| Heavy metal pollution becomes the focus of the modern environmental problems just due to difficult remediat and its huge harm, and the copper pollution is one of them. Copper is one of the essential microelements for plants. But in recent years, the abuse of copper bactericide and industrial pollution has led to the increase of copper content in environment such as in soil. The excessive copper can result in the poisoning effects on plants, the reduction of crops production and the descent of agricultural product quality. And then the excess copper also endanger human health through accumulation in food.In the present study, changes in seed germination and growth of wheat seedlings treated with different concentrations of Cu2+ were studied. A rapid, efficient protocol to detect the toxicity of Cu2+ stress using wheat coleoptile, which is simple, uniformal in structure and sensitive, was established. By using this model, the mechanism of Cu2+ stress leading to the inhibition of cell elongation was also studied. The main results were follows:1. With increasing of Cu2+ concentration, the germination rate of wheat seeds is reduced, the 50% inhibiton concentration is 500μmol/L (equivalent LC50), complete inhibition concentration is 10 mmol/L. For the growth of roots and bud, low concentration treatment has little effect and high concentrations (>100μmol/L) produced a significant inhibition, and the order of inhibition effect roots> bud.2. With increasing of Cu2+ concentration, the chlorophyll content of wheat seedlings decreased, leading to inhibit the photosynthesis, growth and development of wheat seedlings. And the length and number of wheat roots are also decreased. Surprisingly, the root activity increased at the seedling stage.This suggests that the wheat seedlings have acertain adaptability to Cu2+ stress. 3. The activity of Peroxidase (POD) and catalase (CAT) of wheat seedlings and the content of malondialdehyde (MDA) increased with increase of Cu2+ concentrations. It indicates that high concentration of Cu2+ increases the the level of reactive oxygen species (ROS) in seedling cells, and also enhances the seedlings to eliminate ROS, but not enough completely to remove them. In contrast, the ROS accumulation caused the lipid peroxidation and produced some of MDA, and leading to the damane of the membrane system. It was further testified by the significant increase of membrane permeability induced by increasing Cu2+ concentration measuring the electric conductivity of the leaves.4. The wheat coleoptile is a good material to study plant elonggation growth because it is structurally simple and easy to get unifomal materials. It is a good material for identying Cu2+ toxicity for crops such as wheat. With increase of Cu2+ concentration, the coleoptile elongation is hardly hibited first, then significantly reduced. Similar results were also detected with increase of treatment time (24, 48 and72 h). And it was found that the 0.5 cm and 1 cm original length of the coleoptile have the similar results in the further study. However, the effect of 0.5 cm is more obvious. Therefore, the 0.5 cm original length of coleoptile and the 24 h treatment time were proposed for identying wheat Cu2+ toxicity. The growth of wheat coleoptile cells is only elongation, and auxin plays a critical role in this process. The inhibition of coleoptile elongation is alleviated when exogenous auxin was added to the medium under the low concentrations of Cu2+ stress. However, under high concentrations of Cu2+ stress, as the toxicity is so much, exogenous auxin is not available any further. These results suggest that inhibition of heavy metal copper on plant elongation growth primarily results from increasing indole acetic acid oxidase activity/or inhibit synthesis enzymes of IAA leading to the reduction of endogenous IAAcontent. |
PDF Full Text Request