Nonenzymic carotenoid oxidation and photooxidative stress signalling in plants

Abstract

Carotenoids play a crucial protective role in photosynthetic organisms as quenchers of singlet oxygen (1O2). This function occurs either via a physical mechanism involving thermal energy dissipation or via a chemical mechanism involving direct oxidation of the carotenoid molecule. The latter mechanism can produce a variety of aldehydic or ketonic cleavage products containing a reactive carbonyl group. One such molecule, the volatile β-carotene derivative β-cyclocitral, triggers changes in the expression of 1O2-responsive genes and leads to an enhancement of photooxidative stress tolerance. Thus, besides their well-known functions in light harvesting and photoprotection, carotenoids can also play a role through their nonenzymic oxidation in the sensing and signalling of reactive oxygen species and photooxidative stress in photosynthetic organisms. Enzymic carotenoid oxidation does not seem to play a significant role in this phenomenon. Elucidation of the carotenoid-mediated 1O2 signalling pathway could provide new targets for improving photooxidative stress tolerance of plants. © The Author [2012].