Chlorophyll Fluorescence Induction Curves Research Articles

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.

Characteristics of the photosynthetic activity of corn using different drugs under stress

Goal. To study under controlled conditions the effect of hormonal preparations based on humus extracts and anti-stress stimulants with a high content of amino acids and biologically active substances on the development of corn under conditions of stress, as well as their effect on the photosynthetic activity of plants.
 Methods. The research was carried out in a climatic chamber (a room with adjustable control of temperature, daylight and air humidity) of the Ukrainian research plant quarantine station of the Institute of Plant Protection of the National Academy of Sciences. Photosynthetic activity was measured using a portable fluorometer «Floratest». During the growing season, two foliar feedings were carried out in the phase of development of corn VVSN 12, the first application of drugs during the growing season — VVSN 13, — the second application of drugs during the vegetation period — VVSN 14.
 Results. The analysis of the induction curves of chlorophyll fluorescence and the indicators of the maximum background fluorescence showed a difference between the plants that were under soil moisture of 70% and 50% RH. When corn plants were in a state close to stress for a long time, the difference between the curves of chlorophyll fluorescence intensity between the two controls increased. The use of the studied drugs provided the finding of the indicator of the maximum value of fluorescence induction above the dry control in all variants of the experiment. Best results provided: preparation B (high concentrated suspension for nutrition and plant stress decreasing based upon the humus extract. They contented N — 150 g/l, K2O — 300 g/l, Mg — 30 g/l, metal cations in В, Cu, Fe, Mn and Zn with additional adhesive effects and surfactant), at rate of application 0.5 and 0.25 l/ha; Axofol (high concentrated suspension from extract of brown algae Ascophyllum nodosum with microelements, B — 38.1 g/l, Mn — 10.2 g/l, Zn — 6.4 g/l) at rate of application 1.0 and 0.5 l/ha.
 Conclusions. As the time of corn plants being in a state close to stress increases, the difference between the curve of chlorophyll fluorescence intensity in the wet control and the dry control increases. The use of the studied drugs provided the finding of the indicator of the maximum value of fluorescence induction above the dry control in all variants of the experiment. The use of the researched preparations in conditions of soil moisture of 50% ensured the improvement of vegetation indicators of plants.

Comparative study of the efficiency of inducers of cotton resistance to verticillium wilt

The effect of pre-sowing seed treatment with immunostimulant Bisol-2, red light and low frequency electromagnetic field on the content of fungitoxic substances of phenolic nature – phytoalexins (isohemigossypol and gossypol-equivalent) in infected etiolated cotton seedlings of S-4727 cultivar infected with Verticillium wilt pathogen was studied. It was found that photostimulation of seeds by red light induces phytoalexin formation in cotton tissues infected by the pathogen 1.5–2 times more effectively in comparison with Bisol-2 preparation or inducer of electromagnetic nature. The correlation between the content of phytoalexins in the tissues of seedlings, parameters of induction curves of chlorophyll fluorescence and the number of plants with signs of wilt lesions grown from treated and untreated seeds with inducers was revealed. This indicates the possibility of using red light and weak low-frequency electromagnetic fields as factors contributing to the intensification of phytoalexin formation in response to Verticillium wilt infection of cotton.

Parameters for Induction Curves of Prompt and Delayed Fluorescence and Redox State of PSI–P700 for Birch and Linden Leaves in Various Urban Environments

The photosynthetic characteristics of linden leaves (Tilia cordata L.) and birches (Betula verrukosa L.) growing near the city highways of Moscow (MKAD, Moscow Ring Road) by simultaneously recording the induction curves of chlorophyll fluorescence and the redox state of the PSI pigment–P700. In trees near highways, deterioration of electron transport at the level of plastoquinones (δRo) and decrease of P700+ reduction was revealed, despite the rather high rates of photosynthetic efficiency (FV/FM). In birch leaves growing along the Moscow Ring Road, a decrease in the outflow of electrons from PSI and a decrease in the intensity of delayed fluorescence at 30 ms and 1 s, associated with a decrease in the electrical and chemical components of the electrochemical proton gradient on photosynthetic membranes, were revealed. In plants near highways, an increase in the degree of photoinhibition and a slowdown in the reactions of restoring photosynthetic activity in the dark after the cessation of photooxidative stress were noted, which confirms the probable effect of unfavorable urban conditions on the biosynthesis of proteins in PSII reaction centers. The following fluorescence parameters are proposed as indicators of the state of trees in an urban environment: total performance index (PItotal) and the quantum yield of reduction of electron acceptors on the acceptor side of PSI (φRo).

