Alleviating Effects Of Polyaspartic Acid On Tomato Under Copper And Cadmium Combined Stress

Tomato(Lycopersicon esculentum Mill.), an annual vegetable of Lycopersicon of Solanaceae, is one of the widely popular vegetables. With the rapid development of industrial and agricultural production, the heavy metal which enter into the soil through the channel of fertilizer with cadmium and copper, copper fungicide, sewage irrigation becomes more and more serious, leading to the content of Cu and Cd in vegetables, fruits edible and other agricultural products out of limits, and exist potential risks to human health. As a fertilizer synergist, PASP can promote plant growth, as well as chelating heavy metal ion. In this paper,a pot experiment was conducted to study the alleviating effects of exogenous PASP on tomato under Cu and Cd combined stress. The main results were as follows:1. Under the conditions of normal pot treatment and Cu+Cd combined stress, the concentration of PASP in 100 mg·L-1、300 mg·L-1、500 mg·L-1、700 mg·L-1 and 1000 mg·L-1both could made the fresh weight, dry weight, plant height and stem diameter of tomato plant increased. But the content of Cu and Cd in plant and effective state in soil declined. The optimum concentration of PASP on tomato is 700 mg·L-1 and the methods of application is spraying.2. Under combined stress, spraying exogenous PASP could significantly increase the fresh weight of tomato plants, but had no significant effects on plant height and stem diameter.Spraying exogenous PASP could also effectively improve the activities of anti-oxidizing enzyme systems(POD, SOD, CAT) and root activity under Cu+Cd combined stress, and the chlorophyll a, chlorophyll b, carotenoid content and root tolerance index increased significantly either, while the relative electrolyte leakage rate of leaves and MDA and free proline contents remarkably reduced. The content of soluble protein in roots and leaves increased under Cu+Cd treatment, and in roots it was restored to CK level after PASP treatment, while in leaves increased continually. Besides, the activity of NR was improved significantly under Cu+Cd treatment, and spraying PASP made it raised even further.3. Compared with Cu+Cd combined stress, addition of 700 mg·L-1 PASP could made the Cu and Cd content in different organs and the individual plant accumulation of tomato both showed an obviously decrease. In underground, PASP made the accumulation and distribution ratio of Cu and Cd significantly rise, while in the overground was just the reverse. It means that PASP could restrict the transporting ability of Cu and Cd from root to the aboveground.PASP could significantly increase the content and accumulation of Fe、Mn、Zn、Ca、Mg in root, stem and leaf under Cu+Cd treatment, to maintain cytoplasmic ion homeostasis and alleviate the inhibitory effect of excess Cu and Cd on the growth of tomato plants. And the contents of Cu and Cd in each organ were significantly negatively correlated with Mn content in leaf and Zn content in stem, while with the Ca and Mg contents in roots and stems was significantly positively related. The effects of PASP on N and P content in every organ was not obvious under stress, while the K content in stem raised significantly and in leaf dropped dramatically. The contents of Cu and Cd were significantly positively correlated with N content in each organ, while with the P contents in roots and K contents in leaves were a significantly negative correlation.4. Under Cu+Cd treatment, the activity of catalase, urease and sucrase in soil showed a significant rise after spraying PASP. The state of water-soluble, Iron manganese oxidation and Strong organic of Cu were raised slightly, but the contents of Cu in the other forms and the easily absorbing state of Cd were decreased.5. As the extension of processing time, the alleviating effect of PASP on the growth of tomato plants was gradually increased under Cu+Cd stress. And the Cu+Cd+PASP treatment have made the tomato growth and nutrient elements content returned to CK level gradually.The facilitation of PASP on tomato growth was weaker when it applied under low fertility conditions compared with the normal level, but it could made the nutrient content in each organ rise to normal fertility levels. Applying PASP could also make tomato production increased by 18.85% and the content of Vc and soluble sugar in tomato fruit increased significantly under Cu+Cd treatment.