Abstract

Throughout evolution, photosynthetic complexes have been highly conserved in thylakoid membranes of organisms performing oxygenic photosynthesis. Cyanobacteria were the first to evolve this primary metabolic pathway and are claimed to be the evolutionary progenitors of photosynthesising chloroplasts. Both the chloroplast and cyanobacteria contain an extensive system of thylakoid membranes, which harbour the four main components for photosynthetic light reactions: Photosystems I and II, the cytochrome b6f complex and the ATP synthase complex. A striking difference between cyanobacterial and plant-type photosynthesis, however, is the arrangement and composition of light harvesting antenna complexes. In cyanobacteria, a large antenna system, called the phycobilisome, is attached to the stromal surface of the photosystems, whereas in chloroplasts the LHC complexes are embedded within the thylakoid membrane in close proximity to the photosystem reaction centres. In this presentation, I will highlight 1) regulation mechanisms of light harvesting involving the only calcium sensor protein in the multicellular model cyanobacterium Anabaena sp. PCC 7120 , and the role of calcium signalling in cyanobacteria in general; and 2) the specific roles of carotenoid pigments in light harvesting and correlated non-photochemical quenching mechanisms in chloroplasts of higher plant model species.