Chlorophyll Fluorescence Yield Research Articles

The usage of physiological methods in the creation of soybean varieties

The results of a study of the operation of photosystem II in the leaves of nine soybean varieties bred by the All-Russian Research Institute of Soybean are presented in order to identify genotypes with increased photosynthetic activity for inclusion in the breeding process when creating highly productive varieties of a new generation. A comparative assessment of varieties is given in terms of effective quantum yield of photosynthesis (Y) and chlorophyll fluorescence (F0), relative electron transport rate (ETR) and photochemical energy conversion depending on light saturation. The soybean varieties Gracia, Sonata and Kitrossa had the highest indicators for the studied parameters, significantly exceeding the standard variety Lydia. The effective quantum yield of photosynthesis, which shows the degree of absorption of solar energy, in the Gracia and Sonata varieties during the entire growing season was at the level of 0.80–0.83 rel. units, with this indicator exceeding for the Lydia variety by 0.09–0.13 rel. units depending on the phase of plant growth and development. The quantum yield of fluorescence (F0) in the leaves of the Lydia variety during the flowering phase exceeded the Gracia, Sonata and Kitrossa varieties by 60, 56 and 63%, respectively, which indicates a reduced activity of photosystem II in this variety. The efficiency of photochemical conversion of photosynthetic energy during the flowering phase was most stable in the leaves of the Sonata variety at light levels from 600 to 1500 µmol quanta/(m2∙s). Using the soybean variety Gratsia as the maternal form (♀) when crossed with the hybrid Am.2146, which was obtained with the inclusion of the Sonata variety in the hybridization, which also has a high degree of absorption of light quanta, the Radiant variety was create. Variety passed testing in 2021–2022, and in 2023 included in the State Register of Breeding Achievements for cultivation in the Far Eastern (12) region.

Flash-kinetics as a complementary analytical tool in PAM fluorimetry.

A new measuring system based on the already existing Multi-Color-PAM Fluorimeter (Schreiber et al. in Photosynth Res 113:127-144, 2012) was developed that in addition to standard PAM measurements enables pump-and-probe flash measurements and allows simultaneous measurements of the changes in chlorophyll fluorescence yield (F) during application of saturating flashes (ST). A high-power Chip-on-Board LED array provides ST flashes with close to rectangular profiles at wide ranges of widths (0.5µs to 5ms), intensities (1.3mmol to 1.3mol 440nm quanta m-2s-1) and highly flexible repetition times. Using a dedicated rising-edge profile correction, sub-µs time resolution is obtained for assessment of initial fluorescence and rise kinetics. At maximal to moderate flash intensities the flash-kinetics (changes of F during course of ST, STK) are strongly affected by 'High Intensity Quenching' (HIQ), consisting of Car-triplet quenching, TQ, and donor-side-dependent quenching, DQ. The contribution of TQ is estimated by application of a second ST after 20µs dark-time. Upon application of flash trains (ST sequences with defined repetition times) typical period-4 oscillations in dark fluorescence yield (F0) and ST-induced fluorescence yield, FmST, are obtained which can be measured in vivo both with suspensions and from the surface of leaves. Examples of application with dilute suspensions of Chlorella and an intact dandelion leaf are presented. It is shown that weak far-red light (730-740nm) advances the S-state distribution of the water-splitting system by one step, resulting in substantial lowering of FmST and also of the I1-level in the polyphasic rise of fluorescence yield induced by a multiple-turnover flash (MT). Based on comparative measurements of STK and the polyphasic rise kinetics with the same Chlorella sample, it is concluded that the generally observed lower values of maximal fluorescence yields using ST-protocols compared to MT-protocols are due to a higher extent of HIQ (mainly DQ) and the contribution of variable PSI fluorescence to FmST.

