【作者】 曾光辉；

【导师】 郭延平；

【作者基本信息】 浙江大学 ， 果树学， 2004， 硕士

【摘要】 以一年生‘荸荠’种杨梅(Myrica rubra Sieb. et Zucc.)盆栽苗为试验材料，测定了杨梅在自然光强和模拟光强下的光合特征和叶绿素荧光参数，对强光下杨梅叶片是否容易发生光合作用的光抑制有了初步的了解，并进一步探讨除光以外再没有任何其它胁迫条件下发生光抑制的可能机理以及杨梅叶片对强光胁迫的一些防御机制，为寻找能减轻光抑制，提高植物逆境光合能力的有效途径和方法提供了理论依据。主要研究结果如下： 一、杨梅叶片光合和荧光的日变化 晴天条件下，杨梅叶片净光合速率(Pn)和表观量子效率(AQY)的日变化呈双峰型，上午9：00左右达到最大值，随后随光强增加而下降，到下午13：00左右达最低值，此后随光强减弱而缓慢回升，至15：00左右达到次高峰，自然条件下杨梅叶片Pn的午间降低但Ci／Ca并未降低反而略有升高，说明非气孔因素是限制杨梅光合作用的主要因素。杨梅叶片光系统Ⅱ(PSⅡ)的最大光化学效率(Fv／Fm)的日变化呈“V”字型，上午Fv／Fm随光照的增强而降低，至13：00左右达最低值，其后随着光强的减弱Fv／Fm缓慢恢复。同时AQY、Fm和Fv／Fm的下降，说明杨梅叶片在中午高光强下Pn下降主要是由光抑制引起。 二、室内模拟强光胁迫下杨梅叶片的光抑制 室内模拟强光胁迫条件下，杨梅叶片的光抑制程度随着强光照射时间的延长而加重。在强光胁迫4h期间，随着强光胁迫时间的延长，杨梅叶片的Pn和Gs进一步下降，同时Ci上升。Fm、Fv／Fm及Fm／Fo下降；光系统Ⅱ的量子产量(△F／Fm′)、电子传递速率(ETR)、光化学猝灭系数(qP)、光适应下光系统Ⅱ的最大光化学效率(Fv′／Fm′)先上升后下降，与此相反，初始荧光(Fo)及非光化学猝灭系数(qN、NPQ)先下降后上升；荧光快相诱导动力学曲线的Fi-Fo和I—P的斜率下降。但是它们在暗处恢复10～20h后，其值接近正常值，说明仅强光逆境引起的光抑制是可逆的。强光照射2 h时，非光化学猝灭的qNf、qNm和qNs变化不大；强光照射4 h时，qNm升高，而qNf和qNs下降。用二硫苏糖醇(DTT)阻断玉米黄素(Z)的形成后，光抑制程度大大加深，说明与叶黄素循环有关的非辐射能量耗散的增加是产生光抑制的原因之一。10:的破坏作用十分明显，表现为强光胁迫下杨梅u一卜片!O:的生成与处理时I’ll]具了J’显著的正相关。强光胁迫使杨梅叶片中的小PSIF中CO:明显升高。 三、杨梅叶片对强光胁迫的防御 根据实验结果，我们认为非气孔因素是限制杨梅光合作用的主要因素，强光胁迫使杨梅叶片的PSll反应中心可逆失活。在受强光胁迫2小时内，以水一水循环(WWC)为主的多种电子传递途径是杨梅叶片早期响应强光胁迫的一条重要措施。强光胁迫2小时后，随102生成的持续增加，QA的过度还原，加重了杨梅叶片Psll反应中心可逆失活或破坏，导致光化学反应下降及NADPH和ATP的形成减少，因而以叶黄素循环为主的热耗散成为杨梅叶片防御光抑制的主要途径。同时，我们的实验也说明状态转换在耗散过剩光能方面可能具有重要的作用，但目前来说还只处于推测阶段，具体机制还有待于进一步的研究。更多还原

【Abstract】 The one-year-old Myrica rubra were used to research the effects of high light stress on photosynthetic characteristics, chlorophyll fluorescence parameters. In order to find a possible approach or method in theory to improve plant photosynthetic capability through lowering photoinhibition on stress conditions, the effects of high light stress on the operation of photosynthetic apparatus and the different photoprotective mechanism induced by photoinhibition in leaves of Myrica rubra were studied. Some novel and significant results have been obtained as the followings:1. The diurnal variation of gas exchange parameters and chlorophyll fluorescence parameters in Myrica rubra leavesOn sunny day, the net photosynthetic rate (Pn) apparent quantum yield (AQY) and maximal photochemical efficiency of PSII (Fv/Fm) of Myrica rubra leaves decreased after exposed to midday high irradiance, this indicated that photoinhibition of photosynthesis already occurred in Myrica rubra leaves. The diurnal changes of Pn and AQY was two-peaked curve. It reached the maximum values at about 9:00, then declined gradually in the morning, and reached the lowest values at about 13:00 then increased with the decrease of incident light intensity and reached the second peak at about 15:00. But accompanying with the consistent decline of Pn and stomatal conductance (Gs) in the afternoon, the level of intercellular CO2 concentration (Ci) increased. This means that non-stomatal limitation was the main cause of the decrease of photosynthesis under high light stress. The diurnal change of Fv/Fm was the same as "V". In the morning, the Fv/Fm ratio kept on decreasing until it reached its minimum at 13:00, while the reverse change occurred in the later afternoon.2. the photoinhibition of photosynthesis in Myrica rubra leaves under simulated high lightUnder high light (1300umol-m-2 s-1) , Pn Gs decreased, whereas Ci was increased with increasing time of treatment in Myrica rubra leaves, and the chlorophyll fluorescence parameters Fm/Fo Fv/Fm Fm decreased along with the increase of time. Quantum yield of PSII photochemistry (F/Fm ) , linear electron transport rate (ETR) photochemical quenching coefficient (qP) and photochemical efficiency of PSII in the light (Fv’ /Fm’ ) increased within two hours, then decreased. On the contrary, minimal fluorescence intensity (Fo) and non-photochemical quenching coefficient (qN . NPQ) decreased within twohours, then increased. Fi-Fo and the slope of I-P in fluorescence induction kinetic curve declined. Recovery at low light for 10~20 hours, these parameters were recovered partly or completeness. The reduction of zeaxanthin content and enhancement of photoinhibition of photosynthesis after dithiothreitol (DTT) pretreatment suggested that xanthophyll cycle-dependent nonradiation energy dissipation was one of the mechanisms of photoinhibition. At high light stress, PSii / CO2 was elevated obviously. Accompanying with the consistent increase of time, the level of singlet oxygen (1O2) increased. After high light for 4 hours, qNm increased, while qNf and qNs declined.3. the mechanisms of photoprotection against photoinhibition in Myrica rubra leaves These results indicated that the photoinhibition was existed in Myrica rubra leaves under conditions in the absence of any environmental stress other than high light. Photoinhibition only induced by high light is reversible. During the early phase of high light stress, there were alternative electron pathways including water-water cycle in Myrica rubra leaves. On the other hand, during the latter phase of the treatment, PSH reaction center was destroyed by 1O2 and irreversibly inhibited, the proportion of opened photosystem II reaction center was decreased, the electron translate of QA- QB was limited, the number of electron used to carbon fixation reduced, the photo energy dissipated by heat was increased. The above results illustrated that xanthophyll cycle was the major protective mechanism to preventing from the deteriorated effects of stron更多还原