Carotenoids as membrane stabilizers in chloroplasts

In addition to their well-established function as collectors of light energy for photosynthesis and as quenchers of triplet chlorophyll and singlet oxygen, carotenoids of higher plant chloroplasts might also play an important structural role. Recent studies have revealed that carotenoids of the xanthophyll family and some other terpenoids, such as isoprene or alpha-tocopherol, stabilize and photoprotect the lipid phase of the thylakoid membranes. Current evidence suggests that, when plants are exposed to potentially harmful environmental conditions such as strong light and/or elevated temperatures, the xanthophyll violaxanthin and the products of its enzymic de-epoxidation, antheraxanthin and zeaxanthin, partition between the light-harvesting complexes and the lipid phase of the thylakoid membranes. The resulting interaction of the xanthophyll molecules and the membrane lipids brings about a decrease in membrane fluidity, an increase in membrane thermostability and a lowered susceptibility to lipid peroxidation.