Abscisic Acid On Several Aquatic Plant Heavy Metal Stress Relief Effect

Heavy metal (HM) pollution has become an increasingly serious problem. HMs may enter human body through the food chains and lead to various diseases. During the process of HM bioaccumulation, plants play significant roles as primary productions in many habitats. Therfore, much attention has been devoted to the studies on the mechanisms of HM tolerance in plants and how to improve HM tolerance of plants. Abscisic acid(ABA) is an important kind of exgenous hormone and can regulate plant growth and development. In rencent years,there are many studies on the relationship between ABA and HM tolerance to various stresses,such as drought,salt and so on.However,very little systematic work has been done on the ralationship between ABA and HM stress.In this paper, therefore, two aquatic plants with different ecotypes(Potamogeton crispus L.,submerged plant; Nymphoides peltatum (Gel.) Kuntze, floating plant) were chosen as experimental materials. Cd and Mn were as the stress factors;the former is an unessential element,while the latter is an essential microelement of plants. These plants were cultivated in solution containing different concentrations of Cd and Mn under lab condition. The mechanisms for protection of aquatic plants from the toxic effects of HMs was systemically studied. The results are as follow:The most suitable concentrations of ABA is in ranges of 2.5-5μmol·L^-1,respectively,when Potamogeton crispus were treated with different concentrations of exgenous ABA. Excessive amounts of ABA is toxic to Potamogeton crispus. Exgenous ABA (5μmol·L^-1) increased the activities of superoxide dismutase (SOD), Catalase (CAT), ascorbate peroxidase (APX), and decreased the generating rate of O₂^-· in the leaves of Nymphoides peltatum (Gel.) Kuntze under Cd and Mn stress, prevented the increase of membrace permeability induced by HM stress. Mn stress resulted Mn accumulation, while exogenous ABA maintained effectively the balance of elements by decreasing membrane permeability of Nymphoides peltatum (Gel.) Kuntze leaves. Moreover, exogenous ABA prevented the decrease of chlorophyll content.In summary, exogenous ABA enhanced the antioxidative ability of plant, protected the biomembranes of cell, maitained the balance of elements in plants, and thereby enhanced plant resistance.