Primary Photosynthetic Processes Research Articles

Effect of Some Herbicides on Primary Photosynthesis in Malva moschata as a Prospective Plant for Agricultural Grass Mixtures

Musk mallow (Malva moschata) is a perennial European plant that grows in pastures and grass mixtures. M. moschata is a medicinal plant with a high content of polysaccharides, flavonoids, and other biologically active compounds. The sensitivity of the species to herbicides is, however, generally unknown. In our study, we investigated the effects of three herbicides with different active compounds: (1) Propaquizafop (PPQ), (2) Clopyralid (CPR), (3) Metamitron+Quinmerac (MMQ) on primary photosynthetic processes of M. moschata plants cultivated in two different temperatures (12 and 18 °C). Non-photochemical quenching (NPQ) of absorbed light energy by chlorophyll molecules and the parameters derived from fast chlorophyll fluorescence transient (OJIP) were evaluated before and then 1, 2, 5, 24, and 48 h after the herbicides application. Among the herbicides, only MMQ negatively affected the functioning of photosystem II (PSII). The effect, however, was reversible, and the plants reached pre-application values after 48 h. No herbicide-induced changes in NPQ were found over the time after the application. The majority of the OJIP-derived chlorophyll fluorescence parameters were found to be temperature-sensitive. The herbicides tested in our study may be ranked among those with only limited effects on primary photosynthetic processes in PSII. While the application of PPQ and CPR did not bring any negative effects on the functioning of PSII, MMQ application induced a decrease in the potential quantum yield of PSII (FV/FM) and activation of protective mechanisms, increased heat dissipation in particular. These changes, however, were fully alleviated 48 h after MMQ application.

Primary photosynthetic processes of Thalassiosira weissflogii under the effect of ciprofloxacin

Fluoroquinolone antibiotics such as ciprofloxacin have been actively used in medical practice, including the COVID-19 pandemic, to suppress adverse bacterial infections. Widespread application and improper disposal have resulted in the ubiquity of antibiotics in the environment, which can affect aquatic life, including phytoplankton. The effect of fluoroquinolone antibiotics on the photosynthetic processes of marine diatoms, which are the main producers in marine ecosystems, has been little studied. In this work the effect of the antibiotic ciprofloxacin on the primary photosynthetic processes in the marine diatom Thalassiosira weissflogii was studied. It has been shown that ciprofloxacin affects the functioning of PSII, preventing the transfer of absorbed energy from the excited antenna chlorophyll molecules to the PSII RC (φDo). Under the influence of ciprofloxacin, a decrease in the efficiency of electron donation to P680+ (FV / FO), inhibition of the quantum yield of PSII (FV / FM), a decrease in the proportion of active RCs (ABS / RC), and an increase in the dissipation of absorbed energy in RCs (DIo / RC) were revealed. It has been shown that the mechanism of action of ciprofloxacin is associated with damage of PSII RC. Ciprofloxacin enhances the photosensitivity of microalgae and causes an increase in lipid peroxidation products. It is proposed to apply the parameters of chlorophyll fluorescence analyzing the effect of antibiotics on microalgae.

Contents of endogenous brassinosteroids and the response to drought and/or exogenously applied 24-epibrassinolide in two different maize leaves.