The Respective Effects of Vapor Pressure Deficit and Soil Moisture on Ecosystem Productivity in Southwest China

This study aims to examine the individual and combined effects of soil moisture (SM) and vapor pressure deficit (VPD) on ecosystem productivity in Southwest China. Utilizing the community land model (CLM) to simulate the regional soil moisture and vapor pressure deficit, we analyzed their impacts on ecosystem productivity through a data binning approach and employed sun-induced chlorophyll fluorescence yield (SIFyield) as a productivity indicator. Our findings highlight a significant coupling effect between SM and VPD, which diminishes with finer temporal data resolution. The data binning analysis indicates that VPD has a predominant influence on SIFyield across 70% of the study area, whereas SM is more influential in the remaining 30%. Notably, the correlation between SIFyield and SM, modulated by VPD, is stronger in forest and shrubland ecosystems, whereas in grasslands, the influence pattern is reversed, with VPD having a more significant impact. The study concludes that in Southwest China, ecosystem productivity is more significantly affected by VPD than by SM.

Electrical signals of the plasma membrane and their effect on chlorophyll fluorescence in <i>chara</i> chloroplasts <i>in vivo</i>

Action potentials of plant cells are involved in regulation of many cell processes, such as photosynthesis and cytoplasmic streaming. Excitable cells of characean algae submerged in media with elevated K+ content are able to generate hyperpolarizing electrical responses. This active response of plasma membrane arises upon the passage of inward electric current comparable in extent to natural currents circulating in illuminated Chara internodes. It remains currently unknown whether the hyperpolarizing electrical signals in Chara affect the photosynthetic activity. Here we show that the negative shift of cell membrane potential, which causes the K+ influx into the cytoplasm, is accompanied by a delayed decrease in the effective chlorophyll fluorescence yield (F′) and maximal yield (Fm′) under low background light (12.5 µmol m-2 s-1). The transient changes in F′ and Fm′ were evident under illumination only, which indicates their close relation to photosynthetic energy conversion in chloroplasts. The passage of inward current caused an increase in pH at the cell surface (pHo), which reflects a high H+/OH- conductance of the plasmalemma and points to the decrease in cytoplasmic pH due to H+ entry into the cell. The shifts in pHo arising in response to the first hyperpolarizing pulse disappeared upon repeated stimulations, thus indicating the long-term inactivation of plasmalemmal H+/OH- conductance. Despite the suppression of plasmalemmal H+ fluxes, the hyperpolarizing responses and the analyzed chlorophyll fluorescence changes did not disappear. The results indicate the participation of K+ flows between the outer medium, cytoplasm, and stroma in chloroplast functional changes that are reflected by the dynamics of F′ and Fm′.

Water availability and atmospheric dryness controls on spaceborne sun-induced chlorophyll fluorescence yield

Climate change is amplifying the duration, frequency, and intensity of droughts, harming global ecosystems. During droughts, plants can close their stomata to save water, at the expense of a reduced carboxylation rate. When in a carboxylation-limited regime, plants benefit from an increase in water availability, as it increases their photosynthetic rate. The sun-induced chlorophyll fluorescence (SIF) signal, measurable from satellites, is mechanistically linked to this rate. Like canopy photosynthesis, SIF carries an imprint from the available irradiation (PAR) as well as the canopy structure and the efficiency of the photosynthesis at the photosystem level. Normalizing the global TROPOMI SIF observations with TROPOMI reflectance and MODIS Normalised Difference Vegetation Index (NDVI) data, we extracted the fluorescence quantum yield (ϕF), which lab-scale experiments have found to be linked to the photosynthetic electron transport. Plant physiologists have long proved the photosynthetic electron transport to be sensitive to plant water status. Here, the plant water status is controlled by the soil moisture (SM) and the vapour pressure deficit (VPD). Combining data from the TROPOMI, AIRS and SMAP satellite sensors, this study describes how SM and VPD control the ϕF at the global scale. We identify a VPD range (VPD<1.5 kPa) in which the ϕF is mainly controlled by VPD, and another (VPD>1.5 kPa) in which the ϕF is co-regulated by SM and VPD. The precise values of this range, as well as the magnitude of ϕF values, are modulated by the plant isohydricity. To gain a deeper understanding of the link between ϕF and photosynthetic efficiency at large scale, we used the link between ϕF and data on the canopy conductance (Gs), which were calculated using remote sensing data-driven models. A comparison found that the ϕF-Gs relationship at large scale is in line with the ϕF-Gs relationship described in plant-level studies.

