Fluorescence Induction Curves Research Articles

The efficiency of chlorophyll fluorescence as a selection criterion for salinity and climate aridity tolerance in barley genotypes.

In the Near East and North Africa (NENA) region, crop production is being affected by various abiotic factors, including freshwater scarcity, climate, and soil salinity. As a result, farmers in this region are in search of salt-tolerant crops that can thrive in these harsh environments, using poor-quality groundwater. The main staple food crop for most of the countries in this region, Tunisia included, is barley. The present study was designed to investigate the sensitivity and tolerance of six distinct barley genotypes to aridity and salinity stresses in five different natural field environments by measuring their photosynthetic activity. The results revealed that tolerant genotypes were significantly less affected by these stress factors than sensitive genotypes. The genotypes that were more susceptible to salinity and aridity stress exhibited a significant decline in their photosynthetic activity. Additionally, the fluorescence yields in growth phases J, I, and P declined significantly in the order of humid environment (BEJ), semi-arid site (KAI), and arid environment (MED) and became more significant when salt stress was added through the use of saline water for irrigation. The stress adversely affected the quantum yield of primary photochemistry (φP0), the quantum yield of electron transport (φE0), and the efficiency by trapped excitation (ψ0) in the vulnerable barley genotypes. Moreover, the performance index (PI) of the photosystem II (PSII) was found to be the most distinguishing parameter among the genotypes tested. The PI of sensitive genotypes was adversely affected by aridity and salinity. The PI of ICARDA20 and Konouz decreased by approximately 18% and 33%, respectively, when irrigated with non-saline water. The reduction was even greater, reaching 39%, for both genotypes when irrigated with saline water. However, tolerant genotypes Souihli and Batini 100/1B were less impacted by these stress factors.The fluorescence study provided insights into the photosynthetic apparatus of barley genotypes under stress. It enabled reliable salinity tolerance screening. Furthermore, the study confirmed that the chlorophyll a fluorescence induction curve had an inflection point (step K) even before the onset of visible signs of stress, indicating physiological disturbances, making chlorophyll fluorescence an effective tool for identifying salinity tolerance in barley.

Features of the water regime and photosynthesis in hybrid forms of cherry plum under the dry wind season conditions

Background. The results of a study on the drought resistance of cherry plum hybrid forms are presented. Water retention capacity of leaves and chlorophyll fluorescence were measured under the simulated conditions close to the dry wind season.Materials and methods. The water regime parameters were studied for five cherry plum genotypes in 2021 and 2022. Leaves of four hybrid forms developed at the Nikita Botanical Gardens and the reference cherry plum hybrid cultivar ‘Rumyanaya Zorka’ (Prunus rossica Erem.) were taken into the experiments. Using the guidelines by G. N. Eremeev and A. I. Lishchuk, a series of experiments on controlled leaf wilt at the air temperature of +27°C and relative humidity of 30% were conducted on cherry plum to assess the functional state of the photosynthetic apparatus during the development of water stress under dry wind conditions. The experiments were carried out in a Binder climate chamber. Chlorophyll fluorescence was measured using a portable Floratest fluorometer. The measurements were based on the parameters of the chlorophyll fluorescence induction curve (CFI) obtained on native leaves. The leaves of cv. ‘Rumyanaya Zorka’ in the state of complete watering served as the reference.Results and discussion. Dependence was identified between chlorophyll fluorescence and moisture content in the leaves of the studied samples. The hybrids were found to respond to drought in different ways. A relatively increased ability to retain moisture during dehydration was observed in form 12/26 whose leaves gave off moisture more slowly and restored their turgor better. It is promising for cultivation in areas with insufficient water supply. Form 99/36 had the lowest potential drought resistance. Forms 99/14 and 9/28 occupied an intermediate position.

