The protective function of the xanthophyll cycle in photosynthesis.

The rapid conversion of the carotenoid violaxanthin to zeaxanthin via antheraxanthin (xanthophyll cycle) in potato leaves exposed at 23 degrees C to a strong white light of 2000 microE.m-2.s-1 was associated with a slight inhibition of photosynthetic electron transport (as estimated from chlorophyll fluorescence measurements) and a low lipid peroxidation (as estimated from ethane measurements). When the xanthophyll cycle was blocked by dithiothreitol (3 mM) or low temperature (3 degrees C), photoinhibition of electron transport was exacerbated and pronounced lipid peroxidation occurred concomitantly. Accumulation of zeaxanthin and antheraxanthin in potato leaves by a non-photoinhibitory light treatment at 23 degrees C (900 microE.m-2.s-1 for 1 h) considerably reduced the level of lipid peroxidation during subsequent light stress at 3 degrees C. The presented results indicate that one of the functions of the xanthophyll cycle could be the protection of thylakoid membranes against lipid peroxidation, suggesting that zeaxanthin and antheraxanthin synthesized in strong light are present as free pigments in the membrane lipid bilayer.