPOD) in Chinese cabbage, and elevated catalase (CAT) activation in lettuce in response to increases in As concentration in the external solution.