Relative Variable Fluorescence Research Articles

Impact of ZnO NPs on photosynthesis in rice leaves plants grown in saline-sodic soil

Saline-sodic stress restricts the absorption of zinc by rice, consequently impacting the photosynthesis process of rice plants. In this experiment, Landrace 9 was selected as the test material and the potting method was employed to investigate the influence of ZnO nanoparticles (ZnO NPs) on zinc absorption and chlorophyll fluorescence in rice grown in saline-sodic land. The research findings demonstrate that the application of ZnO NPs proves to be more advantageous for the growth of rice in saline-sodic soil. Notably, the application of ZnO NPs significantly decreases the levels of Na+ and MDA in rice leaves in saline-sodic soil, while increasing the levels of K+ and Zn2+. Additionally, ZnO NPs enhances the content of chloroplast pigments, specific energy flux, quantum yield, and the performance of active PSII reaction center (PIABS) in rice leaves under saline-sodic stress. Furthermore, the relative variable fluorescence (WK and VJ) and quantum energy dissipation rate (φDo) of rice are also reduced. Therefore, the addition of ZnO NPs enhances the transfer of electrons and energy within the rice photosystem when subjected to saline-sodic stress. This promotes photosynthesis in rice plants growing in saline-sodic land, increasing their resistance to saline-sodic stress and ultimately facilitating their growth and development.

Zinc regulation of chlorophyll fluorescence and carbohydrate metabolism in saline-sodic stressed rice seedlings.

Saline-sodic stress can limit the absorption of available zinc in rice, subsequently impacting the normal photosynthesis and carbohydrate metabolism of rice plants. To investigate the impact of exogenous zinc application on photosynthesis and carbohydrate metabolism in rice grown in saline-sodic soil, this study simulated saline-sodic stress conditions using two rice varieties, 'Changbai 9' and 'Tonghe 899', as experimental materials. Rice seedlings at 4weeks of age underwent various treatments including control (CT), 2μmol·L-1 zinc treatment alone (Z), 50mmol·L-1 saline-sodic treatment (S), and 50mmol·L-1 saline-sodic treatment with 2μmol·L-1 zinc (Z + S). We utilized JIP-test to analyze the variations in excitation fluorescence and MR820 signal in rice leaves resulting from zinc supplementation under saline-sodic stress, and examined the impact of zinc supplementation on carbohydrate metabolism in both rice leaves and roots under saline-sodic stress. Research shows that zinc increased the chloroplast pigment content, specific energy flow, quantum yield, and performance of active PSII reaction centers (PIABS), as well as the oxidation (VOX) and reduction rate (Vred) of PSI in rice leaves under saline-sodic stress. Additionally, it decreased the relative variable fluorescence (WK and VJ) and quantum energy dissipation yield (φDO) of the rice. Meanwhile, zinc application can reduce the content of soluble sugars and starch in rice leaves and increasing the starch content in the roots. Therefore, the addition of zinc promotes electron and energy transfer in the rice photosystem under saline-sodic stress. It enhances rice carbohydrate metabolism, improving the rice plants' ability to withstand saline-sodic stress and ultimately promoting rice growth and development.

Rice (Oryza sativa L.) exhibits differential responses to salt stress and salt shock in electron transfer efficiency

The study of crop response to soil salinity has traditionally focused on the effects of varying salt concentrations, with less attention given to the methodologies of salt application. This research aimed to elucidate the differential impacts of two distinct salinity exposure methods on the photosynthetic characteristics of rice. Plants subjected to a gradual increase in salinity experience salt stress, whereas those immediately exposed to high salinity levels encounter a salt shock condition. Our findings revealed that rice plants accumulated comparable levels of shoot Na+ under both salt stress and salt shock at 4 and 10 days after the onset of stress. No significant differences were observed in the steady-state photosynthetic rate and electron transport rate (ETR). In contrast, salt stress markedly reduced the relative variable fluorescence at the ‘J’ step (Vj), thereby enhancing the probability of an exciton transferring an electron beyond the primary quinone electron acceptor (QA−) (ΨEo). This led to a notable increase in the activity of leaf photosystem II (PSII), as evidenced by the Performance Index on absorption basis (PIabs), which was twice as high as that of the control group. This mechanism is believed to facilitate the activation of alternative metabolic pathways. Additionally, kinetic measurements of light potential indicated that salt stress improved the initial induction of ETR after a brief exposure to high photosynthetically active radiation (PAR) compared to the control. This effect was not observed in the salt shock treatment group. Our results suggest that plants exhibit distinct physiological responses to salt stress versus salt shock, and the potential positive influence on leaf photosynthetic activity during salt stress may have been previously underestimated.

