胡杨异形叶光抑制发生的PSⅡ行为与光保护机制研究

Populus euphratica Oliv. is ecological keystone species, its existence and development determines the ecosystem structure, function and environmental changes in extremely arid desert. Three typical heteromorphic leaves of P.euphratica were be as research objective and gas exchange, chlorophyll fluorescence were be as probe with combining Western-blotting, biochemical metabolism substances and various treatments of photosynthetic inhibitor, the response of leaf shape adjustment, the characteristics of gas exchange and chlorophyll fluorescence, PSII absorbed light allocation, photosynthetic electron distribution, photorespiration, H2O-H2O cycle, xanthophyll cycle, reactive oxygen and antioxidant substances of heteromorphic leaves to strong light were studied under desert environment and artificial environment. The relationship between D1 protein, LHCII of PSII reaction center and photoinhibition, photosynthetic efficiency were discussed under strong light, and further to analyzed the relationship between xanthophylls’ cycle, D1 protein, water-water circulation ,photorespiration and PSII reaction center and their function of light protection. The forms of light protection, primary-secondary role and coupling coordination mechanism of heteromorphic leaves to defense the light damage under strong light environment were clarified. The difference of light protection mechanism and key mechanism of PSⅡbehavior change of 3 heteromorphic leaves among photoinhibition occurrence were elucidated. Based all above analysis, eco-physiological adaptation mechanisms and survival strategy of P.euphratica heteromorphic leaves at different development stage were revealed. The research results can provide scientific theory for p.euphratica population protection, vegetation restoration and reconstruction of degenerated desert ecosystems in Tarim basin.

生态关键种-胡杨的存在与发展决定着塔里木荒漠生态系统结构、功能与环境变迁。以胡杨异形叶为研究对象，利用光合抑制剂与气体交换、叶绿素荧光、生化代谢物质、蛋白质印迹分析等技术，研究荒漠自然强光(活体)与人工强光(离体)下胡杨异形叶形态调节、气体交换特性与叶绿素荧光参数、叶绿体超微结构、D1蛋白、光呼吸、光合电子传递、PSII吸收光能分配、叶黄素循环组分、活性氧与抗氧化物质对强光的响应；探讨强光下异形叶PSII反应中心D1蛋白、LHCII与光合效率、光抑制发生的关系，分析叶黄素循环、H2O-H2O循环、光呼吸、D1蛋白周转与PSII反应中心的关系及其在光保护中的作用，明确强光下异形叶防御光破坏的光保护途径与主次作用、互补协调机制及差异。阐明异形叶光抑制发生的PSⅡ行为变化的关键机制与光保护机理差异，揭示异形叶发生的生理生态适应机制与生态策略，为荒漠区胡杨种群保护与植被恢复提供科学依据。

荒漠夏季强太阳辐射导致正午胡杨异形叶光合作用发生明显的光抑制，但并未造成PSⅡ反应中心的不可逆破坏。胡杨异形叶在生长发育过程中采取了不同的生理生态策略来适应荒漠强光高温环境。卵形叶多位于树冠外围且暴露于强光照下，其通过提高光能捕获与转化效率、光化学反应能量来保持叶片高光合能力以消耗多余的能量，同时适当降低PSII反应中心开放比例，减少光化学电子传递的份额，加大天线色素热耗散，光抑制程度轻，光能利用率与光合效率高，具最有效的防御光破坏的自我保护机制；锯齿叶PSII反应中心通过减少光能的捕获、增加非光化学荧光猝灭耗散过剩光能来减轻强光对其光合机构的破坏，保持较高光合电子传递能力来缓解光合膜上的还原态压力，主要以热耗散方式清除过剩激发能，通过多种方式协同保护其光合机构免受强光损伤从而维持较高的光合速率，光抑制程度轻，具备有效的光抑制防御保护机制，耐逆性强；条形叶PSII反应中心开放比例大，捕获的光量子转化为化学能的效率高，但暗反应速度慢，来不及消耗过多活跃化学能时导致激发能过剩，且非辐射热耗散效率低，光饱和点低、不耐强光，强光下自我保护机制差，更易发生光抑制甚至光破坏。水-水循环在胡杨异形叶光破坏防御中起主要保护作用，其次为叶黄素循环和光呼吸作用。锯齿叶主要以水―水循环和光呼吸协同耗散过剩激发能来保护光合机构免遭强光破坏，光合效率较高和最耐荒漠强光；卵形叶则主要以水-水循环和叶黄素循环协同保护光合机构，其高量子效率、羧化效率、磷酸丙糖利用效率、PSII实际光化学效率和低光补偿点以及更优的叶氮分配策略是其保持高光合速率的原因；条形叶实际光化学效率、电子传递速率低、用于光化学反应能量少而以高热能、荧光辐射耗散过剩光能，低光合效率及抗逆性差是其被卵形叶、锯齿叶取代的重要原因。此外，胡杨异形叶通过保护酶清除自由基来保护光合机构，其中POD发挥主要作用。

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