Chlorophyll Fluorescence Parameters Research Articles

A mathematical model of photoinhibition: exploring the impact of quenching processes

Abstract Plants are constantly exposed to changing environments, sometimes leading to extreme conditions and stress. For example, sudden exposure to high light leads to excess absorbed light energy, causing reactive oxygen species (ROS) formation. ROS damages the photosynthetic machinery, particularly the D1 protein in photosystem II (PSII), which, therefore, needs to be continuously repaired and replaced. The effect of the damage inflicted by high light is a prolonged decrease in photosynthetic efficiency. Hence, it is not surprising that photoinhibition has been subject to numerous experimental studies investigating its effects in the context of crop productivity. However, it has become apparent that classical measures of photoinhibition, that is, changes in the chlorophyll fluorescence parameter Fv/Fm, are not only determined by the loss of PSII core function but also by processes such as energy transfer and quenching. Mathematical models can help dissect the influences on such fluorescence signals and quantify the contributions of various interacting mechanisms. We present a mathematical model with a dynamic description of the photosynthetic electron transport chain, non-photochemical quenching and photoinhibition. With our model, we investigate the interconnection among quenching, photoprotection and fluorescence using simulations and experimental data. We found that different energy-dissipating properties of intact and damaged PSIIs, as well as energy transfer between PSIIs, are critical components that need to be included in the model to ensure a satisfactory fit to the experimental data. We envisage that our model provides a framework for future investigations of photoinhibition dynamics and its importance for plant growth and yield.

Morphophysiological changes of Acca sellowiana (Myrtaceae: Myrtoideae) saplings under shade gradient.

Understanding morphological and physiological changes under different light conditions in native fruit species in juveniles' stage is important, as it indicate the appropriate environment to achieve vigorous saplings. We aimed to verify growth and morphophysiological changes under shade gradient in feijoa (Acca sellowiana (O. Berg) Burret) to achieve good quality saplings adequate to improve cultivation in orchards. The saplings were grown for twenty-one-month under four shading treatments (0%, 30%, 50%, and 80%). Growth, photosynthetic pigments, gas exchanges, chlorophyll fluorescence, and leaf anatomy parameters were evaluated. Saplings under full sun and 30% shade had higher height and diameter growth and dry mass accumulation due to higher photosynthesis rate. As main acclimatization mechanisms in feijoa saplings under 80% shade were developed larger leaf area, reduced leaf blade thickness, and enhanced quantum yield of photosystem II. Even so, the net CO2 assimilation and the electron transport rate was lower and, consequently, there was a restriction on the growth and dry mass in saplings under deep shade. Therefore, to obtain higher quality feijoa saplings, we recommend that it be carried out in full sun or up to 30% shade, to maximize the sapling vigor in nurseries and, later, this light environment can also be used in orchards for favor growth and fruit production.

Fluorescent reaction of wheat seedlings when infected by <i>Bipolaris sorokiniana</i>

Results of the studies of photosynthetic activity of seedlings of three varieties of spring soft wheat grown under controlled climatic conditions and their response to infection with the pathogen of common root rot of cereals Bipolaris sorokiniana Shoem. by chlorophyll fluorescence (ChlF) parameters are presented. Chlorophyll fluorescence was recorded with a Dual-PAM-100/F fluorimeter in the mode of recording slow kinetics of dark induction curves with pulse saturation analysis (Slow Kinetics). The studies were conducted in 2021, 2022. The varietal specificity of formation of adaptive reactions of 10–16-day-old spring wheat seedlings under infection with B. sorokiniana (5000 conidia per grain) according to the daily dynamics of the ChlF parameters was established. The information content of the ChlF parameters Y(II), ETR, qP, Fv/Fm, Fv/F0, Y(NPQ), qN and Y(NО) as biomarkers for assessing pathogen resistance of the varieties at the level of photosynthetic apparatus was confirmed. The response of the more resistant wheat varieties Novosibirskaya 29 and Sibirskaya 21 to the pathogen introduction was less pronounced compared to the less resistant variety Novosibirskaya 41. The more resistant varieties exhibited the smallest changes in the ChlF parameters relative to the control. The greatest inter-variety differences in infection with B. sorokiniana (from 1.9 to 8.6 times) were manifested in 16-day-old seedlings. The level of the photosynthetic activity in the formation of adaptive reactions during the pathogenesis of B. sorokiniana can serve as a criterion of stress resistance, which will make it possible to conduct complex studies on modeling the system plant – host – pathogen, to assess the primary nonspecific reactions and adaptive components of stress resistance of spring wheat varieties.

