PSII Reaction Center Research Articles

The role of EGY2 protease in response to high light stress.

In this study, we investigated the importance of one of the intramembrane proteases, EGY2, for the proper functioning of PSII under short-term high light stress conditions. EGY2 is a chloroplast intramembrane protease of the S2P family, whose absence in Arabidopsis thaliana affects PSII protein composition. The egy2 mutants exhibited a slower degradation of PsbA and decreased content of PsbC and PsbD. During exposure to high light stress, these stoichiometric changes affect the functional state of PSII, leading to its higher sensitivity to photoinhibition of the PSII reaction centre and increased heat dissipation. Furthermore, we explored the relationship between EGY2 and the pTAC16 transcription factor, which is a potential EGY2 substrate. Under light stress, WT plants showed decreased levels of pTAC16, while it remained unchanged in the egy2 mutants. This finding suggests that EGY2 may release pTAC16 from thylakoid membranes through proteolytic cleavage. We also confirmed the physical interaction between EGY2 and pTAC16 using the yeast two-hybrid system, providing evidence of EGY2's involvement in the regulation of PsbA and PsbC/PsbD operons by releasing pTAC16 from the thylakoid membrane.

Impact of Sodium Nitroprusside on the Photosynthetic Performance of Maize and Sorghum.

Nitric oxide (NO) is an important molecule in regulating plant growth, development and photosynthetic performance. This study investigates the impact of varying concentrations (0-300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the photosynthetic apparatus in sorghum (Sorghum bicolor L. Albanus) and maize (Zea mays L. Kerala) under physiological conditions. Analysis of the chlorophyll fluorescence signals (using PAM and the JIP-test) revealed an increased amount of open PSII reaction centers (qP increased), but it did not affect the number of active reaction centers per PSII antenna chlorophyll (RC/ABS). In addition, the smaller SNP concentrations (up to 150 μM) alleviated the interaction of QA with plastoquine in maize, while at 300 μM it predominates the electron recombination on QAQB-, with the oxidized S2 (or S3) states of oxygen evolving in complex ways in both studied plant species. At the same time, SNP application stimulated the electron flux-reducing end electron acceptors at the PSI acceptor side per reaction center (REo/RC increased up to 26%) and the probability of their reduction (φRo increased up to 20%). An increase in MDA (by about 30%) and H2O2 contents was registered only at the highest SNP concentration (300 µM). At this concentration, SNP differentially affected the amount of P700+ in studied plant species, i.e., it increased (by 10%) in maize but decreased (by 16%) in sorghum. The effects of SNP on the functions of the photosynthetic apparatus were accompanied by an increase in carotenoid content in both studied plants. Additionally, data revealed that SNP-induced changes in the photosynthetic apparatus differed between maize and sorghum, suggesting species specificity for SNP's impact on plants.

The Degradability of Microplastics May Not Necessarily Equate to Environmental Friendliness: A Case Study of Cucumber Seedlings with Disturbed Photosynthesis

In the environment, degradable plastics are decomposed into biodegradable microplastics (Bio-MPs), but there is limited study on the impact on plant growth and development. Therefore, this study aimed to investigate biodegradable polylactic acid microplastics (PLA-MPs) and nonbiodegradable polystyrene microplastics (PS-MPs) with different concentrations (0.02%, 0.2%, and 2% w/w) to explore their short-term toxic effects on cucumbers. The results of this study showed that PLA-MPs significantly (p < 0.05) reduced the aboveground and belowground biomass of cucumber seedlings compared to the control. At the level of 2% MPs, the chlorophyll content and PRI vegetation index of cucumber plants decreased significantly, anthocyanin content increased, and the photosynthetic system was disturbed. Likewise, the antioxidant defensive system of cucumber was affected after exposure to MPs stress, especially under 2% levels. The hyperspectral image is a novel technique which analyzed the chlorophyll content and absorption under MPs treatment; there was still a high correlation between chlorophyll content, anthocyanin content, and MCARI vegetation index, so a single vegetation index could be used for rapid detection of plant physiological status. Our study suggests that Bio-MPs have potential ecological toxicity that could affect the growth of cucumber seedlings through deactivation of the PSII reaction center. Therefore, biodegradable plastics do not seem to be the optimal solution, and there is an urgent need for long-term monitoring and evaluation of the biological toxicity of biodegradable MPs.