Exogenously applied brassinosteroids (BRs) improve plant response to drought. However, many important aspects of this process, such as the potential differences caused by different developmental stages of analyzed organs at the beginning of drought, or by BR application before or during drought, remain still unexplored. The same applies for the response of different endogenous BRs belonging to the C27, C28-and C29- structural groups to drought and/or exogenous BRs. This study examines the physiological response of two different leaves (younger and older) of maize plants exposed to drought and treated with 24-epibrassinolide (epiBL), together with the contents of several C27, C28-and C29-BRs. Two timepoints of epiBL application (prior to and during drought) were utilized to ascertain how this could affect plant drought response and the contents of endogenous BRs. Marked differences in the contents of individual BRs between younger and older maize leaves were found: the younger leaves diverted their BR biosynthesis from C28-BRs to C29-BRs, probably at the very early biosynthetic steps, as the levels of C28-BR precursors were very low in these leaves, whereas C29-BR levels vere extremely high. Drought also apparently negatively affected contents of C28-BRs (particularly in the older leaves) and C29-BRs (particularly in the younger leaves) but not C27-BRs. The response of these two types of leaves to the combination of drought exposure and the application of exogenous epiBL differed in some aspects. The older leaves showed accelerated senescence under such conditions reflected in their reduced chlorophyll content and diminished efficiency of the primary photosynthetic processes. In contrast, the younger leaves of well-watered plants showed at first a reduction of proline levels in response to epiBL treatment, whereas in drought-stressed, epiBL pre-treated plants they were subsequently characterized by elevated amounts of proline. The contents of C29- and C27-BRs in plants treated with exogenous epiBL depended on the length of time between this treatment and the BR analysis regardless of plant water supply; they were more pronounced in plants subjected to the later epiBL treatment. The application of epiBL before or during drought did not result in any differences of plant response to this stressor.

Ambiguous changes in photosynthetic parameters of Lemna minor L. after short-term exposure to naproxen and paracetamol: Can the risk be ignored?

Non-steroidal anti-inflammatory drugs (NSAID) are recently monitored in the aquatic environment. Naproxen (NPX), paracetamol (PCT) and their transformation products can influence the biochemical and physiological processes at the sub-cellular and cellular levels taking part in the growth and development of plants. This study aimed to compare the effects of NPX and PCT, drugs with different physico-chemical properties, on the growth and photosynthetic processes in Lemna minor during a short-term (7 days) exposure. Although duckweed took up more than five times higher amount of PCT as compared to NPX (275.88 µg/g dry weight to 43.22 µg/g when treated with 10 mg/L), only NPX limited the number of new plants by 9% and 26% under 1 and 10 mg/L, respectively, and increased their dry weight (by 18% under 10 mg/L) and leaf area per plant. A considerable (by 30%) drop in the content of photosynthetic pigments under 10 mg/L treatment by both drugs did not significantly affect the efficiency of the primary processes of photosynthesis. Values of induced chlorophyll fluorescence parameters (F0, FV/FM, ΦII, and NPQ) showed just a mild stimulation by PCT and a negative effect by NPX (by up to 10%), especially on the function of photosystem II and electron transport in both intact duckweed plants and isolated chloroplasts. Lowered efficiency of Hill reaction activity (by more than 10% under 0.1 – 10 mg/L treatments) in isolated chloroplasts suspension proved the only inhibition effect of PCT to primary photosynthetic processes. In intact plants, higher treatments (0.5 - 10 mg/L) by both NPX and PCT induced an increase in RuBisCO content. The results prove that the potential effect of various drugs on plants is hard to generalise.

Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8′-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8′-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.

Genotypic variability in the functioning of photosystem II in leaves of covered and naked oats

Background. Comparing the characteristics of primary photosynthetic processes in photosystem II (PSII) in the leaves of two oat (Avena sativa L.) subspecies will help to understand their genetic differentiation. Comparisons between naked and covered oats to assess the efficiency of energy flows within PSII and its relation to useful agronomic traits have not been previously made but can have an effect on their cultivation practices.Materials and methods. Two-week-old plants of 16 covered and 17 naked oat genotypes were assessed for rapid chlorophyll α fluorescence using a Fluor Pen FP 110/S fluorometer. Data on the yield structure were obtained in 2021. The data were processed statistically using descriptive statistics, correlation (Excel 2013) and cluster (StatSoft Statistica 10; Ward's method) analyses.Results. The groups of oat genotypes differed significantly in the absolute magnitude of adsorbed (ABS/RC) and trapped (TRo/RC) light energy flows, which were higher in naked oats (by 7.8 and 7.4%, respectively). The efficiency of electron transfer from plastoquinone QB to PSI in naked oats exceeded that in covered oats by 8.2%. For the whole set of genotypes, a statistically significant correlation of grain yield with the PIABS performance index (r = 0.403), light energy adsorption (r = -0.477) and its utilization at the reaction centers of PSII (r = -0.452) was manifested. The performance indices (PIABS and PIABS_total) positively correlated with part of grain in total biomass (0.571 and 0.418, respectively) and were higher in covered oats (by 28.2 and 21.9%, respectively).Conclusion. The existence of significant differences was shown between covered and naked oats according to six of the nine evaluated structural and functional parameters of the PSII leaf functioning. The results of the cluster analysis demonstrated the tendency to the grouping of genotypes by the presence/absence of grain hullness.