The influence of powdery mildew (Sawadaea bicornis (Wallr.) Miyabe) on chlorophyll fluorescence in Norway maple (Acer platanoides L.) seedlings

The article presents the results of research on impact of Sawadaea bicornis (Wallr.) Miyabe on the state of photosynthetic apparatus in Acer platanoides L. seedlings using a technique of chlorophyll fluorescence induction (ChlF) measurement, which at the present time can be implemented through the use of biosensors. The research was conducted in September 2022 in the territory of the Botanical Garden of Oles Honchar Dnipro National University. To diagnose a violation of the native chlorophyll photosynthesis in fresh leaves of A. platanoides, a portable fluorometer “Floratest” was used (selected spectral range for fluorescence intensity measurement was 670–800 nm). The research was carried out on fresh leaves of Norway maple seedlings both not unaffected and affected with powdery mildew. Analysis of the data obtained indicates a high sensitivity of the parameters of chlorophyll fluorescence induction to damage by the disease regardless of environmental conditions of local growth of A. platanoides seedlings. The high informativeness of induction changes in chlorophyll fluorescence in the structural organization of chloroplasts in Norway maple leaves determined by the parameters Fo, Fm, Fv, Fv/Fо, Fv/Fm, (Fm–Fst)/Fst, (Fp–Fо)/Fv was revealed. This study demonstrated the effectiveness of using the studied chlorophyll fluorescence parameters to detect severe stress in Norway maple seedlings caused by powdery mildew exposure when the fungus affects more than 50% of the leaf blade area. It is further necessary to conduct dynamic studies throughout the growing season to determine the effectiveness of using these parameters to detect mild stress in the early stages of infection. Therefore, our research showed that the method of induction of chlorophyll fluorescence using the “Floratest” device allows you to quickly determine the general condition of the plant by evaluating photosynthesis, which is the main life process. Analysis of chlorophyll fluorescence parameters is a powerful and effective tool for determining the effect of a parasitic fungus on a plant.

Effects of nanoparticle application on Cyclocarya paliurus growth: Mechanisms underlying the particle- and dose-dependent response

Nanoparticles (NPs) have been considered as potential plant growth stimulants in recent years. In this study, three types of oxide NPs with various concentrations, including ZnO-NPs (0, 50 and 100 mg L−1), SiO2-NPS (0, 300 and 500 mg L−1) and MnO2-NPS (0, 30 and 50 mg L−1), were set up to explore their effects on growth, photosynthetic parameters and gene expressions in Cyclocarya paliurus under outdoor conditions for 120 days. Foliar spraying with higher concentration of SiO2- and MnO2-NPs significantly increasedf the net growth of height and ground diameter C. paliurus by 43.1–26.4% and 28.6–26.3% respectively, via improving photosynthetic and chlorophyll fluorescence parameters, whereas a higher concentration spraying of ZnO-NPs showed a negative impact on the net growth. Transcriptomic analysis revealed that in the presence of SiO2- and MnO2-NPs, 9 genes associated with the activities of photosystem (PS) I and Rubisco were up-regulated, while the 7 PSII-related genes were down-regulated under ZnO-NPs application. Moreover, application of SiO2-NPs also up-regulated the gene expressions related to auxin (16 genes) and cytokinin (8 genes). Our study suggests that the effects of NPs appilation on C. paliurus growth are type- and dose-dependent, and regulated via altering the photosynthesis and hormone signaling at the molecular level. The findings not only provide insights into the regulatory mechanisms of nanoparticles on C. paliurus growth but also serve as references for a potential application of these nanoparticles in woody plants.

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.

