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 degr ees C to a strong white light of 2000 mu E.m(-2).s(-1) was associated with a slight inhibition of photosynthetic electron transport (as esti mated from chlorophyll fluorescence measurements) and a low lipid pero xidation (as estimated from ethane measurements). When the xanthophyll cycle was blocked by dithiothreitol (3 mM) or low temperature (3 degr ees C), photoinhibition of electron transport was exacerbated and pron ounced lipid peroxidation occurred concomitantly. Accumulation of zeax anthin and antheraxanthin in potato leaves by a non-photoinhibilory li ght treatment al 23 degrees C (900 mu E.m(-2).s(-1) for 1 h) considera bly reduced the level of lipid peroxidation during subsequent light st ress at 3 degrees C. The presented results indicate that one of the fu nctions of the xanthophyll cycle could be the protection of thylakoid membranes against lipid peroxidation, suggesting that zeaxanthin and a ntheraxanthin synthesized in strong light are present as free pigments in the membrane lipid bilayer.