Mathematical Simulation of Electron Transport in the Primary Photosynthetic Processes.

Summarized results of investigation of regulation of electron transport and associated processes in the photosynthetic membrane using methods of mathematical and computer modeling carried out at the Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, are presented in this review. Detailed kinetic models of processes in the thylakoid membrane were developed using the apparatus of differential equations. Fitting of the model curves to the data of spectral measurements allowed us to estimate the values of parameters that were not determined directly in experiments. The probabilistic method of agent-based Monte Carlo modeling provides ample opportunities for studying dynamics of heterogeneous systems based on the rules for the behavior of individual elements of the system. Algorithms for simplified representation of Big Data make it possible to monitor changes in the photosynthetic apparatus in the course of culture growth in a photobioreactor and for the purpose of environmental monitoring. Brownian and molecular models describe movement and interaction of individual electron carrier proteins and make it possible to study electrostatic, hydrophobic, and other interactions leading to regulation of conformational changes in the reaction complexes. Direct multiparticle models explicitly simulate Brownian diffusion of the mobile protein carriers and their electrostatic interactions with multienzyme complexes both in solution and in heterogeneous interior of a biomembrane. The combined use of methods of kinetic and Brownian multiparticle and molecular modeling makes it possible to study the mechanisms of regulation of an integral system of electron transport processes in plants and algae at molecular and subcellular levels.

Responses of primary photosynthetic processes to repetitive rehydration differ in two representatives of Svalbard moss flora

Global warming in polar regions brings a risk of more frequent and long-lasting dry periods due to warmer and windier climate during polar summers. Mosses are well adapted to desiccation-rehydration events and they have evolved remarkable constitutive and inducible mechanisms of desiccation tolerance. In our study, Sanionia uncinata and Racomitrium lanuginosum were collected in Svalbard and used for laboratory-based repetitive 32-h-lasting rehydration cycles with continuous monitoring of restoration of their primary photosynthetic processes measured by chlorophyll fluorescence parameters. Immediately after the addition of water to dry thalli, potential quantum yield of PSII (FV/FM) was about 50% of its maximum reached after 32 h of rehydration. In a course of time of rehydration, both species showed an increase in FV/FM and effective quantum yield (FPSII) following a S-curve relationship. Non-photochemical quenching did not show clear trend with the rehydration time, It differed between the two species and showed both decrease and increase with the time of rehydration. Relative chlorophyll fluorescence decrease (RFd), which is considered a vitality indicator, increase with the time of rehydration showing similar trends in the first and the third cycle of rehydration. The results indicate that both Sanionia uncinata and Racomitrium lanuginosum are resistant to desiccation since FV/FM and FPSII recovered fully after 32 h of rehydration and there we only minor differences in the two parameters between the first and third rehydration cycle.

The Effects of Foliar Application of Phenoxy and Imidazoline Family Herbicides on the Limitation of Primary Photosynthetic Processes in Galega orientalis L.