Monitoring low O2 stress in apples – What we can learn from chlorophyll fluorescence and respiratory characteristics

Dynamic controlled atmosphere (DCA) is becoming a storage method of choice for apple producers seeking to store long-term. There is limited prior work comparing DCA monitoring chlorophyll fluorescence yield (DCA-CF) and respiratory characteristics (DCA-RQ), particularly for the popular UK-grown apple cultivars ‘Gala’ and ‘Braeburn’. However, these techniques can give an insight into the physiological response of apples to low O2 storage, which could help to design more efficient and sustainable storage regimes. In this study the chlorophyll fluorescence (CF) and respiratory quotient (RQ) responses of ‘Gala’ and ‘Braeburn’ are compared in typical and exaggerated DCA conditions. Results show that not only do the two techniques differ in their detection of low O2 stress but the two cultivars studied also differ noticeably in their behaviour. CF increase was confirmed to be a reaction to a stress signal from inside the fruit. Respiration rate curves were found to reflect the internal structure of the fruit, with ‘Gala’’s more homogeneous tissues and greater gas permeability resulting in a strongly bimodal O2 consumption rate where the change in rate hypothetically corresponds with the majority of the fruit tissue switching to anaerobic respiration at the same time. CF and RQ showed noticeable differences between cultivars, agreeing with previous observations that ‘Braeburn’ is less tolerant of low O2 and elevated CO2 than ‘Gala’ (CF Lower O2 Limit (LOL) for Braeburn of approximately 0.75 kPa O2 relative to 0.5 kPa O2 for Gala). Additionally, the CF and RQ responses indicated different LOLs for ‘Gala’, at approximately 0.5 kPa O2 for CF and 0.25 kPa O2 for RQ. Elevated CO2 depressed both the CF and RQ response, with a strong depressive effect on the rate of CO2 evolution but little effect on the rate of O2 consumption.

Electrical Signals at the Plasma Membrane and Their Influence on Chlorophyll Fluorescence of Chara Chloroplasts in vivo.

Action potentials of plant cells are engaged in the regulation of many cell processes, including photosynthesis and cytoplasmic streaming. Excitable cells of characean algae submerged in a medium with an elevated K+ content are capable of generating hyperpolarizing electrical responses. These active responses of plasma membrane originate upon the passage of inward electric current comparable in strength to natural currents circulating in illuminated Chara internodes. So far, it remained unknown whether the hyperpolarizing electrical signals in Chara affect the photosynthetic activity. Here, we showed that the negative shift of cell membrane potential, which drives K+ influx into the cytoplasm, is accompanied by a delayed decrease in the actual yield of chlorophyll fluorescence F' and the maximal fluorescence yield Fm' under low background light (12.5 µmol m-2 s-1). The transient changes in F' and Fm' were evident only under illumination, which suggests their close relation to the photosynthetic energy conversion in chloroplasts. Passing the inward current caused an increase in pH at the cell surface (pHo), which reflected high H+/OH- conductance of the plasmalemma and indicated a decrease in cytoplasmic pH due to the H+ entry into the cell. The shifts in pHo arising in response to the first hyperpolarizing pulse disappeared upon repeated stimulation, thus indicating the long-term inactivation of plasmalemmal H+/OH- conductance. Suppression of plasmalemmal H+ fluxes did not abolish the hyperpolarizing responses and the analyzed changes in chlorophyll fluorescence. These results suggest that K+ fluxes between the extracellular medium, cytoplasm, and stroma are involved in the functional changes of chloroplasts reflected by transients of F' and Fm'.

