Chlorophyll Fluorescence Parameters Research Articles

Effects of N, P, and K application rates on distribution of 13C assimilates, starch accumulation in grains and fertilizer utilization of wheat

Clarifying the appropriate application rates of N, P, and K fertilizers and the physiological mechanisms of wheat under water-saving recharge irrigation in the North China Plain would provide a theoretical basis for formulating reasonable fertilization plans for high-yield and high-efficiency wheat production. We established four treatments with different amounts of nitrogen (N), phosphorus (P2O5), and potassium (K2O) application: 0, 0, and 0 kg·hm-2 (F0), 180, 75, and 60 kg·hm-2 (F1), 225, 120, and 105 kg·hm-2 (F2), and 270, 165, and 150 kg·hm-2 (F3). During the jointing and anthesis stages of wheat, the relative water content of each treatment in the 0-40 cm soil layer was replenished to 70%, to investigate the differences in wheat flag leaf photosynthetic characteristics, distribution of 13C assimilates, grain starch accumulation, and fertilizer utilization. The results showed that the relative chlorophyll content of flag leaves, photosynthetic and chlorophyll fluorescence parameters, 13C assimilate allocation in each organ, enzyme activities involved in starch synthesis, and starch accumulation in the F1 treatment were significantly higher than that in F0 treatment, which was an important physiological basis for the 20.9% increase in grain yield. The above parameters and yield in the F2 and F3 treatments showed no significant increase compared to F1 treatment, while fertilizer productivity and agronomic efficiency of N, P, and K decreased by 17.5%-58.4% and 12.7%-50.7%, respectively. Therefore, F1 could promote flag leaf photosynthetic assimilate production and grain starch accumulation under water-saving supplementary irrigation conditions, resulting in higher grain yield and fertilizer utilization efficiency.

Estimating of chlorophyll fluorescence parameter Fv/Fm for plant stress detection at peatlands under Ramsar Convention with Sentinel-2 satellite imagery

Monitoring vegetation is essential in Earth Observation (EO) due to its link with the global carbon cycle, playing a crucial role in ecosystem management. The fluorescence of chlorophyll (ChF) is a reliable indicator of plants' photosynthetic activity and growth, especially when they are experiencing unfavourable conditions, particularly in terrestrial wetlands. These wetlands are integral components of the landscape, contributing significantly to climate mitigation, adaptation, biodiversity, and the well-being of both the environment and humanity. We conducted a research study using the XGBoost machine learning algorithm to map the chlorophyll fluorescence parameter Fv/Fm in the Biebrza River Valley, which is known for its marshes, peatlands, and diverse flora and fauna. Our study highlights the benefits of using ensemble classifiers derived from EO Sentinel-2 satellite imagery for accurately mapping Fv/Fm across terrestrial landscapes under the Ramsar Convention at Narew River Valley (Poland) and Čepkeliai Marsh (Lithuania). The XGBoost algorithm provides an accurate estimate of ChF with a robust determination coefficient of 0.747 and minimal bias at 0.013, as validated using in situ data. The precision of Fv/Fm chlorophyll fluorescence parameter estimation from remote sensing sensors depends on the growth stage, emphasizing the importance of identifying the optimal overpass time for S-2 observations. Our study found that biophysical factors, as denoted by spectral indices related to greenness and leaf pigments, were highly impactful variables among the top classifiers. However, incorporating soil, vegetation and meteorological indicators from remote sensing data could further increase the accuracy of chlorophyll fluorescence mapping.

Environmental effects and their impact on yield in adjacent experimental plots of high-stem and short-stem wheat varieties

