Abstract: In order to explore the photosynthetic mechanism of Osmanthus fragrans suffering from cold damage during overwinter period, this study took fluorescence kinetics as means to monitor the changes in photosystemⅡ(PSⅡ) behavior characteristics of Osmanthus fragrans leaves in Beijing region during overwinter period. The results showed that the initial fluorescence (F0), the biggest photochemical efficiency of PSⅡ(Fv/Fm), effective quantum yield of PSⅡ(yield) and electron transport rate of PSⅡ(ETR) decreased with the temperature falling in winter, indicating the light harvesting antenna system of Osmanthus fragrans leaves was destroyed during the overwintering period, therefore inhibited the initial reaction of photosynthesis. The leaves could reduce the excitation voltage of PSⅡ reaction center by decreasing energy captured by the antenna system. In addition, the photochemical quenching (qP) of Osmanthus fragrans leaves was consistently at a high level, indicating that PSⅡ reaction center could maintain a higher degree of openness in overwinter period, so as to reduce the damage of PSⅡ reaction center by excitation energy accumulation in donor side of PSⅡ. While, the non photochemical quenching (NPQ) remarkably decreased with the temperature falling. Thus, it could be inferred that Osmanthus fragrans could resist low temperature stress in winter mainly through the heat dissipation other than the antenna system.

Key words: Osmanthus fragrans, chlorophyⅡ fluorescence kinetics, photosystemⅡ, photoinhibition, low temperature stress

摘要： 为探究桂花在越冬期间遭受寒害时的光合机理，运用叶绿素荧光动力学手段，监测桂花叶片在北京地区越冬过程中光系统Ⅱ（PSⅡ）行为特征的变化。结果表明：随着越冬过程的推进，初始荧光(F0)、PSⅡ最大光化学效率(Fv/Fm)、PSⅡ有效量子产额(yield)和PSⅡ电子传递速率(ETR)均随温度下降出现同步降低，并表明越冬过程中桂花叶片的捕光天线系统遭受破坏，从而抑制了光合作用的原初反应，桂花叶片通过减小天线系统捕获的光能来降低对PSⅡ反应中心的激发压。另外，桂花叶片的光化学猝灭系数（qP）始终较高，说明PSⅡ反应中心能够在越冬期间保持较高的开放程度，进而减少激发能在PSⅡ供体侧积累对PSⅡ反应中心的伤害；而非光化学猝灭系数（NPQ）伴随温度下降而明显降低，由此可以推断，桂花主要通过天线系统以外的热耗散途径来抵御冬季低温胁迫。

关键词: 桂花, 叶绿素荧光动力学, 光系统Ⅱ, 光抑制, 低温胁迫