Nano-Fe nutrition improves soybean physiological characteristics, yield, root features and water productivity in different planting dates under drought stress conditions

Soybean production as an oil and protein crop, especially in water limited conditions, is of global importance. Suitable Nano-iron fertilizer application method can be a useful nutrition technique under water limitation stress. The aim of this study was to investigate the response of yield, physiological and morphological characteristics of soybean to drought stress, planting date and nutrition with iron Nano-oxide in two separate experiments (i.e. 2-year field and a pot) in 2021–2022. Field experiments included planting date (April 09: early planting date, May 05: optimum planting date and June 10: late planting date), nutrition with iron Nano-oxide (control, seed priming 300 ppm, foliar spraying 15 ppm, priming 300 ppm + foliar spraying 15 ppm) and drought stress (100 %, 75 % and 50 % FC). In the pot experiment, all field treatments were applied except planting date. Then, morphological and biochemical characteristics of the root were investigated. The results showed that drought stress, planting date and different methods of iron Nano-oxide nutrition had significant effects on gas exchanges, chlorophyll fluorescence, antioxidant activity and grain yield. The highest gas exchanges, net photosynthesis rate, the maximum photosystem quantum efficiency (FV/Fm) and grain yield were obtained by iron Nano-oxide nutrition as seed priming + spraying in optimum planting date and 100 % FC. However, these traits were decreased with increasing drought intensity (50 % FC), non-use of iron Nano-oxide (control) in early planting date. By increasing the drought severity in the field to 50 % FC, the antioxidant enzyme’s activity increased. The highest activity of catalase and superoxide dismutase were observed in early planting date + non-use of iron Nano-oxide +50 % FC. Based on the results of the pot test, the highest root length, number of nitrogen-fixing nodules, root dry weight, and nitrogenase activity were observed by iron Nano-oxide nutrition (nano priming 300 ppm + 15 ppm spraying) under 100 % FC. The mentioned parameters were reduced by drought, but the number of root branches increased. Combined nutrition (priming + spraying) had more positive effects on the root's morphological and biochemical properties compared with iron spraying only. The water productivity increased due to late plantings, but the negative effect of early planting on this indicator was higher. The maximum water productivity (0.73 kg/m3) obtained from iron Nano-oxide nutrition (seed priming 300 ppm + foliar spraying 15 ppm) in late planting date under 50 % FC conditions and its lowest (0.35 kg/m3) in no iron Nano-oxide nutrition in early planting date under 100 % FC. In general, the optimum planting date (05 May), supply of 100 % FC and combined iron Nano-oxide nutrition (seed priming + foliar application) is suggestible for soybean (Kosar cultivar) production in the climate conditions like the present study.

High-Night Temperature-Induced Changes in Chlorophyll Fluorescence, Gas Exchange, and Leaf Anatomy Determine Grain Yield in Rice Varieties

High-Night Temperature-Induced Changes in Chlorophyll Fluorescence, Gas Exchange, and Leaf Anatomy Determine Grain Yield in Rice Varieties

Transcriptome profiling disclosed the effect of single and combined drought and heat stress on reprogramming of genes expression in barley flag leaf.

Despite numerous studies aimed at unraveling the genetic background of barley's response to abiotic stress, the modulation of the transcriptome induced by combinatorial drought and increased temperature remains largely unrecognized. Very limited studies were done, especially on the flag leaf, which plays an important role in grain filling in cereals. In the present study, transcriptome profiles, along with chlorophyll fluorescence parameters and yield components, were compared between barley genotypes with different flag leaf sizes under single and combined drought and heat stress. High-throughput mRNA sequencing revealed 2,457 differentially expressed genes, which were functionally interpreted using Gene Ontology term enrichment analysis. The transcriptomic signature under double stress was more similar to effects caused by drought than by elevated temperature; it was also manifested at phenotypic and chlorophyll fluorescence levels. Both common and stress-specific changes in transcript abundance were identified. Genes regulated commonly across stress treatments, determining universal stress responses, were associated, among others, with responses to drought, heat, and oxidative stress. In addition, changes specific to the size of the flag leaf blade were found. Our study allowed us to identify sets of genes assigned to various processes underlying the response to drought and heat, including photosynthesis, the abscisic acid pathway, and lipid transport. Genes encoding LEA proteins, including dehydrins and heat shock proteins, were especially induced by stress treatments. Some association between genetic composition and flag leaf size was confirmed. However, there was no general coincidence between SNP polymorphism of genotypes and differential expression of genes induced by stress factors. This research provided novel insight into the molecular mechanisms of barley flag leaf that determine drought and heat response, as well as their co-occurrence.

Effects of neodymium magneto-priming on seed germination and salinity tolerance in tomato.