BackgroundIn regional wheat trials, when short-stem wheat varieties and high-stem wheat varieties are planted adjacent to each other in small plots, changes in their marginal plot environment can lead to bias in yield evaluation. Currently, there is no relevant research revealing the degree of their mutual influence.ResultsIn a regional wheat experiment, when high-stem wheat varieties and short-stem wheat varieties were planted adjacent to one another, there was no significant change in soil temperature or humidity in the high-stem wheat variety experimental plot from November to May compared to the control plot, while the soil humidity in the short-stem wheat variety experimental plot was greater than that in the control plot. In May, the soil temperature of the short-stem wheat varieties in the experimental plot was lower than that in the control plot. Illumination of the wheat canopy in the high-stem wheat variety experimental plot had a significant positive effect in April and May, while illumination of the wheat canopy in the short-stem wheat variety experimental plot had a negative effect. The chlorophyll fluorescence parameters of flag leaves in the high-stem wheat variety experimental plots showed an overall increasing trend, while the chlorophyll fluorescence parameters of flag leaves in the experimental plots of short-stem wheat varieties showed a decreasing trend. The analysis of the economic yield, biological yield, and yield factors in each experimental plot revealed that the marginal effects of the economic yield and 1000-grain weight were particularly significant and manifested as positive effects in the high-stem wheat variety experimental plot and as negative effects in the short-stem wheat variety experimental plot. The economic yield of the high-stem wheat variety experimental plot was significantly greater than that of the control plot, the economic yield of the short-stem wheat variety experimental plot was significantly lower than that of the control plot, and the economic yield of the high-stem experimental plot was significantly greater than that of the short-stem experimental plot. When the yield of the control plot of the high-stem wheat varieties was compared to that of the control plot of the short-stem wheat varieties, the yield of the control plot of the short-stem wheat varieties was significantly greater than that of the control plot of the high-stem wheat varieties.ConclusionsBased on these findings, it is concluded that plots with high-stem and short-stem wheat varieties are adjacent in regional wheat trials, the plots of high-stem wheat varieties are subject to marginal positive effects, resulting in a significant increase in economic yield; the plots of short-stem wheat varieties are subject to marginal negative effects, resulting in a decrease in economic yield. This study reveals the mutual influence mechanism of environment and yield with adjacent planting of high-stem and short-stem wheat varieties in regional wheat trials, providing a useful reference and guidance for optimizing the layout of regional wheat trials.

The responses of pepper plants to nitrogen form and dissolved oxygen concentration of nutrient solution in hydroponics

BackgroundThe presence of oxygen in the growth medium is absolutely essential for root development and the overall metabolic processes of plants. When plants do not have an adequate oxygen supply for respiration, they can experience a condition known as hypoxia. In order to investigate the impact of different nitrogen forms and varying oxygen levels in nutrient solutions on the growth, photosynthesis, and chlorophyll fluorescence parameters of bell pepper plants, a comprehensive study was conducted. The experiment was designed as a factorial experiment, considering two main factors: nitrogen forms (calcium nitrate and ammonium sulfate) with a fixed nitrogen concentration of 5 mM, and the oxygen levels of the nutrient solutions (ranging from 1.8 ± 0.2 to 5.3 ± 0.2 mg. L-1).ResultsThe study examined the effects of nitrogen (NH4+ and NO3−) application on various parameters of vegetative growth. The results demonstrated that the use of ammonium (NH4+) led to a reduction in the most measured parameters, including the fresh and dry mass of both the root and shoot, at low O2 concentrations of 1.8 ± 0.2; 2.6 ± 0.2 and 3.8 ± 0.2 mg. L-1. However, an interesting observation was made regarding the impact of oxygen levels on root growth in plants grown with nitrate (NO3−). Specifically, the highest levels of oxygen significantly increased root growth in NO3−-fed plants. Additionally, the application of NH4+ resulted in an increase in chlorophyll concentration in the leaves, particularly when combined with high oxygen levels in the nutrient solution. On the other hand, leaves of plants fed with NO3− exhibited higher photosynthetic rate (A), intrinsic water use efficiency (iWUE), and instantaneous carboxylation efficiency (A/Ci) compared to those fed with NH4+. Furthermore, it was found that NO3−-fed plants displayed the highest instantaneous carboxylation efficiency at oxygen levels of 3.8 and 5.3 mg. L-1, while the lowest efficiency was observed at oxygen levels of 1.8 and 2.6 mg. L-1. In contrast, NH4+-grown plants exhibited a higher maximal quantum yield of PSII photochemistry (Fv/Fm), as well as increased variable fluorescence (Fv) and maximum fluorescence (Fm), compared to NO3−-grown plants. Interestingly, the NO3−-fed plants showed an increase in Fv/Fm, Fv, and Fm with the elevation of oxygen concentration in the nutrient solution up to 5.3 mg. L-1.ConclusionThis study showed that, the growth and photosynthesis parameters in bell pepper plants are sensitive to oxygen stress in floating hydroponic culture. Therefore, the oxygen level in the nutrient solution must not be lower than 3.8 and 5.3 mg. L-1 in NH4+ and NO3− –supplied culture media or nutrient solutions, respectively.

