The Transiently Generated Nonphotochemical Quenching of Excitation Energy in Arabidopsis Leaves Is Modulated by Zeaxanthin

Abstract

Upon the transition of dark-adapted plants to low light, the energy-dependent quenching (qE) of excitation energy is only transiently induced due to the only transient generation of the transthylakoid pH gradient. We investigated the transient qE (qE(TR)) in different Arabidopsis (Arabidopsis thaliana) mutants. In dark-adapted plants, qE(TR) was absent in the npq4 mutant (deficient in the PsbS protein) and the pgr1 mutant (restricted in lumen acidification). In comparison with wild-type plants, qE(TR) was reduced in the zeaxanthin (Zx)-deficient npq1 mutant and increased in the Zx-accumulating npq2 mutant. After preillumination of plants (to allow the synthesis of large amounts of Zx), the formation and relaxation of qE(TR) was accelerated in all plants (except for npq4) in comparison with the respective dark-adapted plants. The extent of qE(TR), however, was unchanged in npq1 and npq4, decreased in npq2, but increased in wild-type and pgr1 plants. Even in presence of high levels of Zx, qE(TR) in pgr1 mutants was still lower than that in wild-type plants. In the presence of the uncoupler nigericin, qE(TR) was completely abolished in all genotypes. Thus, the transient qE(TR) shows essentially the same characteristics as the steady-state qE; it is strictly dependent on the PsbS protein and a low lumen pH, but the extent of qE(TR) is largely modulated by Zx. These results indicate that qE(TR) does not represent a different quenching mechanism in comparison with the steady-state qE, but simply reflects the response of qE to the dynamics of the lumen pH during light activation of photosynthesis.

The Zeaxanthin-Independent and Zeaxanthin-Dependent qE Components of Nonphotochemical Quenching Involve Common Conformational Changes within the Photosystem II Antenna in Arabidopsis

“…Previously, qE formed under these conditions was ascribed to quenching in the PSII reaction center (Finazzi et al, 2004), but here it was shown to be accompanied by an absorption change with the same spectrum as that associated with steadystate qE formed in high light. It was also shown that the transient qE was affected by alteration in the xanthophyll composition in the same way as steady-state qE, adding to previous results (Kalituho et al, 2007); thus, the transient qE was strongly reduced in lut2 and lut2npq2 and completely absent in the lut2npq1 mutant. When combined with the reported dependence of transient qE upon PsbS (Finazzi et al, 2004;Kalituho et al, 2007), these data strongly suggest that it originates from the same common PSII antenna-based mechanism as steady-state qE in high light.…”

Thylakoid Protein Phosphorylation in Higher Plant Chloroplasts Optimizes Electron Transfer under Fluctuating Light

“…4). This was a clear indication that the xanthophyll cycle is not required to induce the PsbSdependent quenching but that it strongly modulates the strength of thermal dissipation, as was shown recently (Kalituho et al, 2007).…”

Thioredoxin m4 Controls Photosynthetic Alternative Electron Pathways in Arabidopsis

“…No difference in the NPQ transiently generated in dark-adapted leaves from the wild type, ndho-1, and trxm4-1 exposed to low light could be recorded (Supplemental Fig. S5C), indicating that transient generation of the transthylakoidal pH gradient (Kalituho et al, 2007) was similar in wild-type and mutant plants. Knocking out genes encoding NDH subunits either in tobacco (Burrows et al, 1998;Kofer et al, 1998;Shikanai et al, 1998) or in Arabidopsis Shikanai, 2007) did not affect overall photosynthetic electron transport, and plants did not display any visible phenotype.…”