Promising photosynthetic parameters Y(II) and NPQ for predicting barley drought tolerance

The purpose of the current work was to identify photosynthetic parameters that are predictors of barley drought tolerance, determined at early stages of development, and to verify the results obtained in field conditions. The study was carried out with the barley varieties ‘Leon’, ‘Ratnik’ and ‘Foks 1’, used in mutation breeding to develop drought-resistant genotypes. Drought was modeled by stopping irrigation. Plant resistance was estimated by changes in chlorophyll fluorescence (Fv /Fm, Y(II), NPQ) and morphometric parameters (leaf length, wet and dry weight) compared to the control group with normal water supply. Under stress-free conditions, the variety ‘Leon’ demonstrated a statistically significantly lower efficiency of photosynthesis in terms of Y(II) and Fv /Fm (0.535 ± 0.005 and 0.776 ± 0.004, respectively) in comparison with other varieties (0.577 ± 0.005 and 0.788 ± 0.001 for the variety ‘Foks 1’; 0.574 ± 0.004 and 0.787 ± 0.001 for the variety ‘Ratnik’). When modeling drought, there has been established a decrease in all morphometric indicators for all varieties relative to the control, with the highest degree of inhibition for the variety ‘Ratnik’ (70.16 ± 3.88 %; 8.09 ± 0.73 %; 68.50 ± 4.42 % for leaf length, wet and dry weight, respectively) and with the lowest degree for the variety ‘Leon’ (88.06 ± 7.83 %; 26.51 ± 7.11 %; 79.32 ± 11.17 %, respectively). A decrease in the photosynthesis intensity was manifested in the suppression of Fv /Fm and Y(II) and an increase in NPQ, with the earliest changes in the parameters Y(II) and NPQ in the varieties ‘Foks 1’ and ‘Ratnik’ (on the 4th and 5th day, respectively), compared to the variety ‘Leon’ (on the 7th day). In the field conditions, there has been estimated productivity of the varieties and its dependence on precipitation. A positive correlation between the difference in yield of two varieties ‘Leon’ and ‘Ratnik’, contrasting in their response to drought, and the amount of precipitation during the active vegetation period in 2014–2017 and 2022 (Pearson’s R2 = 0.77, p < 0.05) has been identified. The most sensitive parameters of photosynthesis, which can be used to predict resistance to moisture deficiency, were Y(II) and NPQ.

Physiological responses of coriander (Coriandrum sativum L.) to exogenous 2,4-epibrassinolide at different concentrations

BackgroundBrassinolide, known as the seventh plant hormone, can improve the photosynthetic capacity of plants, promote plant growth and development, promote the formation of horticultural crop yield, improve the quality of horticultural crops, and also improve the ability of plants to resist biological and abiotic stresses.ResultsThe effects of different concentrations of exogenously sprayed 2,4-epibrassinolide (EBR) on growth, physiological and photosynthetic characteristics of ‘All-round large leaf coriander’ were studied in substrate culture. The results showed that 0.05, 0.1, and 0.5 mg.L− 1 EBR promoted the growth of coriander and increased the aboveground fresh and dry weights, with 0.5 mg.L− 1 EBR having the most significant effect. Spraying 0.1 mg.L− 1 EBR increased the content of soluble sugars and protein of coriander leaves. Spraying 0.1 and 0.5 mg.L− 1 EBR significantly increased the chlorophyll content and photosynthetic parameters of coriander leaves, and 0.5 mg.L− 1 EBR also significantly increased the chlorophyll fluorescence parameters of coriander leaves. Spraying 0.5 mg.L− 1 EBR upregulated the expression of CsRbcS, CsFBPase, and CsAld. Correlation analysis showed that aboveground fresh weight under exogenous EBR treatment was significantly positively correlated with aboveground dry weight, plant height, Pn, Gs, Ci, and CsAld (P < 0.05), and soluble sugar content was significantly positively correlated with the number of leaves, Y(II), qP, and CsRbcS. The results of the principal component analysis (PCA) showed that there was a significant separation between the treatment and the control groups. Spraying 0.5 mg.L− 1 EBR can promote the growth of coriander, improve the quality of coriander leaves, and strengthen coriander leaf photosynthetic capacity. This study provides new insights into the promotion of coriander growth and development following the application of exogenous EBR.ConclusionExogenous EBR treatment increased coriander plant height, leaf growth and aboveground dry weight, and enhanced photosynthesis. Exogenous spraying of 0.5 mg.L− 1 EBR had the most significant effect.

