Changes in Physiological Responses of Hygrophila schulli Under Cadmium Toxicity

摘要

Cadmium, a heavy metal, is very often found to be contaminating the plants predominantly grown in water bodies adjacent to industrial zone. A number of vegetable crops are thus toxicated by hyper-accumulation of Cd in their leafy shoots. Out of a number of such contaminated plant species, Hygrophila schulli (Buch-Ham. M.R. and S.N. Almeida), a leafy vegetable is most important for its nutritive value. A hydroponic culture of Hygrophila plant was done with increasing concentration of Cd salt: 0, 50, 100 and 300 uM in nutrient solution for 15 days. Plants accumulated a significant amount of Cd in a dose-dependent manner of Cd application. In addition, generation of reactive oxygen species such as hydrogen peroxide (H202) and free radicals (Oj, 1/202,OH~) was assayed from the plants and found to be up-regulated. Lipid peroxidation and protein oxidation were significantly higher under increasing concentration of Cd over control. Total antioxidation activity was measured and it showed a declining trendwith increasing concentration of Cd. Significant rise of non-enzymatic antioxidative molecules like anthocyanin, glutathione and other phenolics were observed in plants. At the cellular level, a significant expression of heat shock protein (HSP-70) wasrecorded according to the function of Cd concentrations. Antioxidative enzymes such as guaiacol peroxidase and glutathione reductase were significantly increased when assayed in vitro from plants under increasing concentration of Cd as compared to control. Accumulation of nitrate and nitrate reductase activity was also changed in plants induced by Cd. The physiological relevance of Cd hyper-accumulation and its induced oxidative stress in Hygrophila plants were discussed.