Fluorescence Induction Kinetics Research Articles

Effects of Cu2O nanoparticles on the kinetic characteristics of rapid chlorophyll fluorescence induction and related genes in wheat seedlings.

Metal nanoparticles could be accumulated in soils, which threatens the ecological stability of crops. Investigating the effects of cuprous oxide nanoparticles (Cu2O-NPs) on photosystem Ⅱ (PSⅡ) of wheat seedling leaves holds considerable importance in comprehending the implications of Cu2O-NPs on crop photosynthesis. Following the hydroponic method, we investigated the effects of 0, 10, 50, 100, and 200 mg·L-1 Cu2O-NPs on chlorophyll fluorescence induction kinetics and photosynthetic-related genes in wheat seedlings of "Zhoumai 18". The results showed that, with the increases of Cu2O-NPs concentrations, chlorophyll contents in wheat leaves decreased, and the standardization of the OJIP curve showed a clearly K-phase (ΔK＞0). Cu2O-NPs stress increased the parameters of active PSⅡ reaction centers, including the absorption flux per active RC (ABS/RC), the trapping flux per active RC (TRo/RC), the electron transport flux per active RC (ETo/RC), and the dissipation flux per active RC (DIo/RC). Cu2O-NPs stress decreased the parameters of PSⅡ energy distribution ratio including the maximum quantum yield of PSⅡ (φPo), the quantum yield of electron transport from QA (φEo), and the probability that a trapped exciton moved an electron further than QA (Ψo), while increased the quantum ratio for heat dissipation (φDo). Moreover, there was a decrease in photosynthetic quantum yield Y(Ⅱ), photochemical quenching coefficient (qP), net photosynthetic rate (Pn), stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) of leaves with the increases of Cu2O-NPs concentration. Under Cu2O-NPs stress, the expression levels of genes which included PSⅡ genes (PsbD, PsbP, Lhcb1), Rubisco large subunit genes (RbcL), cytochrome b6/f complex genes (PetD, Rieske), and ATP synthase genes (AtpA, AtpB, AtpE, AtpI) were downregulated. These results indicated that Cu2O-NPs stress altered the activity and structure of PSⅡ in wheat seedlings, affected the activity of PSⅡ reaction centers, performance parameters of PSⅡ donor and acceptor sides. PSⅡ related genes were downregulated and exhibited significant concentration effects.

Application of Chlorophyll Fluorescence Analysis Technique in Studying the Response of Lettuce (Lactuca sativa L.) to Cadmium Stress.

To reveal the impact of cadmium stress on the physiological mechanism of lettuce, simultaneous determination and correlation analyses of chlorophyll content and photosynthetic function were conducted using lettuce seedlings as the research subject. The changes in relative chlorophyll content, rapid chlorophyll fluorescence induction kinetics curve, and related chlorophyll fluorescence parameters of lettuce seedling leaves under cadmium stress were detected and analyzed. Furthermore, a model for estimating relative chlorophyll content was established. The results showed that cadmium stress at 1 mg/kg and 5 mg/kg had a promoting effect on the relative chlorophyll content, while cadmium stress at 10 mg/kg and 20 mg/kg had an inhibitory effect on the relative chlorophyll content. Moreover, with the extension of time, the inhibitory effect became more pronounced. Cadmium stress affects both the donor and acceptor sides of photosystem II in lettuce seedling leaves, damaging the electron transfer chain and reducing energy transfer in the photosynthetic system. It also inhibits water photolysis and decreases electron transfer efficiency, leading to a decline in photosynthesis. However, lettuce seedling leaves can mitigate photosystem II damage caused by cadmium stress through increased thermal dissipation. The model established based on the energy captured by a reaction center for electron transfer can effectively estimate the relative chlorophyll content of leaves. This study demonstrates that chlorophyll fluorescence techniques have great potential in elucidating the physiological mechanism of cadmium stress in lettuce, as well as in achieving synchronized determination and correlation analyses of chlorophyll content and photosynthetic function.