Exposição de três espécies de Cattleya (Orchidaceae) a pleno sol: efeito sobre sua plasticidade fisiológica e resposta a mudanças nas condições de luz

Abstract In order to establish a link between the evolutionary history and the photochemical attributes, measurements of chlorophyll (Chl) a fluorescence were made in Cattleya warneri, C. shofieldiana and C. harrisoniana exposed to high irradiance for 5, 35, and 120 min (hereafter referred to as treatments T5, T35, and T120, respectively). The following questions are addressed: (1) Is the increased energy dissipation enough to counterbalance the excess energy that drives photosynthesis at different times of high irradiance exposure? (2) Is there an influence of the incidence and duration of light radiation on Cattleya species in full sunlight, compared to Cattleya species submitted to low irradiance? Higher relative variable fluorescence at the J-step (Vj) values followed by the lower quantum yield of electron transport (ψEo) indicate the accumulation of reduced Quinone A (QA) proportionally of sunflecks exposure time in C. warneri. The higher performance index (PIABS) and plasticity index values in C. schofieldiana indicate higher efficiency in modulating the photosynthetic apparatus under sunflecks. C. harrisoniana shows the lowest plasticity index, suppression of maximum fluorescence (Fm), and no recovery of PIABS after sunflecks. This study evidences the importance of physiological plasticity in the current geographic distribution of Cattleya in response to light pulses in species derived from fragmented habitats and the maintenance of shade to species of more primitive clades.

Early Diagnosis of Pine Wilt Disease in Pinus thunbergii Based on Chlorophyll Fluorescence Parameters

As the most severe forestry quarantine disease in several countries, pine wilt disease (PWD) causes substantial economic losses and poses a significant threat to the forest ecosystem. It is necessary to find a rapid and sensitive method for the early diagnosis of the disease to control the development of the disease effectively. This paper investigated the effect of Bursaphelenchus xylophilus (the pinewood nematode; PWN) on the chlorophyll fluorescence kinetic curve (OJIP curve) and the parameters of needles using four-year-old Pinus thunbergii as experimental materials and chlorophyll fluorescence analysis as a technical tool. It was shown by the results in the OJIP curve that the fluorescence intensity of the inoculated plants was significantly increased at points O and I. Additionally, the relative variable fluorescence intensity at points K and J was comparable to that of the control plants. Several chlorophyll fluorescence parameters of the treatment significantly increased or decreased with disease progression. At the same time, the control group had no significant changes in each parameter. Therefore, chlorophyll fluorescence parameters can be used as indicators for the early diagnosis of PWD, among which the DIo/RC parameter was the best. In summary, PWN invasion will produce fluorescence on the PSII of P. thunbergii, and its chlorophyll fluorescence parameters are expected to achieve early PWD diagnosis.

Responses of photosystem to long-term light stress in a typically shade-tolerant species Panax notoginseng.

