水分胁迫下荒漠猪毛菜属C3-C4中间型植物光合碳同化途径的适应性机理研究

Water is one of the important environmental factors which affects the survival, growth and distribution of desert plants. C3-C4 intermediate plants have the particular leaf structures and photosynthetic physiological and biochemical characteristics. They provide a new view of understanding the transition of photosynthetic carbon assimilation pathway from C3 to C4 under water stress. In this study, four species including two C3-C4 intermediate species, Salsola laricifolia and Salsola arbusculiformis, and C3 species Salsola junatovii and C4 species Salsola arbuscula as controls, are studied using water-stressed test. Leaf microstructure and ultrastructure, photosynthetic physiological characteristics and water use efficiency are researched under water stress, with a focus on the following aims: 1) identifying whether the C3-C4 intermediate plants adapt to water stress by enhancing the expression levels of the C4 photosynthetic pathway through changes of leaf strctures and photosynthetic physiological characteristics; 2) comparing the differences of photosynthetic carbon assimilation pathway among C3, C4 and C3-C4 intermediate plants under water stress; 3) exploring adaptative mechanism of plant photosynthetic carbon assimilation of C3-C4 intermediate plants under water stress. The expected results will contribute to understanding adaptative strategies of the desert C3-C4 intermediate plants in arid environments, and studying intensively how desert plants response to environmental factors and their adaptive mechanisms.

水是影响荒漠植物生存、生长和分布的重要环境因子。C3-C4中间型植物特有的叶片结构和光合生理生化特性，将为全面理解植物应答水分胁迫时光合碳同化途径的适应性变化提供新的视野。本研究以荒漠C3-C4中间型植物松叶猪毛菜和白枝猪毛菜为研究对象，C3植物天山猪毛菜和C4植物木本猪毛菜为对照，通过水分胁迫试验研究水分胁迫下植物的叶片显微、超微结构、光合生理特性和水分利用效率，明确C3-C4中间型植物是否通过增强C4光合途径的表达程度来适应水分胁迫，并通过调整植物叶片结构和光合生理特征来适应；揭示水分胁迫下C3-C4中间型植物和C3、C4植物的光合碳同化途径的适应性变化的差异；探讨水分胁迫下C3-C4中间型植物光合碳同化途径的适应性变化规律。预期成果有助于理解荒漠C3-C4中间型植物在干旱环境下的适应策略，对深入研究干旱区植物响应环境因子及其适应机制具有重要意义。

松叶猪毛菜是典型的荒漠C3-C4中间型植物，具有区别于C3/C4植物特有的结构功能。通过分析水分胁迫下植物叶片超微结构、光合生理特性和水分利用效率，明确水分胁迫下松叶猪毛菜光合碳同化代谢途径的适应特征，以及与C3植物天山猪毛菜和C4植物木本猪毛菜的适应差异。研究结果表明：①不同程度干旱胁迫下C4植物木本猪毛菜叶片叶绿体和线粒体受损程度都最低。天山猪毛菜和松叶猪毛菜叶绿体在不同程度干旱胁迫下的受损程度大致相似，不同之处在于，松叶猪毛菜线粒体对干旱胁迫的耐受力要比叶绿体强，而天山猪毛菜线粒体在中度和重度干旱胁迫时都受到较严重的损伤。②C3植物天山猪毛菜和C3-C4中间型植物松叶猪毛菜都通过增强C4酶活性来抵御干旱胁迫。在一定程度干旱胁迫下，两种植物叶片PEPC活性均增加，不同之处在于天山猪毛菜和松叶猪毛菜分别通过增强NAD-ME和NADP-ME活性来适应干旱。C4植物木本猪毛菜通过保持叶片较高的PEPC酶活性来适应干旱胁迫。③干旱胁迫下天山猪毛菜和松叶猪毛菜PEPC活性（在pH7.3下测定）的增加可能是由PEPC酶磷酸化程度的增强、mRNA转录水平的增加和PEPC蛋白表达水平的提高综合引起的，而木本猪毛菜PEPC活性（在pH7.3下测定）的增加可能由PEPC酶磷酸化程度的增强造成的。④3种植物叶片PEPCK对干旱胁迫的响应是一致的，基本不受干旱胁迫的影响，并且在正常供水情况下，3种植物叶片PEPCK活性差异不大，这也从酶活性的角度说明，PEPCK酶可能还有其他的功能，而不是在C4循环中起作用。⑤干旱胁迫对木本猪毛菜的δ13C值影响不大。对于C3植物天山猪毛菜和C3-C4中间型植物松叶猪毛菜来说，一定程度的干旱胁迫诱导δ13C值升高，但是在目前研究的干旱胁迫下，天山猪毛菜和松叶猪毛菜的C3光合途径仍然起到主导作用，其δ13C值处于C3植物范围内。本研究成果有助于理解荒漠C3-C4中间型植物在干旱环境下的适应策略，对深入研究干旱区植物响应环境因子及其适应机制具有重要意义。