Genetic dissection of ten photosynthesis-related traits based on InDel- and SNP-GWAS in soybean.

A total of 416 InDels and 112 SNPs were significantly associated with soybean photosynthesis-related traits. GmIWS1 and GmCDC48 might be related to chlorophyll fluorescence and gas-exchange parameters, respectively. Photosynthesis is one of the main factors determining crop yield. A better understanding of the genetic architecture for photosynthesis is of great significance for soybean yield improvement. Our previous studies identified 5,410,112 single nucleotide polymorphisms (SNPs) from the resequencing data of 219 natural soybean accessions. Here, we identified 634,106 insertions and deletions (InDels) from these 219 accessions and used these InDel variations to perform principal component and linkage disequilibrium analysis of this population. The genome-wide association study (GWAS) were conducted on six chlorophyll fluorescence parameters (chlorophyll content, light energy absorbed per reaction center, quantum yield for electron transport, probability that a trapped exciton moves an electron into the electron transport chain beyond primary quinone acceptor, maximum quantum yield of photosystem II primary photochemistry in the dark-adapted state, performance index on absorption basis) and four gas-exchange parameters (intercellular carbon dioxide concentration, stomatal conductance, net photosynthesis rate, transpiration rate) and revealed 416 significant InDels and 112 significant SNPs. Based on GWAS results, GmIWS1 (encoding a transcription elongation factor) and GmCDC48 (encoding a cell division cycle protein) with the highest expression in the mapping region were determined as the candidate genes responsible for chlorophyll fluorescence and gas-exchange parameters, respectively. Further identification of favorable haplotypes with higher photosynthesis, seed weight and seed yield were carried out for GmIWS1 and GmCDC48. Overall, this study revealed the natural variations and candidate genes underlying the photosynthesis-related traits based on abundant phenotypic and genetic data, providing valuable insights into the genetic mechanisms controlling photosynthesis and yield in soybean.

Photosynthetic response of Chlamydomonas reinhardtii and Chlamydomonas sp. 1710 to zinc toxicity.

Zinc (Zn) is an essential trace element but can lead to water contamination and ecological deterioration when present in excessive amounts. Therefore, investigating the photosynthetic response of microalgae to Zn stress is of great significance. In this study, we assessed the photosynthetic responses of neutrophilic Chlamydomonas reinhardtii and acidophilic Chlamydomonas sp. 1710 to Zn exposure for 96 h. The specific growth rate (μ), chlorophyll-a (Chl-a) content, and chlorophyll fluorescence parameters were determined. The results demonstrated that Chlamydomonas sp. 1710 was much more tolerant to Zn than C. reinhardtii, with the half-maximal inhibitory concentration (IC50) values of 225.4 mg/L and 23.4 mg/L, respectively. The μ and Chl-a content of C. reinhardtii decreased in the presence of 15 mg/L Zn, whereas those of Chlamydomonas sp. 1710 were unaffected by as high as 100 mg/L Zn. Chlorophyll fluorescence parameters indicated that the regulation of energy dissipation, including non-photochemical quenching, played a crucial role in Zn stress resistance for both Chlamydomonas strains. However, in the case of C. reinhardtii, non-photochemical quenching was inhibited by 5 mg/L Zn in the first 48 h, whereas for Chlamydomonas sp. 1710, it remained unaffected under 100 mg/L Zn. Chlamydomonas sp. 1710 also exhibited a 20 times stronger capacity for regulating the electron transfer rate than C. reinhardtii under Zn stress. The light energy utilization efficiency (α) of Chlamydomonas sp. 1710 had the most highly non-linear correlation with μ, indicating the energy utilization and regulation process of Chlamydomonas sp. 1710 was well protected under Zn stress. Collectively, our findings demonstrate that the photosystem of Chlamydomonas sp. 1710 is much more resilient and tolerant than that of C. reinhardtii under Zn stress.

