Molecular mechanisms of stress resistance of photosynthetic machinery

The mechanisms of action of stressors, such as high light intensity and heat stress, on the photosynthetic machinery, primarily on the photosystem II, are reviewed. First of all, stressors alter the chemical composition of thylakoid membranes and decrease the activity of photosynthesis. Photodamage is caused by the direct effect of light on oxygen-evolving complex, whereas accumulation of reactive oxygen species due to high light or high temperatures causes suppression of the de novo synthesis of the reaction center proteins and, ultimately, leads to the inhibition of the recovery of photosystem II. In addition to their destructive and inhibitory action, the reactive oxygen species and products of lipid peroxidation trigger protective processes that lead to acclimatization. Particular attention is paid to the mechanisms that protect photosynthetic machinery from injury and to the inhibitory effect of stressors in the light of varying intensity. The known stress sensory systems of cyanobacteria are also reviewed.