Dissipated Energy Flux Research Articles

Improving the performance of the photosynthetic apparatus of Citrus sinensis with the use of chitosan-selenium nanocomposite (CS + Se NPs) under salinity stress

BackgroundAbiotic stress, such as salinity, affects the photosynthetic apparatus of plants. It is reported that the use of selenium nanoparticles (Se NPs), and biochemical compounds such as chitosan (CS) increase the tolerance of plants to stress conditions. Therefore, this study aimed to elucidate the potential of Se NPs, CS, and their composite (CS + Se NPs) in improving the photosynthetic apparatus of C. sinensis under salt stress in greenhouse conditions. The grafted seedlings of C. sinensis cv. Valencia after adapting to the greenhouse condition, were imposed with 0, 50, and 100 mM NaCl. After two weeks, the plants were foliar sprayed with distilled water (control), CS (0.1% w/v), Se NPs (20 mg L− 1), and CS + Se NPs (10 and 20 mg L− 1). Three months after treatment, the levels of photosynthetic pigments, leaf gas exchange, and chlorophyll fluorescence in the treated plants were evaluated.ResultsUnder salinity stress, total chlorophyll, carotenoid, and SPAD values decreased by 31%, 48%, and 28% respectively, and Fv/Fm also decreased compared to the control, while the ratio of absorption flux (ABS), dissipated energy flux (DI0) and maximal trapping rate of PSII (TR0) to RC (a measure of PSII apparent antenna size) were increased. Under moderate (50 mM NaCl) and intense (100 mM NaCl) salinity stress, the application of CS + Se NPs significantly increased the levels of photosynthetic pigments and the Fv/Fm value compared to plants treated with distilled water.ConclusionsIt may be inferred that foliar treatment with CS + Se NPs can sustain the photosynthetic ability of C. sinensis under salinity stress and minimize its deleterious effects on photosynthesis.

Improving High Light Tolerance of Tobacco Plants: Adequate Magnesium Supply Enhances Photosynthetic Performance

High light (HL) significantly impacts plant photosynthesis. This study investigated the effects of different magnesium (Mg) levels (0, 1, 2, and 5 mol Mg plant−1; HMg0, HMg1, HMg2, and HMg5) on tobacco (Nicotiana tabacum L. cv. Cuibi No. 1) under HL (1500 μmol m−2 s−1), aiming to understand the role of Mg in mitigating the impact of HL on photosynthesis and carbon–nitrogen metabolism. Plants treated with 1 mol Mg plant−1 under 750 μmol m−2 s−1 light conditions served as the control. HL led to a reduced chlorophyll (Chl) content and inhibited the maximum photosynthetic rate (Pmax). It also decreased energy involved in photosynthetic electron transfer (ET) and electron flux to reduction end-electron acceptors at the photosystems I (PSI) acceptor side (RE) and caused photosynthetic system damage. H2O2 accumulation exacerbated membrane lipid peroxidation damage, disrupting carbon and nitrogen metabolism, and inducing antioxidant enzyme activity. HMg2 increased Chl content, stomatal conductance, intercellular CO2 concentration, and the net photosynthetic rate compared to HMg0. It enhanced ET efficiency, PSI and PSII functionality, reduced dissipated energy flux (DI), and minimized photosynthesis damage. Conversely, excessive Mg application (HMg5) decreased Pmax and PSII activity, increasing DI. Adequate Mg supply alleviated HL’s detrimental effects by enhancing Chl content and ET and RE efficiency.

Exogenous methyl jasmonate regulates endogenous hormone synthesis of soilless cultivated Chinese chive to promote growth physiology and photosynthesis

