Higher Electron Transport Rate Research Articles

Effects of Salicylic Acid on Physiological Responses of Pepper Plants Pre-Subjected to Drought under Rehydration Conditions.

Capsicum annuum L. has worldwide distribution, but drought has limited its production. There is a lack of research to better understand how this species copes with drought stress, whether it is reversible, and the effects of mitigating agents such as salicylic acid (SA). Therefore, this study aimed to understand the mechanisms of action of SA and rehydration on the physiology of pepper plants grown under drought conditions. The factorial scheme adopted was 3 × 4, with three water regimes (irrigation, drought, and rehydration) and four SA concentrations, namely: 0 (control), 0.5, 1, and 1.5 mM. This study evaluated leaf water percentage, water potential of shoots, chlorophylls (a and b), carotenoids, stomatal conductance, chlorophyll a fluorescence, and hydrogen peroxide (H2O2) concentration at different times of day, water conditions (irrigation, drought, and rehydration), and SA applications (without the addition of a regulator (0) and with the addition of SA at concentrations equal to 0.5, 1, and 1.5 mM). In general, exogenous SA application increased stomatal conductance (gs) responses and modified the fluorescence parameters (ΦPSII, qP, ETR, NPQ, D, and E) of sweet pepper plants subjected to drought followed by rehydration. It was found that the use of SA, especially at concentrations of 1 mM in combination with rehydration, modulates gs, which is reflected in a higher electron transport rate. This, along with the production of photosynthetic pigments, suggests that H2O2 did not cause membrane damage, thereby mitigating the water deficit in pepper plants. Plants under drought conditions and rehydration with foliar SA application at concentrations of 1 mM demonstrated protection against damage resulting from water stress. Focusing on sustainable productivity, foliar SA application of 1 mM could be recommended as a technique to overcome the adverse effects of water stress on pepper plants cultivated in arid and semi-arid regions.

Reduced diffusional limitations in carnation stems facilitate higher photosynthetic rates and reduced photorespiratory losses compared with leaves.

Green stem photosynthesis has been shown to be relatively inefficient but can occasionally contribute significantly to the carbon budget of desert plants. Although the possession of green photosynthetic stems is a common trait, little is known about their photosynthetic characteristics in non-desert species. Dianthus caryophyllus is a semi-woody species with prominent green stems, which show similar photosynthetic anatomy with leaves. In the present study, we used a combination of gas exchange and chlorophyll fluorescence measurements, some of which were taken under varying O2 and CO2 partial pressures, to investigate whether the apparent anatomical similarities between the species' leaves and stems translate into similar photosynthetic physiology and capacity for CO2 assimilation. Both organs displayed high photosynthetic electron transport rates (ETR) and similar values of steady-state non-photochemical quenching (NPQ), albeit leaves could attain them faster. The analysis of OJIP transients showed that the quantum efficiencies and energy fluxes along the photosynthetic electron transport chain are largely similar between leaves and stems. Stems displayed higher total conductance to CO2 diffusion, similar biochemical properties, significantly higher photosynthetic rates and lower water use efficiency than leaves. Leaf ETR was more sensitive to sub-ambient O2 and super-ambient CO2 partial pressures, while leaves also displayed a higher relative rate of Rubisco oxygenation. We conclude that the highly responsive NPQ and the enhanced photorespiration and WUE in leaves represent photoprotective and water-conserving adaptations to the high incident light intensities they experience naturally, at the expense of higher CO2 assimilation rates, which the vertically orientated stems can readily attain.

Interactions of binary mixtures of metals on rainbow trout (Oncorhynchus mykiss) heart mitochondrial H2O2 homeodynamics

