Fig. 1

Carotenoids play major roles in plants as antioxidants, accessory light-harvesting pigments. As an effect of increased ROS production, the activity and biosynthesis of different plant antioxidants raise up in response for preventing oxidative damage. A novel function for carotenoids relates to the response of plants to abiotic stress factors as shown (left). A compressed version of the carotenoid biosynthesis pathway is shown on the right: Isopentenyl pyrophosphate (IPP) – biosynthesis, Phytoene biosynthesis, Lycopene biosynthesis, Lycopene cyclization, Sequestration and storage [A]. Carotenoid metabolism in light of plastid types in plants and sequestration in relation to these metabolites accumulation are shown in [B].The photoprotective role of these metabolites derives from their ability to quench excited chlorophyll states, scavenge ROS and dissipate excess energy as heat during the light adapted state (Fig.C). The electronic interactions between carotenoid dark states and chlorophylls are shown on the right. If the energy levels of Car S1 and Chl aQy are similar,increased electronic interactions cause to the formation of excitonic states which are delocalized [112]. Part of the figure is adapted from [10]