Methyl jasmonate (MeJA) is involved in regulating various growth and development processes of plants, yet the underlying mechanisms remain unclear. Therefore, the objective of this study was to investigate the effects of exogenous MeJA on physiological growth, photosynthesis, and endogenous hormones in soilless cultivated Chinese chives. Four concentrations of MeJA (0, 300, 500, and 800 μM) were applied to the leaves of substrate-grown and hydroponics Chinese chives. The results showed that MeJA increased the leaf tissues water content and SPAD values of hydroponically Chinese chives, and 500 μM MeJA significantly enhanced the root activity and leaf carotenoids content of soilless cultivated Chinese chive, and promoted the activities of key enzymes of chlorophyll synthesis (ChlM and POR), thereby increasing chlorophyll a, chlorophyll b and total chlorophyll contents. Meanwhile, MeJA (500 μM) enhanced the activity of key enzymes in the Calvin cycle (Rubisco, FBA, FBPase, GAPDH, and TK), promoted CO2 fixation, improved photosynthetic carbon assimilation efficiency, and promoted Gs, Tr, and Pn, thereby enhancing photosynthesis. Moreover, MeJA (500 μM) significantly enhanced the instantaneous distribution (I-P) of the OJIP curve, enhanced the ability of the plastoquinone pool (PQ) to accept electrons, increased the quantum yield, promoted the apparent quantum flux per unit leaf area and energy flux ratio per unit PSII active reaction center, improved the electron transfer efficiency while reducing the heat dissipation energy flux per unit PSII active reaction center, and thus enhanced PSII activity. Additionally, exogenous MeJA (500 μM) promoted the accumulation of endogenous ZT, GA3, IAA, and ABA, but inhibited the upstream substrates for OPDA synthesis (MGDG and DGDG) in the JA synthesis pathway, and decreased the activities of JA synthases (LOX, AOC, and OPR), which in turn inhibited the synthesis of JA and MeJA. Changes in the relative content of MGDG/DGDG altered the membrane lipid composition of the photosynthetic membrane, which in turn altered the energy balance of the light reaction and improved the efficiency of electron transfer within the photosynthetic membrane, thereby enhancing the photosynthetic capacity. In conclusion, our study demonstrates that exogenous MeJA improves root activity and chlorophyll accumulation in soilless cultured Chinese chives, and adjusting the composition of photosynthetic membrane lipids by regulating the levels of endogenous hormones and JA-synthesizing substrates, promoting the efficiency of electron transfer, enhancing PSII activity, and promoting photosynthetic carbon fixation, thereby enhancing photosynthesis and promoting growth.

Bacillus megaterium Compensates for Growth Inhibition from Phosphorus Deficiency by Improving Photosynthetic Capacity, Changing Antioxidant Potential, and Regulating Non-Structural Carbohydrate Concentrations in Glycyrrhiza uralensis

This study assessed the effect of Bacillus megaterium on seedling growth of Glycyrrhiza uralensis Fisch. under control and phosphorus (P) deficiency conditions. The results showed that P deficiency improved 1) G. uralensis root growth, 2) superoxide dismutase, catalase, and peroxidase activities, 3) inorganic P, starch, and soluble sugar contents in roots, 4) dissipated energy flux per reaction center, trapped energy flux per reaction center, and absorption flux per reaction center, and 5) net photosynthetic rate, stomatal conductance, transpiration rate, maximum fluorescence intensity after dark adaptation, and variable fluorescence. However, P deficiency significantly decreased chlorophyll and carotenoid contents in G. uralensis, but enhanced chlorophyll and carotenoid contents in B. megaterium. Our findings on the regulatory mechanisms of B. megaterium in response to P starvation hold promise for improving the success of G. uralensis cultivation.
 Keywords: Bacillus megaterium; Glycyrrhiza uralensis Fisch; Phosphorus deficiency; Chlorophyll fluorescence; Antioxidant enzymes superoxide; Non-structural carbohydrate

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.

Polyvinylpyrrolidone-coated copper nanoparticles dose-dependently conferred tolerance to wheat under salinity and/or drought stress by improving photochemical activity and antioxidant system

