Carotenoids - Properties and Function

Carotenoids are constituents of the photosynthetic reaction centers and the lightharvesting complexes of the antennae [13], playing their role as redox intermediates in electron transfer processes of photosystem II [14] and as accessory pigments in light harvesting [5, 15]. 

The reaction centers are rich in j8-carotene and in some plant species may also contain a-carotene. In contrast, the peripheral light-harvesting complex contains several xanthophylls, including lutein, violaxanthin and neoxanthin [5]. 

Besides their function as light collectors and photoprotectors, carotenoids also have important effects as membrane stabilizers in diloroplasts. The xanthophyll violaxanthin and its enzymatic de-epoxidation products antheraxanthin and zea-xanthin partition between the light-harvesting-complexes (LHCs) of PS I and PS II and the lipid phase of the thylakoid membranes, bringing about a decrease in membrane fluidity, an increase in membrane thermostability and a lowered susceptibility to lipid peroxidation [16]. 

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