调制式荧光影像新技术:叶片内部最大光化学量子效率及其异质性的活体测定

A new technology of modulated Chl a fluorescence image: In vivo measurement of the PSII maximum photochemical efficiency and its heterogeneity within leaves

研究叶片内部光合能力及其异质性,是光合作用生化模型、光抑制机理、光保护机理等光合生理生态热点问题的重要前提,但目前缺少可以进行活体测定的装置。该文作者对Vogelmann和Evans(2002)的装置进行了改进,获得了叶片内部光系统II(PSII)最大光化学量子效率(F_v/F_m)及其异质性影像,并采用基于Matlab软件自编的图像处理程序对其进行了分析,研究了不同时间光抑制处理导致的叶内F_v/F_m及其异质性的变化。研究发现:叶片内部不同层叶肉组织F_v/F_m存在异质性。强光照射导致叶片内部不同层叶肉组织F_v/F_m值下降,但靠近上表皮的栅栏组织具有较强的抗光抑制能力。光抑制导致叶片内部F_v/F_m异质性的变化,短期光抑制导致F_v/F_m异质性变大,这可能与部分叶绿体避光运动相关,长期光抑制导致F_v/F_m异质性变小,说明叶绿体避光运动这种光保护机制已经失效。相比于其他类型叶绿素荧光仪,此装置可以完整获得活体叶片内部F_v/F_m及其异质性影像数据,这对于系统研究叶片内部光合能力及其异质性机制,以及为进一步研究一些光合生理生态热点问题提供了有力工具,具有进一步研发和应用的前景。

The spatial photosynthetic heterogeneity within leaves is an important prerequisite for the studies on the photo-synthetic model, the mechanism（s） of photoinhibition and light protection, etc. However, currently the in vivo measurement of the spatial photosynthetic heterogeneity within leaves is difficult. The present study improved the device assembled by Vogelmann ＆amp; Evans （2002）, thereby acquired the photosystem II （PSII） maximum photo-chemical efficiency （Fv/Fm） images within leaves. Finally, these images were processed and data of Fv/Fm and its spatial variations could be obtained, with the aid of MATLAB software. Based on the innovative technique, an investigation of the effects of strong light on the Fv/Fm and its spatial heterogeneity within leaves has been carried out. It was found that Fv/Fm within leaves was not homogonous. Strong light led to a general decrease of Fv/Fm （PSII photoinhibition） across leaf section, and the palisade tissue close to the epidermis layer had high tolerance to photoinhibition. Compared with control, short-term photoinhibition caused a larger spatial variation of Fv/Fm within leaves, which may be related to the chloroplast-avoidance response induced by high-fluence. On the con-trary, long-term light inhibition led to a smaller spatial variation of Fv/Fm within leaves, indicating such mecha-nism is no longer effective. Compared to other types of chlorophyll fluoremeter, the device in the present study can in vivo obtain the panoramic picture of Fv/Fm within leaves, providing a powerful tool for the studies on the mechanism（s） attributed to the spatial heterogeneity of photosynthetic capacity of leaf, which is critical for the understanding on several hot spots in the research field of photosynthesis.