Effects of Sodium Selenite on the Growth and Photosystem II Activity of Arthrospira platensis Gom.

Arthrospira platensis (A. platensis) is a species of cyanobacteria with high economic value; the species is commercially well known as Spirulina platensis, and A. platensis was used in this paper. Its high adaptability, high photosynthetic efficiency, and fast growth rate make it one of the few cyanobacteria that can be cultivated on a large scale. Therefore, using the selenium enrichment property of A. platensis to cultivate selenium-enriched A. platensis will not only enhance the physiological efficacy of A. platensis but also increase its economic value significantly. In this study, we investigated the effects of sodium selenite on the growth and photosynthetic performance of A. platensis selenium by setting different amounts and methods of sodium selenite addition, and we explored the optimal culture conditions of the best dosage and method of sodium selenite addition. The results showed that the experimental group treated with sodium selenite at 700 μmol/L had the fastest growth, and the contents of soluble protein, phycocyanin C, and chlorophyll a increased by approximately 67.9%, 1.44 times, and 38.8% compared to the control group, respectively. Superoxide dismutase (SOD) and catalase (CAT) activity increased by 1.88-fold and 65%, respectively, and malondialdehyde (MDA) levels were reduced by 62% compared to the control group. The results of the OJIP assay showed that the J and I points were significantly higher at the batch addition and treatment concentration of 700 μmol/L, with the rate of QA being reduced and the proportion of the slowly reduced PQ pool being increased. The values of the maximum light energy conversion efficiency (Fv/Fm) per unit of reaction center were higher in both sodium selenite treatment groups than in the control group, indicating that the light energy conversion efficiency of A. platensis was promoted under all concentration treatment conditions. The batch addition of sodium selenite at concentrations less than 700 μmol/L resulted in significantly higher ABS/RC values than the control, and they were far superior to the one-time addition method. The reason for this may have been that the batch addition of sodium selenite at low concentrations increased the light absorption capacity of the unit reaction center of PSII, resulting in a rise in captured light energy, a rise in the energy captured by the reaction center for electron transfer (ETo/RC), a decrease in the energy dissipated in the absorption of light energy by the reaction center (DIo/RC), and an increase in the photosynthetic performance index (PI abs).

Salicylic Acid Modulates the Osmotic System and Photosynthesis Rate to Enhance the Drought Tolerance of Toona ciliata.

Toona ciliata M. Roem. is a valuable and fast-growing timber species which is found in subtropical regions; however, drought severely affects its growth and physiology. Although the exogenous application of salicylic acid (SA) has been proven to enhance plant drought tolerance by regulating the osmotic system and photosynthesis rate, the physiological processes involved in the regulation of drought tolerance by SA in various plants differ. Therefore, drought mitigation techniques tailored for T. ciliata should be explored or developed for the sustainable development of the timber industry. We selected 2-year-old T. ciliata seedlings for a potting experiment, set the soil moisture at 45%, and subjected some of the T. ciliata seedlings to a moderate drought (MD) treatment; to others, 0.5 mmol/L exogenous SA (MD + SA) was applied as a mitigation test, and we also conducted a control using a normal water supply at 70% soil moisture (CK). Our aim was to investigate the mitigating effects of exogenous SA on the growth condition, osmotic system, and photosynthesis rate of T. ciliata under drought stress conditions. OPLS-VIP was used to analyze the main physiological factors that enable exogenous SA to alleviate drought-induced injury in T. ciliata. The results indicated that exogenous SA application increased the growth of the ground diameter, plant height, and leaf blades and enhanced the drought tolerance of the T. ciliata seedlings by maintaining the balance of their osmotic systems, improving their gas exchange parameters, and restoring the activity of their PSII reaction centers. The seven major physiological factors that enabled exogenous SA to mitigate drought-induced injury in the T. ciliata seedlings were the soluble proteins (Sp), net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), stomatal opening window (Sow), activity of the photosystem II reaction center (ΦPSII), and electron transfer rate (ETR). Of these, Sp was the most dominant factor. There was a synergistic effect between the osmotic system and the photosynthetic regulation of drought injury in the T. ciliata seedlings. Overall, our study confirms that exogenous SA enhances the drought tolerance of T. ciliata by modulating the osmotic system and photosynthesis rate.