Field application of microbial inoculants improved crop foliar morphology and physiology performance: A global meta-analysis

Leaf growth and function play fundamental role for crop development and production. The introduction of functional microbial strains also known as, microbial inoculants (MI) represents promising strategy for enhancing crop vigor and resilience. To obtain a comprehensive understanding of the impact of the MI technique on foliar morphology and physiological performance, a meta-analysis encompassing 168 published articles, comprising of total 1656 paired observations, was conducted. The findings showed that MI amendments resulted in notable enhancements in several key parameters. Specifically the leaf area, leaf area index, and leaf nitrogen content exhibited increases of 16.56 %, 16.28 %, and 13.76 %, respectively. Moreover, the MI-treated crops demonstrated higher values in terms of chlorophyll content, leaf gas exchange indices, and chlorophyll fluorescence parameters suggesting improvements in the MI treatment indicated that light harvesting and utilization by the crops were improved. Additionally, the linear mixed-effects model showed that changes in these parameters (except for intercellular CO2 concentration) after MI addition had a positive effect on crop yield. Upregulated antioxidant enzyme activities, such as POD, CAT, and SOD, in crop leaves increased by 20.91 %, 12.68 %, and 23.08 %, respectively, whereas H2O2 content decreased significantly, by 38.46 %. These results indicate that MI amendment is a promising strategy for improvement of light interception and utilization in crops. MI treatment is expected to increase crop tolerance to stress, thus increasing productivity and yield. Therefore, future adoption of the MI technique could contribute to ensuring food security and agricultural sustainability, however, the factors affecting MI efficacy should be further clarified.

Effects of Different Forms and Proportions of Nitrogen on the Growth, Photosynthetic Characteristics, and Carbon and Nitrogen Metabolism in Tomato.

Optimal plant growth in many species is achieved when the two major forms of N are supplied at a particular ratio. This study investigated optimal nitrogen forms and ratios for tomato growth using the 'Jingfan 502' tomato variety. Thirteen treatments were applied with varying proportions of nitrate nitrogen (NN), ammonium nitrogen (AN), and urea nitrogen (UN). Results revealed that the combination of AN and UN inhibited tomato growth and photosynthetic capacity. Conversely, the joint application of NN and UN or NN and AN led to a significant enhancement in tomato plant growth. Notably, the T12 (75%UN:25%NN) and T4 (75%NN:25%AN) treatments significantly increased the gas exchange and chlorophyll fluorescence parameters, thereby promoting the accumulation of photosynthetic products. The contents of fructose, glucose, and sucrose were significantly increased by 121.07%, 206.26%, and 94.64% and by 104.39%, 156.42%, and 61.40%, respectively, compared with those in the control. Additionally, AN favored starch accumulation, while NN and UN favored fructose, sucrose, and glucose accumulation. Gene expression related to nitrogen and sugar metabolism increased significantly in T12 and T4, with T12 showing greater upregulation. Key enzyme activity in metabolism also increased notably. In summary, T12 enhanced tomato growth by upregulating gene expression, increasing enzyme activity, and boosting photosynthesis and sugar accumulation. Growers should consider using NN and UN to reduce AN application in tomato fertilization.

Unraveling the influence of TiO2 nanoparticles on growth, physiological and phytochemical characteristics of Mentha piperita L. in cadmium-contaminated soil

Among the metals contaminants, cadmium (Cd) is one of the most toxic elements in cultivated soils, causing loss of yield and productivity in plants. Recently, nanomaterials have been shown to mitigate the negative consequences of environmental stresses in different plants. However, little is known about foliar application of titanium dioxide nanoparticles (TiO2 NPs) to alleviate Cd stress in medicinal plants, and their dual interactions on essential oil production. The objective of this study was to investigate the effects of foliar-applied TiO2 NPs on growth, Cd uptake, chlorophyll fluorescence, photosynthetic pigments, malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents, total phenols, anthocyanins, flavonoids, antioxidant enzymes (SOD, CAT and POD) activity and essential oil content of Mentha piperita L. (peppermint) under Cd stress. For this purpose, plants were grown in Cd-contaminated (0, 20, 40, and 60 mg L−1) soil, and different concentrations of TiO2 NPs (0, 75, and 150 mg L−1) were foliar sprayed at three times after full establishment until the beginning of flowering. Exposure to TiO2 NPs significantly (P < 0.01) increased shoot dry weight (37.8%) and the number of lateral branches (59.4%) and decreased Cd uptake in plant tissues as compared to the control. Application of TiO2 NPs increased the content of plastid pigments, and the ratio Fv/Fm (13.4%) as compared to the control. Additionally, TiO2 NPs reduced the stress markers, MDA and H2O2 contents and enhanced the activity of the phenylalanine ammonia-lyase (PAL) enzyme (60.5%), total phenols (56.1%), anthocyanins (42.6%), flavonoids (25.5%), and essential oil content (52.3%) in Cd-stressed peppermint compared to the control. The results also demonstrated that foliar spray of TiO2 NPs effectively improved the growth and chlorophyll fluorescence parameters and reduced Cd accumulation in peppermint, which was mainly attributed to the reduction of oxidative burst and enhancement of the enzymatic (SOD, CAT, and POD) antioxidant defense system due to the uptake of NPs. The findings provide insights into the regulatory mechanism of TiO2 NPs on peppermint plants growth, physiology and secondary metabolites production in Cd-contaminated soil.