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.

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.

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 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.

Intelligent Processing of Data From Chlorophyll Fluorometric Sensors

Introduction. Chlorophyll fluorescence induction (CFI) is a monitoring method of plant objects. CFI is a radiation of chlorophyll in red spectrum during a chlorophyll lighting of alive plant in blue spectrum. Chlorophyll fluorometers – the special devices that are used for measurement of CFI. Series of such devices were developed in V.M. Glushkov Institute of Cybernetics of the NAS of Ukraine. In particular, fluorometer «Floratest» and a network of wireless sensors were developed for CFI measurement. An accumulation of massive amount of measurements resulted into possibility to use intellectual methods like neural networks. The purpose of the paper is to research the possibilities of machine learning methods (neural networks, support vector machine (SVM), XGBoost algorithm) for analysis of CFI curves that were measured by means of sensors developed in V.M. Glushkov Institute of Cybernetics of the NAS of Ukraine. Results. Neural networks, SVM, XGboost ensure early detection of influence of stress factors on state of plants before appearance of external symptoms on plants that was showed on basis of data received during experiments with treatment of plants by herbicide. Analogically there was showed the possibility of using the machine learning methods for determination of soil humidity. The better methods for given tasks were determined. The study of possibilities to enhance the results of mentioned methods by means of normalization was conducted. The best results were demonstrated by z-score normalization and by minimax normalization to the range [-1;1]. Conclusions. The application of different machine learning algorithm for processing CFI curves demonstrated that SVM and XGBoost better suit for task of classification plants treated by means of herbicide. Neural network demonstrated worst results. The application mentioned methods for task of determination of artificial watering necessity demonstrated that neural network shows better result, SVM shows worse result and XGBoost shows worst result. Keywords: Chlorophyll fluorescence induction, neural network, support vector machine, algorithm XGBoost.

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.

Polymer-Modified Single-Walled Carbon Nanotubes Affect Photosystem II Photochemistry, Intersystem Electron Transport Carriers and Photosystem I End Acceptors in Pea Plants.

Single-walled carbon nanotubes (SWCNT) have recently been attracting the attention of plant biologists as a prospective tool for modulation of photosynthesis in higher plants. However, the exact mode of action of SWCNT on the photosynthetic electron transport chain remains unknown. In this work, we examined the effect of foliar application of polymer-grafted SWCNT on the donor side of photosystem II, the intersystem electron transfer chain and the acceptor side of photosystem I. Analysis of the induction curves of chlorophyll fluorescence via JIP test and construction of differential curves revealed that SWCNT concentrations up to 100 mg/L did not affect the photosynthetic electron transport chain. SWCNT concentration of 300 mg/L had no effect on the photosystem II donor side but provoked inactivation of photosystem II reaction centres and slowed down the reduction of the plastoquinone pool and the photosystem I end acceptors. Changes in the modulated reflection at 820 nm, too, indicated slower re-reduction of photosystem I reaction centres in SWCNT-treated leaves. We conclude that SWCNT are likely to be able to divert electrons from the photosynthetic electron transport chain at the level of photosystem I end acceptors and plastoquinone pool in vivo. Further research is needed to unequivocally prove if the observed effects are due to specific interaction between SWCNT and the photosynthetic apparatus.

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.

Flashes of UV-C Light Stimulate Defenses of Vitis vinifera L. 'Chardonnay' Against Erysiphe necator in Greenhouse and Vineyard Conditions.

Using detached leaves, UV-C light in the form of 1-s flashes has recently been shown to stimulate defenses of several plants against different pathogens better than 1-min exposures under greenhouse conditions. In the present work, the pathological tests were conducted using undetached leaves under greenhouse and vineyard conditions. In a first trial, two flashes of UV-C light were applied to plants of Vitis vinifera L. 'Chardonnay' grown under greenhouse conditions, at an interval of 10 days. Plants were inoculated with Erysiphe necator 2 days after the last light treatment. After 18 days of inoculation, the symptom severity on leaves was reduced by 60% when compared with the untreated control. In a second trial, flashes of UV-C light were applied to grapevine Chardonnay plants under field conditions in the southeast of France every 10 days from 18 April until 10 July 2019. The symptom severity resulting from natural contaminations by E. necator was reduced by 42% in leaves on 4 July 2019 and by 65% in clusters on 25 July 2019. In a third trial, we observed that UV-C light did not have any effect on net photosynthesis, maximal net photosynthesis, dark respiration, maximal quantum efficiency of photosystem II, the performance index of Strasser, and, generally, any parameter derived from induction curves of maximal chlorophyll fluorescence. It was concluded that flashes of UV-C light have true potential for stimulating plant defenses against E. necator under vineyard conditions and, therefore, help in reducing fungicide use.