Copper (Cu) is one of the essential micronutrients for plants and has been used extensively in agricultural applications from the past to the present. However, excess copper causes toxic effects such as inhibiting photosynthesis, and disrupting biochemical processes in plants. Nanotechnology applications have offered a critical method for minimizing adverse effects and improving the effectiveness of copper nanoparticles. For this purpose, this study investigated the physiological and biochemical effects of polyvinylpyrrolidone (PVP)-coated Cu nanoparticles (PVP–Cu NP, N1, 100 mg L−1; N2, 400 mg L−1) in Triticum aestivum under alone or combined with salt (S, 150 mM NaCl) and/or drought (D, %10 PEG-6000) stress. Salinity and water deprivation caused 51% and 22% growth retardation in wheat seedlings. The combined stress condition (S + D) resulted in an approximately 3-fold reduction in the osmotic potential of the leaves. PVP-Cu NP treatments to plants under stress, especially N1 dose, were effective in restoring growth rate and regulating water relations. All stress treatments limited gas exchange in stomata and suppressed the maximal quantum yield of PSII (Fv/Fm). More than 50% improvement was observed in stomatal permeability and carbon assimilation rate under S + N1 and S + N2 applications. Examination of OJIP transient parameters revealed that N1 treatments protected photochemical reactions by reducing the dissipated energy flux (DIo/RC) in drought and S + D conditions. Exposure to S and/or D stress caused high hydrogen peroxide (H2O2) accumulation and lipid peroxidation in wheat leaves. The results indicated that S + N1 and S + N2 treatments reduced oxidative damage by stimulating the activities of antioxidant enzymes superoxide dismutase (SOD), peroxidase (POX), and ascorbate peroxidase (APX). Although similar effects were observed at D and S + D conditions with 100 mg L−1 PVP-Cu NP treatments (N1), the curative effect of the N2 dose was not observed. In D + N1 and S + D + N1 groups, AsA regeneration and GSH redox status were maintained by triggering APX, GR, and other enzyme activities belonging to the AsA-GSH cycle. In these groups, N2 treatment did not contribute to the availability of enzymatic and non-enzymatic antioxidants. As a result, this study revealed that N1 dose PVP-Cu NP application was successful in providing stress tolerance and limiting copper-induced adverse effects under all stress conditions.

Natural variation in photosynthesis and water use efficiency of locally adapted Persian walnut populations under drought stress and recovery

Persian walnut is a drought-sensitive species with considerable genetic variation in the photosynthesis and water use efficiency of its populations, which is largely unexplored. Here, we aimed to elucidate changes in the efficiency of photosynthesis and water content using a diverse panel of 60 walnut families which were submitted to a progressive drought for 24 days, followed by two weeks of re-watering. Severe water-withholding reduced leaf relative water content (RWC) by 20%, net photosynthetic rate (Pn) by 50%, stomatal conductance (gs) by 60%, intercellular CO2 concentration (Ci) by 30%, and transpiration rate (Tr) by 50%, but improved water use efficiency (WUE) by 25%. Severe water-withholding also inhibited photosystem II functionality as indicated by reduced quantum yield of intersystem electron transport (φEo) and transfer of electrons per reaction center (ET0/RC), also enhanced accumulation of QA (VJ) resulted in the reduction of the photosynthetic performance (PIABS) and maximal quantum yield of PSII (FV/FM); while elevated quantum yield of energy dissipation (φDo), energy fluxes for absorption (ABS/RC) and dissipated energy flux (DI0/RC) in walnut families. Cluster analysis classified families into three main groups (tolerant, moderately tolerant, and sensitive), with the tolerant group from dry climates exhibiting lesser alterations in assessed parameters than the other groups. Multivariate analysis of phenotypic data demonstrated that RWC and biophysical parameters related to the chlorophyll fluorescence such as FV/FM, φEo, φDo, PIABS, ABS/RC, ET0/RC, and DI0/RC represent fast, robust and non-destructive biomarkers for walnut performance under drought stress. Finally, phenotype-environment association analysis showed significant correlation of some photosynthetic traits with geoclimatic factors, suggesting a key role of climate and geography in the adaptation of walnut to its habitat conditions.

Improving Grapevine Heat Stress Resilience with Marine Plant Growth-Promoting Rhizobacteria Consortia.

Amid climate change, heatwave events are expected to increase in frequency and severity. As a result, yield losses in viticulture due to heatwave stress have increased over the years. As one of the most important crops in the world, an eco-friendly stress mitigation strategy is greatly needed. The present work aims to evaluate the physiological fitness improvement by two marine plant growth-promoting rhizobacteria consortia in Vitis vinifera cv. Antão Vaz under heatwave conditions. To assess the potential biophysical and biochemical thermal stress feedback amelioration, photochemical traits, pigment and fatty acid profiles, and osmotic and oxidative stress biomarkers were analysed. Bioaugmented grapevines exposed to heatwave stress presented a significantly enhanced photoprotection capability and higher thermo-stability, exhibiting a significantly lower dissipation energy flux than the non-inoculated plants. Additionally, one of the rhizobacterial consortia tested improved light-harvesting capabilities by increasing reaction centre availability and preserving photosynthetic efficiency. Rhizobacteria inoculation expressed an osmoprotectant promotion, revealed by the lower osmolyte concentration while maintaining leaf turgidity. Improved antioxidant mechanisms and membrane stability resulted in lowered lipid peroxidation product formation when compared to non-inoculated plants. Although the consortia were found to differ significantly in their effectiveness, these findings demonstrate that bioaugmentation induced significant heatwave stress tolerance and mitigation. This study revealed the promising usage of marine PGPR consortia to promote plant fitness and minimize heatwave impacts in grapevines.