Adventitious root formation confers waterlogging tolerance in cowpea (Vigna unguiculata (L.) Walp.)

Crop adaptation to waterlogging stress necessitates alterations in their morpho-physiological and biochemical characteristics. Cowpeas, which serve as a dual-purpose legume crop (food and fodder), are sensitive to waterlogging stress, especially when exposed to extended periods of water stagnation during the early growth stage. In this study, we subjected five distinct and superior cowpea varieties to 10 days of waterlogging stress at the early seedling stage (V2, 15 days post emergence for 10 days) under controlled conditions. The aim was to comprehend the response of these varieties and identify the ideal trait for screening a large collection of cowpea genetic resources for waterlogging tolerance. We measured and analyzed changes in morpho-physiological and root parameters to gain a deeper understanding of the mechanism underlying waterlogging tolerance. The treatment (waterlogging and control), genotype, and their interactions had a significant impact on the most studied traits (p < 0.05). The results indicated a significant reduction in morpho-physiological parameters such as plant height, leaf area, leaf number, Normalized Difference Vegetation Index (NDVI), chlorophyll content, and chlorophyll fluorescence parameters under stress treatment than control conditions. However, root parameters like the number of adventitious roots (AR) and their length (ARL) significantly increased under waterlogging stress in tolerant cowpea varieties like DC15 and PL4. Correlation and PCA analyses further revealed a positive and significant association between cowpeas’ waterlogging tolerance and AR formation and its AR length. Therefore, the current study reveals that swift development of AR and ARL may serve as potential traits conferring waterlogging tolerance in cowpeas. Using suitable mapping populations, these traits could reveal genomic regions associated with waterlogging tolerance in cowpeas. The tolerant varieties and key traits identified in this study could be beneficial in breeding programs aimed at enhancing waterlogging tolerance in cowpeas.

Toxic effect of ciprofloxacin on the photosynthesis reactions in microalga Scenedesmus quadricauda (Turp.) Bréb.

Ciprofloxacin (CIP) is widely used broad-spectrum antimicrobial drug of fluoroquinolone family. The widespread use of ciprofloxacin increases its release into the environment. Ciprofloxacin is detected in aquatic ecosystems potentially harming aquatic organisms. The CIP effect on photosynthetic organisms is not fully studied. In this study we examined the CIP effect on green freshwater microalgae Scenedesmus quadricauda (Turp.) Bréb. using chlorophyll fluorescence methods (JIP test parameters and rapid light curves). A significant decrease in the cell number was observed at ≥10 mg/L of сiprofloxacin in comparison with control. Analysis of chlorophyll fluorescence parameters obtained from OJIP transients revealed the changes in photosynthetic reactions in сiprofloxacin treatment. Ciprofloxacin was found to inhibit electron transport rate in photosystem II (PSII). The decrease in the quantum yield of electron transport in photosystem II (φEo) was accompanied by the decrease in performance index (PIABS) and an increase in energy dissipation (DI0/RC). Ciprofloxacin enhanced the photosensitivity of microalgae but did not inhibit the recovery of photosynthetic activity after the photooxidative stress. In this regard the effect of CIP differs from that of the well-known antibiotic chloramphenicol that inhibits the resynthesis of plastid proteins and, accordingly, the recovery of photosynthetic activity associated with the resynthesis of PSII protein D1. Among the fluorescence parameters, PIABS was found to be the most stress-specific; therefore it can be proposed to detect an early toxic CIP effect in microalgae.

Response of photosynthetic pigments, gas exchange and chlorophyll fluorescence parameters to light quality in Phoebe bournei seedlings

Response of photosynthetic pigments, gas exchange and chlorophyll fluorescence parameters to light quality in Phoebe bournei seedlings

Responses of leaf traits to altitude in Quercus aquifolioides and Sorbus rehderiana on the eastern edge of the Qinghai-Tibet Plateau, China.

