外源Ca2+对PEG处理下转C4型PEPC基因水稻光合生理的调节

磷酸烯醇式丙酮酸羧化酶(PEPC)通过固定二氧化碳参与光合作用, 是关键的C₄植物光合作用酶。为了揭示高光效转C₄ PEPC基因水稻(Oryza sativa)对干旱胁迫的适应机理, 以高表达转C₄ PEPC水稻(PC)和野生型水稻Kitaake (WT)为供试材料, 在植株的4-5叶期, 使用不同浓度外源CaCl₂溶液处理, 测定在15%聚乙二醇6000 (polyethylene glycol-6000, PEG-6000)胁迫下叶片相对含水量、光合参数、内源钙总含量、叶片总蛋白激酶活性、PEPC酶活性以及相关基因表达和蛋白质含量。结果表明, 0.5 mmol∙L^-1 CaCl₂明显提高PC叶片相对含水量(P<0.05), 2 mmol∙L^-1和10 mmol∙L^-1 CaCl₂则作用不显著, 对WT则影响不显著。不同浓度钙处理对PEG处理PC的净光合速率影响不显著, 而通过维持气孔导度减少水分胁迫。内源总钙浓度的数据显示, 在PEG6000处理下, PC具有维持稳定内源Ca²⁺浓度的能力, 过高浓度(10 mmol∙L^-1 CaCl₂)钙处理反而降低了PEPC酶活性、PEPC基因表达和可溶性蛋白的含量。

Photosynthetic and Physiological Regulation of C4 Phosphoenol- pyruvate Carboxylase Transgenic Rice (Oryza sativa) by Exogenous Ca2+ Under Polyethylene Glycol Stress

Phosphoenolpyruvate carboxylase (PEPC), a key C₄ photosynthetic enzyme, participates in photosynthesis by fixing CO₂ in C₄ plants. In this study, we aimed to understand the drought-tolerance mechanism of C₄ PEPC transgenic rice with high photosynthetic efficiency. C₄ PEPC transgenic rice plants (PC) and wild-type rice plants (WT) at the 4-5 leaf age were used. Using 15% polyethylene glycol-6000 (PEG) treatment for different days, we investigated leaf relative water content (RWC), net photosynthetic rate (P_n), protein kinase activity, PEPCase activity and PEPC gene expression in leaves of rice plants with different concentrations of CaCl₂. RWC of PC leaf was enhanced with 0.5 mmol∙L^-1 CaCl₂ (P<0.05) except under 2 and 10 mmol∙L^-1 CaCl₂, and factors in the WT were unaffected by exogenous CaCl₂. P_n of PC was not affected by CaCl₂ treatments combined with 15% PEG. Moreover, PC showed an certain capacity for maintenance and stabilization of endogenous Ca²⁺ level in leaves under PEG treatment: with higher exogenous Ca²⁺ treatment (10 mmol∙L^-1), PEPCase activity, PEPC expression and soluble protein were all decreased in PC leaves.