温州蜜柑叶片光合作用光抑制的保护机理

晴天条件下，使用便携式调制荧光仪和分光光度计观察了温州蜜柑叶片光合作用光抑制发生过程中几个主要荧光参数（初始荧光F0、最大荧光Fm、PSⅡ的光化学效率Fv/Fm、非光化学猝灭qN及其快相qNf和慢相qNs）、电子传递速率（ETR）和玉米黄素相对含量的日变化，结果表明，随着光强的增强，ETR、qN及其qNr与qNs以及玉米黄素相对含量升高，Fv/Fm、Fm和F0下降。用DTT处理后，qNs较对照明显下降，F0较对照明显上升，可以认为，柑橘在光合作用日变化中存在依赖于叶黄素循环和类囊体膜质子梯度两种非辐射能量耗散方式，而且它们在防御光破坏方面起着重要作用。

Protective mechanism in photoinhibition of photosynthesis in Citrus unshiu leaves

By using a portable PAM-2000 fluorometer and a spectrophotometer (722 Model), the diurnal variation in main chlorophyll fluorescence parameters such as initial fluorescence (F0), maximal fluorescence (Fm), ratio of variable fluorescence to maximal fluorescence (Fv/Fm), non-photochemical quenching (qN), fast-phase (qNf) and slow-phase (qNs) of non-photochemical quenching, electron transport rate (ETR), and relative content of xeaxanthin in Citrus unshiu leaves were observed on fine days. The results showed that ETR, qN, qNf, qNs and relative content of xeaxanthin increased with increasing light intensity, but Fm, F0, photo-chemical efficiency of PS II (Fv/Fm) decreased. After treated by DTT, qNs was much lower, but F0 was much higher than control. These results indicated that xanthophyll cycle and delta pH existed, and played an important protective role against photo-damage to the photosynthetic apparatus in Citrus unshiu leaves during diurnal variation of photosynthetic efficiency.