Photosynthetic adaptive strategies vary with the growth irradiance. The potential photosynthetic adaptive strategies of shade-tolerant species Panax notoginseng (Burkill) F. H. Chen to long-term high light and low light remains unclear. Photosynthetic performance, photosynthesis-related pigments, leaves anatomical characteristics and antioxidant enzyme activities were comparatively determined in P. notoginseng grown under different light regimes. The thickness of the upper epidermis, palisade tissue, and lower epidermis were declined with increasing growth irradiance. Low-light-grown leaves were declined in transpiration rate (Tr) and stomatal conductance (Cond), but intercellular CO2 concentration (C i) and net photosynthesis rate (P n) had opposite trends. The maximum photo-oxidation (P m) was greatly reduced in 29.8% full sunlight (FL) plants; The maximum quantum yield of photosystem II (F v/F m) in 0.2% FL plants was significantly lowest. Electron transport, thermal dissipation, and the effective quantum yield of PSI [Y(I)] and PSII [Y(II)] were declined in low-light-grown plants compared with high-light-grown P. notoginseng. The minimum value of non-regulated energy dissipation of PSII [Y(NO)] was recorded in 0.2% FL P. notoginseng. OJIP kinetic curve showed that relative variable fluorescence at J-phase (V J) and the ratio of variable fluorescent F K occupying the F J-F O amplitude (W k) were significantly increased in 0.2% FL plants. However, the increase in W k was lower than the increase in V J. In conclusion, PSI photoinhibition is the underlying sensitivity of the typically shade-tolerant species P. notoginseng to high light, and the photodamage to PSII acceptor side might cause the typically shade-tolerant plants to be unsuitable for long-term low light stress.

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

The Effects of the Tree Structure of Zaosu Pear on the Transport and Distribution of Photosynthetic Assimilates and Fruit Quality under Desert-Area Conditions

Pear is an important fruit tree in China, and the Hexi area is the main pear-planting area in Gansu Province. Tree shapes have different effects on photosynthesis that influence fruit quality and development. Thus, in the current study, five tree shapes of Zaosu pear, including the Y-shaped, trunk, single-arm, double-arm, and spindle tree shapes, were selected, and their effects on photosynthesis and fruit quality were investigated. The thickness and length of shoot branches were highest in the single-, double-arm, and spindle tree shapes. The level of photosynthetically active radiation (PAR) varied by tree shape; from highest to lowest, the order was double-arm > single-arm > spindle > Y-shaped > trunk tree shapes. Leaf area and chlorophyll content were highest in the single- and double-arm tree shapes, with higher increases in the net photosynthetic rate to light intensity (Pn-PAR), the net photosynthetic rate to CO2 (Pn-CO2), the relative variable fluorescence (Vj), PSII maximum photochemical efficiency (Fv/Fm), and the light energy absorbed per unit reaction centre (ABS/RC). For fruit quality, the fruit shape index, fruit colour parameters, and content of soluble solids increased significantly in the single- and double-arm tree shapes, while the content of total acids, malic acid, and citric acid in the single- and double-arm tree shapes was lower than in the other tree shapes. All these results demonstrated that the single- and double-arm tree shapes are well ventilated and light-transmitting, which can promote fruit growth and quality.

Effect of different concentrations of foliar iron fertilizer on chlorophyll fluorescence characteristics of iron-deficient rice seedlings under saline sodic conditions

The effectiveness of iron is reduced in saline conditions, which can easily lead to iron deficiency and inhibit photosynthesis in rice. In this study, 4-week-old Fe-deficient rice seedlings were treated under saline sodic stress (50 mM) to different concentrations (0, 0.2%, 0.4%, 0.8%, 1.6%, and 3.2%) of foliar iron fertilizer (FeEDDHA). Differences in prompting fluorescence and the MR820 signal of rice leaves after 7 days of treatment were probed using the JIP-test. The results show that the performances of the two rice varieties were in general agreement. Under iron deficiency and soda salinity stress conditions, rice growth was inhibited, and the pigment content, specific energy flux, quantum yield, performance of the active PSII reaction center (PIABS) and the oxidation (Vox) and reduction rates (Vred) of PSI were reduced. These indicators first increase and then decrease with increasing iron fertiliser concentrations. The best results were obtained with the Fe3 treatment (0.8%). Fluorescence parameters such as the relative variable fluorescence (WK and VJ) and the quantum yield of energy dissipation (φDo) showed opposite trends. This suggests that iron deficiency/excess and soda saline stress disrupt the electron and energy transport in the photosystem. Appropriate iron fertilization concentration can repair the photosynthetic electron transport chain, improve electron transport efficiency and promote balanced energy distribution. Therefore, we suggest that moderate amounts of Fe are beneficial for improving the electron and energy transport properties of the photosystem, while spraying high concentrations of Fe fertilizer has a negative effect on improving salt tolerance in rice.

