【作者】 杨广超；

【导师】 张春兰；

【作者基本信息】 南京农业大学 ， 植物营养， 2004， 硕士

【摘要】 本文研究了西瓜残体(根、茎、叶)和西瓜根系分泌物的自毒作用。运用高效液相色谱分析了西瓜根、茎、叶腐解过程中和西瓜根系分泌物中苯丙烯酸、香豆酸、阿魏酸和香草酸的动态变化规律；通过发芽试验和水培法探讨了苯丙烯酸、香豆酸、阿魏酸和香草酸对西瓜种子萌发、西瓜幼苗体内保护酶活性、渗透调节及膜脂过氧化等的影响；通过电镜研究了西瓜幼苗根系在西瓜叶浸提液、根系分泌物和苯丙烯酸、香豆酸作用下的细胞超微结构的变化，探讨了西瓜自毒作用的机理；在此基础上，选用几种有机肥料进行了缓解西瓜自毒作用的研究。研究结果如下： 西瓜植株残体(根、茎、叶)的水浸提液能显著抑制西瓜种子发芽和幼苗生长，降低根系活力，抑制西瓜幼苗体内SOD酶活性，提高了PPO、POD酶活性。当浸提液浓度大于10g／L时，对种子萌发有明显的抑制作用，并随着浓度升高，抑制作用增强。水培过程中，浸提液浓度大于20g／L时，幼苗根部酶活性受抑显著。不同部位相比，西瓜叶浸提液的抑制作用最明显，茎、根次之。 西瓜根系分泌物能显著抑制西瓜幼苗体内保护酶活性，提高MDA含量。西瓜幼苗根系活力下降，养分外渗增加，膜脂过氧化水平提高，叶绿素含量和SOD活性下降，其株高、根长、叶片数、根鲜重、地上部鲜重等生物量指标降低。西瓜幼苗生长受抑，趋向死亡。 经HPLC分析，西瓜根系分泌物中含有苯丙烯酸、香豆酸、香草酸、阿魏酸等酚酸化合物，从第1周到第3周内，香豆酸、香草酸、阿魏酸和苯丙烯酸四种酚酸的绝对含量随时间延长依次增加，各种酚酸量以第3周内为最高。西瓜根、茎、叶在腐解过程中均产生香豆酸、香草酸、阿魏酸等酚酸化合物，茎和叶还产生苯丙烯酸。总酚酸含量为叶＞茎＞根。根、茎在腐解30天时酚酸量达到高峰，叶在腐解20-30天时酚酸量为最高；到40-50天时酚酸量很少，基本稳定。 利用从西瓜残体腐解产物和根系分泌物中检测到的香豆酸、苯丙烯酸、阿巍酸、香草酸作为外源酚酸进行种子发芽和幼苗生长试验，100mg／L的酚酸物质对种子萌发、胚根和胚轴的生长起抑制作用，其抑制作用随着酚酸浓度的增加而增强，当浓度大于200mg／L时抑制作用更加明显。四种酚酸均能降低幼苗根系活力、SOD酶活性，提高POD、PPO酶活性，以苯丙烯酸的抑制作用最为明显，香草酸最小，其它酚酸介于两者之间。西瓜自毒作用极其机制的研究 将西瓜叶水浸提液、苯丙烯酸、香豆酸和根系分泌物处理的西瓜幼苗根系进行电镜观察，在西瓜叶浸提液和根系分泌物处理早期，幼苗根尖分生区细胞内的淀粉颗粒出现不同程度的空泡化现象，并逐渐解体、消失。随着处理时间延长，液泡中出现笋状结构，亦趋向解体;核仁、核膜逐步消失。在苯丙烯酸和香豆酸处理后期，细胞壁较完整，但细胞内残留有细胞器解体后的碎片，核仁、核膜、液泡已基本消失、解体，整个细胞趋向死亡。 施用有机肥改善了西瓜根际土壤微生态环境，增加了土壤细菌和放线菌的数量，减少了病原真菌，增强植株抗病性，促进了西瓜的根系生长，减轻了西瓜的自毒作用，缓解了西瓜连作障碍。更多还原

【Abstract】 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更多还原