Chlorophyll a Fluorescence in Cyanobacteria: Relation to Photosynthesis

Abstract In this chapter, we focus on the use of chlorophyll (Chl) a fluorescence to study various photosynthetic processes and their regulation in cyanobacteria. Compared to algae and plants, thylakoid membranes of cyanobacteria not only have photosynthetic, but also respiratory electron transport components. Further, they have phycobilisomes (containing phycobilins) as outer antenna complexes, instead of Chl-containing light-harvesting complexes. We shall present here the use of Chl a fluorescence in monitoring: (a) excitation energy transfer to and in both the photosystems; (b) quantum yield of photosystem II, as inferred from the ratio of variable ( F V ) to maximum ( F M ) Chl a fluorescence, and its relation to overall photosynthesis; (c) regulation of photosynthesis, especially that of excitation energy distribution between the photosystems (the so-called state transitions); and (d) nonphotochemical quenching of the excitation energy. We will end this chapter by presenting the challenges in using Chl a fluorescence to monitor various photosynthetic processes in cyanobacteria.