【目的】探讨高温对连翘离体叶圆片光系统Ⅱ活性和叶黄素循环脱环化程度的影响，揭示热胁迫下连翘叶片光合机构的行为特征，充实植物光能高效利用研究领域。【方法】以连翘为供试材料，在功能叶片主叶脉两侧打取直径为1 cm的叶圆片，采用热胁迫温度(26，31，34，37，40，43，46，49和52℃)和时间(5，25和45 min)组合处理，之后于26℃室内环境中暗适应30 min，利用叶绿素成像荧光仪( MINI-IMAGING-PAM)和 QE65光谱仪分别进行叶绿素荧光参数和漫反射率的测定。【结果】在5，25，45 min热胁迫下，连翘叶片 PSⅡ光化学活性 Fv/Fm 和实际光化学量子产量 Y(Ⅱ)开始显著降低的温度分别为43，37，37℃和43，31，31℃。随着热胁迫温度和时间的增加，呈现出暗适应下最小荧光 Fo 和光化学荧光猝灭系数 qP 先减后增的变化、暗适应下最大荧光 Fm 大幅度降低、开放的 PSⅡ反应中心的激发能捕获效率 F'v/F'm和 PSII 电子传输活性 Fm/Fo 迅速降低、调节性能量耗散量子产量 Y ( NPQ)与非调节性能量耗散的量子产量 Y( NO)和值的趋饱和增加、PSⅡ与 PSⅠ间的激发能分配不平衡偏离系数β/α－1先增后降的变化趋势。另外，叶黄素循环脱环化程度负相关的 PRI与 Y( NO)呈现相反变化趋势。【结论】在长时间较高的热胁迫温度下，连翘叶片的热胁迫伤害不仅会发生在PSⅡ蛋白复合体的多个位点，也会发生在整个光合机构，还会从暗反应的酶活性衰减转向 PSⅡ活性衰减；同时，对热胁迫伤害的协调保护机制，一方面表现在过剩的激发能量会从以调节性能量耗散 Y( NPQ)为主转向非调节性能量耗散 Y( NO)为主，另一方面也可能会表现在通过调节 PSⅡ与 PSⅠ之间激发能分配平衡性的天线系统的状态转换上。%Objective]In this study,we investigated the effects of high temperature on photosystemⅡkinetics activity and de-epoxidation level of xanthophyll cycle components in leaves of Forsythia suspensa to reveal the behavioral characteristics of photosynthetic apparatus under heat stress,and thereby enrich the research field on plant efficient utilization of light energy. [Method]The leaf discs collected from near the midrib of F. suspensa leaves were used as the material and subjected to nine different temperature levels (26 ℃,31 ℃,34 ℃,37 ℃,40 ℃,43 ℃,46 ℃,49 ℃and 52 ℃) with three different treatment time levels (5 min,25 min and 45 min) . After the treatments,the leaf discs were maintained in darkness for 30 minutes at 26 ℃,and then their chlorophyll fluorescence parameters were measured using MINI-IMAGING-PAM system and their diffusing reflectance was tested by QE65 spectrometer,respectively.[Result]The maximal photochemical efficiency (Fv/Fm) obviously decreased at 43 ℃,37 ℃ and 37 ℃,respectively treated for 5min,25min and 45min,while the actual photochemical efficiency (Y(Ⅱ)) decreased steadily,at 43℃, 31℃ and 31℃ under the heat stress time of 5 min,25 min and 45 min. With the increase of treatment temperature and time,the minimum fluorescence of dark adaptation (Fo) and the photochemical fluorescence quenching coefficient (qP) firstly increased and then decreased; The maximum fluorescence of dark adaptation ( Fm ) decreased significantly; The efficiency of excitation energy capture by open PSⅡreaction centers ( F’v/F’m ) and the electronic transport activity of PSII (Fm/Fo) reduced sharply; The sum of the quantum yield of regulated energy dissipation (Y(NPQ)) and the quantum yield of nonregulated energy dissipation ( Y( NO) ) increased with a trend to saturation; The relative deviation from full balance between PSⅡand PSⅠ(β/α-1 ) presented a sudden rise firstly and then sudden drop tendency. However the photochemical reflectance index ( PRI) and Y( NO) showed the opposite trend.[Conclusion]The heat stress not only led to multiple sites injury of PSII protein complexes,but also destroyed the photosynthetic apparatus under a longer-time treatment with higher temperatures condition. In addition,the stress also turned the limiting factor from enzyme activity decay in dark reaction to PSⅡactivity decay. At the same time,the protection mechanisms against heat stress changed from Y( NPQ) to Y( NO) as the main form of energy dissipation,on the other hand,the protection mechanisms might also present by adjusting a balance of excitation energy between PSⅡand PSⅠin the form of state transition of antenna system.
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