For continuous pumping of blood, the heart needs a constant supply of energy (ATP) that is primarily met via oxidative phosphorylation in the mitochondria of cardiomyocytes. However, sustained high rates of electron transport for energy conversion redox reactions predisposes the heart to the production of reactive oxygen species (ROS) and oxidative stress. Mitochondrial ROS are fundamental drivers of responses to environmental stressors including metals but knowledge of how combinations of metals alter mitochondrial ROS homeodynamics remains sparse. We explored the effects and interactions of binary mixtures of copper (Cu), cadmium (Cd), and zinc (Zn), metals that are common contaminants of aquatic systems, on ROS (hydrogen peroxide, H2O2) homeodynamics in rainbow trout (Oncorhynchus mykiss) heart mitochondria. Isolated mitochondria were energized with glutamate-malate or succinate and exposed to a range of concentrations of the metals singly and in equimolar binary concentrations. Speciation analysis revealed that Cu was highly complexed by glutamate or Tris resulting in Cu2+ concentrations in the picomolar to nanomolar range. The concentration of Cd2+ was 7.2–7.5 % of the total while Zn2+ was 15 % and 21 % of the total during glutamate-malate and succinate oxidation, respectively. The concentration-effect relationships for Cu and Cd on mitochondrial H2O2 emission depended on the substrate while those for Zn were similar during glutamate-malate and succinate oxidation. Cu + Zn and Cu + Cd mixtures exhibited antagonistic interactions wherein Cu reduced the effects of both Cd and Zn, suggesting that Cu can mitigate oxidative distress caused by Cd or Zn. Binary combinations of the metals acted additively to reduce the rate constant and increase the half-life of H2O2 consumption while concomitantly suppressing thioredoxin reductase and stimulating glutathione peroxidase activities. Collectively, our study indicates that binary mixtures of Cu, Zn, and Cd act additively or antagonistically to modulate H2O2 homeodynamics in heart mitochondria.

Electrochemical hydrogenation of furfural under alkaline conditions with enhanced furfuryl alcohol selectivity by self-grown Cu on a Ag electrode

Efficient conversion of furfural to furfuryl alcohol with a high electron transport rate over Cu/PAg catalysts under alkaline conditions.

Development and application of fluorine doped bismuth vanadate reduced graphene oxide Nafion composite electrode as an electrochemical sensor for 4-chlorophenol

This study describes the synthesis of fluorine-doped bismuth vanadate (F0.1BiVO4) and its composite with graphene oxide (GO) to improve charge transport properties. Based on the structural and morphological analysis such as X-Ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and RAMAN the composite of F0.1BiVO4/r-GO/Nafion was successfully prepared with no filth. It was used to selectively detect the environmental contaminant 4-chlorophenol (4-CP) on a modified glassy carbon electrode (GCE). The electron channeling ability of reduced graphene oxide (r-GO) with F0.1BiVO4 yielded a great electrochemical response (ER) in cyclic voltammetry compared to pure GCE and other modified electrodes. The differential pulse voltammetry response of 4-CP was highly sensitive with the detection of limit (LOD) of 0.56 nM and a wide linear response of 0.77–45.0 nM. Fluorine doping, in particular, was able to affect the crystal growth of BiVO4, which was the primary cause of the aforementioned improvement. On the other hand, r-GO acts as an electron bridge to improve charge transfer between electrolytes and F-BiVO4 due to its high electron transport rate. These results demonstrate the effectiveness of F0.1BiVO4/r-GO/Nafion/GCE for the electrochemical detection of 4-CP.

Fabrication, characterization and performance evaluation of an amplified electrochemical sensor based on MOFs nanocomposite for leukemia drug Imatinib determination

In this research, the synthesis, fabrication steps and characterization of a new modified glassy carbon electrode (GCE) with CuFe2O4 magnetic nanoparticles combined with zeolitic imidazolate framework (ZIF-8) embedded graphene quantum dots (GQDs), (CuFe2O4/ZIF-8@GQDs), for electrodetermination of the imatinib (IMB), anti-cancer drug, are reported. The synthesized nanocomposite was characterized using X-ray powder diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FE-SEM). The GCE modified with CuFe2O4/ZIF-8@GQDs nanocomposite shows high electrocatalytic activity toward the oxidation of IMB compared with the bare GCE, GQDs/GCE, ZIF-8@GQDs/GCE, CuFe2O4/GCE and CuFe2O4@GQDs/GCE. The resulted electrocatalytic activity of the CuFe2O4/ZIF-8@GQDs/GCE can be attributed to the synergistic effect of the outstanding magnetic, electrical properties of the CuFe2O4/ZIF-8@GQDs and high conductivity of GQDs, as well as the high electron transport rate of the nanocomposite. Under optimized conditions, the developed sensor, CuFe2O4/ZIF-8@GQDs/GCE, has static properties such as wide linear range responses (0.02–11.85 and 11.85–94.20 μM), low detection limit (1.2 nM), high sensitivity (5.655 μA μM−1), long-term signal stability and reproducibility (RSD = 2.23%). It should be noted that the CuFe2O4/ZIF-8@GQDs/GCE sensor could be used for determination of IMB in biological and pharmaceutical samples, indicating its feasibility for real analysis.