Improving estimates of sub-daily gross primary production from solar-induced chlorophyll fluorescence by accounting for light distribution within canopy

Solar-induced chlorophyll fluorescence (SIF) has long been regarded as a proxy for photosynthesis and has shown superiority in estimating gross primary production (GPP) compared to traditional vegetation indices, especially in evergreen ecosystems. However, current SIF-based GPP estimations regard the canopy as a large leaf and seldom consider the impact of interactions among light, canopy structure, and leaf physiology. In this study, we proposed GPP estimation models with different descriptions of light–structure–physiology interactions (including the layered model, the two-leaf model, and the layered two-leaf model) and compared their performances with the big-leaf model using half-hourly (or hourly) observations at evergreen needleleaf forest sites. First, we found that the big-leaf model underestimated GPP, especially at noon. All models showed higher accuracy than that of the big-leaf model. Second, we investigated the diurnal dynamics of GPP estimations in each canopy layer and found that models with a two-leaf assumption captured the diurnal variations in GPP better than that with the layered assumption. We also deduced that the poor performance of the big-leaf model was related to its overestimation of the overall light stress on the redox state of PSII reaction centers (qL). Finally, we noticed that the qL at the canopy scale had lower sensitivity to light change than the single-leaf qL and that the light response of canopy-scale qL was influenced by the leaf area index during seasonal cycles. Overall, this study describes methods to accurately estimate sub-daily GPP from SIF in evergreen needleleaf forests and demonstrates that the interactions among light, canopy structure, and leaf physiology regulate the SIF-GPP relationship at the canopy scale. Further, it indicates the need to consider the description of light distribution within the canopy in next-generation terrestrial biosphere models, even if they incorporate SIF to constrain their parameterization. Thus, upscaling the established leaf-scale mechanistic SIF-GPP relationship or findings to canopy-scale applications still requires much work, especially when there are significant changes in environmental conditions and their within-canopy distributions.

Amino-functionalized SiO2 microbeads optimize photosynthetic performance, gene expression, ROS production and antioxidant status in chromium and copper-exposed Zea mays

The objective of the current study was to assess the potential of the amino-functionalized SiO2 microbeads (S) in improving the tolerance of maize to chromium and/or copper toxicity. For this purpose, Zea mays L. cv. DKC5685 was grown by exposure at different S concentrations (100–500 mg L-1) alone and with 200 µM chromium (Cr stress) and 100 µM copper (Cu stress) for 7 days. The photosynthesis-related parameters (Fv/Fm, Fv/Fo), relative growth rate (RGR), and relative water content (RWC) levels were suppressed under Cr and/or Cu stresses. In addition, stress altered antioxidant activities and gas exchange parameters. S applications abolished the negative impacts of stress on the physiological state of the photosynthetic system, potential photochemical efficiency and chlorophyll fluorescence. S increased the performance index by reversing the detrimental effects on the electron flow rate through the PSII electron transport flux and electron transfer from the decreased plastoquinone pool to the PSI reaction center. Following exposure to S, the effects of stress on photosystem I-associated reaction center proteins were rearranged by induced expression levels of PsaA and PsaB genes. S treatments had potent ROS scavengers in maize leaves. In the Cr+S groups, the AsA-GSH cycle was regulated by increasing the activities of all the responsible enzymes mentioned above, such as SOD, CAT, APX and GR, and the accumulation of H2O2 and TBARS effectively removed. CAT and POX activities in Cu+S groups were not effective in these adjustments. In Cr+Cu+S applications, although H2O2 and TBARS contents were reduced as evidenced by ROS visualization using fluorescence of dye, AsA regeneration could not be achieved, and low tAsA/DHA levels were detected. Our results show that amino-functionalized SiO2 microbeads have significant promise to offer resistance to maize by minimizing oxidative damage brought on by heavy metal uptake and preserving the metabolic processes involved in photosynthesis.

