Photosynthetica - Ahead of Print
A life in light: celebrating the 75th birthday of Professor Suleyman I. Allakhverdiev
B.D. BRUCE, T. TATSUYA, G. GOVINDJEE, G. GARAB, A S. RAGHAVENDRA, S. RAMAKRISHNA, A. LARKUM, J.J. EATON-RYE, J.R. SHEN, R. SUBRAMANYAM, M.M. NAJAFPOUR
Photosynthetica X:X | DOI: 10.32615/ps.2026.007 
This Special Issue of Photosynthetica is dedicated to celebrating the distinguished scientific life and 75th birthday of Professor Suleyman I. Allakhverdiev (born 1 August 1950), whose contributions have left an enduring mark on modern photosynthesis research, photobiology, and bioenergetics. His pioneering studies of Photosystem II advanced the field in fundamental ways, including establishing pheophytin as the primary electron acceptor, defining the functional Mn₄ water-oxidizing cluster and its reconstitution, and clarifying the redox properties of key cofactors such as QA, QB, and P680....
Role of pheophytin in chlorophyll a fluorescence transients
G. GARAB
Photosynthetica X:X | DOI: 10.32615/ps.2026.008
In this review, I revisit the groundbreaking discovery of pheophytin a (Pheo) in the primary charge separation of photosystem II (PSII) reaction centres (RCs) and draw attention to key observations that concern the origin of the variable chlorophyll a fluorescence (Fv) of PSII as well as the partitioning of the absorbed quanta between different de-excitation pathways. In particular, I recall data from the 1970s and 1980s, which have revealed photoreduction of Pheo in closed PSII (PSIIC) containing the primary quinone acceptor in reduced form, and in photoinhibited PSII with largely suppressed Fv. Taken...
Chloroplast structure and photosynthetic acclimation in shade-adapted lycophyte Selaginella: a window into photosynthesis of ancient vascular plants?
L. FERRONI
Photosynthetica X:X | DOI: 10.32615/ps.2026.010
Selaginella is a diverse genus of lycophytes, an ancient group of vascular plants that is sister to all other vascular plants (euphyllophytes, including angiosperms). The majority of Selaginella species thrive in environments with humid, shaded conditions. This review examines current knowledge and unresolved issues concerning the distinctive photosynthetic adaptations of shade-adapted Selaginella species, addressing aspects from cell morphology to thylakoid organisation. Unique is their giant chloroplast, in which the thylakoid system can differentiate into lamellar and granal (bizonoplast). Optimisation of light harvesting and photoprotection...
A perspective on why modeling the water-oxidizing complexin photosystem II remains functionally elusive
M.M. NAJAFPOUR
Photosynthetica X:X | DOI: 10.32615/ps.2026.011
The water-oxidation reaction (WOR) is a critical yet kinetically sluggish process, requiring a complex four-electron transformation. Manganese (Mn) is a premier candidate for WOR catalysts due to its low cost, low toxicity, and its fundamental role in natural photosynthesis. Consequently, extensive research has focused on designing Mn-based ligands and compounds. However, a significant challenge persists: harsh oxidizing conditions necessary for WOR often trigger unintended phase transformations. Spectroscopy reveals that many Mn complexes and salts - even biomimetic clusters - eventually degrade or rearrange into various Mn oxides. This typically...
What's in your pellet? 16S rRNA V4 amplicon-profiling reveals persistent microbiomes in laboratory cyanobacterial cultures
M.S. RAO, J. MONDAL, B.D. BRUCE
Photosynthetica X:X | DOI: 10.32615/ps.2026.013
Cyanobacterial laboratory cultures are widely assumed to be axenic, yet the diversity and associated microorganisms are rarely examined. In this study, 16S rRNA V4 amplicon sequencing was used to characterize microbial communities associated with multiple cyanobacterial strains maintained in laboratory cultures and large-scale photobioreactors. Analysis of 24 samples revealed persistent, culture-specific microbiomes dominated by heterotrophic bacteria. Distinct ecological patterns were observed, including consistent differences between thermophilic and mesophilic cyanobacterial cultures and repeated detection of taxa linked to geothermal or freshwater...
