Chlorophyll Fluorescence Measurements Research Articles

Exploring Nitric Oxide as a Regulator in Salt Tolerance: Insights into Photosynthetic Efficiency in Maize.

The growing issue of salinity is a significant threat to global agriculture, affecting diverse regions worldwide. Nitric oxide (NO) serves as an essential signal molecule in regulating photosynthetic performance under physiological and stress conditions. The present study reveals the protective effects of different concentrations (0-300 µM) of sodium nitroprusside (SNP, a donor of NO) on the functions of the main complexes within the photosynthetic apparatus of maize (Zea mays L. Kerala) under salt stress (150 mM NaCl). The data showed that SNP alleviates salt-induced oxidative stress and prevents changes in the fluidity of thylakoid membranes (Laurdan GP) and energy redistribution between the two photosystems (77K chlorophyll fluorescence ratio F735/F685). Chlorophyll fluorescence measurements demonstrated that the foliar spray with SNP under salt stress prevents the decline of photosystem II (PSII) open reaction centers (qP) and improves their efficiency (Φexc), thereby influencing QA- reoxidation. The data also revealed that SNP protects the rate constants for two pathways of QA- reoxidation (k1 and k2) from the changes caused by NaCl treatment alone. Additionally, there is a predominance of QA- interaction with plastoquinone in comparison to the recombination of electrons in QA QB- with the oxygen-evolving complex (OEC). The analysis of flash oxygen evolution showed that SNP treatment prevents a salt-induced 10% increase in PSII centers in the S0 state, i.e., protects the initial S0-S1 state distribution, and the modification of the Mn cluster in the OEC. Moreover, this study demonstrates that SNP-induced defense occurs on both the donor and acceptor sides of the PSII, leading to the protection of overall photosystems performance (PIABS) and efficient electron transfer from the PSII donor side to the reduction of PSI end electron acceptors (PItotal). This study clearly shows that the optimal protection under salt stress occurs at approximately 50-63 nmoles NO/g FW in leaves, corresponding to foliar spray with 50-150 µM SNP.

Exploring natural genetic variation in photosynthesis-related traits of barley in the field.

Optimizing photosynthesis is considered an important strategy for improving crop yields to ensure food security. To evaluate the potential of using photosynthesis-related parameters in crop breeding programs, we measured chlorophyll fluorescence along with growth-related and morphological traits of 23 barley inbreds across different developmental stages in field conditions. The photosynthesis-related parameters were highly variable, changing with light intensity and developmental progression of plants. Yet, the variations in photosystem II (PSII) quantum yield observed among the inbreds in the field largely reflected the variations in CO2 assimilation properties in controlled climate chamber conditions, confirming that the chlorophyll fluorescence-based technique can provide proxy parameters of photosynthesis to explore genetic variations under field conditions. Heritability (H2) of the photosynthesis-related parameters in the field ranged from 0.16 for the quantum yield of non-photochemical quenching to 0.78 for the fraction of open PSII center. Two parameters, the maximum PSII efficiency in light-adapted state (H2 0.58) and the total non-photochemical quenching (H2 0.53), showed significant positive and negative correlations, respectively, with yield-related traits (dry weight per plant and net straw weight) in the barley inbreds. These results indicate the possibility of improving crop yield through optimizing photosynthetic light use efficiency by conventional breeding programs.

Improvement of the Quality of Wild Rocket (Diplotaxis tenuifolia) with Respect to Health-Related Compounds by Enhanced Growth Irradiance.

For healthier human nutrition, it is desirable to provide food with a high content of nutraceuticals such as polyphenolics, vitamins, and carotenoids. We investigated to what extent high growth irradiance influences the content of phenolics, α-tocopherol and carotenoids, in wild rocket (Diplotaxis tenuifolia), which is increasingly used as a salad green. Potted plants were grown in a climate chamber with a 16 h day length at photosynthetic photon flux densities varying from 20 to 1250 μmol m-2 s-1. Measurements of the maximal quantum yield of photosystem II, FV/FM, and of the epoxidation state of the violaxanthin cycle (V-cycle) showed that the plants did not suffer from excessive light for photosynthesis. Contents of carotenoids belonging to the V-cycle, α-tocopherol and several quercetin derivatives, increased nearly linearly with irradiance. Nonintrusive measurements of chlorophyll fluorescence induced by UV-A and blue light relative to that induced by red light, indicating flavonoid and carotenoid content, allowed not only a semiquantitative measurement of both compounds but also allowed to follow their dynamic changes during reciprocal transfers between low and high growth irradiance. The results show that growth irradiance has a strong influence on the content of three different types of compounds with antioxidative properties and that it is possible to determine the contents of flavonoids and specific carotenoids in intact leaves using chlorophyll fluorescence. The results may be used for breeding to enhance healthy compounds in wild rocket leaves and to monitor their content for selection of appropriate genotypes.