Comparative modeling of fluorescence and P700 induction kinetics for alga Scenedesmus sp. obliques and cyanobacterium Synechocystis sp. PCC 6803. Role of state 2–state 1 transitions and redox state of plastoquinone pool

Comparative modeling of fluorescence and P700 induction kinetics for alga Scenedesmus sp. obliques and cyanobacterium Synechocystis sp. PCC 6803. Role of state 2–state 1 transitions and redox state of plastoquinone pool

Enhanced photochemical efficiency of PSII in Prosopis juliflora suggests contribution to invasion advantage over native C3 xero-halophytes under salt stress.

Chlorophyll a fluorescence parameters related to PSII photochemistry, photoprotection and photoinhibition were investigated in four C3 plant species growing in their natural habitat: Prosopis juliflora ; Abutilon indicum ; Salvadora persica ; and Phragmites karka . This study compared the light reaction responses of P. juliflora , an invasive species, with three native co-existing species, which adapt to varying water deficit and high salt stress. Chlorophyll a fluorescence quenching analyses revealed that P. juliflora had the highest photochemical quantum efficiency and yield, regulated by higher fraction of open reaction centres and reduced photoprotective energy dissipation without compromising the integrity of photosynthetic apparatus due to photoinhibition. Moreover, the elevated values of parameters obtained through polyphasic chlorophyll a fluorescence induction kinetics, which characterise the photochemistry of PSII and electron transport, highlighted the superior performance index of energy conservation in the transition from excitation to the reduction of intersystem electron carriers for P. juliflora compared to other species. Enhanced pigment contents and their stoichiometry in P. juliflora apparently contributed to upregulating fluxes and yields of energy absorbance, trapping and transport. This enhanced photochemistry, along with reduced non-photochemical processes, could explain the proclivity for invasion advantage in P. juliflora across diverse stress conditions.

Exogenous Melatonin Alleviates the Inhibitory Effect of NaHCO3 on Tomato Growth by Regulating the Root pH Value and Promoting Plant Photosynthesis

Soil salinity is a severe threat to agricultural production. Most saline soils turn alkaline, increasing the soil pH and, in turn, hampering the growth and development of crops. In this study, the effects of a foliar spray of melatonin (MT; 100 μmol·L−1) on the pH of the root environment, growth of tomato seedlings, endogenous MT levels, rapid chlorophyll fluorescence induction kinetics, and key enzymes of the Calvin cycle under alkaline (60 mmol·L−1 NaHCO3) stress were studied in Riegel 87-5 tomatoes. The results revealed that the growth and photosynthesis of tomato seedlings were inhibited by increased pH in the root environment under alkali stress; however, the application of exogenous MT reduced the pH of the root environment, alleviated the inhibition of growth of tomato seedlings under alkali stress, increased the content of photosynthetic pigments, alleviated the damage of the donor and acceptor sides of the photosynthetic electron transport chain, increased the activity and efficiency of photosynthetic electron transport, and optimized the share of the light energy allocated to PSII reaction centers. Increased expression levels of Calvin-cycle enzymes, including fructose-1,6-bisphosphate aldolase (FBA), fructose-1,6-bisphosphate esterase (FBP), and phosphoglycerate kinase (PGK), led to enhanced photosynthetic performance in tomato seedlings. Exogenous MT boosted endogenous MT levels and stimulated the production and secretion of organic acids in the root system. This regulation of organic acid content reduced the environmental pH in the inter-root zone, alleviating the damage caused by alkali stress. This study indicated that the exogenous administration of MT may mediate an increase in endogenous MT levels, regulate the efficiency of photosynthesis and root pH levels, and play a crucial role in mitigating injury caused by alkali stress in tomato seedlings.

Effects of Elevated CO2 Concentration and Temperature on the Growth and Photosynthetic Characteristics of Populus simonii × P. nigra ‘1307’ Leaves