Salt stress in cyanobacteria and its relevance to energy management
I. ALAMIN, J. SEBESTA, V.A. DENNIS, J. YU, H.J.M. HOU
Photosynthetica X:X | DOI: 10.32615/ps.2026.015
Energy management in photosynthetic organisms occurs at multiple levels, including the electron transfer and metabolic reactions. Salt stress imposes osmotic, ionic, energetic, and oxidative constraints on cyanobacteria, profoundly reshaping carbon allocation and photosynthetic performance. To maintain osmotic balance, cyanobacteria employ a salt-out strategy, accumulating compatible solutes such as glucosylglycerol and sucrose while maintaining low intracellular Na⁺ concentrations. This review provides a comprehensive perspective by synthesizing current knowledge on cyanobacterial overflow under salt stress, emphasizing its physiological context...
Response of the photosynthetic apparatus of turfgrass varieties of perennial ryegrass and red fescue to naphthalene and fluoranthene contamination
P. DˇBROWSKI, T. GNATOWSKI, J. PRZYBYŁOWSKI, M.J. MAŁUSZYŃSKI, I. MAŁUSZYŃSKA, B. PAWLU¦KIEWICZ, H.M. KALAJI
Photosynthetica X:X | DOI: 10.32615/ps.2026.016
The accumulation of polycyclic aromatic hydrocarbons (PAH) in urban soils poses a serious threat to plants. In this study, we compared the effects of naphthalene and fluoranthene on the photosynthetic apparatus of two lawn grass species: Lolium perenne L. (vars. Nira and Roadrunner) and Festuca rubra L. (var. Nimba). Compounds were applied to the substrate at concentrations of 20 and 40 mg kg-1(DM). Plant gas exchange and chlorophyll a fluorescence parameters were measured at 0, 240, and 480 h after their application. All treatments caused a progressive, time-dependent decline in the photosynthetic performance of the...
Modulation of growth and photosynthetic efficiency in common buckwheat through combined seed priming and foliar application of silicon under drought
M.R.H. RAIHAN, F. AHMED, A. RASTOGI
Photosynthetica X:X | DOI: 10.32615/ps.2026.017
This study aimed to evaluate the effectiveness of silicon (0.5 and 1.0 mM), applied through seed priming, foliar spray, and their combined application, in enhancing drought tolerance in buckwheat under 30% field water capacity by modulating key physiological mechanisms. Drought markedly reduced growth attributes and impaired PSII efficiency and gas exchange. Under drought conditions, the combined 1.0 mM Si treatment increased fresh and dry biomass by 54 and 96%, respectively, and enhanced leaf thickness by 39% compared with untreated plants. The photosynthetic rate increased from -0.22 to 1.87 µmol(CO2) m-2 s-1,...
Differentiating seasonal trends and environmental responses in wheat through longitudinal chlorophyll a fluorescence phenotyping
M. ZIVCAK, M. KOVAR, A. DAS, M. BARBORICOVA, D. PALOVOVA, P. HAUPTVOGEL, M. BRESTIC
Photosynthetica X:X | DOI: 10.32615/ps.2026.020
Broad adoption of chlorophyll fluorescence kinetics in crop phenotyping remains limited by inconsistent parameter definitions and insufficient physiological validation. This study employed a longitudinal phenomic approach to evaluate the diagnostic value of rapid chlorophyll a fluorescence kinetics across diverse wheat genotypes throughout a spring growing season. By combining JIP-test parameters with detailed growth analysis, we built a statistical framework quantifying the predictive power and unexplained variance of biophysical parameters derived from the JIP-test, with an emphasis on performance-estimating indices. Results show that conventional...
Functional variation in PSII traits along post-disturbance successional gradient in montane springs
G. JAMNICKÁ, H. HÚDOKOVÁ, P. FLEISCHER Jr., A. RAZZAK, Ą. DITMAROVÁ, M. SLEZÁK
Photosynthetica X:X | DOI: 10.32615/ps.2026.021
The effects of post-windstorm succession on mountain spring vegetation were studied in the High Tatra Mountains (Slovakia, Central Europe) through field sampling conducted over the 2020-2025 period, assessing chlorophyll a fluorescence to compare windthrow-affected and unaffected plots. Variance partitioning revealed that structural PSII parameters (absorption flux per RC, relative variable fluorescence at the J step) are primarily species-dependent, whereas maximum quantum yield is environment-driven. Within-site analyses validated that species-specific PSII architecture persists under uniform conditions. The invasive Impatiens parviflora...