Earth's biosphere is surrounded by magnetic fields that affect all living organisms. A plant's response to magnetic fields is displayed in terms of its seed's vigor, growth, and yield. Examining seed germination in such magnetic fields is the first step in the investigation of how magnetic fields might be used to enhance plant growth and maximize crop performance. In this study, salinity-sensitive Super Strain-B tomato seeds were primed with the northern and southern poles of neodymium magnets of 150, 200, and 250 mT. The magneto-primed seeds showed a significant increase in germination rate and speed, where the orientation of the magnet was identified as being crucial for germination rate and the orientation of seeds towards the magnet was shown to affect the germination speed. The primed plants exhibited enhanced growth characteristics, including longer shoots and roots, larger leaf area, more root hairs, higher water content, and more tolerance to salinity levels, up to 200 mM NaCl. All magneto-primed plants showed a significant decrease in chlorophyll content, continuous chlorophyll fluorescence yield (Ft), and quantum yield (QY). The salinity treatments decreased all chlorophyll parameters in control plants, significantly, but did not lower such parameters in magneto-primed tomatoes. The results of this study illustrate the positive effects of neodymium magnet on the growth and development of tomato plants in terms of their germination, growth, and salinity tolerance, and negatively affected the chlorophyll content in tomato leaves. © 2023 Bioelectromagnetics Society.

Seasonal Variation in Physiological Traits of Amazonian Coffea canephora Genotypes in Cultivation Systems with Contrasting Water Availability

Climate variation throughout the year affects photosynthesis and other physiological processes correlated with plant development and yield. This study aimed to evaluate the changes in the physiological attributes of Coffea canephora genotypes over the year in the Brazilian Amazon and assess their relationship with crop yield. The experiment was carried out in three cultivation systems with three genotypes. The evaluations were carried out in four periods: the peak of the dry season (S1); the beginning of the rainy season (S2); the peak of the rainy season (S3); and the beginning of the dry season (S4). A dataset of gas exchange, pigment indices, chlorophyll fluorescence, branch growth, and coffee yield was obtained. The group of gas exchange variables was the main contributor to treatment discrimination and was most affected by seasons. As expected, the values of gs, E, and A were significantly lower in S1, while the values of VPDLeaf-ar, TLeaf, and IWUE were significantly higher. Our results demonstrate that climatic seasonality affects the photosynthesis of Amazonian Robustas coffee, even under irrigated conditions, particularly in response to increased VPD. The physiological variables analyzed at the leaf level, even in different periods, did not explain the differences in the yield of C. canephora.

Physio-biochemical, agronomical, and gene expression analysis reveals different responsive approach to low nitrogen in contrasting rice cultivars for nitrogen use efficiency.

Nitrogen (N) is an essential macronutrient for plant growth and development as it is an essential constituent of biomolecules. Its availability directly impacts crop yield. Increased N application in crop fields has caused environmental and health problems, and decreasing nitrogen inputs are in demand to maintain crop production sustainability. Understanding the molecular mechanism of N utilization could play a crucial role in improving the nitrogen use efficiency (NUE) of crop plants. In the present study, the effect of low N supply on plant growth, physio-biochemical, chlorophyll fluorescence attributes, yield components, and gene expression analysis were measured at six developmental stages in rice cultivars. Two rice cultivars were grown with a supply of optimium (120kgha-1) and low N (60kgha-1). Cultivar Vikramarya excelled Aditya at low N supply, and exhibits enhanced plant growth, physiological efficiency, agronomic efficiency, and improved NUE due to higher N uptake and utilization at low N treatment. Moreover, plant biomass, leaf area, and photosynthetic rate were significantly higher in cv. Vikramarya than cv. Aditya at different growth stages, under low N treatment. In addition, enzymatic activities in cultivar Vikramarya were higher than cultivar Aditya under low nitrogen, indicating its greater potential for N metabolism. Gene expression analysis was carried out for the most important nitrogen assimilatory enzymes, such as nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT). Expression levels of these genes at different growth stages were significantly higher in cv. Vikramarya compared to cv. Aditya at low N supply. Our findings suggest that improving NUE needs specific revision in N metabolism and physiological assimilation. Overall differences in plant growth, physiological efficiency, biochemical activities, and expression levels of N metabolism genes in N-efficient and N-inefficient rice cultivars need a specific adaptation to N metabolism. Regulatory genes may separately or in conjunction, enhance the NUE. These results provide a platform for selecting crop cultivars for nitrogen utilization efficiency at low N treatment.

