钙提高烟草叶片光合作用对高温的耐性#
 

摘要：本文研究喷施20 mMCaCl2 对高温胁迫下烟草叶片光合荧光特性及抗氧化酶活性的影响。结果表明：高温胁迫降低了净光合速率(Pn)、气孔导度、表观量子效率（AQY）和羧化效率（CE）。高温胁迫同样导致了原初最大光化学效率（Fv/Fm）。而喷施CaCl2 提高了高温胁迫下的Pn、AQY、CE 和Fv/Fm。高温胁迫降低了超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)和过氧化物酶(POD)的活性，而CaCl2预处理后，这些酶活性降低的幅度较小或者活性升高。高温处理后，谷胱甘肽还原酶（GR）活性升高，而CaCl2预处理显著增加了其升高幅度。CaCl2 预处理降低了高温胁迫下H2O2 和O2-的明显积累，且进一步提高了高温胁迫下热激蛋白（HSP70）的积累。以上结果表明，CaCl2 预处理提高了烟草叶片的光合作用，这可能与气孔导度的维持和放氧复合体耐热性的提高有关，而后两者可能与活性氧的积累较低有关。
 

关键词：光合作用；CaCl2；高温胁迫；耐热性；烟草 (Nicotiana tabacum L.)

0 引言
由于全球变暖和气候改变，高于正常条件10–15 oC 的热激或高温胁迫已经对全球的作物生产造成严重的威胁[1]。许多研究表明Ca2+ 参与了植物对许多环境胁迫的响应调节，包括高温 [2]。高温胁迫下胞质Ca2+增加，可能减轻了热伤害，使植物细胞能够更好的生存[3]。已经报道，外源Ca2+ 提高了许多植物的耐热性，可能与较高的抗氧化酶活性和细胞膜的脂质过氧化作用较低有关[4-6]。 外施Ca2+能够抑制高温胁迫下叶绿素的降解，可能是因为其降低了光氧化[7]，或者是维持了膜的完整性 [8]。Ca2+ 处理也提高了高温胁迫下热激蛋白的合成，如HSP26、HSP70 [9]50 。 Schöffl et al. (1999)的研究表明细胞和组织耐热性的提高几乎全部依赖于HSP70 的诱导[10]。然而psbU 基因突变的藻类（Synechococcus）中， HSP70 并没有受影响[11]。

光合作用是植物对高温最敏感的生理过程之一，光系统II（PSⅡ）是光合作用过程中对高温最敏感的部位，高温胁迫可以抑制放氧和PSII 活性[12]。但是关于外源CaCl2 对高温胁迫下烟草叶片光系统II受体侧及放氧复合体的影响，特别是外源CaCl2提高耐热性与光合作用维持的关系研究较少。本文通过研究CaCl2 预处理提高烟草耐热性，探讨外源钙提高高温胁迫下植物光合作用。

4 结论
由以上结果，我们总结了CaCl2 处理提高烟草耐热性，可能主要是因为以下几个方面：(1) 较高气孔导度的维持，可能与较高的光合速率有关；(2) 放氧复合体和PSII 反应中心耐热性的提高可能是由于ROS 积累的较少，而后者与抗氧化酶活性的提高有关；(3) 较高的HSP70 水平可能对其高温胁迫下耐性的提高有关。

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