Stress-induced delay of the I-P rise of the fast chlorophyll a fluorescence transient in tomato

Fast chlorophyll a fluorescence induction curve (OJIP) provides a powerful tool for rapidly assessing the photosynthetic performance of plants. However, the application of this technology in tomato plants is scarce. Here, OJIP curve was used to evaluate the photosynthetic performance of tomato plants under chilling and drought stress, and interpretation of the obtained OJIP curves was improved. The results showed that the performance index (PI-abs) and the amplitude of I-P phase of greenhouse-grown tomato plants decreased rapidly with the decline of ambient temperatures and fluctuated with the changes in temperature during the autumn-winter transition. However, photosystem II efficacy (Fv/Fm) showed slow response. In the chambers, net photosynthetic rate (PN) and photochemical efficiency were inhibited by short-term chilling stress. The amplitudes of O-J phase and I-P phase were slightly affected by chilling stress. Interestingly, the appearance of I points of OJIP curves was delayed by chilling stress. Consequently, the corrected amplitudes of I-P phase were found to be significantly inhibited by chilling. Moreover, the corrected amplitudes of I-P phase correlated well with PN and PI-abs, during chilling and subsequent recovery. Mutation of PGR5, which is involved in cyclic electron flow, resulted in declines of photosynthetic parameters including the corrected amplitudes of I-P phase under control and chilling conditions. Under drought stress, the corrected amplitudes of I-P phase and operational photochemical efficiency [Y(II)] also progressively declined in parallel. However, Fv/Fm remained stable even when plants showed a wilting phenotype. Our results indicate that the delay of I point by stress should be considered when using the amplitude of I-P phase to reflect the status of photosynthetic apparatus in response to stress.

Ultrastructure, CO2 Assimilation and Chlorophyll Fluorescence Kinetics in Photosynthesizing Glycine max Callus and Leaf Mesophyll Tissues

The ultrastructural and functional features of photosynthesizing callus cells are poorly known. Electron microscopy studies on green, compact Glycine max calluses have shown that they are composed of photosynthesizing cells characterized by clear ultrastructural signs of senescence. Studies on chlorophyll fluorescence and CO2 assimilation kinetics have shown that such cells were still able to maintain photosynthesis but could not compensate for the respiratory CO2 uptake. Having a one-step CO2 assimilation kinetics, photosynthesis in calluses differed from photosynthesis in leaves, which had a two-step CO2 assimilation kinetics. In contrast to leaves, the fluorescence induction curves in G. max calluses strongly differed in shape depending on the color of actinic light (red or blue). Red (in contrast to blue) light excitation did not lead to CO2 assimilation in the calluses, thus suggesting anoxygenic photosynthesis in this case. In particular, the data obtained indicate that the actinic light spectrum should be considered when cultivating calluses for micropropagation of plants and for callus tissue research.

Effects of UV radiation on photosynthesis of Sargassum muticum

As an invasive species of macroalgae, Sargassum muticum (Yendo) Fensholt has invaded European shores and the Mediterranean, and even drifting individuals have been observed in sea area near the Canary Islands, becoming a potential species responsible for the “Sargassum golden tide”. When drifting on the sea surface, algae receive more ultraviolet radiation (UVR). However, photosynthetic responses and adaptation mechanism of S. muticum to UVR remain unclear. In this study, thalli of S. muticum were respectively exposed under two radiation treatments of 200 W m−2 PAR (photosynthetically active radiation, 400–700 nm), and 200 W m−2 PAR + 38 W m−2 UVR (280–700 nm) for 120 mins, and then recovered at a low light (PAR) of 10 μmol photons m−2 s−1 for 240 mins. During this treatment, the photosynthetic properties of algae were measured, to investigate the responses and protection mechanism of S. muticum to UVR. The results showed that photosynthesis of thalli was significantly inhibited by UVR, reflected by decreased maximum photochemical quantum yield (Fv/Fm) and chlorophyll content, and changes of parameters of rapid light response curve and chlorophyll fluorescence induction curve in PAR and PAR + UVR treatments. Meanwhile, algae actively adopted several strategies to alleviate the inhibition caused by UVR, including photoprotection characterized by increased contents of UV-absorbing compounds (UVACs) and carotenoids (Car), excess light energy dissipation by elevated non-photochemical quenching (NPQ) coupled to the xanthophyll cycle, and photorepair manifested as an accelerated synthesis of D1 protein and enhanced antioxidant for scavenging ROS. Benefiting from the effects of the above several pathways, after 240 mins of low light recovery, photosynthesis was greatly restored in these two radiation treatments, with the restoration of Fv/Fm and parameters of rapid light response curve and chlorophyll fluorescence induction curve. Based on these results, we conservatively speculate that the photosynthesis of drifting S. muticum individuals may be restored in the evening with low light levels after being damaged by UVR on the surface of sea at midday, resulting in maintaining rapid growth and forming a golden tide.