Physiological insights on soybean response to drought

As most of the soybean in Europe is grown in rainfed conditions, climate aberrations are causing significant crop yield variability. To stabilise the yield and shift the sources of supply to European-grown soybean, stable and adaptable cultivars must be created by breeding. To better understand the mechanism of drought tolerance in specific germplasm, more knowledge needs to be acquired by research. Therefore, this research aimed to examine the physiological insights on soybean response to drought exposed plants (50% available water holding capacity) by monitoring the relative water content (RWC), lipid peroxidation (TBARS), pigments (Chl a and b), proteins and photosynthetic efficiency during five days in the pod stage. The decrease of RWC in both tested genotypes due to the drought effect, coupled with TBARS increase, indicates lipid peroxidation, which resulted in photosynthetic pigment and protein changes. Most of the chlorophyll a fluorescence parameters suggested plants initiated a defence mechanism to water deficiency, i.e. there was an initial adjustment on the first and second day of drought exposed plants, followed by drastic changes in electron flow in photosystem II (PSII). According to the correlation analysis, the effect of drought was prevalent for Chl b, Chl a/b, relative variable fluorescence at 30 ms (VI), the density of reaction centres (RC/CS0), absorption, trapping, electron transport and dissipation flux per reaction centre (ABS/RC, TR0/RC, ET0/RC and DI0/RC), plastoquinone at quinone A binding niche reducing RCs per PSII antenna chlorophylls (RC/ABS) and performance index (PIABS), meaning these parameters are good indicators of drought stress, that can facilitate the selection of genotypes and increase the efficiency of breeding programmes. Among tested materials, Korana had lower sensitivity to drought and smaller reduction of yield components than OS-211, indicating a better response of its defence mechanism to oxidative stress caused by lack of water. The methods tested and confirmed in this research could be used for screening large numbers of genotypes to determine in the soybean breeding programs aiming to select superior genotypes adaptable to weather changes.

Higher alterations in leaf fluorescence parameters of wheat cultivars predict more extensive necrosis in response to Zymoseptoria tritici

AbstractSeptoria tritici blotch (STB) is one of the main causes of wheat yield loss in the world. Apart from good agrotechnical practice, disease‐resistant cultivars are required to prevent yield losses. Breeding of such cultivars is time‐consuming and laborious, mainly due to the quantitative character of such resistance, but can be shortened using precise phenotyping. We show that fluorescence parameters, collected in a high‐throughput system, can be used for estimating wheat STB resistance. Using machine learning methods (deep learning network, random forest), we demonstrate that disease resistance based on the percentage of necrotic leaf area can be estimated by alterations in fluorescence parameters 8 days after inoculation, and before disease symptoms become visible. Moreover, we applied a random forest classifier to assess the significance of fluorescence parameters in an informative way (classification accuracy = 64.84%, p value [Accuracy >No information rate] <0.001). Based on this, we observed extensive alterations in parameters of sensitive cultivars, reflecting worse photosynthetic performance. The most highly altered parameters were fluorescence intensity measurements and descriptors of energy flux through photosystem II (PSII) reaction centres towards PSI such as F2, F3 and F4 fluorescence intensities at 0.1, 0.270 and 2 ms; initial to maximal fluorescence ratio (F0/Fm); the time derivative of relative variable fluorescence (dV/dT0); maximum quantum yield of PSII in the dark‐adapted state (Fv/Fm); maximum electron transport flux at PSII (ET0/RC); maximum trapped excitonic energy flux per excited PSII cross section (CS) at time T0 (TR0/CS0); and quantum efficiency of the reduction of end acceptors dR0 [dR0/(1 − dR0)].