Application of fluorescent transients to indicate nutrient deficiencies in a microalga Nannochloropsis oceanica

Here we studied the effects of nutrient deficiency, focusing on Ca, N, S, Mg, Fe, on photosynthetic performance of Nannochloropsis oceanica to determine the abilities of fluorescence transients to detect nutrient limitation. We conducted a two-level (replete/deplete) fully factorial experiment for each of 5 nutrients and found different responses to nutrient limitation. A potential indicator of N limitation was trapped energy per reaction center (TRO/RC), as the synthesis of photosynthetic reaction center (RC) declined under N deficiency and eventually the ratio of TRO/RC increased. Photosystem II performance measured by performance index (PIABS) was not compromised under Fe, S and Mg deficiency, whereas the impact of Ca and N was critical. Although interactive nutrient interactions on photosynthetic parameters were observed, relationships were established between net reaction closure (MO) and Mg; dissipated energy flux per RC (DIO/RC) and S; and average quantum yield of photochemistry (ΦPav) and Ca.

Photosynthetic efficiency of young Rhizophora mangle L. in a mangrove in southeastern Brazil

The study proposes to evaluate the photosynthetic plasticity of Rhizophora mangle L. in four mangrove sites distributed along with the Great VitĂłria Estuarine System. The variation in organic matter content, which implies the higher essential nutrient availability, contributed to better energy flux performance related to electron transport. Furthermore, salinity damaged the reaction centers (RC), since the site with the highest salinity showed changes in the number and size of active photosynthetic RC and in the specific energy flows per active RC (absorption flux, trapped energy flux, and dissipated energy flux), but the plasticity of the species in response to salt stress was confirmed by the increase of performance index for energy conservation (PITotal), net photosynthetic rate (PN), and the water-use efficiency (WUE). Also, the results showed that the luminous intensity available compromises the functionality of PSII, in turn, it increases WUE. The results indicate the effect of the chlorophyll a content, which provides more substrate for light absorption, on the electron flow and PITotal is related to PN and WUE. The study indicates the ecological plasticity of R. mangle to the conditions of the evaluated area.

Electro-Thermo-Mechanical multiple fields coupled wave propagation through piezoelectric semiconductor sandwich structure

Based on the electro-thermo-mechanical multiple physical fields coupling model, the propagation of coupled elastic waves through a piezoelectric semiconductor sandwich structure is studied. Due to the consideration of non-Fourier heat conduction (G-N III-type) and non-Fick diffusion, there are totally five kinds of coupled waves in the piezoelectric semiconductor, i.e. quasi-longitudinal elastic wave, quasi-transverse elastic wave, charge carrier wave, thermal wave and piezopotential wave. The state vector is appropriately defined and the transfer matrix of state vector in the piezoelectric semiconductor is derived from the coupled equations which govern the piezopotential, charge carrier, thermal and mechanical multiple physical fields. The mathematic model of reflection/transmission through the piezoelectric semiconductor sandwich structure is finally established by considering the continuous condition of the state vectors at two interfaces. The reflection/transmission coefficients, the energy flux allocation and dissipated energy flux are studied numerically. The effects of steady carrier density, lifetime of carrier, thermal-elastic coupling parameters and the interlayer thickness on the dispersion and attenuation of coupled waves as well as the reflection transmission behavior are discussed based on the numerical results.

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

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

Microalgae-based swine wastewater treatment: Strain screening, conditions optimization, physiological activity and biomass potential