Smart-Systems for Precision Agriculture, Environmental Protection and Healthcare

Appearance of innovative tools of informatics in the world is determined by development of information-communication technology, microelectronics, sensor and biosensor technologies. Spreading of these technologies on precision agriculture, environmental protection and health care gives opportunity to create smart fields, gardens, greenhouses, forests and parks, and also smart health monitors, which estimate the health state of person as in rehabilitation, so in emergency situations. Results of research of authors in the development of new information technologies and creation of main components of the smart systems for different purposes on this base are shows in this paper. Main requirements for knowledge bank for precision agriculture and ecological monitoring are defined. Main principles of creating knowledge bank on base of requirements are proposed. The typical smart system models and their development stages are considered. Structure of wireless multilevel networks for the estimation of state of biological objects of different origin and their nodes are described. Developed sensor networks and smart systems for agriculture are considered. Structure of proposed smart system for agriculture and ecological monitoring is given. Approaches for chlorophyll fluorescence induction curves analysis are studied. Results of network testing for the estimation of the autonomous work time of network nodes and possible errors are given. Wireless sensor network and smart system for remote medical monitoring are described. Diagnostic smart systems for estimation of quality of life are considered. Medical communicator, computer device on base of tablet computer, was used for their development. The short form of Survey Instrument (SF-36) for life quality estimation and abnormal uterine bleeding questionnaire, which was developed in State Scientific Institution "Center for Innovative Medical Technologies of the National Academy of Sciences of Ukraine", were embedded in communicator. STEPS questionnaire which was designed for epidemiological monitoring of the prevalence of noncommunicable diseases and their risk factors in the target subpopulations could be added to communicator. Development of smart systems for estimation of quality of life and prevalence of noncommunicable diseases was made in cooperation with R.E. Kavetsky Institute of Experimental Pathology, Oncology and Radiobiology NAS of Ukraine (department of research management and innovation), Chebotarev Institute of Gerontology of the National Academy of Medical Sciences of Ukraine, Center for Innovative Medical Technologies of the National Academy of Sciences of the Ukraine. Keywords: wireless sensor network, precision agriculture, chlorophyll fluorescence induction, express-diagnostics of plant state, quality of life, SF-36.

Water-Deficit Stress in the Epiphytic Elkhorn Fern: Insight into Photosynthetic Response.

Progressive climate changes cause disturbance of water relations in tropical rainforests, where epiphytic ferns are an important element of biodiversity. In these plants, the efficiency of photosynthesis is closely related to the efficiency of water transport. In addition, due to the lack of contact with the soil, epiphytes are extremely susceptible to water-deficit stress. The aim of this experiment was to determine the response of the photosynthetic apparatus of Platycerium bifurcatum to a 6-week water deficit. The hydration and pigment composition of leaves were determined using reflectance spectroscopy and epifluorescence microscopy. Chlorophyll a fluorescence kinetics parameters, fluorescence induction curves (OJIP), low-temperature fluorescence curves at 77 K and proline concentration were analyzed at seven time points. After a decrease in leaf hydration by 10-15%, there were disturbances in the oxidation-reduction balance, especially in the initial photochemical reactions, a rapid decrease in plant vitality (PI) and significant fluctuations in chlorophyll a fluorescence parameters. The relative size of PSI antenna structures compared to PSII decreased in the following weeks of water deficit. Changes in photochemical reactions were accompanied by a decrease in gross photosynthesis and an increase in proline concentration. Changes in the functioning of photosynthesis light phase and the pigment composition of leaves are related to the resistance of elkhorn fern to long-term water deficit.