Synthetic polyploid induction influences morphological, physiological, and photosynthetic characteristics in Melissa officinalis L.

Melissa officinalis L., a well-known herb with diverse industrial and ethnopharmacological properties. Although, there has been a significant lack in the breeding attempts of this invaluable herb. This study aimed to enhance the agronomical traits of M. officinalis through in vitro polyploidization. Nodal segments were micropropagated and subjected to oryzalin treatment at concentrations of 20, 40, and 60 mM for 24 and 48 hours. Flow cytometry, chromosome counting, and stomatal characteristics were employed to confirm the ploidy level of the surviving plants. The survival rate of the treated explants decreased exponentially with increasing oryzalin concentration and duration. The highest polyploid induction rate (8%) was achieved with 40 mM oryzalin treatment for 24 hours. The induced tetraploid plants exhibited vigorous growth, characterized by longer shoots, larger leaves, and a higher leaf count. Chlorophyll content and fluorescence parameters elucidated disparities in photosynthetic performance between diploid and tetraploid genotypes. Tetraploid plants demonstrated a 75% increase in average essential oil yield, attributed to the significantly larger size of peltate trichomes. Analysis of essential oil composition in diploid and tetraploid plants indicated the presence of three major components: geranial, neral, and citronellal. While citronellal remained consistent, geranial and neral increased by 11.06% and 9.49%, respectively, in the tetraploid population. This effective methodology, utilizing oryzalin as an anti-mitotic agent for polyploid induction in M. officinalis, resulted in a polyploid genotype with superior morpho-physiological traits. The polyploid lemon balm generated through this method has the potential to meet commercial demands and contribute significantly to the improvement of lemon balm cultivation.

Effects of biofertilizers on the growth, leaf physiological indices and chlorophyll fluorescence response of spinach seedlings.

Chemcial fertilizer as the main strategy for improving the vegetable yields was excessively applied in recent years which led to progressively serious soil problems such as the soil acidification. According the situation, five different biofertilizer treatments [no fertilizer (CK), inoculations of Bacillus subtilis (Bs, T1), combination of Bs and Bacillus mucilaginosus (Bs+Bm, T2), Bs and Bacillus amyloliquefaciens (Bs+Ba, T3), and Bm+Ba (T4)] were conducted to investigate the effect of the growth, leaf physiological indices, and chlorophyll fluorescence of spinach seedlings in the growth chamber. The growth and physiological indices of the spinach seedlings attained a maximum under the T2 treatments. Under the T2 treatment, the ABS/RC (Absorption flux per RC), TR0/RC (Trapping flux per RC), and ET0/RC (Electron transport flux per RC) was significantly increased, while the DI0/RC [Dissipated energy flux per RC (at t = 0)] was decreased. The OJIP curve was improved under of the inoculations of fertilizers, and the increasing range was the largest under the T2 treatment. The leaf light response curve (LC) was also significantly increased under the T2 treatment. The plant growth characteristics [leaf length (LL), leaf weight (LW), plant height (PH)] were positively correlated with the J-I-P test chlorophyll fluorescence parameters [PIABS (Performance index for energy conservation from exciton to the reduction of intersystem electron acceptors), φP0 (Maximum quantum yield of primary photochemistry), φE0 (Quantum yield of electron transport), ψ0 (The probability that a trapped exciton moved an electron in electron transport chain further than QA-), TR0/RC, and ET0/RC] while negatively correlated with φD0 (Quantum yield of energy dissipation) and DI0/RC. The leaf physiological characteristics [SP (soluble protein concentrations), SC (soluble carbohydrate concentrations), Chl a (chlorophyll a), Chl b (chlorophyll b), Chl a+b, Chl a/b, and WP (water potential)] were positively correlated with the J-I-P test chlorophyll fluorescence parameters (PIABS, φP0, φE0, ψ0, ABS/RC, TR0/RC, and ET0/RC) while negatively correlated with φD0 and DI0/RC. These results indicated that the combination of Bs+Bm inoculations promoted the growth of the spinach and improved the adaptability of the vegetable to acid soil while Ba inoculation didn't have any effects to plants.