Characterization of tryptophan oxidation affecting D1 degradation by FtsH in the photosystem II quality control of chloroplasts.

Photosynthesis is one of the most important reactions for sustaining our environment. Photosystem II (PSII) is the initial site of photosynthetic electron transfer by water oxidation. Light in excess, however, causes the simultaneous production of reactive oxygen species (ROS), leading to photo-oxidative damage in PSII. To maintain photosynthetic activity, the PSII reaction center protein D1, which is the primary target of unavoidable photo-oxidative damage, is efficiently degraded by FtsH protease. In PSII subunits, photo-oxidative modifications of several amino acids such as Trp have been indeed documented, whereas the linkage between such modifications and D1 degradation remains elusive. Here, we show that an oxidative post-translational modification of Trp residue at the N-terminal tail of D1 is correlated with D1 degradation by FtsH during high-light stress. We revealed that Arabidopsis mutant lacking FtsH2 had increased levels of oxidative Trp residues in D1, among which an N-terminal Trp-14 was distinctively localized in the stromal side. Further characterization of Trp-14 using chloroplast transformation in Chlamydomonas indicated that substitution of D1 Trp-14 to Phe, mimicking Trp oxidation enhanced FtsH-mediated D1 degradation under high light, although the substitution did not affect protein stability and PSII activity. Molecular dynamics simulation of PSII implies that both Trp-14 oxidation and Phe substitution cause fluctuation of D1 N-terminal tail. Furthermore, Trp-14 to Phe modification appeared to have an additive effect in the interaction between FtsH and PSII core in vivo. Together, our results suggest that the Trp oxidation at its N-terminus of D1 may be one of the key oxidations in the PSII repair, leading to processive degradation by FtsH.

Characterization of tryptophan oxidation affecting D1 degradation by FtsH in the photosystem II quality control of chloroplasts

Photosynthesis is one of the most important reactions for sustaining our environment. Photosystem II (PSII) is the initial site of photosynthetic electron transfer by water oxidation. Light in excess, however, causes the simultaneous production of reactive oxygen species (ROS), leading to photo-oxidative damage in PSII. To maintain photosynthetic activity, the PSII reaction center protein D1, which is the primary target of unavoidable photo-oxidative damage, is efficiently degraded by FtsH protease. In PSII subunits, photo-oxidative modifications of several amino acids such as Trp have been indeed documented, whereas the linkage between such modifications and D1 degradation remains elusive. Here, we show that an oxidative post-translational modification of Trp residue at the N-terminal tail of D1 is correlated with D1 degradation by FtsH during high-light stress. We revealed that Arabidopsis mutant lacking FtsH2 had increased levels of oxidative Trp residues in D1, among which an N-terminal Trp-14 was distinctively localized in the stromal side. Further characterization of Trp-14 using chloroplast transformation in Chlamydomonas indicated that substitution of D1 Trp-14 to Phe, mimicking Trp oxidation enhanced FtsH-mediated D1 degradation under high light, although the substitution did not affect protein stability and PSII activity. Molecular dynamics simulation of PSII implies that both Trp-14 oxidation and Phe substitution cause fluctuation of D1 N-terminal tail. Furthermore, Trp-14 to Phe modification appeared to have an additive effect in the interaction between FtsH and PSII core in vivo. Together, our results suggest that the Trp oxidation at its N-terminus of D1 may be one of the key oxidations in the PSII repair, leading to processive degradation by FtsH.

Improves the Resilience of Cucumber Seedlings under High-Light Stress through End-of-Day Addition of a Low Intensity of a Single Light Quality