Interactive effect of water and nitrogen fertilization improve chlorophyll fluorescence and yield of maize

AbstractWater scarcity and excessive N fertilization have a negative effect on maize (Zea mays L.) production. Low water and N fertilization are the major problem in sustainable agriculture by limiting crop growth and development. However, the combined effect of N fertilization and supplementary irrigation on chlorophyll fluorescence and maize yield is still not understood. The objective of the study was to signify the effect of supplementary irrigation and N fertilization on leaf area index (LAI), relative chlorophyll content (SPAD), maximum photosynthetic capacity (Fv/Fm), photochemical quenching coefficient (qP), and yield. The experiment was conducted in a split‐plot design, with water management in main plot and N fertilization in subplot with three replications. Treatments included two water managements, that is, rainfed (natural rainfall) and irrigation water (70% field capacity). Five N fertilization rates were N0 (0 kg N ha−1), N150 (150 kg N ha−1), N200 (200 kg N ha−1), N250 (250 kg ha−1), and N300 (300 kg N ha−1). The LAI, SPAD, Fv/Fm, qP, and yield were significantly affected by water management, N rates, and their interaction (P &lt; .05). The LAI, SPAD, Fv/Fm, qP, total dry matter accumulation, and yield under supplementary irrigation were significantly increased by 10.99, 5.75, 6.57, 9.14, 15.64, and 14.58% than those under rainfed conditions, but the nonphotochemical quenching coefficient was significantly decreased by 22.82%. The 250 kg N ha−1 increased grain yield under irrigated conditions than that of other N treatments. The interaction between water management and N fertilization significantly and positively affected the SPAD, Fv/Fm, and grain yield in both years, but had no significant effect on LAI during 2021 and HI during 2020 and 2021. We concluded that N250 treatment with supplementary irrigation increased grain yield.

Improvement of Photosynthesis by Biochar and Vermicompost to Enhance Tomato (Solanum lycopersicum L.) Yield under Greenhouse Conditions

Chlorophyll fluorescence is an important tool in the study of photosynthesis and its effect on the physiological indicators of crop growth is worth exploring. The trial was conducted to investigate the effect of biochar (CK, 0%; BA3, 3%; BA5, 5%; by mass of soil) and vermicompost (VA3, 3%; VA5, 5%) on photosynthesis, chlorophyll fluorescence, and tomato yield under greenhouse condition. Results revealed that photosynthetic parameters and chlorophyll fluorescence traits of BA3, VA3, BA5, and VA5 were significantly higher than those of CK, and the improvement of vermicompost was more effective than biochar at the same application rate. VA3 treatment had the highest net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), variable fluorescence (Fv), maximum fluorescence (Fm), PSII maximum photochemical efficiency (Fv/Fm), PSII potential photochemical activity (Fv/Fo), absorption flux per cross section (CS; ABC/CSm), trapped energy flux per CS (TRo/CSm), and electron transport flux per CS (ETo/CSm), which increased by 49%, 65%, 17%, 12%, 4%, 25%, 10%, 15%, and 30%, respectively, compared with CK. The study also found that BA and VA rates could effectively improve tomato yield and water use efficiency (WUE). The yield under BA3, VA3, BA5, and VA5 treatments was 21%, 33%, 23%, and 25% higher than that under CK, and the WUE increased from 31.2 kg·m-3 under CK to 41.4 kg·m-3 under VA3. Pearson correlation analysis indicated that the increment of photosynthesis showed a highly significant correlation with Fv/Fo, ABC/CSm, TRo/CSm, and ETo/CSm and enhanced the light energy absorbed, trapped, and transported per CS of plant leaves, thereby contributing to the increase in tomato yield. Therefore, for one-season tomato production, the application of 3% vermicompost was considered economical with regard to improving photosynthesis, enhancing WUE, and increasing tomato yield.