Data-based investigation of the effects of canopy structure and shadows on chlorophyll fluorescence in a deciduous oak forest

Abstract. Data from satellite, aircraft, drone, and ground-based measurements have already shown that canopy-scale sun-induced chlorophyll fluorescence (SIF) is tightly related to photosynthesis, which is linked to vegetation carbon assimilation. However, our ability to effectively use those findings are hindered by confounding factors, including canopy structure, fluctuations in solar radiation, and sun–canopy geometry that highly affect the SIF signal. Thus, disentangling these factors has become paramount in order to use SIF for monitoring vegetation functioning at the canopy scale and beyond. Active chlorophyll fluorescence measurements (FyieldLIF), which directly measures the apparent fluorescence yield, have been widely used to detect physiological variation of the vegetation at the leaf scale. Recently, the measurement of FyieldLIF has become feasible at the canopy scale, opening up new opportunities to decouple structural, biophysical, and physiological components of SIF at the canopy scale. In this study, based on top-of-canopy measurements above a mature deciduous forest, reflectance (R), SIF, SIF normalized by incoming photosynthetically active radiation (SIFy), FyieldLIF, and the ratio between SIFy and FyieldLIF (named Φk) were used to investigate the effects of canopy structure and shadows on the diurnal and seasonal dynamics of SIF. Further, random forest (RF) models were also used to not only predict FyieldLIF and Φk, but also provide an interpretation framework by considering additional variables, including the R in the blue, red, green, red-edge, and near-infrared bands; SIF; SIFy; and solar zenith angle (SZA) and solar azimuth angle (SAA). Results revealed that the SIF signal is highly affected by the canopy structure and sun–canopy geometry effects compared to FyieldLIF. This was evidenced by the weak correlations obtained between SIFy and FyieldLIF at the diurnal timescale. Furthermore, the daily mean SIF‾y captured the seasonal dynamics of daily mean F‾yieldLIF and explained 58 % of its variability. The findings also revealed that reflectance in the near-infrared (R-NIR) and the NIRv (the product of R-NIR and normalized difference vegetation index (NDVI)) are good proxies of Φk at the diurnal timescale, while their correlations with Φk decrease at the seasonal timescale. With FyieldLIF and Φk as outputs and the abovementioned variables as predictors, this study also showed that the RF models can explain between 86 % and 90 % of FyieldLIF, as well as 60 % and 70 % of Φk variations under clear-sky conditions. In addition, the predictor importance estimates for FyieldLIF RF models revealed that R at 410, 665, 740, and 830 nm; SIF; SIFy; SZA; and SAA emerged as the most useful and influential factors for predicting FyieldLIF, while R at 410, 665, 705, and 740 nm; SZA; and SAA are crucial for predicting Φk. This study highlighted the complexity of interpreting diurnal and seasonal dynamics of SIF in forest canopies. These dynamics are highly dependent on the complex interactions between the structure of the canopy, the vegetation biochemical properties, the illumination angles (SZA and SAA), and the light conditions (ratio of diffuse to direct solar radiation). However, such measurements are necessary to better separate the variability in SIF attributable to radiation and measurement conditions from the subtler variability attributable to plant physiological processes.

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.