As the most senstitive plant organs to environmental changes, leaves serve as crucial indicators of plant survival strategies. We measured the morphology, anatomical traits, gas exchange parameters, and chlorophyll fluorescence parameters of Quercus aquifolioides (evergreen broad-leaved) and Sorbus rehderiana (deciduous broad-leaved) at altitudes of 2600, 2800, 3000, 3200 and 3400 m on the eastern edge of the Qinghai-Tibet Plateau, China. We explored the similarity and difference in their responses to altitude change and the ecological adaptation strategy. The results showed that as the altitude increased, leaf dry matter content of Q. aquifolioides decreased, that of S. rehderiana increased, leaf size for both species gradually decreased, and the palisade coefficient of Q. aquifolioides showed a decreasing trend, contrasting with the increasing trend in S. rehderiana. As the altitude increased, the thickness of leaves, palisade tissue, spongy tissue, upper epidermis, and lower epidermis of both species increased significantly, with the increment of 22.4%, 4.9%, 45.1%, 23.3%, 19.6%, and 28.2%, 46.9%, 8.9%, 25.9%, 20.8% at altitude of 3400 m, respectively, compared with the altitude of 2600 m. The gas exchange and chlorophyll fluorescence parameters of S. rehderiana significantly increased with increasing altitude, while Q. aquifolioides showed the opposite trend. Leaf anatomical traits, gas exchange, and chlorophyll fluorescence parameters of both species displayed considerable plasticity. There were significant correlations among most leaf traits and between leaf traits and altitude. The survival strategy of Q. aquifolioides was more conservative in response to altitude changes, while that of S. rehderiana was more active. Both species adapted to different altitudes by adjusting their own traits.

Comparative physiological and anatomical responses of Tagetes erecta L. and Zinnia elegans Jacq. seedlings to AgNO3 and ZnSO4 metals and their nanoparticles

Heavy metals (HMs) pose a significant ecological risk due to their enduring presence in the ecosystem. They become more prevalent as a result of urbanization and industrialization, disrupting critical functions of plant life such as photosynthesis, seedling growth, and germination. Understanding the impact of HMs and nanoparticle exposure on plants is crucial for developing effective strategies to mitigate their potential hazards. Therefore, an effort was made to elucidate the impact of biosynthesized Ag NPs (nanoparticles) and ZnO NPs versus their precursor metal salts, AgNO3 and ZnSO4, respectively on two Asteraceous plants, Mexican marigold (Tagetes erecta L.) and Zinnia (Zinnia elegans Jacq.) in hydroponic solution by monitoring the changes in photosynthetic pigments and their associated photochemistry of photosystem II along with the anatomical attributes. In the present study, two concentrations (50 μM and 100 μM) for each treatments viz., AgNO3, Ag NPs, ZnSO4 and ZnO NPs were given to the seedlings. Metal salts were found to be more toxic than their nanoparticles, and this was manifested in terms of reduction in photosynthetic pigments, especially chlorophylla content (by 32% in marigold and 27% in Zinnia upon exposure to 100 µM of AgNO3, respectively) in both test seedlings. Reduction in chlorophyll fluorescence parameters was also found under metal as well as nanoparticle toxicity. In contrast, energy flux parameters such as absorption of photon per active reaction centre (ABS/RC), trapped energy flux per active reaction centre (TR0/RC), electron transport flux per active reaction centre (ET0/RC) and energy dissipation flux per active reaction centre (DI0/RC) increased significantly to cope with stress toxicity. Similarly, metals and nanoparticles also distorted the anatomy of the root and leaf, and the effect was more intense under AgNO3 treatment than with ZnSO4 in Zinnia. In conclusion, Zinnia seedlings were more resilient towards all the tested conditions, which might be attributed to their adaptability to various environmental factors, indicating their potential for thriving in diverse climates.

Towards a comprehensive understanding of zinc tolerance in Limonium brasiliense as a useful tool for environmental remediation and monitoring.