The role of potassium on drought resistance of winter wheat cultivars under cold dryland conditions: Probed by chlorophyll a fluorescence

Potassium (K) is an important cation that regulates plant metabolism. Therefore the effect of different concentrations of potassium (0, 75, 150 kg ha−1 K2SO4) on photosynthesis efficiency of three winter wheat cultivars (Baran, Homa, Hashtrud) was investigated during the growing seasons of 2017–18 and 2018–19 under cold dryland conditions in Maragheh, Iran. Accumulation of potassium ion (K+) was observed to be increased with an increase in the concentration of K2SO4. With an increase in K+ the Hashtrud cultivar was observed to have more relative water content (RWC), normalized differential vegetation index (NDVI), and stomatal conductance (gs) than other cultivars. This resulted in a higher grain yield for the Hashtrud cultivar. RWC (R2 = 0.97), NDVI (R2 = 0.96), and gs (R2 = 0.92) had a positive relationship with KUE (grain yield/unit of K fertilizer used), especially in dryer years. K deficiency induced hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentration in plants. The application of K increased superoxide dismutases and reduced abscisic acid, to maintain the plants' stomatal conductance. Chlorophyll a fluorescence (ChlF) and the calculation of double normalized relative variable fluorescence reveal detailed information's about the response of wheat plants to K application under dryland conditions. The application of a high concentration of K (150 kg ha−1 K2SO4) on Hashtrud plants had a beneficial effect on the ChlF efficiency at different OJIP phases (KJ and JI). We found the efficiency of ChlF at the ΔWK-I phase with the values of FV/FO and PIABS improved with the application of 150 kg ha−1 K2SO4 and can be correlated with total yield improvement. These observations indicated that the application of a high concentration of K in stressed conditions for dryland areas could improve photosynthetic efficiency and wheat plant performance.

Cold acclimation alleviates cold stress-induced PSII inhibition and oxidative damage in tobacco leaves

ABSTRACT This study aimed to explore how cold acclimation (CA) modulates cold stress in tobacco leaves and reveal the relationship between CA and cold stress resistance, and the mechanism of CA-induced plant resistance to cold stress. This study examined the effects of CA treatment (at 8–10℃ for 2 d) on the cold tolerance of tobacco leaves under 4°C cold stress treatment using seedlings without CA treatment as the control (NA). In both CA and NA leaves, cold stress treatment resulted in a decrease in maximum photochemical efficiency of PSII (F v /F m), increase in relative variable fluorescence (V J) at 2 ms on the standardized OJIP curve, inhibition of PSII activity, and impairment of electron transfer on the acceptor side. Besides increasing the malondialdehyde (MDA) content and electrolyte leakage rate, the cold stress exacerbated the degree of membrane peroxidation. The CA treatment also induced the accumulation of reactive oxygen species (ROS), including superoxide anion (O2·−) and H2O2, and increased the activities of antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbic acid peroxidase (APX). The CA treatment also enhanced the accumulation of soluble sugar (SS) and soluble protein (SP), cyclic electron flow (CEF), and the proportion of regulatory energy dissipation Y(NPQ). Moreover, CA+ cold stress treatment significantly reduced CEF and Y(NPQ) in tobacco leaves than under NA+ cold stress treatment, thus significantly alleviating the degree of PSII photoinhibition. In conclusion, CA treatment significantly alleviated PSII photoinhibition and oxidative damage in tobacco leaves under cold stress treatment. Improvement in cold resistance of tobacco leaves is associated with the induction of antioxidant enzyme activity, accumulation of osmoregulation substances, and initiation of photoprotective mechanisms.

