Photosynthesis Research最新文献

{"title":"Chirality distribution in the fifth ligand coordination of chlorophylls-c in photosynthetic pigment-protein complexes.","authors":"Toru Oba, Hitoshi Tamiaki","doi":"10.1007/s11120-026-01232-2","DOIUrl":"10.1007/s11120-026-01232-2","url":null,"abstract":"<p><p>Chlorophylls (Chls) and bacteriochlorophylls (BChls) in photosynthetic organisms are embedded in pigment-protein complexes, mostly through the coordination of peptidyl residues to their central metal atoms. An asymmetry occurs at the axially coordinated metal centers of (B)Chls. The stereochemistry of the ligand coordination toward 42 molecules of Chls-c, the fully π-conjugated porphyrin pigments lacking C17- and C18-chiralities and a long ester chain in the C17-substituent, was surveyed across 21 pigment-protein complexes registered in the Protein Data Bank. It was found that 24 of 42 Chl-c molecules in these complexes were coordinated from the β-side of the macrocyclic π-plane, revealing a tendency opposite to the preferential α-ligation observed for the structurally different (B)Chls with a (bacterio)chlorin π-system in other proteins (129/163 surveyed sites). The most common binding sites for Chl-c molecules in the proteins correspond to the a603 and a612 sites in Chl-a/b-binding light-harvesting complex II (LHCII), both of which accommodate β-epimers. In some cases, a carotenoid molecule contacts Chl-c to occupy the space where the C17²-ester group of the Chl-a/b molecule is situated at the corresponding sites in LHCII, and its position of the carotenoid molecule is related to the macrocycle side of the axial ligand coordination of Chl-c. The absence or presence of chirality and bulky substituents at the C17-position of (B)Chls may be concerned with the stereochemistry of the axial coordination and the formation of these pigment-protein complexes.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13461745/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148707200","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Water use efficiency in cereal crops: stomatal, hydraulic, biochemical mechanisms, and translational strategies for improvement.","authors":"Baber Ali, Aqsa Hafeez, Nijat Imin","doi":"10.1007/s11120-026-01233-1","DOIUrl":"10.1007/s11120-026-01233-1","url":null,"abstract":"<p><p>Water use efficiency in cereal crops is governed by molecular processes operating across biological scales that are connected imperfectly and non-linearly, from guard cell ion channel gating to canopy evapotranspiration. Despite the global urgency of improving yield under water limitation, no existing synthesis has integrated the molecular machinery of stomatal regulation, mesophyll CO₂ conductance, root hydraulic conductance, isohydric and anisohydric stomatal strategies, carbon isotope discrimination as a proxy tool, and specific genetic targets for improvement within a single cereal-focused mechanistic framework. This review advances that synthesis, examining WUE primarily through the lens of non-stomatal carbon fixation rather than stomatal regulation alone. The ABA-dependent stomatal closure cascade and the opposing blue-light opening pathway are conserved in core architecture across cereals, but their calcium-dependent and H⁺-ATPase branches remain characterised mainly by sequence homology rather than direct cereal evidence. Mesophyll conductance and Rubisco carboxylation efficiency represent underexploited, genetically undefined targets for improving carbon gain. Root hydraulic conductance connects soil water to canopy transpiration on timescales of minutes to days, while whole-plant isohydric to anisohydric strategy is best understood as an emergent, environment-dependent outcome of these faster processes rather than a fixed trait. Carbon isotope discrimination remains a practical relative-ranking proxy rather than a direct measurement. The EPFL-ERECTA stomatal density pathway and the H⁺-ATPase aperture system show the strongest cereal-specific experimental support among engineering targets, though compensatory anatomical and physiological responses mean anatomical change alone is insufficient evidence of durable benefit. Nitrogen-water signalling through CEP-CEPR1 peptide signalling likely shapes WUE as a downstream emergent property, though direct experimental validation is lacking. Five specific research priorities are identified to advance WUE improvement from mechanistic understanding toward field-level translation.