Heavy metal pollution is a serious environmental problem worldwide, creating the necessity to find eco-friendly strategies for monitoring and remediating environments. This study aimed to evaluate morphological, physiological, and biochemical responses as indicative of Zn tolerance in Limonium brasiliense and to determine the ability of this halophyte to accumulate different concentrations of Zn (0, 100, and 200 μM) in hydroponic conditions. The leaf shape at high Zn concentration showed enlarged petioles and lanceolate blades, whereas the leaf size was reduced. Water content, chlorophyll fluorescence parameters, and pigment content decreased with Zn addition. Of the antioxidant activities, only APx increased 75% compared to the control by Zn stress. Zn concentration was higher in aerial structures than in roots (BAC>1 and TF>1), suggesting that L. brasiliense could function as an accumulator of Zn. Its great ability to resist metal stress and its strong capacity to protect itself against high Zn concentration postulate it as a good phytoremediation of environments enriched with Zn. The study emphasizes using leaf morphology as an early biomonitoring tool for detecting Zn pollution, providing more evidence of their potential use as a biomarker for evaluating and assessing ecosystem health in biomonitoring programs.

Effects of Different Biostimulants on Growth and Development of Grapevine Seedlings under High-Temperature Stress

High temperatures significantly affect the growth and development of grapevines, cause irreversible damage to plants, and severely impact grape production and quality. Biostimulants can promote the growth of plants and enhance their resistance to adverse stress. However, the effects of biostimulants on grapevines under high temperatures have not been studied in detail. To analyze the effects of various biostimulants on the growth and development of grape seedlings under high temperatures, we measured chlorophyll fluorescence parameters with observed seedling phenotypes under high temperatures in open field conditions in Turpan. We conducted a comprehensive analysis of the effects of different biostimulants on the growth, development, and photosynthesis of grapevine seedlings. Our study aimed to provide scientific evidence to improve cultivation methods for grapevines under high-temperature stress. The results revealed that biostimulants have a positive effect on promoting the growth of grapevine seedlings under high-temperature stress conditions. They also positively affect the accumulation of chlorophyll components in grapevine leaves, inhibiting chlorophyll degradation and maintaining photosynthesis. However, the effects of different biostimulants were inconsistent. A comprehensive analysis revealed the following effectiveness order: T2 > T1 > T3 > Control. These findings suggest that T2 is the most effective in alleviating high-temperature stress and promoting grapevine growth. We recommend the use of T2 to improve the cultivation of grapevine seedlings during high-temperature periods. This has implications for grape production in hot and arid climatic areas.

Bacteria Associated with Spores of Arbuscular Mycorrhizal Fungi Improve the Effectiveness of Fungal Inocula for Red Raspberry Biotization

Intensive crop production leads to the disruption of the symbiosis between plants and their associated microorganisms, resulting in suboptimal plant productivity and lower yield quality. Therefore, it is necessary to improve existing methods and explore modern, environmentally friendly approaches to crop production. One of these methods is biotization, which involves the inoculation of plants with appropriately selected symbiotic microorganisms which play a beneficial role in plant adaptation to the environment. In this study, we tested the possibility of using a multi-microorganismal inoculum composed of arbuscular mycorrhizal fungi (AMF) and AMF spore-associated bacteria for biotization of the red raspberry. Bacteria were isolated from the spores of AMF, and their plant growth-promoting properties were tested. AMF inocula were supplemented with selected bacterial strains to investigate their effect on the growth and vitality of the raspberry. The investigations were carried out in the laboratory and on a semi-industrial scale in a polytunnel where commercial production of seedlings is carried out. In the semi-industrial experiment, we tested the growth parameters of plants and physiological response of the plant to temporary water shortage. We isolated over fifty strains of bacteria associated with spores of AMF. Only part of them showed plant growth-promoting properties, and six of these (belonging to the Paenibacillus genus) were used for the inoculum. AMF inoculation and co-inoculation of AMF and bacteria isolated from AMF spores improved plant growth and vitality in both experimental setups. Plant dry weight was improved by 70%, and selected chlorophyll fluorescence parameters (the contribution of light to primary photochemistry and fraction of reaction centre chlorophyll per chlorophyll of the antennae) were increased. The inoculum improved carbon assimilation, photosynthetic rate, stomatal conductance and transpiration after temporary water shortage. Raspberry biotization with AMF and bacteria associated with spores has potential applications in horticulture where ecological methods based on plant microorganism interaction are in demand.

Deciphering the Enhancing Impact of Exogenous Brassinolide on Physiological Indices of Melon Plants under Downy Mildew-Induced Stress.