Using microalgae to treat swine wastewater (SW) can achieve wastewater purification and biomass recovery at the same time. The algae species suitable for growth in SW were screened in this study, and the response surface combined with the desirability function method was used for multi-objective optimization to obtain high algal biomass and pollutant removal. Chlorophyll fluorescence parameters and biomass composition were analyzed to evaluate the cell physiological activity and its application potential. Chlorella sp. HL was selected as the most suitable species for growth in SW, and after 9 d of cultivation, the maximum specific growth rate and highest algal density were achieved 0.51 d−1 and 2.43 × 107 cells/mL, respectively. In addition, the removal of total phosphate and chemical oxygen demand were reached 69.13% and 72.95%, respectively. The optimum conditions for maximum algal density and highest pollutant removal were determined as the light intensity of 58.73 μmol/m2/s, inoculation density of 5.0 × 106 cells/mL, and a light/dark ratio of 3 using response surface model, and the predicted overall desirability value was 0.96. The potential maximum quantum yield of PSII (Fv/Fm) of Chlorella sp. HL in the early stage of cultivation was 0.60–0.70, while under high light and long photoperiod, the value of Fv/Fm and performance index of Chlorella decreased, trapped and dissipated energy flux per reaction center increased. The higher heating value of 18.25 MJ/kg indicated that the Chlorella cultivated in SW could be a good feedstock for biofuel production.

Analysis of the changes of electron transfer and heterogeneity of photosystem II in Deg1-reduced Arabidopsis plants.

Deg1 protease functions in protease and chaperone of PSII complex components, but few works were performed to study the effects of Deg1 on electron transport activities on the donor and acceptor side of PSII and its correlation with the photoprotection of PSII during photoinhibition. Therefore, we performed systematic and comprehensive investigations of electron transfers on the donor and acceptor sides of photosystem II (PSII) in the Deg1-reduced transgenic lines deg1-2 and deg1-4. Both the maximal quantum efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII) decreased significantly in the transgenic plants. Increases in nonphotochemical quenching (NPQ) and the dissipated energy flux per reaction center (DI0/RC) were also shown in the transgenic plants. Along with the decreased D1, CP47, and CP43 content, these results suggested photoinhibition under growth light conditions in transgenic plants. Decreased Deg1 caused inhibition of electron transfer on the PSII reducing side, leading to a decline in the number of QB-reducing centers and accumulation of QB-nonreducing centers. The Tm of the Q band shifted from 5.7 °C in the wild-type plant to 10.4 °C and 14.2 °C in the deg1-2 and deg1-4 plants, respectively, indicating an increase in the stability of S2QA¯ in transgenic plants. PSIIα in the transgenic plants largely reduced, while PSIIβ and PSIIγ increased with the decline in the Deg1 levels in transgenic plants suggesting PSIIα centers gradually converted into PSIIβ and PSIIγ centers in the transgenic plants. Besides, the connectivity of PSIIα and PSIIβ was downregulated in transgenic plants. Our results reveal that downregulation of Deg1 protein levels induced photoinhibition in transgenic plants, leading to loss of PSII activities on both the donor and acceptor sides in transgenic plants. These results give a new insight into the regulation role of Deg1 in PSII electron transport.

Effects of Autotoxicity on Seed Germination, Gas Exchange Attributes and Chlorophyll Fluorescence in Melon Seedlings

In recent years, continuous cropping is more and more common in melon production, which shows significant adverse effects on melon cultivation. Autotoxicity is a critical factor for continuous cropping obstacle. The purpose of this study was to investigate whether the changes of chlorophyll fluorescence parameters could sensitively reflect the degree of melon autotoxicity and its damage. The root aqueous extract of melon plant was used to simulate the autotoxicity. The effects of autotoxicity on seed germination, seedling morphology, photosynthesis and chlorophyll a fluorescence transient (OJIP) were determined. The results showed that autotoxicity significantly inhibited seed germination and subsequent growth. The content of chlorophyll and carotenoid, photosynthetic rate, stomatal conductance, water-use efficiency and transpiration rate decreased significantly in melon seedlings under autotoxicity. The OJIP test parameters showed slight improvement or no obvious change at low treatment concentration (0.01 and 0.02 g·mL−1) and deteriorated rapidly at high concentration (0.03 and 0.04 g·mL−1), which was consistent with the concentration-dependent characteristics of autotoxicity. Under high autotoxicity stress concentration, most parameters related specific fluxes or activities per photosystem II (PS II) reaction centers (RC), such as absorption flux per active RC (ABS/RC), dissipated energy flux per active RC (DIo/RC) and other parameters, increased significantly in OJIP test. At the same time, most parameters related yields or flux ratios and performance index, such as maximum quantum yield of primary photochemistry (φPo), performance index on absorption basis (PIabs) and other parameters, decreased significantly. Photoinhibition induced by autotoxicity affected both the donor and the acceptor side of PS II, and then inhibited the growth of plants, decreased of photosynthetic pigment content. OJIP test parameters can be used to measure effectively the effect of autotoxicity on melon seedlings.