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148679703","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diazotrophy affects the state transitions in unicellular nitrogen fixing cyanobacteria.","authors":"Saverio Rana, Tatsuhiro Tsurumaki, Eva Kotabová, Radek Kaňa, Alžběta Prášilová, Takako Masuda, Ondřej Prášil","doi":"10.1007/s11120-026-01231-3","DOIUrl":"10.1007/s11120-026-01231-3","url":null,"abstract":"<p><p>State transitions balance excitation energy between photosystem II and photosystem I and represent a key photoprotective mechanism in oxygenic photosynthesis. While extensively characterized in model cyanobacteria, the regulation of state transitions in diazotrophic species remains poorly understood. Here, we present a comparative physiological study of two unicellular nitrogen-fixing cyanobacteria, Crocosphaera watsonii WH 8501 and Crocosphaera subtropica ATCC 51142 under diazotrophic and non-diazotrophic conditions. Using growth analyses, whole-cell absorption spectroscopy, and low-temperature (77 K) fluorescence spectroscopy, we examined how nitrogen availability shapes photosynthetic energy distribution across species and conditions. Our results showed that state transitions are tightly linked to nitrogen metabolism in both species, but with distinct species-specific regulatory strategies. Diazotrophic cultures exhibited a higher capacity for state transitions than non-diazotrophic cultures, indicating enhanced flexibility in excitation energy redistribution. In C. watsonii, pronounced state transitions were observed exclusively under diazotrophic conditions, whereas non-diazotrophic cultures relied on alternative modes of excitation regulation. In contrast, C. subtropica displayed a more flexible response, with state transitions influenced by both nitrogen availability and light intensity. Fluorescence analyses revealed that state transitions involve a combination of excitation spillover between photosystems and dynamic coupling-decoupling of phycobilisomes. Together, these findings suggest that nitrogen fixation is associated with changes in photosynthetic energy regulation in marine diazotrophic cyanobacteria.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13408156/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148593176","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Unique properties of light-induced changes of variable chlorophyll fluorescence in purified PSII core complexes of Thermosynechococcus vestitus.","authors":"Ulrich Schreiber, Ivan Bobkov, Marc Nowaczyk","doi":"10.1007/s11120-026-01228-y","DOIUrl":"10.1007/s11120-026-01228-y","url":null,"abstract":"<p><p>A new type of kinetic chlorophyll fluorometer (Klughammer et al. 2024, Photosynth Res 161:151-176) which enables measuring the changes of rel. fluorescence yield during application of saturating single-turnover 15µs flashes (ST-kinetics, STK) simultaneously with the PAM relaxation kinetics induced by the same flash, was applied on purified PSII core complexes (PSII CC) isolated from Thermosynechococcus vestitus (Lambertz et al. 2023, Biochim Biophys Acta 1864:148953). While the main text concentrates on purified PSII dimers, under Supplementary Materials also comparative measurements with purified monomers and heterodimers are presented. Freshly solubilized, non-preilluminated samples display extremely high ratios of maximal/minimal fluorescence yields up to 26, corresponding to F_v/F_m = 0.96. Both PAM and STK techniques reveal period-4 oscillations in presence of 2 µM dichlorobenzoquinone (DCBQ). Period-2 oscillations are observed in the PAM relaxation kinetics after relaxation of donor-side dependent quenching (DQ). Maximal fluorescence yields in STK responses are lowered with respect to the corresponding PAM responses by High Intensity Quenching (HIQ), consisting of DQ and carotenoid triplet quenching (TQ). The DQ observed in presence of 20µM DCMU lowers flash-induced F_v by about 30%, relaxing with a half-time of about 40µs, as revealed by double flash STK measurements. When a train of ST with 5s dark intervals is applied in the absence of artificial acceptors, up to ST#3 both STK and PAM measurements show about 30% quenching (DQ) with respect to maximal fluorescence yield (F_m). Suppression of DQ occurs in a train of additional ST, reflected in a multi-step further rise to F_m. This \"terminal rise\" is inhibited by 20 µM DCMU and by 2µM DCBQ, suggesting that redox-reactions involving reduced Q_B are involved in this phenomenon. It is proposed that double reduced Q_B is either protonated, so that after release of PQH₂ the PSII acceptor side is inactivated, or reoxidized by the donor side (via cyclic PSII, PSII-CEF). Based on this rationale a simple scheme is presented to explain the phenomenon. A similar \"terminal rise\" is observed using the PAM technique upon illumination by strong continuous light. It is suggested that the \"terminal rise\" in PSII CC and the \"thermal\" I₁-I₂ phase in vivo may involve the same pathways of DQ suppression, the molecular steps of which remain to be clarified by further research.