Effect of the temperature on violaxanthin de-epoxidation : comparison of the in vivo and model systems

Abstract

The xanthophyll cycle is a photoprotective mechanism operating in the thylakoid membranes of all higher plants, ferns, mosses and several algal groups. The occurrence of inverted hexagonal domains of monogalactosyldiacylglycerol (MGDG) in the membrane is postulated as an essential factor involved in violaxanthin de-epoxidation. The violaxanthin de-epoxidation was investigated in high-light illuminated Lemna trisulca at three temperatures (4, 12, and 25°C). The temperature dependence of this reaction was compared with kinetics of violaxanthin de-epoxidation at the same temperatures in MGDG micelles and in phosphatidylcholine (PC)–MGDG unilamellar liposomes. In both model systems and in the illuminated plants, a decrease in temperature resulted in lower zeaxanthin production. We found that the presence of MGDG in PC liposomes was necessary for the de-epoxidation reaction. With the increase in MGDG proportion in liposomes, the percentage of transformed violaxanthin was also increasing. We suggest that the violaxanthin de-epoxidation takes place within lipid matrix of the thylakoid membranes inside the MGDG-rich domains. Presence of the reversed hexagonal phase in the thylakoid membranes has been already reported in our previous papers and by other authors using 31P-NMR and freeze-fracturing techniques.