Выявление токсического воздействия тяжёлых металлов на фитопланктон с помощью анализа индукционных кривых флуоресценции хлорофилла методами машинного обучения

The creation of a network of autonomous stations for bioindication of water bodies state requires the development of methods for analyzing large data arrays. The combination of machine learning methods with traditional statistical methods is used to identify implicit patterns in the dataset for the effect of heavy metals on natural phytoplankton. The array of experimental data consists of 465 fluorescence induction curves measured on phytoplankton samples from 9 water bodies of the Pskov region, and reflecting the dynamics of electron transfer in the photosynthetic apparatus. Each curve is characterized by 14 JIP-test parameters, some of which directly describe the shape of the curve; the others connect the shape of the curve with the energy flows that occur in the photosynthetic apparatus under illumination. Cluster analysis based on a set of JIP-test parameters was used to distinguish photosynthetic activity first among phytoplankton samples in control and then under long-term exposure to cadmium and chromium salts. In the control samples, two groups were identified that differ in the photosynthetic activity of phytoplankton. It is assumed that the lower photosynthetic activity of phytoplankton samples is associated with anthropogenic pressure on the water bodies. It was shown that the samples with initially low photosynthetic activity responded to the toxic effect of heavy metals at later periods of incubation compared to more active samples. The proposed approach can be easily scaled to analyze large arrays of experimental data that makes it a promising tool for the early detection of toxic pollution of natural waters.

Adaptation of gooseberry varieties to the changed agro-climatic conditions of Kyiv Polissia

In connection with global warming, the study of plant adaptation to climate change, resistance to lack of moisture and high temperatures becomes relevant. Meteorological and phenological observations prove that a change in temperature conditions leads to an earlier start of vegetation and a lengthening of the growing season in all investigated gooseberry varieties. To assess the functional state of the photosynthetic apparatus of plants, a minimally invasive instrumental method of determining the intensity of chlorophyll fluorescence in plant leaves, adapted to work on the domestic photofluorimeter "Floratest", was used. Based on the results of the analysis of the parameters of the chlorophyll fluorescence induction curves (Fo, Fpl, Fmax, Ft) and the comparison of the coefficients for these values (Kpl, K1, K2), it was established that Fo and Kpl are the most informative. A strong correlation dependence of the indicator of the background level of fluorescence at the time of full opening of the shutter (Fo) was established. The value of Fо correlates positively with indicators of the moisture regime, negatively – with temperature indicators. Correlations between the fluorescence growth index and the variable (Kpl) showed the opposite: the largest positive correlation was observed with mean maximum temperature, the smallest with precipitation. On the basis of mathematical analysis and modeling of the obtained FIC curves and indicators of agro-climatic conditions, the values of the maximum temperature and the minimum amount of precipitation, which are critical for the functioning of the gooseberry photosynthetic apparatus, were determined. Such a study makes it possible to evaluate the course of photochemical reactions associated with the work of plant photosystems according to standard coefficients of photochemical activity, which have already been tested in numerous works of domestic researchers on a wide range of agricultural crops.

Growth, Photosynthesis, and Gene Expression of Bermudagrass in Response to Salinity and Shade Stress

Soil salinization is an environmental problem globally. Bermudagrass (Cynodon dactylon) has long been used for soil restoration in saline-alkali land. Urbanization and the compound planting pattern combining trees, bushes, and grasses induced shading are becoming one of the most significant environmental constraints on the management of bermudagrass, which directly affects photosynthetic characteristics. Salinity and shade have become the most important environmental constraints on lawn development and implementation. Previous studies have shown that the plant physiological response under combined stress was different from that under single stress. The purpose of this research was to investigate the effects of salinity stress, shade stress, and the combined stress on bermudagrass. Shade nets were used to simulate shade stress to 85% shade. The NaCl concentration gradient for salinity stress was 1.0% for 7 days, 1.5% for 7 days, and 2.0% for 13 days, respectively. The combined stress combines the two approaches mentioned previously. The results showed that the salinity stress significantly inhibited the plant height, leaf relative water content, chlorophyll content, the chlorophyll a fluorescence induction (OJIP) curve and other photosynthetic parameters of bermudagrass while increasing electrolyte leakage when compared with control. Shade stress significantly enhanced the plant height, chlorophyll content, electrolyte leakage, the OJIP curve, and other photosynthetic parameters. Under the combined stress, the plant height and relative water content did not change significantly, but the photosynthetic parameters such as chlorophyll content and the OJIP curve increased. Furthermore, under the combined stress, the photosynthesis-related genes were regulated. Salinity stress inhibited the photosynthetic ability of bermudagrass more than shade stress, while the combined stress exhibited a considerably better photosynthetic ability. These findings provide information for the usage of bermudagrass in salinized shade conditions.