The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress.

With the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances. The effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids. C. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses. The different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.

Method for early diagnosis of verticillium wilt in cotton based on chlorophyll fluorescence and hyperspectral technology

Early and accurate detection of verticillium wilt (VW), the most common and devastating disease of cotton, is essential to prevent the spread of VW. However, it remains challenging to achieve accurate detection of VW in cotton before symptoms appear after infection with Verticillium dahliae (asymptomatic phase). This study evaluated the feasibility of detection of VW in the asymptomatic phase based on cotton main stem leaf chlorophyll fluorescence parameters (CFPs) and spectral features extracted based on continuous wavelet transform (CWT) in two different environments. The aim was to achieve accurate detection of cotton VW in the asymptomatic period by convenient methods. Hyperspectral data of cottons inoculated with V. dahliae were collected at different times, and the CFPs of main stem leaves were measured simultaneously. After preprocessing the hyperspectral data with CWT, common wavelet features for all spectral acquisition days and sensitive CFPs were extracted based on the results of ANOVA. Then, the variance inflation factor combined with least absolute shrinkage and selection operator (LASSO-VIF) was used to select the optimal wavelet features. Finally, the support vector machine, logistic regression, and k-nearest neighbors (KNN) were used to construct the models for detecting VW in asymptomatic leaves based on CFPs and optimal wavelet features, and the accuracy of the models were compared.The results showed that the CFPs were significantly affected 24 h after V. dahliae infection. V. dahliae infection reduced the maximum quantum yield (Pm') of photosystem II (PSII) and increased non-photochemical quenching (NPQt) in cotton leaves. Compared with the raw spectrum, the spectral features in the near-infrared region (800–1350 nm) extracted based on CWT could accurately reflect the subtle changes of leaves in the asymptomatic phase. Besides, compared with CFPs, the 4–5 wavelet features selected based on the LASSO-VIF were more helpful to accurately identify asymptomatic cotton leaves infected with V. dahliae, with an accuracy greater than 80 % and a Kappa coefficient higher than 0.6. Among them, the average accuracy of the logistic regression model based on wavelet features was as high as 90.62 %. The results of this study confirm the changes in CFPs in cotton leaves in the VW-asymptomatic period and the feasibility of accurate identification by using wavelet features. This study will provide a reliable reference for accurate large-scale identification of V. dahliae infection in cotton in the asymptomatic phase.

MWCNTs Alleviated saline-alkali stress by optimizing photosynthesis and sucrose metabolism in rice seedling

