两个玉米品种维管束鞘叶绿体的非光化学淬灭对干旱胁迫的响应

Response of Non-Photochemical Quenching in Bundle Sheath Chloroplasts of Two Maize Hybrids to Drought Stress

【目的】光系统Ⅱ的非光化学叶绿素荧光淬灭是高等植物响应环境变化最快速的光保护机制,玉米具备叶肉和维管束鞘2种叶绿体结构,本研究通过比较2个玉米品种的光合耐旱能力,探究维管束鞘叶绿体的非光化学淬灭对玉米耐旱性的意义。【方法】以成单30和仲玉3号2个玉米品种为研究材料,设置土壤相对含水量为70%-80%田间持水量(FWC)(充足浇水,对照)、50%-60%FWC(中度干旱胁迫)和35%-45%FWC(重度干旱胁迫)3个土壤水分梯度处理。测定玉米叶片的水分状况、叶绿素含量、活性氧积累、质膜透性和气体交换等参数;应用叶绿素荧光动力学显微成像观测,比较玉米叶肉和维管束鞘叶绿体的叶绿素荧光参数Fv/Fm和NPQ;通过免疫印迹法,分析玉米叶肉和维管束鞘细胞光系统Ⅱ亚基S(PsbS)稳态水平的变化差异;采用蓝-绿胶温和电泳分离,检测玉米光系统Ⅱ蛋白复合体的水平。【结果】干旱胁迫导致叶片气孔导度和蒸腾速率下降,2个玉米品种间没有明显差异。但成单30在重度干旱下表现出更好的水分状况、更低的活性氧损伤以及更高的光合速率。玉米叶肉和维管束鞘叶绿体的NPQ水平及PsbS蛋白含量受干旱诱导明显上升,维管束鞘中的上升更显著,成单30表现尤为突出。不同于仲玉3号光系统Ⅱ蛋白复合体水平的下降,重度干旱胁迫后,成单30的捕光蛋白三聚体水平在叶肉和维管束鞘细胞中均有所升高。【结论】2个玉米品种的光合机构对干旱胁迫的气孔响应能力相当,但相较仲玉3号,成单30的维管束鞘叶绿体具备更优越的非光化学淬灭能力,这对其更强的非气孔限制的光合耐旱性具有积极意义。

【Objective】 Non-photochemical chlorophyll fluorescence quenching(NPQ) of photosystem Ⅱ(PSⅡ) is the most rapid photoprotective mechanism of higher plants that responds to a changing environment. Maize has two distinctly different classes of chloroplasts in mesophyll and bundle sheath cells. In the present study, the drought tolerance of two maize hybrids was compared to explore the significance of non-photochemical quenching in bundle sheath chloroplasts to maize tolerance. 【Method】 The experiment was conducted with two maize hybrids, Chengdan 30 and Zhongyu 3, and consisted of three soil moisture regimes,including 70%-80% of field water capacity(FWC)(sufficient irrigation), 50%-60% FWC(moderate drought stress), and 35%-45% FWC(severe drought stress). Physiological and biochemical parameters of maize leaves, including relative water content, chlorophyll contents, reactive oxygen species(ROS) accumulation, lipid peroxidation, and gas exchange, were measured. Fv/Fm and NPQ of PSⅡ in mesophyll and bundle sheath chloroplasts of two maize hybrids were investigated through a chlorophyll fluorescence kinetic microscope. The steady-state levels of PSⅡ subunit S(PsbS) in mesophyll and bundle sheath cells were analyzed using method of western blotting. PSⅡ complexes levels were detected by blue native PAGE. 【Result】 The stomatal conductance and transpiration rate of maize leaves decreased under drought stress. There were no remarkably difference in decline degree of stomatal index between Chengdan 30 and Zhongyu 3. However, under severe drought conditions, Chengdan 30 showed better leaf water status, lower ROS damages, and higher photosynthetic efficiency compared with Zhongyu 3. NPQ levels and PsbS contents in bundle sheath chloroplasts increased more markedly than that in mesophyll chloroplasts when maize plant suffered with drought treatment, which was especially outstanding in Chengdan 30. The PSⅡ complexes contents of Zhongyu 3 reduced obviously under drought stress, while the steady-state levels of light-harvesting complex Ⅱ(LHCⅡ) trimer of Chengdan 30 enhanced after severe drought. 【Conclusion】 The responses of photosynthetic mechanism to stomatal limitation were no significant difference in two maize hybrids under drought stress. However, compared with Zhongyu 3, Chengdan 30 had a higher non-photochemical quenching capacity in bundle sheath chloroplasts, which might play a positive influence on its superior drought tolerance of non-stomatal limitation.