Effect Of Melatonin Pretreament On Cucumber Seedlings Growth Under Cadmium Stress And Nitrate Stress

Cadmium (Cd) is a heavy metal element widely found in nature. It is one of the most toxic to farmland and widespread heavy metals. It can be easily absorbed and accumulated by plants. The high accumulation of Cd not only inhibits the plant growth and negatively affects crop yield and quality, but also causes harm to human health through the food chain. As the advance development of protected cultivation, misuse of nitrogen fertilizer is generally widespread. However, its over-accumulation can result in the secondary salinization of soils and injure the plant growth and product safety. Because of the universality and damage severity of cadmium stress and nitrates stress, they have become two serious issues that affect the safety and high-quality of vegetable production. It is known that melatonin (MT) enhances the resistance of plants on adversity stresses. However, it is unclear that how melatonin alleviate the stresses of cadmium and nitrates.Our experiments were conducted with wildly cultivated cucumber as a research object, and studied the alleviation effect of melatonin pretreatment on the growth of Cucumis sativus L. ’Jin You No.1’under cadmium stress and nitrate stress in black plastic pots filled with soil and sand. The results showed as followings:1. Melatonin pretreatment can significantly increase the plant height, stem diameter, total fresh weight, dry weight of root and shoot, thereby increasing the capacity to absorb water and nutrients of cucumber and guaranteeing its growth.2. Melatonin pretreatment can significantly increase chlorophyll content and net photosynthesis rate (Pn), and then enlarge its production.3. Melatonin pretreatment can significantly decrease relative leaf conductivities, reduce MDA content and O2- production rate, and increase the activity of SOD, CAT and POD. Then enhanced antioxidant captivity of cucumber and improve the cadmium tolerance.4. Melatonin pretreatment can promote the absorption of cucumber leaf to Mg, Fe and Zn, root and stem to Ca, and suppress the accumulation of Cd in the whole plants and Mn in the fruit.5. Melatonin pretreatment can significantly decrease the weight and length of individual cucumber and the early yield per plant, but increase the total yield per plant; improve the content of VC and soluble protein of the fruit, but reduce RWC and soluble sugar content of fruit, which further influence the fruit quality.6. Melatonin pretreatment can significantly increase the plant height, stem diameter, dry weight of root and shoot, the length and activity of root; inhibit the damage of intrate to seeding; reduce the salt injury index and guarantee the vigorous growth.7. Melatonin pretreatment can promote the absorption of cucumber plant to Ca and P, and leaf to Mg, but suppress the absorption of cucumber to N, K.8. Melatonin pretreatment can significantly supress the cucumber leaf to accumulate nitric nitrogen and ammonium nitrogen, and promote the enzyme activity, such as NR, GS, GOGAT and GDH, and then improve the process of nitrogen metabolism.