Effects of Novel Photosynthetic Inhibitor [CuL2]Br2 Complex on Photosystem II Activity in Spinach.

The effects of the novel [CuL2]Br2 complex (L = bis{4H-1,3,5-triazino [2,1-b]benzothiazole-2-amine,4-(2-imidazole)}copper(II) bromide complex) on the photosystem II (PSII) activity of PSII membranes isolated from spinach were studied. The absence of photosynthetic oxygen evolution by PSII membranes without artificial electron acceptors, but in the presence of [CuL2]Br2, has shown that it is not able to act as a PSII electron acceptor. In the presence of artificial electron acceptors, [CuL2]Br2 inhibits photosynthetic oxygen evolution. [CuL2]Br2 also suppresses the photoinduced changes of the PSII chlorophyll fluorescence yield (FV) related to the photoreduction of the primary quinone electron acceptor, QA. The inhibition of both characteristic PSII reactions depends on [CuL2]Br2 concentration. At all studied concentrations of [CuL2]Br2, the decrease in the FM level occurs exclusively due to a decrease in Fv. [CuL2]Br2 causes neither changes in the F0 level nor the retardation of the photoinduced rise in FM, which characterizes the efficiency of the electron supply from the donor-side components to QA through the PSII reaction center (RC). Artificial electron donors (sodium ascorbate, DPC, Mn2+) do not cancel the inhibitory effect of [CuL2]Br2. The dependences of the inhibitory efficiency of the studied reactions of PSII on [CuL2]Br2 complex concentration practically coincide. The inhibition constant Ki is about 16 µM, and logKi is 4.8. As [CuL2]Br2 does not change the aromatic amino acids’ intrinsic fluorescence of the PSII protein components, it can be proposed that [CuL2]Br2 has no significant effect on the native state of PSII proteins. The results obtained in the present study are compared to the literature data concerning the inhibitory effects of PSII Cu(II) aqua ions and Cu(II)-organic complexes.

High-resolution dissection of photosystem II electron transport reveals differential response to water deficit and heat stress in isolation and combination in pearl millet [Pennisetum glaucum (L.) R. Br.

Heat and Water Deficit Stress (WDS) tend to impede and restrict the efficiency of photosynthesis, chlorophyll fluorescence, and maximum photochemical quantum yield in plants based on their characteristic ability to interfere with the electron transport system in photosystem II. Dissection of the electron transport pathway in Photosystem II (PSII) under water deficit and Heat Stress (HS) can be insightful in gaining knowledge on the various attributes of the photosynthetic performance of a plant. We attempt a high-resolution dissection of electron transport in PSII with studies on chlorophyll a fast fluorescence kinetics and non-photochemical quenching (NPQ) as a response to and recovery from these stresses in pearl millet [Pennisetum glaucum (L.) R. Br.] in isolation and combination. In this study, we bring out the mechanisms by which both heat and water stress, in isolation and in combination, affect the photosynthetic electron transport in Photosystem II. Our results indicate that oxygen evolution complex (OEC) damage is the primary effect of heat stress and is not seen with the same intensity in the water-stressed plants. Low exciton absorption flux in heat stress and combined stress was seen due to OEC damage, and this caused an electron transport traffic jam in the donor side of PS II. Both the specific energy flux model and the phenomenological flux model developed from the derived values in our study show that water deficit stress in combination with heat stress has a much stronger effect than the stresses in isolation on the overall electron transport pathway of the PS II in pearl millet plants.

Morphophysiological adjustments to shade of jaboticaba tree saplings

We aimed to verify the morphophysiological changes in jaboticaba tree (Plinia peruviana (Poir.) Govaerts) saplings under shade gradient to improve knowledge on the appropriate light environmental conditions for the saplings production and field homogeneous or intercropping cultivation of this species. The saplings were grown under full sun and artificial shade levels (30%, 50%, and 80%). Growth, photosynthetic pigments, gas exchanges, chlorophyll fluorescence, and leaf anatomy characters were evaluated. Our results showed that jaboticaba tree saplings growth was improved under full sun and 30% of shade. Under 50% and 80% shade the saplings demonstrate phenotypic plasticity, such as larger and thinner leaves. Chlorophyll fluorescence, chlorophyll content, and quantum yield of photosystem II were higher under higher shade level, but the CO2 assimilation rate was not different between light conditions. These changes are typically found in shade-tolerant plants and is related to perform photosynthesis more efficiently in highly variable light conditions. Despite that, we recommend that cultivation be carried out under full sun or up to 30% shade to maximize jaboticaba tree saplings growth in nurseries and orchards.