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13400723/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148579989","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Improved state‑transition analysis in tobacco lines differing in isoprene emission via spectral‑retrieval separation of PSI and PSII fluorescence at physiological temperature.","authors":"Lorenzo Palombi, Susanna Pollastri, Francesco Loreto, Giovanni Agati","doi":"10.1007/s11120-026-01227-z","DOIUrl":"10.1007/s11120-026-01227-z","url":null,"abstract":"<p><p>State transition (ST) is a key regulatory mechanism that balances excitation energy between photosystem II (PSII) and photosystem I (PSI). Although its general principles have been known for decades, methodological constraints have limited precise quantification of ST kinetics and of the associated changes in photosystem absorption cross sections. We present a PCA‑assisted fluorescence spectral analysis that enables in vivo separation of PSI and PSII chlorophyll fluorescence at physiological temperatures. Applied to intact Nicotiana tabacum leaves undergoing ST, this method provides more accurate estimates of both the rates and the extent of the process than earlier approaches. The half‑time of the State 1 to State 2 (St1→St2) transition was approximately 1 min, nearly twice as fast as values inferred from traditional F_far‑red/F_red fluorescence ratios measured at room temperature or 77 K. The analysis also clarifies how PSI and PSII fluorescence changes relate to variations in their absorption cross sections. Accounting for PSII‑to‑PSI spillover, we found that the mobile LHCII fraction associating with PSI during the St1→St2 transition increased the PSI absorption cross section by 31%, whereas LHCII reassociation with PSII during the reverse transition produced a more modest 17% increase in PSII absorption cross section. These asymmetric adjustments likely have important physiological implications under fluctuating environmental conditions. Finally, applying the method to isoprene‑emitting and non‑emitting tobacco lines revealed that isoprene accelerates excitation‑energy redistribution during the St2→St1 transition, consistent with its proposed role in maintaining optimal thylakoid ultrastructure and fluidity. Overall, this approach offers a powerful tool for dissecting photosynthetic energy‑distribution dynamics in vivo.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13396053/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148562754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Probing the influence of PsbS on thylakoid lipid fluidity.","authors":"Shiun-Jr Yang, Henry E Lam, Katherine H Richardson, Matthew P Johnson, Gabriela S Schlau-Cohen","doi":"10.1007/s11120-026-01229-x","DOIUrl":"10.1007/s11120-026-01229-x","url":null,"abstract":"<p><p>Due to fluctuations in sunlight intensity, balancing light-harvesting efficiency and photoprotection is critical for plant fitness. To achieve this balance, plants have evolved a highly regulated mechanism, non-photochemical quenching (NPQ), which is activated under excess light to dissipate absorbed energy and deactivated under low light to preserve photosynthetic efficiency. A key component that allows NPQ to respond rapidly to changing light conditions is photosystem II subunit S (PsbS). Several hypotheses have been proposed to explain the working mechanism of PsbS, including the idea that it modulates thylakoid membrane macrostructure and protein mobility by altering membrane fluidity. To test this hypothesis, we employed a proteoliposome system containing only thylakoid lipids, PsbS, and the fluorescent probe laurdan, enabling direct detection of PsbS-lipid interactions under different pH conditions. Our results show that the presence of PsbS increases membrane fluidity, but the magnitude of this change in the overall bilayer is small compared with temperature-induced effects. These findings indicate that direct interactions between PsbS and thylakoid lipids are insufficient to account for NPQ regulation and suggest that interactions with other components in the thylakoid membranes are likely essential. This study provides insight into the functional mechanism of PsbS and establishes a framework for further investigation of PsbS-mediated regulation of NPQ and its role in optimizing photosynthetic performance under fluctuating light.