Early detection of Kentucky bluegrass and perennial ryegrass responses to drought stress by measuring chlorophyll fluorescence parameters

AbstractKentucky bluegrass (Poa pratensis L.; drought resistant) and perennial ryegrass (Lolium perenne L.; drought sensitive) are economically important grass species contrasting in drought stress resistance. This study determined the optimal chlorophyll fluorescence parameters to indicate drought incidence and whether the parameters differentiate intra‐ and interspecies variations in drought stress. For each species, nine cultivars were exposed to well‐watered or drought (water withheld) conditions in growth chambers containing high‐throughput photosynthetic imagers to track real‐time responses of maximum quantum efficiency of photosystem II (Fv/Fm), quantum yield of photosystem II (ΦII), non‐photochemical quenching (NPQ), energy‐dependent quenching (qE), and photoinhibition‐associated quenching (qI). Soil moisture content and relative water content of leaf tissues were evaluated. Due to drought, Fv/Fm and ΦII decreased for cultivars of both species but earlier for perennial ryegrass compared to Kentucky bluegrass. The NPQ, qI, and qE values exhibited more dynamic and earlier changes due to drought compared to Fv/Fm and ΦII and allowed for early, mid, and late drought responses to be illustrated. Drought induced an increase in NPQ, qI, and qE values, which corresponded to activation of photoprotection mechanisms, and was exhibited earlier for perennial ryegrass compared to Kentucky bluegrass. As the drought treatment progressed, a decrease or stabilization of low values of NPQ, qI, and qE was observed, and the lowest values were associated with the most drought‐sensitive cultivars. These results indicate important stress tolerance protection mechanisms for grass species and will broadly impact basic and applied grass research as a nondestructive phenotyping tool.

A High-Throughput Approach for Photosynthesis Studies in a Brassicaceae Panel.

The study of natural variations in photosynthesis in the Brassicaceae family offers the possibility of identifying mechanisms to enhance photosynthetic efficiency in crop plants. Indeed, this family, and particularly its tribe Brassiceae, has been shown to harbor species that have a higher-than-expected photosynthetic efficiency, possibly as a result of a complex evolutionary history. Over the past two decades, methods have been developed to measure photosynthetic efficiency based on chlorophyll fluorescence. Chlorophyll fluorescence measurements are performed with special cameras, such as the FluorCams, which can be included in robotic systems to create high-throughput phenotyping platforms. While these platforms have so far demonstrated high efficiency in measuring small model species like Arabidopsis thaliana, they have the drawback of limited adaptability to accommodate different plant sizes. As a result, the range of species that can be analyzed is restricted. This chapter presents our approach to analyze the photosynthetic parameters: ϕPSII and Fv/Fm for a panel of Brassicaceae species, including a high-photosynthesis species, Hirschfeldia incana, and the adaptations to the phenotyping platform that are required to accommodate this varied group of plants.

Novel methods facilitating the mechanistic interpretation of multiscale optical remote sensing measurements

Plant physiology concentrates on the study of plant internal processes, such as growth, nutrient uptake and photosynthesis. The quantification of photosynthesis regulation is significant in understanding how plants react to the changing climate. Spectral remote sensing methods, using both reflected light in the visible and near infrared wavelengths, as well as chlorophyll fluorescence, are used to gather information about plant physiological variables. These methods have developed rapidly, prompted by the advances in remote sensing platforms and sensors. However, interpretation of remote sensing signals can be challenging. Due to canopy heterogeneity, the signal is affected by various elements, such as scattering, soil background and canopy structural effects. Additionally, open questions remain linked to the underlying mechanistic processes in the leaf modulating the optical signal, such as nutrient contents and leaf photochemistry, and how these processes and the optical signals diverge in response to temporal variation. Through multi-scale measurements, this thesis aims to advance the interpretation of optical remote sensing signals as they are affected by spatial and temporal variation, while promoting the use of novel methods and devices. Results indicate that diurnal and long-term variation of solar induced fluorescence (SIF) is driven by photosynthetic and structural factors, causing possible misinterpretations in SIF data. Additionally, depending on the scale of observation, results show that the capacity of remote sensing to detect changes in foliar nutrients depends on the covariation of nutrients, pigments and canopy structure, underlining the need for both leaf and canopy level measurements. Finally, we advocate for the implementation of a novel miniaturized fluorometer, demonstrating the ability to track the seasonal regulation of photosynthesis using integrated measurements of chlorophyll fluorescence and gas exchange. The results from this thesis underline the need for simultaneous multi-scale measurements of leaf and canopy physiological factors to further our understanding of photosynthesis regulation.