This study aimed to establish the effects of elevated CO2 concentration and temperature on the photosystem II (PSII) performance and photosynthetic characteristics of Populus simonii × P. nigra ‘1307’ leaves. Different CO2 concentrations (400 and 800 µmol·mol−1) and temperatures (room temperature and room temperature +2 °C) were set in artificial climate change simulation and control chambers, and the rapid chlorophyll fluorescence induction kinetics curve (OJIP curve) of Populus simonii × P. nigra ‘1307’ was determined. The generated OJIP curve was used to analyze the change characteristics in photosynthetic performance. The results revealed that under elevated temperature conditions, the concentrations of chlorophyll a, b in Populus simonii × P. nigra ‘1307’ leaves were significantly increased. At the same time, there were no significant changes in the chlorophyll concentration under the superimposed effect of elevated CO2 concentration and temperature. The PSII comprehensive performance index (PIABS) of Populus simonii × P. nigra ‘1307’ was significantly inhibited under elevated temperatures due to the increased closure degree (Vj) of the PSII reaction center and the damage of the receptor side. This reduced the electron transfer capacity per unit reaction center (ETo/RC) and unit cross-sectional area, which decreased the quantum yield of the electron transfer. Under the elevated CO2 concentration, ETo/RC was also inhibited. Still, PIABS was enhanced owing to the increased number of active PSII per unit area and the low reduction rate of the primary quinone receptor (QA). Under the superimposed effect of the two factors, the electron transfer performance of the donor and receptor sides of PSII was improved compared to the treatments only subjected to elevated temperature; thus, PIABS was not significantly reduced compared to the control. Therefore, the continuous increase in temperature by 2 °C significantly inhibits the electron transfer capacity of the photosynthetic system of Populus simonii × P. nigra ‘1307’ leaves. On the other hand, an increase in CO2 concentration expands the PSII reaction center, while enhancing the electron transfer capacity of the donor and receptor sides, which alleviates the photosynthetic inhibition caused by the elevated temperature.

Photosynthetic response mechanism to polybrominated diphenyl ether exposure in Chlorella pyrenoidosa

Polybrominated diphenyl ether (PBDE) contamination is common in aquatic environments and can severely damage aquatic organisms. However, there is a lack of information on the response and self-adaptation mechanisms of these organisms. Chlorella pyrenoidosa was treated with 2,2′,4,4′-tetrabromodiphenyl ether (BDE47), causing significant growth inhibition, pigment reduction, oxidative stress, and chloroplast atrophy. Photosynthetic damage contributed to inhibition, as indicated by Fv/Fm, Chl a fluorescence induction, photosynthetic oxygen evolution activity, and photosystem subunit stoichiometry. Here, Chl a fluorescence induction and quinone electron acceptor (QA−) reoxidation kinetics showed that the PSII donor and acceptor sides were insensitive to BDE47. Quantitative analyses of D1 and PsaD proteins illustrated that PSII and PSI complexes were the main primary targets of photosynthesis inhibition by BDE47. Significant modulation of PSII complex might have been caused by the potential binding of BDE47 on D1 protein, and molecular docking was performed to investigate this. Increased activation of antioxidant defense systems and photosystem repair as a function of exposure time indicated a positive resistance to BDE47. After a 5-day exposure, 23 % of BDE47 was metabolized. Our findings suggest that C. pyrenoidosa has potential as a bioremediator for wastewater-borne PBDEs and can improve our understanding of ecological risks to microalgae.

A Sensitive Response Index Selection for Rapid Assessment of Heavy Metals Toxicity to the Photosynthesis of Chlorella pyrenoidosa Based on Rapid Chlorophyll Fluorescence Induction Kinetics.

