中文摘要：

【目的】研究喷施不同浓度CaCl2对高温胁迫下烟草叶片光合荧光特性及活性氧清除酶系统的影响,探讨外源Ca^2＋对高温胁迫下烟草叶片光合作用的保护机制。【方法】以烟草品种K326为材料,喷施0、10、20、30mmol·L^-1CaC12,43℃高温处理2h,测定处理前后及恢复1d后烟草叶片光合速率、叶绿素荧光诱导动力学曲线、丙二醛（MDA）含量、过氧化氢（H2O2）含量和抗氧化酶活性等生理指标。【结果】高温胁迫下,CaCl2处理缓解了净光合速率（Pn）和PSII最大光化学效率（Fv/Fm）的降低程度。施钙显著缓解了PSII反应中心电子传递受阻程度和放氧复合体受破坏的程度,使PSII维持较高的活性。施钙明显激活了高温胁迫下烟草叶片超氧化物歧化酶（SOD）、过氧化物酶（POD）、过氧化氢酶（CAT）和抗坏血酸过氧化物酶（APX）的活性,减少了H2O2的积累;膜脂过氧化产物MDA含量显著降低。以喷施20mmol·L^-1CaCl2时,烟草叶片的抗氧化酶活性较高,光合活性最高。【结论】施钙增强了烟草叶片抗氧化酶活性,H2O2的积累降低,从而减轻了高温胁迫对烟草叶片PSII反应中心和放氧复合体（OEC）的破坏,提高了烟草叶片的耐热性。

英文摘要：

[Objective] The effects of CaCl2 on photosynthesis and antioxidative enzyme activities in tobacco under high temperature stress were investigated to reveal the mechanism of external Ca^2＋ enhances the thermotolerance of tobacco plants. [Method] The K326 tobacco plants were sprayed with different concentrations （0, 10, 20, 30） of CaCl2 for four days, at the fifth day exposed to 43℃ for 2 hours, then returned to normal growth condition for one day recovery. Photosynthetic rate, chlorophyll fluorescence transients （OJIP）, MDA content, H2O2 content and the activities of antioxidative enzymes were studied during the process. [Result] Under heat stress, CaCl2 pretreatment greatly reduced the decrease in net photosynthesis rate （Pn） and maximum photochemical efficiency of PS II （Fv/Fm）. Moreover, it alleviated the damage of heat stress to electron transportation of PSII center and oxygen-evolving complex, so that the PSII could maintain high activity. CaCl2 pretreatment also greatly enhanced the activities of SOD, POD, CAT and APX, reduced the accumulation of H202, and thus, the active oxygen species were scavenged efficiently; the accumulation of final product of membrane lipid peroxidation （MDA） greatly decreased. The tobacco plants pretreated with 20 mmol.L^-1 CaCl2 maintained the highest antioxidant enzymes activities and photosynthetic ability. [Conclusion] CaCl2 pretreatment alleviated the heat stress damage to PSII center and oxygen evolving complex via enhancing the antioxidant enzymes activities, reducing the accumulation of H2O2 and protecting the membrane from peroxidation. Exogenous CaCl2 application enhanced thermotolerance of tobacco plants under high temperature stress.