ABSTRACTSaline and alkali stress affects the growth and development, survival rate, and final yield of rice, while new nano materials can have a positive effect on rice growth. In order to investing the effects of carboxymethyl multi walled carbon nanotubes (MWCNTs) on the growth and development of rice seedlings under salt alkali stress, rice seedlings were cultured using rice variety “Songjing 3” using nutrient solution water culture method. The effects of MWCNTs on water absorption capacity, leaf photosynthesis, and sucrose metabolism of rice seedlings under 50 mmol/L saline-alkali stress (1NaCl: 9Na2SO4: 9NaHCO3: 1Na2CO3) conditions were investigated. The results showed that MWCNTs can improve the water use ability of roots and leaves, especially the water absorption ability of roots, which provides a guarantee for the improvement of rice biomass and the enhancement of leaf photosynthetic capacity under adverse conditions. After treatment with MWCNTs, the photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) of leaves increased significantly, and the photochemical quenching value (qP), photochemical quantum efficiency value (Fv/Fm), and electron transfer rate value (ETR) of chlorophyll fluorescence parameters increased significantly, which is beneficial to the improvement of the PSII photosynthetic system. MWCNTs treatment promoted the increase of photosynthetic pigment content in leaves under salt and alkali stress, improved the ratio of Chla and Chlb parameters, increased the activities of key photosynthetic enzymes (RUBPCase and PEPCase) in leaves, increased the value of total lutein cycle pool (VAZ), and significantly enhanced the deepoxidation effect of lutein cycle (DEPS), which can effectively alleviate the stomatal and non stomatal constraints on leaf photosynthesis caused by salt and alkali stress. MWCNTs treatment significantly enhanced the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) under salt and alkali stress, and decreased the activities of soluble acid invertase (SAInv) and alkaline/neutral invertase (A/N-Inv), indicating that MWCNTs promoted sucrose synthesis while inhibiting sucrose decomposition, thereby promoting sucrose accumulation in rice leaves. This study can provide theoretical and experimental basis for the application of MWCNTs to the production of rice under salt and alkali stress, and can find a new way for rice production in saline and alkaline lands.

INTERAKCJA POMIĘDZY INTENSYWNOŚCIĄ ŚWIATŁA A STRESEM SUSZY I ICH WPŁYW NA WZROST SIEWEK PSZENICY

In this paper, wheat seedlings were exposed to different levels of photon flux density (PFD) and drought stress. Seedlings of the wheat cv. Goplana were cultivated in controlled conditions in a miniphytotrone and exposed to three different photosynthetic photon flux densities (400, 800, and 1200 μmol⋅m−2⋅s−1) and drought stress (a water potential of −0.6 MPa). The Hoagland’s solution-treat- ed seedlings served as a control. The fresh and dry matter of the overground parts and roots, rela- tive chlorophyll concentration, electrical conductivity and chlorophyll fluorescence parameters were measured. Drought stress decreased the biomass of wheat seedlings, cv. Goplana. Higher intensities of photosynthetically active irradiation stimulated biomass growth both under control conditions and under drought stress. Drought and higher PFD intensity resulted in a decrease in chlorophyll content. Only the highest light intensity, together with drought stress, negatively affected the structure of cell membranes, increasing their permeability. Both of the applied stress factors did not cause significant changes in the values of the determined parameters of chlorophyll fluorescence in the leaves of wheat seedlings. These results suggest that the increase in light intensity has a mobilising effect on the plant, stimulating the development of biomass both under control conditions and under drought stress. No changes in the values of chlorophyll fluorescence parameters under the influence of different light intensities and drought stress may indicate that there were no significant disturbances in the course of the light phase of photosynthesis in the leaves of the tested seedlings.

Chlorophyll Fluorescence Parameter as a Tool in Selecting Heat-tolerant Summer-flowering Chrysanthemum (Dendranthema ×grandiflorum)

Chrysanthemum ‘Bai Tian Xing’, ‘Huang Ching Chin’, ‘Pink Pearl’, and ‘NCHU-001’ plants were preheated at 35 °C for 24 hours to induce heat tolerance. The recently fully expanded leaves were detached, kept in a moist Ziploc bag, and then subjected to 35, 40, 45, 47.5, 50, 52.5, 55, 60, or 65 °C for 20 minutes. After dark-acclimatized at room temperature for 30 minutes, leaves were measured for Fv/Fm value with a chlorophyll fluorescence parameter. Results showed that ‘Bai Tian Xing’ had the highest critical (Tcrit) and midpoint temperature (Tmid). Mean Tcrit and Tmid were shown to be 47 and 50 °C, respectively, and Tmid gave greater distinguishment of Fv/Fm value among cultivars. Plants of four cultivars were acclimatized at 15 to 40 °C for 3 days and 35 °C being the most effective temperature to induce a heat-tolerant response in chrysanthemum. Required inducing time to reach a stable leaf Fv/Fm value ranged from 4.6 to 11.1 hours among cultivars. All cultivars had similar required time to reach visible bud between summer and autumn crops (except NCHU-001), but all had delayed flowering in the summer crop. There is a negative linear relationship between flowering heat delay and leaf Fv/Fm value (R2 = 0.93). Progenies from reciprocal crossing of ‘Bai Tian Xing’ × ‘NCHU-001’ and ‘Huang Ching Chin’ × ‘Pink Pearl’ were also subjected to treatments for Fv/Fm measurements and observed for time to flowering in the summer crop. All combinations showed negative linear relationship between time to flowering and leaf Fv/Fm value (R2 = 0.70–0.87). Two plants, 109-W001Y and 109-W003Pi, showed early flowering habit and good flower performance under heat conditions were selected. All four cultivars and the two selected lines were measured for photosynthetic parameters under day/night temperatures of 35/30 or 25/20 °C in growth chambers. All cultivars and lines showed decreased net photosynthetic rate and dark respiration rate under 35/30 °C when compared with 25/20 °C. Relatively higher net photosynthetic rate and lower dark respiration rate in ‘Bai Tian Xing’, ‘109-W001Y’, and ‘109-W003Pi’ under 35/30 °C, when compared with the other three cultivars, might have contributed to better flowering performance in the summer.