Heavy metals as toxic pollutants have important impacts on the photosynthesis of microalgae, thus seriously threatening the normal material circulation and energy flow of the aquatic ecosystem. In order to rapidly and sensitively detect the toxicity of heavy metals to microalgal photosynthesis, in this study, the effects of four typical toxic heavy metals, chromium (Cr(VI)), cadmium (Cd), mercury (Hg), and copper (Cu), on nine photosynthetic fluorescence parameters (φPo, ΨEo, φEo, δRo, ΨRo, φRo, FV/FO, PIABS, and Sm) derived from the chlorophyll fluorescence rise kinetics (OJIP) curve of microalga Chlorella pyrenoidosa, were investigated based on the chlorophyll fluorescence induction kinetics technique. By analyzing the change trends of each parameter with the concentrations of the four heavy metals, we found that compared with other parameters, φPo (maximum photochemical quantum yield of photosystem II), FV/FO (photochemical parameter of photosystem II), PIABS (photosynthetic performance index), and Sm (normalized area of the OJIP curve) demonstrated the same monotonic change characteristics with an increase in concentration of each heavy metal, indicating that these four parameters could be used as response indexes to quantitatively detect the toxicity of heavy metals. By further comparing the response performances of φPo, FV/FO, PIABS, and Sm to Cr(VI), Cd, Hg, and Cu, the results indicated that whether it was analyzed from the lowest observed effect concentration (LOEC), the influence degree by equal concentration of heavy metal, the 10% effective concentration (EC10), or the median effective concentration (EC50), the response sensitivities of PIABS to each heavy metal were all significantly superior to those of φRo, FV/FO, and Sm. Thus, PIABS was the most suitable response index for sensitive detection of heavy metals toxicity. Using PIABS as a response index to compare the toxicity of Cr(VI), Cd, Hg, and Cu to C. pyrenoidosa photosynthesis within 4 h by EC50 values, the results indicated that Hg was the most toxic, while Cr(VI) toxicity was the lowest. This study provides a sensitive response index for rapidly detecting the toxicity of heavy metals to microalgae based on the chlorophyll fluorescence induction kinetics technique.

Study on Heat Resistance of Peony Using Photosynthetic Indexes and Rapid Fluorescence Kinetics

To investigate the effects of high-temperature stress on the chlorophyll fluorescence induction kinetics of peony and to determine indicators for the rapid screening of varieties responding to high temperatures, three four-year-old peony variety, ‘Fengdanbai’, ‘Huhong’, and ‘Yinhongqiaodui’, were selected as materials. The photosynthetic curves (Pn-PAR) and fast chlorophyll fluorescence curves (OJIP curves) of peony leaves were measured at different times under high-temperature stress conditions (40 °C), the changes in the photosynthetic characteristics of different peony varieties under high-temperature stress were analyzed, and the heat tolerance of peony was evaluated. The results showed that ‘Huhong’ grew well within 16 days, while all of the other varieties showed obvious wilting at 6–9 days. High temperatures damaged the structure and function of the photosystem of peony leaves, indicating that the maximum net photosynthetic rate (Pnmax), apparent quantum efficiency (AQE), maximum photochemical efficiency (Fv/Fm), and photosynthetic performance index (PIABS) all tended to decrease under high-temperature stress, while the rate of closing the PS II reaction center (Mo) and the absorption per reaction center (ABS/RC), the capture (TRo/RC), and the dissipation (Dio/RC) of light energy per reaction center showed an overall increasing trend. The ability to cope with high-temperature stress differed among varieties, and the heat tolerance was determined to be in the descending order of ‘Fengdanbai’ < ‘Yinhongqiaodui’ < ‘Huhong’. The correlation analysis among the parameters and the analysis of the morphological change patterns in peony leaves concluded that PIABS, Dio/RC, and Mo could be used as indicators of peony tolerance to high-temperature stress. The results of the study can provide a basis for the screening of heat-tolerant peony species and peony heat defense in the Jiangnan area.