Ecophysiological characterisation of a Klebsormidium strain isolated from a cave environment

AbstractMembers of the genus Klebsormidium are ubiquitously distributed over the Earth and are among the major biological soil crust (BSC) forming microalgae. Their representatives can be found in terrestrial, aquatic, polar, desert regions and have been investigated so far from various aspects. However, the available information about Klebsormidium isolates from lamp-flora is very limited. In our work, we examined a Klebsormidium strain isolated from a Hungarian cave. The temperature optimum of its photosynthetic performance was tested by oxygen yield measurements and pulse-amplitude-modulated fluorescence, which were completed by determination of specific growth rates at different temperatures, from 10 to 40 °C. In addition, we also evaluated the brassinosteroid (BR) content of these cultures. Our results indicated that the studied microalga is capable of growing from 10 to 40 °C, with a 20–25 °C temperature optimum; these findings were in accordance with the observed hormone levels. Regarding photosynthetic performance, the oxygen yield and chlorophyll fluorescence measurements showed maxima at 30–40 °C and 35–40 °C, respectively. Moreover, the examined Klebsormidium strain demonstrates traits associated with cave adaptation, i.e., by high light utilisation factor (α) and diminished light adaptation parameter (Ik) values.

Response of leaf day respiration in C4 plants to irradiance and vapour pressure deficit

Leaf day respiration rate (RL) plays a crucial role in the global carbon cycle. However, RL of C4 species has not been sufficiently studied and its response to environmental factors is largely unknown. This work studied the response of RL of three C4 species, Setaria viridis, Sorghum sudanense, and Zea mays, to alterations in the vapour pressure deficit (VPD) and irradiance of the growth environment. RL was estimated using the Kok method (RL Kok) and an improved method that combined gas exchange and chlorophyll fluorescence measurements (RL Yin). On average, shade treatment led to a 24% reduction in RL Yin and a 20% reduction in respiration in the dark (RDk), while a consistent VPD effect on RL was not observed. RL and RDk were positively correlated with nitrogen content per leaf area and net CO2 assimilation rate but were not correlated with the capacity of carboxylation enzymes. We found a non-significant light inhibition of respiration (1 ​± ​2%), contradicting the assumption that respiration is inhibited by light and affected by light intensity. Our findings indicate that assuming RL to be equal to RDk at the same temperature is a straightforward but reliable approach to model respiration of the examined C4 species.

Alternative method for determining leaf CO2 assimilation without gas exchange measurements: Performance, comparison and sensitivity analysis.

We present an alternative method to determine leaf CO2 assimilation rate (An ), eliminating the need for gas exchange measurements in proximal and remote sensing. This method combines the Farquhar-von Caemmerer-Berry photosynthesis model with mechanistic light reaction (MLR) theory and leaf energy balance (EB) analysis. The MLR theory estimates the actual electron transport rate (J) by leveraging chlorophyll fluorescence via pulse amplitude-modulated fluorometry for proximal sensing or sun-induced chlorophyll fluorescence measurements for remote sensing, along with spectral reflectance. The EB equation is used to directly estimate stomatal conductance from leaf temperature. In wheat and soybean, the MLR-EB model successfully estimated An variations, including midday depression, under various environmental and phenological conditions. Sensitivity analysis revealed that the leaf boundary layer conductance (gb ) played an equal, if not more, crucial role compared to the variables for J. This was primarily caused by the indirect influence of gb through the EB equation rather than its direct impact on convective CO2 exchange on the leaf. Although the MLR-EB model requires an accurate estimation of gb , it can potentially reduce uncertainties and enhance applicability in photosynthesis assessment when gas exchange measurements are unavailable.

