Electron Transport Processes
Imaging of chlorophyll a fluorescence: theoretical and practical aspects of an emerging technique for the monitoring of photosynthetic performance
Department of Biological Sciences, John Tabor Laboratories, University of Essex, Colchester, Essex CO4 3SQ, UK
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Abbreviations: adc, analogue to digital converter; CCD, charge coupled device; Chl, chlorophyll; F', Chl a fluorescence level at any point between F'o and F'm; Fm, maximal Chl a fluorescence level from a dark-adapted sample; F'm, maximal Chl a fluorescence level from sample in light; Fo, minimal Chl a fluorescence level from a dark-adapted sample; F'o, minimal Chl a fluorescence level of sample in light; F'q, difference in Chl a fluorescence between F'm and F' (F'q = F'm – F'); Fv, variable Chl a fluorescence level from a dark-adapted sample (Fv = Fm – Fo); F'v, variable Chl a fluorescence level from a light-adapted sample (F'v = F'm – F'o); PSII (I), Photosystem II (I); QA, primary quinone acceptor of PSII.
The development of chlorophyll (Chl) a fluorescence imaging systems has greatly increased the versatility of Chl a fluorometry as a non-invasive technique for the investigation of photosynthesis in plants and algae. For example, systems that image at the microscopic level have made it possible to measure PSII photochemical efficiencies from chloroplasts within intact leaves and from individual algal cells within mixed populations, while systems that image over much larger areas have been used to investigate heterogeneous patterns of photosynthetic performance across leaves and in screening programmes that image tens or even hundreds of plants simultaneously. In addition, it is now practical to use fluorescence imaging systems as real-time, multi-channel fluorometers, which can be used to record continuous fluorescence traces from multiple leaves, plants, or algal cells. This paper discusses some of the theoretical and practical issues associated with the imaging of Chl a fluorescence and with Chl a fluorometry in general. This discussion includes a review of the most commonly used Chl a fluorescence parameters.
Key words: Chlorophyll fluorescence, imaging, photochemistry, photosynthesis.
Source: Journal of Experimental Botany, Vol. 55, No. 400, pp. 1195-1205, May 1, 2004.