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13379455/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148472194","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Photoprotection in a desert moss: dynamic excitation quenching during the hydration cycle of the Syntrichia caninervis.","authors":"Simona Streckaite, Jevgenij Chmeliov, Vilius Čirgelis, Marius Franckevičius, Lena Golubewa, Benfeng Yin, Danielis Rutkauskas, Chunhong Yang, Leonas Valkunas, Yuanming Zhang, Bruno Robert","doi":"10.1007/s11120-026-01230-4","DOIUrl":"10.1007/s11120-026-01230-4","url":null,"abstract":"<p><p>Desiccation-tolerant mosses survive extreme water loss by activating efficient photoprotective mechanisms that prevent damage to the photosynthetic apparatus. The most resistant moss Syntrichia caninervis (S. caninervis) represents an important model for studying the molecular basis of dehydration resilience; however, the membrane and protein level processes, which enable rapid recovery of photosynthetic activity upon rehydration, remain insufficiently understood. In this work, we investigate the fluorescence (FL) dynamics of the photosynthetic apparatus of S. caninervis under three hydration states (hydrated, dehydrated and desiccated) in whole leaves using time-resolved FL spectroscopy. Time-resolved measurements with ~ 10 ps resolution were performed to resolve excitation dynamics in both photosystems I (PSI) and II (PSII). The complex FL datasets were analysed using the spectral decomposition approach. Dehydrated and desiccated samples exhibit substantially reduced FL intensity compared to hydrated moss in steady-state experiments, indicating efficient quenching of chlorophyll excitation upon drying. The time-resolved FL measurements revealed that excitation transfer rates and the nature of quenched states strongly depend on hydration level in S. caninervis. In the hydrated state, FL dynamics are consistent with functional photosystems in plants. Upon dehydration, non-photochemical quenching is activated in both PSII and PSI, with PSII quenching persisting even at low temperatures. We therefore conclude, that S. caninervis employs few hydration-dependent photoprotective regimes, including distinct quenching mechanisms at both photosystems. Our results suggest the presence of ultrafast quenching processes under severe dehydration, which are progressively relieved during rehydration and replaced by alternative mechanisms supporting the recovery of photosynthetic activity.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13354704/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148423287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Energy quenching via triplet-excited state formation of glycosylated carotenoids in the photosynthetic reaction center complex of the green sulfur bacterium Chlorobaculum tepidum.","authors":"Tomomi Inagaki, Masatoshi Kida, Daisuke Kosumi, Chihiro Azai","doi":"10.1007/s11120-026-01226-0","DOIUrl":"10.1007/s11120-026-01226-0","url":null,"abstract":"<p><p>Some carotenoids have a function to quench excitation energy of chlorophyll in photosynthetic apparatuses. This is a part of the photoprotective mechanism, non-photochemical quenching (NPQ), which prevents the inhibitory effects of high-light irradiation. In the green sulfur bacterium Chlorobaculum tepidum, which is a strictly anaerobic photosynthetic bacteria, a glycosylated carotenoid (Car-G) has been found to dissipate excitation energy of bacteriochlorophyll (BChl) a in the photochemical reaction center (RC) complex. In this study, we used ultrafast transient absorption spectroscopy to investigate excitation energy transfer (EET) mediated by Car-G in the reaction center complex of C. tepidum. Two spectral changes in carotenoids were identified when a core-antenna BChl a was selectively excited. One was sensitive to detergent replacement, while the other was not. The latter was the formation of a triplet-excited state of carotenoid (³Car) and observed when the primary electron donor accumulated in the oxidized state. The corresponding signal was absent in the RC complex from the ΔcruC mutant strain lacking Car-G. Kinetic analyses and structural insights revealed that ³Car is formed on a tightly-bound Car-G through triplet-to-triplet (TT)-EET from one of the excited states of the core-antenna BChl a. This TT-EET to ³Car is responsible for the anaerobic energy dissipation in the RC complex of C. tepidum.