Melon (Cucumis melo L.) is a valuable horticultural crop of the Cucurbitaceae family. Downy mildew (DM), caused by Pseudoperonospora cubensis, is a significant inhibitor of the production and quality of melon. Brassinolide (BR) is a new type of phytohormone widely used in cultivation for its broad spectrum of resistance- and defense-mechanism-improving activity. In this study, we applied various exogenous treatments (0.5, 1.0, and 2.0 mg·L-1) of BR at four distinct time periods (6 h, 12 h, 24 h, and 48 h) and explored the impact of BR on physiological indices and the genetic regulation of melon seedling leaves infected by downy-mildew-induced stress. It was mainly observed that a 2.0 mg·L-1 BR concentration effectively promoted the enhanced photosynthetic activity of seedling leaves, and quantitative real-time polymerase chain reaction (qRT-PCR) analysis similarly exhibited an upregulated expression of the predicted regulatory genes of photosystem II (PSII) CmHCF136 (MELO3C023596.2) and CmPsbY (MELO3C010708.2), thus indicating the stability of the PSII reaction center. Furthermore, 2.0 mg·L-1 BR resulted in more photosynthetic pigments (nearly three times more than the chlorophyll contents (264.52%)) as compared to the control and other treatment groups and similarly upregulated the expression trend of the predicted key enzyme genes CmLHCP (MELO3C004214.2) and CmCHLP (MELO3C017176.2) involved in chlorophyll biosynthesis. Meanwhile, the maximum contents of soluble sugars and starch (186.95% and 164.28%) were also maintained, which were similarly triggered by the upregulated expression of the predicted genes CmGlgC (MELO3C006552.2), CmSPS (MELO3C020357.2), and CmPEPC (MELO3C018724.2), thereby maintaining osmotic adjustment and efficiency in eliminating reactive oxygen species. Overall, the exogenous 2.0 mg·L-1 BR exhibited maintained antioxidant activities, plastid membranal stability, and malondialdehyde (MDA) content. The chlorophyll fluorescence parameter values of F0 (42.23%) and Fv/Fm (36.67%) were also noticed to be higher; however, nearly three times higher levels of NPQ (375.86%) and Y (NPQ) (287.10%) were observed at 48 h of treatment as compared to all other group treatments. Increased Rubisco activity was also observed (62.89%), which suggested a significant role for elevated carbon fixation and assimilation and the upregulated expression of regulatory genes linked with Rubisco activity and the PSII reaction process. In short, we deduced that the 2.0 mg·L-1 BR application has an enhancing effect on the genetic modulation of physiological indices of melon plants against downy mildew disease stress.

Glucose-G protein signaling plays a crucial role in tomato resilience to high temperature and elevated CO2.

Global climate change is accompanied by carbon dioxide (CO2) enrichment and high temperature (HT) stress; however, how plants adapt to the combined environments and the underlying mechanisms remain largely unclear. In this study, we show that elevated CO2 alleviated plant sensitivity to HT stress, with significantly increased apoplastic glucose (Glc) levels in tomato (Solanum lycopersicum) leaves. Exogenous Glc treatment enhanced tomato resilience to HT stress under ambient CO2 conditions. Cell-based biolayer interferometry, subcellular localization, and Split-luciferase assays revealed that Glc bound to the tomato regulator of G protein signaling 1 (RGS1) and induced RGS1 endocytosis and thereby RGS1-G protein α subunit (GPA1) dissociation in a concentration-dependent manner. Using rgs1 and gpa1 mutants, we found that RGS1 negatively regulated thermotolerance and was required for elevated CO2-Glc-induced thermotolerance. GPA1 positively regulated the elevated CO2-Glc-induced thermotolerance. A combined transcriptome and chlorophyll fluorescence parameter analysis further revealed that GPA1 integrated photosynthesis- and photoprotection-related mechanisms to regulate thermotolerance. These results demonstrate that Glc-RGS1-GPA1 signaling plays a crucial role in the elevated CO2-induced thermotolerance in tomato. This information enhances our understanding of the Glc-G protein signaling function in stress resilience in response to global climate change and will be helpful for genetic engineering approaches to improve plant resilience.