In order to investigate whether an end-of-day (EOD) addition of a single light quality could help alleviate high-light stress in a cucumber, cucumber seedlings were subjected to a 9 d period of high-light stress (light intensity was 1300 ± 50 μmol·m−2·s−1) when they were growing to 3 leaves and 1 heart, while the red light (R), blue light (B), green light (G), far-red light (FR), and ultraviolet A (UVA) light were added in the end-of-day period. The present study was conducted to measure antioxidants, chlorophyll content, and its synthetic degradative enzymes and chlorophyll a fluorescence in response to the degree of stress in cucumber seedlings. The experimental results demonstrated that the addition of blue light, UVA light, and green light significantly decreased the SOD and POD activities in the middle of the treatment (6th day) compared to the dark (D) treatment and improved the absorption performance of the PSI reaction centre of the cucumber seedling leaves to a certain extent (PIABS), but the PSII capacity capture ability (TRo/RC) of the three treatments decreased compared to the D treatment. The MDA content of all the treatments had a significant decrease compared to that of the D treatment. The MDA content of all the treatments was significantly lower than that of D, and its FV/FM was increased to different degrees; the chlorophyll degrading enzyme PPH activity was significantly lower than that of the D treatment when a single light quality was added at the EOD period on the 9th d of treatment. In conclusion, cucumber seedlings subjected to short-term high-light stress can be added during the EOD period with a low-light intensity of a single R, G, B, or UVA light.

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.

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

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

Effects of Xanthomonas campestris pv. campestris on the photosynthesis of cabbage in the early stage of infection

Cabbage is one of the most important cruciferous vegetables. Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) seriously affects cabbage production; therefore, it is important to study the resistance mechanism to black rot in cabbage. In this study, cabbage photosynthetic physiology changes in the early stages of Xcc infection were analyzed using physiological index determination and transcriptome analysis. The results showed that the Xcc infection can lead the chlorophyll degradation and decreased the net photosynthetic rate (Pn), and the decrease in Pn was mainly due to non-stomatal factors. In addition, the maximum photosynthetic efficiency (Fv/Fm), actual photosynthetic efficiency of photosystem II (PSII) gradually decreased, and the OJIP curve tended to be flat, indicating that Xcc infection reduced the activity of the PSII reaction center and affected the chlorophyll fluorescence intensity. Moreover, the primary photochemical reaction of cabbage leaves was damaged, and electron transfer on the PSII receptor side was inhibited after Xcc infection. NADP-GAPDH and FBPase activities in the Calvin cycle decreased after Xcc invasion. Using transcriptome analysis, 173, 77, 63, and 53 differentially expressed genes (DEGs) were enriched in "carbon metabolism", "photosynthesis", "carbon fixation in photosynthetic organisms", and "metabolism of porphyrins and chlorophyll" metabolic processes, respectively. These results suggest that Xcc infection affects cabbage photosynthesis via multiple pathways. Our results provide a theoretical basis for further research on black rot-resistant breeding and cabbage resistance mechanisms.

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.

Regulatory effects of silicon nanoparticles on the growth and photosynthesis of cotton seedlings under salt and low-temperature dual stress

BackgroundSilicon nanoparticles (SiO2-NPs) play a crucial role in plants mitigating abiotic stress. However, the regulatory mechanism of SiO2-NPs in response to multiple stress remains unclear. The objectives of this study were to reveal the regulatory mechanism of SiO2-NPs on the growth and photosynthesis in cotton seedlings under salt and low-temperature dual stress. It will provide a theoretical basis for perfecting the mechanism of crop resistance and developing the technology of cotton seedling preservation and stable yield in arid and high salt areas.ResultsThe results showed that the salt and low-temperature dual stress markedly decreased the plant height, leaf area, and aboveground biomass of cotton seedlings by 9.58%, 15.76%, and 39.80%, respectively. While SiO2-NPs alleviated the damage of the dual stress to cotton seedling growth. In addition to reduced intercellular CO2 concentration, SiO2-NPs significantly improved the photosynthetic rate, stomatal conductance, and transpiration rate of cotton seedling leaves. Additionally, stomatal length, stomatal width, and stomatal density increased with the increase in SiO2-NPs concentration. Notably, SiO2-NPs not only enhanced chlorophyll a, chlorophyll b, and total chlorophyll content, but also slowed the decrease of maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and the increase in non-photochemical quenching. Moreover, SiO2-NPs enhanced the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, improved leaf water potential, and decreased abscisic acid and malondialdehyde content. All the parameters obtained the optimal effects at a SiO2-NPs concentration of 100 mg L− 1, and significantly increased the plant height, leaf area, and aboveground biomass by 7.68%, 5.37%, and 43.00%, respectively. Furthermore, significant correlation relationships were observed between photosynthetic rate and stomatal conductance, stomatal length, stomatal width, stomatal density, chlorophyll content, maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and Rubisco activity.ConclusionThe results suggested that the SiO2-NPs improved the growth and photosynthesis of cotton seedlings might mainly result from regulating the stomatal state, improving the light energy utilization efficiency and electron transport activity of PSII reaction center, and inducing the increase of Rubisco activity to enhance carbon assimilation under the salt and low-temperature dual stress.

