CHLOROPHYLL FLUORESCENCE ANALYSIS OF CYANOBACTERIAL PHOTOSYNTHESIS AND ACCLIMATION

Cyanobacteria are ecologically important photosynthetic prokaryotes th at also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanoba cteria benefit from real-time information on photosynthesis and acclim ation. Monitoring in vivo chlorophyll fluorescence can provide noninva sive measures of photosynthetic physiology in a wide range of cyanobac teria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of k ey structural and functional properties of cyanobacteria. These includ e significant fluorescence emission from the light-harvesting phycobil iproteins; large and rapid changes in fluorescence yield (state transi tions) which depend on metabolic and environmental conditions; and fle xible, overlapping respiratory and photosynthetic electron transport c hains. The fluorescence parameters F-V/F-M. F-V'/F-M', q(p),q(N), NPQ, and phi PS II were originally developed to extract information from t he fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and us ed to extract biologically useful information from cyanobacterial in v ivo chlorophyll fluorescence signals. We describe how the pattern of f luorescence yield versus light intensity can be used to predict the ac climated light level for a cyanobacterial population, giving informati on valuable for both laboratory and field studies of acclimation proce sses. The size of the change in fluorescence yield during dark-to-ligh t transitions can provide information on respiration and the iron stat us of the cyanobacteria. Finally, fluorescence parameters cart be used to estimate the electron transport rate at the acclimated growth ligh t intensity.