Using Chlorophyll a Fluorescence Imaging to Monitor Photosynthetic Performance

Chlorophyll (Chi) a fluorometry is now well established as a non-invasive technique for the investigation of photosynthesis in plants and algae. In recent years, the versatility of this technique has been increased significantly by the development of Chi a fluorescence imaging systems. For example, high resolution systems make it possible to compare Photosystem (PS) II photochemical efficiency from chloroplasts within guard and mesophyll cells and from individual algal cells within mixed populations, while lower resolution systems can be used to investigate heterogeneous patterns of photosynthetic performance across leaves. In addition, it is now practical to use fluorescence imaging systems as real-time, multi-channel fluorometers, which can be used to screen large numbers of plants or to record continuous fluorescence traces from multiple leaves or algal cells. This chapter describes the theoretical and practical issues associated with imaging, both at high resolution (at the level of individual algal cells and chloroplasts within plant cells) and at low resolution (whole leaves and the screening of large numbers of plants). After a brief introduction, a section on the theoretical background to Chi a fluorometry concentrates on those aspects that are of particular relevance to imaging. This is followed by a section which covers a number of technical issues. Next, a range of examples are provided, to illustrate how Chi a fluorescence imaging can be used in physiological investigations. The final section considers the immediate future of this technique.