Photoprotective roles of ascorbate and PSII cyclic electron flow in the response of the seagrass Zostera marina to oxygen-evolving complex photoinactivation

The oxygen-evolving complex (OEC) of Zostera marina is prone to deactivation under visible light, which results in a formation of the long-lived radical P680+. The mechanism to prevent damage caused by P680+ remains unclear. In this study, following light exposure, the upregulation in ascorbate (AsA) content and the presence of PSII cyclic electron flow (PSII-CEF) provide evidence that AsA and PSII-CEF donate electrons to PSII. Furthermore, a factorial design experiment with different combinations of inhibition of AsA and PSII-CEF demonstrates that both inhibition treatments lead to decreases in maximal photochemical yield of PSII, increases in relative variable fluorescence at the K-step, as well as the net loss of PSII reaction center proteins and further degradation of OEC peripheral proteins. These results suggest that AsA and PSII-CEF play photoprotective roles by providing electrons to efficiently prevent damage to PSII from the highly oxidizing radical P680+ in Z. marina.

An autonomous and wireless pulse-amplitude modulated chlorophyll fluorometer

Abstract Measuring chlorophyll fluorescence is an important tool in plant research, since it is a reliable non-invasive method for capturing photosynthetic efficiency of a plant and, hence, an indicator of plant stress/health. The principle of chlorophyll fluorometry is based on the optical illumination of a plant’s leaf at a certain wavelength, while simultaneously measuring the emitted fluorescence light intensity at a different optical wavelength. By relating the fluorescence light energy at small and large excitation power, conclusions on the efficiency of the photosystem and, therefore, on the plant’s photosynthesis capability can be drawn. Current mobile chlorophyll fluorometers are either (i) compact and energy efficient but limited in functionality and accuracy by omitting modulated measurement signals or (ii) sophisticated and precise with respect to the measurement, but with the drawback of extended weight, size, energy consumption and cost. This contribution presents a smaller, lighter and cheaper sensor device that can be built with sufficiently low energy consumption to be powered by energy harvesting while being light enough to be attached nearly anywhere such as tree branches. With a device cost below 250 €, the performance of the developed device is similar to more expensive commercial devices considering measurements of the relative variable fluorescence. Moreover, the sensor device provides a wireless interface in the European 868 MHz SRD band with up to 10 km of range in free space while just consuming 150 µW in receiving mode due to a custom duty cycling technique.

Low sink demand caused net photosynthetic rate decrease is closely related to the irrecoverable damage of oxygen-releasing complex and electron receptor in peach trees

Source sink balance is one of the major determinants of carbon partitioning in plants. However, its effects on photosynthesis in fruit trees are largely unknown. In this work, the effects of low sink demand on net photosynthetic rate (Pn) and chlorophyll fluorescence after fruit removal (-fruit) in peach (Prunus persica (L.) Batsch cv. ‘Zaojiubao’) trees were investigated. The stepwise energy flow through photosystem II (PSII) at the reaction center (RC) was analyzed with quantitative analyses of fluorescence transient, also called JIP-test. We found that Pn was significantly lower and closely correlated to the leaf stomatal conductance (Gs) of -fruit trees than that of fruit retained (+fruit) trees. Leaf temperature (Tleaf) of -fruit trees was remarkably higher than that of +fruit trees. Day-time-period assays of chlorophyll (Chl) fluorescence revealed that, in the leaves of -fruit trees, the fluorescence parameters, such as NPQ (non-photochemical quenching coefficient) and ΦD0 (maximum quantum yield of non-photochemical de-excitation), decreased in the morning and recovered to the normal level in the afternoon, whereas other parameters, such as ΦE0 (quantum yield for electron transport at t = 0), Ψ0 (probability that a trapped exciton moves an electron to QA pool), F0 (minimum fluorescence, when all PSII RCs are open) and Wk (relative variable fluorescence at 300 μs of the chlorophyll fluorescence transient), did not. These results suggest that OEC complex and QA pool were irreversibly affected by low sink demand, whereas light harvest antenna and PSII potential efficiency retained a strong ability to recover.

