Photoprotection in chilling-sensitive and -resistant plants illuminated at a chilling temperature: role of the xanthophyll cycle in the protection against lumen acidification.

The role of the xanthophyll cycle in the protection against photoinhibition of photosystem II (PSII) induced by chilling in moderate light was investigated in leaves of eight species or varieties of higher plants differing widely in chilling sensitivity. The extent of photoinhibition measured as the increase in the slowly reversible fluorescence quenching (qI) was found not to correlate with the overall amount of zeaxanthin formed during photo-inhibitory treatment. On the other hand, a strong, positive correlation existed between qI and the rate difference between the development of the rapidly relaxing, DpH-dependent quenching component (qf) and the formation of zeaxanthin (DR) across all examined species or varieties. There was also found to be a weaker, negative correlation between qI and the rate of zeaxanthin formation. Ascorbate feeding markedly increased the resistance to chilling-induced photoinhibition mainly by increasing the rate of zeaxanthin formation and therefore by decreasing DR. The possible implications of the present findings in explaining the mechanistic basis for the reversible, sustained photo-inhibition are discussed. It is suggested that the xanthophyll cycle may play a critical role in the protection of the thylakoid lumen against over-acidification and the resulting photoinhibition of PSII reaction centers.