Fodder galega (Galega orientalis) is a perennial, wintering plant with great potential for agricultural development. The species has a large yield potential and exceptional adaptability to various environmental conditions. The sensitivity of G. orientalis to herbicides, however, as well as the photosynthetic performance of the species, are generally unknown. Our study aimed to evaluate the effects of the application of selected phenoxy herbicides (MCPA, MCPB) and the imidazoline family herbicide (IMA) on the parameters of primary photosynthetic processes as understood through fast chlorophyll fluorescence kinetics (OJIP). The effect of cultivation temperature was also investigated in the plants grown at 5, 18 and 25 °C. Time courses of OJIP-derived parameters describing photosystem II functioning after foliar application revealed that the plants showed negative responses to the herbicides in the order MCPB–MCPA–IMA within 24 h after the application. The application of herbicides decreased the values of maximum chlorophyll fluorescence (FM) and increased minimum fluorescence (F0), which led to a reduction in the maximal efficiency of PSII (FV/FM). Applications of MCPA and MCPB decreased variable chlorophyll fluorescence at 2 ms (VJ), 30 ms (VI) and VP, as well as the performance index (PIABS), which is considered a vitality proxy. The application increased absorption flux (ABS/RC), trapped energy flux (TRo/RC) and dissipated energy flux (DIo/RC). The effects were more pronounced in plants grown at 18 and 25 °C. The study revealed that the OJIP-derived parameters sensitively reflected an early response of G. orientalis to the foliar application of herbicides. Negative responses of PSII were more apparent in MCPA- and MCPB- exposed plants than IMA-exposed plants.

Combined chlorophyll fluorescence techniques to study environmental impact on the mountain moss Polytrichum commune

Two chlorophyll fluorescence (ChlF) methods were used to study the effects of high light (photoinhibition) and dehydration, common stressors of the alpine environment, on primary photosynthetic processes in the moss Polytrichum commune from the Czech Republic, the Jeseníky Mountains. Photoinhibition (PI) was studied in fully hydrated thalli of P. commune and during the period of spontaneous desiccation. Time courses of Kautsky kinetics (KK) of ChlF and derived parameters: maximum quantum yield (FV/FM), effective quantum yeld (ΦPSII), and non-photochemical quenching parameters, were measured before and after the samples were treated with high light (1500 µmol m-2 s-1 PAR) for 60 min. Dehydration effects were tested in two sets of experiments with a Pulse-Amplitude-Modulation fluorometry (PAM) and Fast Chlorophyll Fluorescence induction curve (OJIP) techniques. In PAM tests, the desiccating samples were exposed to saturating light pulses every 10 min. in order to obtain ΦPSII and non-photochemical quenching (NPQ). In the second dehydration experiment, OJIP transients of ChlF were repeatedly recorded, OJIP-derived ChlF parameters were plotted against relative water content (RWC) monitored during desiccation. Combined ChF techniques provided insights into the mechanisms activated during P. commune desiccation, such as dissipation of excess absorbed energy through heat dissipation, and conformational changes or destructions of the light harvesting complexes. Combination of stressors resulted in amplified interference with the photosynthetic machinery, even when the added stressor (dehydration) was applied in low dose.

Multiple invivo Effects of Cadmium on Photosynthetic Electron Transport in Pea Plants.

The inhibitory effects of cadmium (CdSO4 ) on the primary photosynthetic processes were studied invivo in Pisum sativum by using Multi-function Plant Efficiency Analyser (M-PEA-2). Photosynthetic parameters related to photosystem (PS) II, PS I and intersystem electron carriers were calculated from the light-induced kinetics of prompt chlorophyll a fluorescence (OJIP transient), delayed chlorophyll a fluorescence (DF), and 820 nm modulated reflection (MR). Low-dose exposure to cadmium (20 μm CdSO4 for 48 h) reduced probability of electron transfer from plastoquinones to the terminal electron acceptors of PSI (δRo ) accompanied by a decrease in the rate of P700 + and PC reduction (Vred ) and the magnitude of the I2 step on the DF kinetics. Electron transport through PSI remained unaltered. The obtained results allowed us to propose existence of the potential site of inhibition of photosynthetic electron flow by cadmium between PSII and PSI. We propose to use parameters δRo , Vred , and I2 /I1 as sensitive indicators of an early contamination by heavy metals.

Inhibition of Primary Photosynthesis in Desiccating Antarctic Lichens Differing in Their Photobionts, Thallus Morphology, and Spectral Properties.

