ABSTRACT
This chapter focuses on cyanobacterial photoresponsive systems to briefly outline the photoreceptors and the photoresponsive phenomena regulated by these photoreceptors. Oxygen-evolving photosynthesis performed by land plants, eukaryotic algae, and cyanobacteria consists of two photosynthetic reaction centers, photosystem II and photosystem I. Linear tetrapyrrole-binding photoreceptors in cyanobacteria are categorized into phytochromes and cyanobacteriochromes. In addition to the photosynthetic reaction centers, the photosynthetic organisms develop light-harvesting antennae complexes absorbing light energy and transferring the energy into the reaction centers. Thermophilic cyanobacteria isolated from hot springs show cell aggregation composed of a large number of cells under low-temperature light conditions. Because dark reactions are rate-limiting in the photosynthetic process under the low-temperature light conditions, cyanobacteria under such conditions are thought to be more susceptible to photoinhibition than normal conditions. There are various species within the cyanobacterial phylum, and it has been clarified that each species has developed a highly organized photoresponsive strategy coping with the adapted environment.