Genome-wide identification of the melon (Cucumis melo L.) response regulator gene family and functional analysis of CmRR6 and CmPRR3 in response to cold stress

The response regulator (RR) gene family play crucial roles in cytokinin signal transduction, plant development, and resistance to abiotic stress. However, there are no reports on the identification and functional characterization of RR genes in melon. In this study, a total of 18 CmRRs were identified and classified into type A, type B, and clock PRRs, based on phylogenetic analysis. Most of the CmRRs displayed tissue-specific expression patterns, and some were induced by cold stress according to two RNA-seq datasets. The expression patterns of CmRR2/6/11/15 and CmPRR2/3 under cold treatment were confirmed by qRT-PCR. Subcellular localization assays indicated that CmRR6 and CmPRR3 were primarily localized in the nucleus and chloroplast. Furthermore, when either CmRR6 or CmPRR3 were silenced using tobacco ringspot virus (TRSV), the cold tolerance of the virus-induced gene silencing (VIGS) melon plants were significantly enhanced, as evidenced by measurements of chlorophyll fluorescence, ion leakage, reactive oxygen, proline, and malondialdehyde levels. Additionally, the expression levels of CmCBF1, CmCBF2, and CmCBF3 were significantly increased in CmRR6-silenced and CmPRR3-silenced plants under cold treatment. Our findings suggest that CmRRs contribute to cold stress responses and provide new insights for further pursuing the molecular mechanisms underlying CmRRs-mediated cold tolerance in melon.

Comparative flooding tolerance of Typha latifolia and Phalaris arundinacea in wetland restoration: Insights from photosynthetic CO2 response curves, photobiology and biomass allocation

Tall helophytes such as Typha latifolia and Phalaris arundinacea often rapidly colonise after rewetting of former agricultural soil and are therefore often the first plants to contribute to the soil carbon pool. In this study we carried out a mesocosm experiment where these two species grew at three different water levels relative to the soil surface (−15 cm, 0 cm, +15 cm). After eight weeks' growth, measurements of photosynthetic CO2-response curves, stomatal conductance and chlorophyll fluorescence of photosystem II were carried out to detect flooding stress. After 10 weeks’ growth, the plants were harvested and biomass production, biomass allocation and specific leaf area were determined. T. latifolia had a higher and more stable photosynthetic performance across all water level treatments, which resulted in an overall higher aboveground and belowground production than P. arundinacea. In contrast, Vcmax and Jmax decreased by 41 % and 42 %, respectively from drained to flooded conditions with signs of flooding stress as impairment of the photosynthetic apparatus. Moreover, increasing water level resulted in maintenance of aboveground organs for P. arundinacea but a decrease in allocation to belowground organs. P. arundinacea did not invest in a higher specific leaf area to counter the decreased photosynthesis under flooding. From −15 cm to 0 cm water levels, P. arundinacea showed a 68 % reduction in belowground biomass, which has negative implication for carbon retention immediately after rewetting. In contrast, recolonization of T. latifolia is likely to be a suitable contributor to the soil carbon pool due to its stable physiology and high above- and belowground biomass production at all water depths, and also likely under natural water level fluctuations. We showed that even though both species are generally considered wetland plants, they are likely to support considerably different photosynthetic carbon assimilation and soil carbon sequestration rates.

The metabolism of nonstructural carbohydrates, lipids, and energy in two Cycas species with differential tolerance to unexpected freezing stress.

With the climate warming, the occurrence of freezing events is projected to increase in late spring and early autumn in the Northern Hemisphere. Observation of morphological traits showed that Cycas panzhihuaensis was more tolerant to unexpected freezing stress than C. bifida. Energy balance is crucial for plant tolerance to stress. Here, we aimed to determine whether the different responses of the two species to the unpredicted freezing stress were associated with the metabolism of energy and related substances. The effects of unexpected freezing temperatures on C. panzhihuaensis and C. bifida were studied by measuring chlorophyll fluorescence parameters, energy charge and the profile of nonstructural carbohydrates (NSC) and lipids. C. panzhihuaensis exhibited higher stability of photosynthetic machinery than C. bifida under unpredicted freezing events. Significant interaction between species and treatments were observed in the energy charge, the level of NSC and its most components and the amount of most lipid categories and lipid classes. The decrease of soluble sugar and the increase of neutral glycerolipids at the early freezing stage, the accumulation of membrane glycerolipids at the late freezing stage and the continuous decrease of energy charge during the freezing period were the characteristics of C. panzhihuaensis responding to unexpected freezing stress. The degradation of membrane glycerolipids and the continuous decrease of soluble sugar during the freezing period and the accumulation of neutral glycerolipids and energy charge at the late freezing stage represented the characteristics of C. bifida responses. The different freezing sensitivity between C. panzhihuaensis and C. bifida might be associated with the differential patterns of the metabolism of energy, NSC and lipids. C. panzhihuaensis possesses the potential to be introduced to the areas of higher latitudes and altitudes.