Five macrolichens of different thallus morphology from Antarctica (King George Island) were used for this ecophysiological study. The effect of thallus desiccation on primary photosynthetic processes was examined. We investigated the lichens’ responses to the relative water content (RWC) in their thalli during the transition from a wet (RWC of 100%) to a dry state (RWC of 0%). The slow Kautsky kinetics of chlorophyll fluorescence (ChlF) that was recorded during controlled dehydration (RWC decreased from 100 to 0%) and supplemented with a quenching analysis revealed a polyphasic species-specific response of variable fluorescence. The changes in ChlF at a steady state (Fs), potential and effective quantum yields of photosystem II (FV/FM, ΦPSII), and nonphotochemical quenching (NPQ) reflected a desiccation-induced inhibition of the photosynthetic processes. The dehydration-dependent fall in FV/FM and ΦPSII was species-specific, starting at an RWC range of 22–32%. The critical RWC for ΦPSII was below 5%. The changes indicated the involvement of protective mechanisms in the chloroplastic apparatus of lichen photobionts at RWCs of below 20%. In both the wet and dry states, the spectral reflectance curves (SRC) (wavelength 400–800 nm) and indices (NDVI, PRI) of the studied lichen species were measured. Black Himantormia lugubris showed no difference in the SRCs between wet and dry state. Other lichens showed a higher reflectance in the dry state compared to the wet state. The lichen morphology and anatomy data, together with the ChlF and spectral reflectance data, are discussed in relation to its potential for ecophysiological studies in Antarctic lichens.

Effect of exogenously applied 20-hydroxyecdysone on the efficiency of primary photosynthetic processes substantially differs across plant species

The effects of 20-hydroxyecdysone on the primary photosynthetic processes (PPP) were examined across twelve plant species using the OJIP chlorophyll fluorescence analysis. Our experiments brought evidence that the ecdysteroids can function not only as protective compounds in plants but participate also in the regulation of photosynthesis. Exogenously applied 20-hydroxyecdysone positively affected the PPP particularly in French bean and canola. Contrary to this, the PPP were negatively influenced by 20-hydroxyecdysone in pea, sunflower, and wheat. The performace of the oxygen-evolving complex, the excitonic connectivity among PSII units, the electron transport between PSII and PSI, the size of the pool of the end electron acceptors, and the absorption and trapping of the excitation energy in the light-harvesting antennae were differently affected in individual plant species. Additionally, the older and younger leaves did not respond to 20-hydroxyecdysone in the same way and this was also a species-specific phenomenon.

Models of Photosynthetic Electron Transport

Energy transduction reactions in the photosynthetic membrane are a primary step in storing solar energy to be used later in biosynthetic and other processes in living systems. This review summarizes the recent data on modeling photosynthetic electron transport that were obtained at the Department of Biology, Moscow State University. Mathematical models of various types were used to simulate the processes that occur at the levels of macromolecules, their complexes, and molecular ensembles and at the subcellular and cell levels. Detailed kinetic models act by fitting model curves to experimental data and make it possible to estimate the contributions of individual processes to the observed processes and to identify the system parameters. The Monte Carlo method helps to simulate the processes that occur in ensembles of several millions of photosynthetic chains. Brownian and molecular dynamics were used to study the formation of electron-transport protein–protein complexes. A combination of the above methods provides the ability to study the basic mechanisms of energy conversion in multiscale energy-converting systems, such as the system of primary photosynthetic processes.