Photoinactivation of the oxygen-evolving complex regulates the photosynthetic strategy of the seagrass Zostera marina

Zostera marina, a widespread seagrass, evolved from a freshwater ancestor of terrestrial monocots and successfully transitioned into a completely submerged seagrass. We found that its oxygen-evolving complex (OEC) was partially inactivated in response to light exposure, as evidenced by both the increment of the relative variable fluorescence at the K-step and the downregulation of the OEC genes and proteins. This photosynthetic regulation was further addressed at both proteome and physiology levels by an in vivo study. The unchanged content of the ΔpH sensor PsbS protein and the non-photochemical quenching induction dynamics, described by a single exponential function, verified the absence of the fast qE component. Contents and activities of chlororespiration, Mehler reaction, malic acid synthesis, and photorespiration key enzymes were not upregulated, suggesting that alternative electron flows remained unactivated. Furthermore, neither significant production of singlet oxygen nor increment of total antioxidative capacity indicated that reactive oxygen species were not produced during light exposure. In summary, these low electron consumptions may allow Z. marina to efficiently use the limited electrons caused by partial OEC photoinactivation to maintain a normal carbon assimilation level.

Exogenous methyl jasmonate enhances lipid production in Isochrysis galbana under nitrogen deprivation and high light

Nitrogen deprivation under high light is the most employed cultivation condition for the lipid's accumulation in microalgae. However, nitrogen deprivation causes the over-reduction of the photosystem (PS) II acceptor side in the presence of high light, confirmed by an increased VJ (the relative variable fluorescence at J-step) during cultivation. This in turn results in photo-inhibition of microalgal cells and photodamage to cellular metabolism which hinders the lipid production. To explore modifications for lipid accumulation, the exogenous methyl jasmonate (MeJA) effect was investigated on antioxidant capacity and lipid accumulation in Isochrysis galbana. Treatment with MeJA under high light nitrogen deprivation, (100 μM concentration), significantly enhanced the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and facilitated the electron transport in photosynthesis as indicated by increased ΦPSII (effective quantum yield of PSII) after MeJA treatment. The exogenous MeJA increased the antioxidant potential of related enzymes (ascorbate peroxidase and superoxide dismutase) and significantly alleviated the accumulation of reactive oxygen species (ROS) under high light nitrogen deprivation for improved cell survival and cellular metabolism in I. galbana. The improved cellular metabolism further increased the pyruvate content, which can be converted into acetyl coenzyme A (an important precursor for fatty acid synthesis). MeJA addition increased the substrate pool required for fatty acid and lipid production. Overall, exogenous MeJA enhanced lipid production in I. galbana under high light nitrogen deprivation by regulating the antioxidant capability and biosynthesis of the substrate.

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.

Chlororespiration protects the photosynthetic apparatus against photoinhibition by alleviating inhibition of photodamaged-PSII repair in Haematococcus pluvialis at the green motile stage

During outdoor mass cultivation, Haematococcus pluvialis cells, especially at the green motile stage, are frequently exposed to high light. However, the photoprotective mechanisms in H. pluvialis have not been well characterized. This study aimed to confirm the photoprotection of chlororespiration in H. pluvialis at the green motile stage. Under high light, inhibition of plastid terminal oxidase (PTOX), a key enzyme of chlororespiration, increased the relative variable fluorescence at the I-step (VI), causing a decrease in the plastoquinone (PQ) pool, which further led to photosystem II (PSII) acceptor side over-reduction. This condition disturbed the balance between light absorption and energy utilization, causing the over-excitation of PSII reaction centers, which was indicated by the fact that the inhibition of PTOX increased the relative variable fluorescence at the J-step (VJ) and the light absorption flux per active reaction center (ABS/RC), but decreased the electron transport flux per active reaction center (ETo/RC) in H. pluvialis. The over-reduction of the PSII acceptor side and the over-excitation of PSII reaction centers inevitably caused more severe photoinhibition as shown by a decrease in Fv/Fm (maximal photochemical efficiency of PSII). Furthermore, the level of photoinhibition was not changed when the PTOX was inhibited in the presence of the photodamaged-PSII repair inhibitor chloramphenicol, indicating that the inhibition of PTOX did not accelerate the photodamage to PSII directly. The above results suggest that the chlororespiration pathway protects H. pluvialis at the green motile stage against photoinhibition by decreasing the inhibition of the photodamaged-PSII repair mechanism.