Acclimation of the Grapevine Vitis vinifera L. cv. Assyrtiko to Water Deficit: Coordination of Structural and Functional Leaf Traits and the Dynamic of Calcium Oxalate Crystals

Grapevine leaves contain abundant CaOx crystals located either within the mesophyll in the form of raphides, or in the bundle sheaths as druses. CaOx crystals function as internal carbon pools providing CO2 for a baseline level of photosynthesis, named “alarm photosynthesis”, despite closed stomata; thus, preventing the photoinhibition and the oxidative risk due to carbon starvation under adverse conditions. Structural and functional leaf traits of acclimated grapevine plants (Vitis vinifera L. cv. Assyrtiko) were investigated in response to water availability, in order to evaluate the dynamic functionality of CaOx. Leaf water potential, leaf area, leaf mass per area, stomatal properties, gas exchange parameters and performance index (PI) were decreased in leaves of vines acclimated to water deficit in comparison to the leaves of well-irrigated vines, although the chlorophyll fluorescence parameters showed that the operational efficiency of the photosystem II (PSII) photochemistry (Fv/Fm) did not change, indicating that the photosynthetic apparatus was not subjected to water stress. During the afternoon, more than half of the morning’s existing druses disappeared in the drought-acclimated leaves. Also, the raphides’ area of the drought-acclimated leaves was reduced more than that of the well-watered leaves. The substantial decomposition of druses under water deficit conditions compared to that of the raphides may have important implications for the maintenance of their different though overlapping roles. According to the results, it seems likely that, under water deficit conditions, a mechanism of “alarm photosynthesis” provides an additional tolerance trait in the leaves of Vitis vinifera cv. Assyrtiko; hence, leaf structure relates to function.

Comparative Transcriptome Combined with Morphophysiological Analyses Revealed Carotenoid Biosynthesis for Differential Chilling Tolerance in Two Contrasting Rice (Oryza sativa L.) Genotypes

Early spring cold spells can lead to leaf chlorosis during the rice seedling greening process. However, the physiological and molecular mechanisms underlying the rice greening process under low-temperature conditions remain unknown. In this study, comparative transcriptome and morphophysiological analyses were performed to investigate the mechanisms mediating the responses of the Koshihikari (Kos) and Kasalath (Kas) rice cultivars to chilling stress. According to their growth-related traits, electrolyte leakage, and chlorophyll fluorescence parameters, Kos was more tolerant to low-temperature stress than Kas. Moreover, chloroplast morphology was more normal (e.g., oval) in Kos than in Kas at 17 °C. The comparative transcriptome analysis revealed 610 up-regulated differentially expressed genes that were common to all four comparisons. Furthermore, carotenoid biosynthesis was identified as a critical pathway for the Kos response to chilling stress. The genes in the carotenoid biosynthesis pathway were expressed at higher levels in Kos than in Kas at 17 °C, which was in accordance with the higher leaf carotenoid content in Kos than in Kas. The lycopene β-cyclase and lycopene ε-cyclase activities increased more in Kos than in Kas. Additionally, the increases in the violaxanthin de-epoxidase and carotenoid hydroxylase activities in Kos seedlings resulted in the accumulation of zeaxanthin and lutein and mitigated the effects of chilling stress on chloroplasts. These findings have clarified the molecular mechanisms underlying the chilling tolerance of rice seedlings during the greening process.