亚热带森林演替阶段下不同光环境对芒萁光合生理的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 亚热带森林演替阶段下不同光环境对芒萁光合生理的影响 DOI: 10.5846/stxb202112273661 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31971623）；浙江省"尖兵""领雁"研发攻关计划项目（2022C02019） Effects of different light environments on photosynthetic physiology of Dicranopteris dichotoma under successional stages in subtropical forests Author: Affiliation: Fund Project: The National Natural Science Foundation of China (31971623)； 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:光环境的变化是群落演替进程中植物进入和退出群落的重要因素。为研究亚热带森林次生演替不同阶段的光照对芒萁光合生理的影响，对灌草丛、马尾松林和常绿阔叶林这3种群落内盆栽芒萁的光响应过程和叶绿素荧光诱导动力学参数进行了研究。结果表明：芒萁在光强为400 μmol m-2 s-1左右且日变化幅度较小的马尾松林下净光合速率（Pn）最高，在光强50 μmol m-2 s-1左右的常绿阔叶林下次之，在400-1800 μmol m-2 s-1左右波动的灌草丛内最低。这是因为灌草丛内芒萁J点相对可变荧光（Vj）、K点标准化后的相对可变荧光（Wk）显著升高，以吸收光能为基础的光系统Ⅱ性能指数（PSⅡ）（PIABS）显著降低，而热耗散参数（φDo）基本不变，即强光破坏了芒萁光合机构PSⅡ的供体侧和受体侧，使其产生了光抑制。常绿阔叶林内芒萁叶绿素荧光诱导动力学参数与马尾松林下差异不明显，且最大净光合速率（Pmax）下降是光强变弱导致的，但是暗呼吸速率（Rd）、光补偿点（LCP）和光饱和点（LSP）均随之降低，可见芒萁光合机构对该光强有一定的适应性。由此可知，芒萁喜光但不耐强光，对弱光具有一定耐受性。 Abstract:The light changes of forest succession play important roles in the presence or absence of plant species in communities. To reveal the effects of light on photosynthetic physiology of Dicranopteris dichotoma at different stages of secondary succession in subtropical forests, light response process and chlorophyll fluorescence induction kinetic parameters of D. dichotoma growing in three different communities (scrub, Pinus massoniana forest, and evergreen broadleaf forest) were investigated in this experiment. The results showed that the net photosynthetic rate (Pn) was the highest in the P. massoniana forest with a light intensity of about 400 μmol m-2 s-1 and a small daily variation, followed by the evergreen broadleaf forest with a light intensity of about 50 μmol m-2 s-1, and the lowest in the scrub with a fluctuation of about 400-1800 μmol m-2 s-1. The lowest Pn in the scrub was because high light disrupted donor and acceptor sides of photosystem II (PSII) of D. dichotoma, and resulted in photoinhibition of D. dichotoma, which were proved by significantly increased relative variable fluorescence (Vj) at point J, normalized relative variable fluorescence (Wk) at point K, and significantly decreased PSII performance index (PIABS), and unchanged heat dissipation parameter (φDo). No significant differences in chlorophyll fluorescence induction kinetics between the D. dichotoma growing in evergreen broad-leaved forest and P. massoniana forest indicated that its PSII was not damaged, and the decrease of the maximum net photosynthetic rate (Pmax) was caused by the low light. At the same time, the reduced dark respiration rate (Rd), light compensation point (LCP), and light saturation point (LSP) showed that D. dichotoma photosynthetic system could adapt to the low light in the evergreen broad-leaved forest. This study showed that D. dichotoma was a light-loving but not light-tolerant species, with the modest low-light tolerance. 参考文献 相似文献 引证文献

Sunflower Leaf Structure Affects Chlorophyll a Fluorescence Induction Kinetics In Vivo

Chlorophyll a fluorescence induction kinetics (CFI) is an important tool that reflects the photosynthetic function of leaves, but it remains unclear whether it is affected by leaf structure. Therefore, in this study, the leaf structure and CFI curves of sunflower and sorghum seedlings were analyzed. Results revealed that there was a significant difference between the structures of palisade and spongy tissues in sunflower leaves. Their CFI curves, measured on both the adaxial and abaxial sides, also differed significantly. However, the differences in the leaf structures and CFI curves between both sides of sorghum leaves were not significant. Further analysis revealed that the differences in the CFI curves between the adaxial and abaxial sides of sunflower leaves almost disappeared due to reduced incident light scattering and refraction in the leaf tissues; more importantly, changes in the CFI curves of the abaxial side were greater than the adaxial side. Compared to leaves grown under full sunlight, weak light led to decreased differences in the CFI curves between the adaxial and abaxial sides of sunflower leaves; of these, changes in the CFI curves and palisade tissue structure on the adaxial side were more obvious than on the abaxial side. Therefore, it appears that large differences in sunflower leaf structures may affect the shape of CFI curves. These findings lay a foundation for enhancing our understanding of CFI from a new perspective.