Different Responses of Solar-Induced Chlorophyll Fluorescence at the Red and Far-Red Bands and Gross Primary Productivity to Air Temperature for Winter Wheat

Solar-induced chlorophyll fluorescence (SIF) is closely related to the light-reaction process and has been recognized as a good indicator for tracking gross primary productivity (GPP). Nevertheless, it has not been widely examined how SIF and GPP respond to temperature. Here, we explored the linkage mechanisms between SIF and GPP in winter wheat based on continuous measurements of canopy SIF (cSIF), GPP, and meteorological data. To separately explore the structural and physiological mechanisms underlying the SIF–GPP relationship, we studied the temperature responses of the estimated light use efficiency (LUEp), canopy-level chlorophyll fluorescence yield (cSIFyield) and photosystem-level chlorophyll fluorescence yield (ΦF) estimated using canopy-scale remote sensing measurements. We found that GPP, red canopy SIF (cSIF688) and far-red canopy SIF (cSIF760) all exhibited a decreasing trend during overwintering periods. However, GPP and cSIF688 showed relatively more obvious changes in response to air temperature (Ta) than cSIF760 did. In addition, the LUEp responded sensitively to Ta (the correlation coefficient, r = 0.83, p-value &lt; 0.01). The cSIFyield_688 and ΦF_688 (ΦF at 688 nm) also exhibited significantly positive correlations with Ta (r &gt; 0.7, p-value &lt; 0.05), while cSIFyield_760 and ΦF_760 (ΦF at 760 nm) were weakly correlated with Ta (r &lt; 0.3, p-value &gt; 0.05) during overwintering periods. The results also show that LUEp was more sensitive to Ta than ΦF, which caused changes in the LUEp/ΦF ratio in response to Ta. By considering the influence of Ta, the GPP estimation based on the total SIF emitted at the photosystem level (tSIF) was improved (with R2 increased by more than 0.12 for tSIF760 and more than 0.05 for tSIF688). Therefore, our results indicate that the LUEp/ΦF ratio is affected by temperature conditions and highlights that the SIF–GPP model should consider the influence of temperature.

PROLINE INDUCED CHANGES IN REDOX BALANCE AND PHOTOSYNTHETIC ACTIVITY OF WHEAT (TRITICUM AESTIVUM L.) UNDER SALINE CONDITIONS

Salinity is a major environmental constraint that reduces plant development, growth, and yield. To appraise the potential role of foliar-applied proline as an alternative shotgun approach to ameliorate the adverse effects of salinity on wheat, a pot experiment was conducted under controlled environmental conditions using two wheat cultivars (Galaxy-13 salt-sensitive) and (Pasban-90 salt-tolerant). The experiment was laid out in a completely randomized design with the factorial arrangement and four replications. After ten days of germination, the plants were thinned to maintain six plant seedlings in each pot and the germinating seedlings were irrigated weekly with full strength Hoagland’s nutrient solution and salinity stress (NaCl) was applied after three weeks of germination. Foliar spray of proline (100 mM) was applied with the treatment of salinity. Salinity stress caused a significant reduction in morphological attributes like lengths and fresh weights of root and shoot, number of leaves and leaf area as well as yield attributes like spike length, number of spikelets per spike, number of grains per spike, yield per plant and 100 seed weight. Furthermore, chlorophyll fluorescence, chlorophyll contents, quantum yield, and electron transport rate (ETR) were also reduced by salt stress. However, foliar spray of 100 mM proline was the most effective to ameliorate the toxic effects of salinity by improving biomass production, chlorophyll fluorescence, chlorophyll contents, and quantum yield in both the cultivars. The findings confirmed the ability of foliar spray of proline to stimulate salt tolerance in wheat plants.