Linear models relating xanthophylls and lumen acidity to non-photochemical fluorescence quenching. Evidence that antheraxanthin explains zeaxanthin-independent quenching

Abstract

Zeaxanthin has been correlated with high-energy non-photochemical fluorescence quenching but whether antheraxanthin, the intermediate in the pathway from violaxanthin to zeaxanthin, also relates to quenching is unknown. The relationships of zeaxanthin, antheraxanthin and ΔpH to fluorescence quenching were examined in chloroplasts ofPisum sativum L. cv. Oregon andLactuca sativa L. cv. Romaine. Data matrices as five levels of violaxanthin de-epoxidation against five levels of light-induced lumen-proton concentrations were obtained for both species. The matrices included high levels of antheraxanthin as well as lumen-proton concentrations induced by subsaturating to saturation light levels. Analyses of the matrices by simple linear and multiple regression showed that quenching is predicted by models where the major independent variable is the product of lumen acidity and de-epoxidized xanthophylls, the latter as the sum of zeaxanthin and antheraxanthin. The interactions of lumen acidity and xanthophyll concentration are shown in three-dimensional plots of the best-fit multiple regression models. Antheraxanthin apparently contributes to quenching as effectively as zeaxanthin and explains quenching previously not accounted for by zeaxanthin. Hence, we propose that all high-energy dependent quenching is xanthophyll dependent. Quenching requires a threshold lumen pH that varies with xanthophyll composition. After the threshold, quenching is linear with lumen acidity or xanthophyll composition.

Snapshot Transient Absorption Spectroscopy of Carotenoid Radical Cations in High-Light-Acclimating Thylakoid Membranes

“…It is also possible that antheraxanthin is involved in the quenching as early antheraxanthin levels were similar across untreated, DTT-treated, and DTSSP-treated thylakoids ( Figure S3b). 37,42 It is noteworthy that a dip in the signal was observed at 5 min in both fluorescence and TA snapshot data. This suggests that the CT quenching is still important in the early stages of NPQ even with reduced VDE activity.…”

A molecular mechanism for qE‐quenching

“…However, q,-quenching can occur in the absence of zeaxanthin [ 141, and more recently, Horton and colleagues have shown that the presence of zeaxanthin in leaves preilluminated before rapid preparation of chloroplasts correlated strongly with an enhanced level of q,-quenching [12], which otherwise shows properties similar to those in the absence of zeaxanthin. Gilmore and Yamamoto [45] showed that the amplitude of quenching was proportional to the sum of antheraxanthin and zeaxanthin, and suggested that the de-epoxidation products are necessary for quenching.…”

“…A number of laboratories have looked at the distribution of carotenoid pigments among the different light-harvesting chlo- rophyll protein complexes [29,44,45]. Violaxanthin, the precursor of antheraxanthin and zeaxanthin in the xanthophyll cycle, partitioned predominantly into the minor complexes, CP29, CP26 and CP24.…”

“…The formation of zeaxanthin is enhanced at low lumenal pH, but has a slower onset and longer decay, and thus represents a secondary process to cope with more extended exposure. Association of zeaxanthin (and possibly antheraxanthin, [45]) with CP29 (or the other minor LHCs) [12,29&l], amplifies (or is required for) the effect of low lumenal pH in quenching the fluorescence. Structural models [29] of the interface between PS II and the antenna, and fluorescence emission spectra [30], suggest that the minor complexes serve as 'bridges' between the major LHCIIs and the reaction center antenna proteins.…”

Epoxidation of zeaxanthin and antheraxanthin reverses non‐photochemical quenching of photosystem II chlorophyll a fluorescence in the presence of trans‐thylakoid ΔpH

“…The linkage between the acidification of the thylakoid lumenal space and the biophysical mechanism of Chl fluorescence quenching, however, is complex and much of it remains to be understood [l]. The most concise picture indicates that NPQ correlates linearly with the product of the lumen proton concentration and the combined concentrations of the monoepoxide antheraxanthin (Anth) and epoxide-free zeaxanthin (Zeax) [4]. The biochemistry of the interconversions of Violaxanthin (Viol), Anth and Zeax in the xanthophyll cycle has been extensively characterized using isolated chloroplast systems [5] and is outlined schematically as follows: …”