Screening of tomato landraces for drought tolerance based on growth and chlorophyll fluorescence analyses

To investigate the effects of water withholding on 17 tomato (Solanum lycopersicum L.) landraces collected from different climatic zones of Iran and two commercial hybrids, the polyphasic OJIP fluorescence transient, relative water content (RWC), electrolyte leakage (EL) and vegetative growth parameters were analyzed. Duncan’s multiple range test (DMRT) for all the studied parameters and drought factor index (DFI) based on performance index on the absorption basis (PIabs) were used for screening the plants based on their tolerance to drought condition. Result showed that compared to the control plants, vegetative growth parameters, RWC, PIabs, relative maximal variable fluorescence (FM/F0), maximum quantum efficiency of PSII (FV/FM), quantum yield of electron transport (ΦE0) and electron transport flux per reaction center (RC) (ET0/RC) were decreased, whereas, EL, quantum yield of energy dissipation (ΦD0), specific energy fluxes per RC for energy absorption (ABS/RC) and dissipated energy flux (DI0/RC), which are closely related to the incidence of photoinhibition were increased in plants exposed to water withholding. DMRT and DFI screening results clearly categorized the landraces into three groups (tolerant, moderately sensitive and sensitive). Tolerant landraces showed less change for most of the measured parameters compared to sensitive and moderately sensitive landraces. We found that adapted landraces to dry climates had a higher tolerance to drought stress. Principal component analysis (PCA) revealed that FM/F0, FV/FM, ΦE0, ΦD0, PIabs, ABS/RC, ET0/RC and DI0/RC parameters are the most sensitive parameters for detection of impact of drought stress on tomato plants. In conclusion, the eight parameters have the potential to identify the drought injury in tomato seedlings.

Leaf anatomy, photosynthesis and chlorophyll fluorescence of lettuce as influenced by arbuscular mycorrhizal fungi under high temperature stress

In order to elucidate the mechanism of how arbuscular mycorrhiza (AM) fungi offer protection in lettuce (Lactuca sativa L.) from high temperature stress, the effects of mycorrhizal fungi, Funneliformis mosseae, on chloroplast ultrastructure, photosynthetic pigments, chlorophyll fluorescence of lettuce (cv. Shuangzi) grown under temperature at 25℃ and 35℃, respectively, were investigated in this study. Results showed that non-AM lettuce grown under high temperature at 35°C had damaged thylakoid organization and greater accumulation of starch granules, less chlorophyll contents and lowered net photosynthetic rate compared with those grown under 25°C. However, chlorophyll a content, chlorophyll b content, net photosynthetic rate and transpiration rate of lettuce inoculated with F. mosseae grown under high temperature increased by 4.5 %, 4.5 %, 7.7 % and 5.9 %, respectively, compared with those grown without AM fungi. Under high temperature, a depression at the P-step was observed in chlorophyll fluorescence transient in non-AM lettuce, accompanied by a significant increase in L‑step. The maximal fluorescence (Fm) of non-AM lettuce was reduced by 8.6 % as temperature increased from 25℃ to 35℃, while no significant differences were observed in Fm between AM lettuce grown under temperature at 35℃ and non-AM lettuce grown under temperature at 25℃. Absorption energy flux, dissipation energy flux and trapped energy flux per reaction center were increased with an decrease in quantum yield for electron transport (φEo) and performance index for energy conservation (PIabs) in lettuce grown under high temperature. However, opposite results were observed in lettuce inoculated with F. mosseae under high temperature. In conclusion, AM inoculaiton significantly improved lettuce tolerance to high temperature, by increasing photochemistry and preventing PSII system from heat damage.

Influence of salinity stress on PSII in barley (Hordeum vulgare L.) genotypes, probed by chlorophyll-a fluorescence

