LIGHT REGULATION OF PHOTOSYNTHETIC APPARATUS IN CYANOBACTERIA

Cyanobacterial photosynthetic apparatus contains two photosystems, pho tosystem I (PS I) and photosystem II (PS II). In addition, the primary light harvesting antenna in these organisms is composed of pigmented and non-pigmented protein complex called phycobilisome. It is argued t hat both the photosystems and the phycobilisome are highly responsive to the changing light environment, The response of the cyanobacterial photosynthetic apparatus under different light conditions is discussed . It is presented that this response provides an indication whether it is an adaptation process ora signal for damage. Both visible and ultr aviolet radiations have been shown to bring about this response. It is reported that in addition to its effect on the photosynthetic apparat us, ultraviolet radiation has also been shown to cause damage to nucle ic acids. Finally, the possible protective mechanisms in cyanobacteria against light stress are discussed wherein it is argued that cyanobac teria have the capability to protect themselves against extreme light situations through various mechanisms involving modulations in the pre existing components of the photosynthetic apparatus or acquiring new p rotection mechanisms against light stress.