Physiological and biochemical parameters of apricot varieties characterized by various drought resistance

The aim of the presented work was to identify the peculiarities of the photosynthetic apparatus, the activity of redox enzymes and proline content in apricot varieties with different drought tolerance. Four apricot varieties such as Kazachok, Nagycorosi Orias, Khurmai and Krymsky Amur were used as objects of the studies. To determine the effect of drought on the state of the photosynthetic apparatus, a series of experiments was carried out to analyze chlorophyll fluorescence induction (ChFI) parameters, peroxidase and polyphenol oxidase activity and proline content in apricot leaves. It was found out that in summer 2018, when the amount of precipitation exceeded the climatic norm, during the period of the maximum drought probability, catalase activity decreased, polyphenol oxidase activity increased or was unchanged and the proline content did not change significantly. Extremely arid conditions in summer 2019 resulted in peroxidase and polyphenol oxidase activation and a decrease in the proline concentration in all the studied apricot varieties. However, the drought tolerant variety Nagycorosi Orias was characterized by the most stable indexes of peroxidase activity during the entire experiment. A decrease in the leaf tissue hydration was the reason for the increase in the base fluorescence and the decrease in the correlation index of the rate constants of photochemical and nonphotochemical deactivation of excitation in PS 2. In the drought tolerant varieties Nagycorosi Orias and Kazachok changes in the ChFI parameters were reversible. It has been demonstrated that disturbances during primary photosynthetic processes were most pronounced during the restoration of turgidity. It was revealed that the most sensitive parameters of ChFI in apricot are the characteristics of the fast phase. A decrease in reparative abilities in the midsummer was probably associated with age-related changes in leaves and fruit load.

Chilling effects on primary photosynthetic processes in Medicago sativa: Acclimatory changes after short- and long-term exposure to low temperatures

Two cutivars (cv.) of alfalfa (Medicago sativa L.) were used to study the influence of chilling on chlorophyll fluorescence parameters related to the photosynthetic performance of photosystem II (PS II). Potted plants were exposed to two chilling treatments (10 and 5 °C) for 15 and 22 days, respectively. After the chilling, basic chlorophyll fluorescence parameters (FV/FM, ΦPSII, qN) and chlorophyll fluorescence signals emitted from light-harvesting complexes (F0 — backgroung chlorophyll fluorescence) were measured by slow Kautsky kinetics supplemented by quenching analysis. Short-term effect of 5 °C was evaluated by fast chlorophyll fluorescence transients (OJIPs). Chilling did not lead to any change in FV/FM and ΦPSII in both cultivars, indicating their chilling tolerance. Background chlorophyll fluorescence showed a chilling-induced increase in the cv. Zuzana but not the cv. Holyna. The F0 increase was attributed to functional detachment of light-harvesting complexes from core PS II. In both cultivars, chilling treatment led to a decrease in non-photochemical quenching (qN). This decrease was attributed to a long-term acclimation of plants to low temperatures and the adjustment of PS II processes and photosynthetic performance. The shape of OJIP curves and OJIP-derived chlorophyll fluorescence parameters were found to be temperature-dependent after a short-term exposition to 5 °C. Both alfalfa cultivars showed chilling tolerance; however, the results suggest that the cv. Holyna may be more chilling-tolerant than the cv. Zuzana.

24-Epibrassinolide alleviates the toxic effects of NaCl on photosynthetic processes in potato plants.

Brassinosteroids are promising agents for alleviating the negative effects of salinity on plants, but the mechanism of their protective action is far from being understood. We investigated the effect of pretreatment with 24-epibrassinolide (24-EBL) on the photosynthetic and physiological parameters of potato plants under progressive salinity stress caused by root application of 100mM NaCl. Salinity clearly inhibited primary photosynthetic processes in potato plants by reducing the contents of photosynthetic pigments, photosynthetic electron transport and photosystem II (PSII) maximal and effective quantum yields. These negative effects of salinity on primary photosynthetic processes were mainly due to toxic ionic effects on the plant's ability to oxidize the plastoquinone pool. Pretreatment with 24-EBL alleviated this stress effect and allowed the maintenance of plastoquinone pool oxidation and the efficiency of photosystem II photochemistry to be at the same levels as those in unstressed plants; however, the pretreatment did not affect the photosynthetic pigment content. 24-EBL pretreatment clearly alleviated the decrease in leaf osmotic potential under salinity stress. The stress-induced increases in lipid peroxidation and proline contents were not changed under brassinosteroid pretreatment. However, 24-EBL pretreatment increased the peroxidase activity and improved the K+/Na+ ratio in potato leaves, which were likely responsible for the protective 24-EBL action under salt stress.