The slow-phase of chlorophyll fluorescence induction curve reflects the electron transport rates of Photosystem II in vivo in Chlorella vulgaris

The slow-phase of chlorophyll fluorescence induction curve reflects the electron transport rates of Photosystem II in vivo in Chlorella vulgaris

Assessment of vitality Berberis thunbergii DC. in Kyiv: Photosynthesis and Phytopathology

The process of functioning of the photosynthetic apparatus is one of the most vulnerable to stress factors. The information about the functional state of plants and the prospects for their use in urban greening can provide methods of fluorescence analysis. The objective of this research was to develop the state of plants Berberis thunbergii DC. which grow in the Mariinskyi Park (Kyiv) by the content of photosynthetic pigments and fluorescence induction chlorophyll (FIC). The article presents the results of the evaluation of fluorescence induction (FI) indicators and the content of photosynthetic pigments B. thunbergii according to the degree of damage by powdery mildew. Experimental plants were planted in the chernozem layer of 50 cm (humus content 4 %). The plants grow in a group planting of Picea glauca ‘Conica’ and Chlorophytum comosum ‘Variegatum’ directly 1.5–5 m from the highway under the canopy of Tilia cordata Mill. Moreover, the variability of FI curves in the absence/presence of plant lesions. The authors investigated the relationship between the content of photosynthetic pigments and FI. The degree of damage to experimental plants by powdery mildew affects the total chlorophyll content (a+b) and decreases by approximately 16 %, 7 %, and 5 % compared to the control. Recorded gradually disappear FI curves in plants with the highest degree of damage which affect photochemical reactions due to the slowing down of the outflow of Calvin cycle enzymes.

ASSESSMENT OF CRITICAL PERIODS OF GROWTH AND DEVELOPMENT OF OILSEED RADISH PLANTS (RAPHANUS SATIVUS L. VAR. OLEIFORMIS PERS.) ON THE BASIS OF CHLOROPHYLL FLUORESCENCE INDUCTION METHOD

The article highlights the results of studying critical periods in the phenological development of oilseed radish varieties based on the use of basic indicators of the chlorophyll fluorescence induction curve (initial fluorescence (F0), plateau zone fluorescence (Fpl), maximum fluorescence (Fm), and stationary fluorescence (Fst). This complex was applied to oilseed radish plants of three varieties – ‘Rayduga’, ‘Zhuravka’ and ‘Lybid’ with the presentation of results for the variety ‘Zhuravka’ due to the similarity of the obtained data. phases of growth and development of oilseed radish: cotyledon phase, budding phase, flowering phase, green pod phase and yellow-green pod phase. Based on the use of a single-beam porous fluorimeter ‘Floratest’, developed by the Research and Engineering Center of Microelectronics of the Institute of Cybernetics named after V.M. Glushkova (Ukraine) formed curves of chlorophyll fluorescence induction (CFI) in the mode of 90-second fixation of parameters for each phenological phase of oilseed radish plants.The system of graphical display of regularity of formation of basic indicators of CFI curve within the main phenological phases is analyzed and generalizations and conclusions concerning dynamics of course of photochemical physiological processes of photosystem II of plants are made. in the process of phenological stage changes and the corresponding processes of morphogenesis of oilseed radish plants. The dynamics of exogenous and endogenous factors on the formation of indicators of assimilative activity of oilseed radish plant photosystems is analyzed on the basis of analysis of position and changes in time of main points of CFI schedule and substantiated obtained indicators with predicted physiological state of plants and possible assimilation activity. The values of baseline and indication indicators of CFI curve are compared to the main phenological phase of flowering, which is defined as the baseline in ensuring the realization of the productive potential of oilseed radish plants.

Molecular, Brownian, kinetic and stochastic models of the processes in photosynthetic membrane of green plants and microalgae.

The paper presents the results of recent work at the Department of Biophysics of the Biological Faculty, Lomonosov Moscow State University on the kinetic and multiparticle modeling of processes in the photosynthetic membrane. The detailed kinetic models and the rule-based kinetic Monte Carlo models allow to reproduce the fluorescence induction curves and redox transformations of the photoactive pigment P700 in the time range from 100ns to dozens of seconds and make it possible to reveal the role of individual carriers in their formation for different types of photosynthetic organisms under different illumination regimes, in the presence of inhibitors, under stress conditions. The fitting of the model curves to the experimental data quantifies the reaction rate constants that cannot be directly measured experimentally, including the non-radiative thermal relaxation reactions. We use the direct multiparticle models to explicitly describe the interactions of mobile photosynthetic carrier proteins with multienzyme complexes both in solution and in the biomembrane interior. An analysis of these models reveals the role of diffusion and electrostatic factors in the regulation of electron transport, the influence of ionic strength and pH of the cellular environment on the rate of electron transport reactions between carrier proteins. To describe the conformational intramolecular processes of formation of the final complex, in which the actual electron transfer occurs, we use the methods of molecular dynamics. The results obtained using kinetic and molecular models supplement our knowledge of the mechanisms of organization of the photosynthetic electron transport processes at the cellular and molecular levels.

