A micellar model system for the role of zeaxanthin in the non-photochemical quenching process of photosynthesis—chlorophyll fluorescence quenching by the xanthophylls

Abstract

To get an insight to the mechanism of the zeaxanthin-dependent non-photochemical quenching in photosystem II of photosynthesis, we probed the interaction of some xanthophylls with excited chlorophyll-a by trapping both pigments in micelles of triton X-100. Optimal distribution of pigments among micelles was obtained by proper control of the micelle concentration, using formamide in the reaction mixture, which varies the micellar aggregation number over three orders of magnitude. The optimal reaction mixture was obtained around 40% (v/v) formamide in 0.2-0.4% (v/v) triton X-100 in water. Zeaxanthin in the micellar solution exhibited initially absorption and circular dichroism spectral features corresponding to a J-type aggregate. The spectrum was transformed over time (half-time values vary-an average characteristic figure is roughly 20 min) to give features representing an H-type aggregate. The isosbestic point in the series of spectral curves favors the supposition of a rather simple reaction between two pure J and H-types dimeric species. Violaxanthin exhibited immediately stable spectral features corresponding to a mixture of J-type and more predominately H-type dimers. Lutein, neoxanthin and beta-carotene did not show any aggregated spectral forms in micelles. The spectral features in micelles were compared to spectra in aqueous acetone, where the assignment to various aggregated types was established previously. The specific tendency of zeaxanthin to form the J-type dimer (or aggregate) could be important for its function in photosynthesis. The abilities of five carotenoids (zeaxanthin, violaxanthin, lutein, neoxanthin and beta-carotene) to quench chlorophyll-a fluorescence were compared. Zeaxanthin, in its two micellar dimeric forms, and beta-carotene were comparable good quenchers of chlorophyll-a fluorescence. Violaxanthin was a much weaker quencher, if at all. Lutein and neoxanthin rather enhanced the fluorescence. The implications to non-photochemical quenching process in photosynthesis are discussed.

Glyceroglycolipids Affect Uptake of Carotenoids Solubilized in Mixed Micelles by Human Intestinal Caco‐2 Cells

“…The absorption spectrum of carotenoids is known to be affected by the interaction of carotenoid molecules with a solvent and by the interaction among the carotenoid molecules themselves [16,[29][30][31][32][33][34][35][36][37][38][39][40][41]. In the present study, the λ max values of carotenoids in the NoPL micelles showed a bathochromic shift compared to those in organic solvents.…”

Xanthophyll cycle – a mechanism protecting plants against oxidative stress

“…It has been postulated that this dimerization may play a role in Zx functioning in the photosynthetic apparatus. 35 It also should be mentioned that some of the recent determinations of the energy levels of the xanthophyll cycle pigments show that the difference between the energies of the S 1 state of Vx and Zx is very small, and therefore essentially different Chl excitation quenching efficiencies for these two compounds may not be expected. 36 Accordingly, no exceptional Chl singlet excitation quenching has been observed in the antenna complexes isolated from the L mutants of Arabidopsis thaliana, in which L was replaced with Zx.…”

Biomembrane models

“…Micellar systems can also be used as models of thylakoid membranes to investigate the quenching of chlorophyll fl uorescence by xanthophylls such as zeaxanthin or lutein. 51 Micelles of Triton X-100 have been used to trap the pigments chlorophyll and xanthophyll, and CD and fl uorescence measurements showed the aggregation state of the pigments and the non-photochemical quenching effi ciency of chlorophyll fl uorescence by the xanthophylls.…”