Photoinhibition of primary photosynthetic processes in hydrated Polytrichum commune: Analysis of non-photochemical quenching affecting species resistance

A moss from the alpine environment of the Jeseníky mountains, Polytrichum commune, was studied under lab-induced light stress to analyse photoinhibition (PI) stress response; three PI doses were used: PAR 1500 µmol m-2 s-1 for 60 min., 1200 µmol m-2 s-1 for 60 min. and 1200 µmol m-2 s-1 for 30 min.; in the last one the added component of slight desiccation stress was added. Chlorophyll fluorescence parameters were plotted as time series, immediately before and after the PI treatments, then every 20 minutes for three hours (recovery period). FV/FM, ΦPSII and NPQ parameters and quenching components were analysed. Decreasing courses and final values of FV/FM and ΦPSII parameters along with increased values of NPQ clearly indicated PI stress response, although not very severe. Quenching parameters analysis showed a dominant role played by xanthophyll pigments along with changes in PS II in the non-photochemical energy quenching. Dehydration contributed additional value to NPQ. All these factors are consistent with the adaptation of the species to harsh conditions of alpine environments.

β-Carotene Probes the Energy Transfer Pathway in the Photosystem II Core Complex.

The dynamics of the intact photosystem II core complex (PSII-CC) has been investigated extensively to elucidate its excellent photofunction. However, it is significantly difficult to observe the primary photosynthetic processes in PSII-CC because a vast number of chlorophylls (Chl) in the core complex show similar spectral features. In the present work, the dynamics of the energy transfer (ET) from β-carotene (Bcr) in intact PSII-CC followed by charge separation (CS) at the reaction center (RC) with different excitation wavelengths were compared. Upon excitation at 510 nm, which selectively excites Bcr (Bcr651) inside of the D1-D2 RC, the pheophytin anion absorption band appeared within 9.6 ps. On the other hand, upon excitation at 490 nm, mainly exciting unspecified Bcr in the antenna complex, the anion band appeared after 20 ps. These excitation wavelength dependence experiments revealed a new ET pathway of PSII-CC, which indicates that the initial CS of PSII-CC is limited by ET to the RC.

Temperature effects on photosynthetic performance of Antarctic lichen Dermatocarpon polyphyllizum: a chlorophyll fluorescence study

Chlorophyll fluorescence is an important indicator of a photosynthetic energy conversion in chloroplast photosystem II and responds sensitively to stress factors affecting photosynthesizing organisms. Three different methods were employed to identify the most sensitive fluorescence parameters responding to thallus temperature decrease within Antarctic lichen Dermatocarpon polyphyllizum: (1) Fast chlorophyll fluorescence transient (OJIP with parameters characterizing photosystem II functioning) (2) Slow Kautsky kinetics supplemented by saturation pulses (to evaluate quantum yield of photosynthetic processes in photosystem II, as well as maximum quantum PSII efficiency and non-photochemical and photochemical quenching), and (3) Linear cooling from + 22 to − 40 °C (to determine change in ΦPSII and the critical temperature for PSII). A K-step (usually documented at highly stressed organisms) was found in OJIPs measured at + 22 °C at 0.22–0.40 ms and attributed to the negative effect of high temperature on PSII functioning, PSII donor side limitation in particular. At subzero temperature (− 0.5, − 5 °C), an L-step was detected at 0.05 ms and related to a low temperature-induced decrease in connectivity between light-harvesting complexes and PSII. An increase of DI0/RC (the flux of dissipated excitation energy) was reported for the first time in lichens. The OJIP-derived parameters, DI0/RC and Phi_D0 (quantum yield of energy dissipation) in particular, indicated that they might be used for the detection of early events in low temperature-affected lichens. Linear cooling data determined the critical temperature (− 12 °C) for primary photosynthetic processes (ΦPSII) in Dermatocarpon.