The xanthophyll cycle and carotenoid-mediated dissipation of excess excitation energy in photosynthesis

Abstract

Light is a major stress factor in plants and algae, resulting in photoinhibition and photooxidation in photosynthetic tissues, with a concomitant loss in productivity. Protection from such light-mediated stress is therefore of key importance. Recent studies have determined a clear correlation between the dissipation of excess excitation energy and the formation of zeaxanthin from violaxanthin in the light-harvesting complexes of plants and some algae. Although the mechanism of carotenoid-mediated energy dissipation is still not fully understood, two main models have been proposed: the "Molecular Gear Shift Model" (singlet-singlet energy transfer from chlorophyll to carotenoid) and the "LHCII Model" (carotenoid-mediated changes to light-harvesting complex organisation leading to the formation of a 'quencher'). The main features of these two models are discussed.