Interactions Between Carbon Metabolism and Photosynthetic Electron Transport in a Chlamydomonas reinhardtii Mutant Without CO2 Fixation by RuBisCO.

A Chlamydomonas reinhardtii RuBisCO-less mutant, ΔrbcL, was used to study carbohydrate metabolism without fixation of atmospheric carbon. The regulatory mechanism(s) that control linear electron flow, known as “photosynthetic control,” are amplified in ΔrbcL at the onset of illumination. With the aim to understand the metabolites that control this regulatory response, we have correlated the kinetics of primary carbon metabolites to chlorophyll fluorescence induction curves. We identify that ΔrbcL in the absence of acetate generates adenosine triphosphate (ATP) via photosynthetic electron transfer reactions. Also, metabolites of the Calvin Benson Bassham (CBB) cycle are responsive to the light. Indeed, ribulose 1,5-bisphosphate (RuBP), the last intermediate before carboxylation by Ribulose-1,5-bisphosphate carboxylase-oxygenase, accumulates significantly with time, and CBB cycle intermediates for RuBP regeneration, dihydroxyacetone phosphate (DHAP), pentose phosphates and ribose-5-phosphate (R5P) are rapidly accumulated in the first seconds of illumination, then consumed, showing that although the CBB is blocked, these enzymes are still transiently active. In opposition, in the presence of acetate, consumption of CBB cycle intermediates is strongly diminished, suggesting that the link between light and primary carbon metabolism is almost lost. Phosphorylated hexoses and starch accumulate significantly. We show that acetate uptake results in heterotrophic metabolism dominating phototrophic metabolism, with glyoxylate and tricarboxylic acid (TCA) cycle intermediates being the most highly represented metabolites, specifically succinate and malate. These findings allow us to hypothesize which metabolites and metabolic pathways are relevant to the upregulation of processes like cyclic electron flow that are implicated in photosynthetic control mechanisms.

Characteristics of the photosynthetic apparatus of Pinus sylvestris L. and Larix sibirica Ledeb. from different locations of the Irkutsk region (Eastern Siberia)

The characteristics of the photosynthetic apparatus of coniferous growing in various forest types and climatic conditions of the Irkutsk region (Taishet, Bratsk, Shelekhov, Irkutsk districts) have been explored. The content of photosynthetic pigments, total, free, and bound water in the needles of P. sylvestris and L. sibirica were studied. Using a pulse fluorimeter PAM 2500 (Waltz, Germany), the chlorophyll fluorescence in needles was measured based on such induction curve indices as Fv/Fm, Y(II), NPQ, and ETR. According to the chlorophyll fluorescence induction curve parameters of Scots pine and Siberian larch needles growing in different forest growth conditions, the most effective potential of primary photochemical processes in PSII was observed in Scots pine. While studying the pigment fund of Scots pine and Siberian larch needles, it was found that the highest values of the content of chlorophyll (Chl) a, b, and carotenoids were observed in P. sylvestris and L. sibirica growing in the climatic and forest growth conditions of the Shelekhov district. It is assumed that the revealed characteristics of the parameters reflect the processes of adaptation of the photosynthetic apparatus to various environmental conditions during vegetation development, as well as its high plasticity in different climatic growth conditions.

Effects of chloroplast-cytoplasm exchange and lateral mass transfer on slow induction of chlorophyll fluorescence in Characeae.

