高温强光对温州蜜柑叶绿素荧光、D1蛋白和Deg1蛋白酶的影响及SA效应

Effects of high temperature and strong light on chlorophyll fluorescence,the D1 protein,and Deg1 protease in Satsuma mandarin,and the protective role of salicylic acid

以3年生温州蜜柑(Citrus unishiuMarc.)植株为试材,用叶绿素荧光分析、Western-blotting蛋白质印记技术及DAB(3,3′-二氨基联苯胺)显色法,研究了高温强光(38℃和1600μmo.lm-.2s-1)对叶片叶绿素荧光参数、PS(光系统)Ⅱ反应中心D1蛋白和Deg1蛋白酶的影响和SA(水杨酸)的效应。结果表明,高温强光交互作用4 h后,叶片的初始荧光Fo升高,最大光能转化效率Fv/Fm、表观光合电子传递速率ETR及PSⅡ的量子产额ΦPSⅡ显著降低;在D1蛋白降解的同时,Deg1蛋白酶含量也下降,并伴有H2O2的积累。在高温强光下,外源的H2O2使叶绿素荧光动力学快相参数(Fi-Fo)/(Fp-Fo)值(反映PSⅡ中QB非还原中心的数量)升高和I-P的斜率(反映PSⅡ活化中心还原态QA积累的值)下降,Fv/Fm、ETR、ΦPSⅡ及D1蛋白和Deg1蛋白酶下降幅度增大;而外源的SA使这些参数下降幅度减小。这些结果说明,高温强光诱导H2O2的积累造成Deg1蛋白酶和光系统反应中心D1蛋白的降解,Deg1蛋白酶的减少也进一步限制了D1蛋白的周转,进而使温州蜜柑PSⅡ反应中心遭到破坏,SA对光合机构光破坏有保护作用。

Photosynthesis is the key physiological process for crop yield and quality.Environmental stresses,especially light and temperature stresses,are important limiting factors for photosynthesis.Light and heat stress often co-occur under natural conditions,especially during day time in summer when temperatures and light intensity can reach 30—40℃ and 1000—2000 μmol · m-2 · s-1,respectively.Such combined stresses severely restrict growth and photosynthesis of plants in many regions of the world,and have more severe effects than either stress alone.Satsuma mandarin（Citrus unshiu Marc.） is widely cultivated in the Yangtze River Valley.For growth of citrus species,the optimum temperatures are between 22 and 30℃,and the saturation light intensity ranges from 600 μmol · m-2 · s-1 to 800 μmol · m-2 · s-1.The decreased photosynthesis resulting from high temperatures and strong light has become a serious problem for citrus cultivation because of decreased yield.Although the effects of high temperature or strong light on photosynthesis have been studied,less is known about their combined effects on photosynthesis.We selected 3-year-old Satsuma mandarin plants to study the effects of high temperature（38℃） and strong light（1600 μmol · m-2 · s-1） on chlorophyll fluorescence parameters and the relative contents of D1 protein（the reaction center protein of photosystem Ⅱ） and Deg1 protease in leaves.Fluorescence parameters were measured using a chlorophyll fluorometer,the D1 protein and Deg1 protease were analyzed by Western-blotting,and hydrogen peroxide（H2O2） was detected using the 3,3-diaminobenzidine-uptake method.We also investigated the effects of exogenous hydrogen peroxide（H2O2） and salicylic acid（SA） on leaf parameters under high temperature and strong light.The results showed that the initial fluorescence（Fo） significantly increased when Satsuma mandarin leaves were exposed to high temperature and strong light for 4 h,whereas the maximal photochemical efficiency of PSⅡ（Fv/Fm）,electron transport rate（ETR） and quantum yield of PSⅡ（ΦPSⅡ） decreased.The relative content of Deg1 protease decreased when the D1 protein degraded,while simultaneously,H2O2 accumulated in the leaves.Analysis of the fast phase of chlorophyll fluorescence kinetics showed that exogenous H2O2 increased the（Fi-Fo）/（Fp-Fo） value（the number of non-reductive QB centers in PSⅡ）,but decreased the slope of Fi to Fp（the redox state of QA in the activation center of PSⅡ）.Thus,exogenous H2O2 increased the PSⅡ photoinactivation ratio.The Fv/Fm,ETR,ΦPSⅡ,and relative contents of D1 protein and Deg1 protease also decreased,compared with their respective values in the control.These parameters include： the slop from Fi to Fp,（Fi-Fo）/（Fp-Fo）,Fv/Fm,ETR,ΦPSⅡ,and relative contents of D1 protein and Deg1 protease were somewhat decreased by exogenous SA under high temperature and strong light.These results suggested that the accumulation of H2O2 induced by high temperature and strong light caused the net contents of D1 protein and Deg1 protease to decrease by inhibiting protein synthesis,and the decrease in Deg1 protease further limited the D1 protein turnover,which resulted in damage to the PSⅡ reaction center in Satsuma mandarin leaves.These results also indicate that exogenous SA could protect the photosynthetic apparatus against photo-damage in Satsuma mandarin leaves.