Tracking the light environment by cyanobacteria and the dynamic nature of light harvesting.

In nature photosynthetic organisms cope with fluctuating light conditions. Light intensity and quality vary dramatically during the day or from one habitat to another. Photosynthetic organisms sense intensities and wavelengths of light both directly and indirectly. Because light fuels photosynthetic electron transport and CO2 fixation, it is the primary determinant of levels of NADP/ NADPH, ATP, and carbon metabolites, all of which can serve to modulate cellular processes. Light is also absorbed by photoreceptors that link light cues to cellular metabolism. However, light represents a single environmental cue, and other signals interact with light through a web of regulatory circuits that result in dynamic acclimatory responses. This review focuses on two specific aspects of light-influenced processes in Cyanobacteria; both concern changes in light harvesting structure and biosynthesis. The first part of this review discusses effects of changing wavelengths of light on the biosynthesis of the phycobilisomes (PBS), dominant light harvesting complexes of Cyanobacteria. The other discusses how Cyanobacteria tune light harvesting and photosynthetic function to both light intensity and nutrient availability and how the two responses are integrated.