Rapid cytoplasmic streaming in characean algae mediates communications between remote cell regions exposed to uneven irradiance. The metabolites exported from brightly illuminated chloroplasts spread along the internode with the liquid flow and cause transient changes in chlorophyll fluorescence at cell areas that are exposed to dim light or placed shortly in darkness. The largest distance to which the photometabolites can be transported has not yet been determined. Neither is it known if lateral transport has an influence on the induction of chlorophyll fluorescence. In this study, the relations between spatial connectivity of anchored chloroplasts in characean internodes and fluorescence induction curves were examined. Connectivity between remote cell parts was pronounced upon illumination of a cell spot at a distance up to 10 mm from the area of fluorescence measurement, provided the spot was located upstream in the cytoplasmic flow. Spatial interactions between distant cell sites were also manifested in strikingly different slow stages of fluorescence induction caused by narrow- and wide-field illumination. Cytochalasin D, cooling of bath solution, and inactivation of light-dependent envelope transporters were used to disturb cyclosis-mediated spatial interactions. Although fluorescence induction curves induced by narrow- and wide-field illumination differed greatly under control conditions, they became similar after the inhibition of cyclosis with cytochalasin D. The results indicate that cytoplasmic streaming not only drives the lateral translocation of photometabolites but also promotes the export of reducing power from illuminated chloroplasts due to flushing the chloroplast surface and keeping sharp concentration gradients.

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.

Methyl Jasmonate Protects the PS II System by Maintaining the Stability of Chloroplast D1 Protein and Accelerating Enzymatic Antioxidants in Heat-Stressed Wheat Plants.

The application of 10 µM methyl jasmonate (MeJA) for the protection of wheat (Triticum aestivum L.) photosystem II (PS II) against heat stress (HS) was studied. Heat stress was induced at 42 °C to established plants, which were then recovered at 25 °C and monitored during their growth for the study duration. Application of MeJA resulted in increased enzymatic antioxidant activity that reduced the content of hydrogen peroxide (H2O2) and thiobarbituric acid reactive substances (TBARS) and enhanced the photosynthetic efficiency. Exogenous MeJA had a beneficial effect on chlorophyll fluorescence under HS and enhanced the pigment system (PS) II system, as observed in a JIP-test, a new tool for chlorophyll fluorescence induction curve. Exogenous MeJA improved the quantum yield of electron transport (ETo/CS) as well as electron transport flux for each reaction center (ET0/RC). However, the specific energy fluxes per reaction center (RC), i.e., TR0/RC (trapping) and DI0/RC (dissipation), were reduced by MeJA. These results indicate that MeJA affects the efficiency of PS II by stabilizing the D1 protein, increasing its abundance, and enhancing the expression of the psbA and psbB genes under HS, which encode proteins of the PS II core RC complex. Thus, MeJA is a potential tool to protect PS II and D1 protein in wheat plants under HS and to accelerate the recovery of the photosynthetic capacity.

Alleviating damage of photosystem and oxidative stress from chilling stress with exogenous zeaxanthin in pepper (Capsicum annuum L.) seedlings

As a typical thermophilous vegetable, the growth and yield of peppers are easily limited by chilling conditions. Zeaxanthin, a crucial carotenoid, positively regulates plant abiotic stress responses. Therefore, this study investigated the regulatory mechanisms of zeaxanthin-induced chilling tolerance in peppers. The results indicated that the pretreatment with zeaxanthin effectively alleviated chilling damage in pepper leaves and increased the plant fresh weight and photosynthetic pigment content under chilling stress. Additionally, alterations in photosynthetic chlorophyll fluorescence parameters and chlorophyll fluorescence induction curves after zeaxanthin treatment highlighted the participation of zeaxanthin in improving the photosystem response to chilling stress by heightening the quenching of excess excitation energy and protection of the photosynthetic electron transport system. In chill-stressed plants, zeaxanthin treatment also enhanced antioxidant enzyme activity and transcript expression, and reduced hydrogen peroxide (H2O2) and superoxide anion (O2•-) content, resulting in a decrease in biological membrane damage. Additionally, exogenous zeaxanthin upregulated the expression levels of key genes encoding β-carotene hydroxylase (CaCA1, CaCA2), zeaxanthin epoxidase (CaZEP) and violaxanthin de-epoxidase (CaVDE), and promoted the synthesis of endogenous zeaxanthin during chilling stress. Collectively, exogenous zeaxanthin pretreatment enhances plant tolerance to chilling by improving the photosystem process, increasing oxidation resistance, and inducing alterations in endogenous zeaxanthin metabolism.