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.

The effect of moisture deficiency on the photosynthesis of evergreen shrubs of the genus Cotoneaster L

The paper presents data on the features of the water regime (water deficit, water-retaining forces, and total hydration of leaf tissues) in four evergreen species of the genus Cotoneaster , as well as the effect of the growing water stress on the course of primary photosynthesis processes. It was found that during the periods of maximum impact of dry factors of the summer season on the Southern Coast of the Crimea, the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus show signs of increased drought resistance, which is manifested in the ability to economically consume moisture by leaf tissues during wilting, and subsequently restore the normal turgescence of leaf tissues. These species maintained minimal levels of water deficit in the leaves, and the sublethal level was 12% water loss. The genotypes Cotoneaster × watereri 'Cornubia' and Cotoneaster franchetii showed relatively weak water retention capacity combined with low leaf repair capability. Water loss of more than 8-10% was already critical, after which the number of intact leaf blade tissues was unsatisfactory (less than 60%). It was found that the parameters of chlorophyll fluorescence induction (CPI) are most sensitive to lack of moisture and they are features of fast phase. Water deficiency within 10% leads to irreversible disturbances in the photosynthetic apparatus in Cotoneaster franchetii , which was expressed in a decrease in the ratio of variable and base fluorescence below the norm of vitality and the absence of pronounced peaks on the CPI curve. In the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus , an increase in the level of water deficiency was accompanied by a decrease in the efficiency of the light phase of photosynthesis and an increase in the number of unrecoverable Q a in the reaction centers of PS2. However, these changes were reversible. It is concluded that the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus are relatively resistant to lack of moisture and are characterized by a high level of water-retaining forces and stable operation of the photosynthetic apparatus. Controlled wilting in combination with the CPI method can be used for quick diagnostics of the drought resistance of Cotoneaster species.

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.

Assessing drought tolerance of traditional maize genotypes of Mozambique using chlorophyll fluorescence parameters

Just behind wheat and rice, maize is the third most important grain crop in the world, grown in many agricultural areas. In Mozambique, rainfall is declining, posing serious threats to national food sovereignty and security, particularly in southern regions of the country. Despite this fact, few research studies have been conducted on the performance of Mozambique´s maize germplasm under drought stress conditions. A randomized design combining eight maize genotypes (six traditional Mozambican genotypes: LVA34, TCDE, G234, D456C, MABC, C123; and two commercial cultivars from DuPont Pioneer: P0023 and P9838) and three water regimes (control (irrigated), stress and recovery) was used to characterize the maize resilience to water deficit. The photochemical performance was accessed by rapid chlorophyll fluorescence induction curves (JIP-test). The use of Performance Index based dendrogram analysis allowed to explain genotypes behavior on the different experimental sets (control, drought stress and recovery). G234 and C123 presented the best performance with the lowest mortality rates, showing a better ability to cope with drought stress when compared to other genotypes from Mozambique and to the commercial cultivars from DuPont Pioneer.

Disturbance mechanism of coal mining subsidence to typical plants in a semiarid area using O-J-I-P chlorophyll a fluorescence analysis

The response of individual plants to coal mining subsidence disturbance reflects the micro-ecological mechanism implied in the macro-response, which is the basis of studying the rule of vegetation disturbance of large-scale coal mining. In this study, O-J-I-P chlorophyll a fluorescence analysis was used to diagnose the disturbance mechanism of typical individual plants by coal mining subsidence in a semiarid area. The results showed that the groundwater level and soil water content decreased due to the disturbance of coal mining subsidence and the plant growth was affected by drought stress. The rapid chlorophyll fluorescence induction curve of leaves was deformed, the stomatal limitation increased, and the photosynthetic electron transfer was inhibited. Stomatal conductance, photosynthetic rate, and transpiration rate decreased significantly. The spatial heterogeneity of soil water content after mining subsidence is the main reason for the differing degree of plant drought stress in different subsidence areas.