Exogenous trehalose protects photosystem II in heat-stressed wheat

Background: Photosystem II (PSII) is susceptible to heat stress. Plants naturally accumulate trehalose to improve stress tolerance. However, the mechanism by which trehalose affects PSII during heat stress is still unknown.
 Questions: How does trehalose affect PSII during heat stress?
 Studied species: Triticum aestivum L.
 Study site and dates: Shanghai, China. 2019-2021.
 Methods: Trehalose -pretreated wheat seedlings suffered from heat stress and their photosynthetic parameters were measured.
 Results: Heat stress caused a reduction in the photochemical efficiency of PSII, the electron transfer rate (ETR(II)), the quantum yield of regulated energy dissipationY(NPQ) and the coefficient of photochemical quenching (qP), but increased the quantum yield of non-regulated energy dissipation of PSII (Y[NO]). The shape of the fast chlorophyll fluorescence induction kinetics (OJIP) curve in the heat-stressed wheat was altered and the primary photochemistry maximum yield of PSII (Fv/Fo) and the PSII performance indicator PIabs were reduced. Accordingly, the activities of PSII and electron transport chain, the amount of ordered α-helix structures and the content of D1 protein also decreased. However, in trehalose-pretreated wheat, D1 protein and protein secondary structures of PSII were both protected, the electron transport activities of PSII and the whole chain were improved and greater fluorescence parameters values were maintained. Lower Y(NO) and more stable OJIP were obtained.
 Conclusions: Exogenous trehalose acted a vital role in the protection of the function of PSII, resulting in higherphotosynthetic capacity under heat stress.

Toxic effects of Rhodamine B on antioxidant system and photosynthesis of Hydrilla verticillata

Rhodamine B is a synthetic dye released in huge quantities as hazardous colored effluents into aquatic ecosystems. It negatively affects the metabolic and physiological processes in aquatic plants. The goal of current study was to assess the impact of various Rhodamine B concentrations (5, 10, 15, 20, and 25 mg/L) on antioxidant and photosynthetic performance of Hydrilla verticillata exposed for 24, 48, and 72 h. Results of present study clearly demonstrate that Rhodamine B inhibits the activity of the superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPOD) in H. verticillata. Activities of SOD, CAT, and GPOD were constantly raised at lower concentrations and then decreased with increasing concentration and exposure duration of Rhodamine B. In vivo chlorophyll fluorescence experiments were used to examine its inhibitory effects on H. verticillata photosystem II (PSII). The OJIP fluorescence induction kinetics were altered by increasing the Rhodamine B concentration and treatment time as a result increasing the parameters Fo/Fm and φDo while decreasing Fm, φPo, Ψo, φEo, RC/CSm, ABS/CSm, TR/CSm, ET/CSm and, PIabs. When exposed to Rhodamine B, electron transport is slowed down on both the acceptor and donor sides and overall decreases the photosynthetic performance of H. verticillata.

Detection of antibiotic and microplastic pollutants in Chrysanthemum coronarium L. based on chlorophyll fluorescence

Large amounts of antibiotics and microplastics are used in daily life and agricultural production, which affects not only plant growth but also potentially the food safety of vegetables and other plant products. Fast detection of the presence of antibiotics and microplastics in leafy vegetables is of great interest to the public. In this work, a method was developed to detect sulfadiazine and polystyrene, commonly used antibiotics and microplastics, in vegetables by measuring and modeling photosystem II chlorophyll a fluorescence (ChlF) emission from leaves. Chrysanthemum coronarium L., a common beverage and medicinal plant, was used to verify the developed method. Scanning electron microscopy, transmission electron microscopy, and liquid chromatograph-mass spectrometer analysis were used to show the presence of the two pollutants in the samples. The developed kinetic model could describe measured ChlF variations with an average relative error of 0.6%. The model parameters estimated for the chlorophyll a fluorescence induction kinetics curve (OJIP) induction can differentiate the two types of stresses while the commonly used ChlF OJIP induction characteristics cannot. This work provides a concept to detect antibiotic pollutants and microplastic pollutants in vegetables based on ChlF.

Prolonged Use of Insecticide Dimethoate Inhibits Growth and Photosynthetic Activity of Wheat Seedlings: A Study by Laser-Induced Chlorophyll Fluorescence Spectroscopy.

