Inhibition of Zeaxanthin Formation and of Rapid Changes in Radiationless Energy Dissipation by Dithiothreitol in Spinach Leaves and Chloroplasts

Abstract

Dithiothreitol, which completely inhibits the de-epoxidation of violaxanthin to zeaxanthin, was used to obtain evidence for a causal relationship between zeaxanthin and the dissipation of excess excitation energy in the photochemical apparatus in Spinicia oleracea L. In both leaves and chloroplasts, inhibition of zeaxanthin formation by dithiothreitol was accompanied by inhibition of a component of nonphotochemical fluorescence quenching. This component was characterized by a quenching of instantaneous fluorescence (Fo) and a linear relationship between the calculated rate constant for radiationless energy dissipation in the antenna chlorophyll and the zeaxanthin content. In leaves, this zeaxanthin-associated quenching, which relaxed within a few minutes upon darkening, was the major component of nonphotochemical fluorescence quenching determined in the light, i.e. it represented the 'high-energy-state' quenching. In isolated chloroplasts, the zeaxanthin-associated quenching was a smaller component of total nonphotochemical quenching and there was a second, rapidly reversible high-energy-state component of fluorescence quenching which occurred in the absence of zeaxanthin and was not accompanied by Fo quenching. Leaves, but not chloroplasts, were capable of maintaining the electron acceptor, Q, of photosystem 11 in a low reduction state up to high degrees of excessive light and thus high degrees of nonphotochemical fluorescence quenching. When ascorbate, which serves as the reductant for violaxanthin de-epoxidation, was added to chloroplast suspensions, zeaxanthin formation at low photon flux densities was stimulated and the relationship between nonphotochemical fluorescence quenching and the reduction state in chloroplasts then became more similar to that found in leaves. We conclude that the inhibition of zeaxanthin-associated fluorescence quenching by dithiothreitol provides further evidence that there exists a close relationship between zeaxanthin and potentially photoprotective dissipation of excess excitation energy in the antenna chlorophyll. light is thought to result in an increase in the activity of (one or several) energy dissipation processes within the photochemical apparatus as evidenced by nonphotochemical fluorescence quenching (5,9,15,17,18). Recently, a linear relationship has been reported between the rate constant for radiationless energy dissipation in the antenna Chl (kD3), as calculated from Chl fluorescence, and the leaf content of the carotenoid zeaxanthin (6,7,9,10), which is formed in the thylakoid membranes via de-epoxidation of violaxanthin and antheraxanthin (13,23,26). With leaves, this correlation with zeaxanthin was obtained for the so-called 'energy-dependent' or 'high-energy-state' quenching determined in the light, i.e. a rapidly induced and rapidly reversible kind of fluorescence quenching (9), and also for a sustained kind of fluorescence quenching which developed, for example, over days in Nerium oleander subjected to water stress (7). These correlations have sugge...

A Mechanism of Nonphotochemical Energy Dissipation, Independent from PsbS, Revealed by a Conformational Change in the Antenna Protein CP26

“…Moreover, the kinetics of NPQ in the light are faster in npq2 with respect to npq1 and the wild type,suggesting that the presence of Zea instead of Viola in the complex before illumination allows for faster transition to the fully quenched state. These findings are consistent with an earlier report (Demmig-Adams et al, 1990;Ruban et al, 1993). It is not clear if the constitutive presence of Zea, effective in increasing the rate and amplitude of light-induced quenching in npq2, belongs to Lhcb proteins or to other subunits, such as PsbS (Li et al, 2002a).…”

“…Thus, qE and pH-independent quenching are connected through the availability of Zea, as released from Lhcb proteins or produced by violaxanthin deepoxidase enzyme activity, for activation of PsbS. In this way, a plant that has stored Zea upon previous exposure to high light is able to trigger qE more promptly (Demmig-Adams et al, 1990) by avoiding the temporal lag necessary to release Viola from the V1 site (Caffarri et al, 2001) and its deepoxidation when no Zea is present. Published results suggest a more general role for xanthophyll cycle: it was shown that downregulation of nitrate reductase activity, and thus lower NADPH use, increases zeaxanthin levels (Foyer et al, 1994).…”

Regulation of the photosynthetic apparatus under fluctuating growth light

“…Despite the requirement of PsbS for rapid induction of qE, a slow induction of qE can be achieved without PsbS [68]. Both the slow induction of NPQ in the absence of PsbS and the development of full NPQ in the presence of PsbS are dependent on the carotenoid violaxanthin, which is converted to another carotenoid, zeaxanthin [61,64].…”

Zeaxanthin Formation and Energy-Dependent Fluorescence Quenching in Pea Chloroplasts under Artificially Mediated Linear and Cyclic Electron Transport

“…Exchange of protons for Mg2+ (16), conversion of PSII from fluorescent to nonfluorescent forms (32), and zeaxanthin formation have been implicated (9). Zeaxanthin is formed from violaxanthin (34) by action of violaxanthin deepoxidase whose activity requires an acidified lumen (11).…”

“…Zeaxanthin is formed from violaxanthin (34) by action of violaxanthin deepoxidase whose activity requires an acidified lumen (11). Depending on treatment, zeaxanthin formation results in increased irreversible or reversible qN (8,9). Irreversible or slowly reversible zeaxanthin-dependent nonphotochemical quenching may be related to photoinhibition (8).…”