Modification of Tomato Photosystem II Photochemistry with Engineered Zinc Oxide Nanorods.

We recently proposed the use of engineered irregularly shaped zinc oxide nanoparticles (ZnO NPs) coated with oleylamine (OAm), as photosynthetic biostimulants, to enhance crop yield. In the current research, we tested newly engineered rod-shaped ZnO nanorods (NRs) coated with oleylamine (ZnO@OAm NRs) regarding their in vivo behavior related to photosynthetic function and reactive oxygen species (ROS) generation in tomato (Lycopersicon esculentum Mill.) plants. ZnO@OAm NRs were produced via solvothermal synthesis. Their physicochemical assessment revealed a crystallite size of 15 nm, an organic coating of 8.7% w/w, a hydrodynamic diameter of 122 nm, and a ζ-potential of -4.8 mV. The chlorophyll content of tomato leaflets after a foliar spray with 15 mg L-1 ZnO@OAm NRs presented a hormetic response, with an increased content 30 min after the spray, which dropped to control levels 90 min after the spray. Simultaneously, 90 min after the spray, the efficiency of the oxygen-evolving complex (OEC) decreased significantly (p < 0.05) compared to control values, with a concomitant increase in ROS generation, a decrease in the maximum efficiency of PSII photochemistry (Fv/Fm), a decrease in the electron transport rate (ETR), and a decrease in the effective quantum yield of PSII photochemistry (ΦPSII), indicating reduced PSII efficiency. The decreased ETR and ΦPSII were due to the reduced efficiency of PSII reaction centers (Fv'/Fm'). There were no alterations in the excess excitation energy at PSII or the fraction of open PSII reaction centers (qp). We discovered that rod-shaped ZnO@OAm NRs reduced PSII photochemistry, in contrast to irregularly shaped ZnO@OAm NPs, which enhanced PSII efficiency. Thus, the shape and organic coating of the nanoparticles play a critical role in the mechanism of their action and their impact on crop yield when they are used in agriculture.

Exogenous Salicylic Acid Alleviates Water Deficit Stress by Protecting Photosynthetic System in Maize Seedlings

Water deficit is a significant abiotic stress affecting crop growth and production. While many studies have indicated that salicylic acid (SA) plays a crucial role in mitigating the detrimental effects of environmental stress on plants, its mechanism regulating the photosynthetic adaptability of maize seedlings under water deficit is still unclear. This study aimed to investigate the impact of exogenous SA on maize seedling performance under polyethylene glycol (PEG)-induced water deficit. The results showed that PEG treatment destroyed the integrity of chloroplast and reduced chlorophyll content and photosynthesis rate (Pn), leading to growth retardation of maize seedlings with lower biomass accumulation and leaf relative water content (RWC). Moreover, chlorophyll fluorescence index, including potential photochemical activity (Fv/Fo), maximum Photosystem II (PSII) quantum yield (Fv/Fm), and energy captured by PSII reaction center for electron transfer (Eto/RC), were decreased, but energy dissipated by unit reaction center (DIo/RC) was enhanced in maize seedlings under water deficit. In addition, PEG treatment also significantly declined the activity of Rubisco and Rubisco activase (RCA) in maize seedlings. In contrast, SA treatment enhanced the content of chlorophyll, as well as the transcription level of psbA, and RCA and Rubisco small subunit (rbcS) reduced the damaging effects of PEG treatment by protecting the integrity of chloroplast and repairing the damaged PSII reaction center, thus positively regulating photosynthetic reaction and water-deficit tolerance in maize seedlings. Our data implied that SA played an important regulatory role in plant resistance to water-deficit stress, and the result will further supply the regulatory network of SA-mediated photosynthetic adaptability.