This paper is an extension of the work published in Journal of Fluorescence (2011) 21: 785-791. In the previous work, we studied the effect of dimethoate (50, 100 and 200ppm) on growth and photosynthetic activity of wheat seedlings after 10days of dimethoate treatment. In the present study, new measurement conditions (dimethoate concentration: 25ppm, treatment period: 20days and 30days) were used in addition to those used in the past work. Various plant growth parameters, photosynthetic pigment content, laser-induced chlorophyll fluorescence (LICF) spectra and fluorescence induction kinetics (FIK) curves were recorded after 10, 20 and 30days of dimethoate treatments. LICF spectra were recorded in the region of 650-780nm using violet diode laser (405nm). FIK curves were recorded at 685nm using red diode laser (635nm). Fluorescence intensity ratio (FIR) of two fluorescence peaks around 685 and 730nm, and variable chlorophyll fluorescence decrease ratio (Rfd) were determined from LICF spectra and FIK curves respectively. Curve-fitted parameters of LICF spectra were used for determination of FIR (F685/F730). The effect of treatment of the insecticide dimethoate on growth and photosynthetic activity of wheat seedlings was examined by using these parametersas well as the past work. In 10-days treatment, 25 and 50ppm dimethoate showed stimulatory effect with better stimulation being observed at 25ppm. All studied concentrations higher than 50ppm exhibited inhibitory effect on wheat seedlings. In case of dimethoate treatment studied for longer durations (more than 10days), all concentrations showed inhibitory effect. Lower doses which showed some positive response for short time duration become toxic with the extension of treatment periods. Thus, this study clearly confirms the toxic effect of dimethoate on wheat plants.

Effects of exposure of the leaf abaxial surface to direct solar radiation on the leaf anatomical traits and photosynthesis of soybean (Glycine max L.) in dryland farming systems

The frequent occurrence of monsoon winds usually leads to the formation of inverted soybean leaves. However, the effect of leaf inversion on photosynthetic capacity remains unclear. The responses of leaf anatomical traits, chlorophyll fluorescence induction kinetics parameters, photosynthetic capacity, and nonstructural carbohydrates of fully expanded leaves to inversion of leaves in two soybean cultivars were studied. Leaf inversion decreased the stomatal size and thickness of developed leaves. The net photosynthetic rate was significantly reduced under leaf inversion, which resulted from reduced excitation energy trapping and electron transport of PSII reaction center. Leaf inversion increased leaf temperature 10 d after leaf inversion but reduced the instantaneous water-use efficiency compared to normally oriented leaves. Due to the decreased light-saturated net photosynthetic rate, the soluble sugars of light-sensitive cultivar decreased significantly. In summary, leaf inversion deactivated the PSⅡ reaction centers, reduced photosynthesis and nonstructural carbohydrates in upper canopy soybean leaves.

Respiration Interacts With Photosynthesis Through the Acceptor Side of Photosystem I, Reflected in the Dark-to-Light Induction Kinetics of Chlorophyll Fluorescence in the Cyanobacterium Synechocystis sp. PCC 6803.

In cyanobacteria, the photosynthetic prokaryotes, direct interaction between photosynthesis and respiration exists at plastoquinone (PQ) pool, which is shared by the two electron transport chains. Another possible point of intersection of the two electron transport chains is NADPH, which is the major electron donor to the respiratory chain as well as the final product of the photosynthetic chain. Here, we showed that the redox state of NADPH in the dark affected chlorophyll fluorescence induction in the cyanobacterium Synechocystis sp. PCC 6803 in a quantitative manner. Accumulation of the reduced NADPH in the dark due to the defect in type 1 NAD(P)H dehydrogenase complex in the respiratory chain resulted in the faster rise to the peak in the dark-to-light induction of chlorophyll fluorescence, while depletion of NADPH due to the defect in pentose phosphate pathway resulted in the delayed appearance of the initial peak in the induction kinetics. There was a strong correlation between the dark level of NADPH determined by its fluorescence and the peak position of the induction kinetics of chlorophyll fluorescence. These results indicate that photosynthesis interacts with respiration through NADPH, which enable us to monitor the redox condition of the acceptor side of photosystem I by simple measurements of chlorophyll fluorescence induction in cyanobacteria.