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148387913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantitative phosphoproteomics profiling reveals the regulatory mechanisms underlying high light stress in maize and rice.","authors":"Yanmei Chen, Mingyang Gu, Jing Li, Mengyue Qi, Xia Li, Jiaxing Luo, Huimin Xu, Fengying Duan, Shaobo Wei, James Richard Lloyd, Wenbin Zhou","doi":"10.1007/s11120-026-01224-2","DOIUrl":"10.1007/s11120-026-01224-2","url":null,"abstract":"<p><p>High light stress seriously compromises crop yields and food security. Protein phosphorylation plays a key regulatory role in high light responses; however, their complexity hinders a full understanding of these processes. To address this, we performed a system-wide quantitative phosphoproteomic analysis in maize and rice over a four-hour high light exposure. By comparing site-specific phosphorylation dynamics between the two species, we identified both conserved and species-specific phosphorylation events associated with light harvesting, electron transport, metabolism, ROS scavenging, and signal transduction. Enhanced phosphorylation of LHCB4 at a conserved phosphosite was observed for both plants, indicating a shared mechanism for light-harvesting complex remodeling. Specifically, maize showed unique phosphorylation regulation of D1 and the PSI subunit PsaE, implying a mechanism for restoring photodamaged reaction centers. In contrast, rice rapidly attenuated electron supply via reduced plastocyanin phosphorylation, concurrent with the early induced phosphorylation of phototropin and a receptor-like kinase. Furthermore, we found that phosphorylation dynamics of metabolic enzymes affect their activities, maize preferentially enhanced photosynthetic efficiency, whereas rice exhibited more tunable regulation across primary metabolism. Overall, this study provides a comprehensive phospho-signaling atlas, revealing convergent and divergent phosphorylation process that underlie differential high light acclimation in maize and rice.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148339510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Siphonous green macroalgae with contrasting capacities for the energy-dependent quenching, qE, rely on different photoprotective mechanisms.","authors":"Heta Mattila, Vesa Havurinne, Paulo Cartaxana, Sónia Cruz","doi":"10.1007/s11120-026-01225-1","DOIUrl":"10.1007/s11120-026-01225-1","url":null,"abstract":"<p><p>Bryopsidales green macroalgae can induce non-photochemical quenching (NPQ) only slowly, presumably due to the lack of the proton gradient-induced component (qE) of NPQ and xanthophyll cycle. Here, two morphologically rather similar siphonous macroalgae, a Bryopsidales alga Bryopsis sp. and a Dasycladales alga Acetabularia acetabulum, latter of which is capable of qE, were given high light treatments with both constant and fluctuating intensity. No differences in the rate of photoinhibition of Photosystem II (PSII), estimated with the chlorophyll a fluorescence parameter F_V/F_M, in the absence or presence of lincomycin, were observed between constant and fluctuating light, nor between the two algae. Bryopsis sp. showed slower PSII recovery than A. acetabulum, possibly reflecting a regulatory response rather than increased oxidative stress, as the recovery rates increased with increasing amounts of PSII photoinhibition in both algae. In Bryopsis sp., however, high light treatments led to decreased electron transfer rates, estimated by both chlorophyll a fluorescence and net oxygen production, whereas a stimulation was observed in A. acetabulum. Nigericin, which prevents the formation of qE, increased photoinhibition in A. acetabulum but not in Bryopsis sp. Microoxic conditions as well as inhibitors of plastid terminal oxidase and mitochondrial respiration, on the other hand, enhanced photoinhibition only in Bryopsis sp., suggesting that, in the absence of qE, oxygen-dependent pathways (including flavodiiron proteins) are important for photoprotection. Near-infra-red absorption measurements suggest decreased Photosystem I (PSI) donor side limitation in Bryopsis sp., compared to A. acetabulum, and a lower capacity to keep P700 oxidised.</p>","PeriodicalId":20130,"journal":{"name":"Photosynthesis Research","volume":"164 4","pages":""},"PeriodicalIF":3.8,"publicationDate":"2026-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13309506/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148339567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}