Effect of 1-MCP treatment on tomato photosynthetic chlorophyll activity during storage

AbstractEthylene has key roles in triggering and speeding up ripening processes, which in tomatoes take the form of various qualitative changes. Tomatoes, just like all climacteric fruits, need a continuous ethylene exposure to accelerate ripening. Therefore, it is possible to use ripening regulators preventing ethylene binding. According to some studies, chlorophyll fluorescence measurements can be used at least as efficiently as tristimulus colorimetry classifying tomatoes based on maturity. Measurements were carried out by treating fresh tomatoes with 1-MCP (1-methylcyclopropene) at six different stages of ripening and studying the changes in chlorophyll content related quality characteristics (e.g. surface colour, chlorophyll fluorescence) during postharvest storage (two-week refrigerated storage at 15 °C followed by a two-week shelf life). According to our results, chlorophyll content and photosynthetic activity of the treated samples decreased much less than those of untreated ones. Additionally, anti-ripening treatment proved to be more effective on tomatoes at an earlier stage of ripening.

The Linearly Polarized Light Effect on Maize Development

The main purpose of the work was to study the linearly polarized light impact on the maize plants development. The other purpose was to confirm the model proposed earlier. The methods used in this work include the development of LED light sources, the polarization parameter (degree of polarization) assessment and statistical analysis. Maize (Zea mays L.) plants, Hansatech FMS 1+ pulsed fluorimeter and software TXP Series Instrumentation were used. Plants were grown under white light (WW) with intensity of 200 µmol m–2 s–1. The morphometric parameters measured on the 21st day demonstrated that maize plants of different varieties grown under linearly polarized light developed better than under non-polarized light conditions. In addition, the fact was confirmed by chlorophyll fluorescence measurements. The mechanism has been proposed to explain significant polarized radiation impact on maize, according to which this impact depends on the shape and arrangement of the leaf epidermal cells. The monocotyledonous maize plants have leaves with an ordered arrangement of epidermal cells in comparison with dicotyledonous plants, which cells placed in chaotic order and have no certain shape. Thus, the maize cells layer can transform linearly polarized radiation into elliptically polarized radiation, thus latter should be more efficiently absorbed by the chiral chromophores of photosensitive structures in underlying photosynthetic cells.

Determinants of photochemical characteristics of the photosynthetic electron transport chain of maize.

The photosynthetic electron transport chain (ETC) is the bridge that links energy harvesting during the photophysical reactions at one end and energy consumption during the biochemical reactions at the other. Its functioning is thus fundamental for the proper balance between energy supply and demand in photosynthesis. Currently, there is a lack of understanding regarding how the structural properties of the ETC are affected by nutrient availability and plant developmental stages, which is a major roadblock to comprehensive modeling of photosynthesis. Redox parameters reflect the structural controls of ETC on the photochemical reactions and electron transport. We conducted joint measurements of chlorophyll fluorescence (ChlF) and gas exchange under systematically varying environmental conditions and growth stages of maize and sampled foliar nutrient contents. We utilized the recently developed steady-state photochemical model to infer redox parameters of electron transport from these measurements. We found that the inferred values of these photochemical redox parameters varied with leaf macronutrient content. These variations may be caused either directly by these nutrients being components of protein complexes on the ETC or indirectly by their impacts on the structural integrity of the thylakoid and feedback from the biochemical reactions. Also, the redox parameters varied with plant morphology and developmental stage, reflecting seasonal changes in the structural properties of the ETC. Our findings will facilitate the parameterization and simulation of complete models of photosynthesis.