H2O2 signaling regulates seed germination in ZnO nanoprimed wheat (Triticum aestivum L.) seeds for improving plant performance under drought stress

Nanopriming has proved to be an effective technique to protect plants from various stresses. The aim of the present work is to investigate the underlying mechanism of zinc oxide (ZnO) nanopriming in imparting drought stress tolerance in wheat. The changes in primed and unprimed wheat plants associated during drought stress were studied by monitoring their physiological and biochemical performance. Results showed that zinc oxide nanoparticles (ZnO NPs) pre-treatment prevented chlorophyll degradation under drought condition thereby improving overall photosynthetic performance and overall plant growth. Study of Chl a fluorescence induction kinetics showed a drastic increase in various photosynthetic parameters in primed drought stressed plants. Nanopriming seems to have protected the photosynthetic apparatus of plant by improving the efficiency of primary photochemistry of PSII under drought stress conditions. Furthermore, the activity of antioxidant enzymes such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) as well as malondialdehyde (MDA) content were decreased significantly in nanoprimed drought stressed (NP + DS) plants as compared to unprimed drought stressed (UP + DS) plants. Generation of more reactive oxygen species (ROS) mainly hydrogen peroxide (H2O2) was observed in nanoprimed germinating seeds. We propose role of H2O2 to act as signaling molecule in improving seed germination and vigor by enhancing activity of α-amylase. Lower levels of reactive oxygen species (ROS) production in NP + DS plants was observed which indicates better tolerance to drought stress in nanoprimed plants. It is concluded that nanopriming facilitates improved seed germination and increased seedling vigor through H2O2 signaling networks.

Photosynthetic monitoring techniques indicate maximum glycogen accumulation in nitrogen-limited Synechocystis sp. PCC 6803 culture

Chlorophyll fluorescence and oxygen evolution are rapid and non-invasive monitoring techniques to obtain information about the photosynthesis performance of microalgae cultures. These methods may be employed for optimizing the biomass productivity as well as indicate increased production of some valuable compounds.In this work photosynthesis monitoring techniques – saturation pulse analysis of fluorescence quenching, fast fluorescence induction kinetics and photosynthetic oxygen production/respiration – were employed for monitoring of the physiological state of the nitrogen-limited culture of Synechocystis sp. PCC 6803. The correlation between changes of photosynthetic activities, growth and glycogen accumulation was examined in these cultures. The aim was to determine proper point for biomass harvest comparing the changes of photosynthetic activities and the kinetics of glycogen accumulation. In a 4-day trial the highest glycogen accumulation in biomass was found on day 2 showing an inflection point which was accompanied by the reversal of the chlorophyll fluorescence variables, namely maximal photochemical efficiency of PSII Fv/Fm, relative electron transport rate rETR, photochemical efficiency α and photosynthesis saturating irradiance Ik. The rapid increase of cell respiration after day 2 also indicated the relation of these changes with onset of glycogen catabolism.Our laboratory experiments revealed that the three photosynthetic monitoring techniques provided good indication of the physiological changes leading to high glycogen accumulation in biomass of the nitrogen-limited Synechocystis culture. In this way the glycogen accumulation can be manipulated. The photosynthesis measurements can indicate the right time to harvest the culture rich in glycogen in biotechnological applications.

Ameliorating Effect of Bicarbonate on Salinity Induced Changes in the Growth, Nutrient Status, Cell Constituents and Photosynthetic Attributes of Microalga Chlorella vulgaris

The cells of Chlorella vulgaris exhibited NaCl (0-400mM) induced decrease in the growth, protein, chlorophyll, carbohydrate and total organic carbon, whereas total lipid and proline content increased with rising level of NaCl. Addition of NaHCO3 (20mM) exhibited antagonistic effect against the adverse effect of salinity on the growth, level of macromolecules except proline. The SEM-EDS analysis of NaCl treated cells exhibited morphological variations as well as reduced accumulation of Na and Cl due to the presence of NaHCO3. The results on chlorophyll fluorescence induction kinetics revealed NaCl induced decline in the photosynthetic performance and quantum yield, while non-photochemical quenching of chlorophyll was enhanced, particularly at lower concentrations of NaCl. Addition of NaHCO3 to NaCl treated cells exhibited further increase in the non-photochemical quenching values. Thus, these results demonstrated that adverse impact of NaCl on the C. vulgaris cells was significantly mitigated in the presence of bicarbonate.