中文摘要：

【目的】对接种白粉病菌前后的甜瓜叶片中Ca^2＋进行细胞定位分析，并探讨外源Ca^2＋对白粉病菌胁迫下3种同工酶的影响，为研究甜瓜在白粉病胁迫下的信号转导及抗病机制奠定基础。【方法】通过电镜和细胞化学技术对抗病性不同的甜瓜幼叶在白粉病菌胁迫下的Ca^2＋进行超微细胞化学定位研究，采用Hoagland营养液栽培法，对不同外源Ca^2＋作用并接种白粉病菌的甜瓜叶片的POD、CAT和SOD同工酶进行分析。【结果】接种白粉病菌2d时，Ca^2＋在抗病品种和感病品种叶肉细胞胞质内聚集；液泡和细胞间隙内Ca^2＋水平急剧下降；接种白粉病菌6d后，抗病品种‘MR-1’胞质内Ca^2＋水平又逐渐恢复至接种前的状态，Ca^2＋主要分布在液泡和细胞间隙，而感病品种‘Js’叶肉细胞内Ca^2＋在细胞基质中分布集中并聚集成大的沉淀颗粒，细胞结构逐渐破坏，直至死亡，在液泡和细胞间隙未发生Ca^2＋恢复现象。外源Ca^2＋对3种同工酶谱的作用结果为：与对照相比，营养液增施6mmol·L^-1CaCl2可明显缓解白粉菌对甜瓜的伤害，其POD、CAT和SOD同工酶活性高于对照水平；营养液增施75lnlnol·L^-1的LaCl3显著抑制了甜瓜幼叶POD、CAT和SOD同工酶的活性。【结论】白粉病菌胁迫下，抗病性不同的甜瓜叶片中Ca^2＋的时空定位分布有差异：抗病品种中cCa^2＋由胞内钙库（即液泡）释放入细胞基质，之后又被泵回液泡，而感病品种中Ca^2＋仅发生从液泡向胞质释放的过程；外源Ca^2＋可能增加了Ca^2＋向甜瓜叶片内的运输，促进白粉病胁迫信号向植株体内的传递，提高甜瓜叶片保护酶的表达量及其活性氧清除水平，从而延缓自粉病胁迫对甜瓜叶片的伤害。

英文摘要：

[Objective] The aim of this experiment is to study the uhracytochemical localization of calcium in mesophyll cells of Cucurnis melo L. before and after inoculating Podosphaera xanthii and the effects of exogenous calcium on three isoenzymes of defense enzymes which will be useful for further elucidating the process of calcium signal transduction and resistance mechanism to powdery mildew of melon. [Method] With the method of electron microscope and cytochemistry technology, a hydroponic experiment was carried out to explore the effects of different calcium treatments on isoenzymes of peroxidase （POD）, catalase （CAT） and superoxide dismutase （SOD） in leaves of the melon seedlings under powdery mildew stress. [ Result ] The calcium in mesophyll cells of resistant variety ‘MR-I＇ and in susceptible variety ‘JS＇ gathered in cytoplasm and there were a remarkable increase of calcium level in cytoplasm and reduced greatly in vacuolate and intercellular space when inoculating P. xanthii for 2 d. The calcium localization in leaf cells of ‘MR-I＇ trended to the status as before inoculating when the seedlings were treated for 6 d. However, larger calcium deposited and localized together in the cytoplasm of ‘JS＇ and the structure of mesophyll cells were destroyed until to death and there were no recover of calcium from cytoplasm into vacuolate and intercellular space. Compared with the control, the application 6 mmol·L^-1 CaCl2 in nutrient solution significantly alleviated the stress on the melon leaves system that the activities of SOD, POD and CAT isoenzymes were significantly improved, while application of 75 mmol·L^-1 LaCl3 in nutrient solution significantly inhibited the three isoenzymes activities. [ Conclusion ] Calcium ditribution in leaf cells of C. melo L. changed greatly due to its resistance ability at the stress of powdery mildew. A lot of Ca^2＋was released from Ca^2＋ pool （vacuoles） into cytoplasm, then was pumped return vacuoles in mesophyll cells of resistance variety ‘MR