Freezing tolerance and tolerance to de-acclimation of European accessions of winter and facultative barley

Due to global warming, winter hardiness may seem to become less important for plant survival and yield. However, this is a superficial assumption, as probably only the most important factors locally affecting plant overwintering will change. For example, the frequency, degree, and length of extreme winter warming events may increase, leading to de-acclimation of plants. This study aimed to investigate existing variability in de-acclimation tolerance in Polish winter barley breeding materials and European winter and facultative barley cultivars, and to identify accessions with the highest and the lowest tolerance to de-acclimation by means of visual estimation of regrowth after freezing, measurements of electrolyte leakage and chlorophyll fluorescence, and LT50 assessment. The results of this study showed that freezing tolerance and tolerance to de-acclimation are independent traits, and even highly freezing tolerant plants can be susceptible to de-acclimation. Our results highlight the role of photosynthetic apparatus in de-acclimation, proving that chlorophyll fluorescence parameters, especially ET0/CS, can be useful indicators of tolerance to de-acclimation. This study also confirmed that although the mechanisms of response to de-acclimation seem to be common for susceptible barley accessions, the mechanisms of tolerance are different, and may be related to the accession’s origin.

Detecting QTLs controlling chlorophyll fluorescence parameters in Iranian wheat recombinant inbred lines

Measurement of chlorophyll fluorescence is one of the methods to detect a disorder in the photosynthetic system, which reflects the photochemical state of the plant. Identification of the genetic structure of chlorophyll fluorescence parameters can provide useful solutions for breeding varieties with higher potential. The present study was conducted with the aim of identifying quantitative loci (QTL) related to chlorophyll fluorescence parameters in an Iranian RILs wheat population. One hundred and twenty F8 RILs of wheat derived from crossing Kohdasht (KHD) and Gonbad (GND) cultivars in the form of an alpha lattice design were studied in 2019 and 2020. The analysis of QTLs was performed in the software R using the package QTL.gCIMapping.GUI v2.0. The genetic map was constructed with 423 SSR markers, 21 CBDP markers, 58 ISJ markers, and 19 SCoT markers (521 polymorphic alleles) distributed on 21 wheat chromosomes. This map covered 3167.9 cM of the wheat genome and had an average marker spacing of 6.1, 6, and 6.2 cM for the A, B, and D genomes, respectively. Thirteen of the fourteen QTLs discovered in 2019 and four of the nine QTLs discovered in 2020 had an explanatory coefficient greater than 15% and were considered major QTLs. In 2019, pleiotropic QTLs were found at position 1.79 cM on chromosome 3A and between two markers Xwmc11-3A and BARC1177. In 2020, two QTLs, qABS/ RC 1B and qTRo/ RC 1B were located at position 36.80 cM 1B and between two markers Xgpw4331-1B and Xgpw5162-1B, and two QTLs, qETo/ RC-5D and qREo / RC-5D were located at position 63.25 cM chromosome 5D and correspond to the position of marker cfd266. Pleiotropic QTLs as well as major QTLs can be used in marker-assisted selection for chlorophyll fluorescence traits in wheat breeding projects.

Germination Characteristics and Seedling Growth of <italic>Pseudolysimachion nakaianum</italic> (Ohwi) T. Yamaz. Seeds According to Light Quality Type

Background and objective: This study was conducted to understand the effect of different quality of light-emitting diodes (LED) on the germination characteristics and growth of <i>Pseudolysimachion nakaianum</i>.Methods: The LED light irradiation was divided into white, red, blue, and red:blue (1:1). To investigate the germination characteristics, 30 seeds were placed in a Petri dish in three replicates for 8 days. Average germination rate, germination speed, germination uniformity, and average germination time were measured. To investigate the growth of seedlings, plant height, plant width, leaf length, leaf width, leaf number, fresh weight, dry weight and T/R ratio were examined 6 weeks after sowing, and chlorophyll fluorescence (maximum quantum yield, electron transport rate) was measured.Results: The final germination rate and germination speed were highest at red:blue (1:1) LED irradiation. Regarding growth and chlorophyll fluorescence measurements, red:blue LED showed the best growth results, with no significant difference in Fv/Fm between different types of light quality, and the electron transport rate was the highest under red:blue LED irradiation. Also, total fresh/dry weight and T/R ratio were highest for red:blue LED, it is presumed to promote the biomass of entire plant.Conclusion: The results proved that <i>Pseudolysimachion nakaianum</i> showed red LED conditions promoted germination, but cultivation under red:blue LED conditions is judged to be suitable for seedling growth and photosynthesis.