Modeling the Characteristic Residues of Chlorophyll f Synthase (ChlF) from Halomicronema hongdechloris to Determine Its Reaction Mechanism.

Photosystem II (PSII) is a quinone-utilizing photosynthetic system that converts light energy into chemical energy and catalyzes water splitting. PsbA (D1) and PsbD (D2) are the core subunits of the reaction center that provide most of the ligands to redox-active cofactors and exhibit photooxidoreductase activities that convert quinone and water into quinol and dioxygen. The performed analysis explored the putative uncoupled electron transfer pathways surrounding P680+ induced by far-red light (FRL) based on photosystem II (PSII) complexes containing substituted D1 subunits in Halomicronema hongdechloris. Chlorophyll f-synthase (ChlF) is a D1 protein paralog. Modeling PSII-ChlF complexes determined several key protein motifs of ChlF. The PSII complexes included a dysfunctional Mn4CaO5 cluster where ChlF replaced the D1 protein. We propose the mechanism of chlorophyll f synthesis from chlorophyll a via free radical chemistry in an oxygenated environment created by over-excited pheophytin a and an inactive water splitting reaction owing to an uncoupled Mn4CaO5 cluster in PSII-ChlF complexes. The role of ChlF in the formation of an inactive PSII reaction center is under debate, and putative mechanisms of chlorophyll f biosynthesis are discussed.

Revelations on photosystem II, thermoluminescence, and artificial photosynthesis: a retrospective of Govindjee from fundamentals to applications.

Photosynthesis, as one of the most important chemical reactions, has powered our planet for over four billion years on a massive scale. This review summarizes and highlights the major contributions of Govindjee from fundamentals to applications in photosynthesis. His research included primary photochemistry measurements, in the picosecond time scale, in both Photosystem I and II and electron transport leading to NADP reduction, using two light reactions. He was the first to suggest the existence of P680, the reaction center of PSII, and to prove that it was not an artefact of Chlorophyll a fluorescence. For most photobiologists, Govindjee is best known for successfully exploiting Chlorophyll a fluorescence to understand the various steps in photosynthesis as well as to predict plant productivity. His contribution in resolving the controversy on minimum number of quanta in favor of 8-12 vs 3-4, needed for the evolution of one molecule of oxygen, is a milestone in the area of photosynthesis research. Furthermore, together with Don DeVault, he is the first to provide the correct theory of thermoluminescence in photosynthetic systems. His research productivity is very high: ~ 600 published articles and total citations above 27,000 with an h-index of 82. He is a recipient of numerous awards and honors including a 2022: Lifetime Achievement Award of the International Society of Photosynthesis Research. We hope that the retrospective of Govindjee described in this work will inspire and stimulate the readers to continue probing the photosynthetic apparatuses with new discoveries and breakthroughs.

Physiological differences of green-leaf and variegated - leaf ivy (hedera helix L.) Cultivars

To screen sun-resistant cultivars of ivy for the three-dimensional greening of urban roofs and balconies, the chlorophyll content, photosynthetic response index, and chlorophyll fluorescence parameters of 5 green-leaf and 5 variegated leaf cultivars of ivy were measured, and compared the photosynthetic characteristics of different cultivars. Results showed that ivy seedlings were very shade tolerant. The photosynthetic adaptation range, maximum net photosynthetic rate, and electron transfer efficiency of the PSII reaction center of the green-leaf ivy cultivars were significantly higher than those of the variegated ivy cultivars. The photochemical conversion efficiency and photosynthetic capacity of Hedera helix ‘Shamrock’ were higher than those of the other tested green-leaf cultivars, suggesting that Hedera helix ‘Shamrock’ had a strong light tolerance. The differences in photosynthetic characteristics among the variegated cultivars were greater than those within the green-leaf cultivars. Among the tested cultivars, Hedera helix ‘Mini Kolibri’ had a relatively high light adaptation range and high light efficiency potential. Bangladesh J. Bot. 52(2): 539-549, 2023 (June) Special