The Study Of Autointoxication In Watermelon And Its Mechanism

The autointoxication of watermelon residuces (root, stem and leaf ) and its root exudates was studied. Cinnamic, ferulic acid, vanillic and p-coumaric acid in watermelon root exudates and during decomposition of its residuces were analysed by means of HPLC. The effects of cinnamic, ferulic acid, vanillic and p-coumaric acid on seed germination and enzyme activities, osmoregulation, membrane-1ipid of seedlings was tested through germination and hydroponics. With electronic microscope, the root ultrastructre , treated with abstracts of leaf, root exudates of watermelon and cinnamic and p-coumaric acid , was studied to find autointoxication mechanism. Several organic fertilizer was used to study the watermelon autointoxication in a soil culture system. The main results were presented as follows:The autointoxication of watermelon are studied through the seed germination and growth experiment, with the water extracts of root, stem and leaf. The results showed that the extracts of root, stem and leaf of watermelon have some inhibiting effects on seed germination and enzyme activities of seedlings, such as germination rate, root length, embryonal axis length, root activity, SOD.POD and PPO activities. The abstracts began to restrain seed germination(enzyme activities of seedlings) at 10(20) g/L.The higher the density, the stronger the inhibition. And the effect of leaf is the strongest. It indicates that the self-poisoning effects of watermelon might be one of the reasons for poor natural regeneration and soil degradation of watermelon plantation.The root exudates of watermelon had obvious inhibiting effects on the growth of watermelon seedlings on effecting enzyme activities, enhancing MDA content, weakening photosynthesis. The effect on inhibiting the growth of watermelon seedlings lied in reducing the plant height, root length, leaf numbers, root fresh weight and aerial part weight. Root exudates inhibited the development of watermelon seedlings on reducing root activity, increasing conductance, improving membrane-lipid, reducing SOD activity , chlorophyll content and photosynthesis rate which leaded to the slow growth and even the death of watermelon. Too much root exudates could poison watermelon and lead to continual cropping obstacle.Variation of phenolic acids in root exudates and during decomposition of residuces of watermelon was studied by means of HPLC. The results showed that root exudates contained p-coumaric, ferulic vanillic and cinnamic acid and the contents increased in three weeks, and the content in the third week38was the highest. Root, stem, leaf contained some kinds of phenolic acids such as p-coumaric acid, ferulic acid, vanillic acid and stem and leaf contained cinnamic acid. Stem and leaf contained cinnamic acid. The total phenolic acids contents in the following order, leaf> stem > root. The total phenolic acids contained in the root and stem reached the maximum after 30 days of decomposition, while the leaf in 20-30days. After 40-50 days of decomposition, the total phenolic acids contained in the residuces reached a stable state at low concentration.Cinnamic, p-coumaric, ferulic and vanillic acid, identified from root exudates and residuces of watermelon, effected watermelon germination and seedling root's physiological activities. The effects became strong as the concentration increased. It became to restrain seed germination at 200 mg/L. The four phenolic acids could reduce SOD and root activity, increase PPO and POD activity. The inhibiting effects of cinnamic acid was the highest while vanillic acid was the lowest on seed germination and seedling growth among the four phenolic acids.The ultrastructre of watermelon root tip treated with abstract of leaf, root exudates, cinnamic and p-coumaric acid was observed by EM. At the beginning of the treatment of root exudates and leaf abstract, the starch grain became vacuolizated and disintegrated and disappeared gradually, and so did the vacuole, nucleolus and nucleus membrance at the last period of treatment. The starch grain became...