Functional plasticity of pigment systems in microalgae and cyanobacteria under variable environmental conditions
B.D. KOSSALBAYEV, A.K. SADVAKASOVA, S.K. SANDYBAYEVA, D.E. ZALETOVA, E.M. ZAIYR
Photosynthetica X:X | DOI: 10.32615/ps.2026.022
Microalgae and cyanobacteria reconfigure pigment-protein complexes as environments change, coupling light harvesting, photochemistry, and redox homeostasis. This review synthesizes the mechanisms driving shifts in chlorophylls, carotenoids, and phycobiliproteins in response to abiotic and anthropogenic stressors, including irradiance, temperature, salinity, nutrient limitation, and pollutants. Pigment measurements are most informative when interpreted as profiles of individual pigments, absolute abundances, and diagnostically relevant ratios, and when analyzed together with photosystem performance and independent oxidative-damage markers. Key strategies...
Interactions of PsbT with Val247 and Ser254 in the DE-loop of the D2 protein stabilize the quinone-iron electron acceptor complex of Photosystem II
V. ZHONG, I. VASS, J.J. EATON-RYE
Photosynthetica X:X | DOI: 10.32615/ps.2026.024
The non-heme iron of Photosystem II (PSII), found between the primary (QA) and secondary (QB) plastoquinone electron acceptors, is coordinated by histidine residues from the D1 and D2 reaction center proteins and a bicarbonate ion. The D2-Val247 and D2-Ser254 residues of the DE hydrophilic loop of D2 are located in the QA-binding region and interact with the PsbT subunit. Substitutions at these residues caused reductions in photoautotrophic growth, increased sensitivity to high light, and weakened bicarbonate binding. In addition, the core antenna CP43 protein accumulated in these mutants and electron transfer from...
Bioengineering photosynthesis to cope with combined stresses for future climates
P. YUN, S. SHABALA
Photosynthetica X:X | DOI: 10.32615/ps.2026.029
Global climate change is leading to a challenging environment for agriculture. With more frequent and severe weather extremes, agricultural systems will need to deal with complex combinations of abiotic stresses under future climate scenarios. In this review, we discuss four types of combined stresses likely to occur in the foreseeable future and their impacts on plant photosynthesis. We also briefly review progress and bioengineering targets for improving photosynthesis under such future scenarios, focusing on transcription factors, the trehalose 6-phosphate pathway, light reactions, and the Calvin-Benson-Bassham cycle of photosynthesis. We then proposed...
Exogenous γ-aminobutyric acid (GABA) application delays physiological damage caused by acute water deficit in Persian lime
F.R. FLORES-DE LA ROSA, N.A. GONZÁLEZ-OVIEDO, L.E. SAUCEDO-PICAZO, H. ESTRELLA-MALDONADO, G. FUENTES, R. SANTILLÁN-MENDOZA, J.M. SANTAMARÍA
Photosynthetica X:X | DOI: 10.32615/ps.2026.036
Persian lime (Citrus latifolia) is one of Mexico's most important fruit crops and is increasingly exposed to sudden drought events caused by climate change. This study evaluated the effect of foliar γ-aminobutyric acid (GABA) application on the physiological response of Persian lime plants subjected to acute water deficit. Six-month-old plants grafted onto Volkameriana rootstock were treated with 100 mM GABA and subjected to 14 days of irrigation withdrawal, followed by 7 days of rewatering. We assessed chlorophyll fluorescence, gas exchange, and plant water relations. Untreated plants exhibited severe physiological decline, irreversible...
Leaf photosynthesis is enhanced, not impaired, under severe potassium limitation in spinach despite arrested growth
K. NOMURA, Y. TANAKA, M. KOBAYASHI, M. SAITO, I. TADA, M. KITANO
Photosynthetica X:X | DOI: 10.32615/ps.2026.037
Potassium (K) deficiency has conventionally been reported to suppress leaf photosynthesis and growth. We show that in hydroponically grown spinach (Spinacia oleracea L.), severe K limitation maintained or increased the net photosynthetic rate per unit leaf area (PN) at both ambient and saturating CO2 concentrations with increased stomatal conductance, while whole-plant growth was severely restricted. Compared with K-sufficient controls, K-limited leaves had higher leaf mass per area, nitrogen and phosphorus concentrations, and SPAD values, whereas CO2-saturated photosynthetic rates per unit dry mass...