Zeaxanthin-dependent nonphotochemical quenching does not occur in photosystem I in the higher plant Arabidopsis thaliana

Abstract

Nonphotochemical quenching (NPQ) is the process that protects the photosynthetic apparatus of plants and algae from photodamage by dissipating as heat the energy absorbed in excess. Studies on NPQ have almost exclusively focused on photosystem II (PSII), as it was believed that NPQ does not occur in photosystem I (PSI). Recently, Ballottari et al. [Ballottari M, et al. (2014) Proc Natl Acad Sci USA 111:E2431-E2438], analyzing PSI particles isolated from an Arabidopsis thaliana mutant that accumulates zeaxanthin constitutively, have reported that this xanthophyll can efficiently induce chlorophyll fluorescence quenching in PSI. In this work, we have checked the biological relevance of this finding by analyzing WT plants under high-light stress conditions. By performing timeresolved fluorescence measurements on PSI isolated from Arabidopsis thaliana WT in dark-adapted and high-light-stressed (NPQ) states, we find that the fluorescence kinetics of both PSI are nearly identical. To validate this result in vivo, we have measured the kinetics of PSI directly on leaves in unquenched and NPQ states; again, no differences were observed. It is concluded that PSI does not undergo NPQ in biologically relevant conditions in Arabidopsis thaliana. The possible role of zeaxanthin in PSI photoprotection is discussed.photosystem I | NPQ | time-resolved fluorescence | LHCI | light stress P hotosystem I (PSI) is a crucial pigment-binding protein complex for oxygenic photosynthetic organisms. It absorbs sunlight and uses its energy to drive electron transport from plastocyanin to ferredoxin. In higher plant, PSI comprises a core complex that holds P700, the reaction center (RC), and four light-harvesting complexes (Lhca 1-4), and coordinates a total of 155 chlorophylls (Chls) (1, 2). PSI has a very fast (<100-ps) excited-state energy relaxation (3, 4), and it can generate electron-hole pair with near-unity quantum yield (5, 6). Its decay kinetics is virtually independent of the redox state of the RC as both P700 and P700+ are equally good quenchers (4). The rapid kinetics dramatically reduces the yield of Chl triplet states, and then the production of reactive oxygen species, one of the main causes of photodamage (7). This makes PSI a very robust complex and the favorite system for biohybrid applications (e.g., refs. 8 and 9). PSI is also resistant to high-light (HL) stress. In vivo, it is only damaged at low temperature and in the presence of an active PSII (10, 11). In contrast, PSII is sensitive to strong sunlight (7, 12).Higher plants have evolved several strategies to avoid photodamage (13,14). Among these, the process of nonphotochemical quenching (NPQ) is active in seconds/minutes and leads to a strong decrease of the excited-state population in the membrane. It depends on the presence of the protein PsbS (15) and the carotenoid zeaxanthin (16). Both induce fluorescence quenching, but their molecular mechanisms are still under debate (13). Until recently, it was believed that both PsbS and zeaxanthin only act at the level of ...

Evolutionary divergence of photoprotection in the green algal lineage: a plant‐like violaxanthin de‐epoxidase enzyme activates the xanthophyll cycle in the green alga Chlorella vulgaris modulating photoprotection

“…In PSI complexes isolated from npq2, all the violaxanthin binding sites were occupied by zeaxanthin, whereas in the zeaxanthin binding complex isolated from C. vulgaris we observed a DI of 0.34, with almost two zeaxanthin molecules per PSI complex that are likely bound to the external LHC antenna complexes (Wehner et al, 2004). When the PSI complex was isolated from A. thaliana with a similar DI and zeaxanthin : PSI stoichiometry, no evident effect of zeaxanthin in PSI quenching was observed (Tian et al, 2017), suggesting a much higher influence of zeaxanthin in PSI quenching in C. vulgaris than in A. thaliana. All these findings thus demonstrate the role of zeaxanthin in NPQ and excitation energy quenching in both PSII and PSI.…”

LHCSR1-dependent fluorescence quenching is mediated by excitation energy transfer from LHCII to photosystem I in Chlamydomonas reinhardtii

“…Recently, an NPQ effector zeaxanthin was modeled at an atomic resolution in PSI of land plants (27,28). Although there has been debate about the contribution of zeaxanthin to PSI quenching, the detailed molecular mechanisms of the fluorescence quenching in land plants have been reported (29,30). Direct excitation energy quenching by LHCSRs surrounding PSI has also been observed in moss (31), implying that the quenching around PSI could be conserved in the green lineage.…”

Light Acclimation of the Colonial Green Alga Botryococcus braunii Strain Showa

“…Time-resolved fluorescence measurements were performed using the timecorrelated single-photon counting setup described previously (Müller et al, 1992) with modifications (Tian et al, 2017). Excitation at 650 nm was used to preferentially excite Chl b and 662 nm for Chl a (0.5-mm spot size).…”