ObjectivesChlorophyll-a fluorescence is an efficient tool to determine the photosynthetic capacity of plants and the health status of plants under normal or stress conditions including salinity stress. This study was aimed to elucidate changes in the efficiency of photosystem II (PSII) in barley genotypes differing in degree of salt tolerance, which can be used for phenotyping in the breeding program for developing salt-tolerant cultivars. MethodologyTwelve barley (Hordeum vulgare L.) genotypes were subjected to salt stress and salt stress reduced the growth of all barley genotypes, which is associated with a decline in chlorophyll and K+ contents (roots and leaves) and increase in Na+. Of the 12 barley genotypes, one salt-tolerant (B-10008) and one salt-sensitive barley genotype (B-14011) was selected to further investigate the structural stability of PSII using fast chlorophyll a kinetic analysis under salinity stress. ResultsThe shape of OJIP transients changed due to salt stress in both salt-sensitive and salt-tolerant barley genotypes indicating a disturbance in structural stability at various points of PSII. The detailed analysis of JIP-test parameters suggested that salt stress caused photoinhibition of PSII due to enhanced inactive reaction centers, reduced absorption flux (ABS/RC), low transfer of electrons per reaction center (ETO/RC) and enhanced accumulation of QA¯ (VJ) thus reducing primary photochemistry (TRO/RC, ɸPO). These changes in PSII resulted in the reduction of the maximum quantum yield of PSII (Fv/Fm) and performance index (PIABS). Moreover, salinity stress enhanced dissipation energy flux per reaction center (DIO/RC) as a protective measure to save PSII from photooxidative damage in thylakoid membrane. ConclusionThe appearance of positive K and L-bands supported the idea that salt stress dissociated the light-harvesting complex from core proteins of PSII, damaged oxygen-evolving complex and reduced the structural stability of PSII by disturbing the electron transfer between acceptor and donor sides of PSII especially in salt sensitive genotype (B-14011). Moreover, such an adverse effect of salt stress on PSII was less in salt-tolerant barley genotype (B-10008). Thus, some JIP-test parameters can be used as potential phenotype marker for screening salt-tolerant genotypes.

Silencing of the receptor-like cytoplasmic kinase gene TaRKL1 reduces photosynthetic capacity in wheat

To explore the role of receptor-like kinases in the regulation of photosynthesis, an uncharacterized TaRKL1 encoding a receptor-like cytoplasmic kinase was investigated in Triticum aestivum cv. Xiaoyan 101 with Barley stripe mosaic virus-induced gene silencing system (BSMV-VIGS). The results showed that the CO2 assimilation rate, stomatal conductance, and transpiration rate were significantly lower in the BSMV:TaRKL1 plants than those in the BSMV:γ00 plants (control). Moreover, the maximum photochemical efficiency and electron transport flux decreased while the dissipated energy flux was enhanced in the BSMV:TaRKL1 plants compared to the control. Additionally, the contents of chlorophylls and carotenoids were reduced in the BSMV:TaRKL1 plants. However, the hydrogen peroxide content was significantly enhanced in the BSMV:TaRKL1 plants, which resulted from lower ascorbate peroxidase activity. Consistent with the inhibition of photosynthesis, the transcription levels of the photosynthesis-related, antioxidant enzymes, senescence-associated genes, and four abscisic acid biosynthesis genes were downregulated substantially. Collectively, this study for the first time showed that TaRKL1 regulates photosynthesis and H2O2 homeostasis. It may be a potential target gene for radiation-use efficiency improvement in wheat.

Special issue in honour of Prof. Reto J. Strasser - Characterization of photosynthetic performance during natural leaf senescence in winter wheat: Multivariate analysis as a tool for phenotypic characterization

In the current research, we used chlorophyll fluorescence measurements and photosynthetic pigment content to evaluate onset and rate of the flag leaf senescence every 7 d beginning at the flowering stage (0 d after flowering, DAF) until late senescence stage (35 DAF) on three winter wheat field-grown varieties (Alka, Žitarka, and Olimpija) with the similar maturation time. OJIP curves implied that flag leaves of variety Alka detained the longest photosynthetic efficiency, while the earliest symptoms of senescence onset were indicated by positive L-band at 7 DAF and K-band at 14 DAF in variety Olimpija. A shift in I-P phase in the wheat flag leaves suggested the reduction of first acceptors in PSI, implying degradation of photosynthetic apparatus. Performance index (PItotal) proved to be the sensitive indicator of senescence; it decreased very early at 7 DAF in the flag leaves of variety Olimpija compared to Alka and Žitarka. Principal component analysis elucidated quantum yield of energy dissipation and dissipated energy flux per reaction centre as the earliest indicators of senescence in wheat flag leaves and thus showed that multivariate approach may be useful in detection of senescence onset. Sustainability indexes (SIs) corroborated the statistical significance results of evaluated parameters implying that SIs can be used as user friendly data analysis for screening purposes. Selection for functional stay-green trait could contribute to increasing crop yields.