Effects of summer pruning on the growth and photosynthetic characteristics of pepper (Capsicum annuum L.)

The objective of the study is to investigate the mechanism by which summer pruning enhances the growth of pepper plants, as indicated by growth and fruit appearance indicators, photosynthetic rate and gas exchange parameters, rapid light response and induction kinetics curves and the related chlorophyll fluorescence parameters. The results indicated that the leaf growth rate, the individual pepper fruit weight, and the fruit longitudinal and cross diameters of the pruned group were significantly higher than those of the control. The stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) of the pruned group were significantly higher than those of the control. The initial slope of the rapid light response curve, which represents light energy utilisation efficiency (α), the maximum electron transfer rate (Jmax) and saturated light intensity (PARsat) were all higher in the summer pruning group than in the control group. The F0 of the pruned group decreased by 16.83%, Fv/F0 increased by 23.69%, PIabs increased by 58.33%, and DIo/RC decreased by 22.09% compared to the control group. In summary, summer pruning significantly improves the leaf growth rate and fruit appearance quality of pepper, effectively promotes the photosynthesis of functional leaves, and reduces the degree of stress under adverse environmental conditions.

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.

Non-invasive measurements to identify mungbean genotypes for waterlogging tolerance.

As the best-fit leguminous crop for intercropping across time and space, mungbean promises to sustain soil health, carbon sequestration, and nutritional security across the globe. However, it is susceptible to waterlogging, a significant constraint that persists during heavy rains. Since the predicted climate change scenario features fewer but more intense rainy days. Hence, waterlogging tolerance in mungbean has been one of the major breeding objectives. The present experiment aimed to employ non-destructive tools to phenotype stress tolerance traits in mungbean genotypes exposed to waterlogging and estimate the association among the traits. A total of 12 mungbean genotypes were used in the present study to assess waterlogging tolerance at the seedling stage. Plant responses to stress were determined non-destructively using normalized difference vegetation index (NDVI) and chlorophyll fluorescence parameters at different time intervals. NDVI and grain yield were positively associated with control (r = 0.64) and stress (r = 0.59). Similarly, chlorophyll fluorescence (quantum yield of PS-II) also had a significant positive association with grain yield under both control (r = 0.52) and stress (r = 0.66) conditions. Hence, it is suggested that NDVI and chlorophyll fluorescence promise to serve as traits for non-destructive phenotyping waterlogging tolerance in mungbean genotypes. With the methods proposed in our study, it is possible to phenotype hundreds of plants for waterlogging tolerance efficiently.

Photosynthesis-related Parameters in Leucobryum aduncum Moss Bags as Bioindicators of Environmental Stress Caused by Road Traffic

The physiological response in moss samples is often used as an early warning signal of environmental stress caused by air pollution. This study aimed to test the efficiency of photosynthesis-related parameters in Leucobryum aduncum moss bags as bioindicators of environmental stress related to road traffic. The moss samples were collected and prepared in a relatively unpolluted area and then transplanted at 7 sites in forested, rural, and urban areas. The moss samples were picked up after being exposed for 1 and 3 months for physiological measurements. The results showed that the average values of all physiological parameters were highest in the forested area and lowest in the urban area. All parameters at most roadside (R site) sites were lower or significantly lower than those at the site away from the road (A site). This was particularly true for the 3-month exposure period, suggesting that the length of exposure should be longer than 1 month, but exposure up to 3 months could fully damage the photosystem II (PSII) and destroy the moss bags. The vitality index (VI) also clearly indicated that the moss bags were more affected in the urban area, at the R sites, and at the 3-month exposure. Among all six parameters, the most susceptible parameter was the chlorophyll fluorescence parameter (Fv/Fm), followed by the total carotenoids, chlorophyll a, total chlorophylls, chlorophyll b, and chlorophyll a degradation (OD435/OD415). The moss bag technique used in this study did not negatively affect the studied physiological parameters, but a great elevation difference could affect the moss bag physiology. This study illustrated that the photosynthesis-related parameters of L. aduncum moss bags can be used as effective bioindicators of environmental stress caused by road traffic. This study is among the priority studies of moss bioindication of air pollution in Thailand and can pave the way for future studies.