Heteroatom-doped layered hierarchical porous carbon electrodes with high mass loadings for high-performance supercapacitors

Electrodes with high mass loadings are the impetus for improving the energy density of supercapacitors. However, such electrodes have poor charge and ion kinetics in most cases, and rationally designing them which have high electron and ion transport rates is a major challenge. In this work, a new heteroatom-doped hierarchical porous carbon material, called LPC-2, was developed with longan shell and KOH as its precursor and an activator, respectively, through heteroatom self-doping and architecture design integration, in which heteroatoms of nitrogen, oxygen and sulfur were found. Its frequency response was excellent at a scan rate up to 5 and 0.3 V s−1 when the mass loading was set to be 1.0 and 12 mg cm−2, respectively. At a high mass loading of 12 mg cm−2, LPC-2 had gravimetric and areal specific capacitances of 171 F g−1 and 2052 mF cm−2, respectively. The assembled LPC-2//LPC-2 symmetric supercapacitor can complete charge and discharge in 0.4 s, showing a high energy density of 10.8 Wh kg−1 at a high power density of 97.4 kW kg−1 in 6 M KOH. In addition, 99.5 % of the original capacitance was retained after 20,000 cycles at 10 A g−1, which embodies the application value of biomass-derived carbon in supercapacitors.

Salt-Induced Modulation of Ion Transport and PSII Photoprotection Determine the Salinity Tolerance of Amphidiploid Brassicas.

Brassica species show varying levels of resistance to salt stress. To understand the genetics underlying these differential stress tolerance patterns in Brassicas, we exposed two widely cultivated amphidiploid Brassica species having different genomes, Brassica juncea (AABB, n = 18) and Brassica napus (AACC, n = 19), to elevated levels of NaCl concentration (300 mM, half the salinity of seawater). B. juncea produced more biomass, an increased chlorophyll content, and fewer accumulated sodium (Na+) and chloride (Cl-) ions in its photosynthesizing tissues. Chlorophyll fluorescence assays revealed that the reaction centers of PSII of B. juncea were more photoprotected and hence more active than those of B. napus under NaCl stress, which, in turn, resulted in a better PSII quantum efficiency, better utilization of photochemical energy with significantly reduced energy loss, and higher electron transport rates, even under stressful conditions. The expression of key genes responsible for salt tolerance (NHX1 and AVP1, which are nuclear-encoded) and photosynthesis (psbA, psaA, petB, and rbcL, which are chloroplast-encoded) were monitored for their genetic differences underlying stress tolerance. Under NaCl stress, the expression of NHX1, D1, and Rubisco increased several folds in B. juncea plants compared to B. napus, highlighting differences in genetics between these two Brassicas. The higher photosynthetic potential under stress suggests that B. juncea is a promising candidate for genetic modifications and its cultivation on marginal lands.

The sensitivity of photosynthesis to magnesium deficiency differs between rice (Oryza sativa L.) and cucumber (Cucumis sativus L.).

Magnesium is an essential macronutrient for plant photosynthesis, and in response to Mg deficiency, dicots appear more sensitive than monocots. Under Mg deficiency, we investigated the causes of differing photosynthetic sensitivities in a dicot and a monocot species. Rice (Oryza sativa L.) and cucumber (Cucumis sativus L.) were grown in hydroponic culture to explore their physiological responses to Mg deficiency stress. Both Mg-deficient rice and cucumber plants exhibited lower biomass, leaf area, Mg concentration, and chlorophyll content (Chl) compared with Mg-sufficient plants. However, a more marked decline in Chl and carotenoid content (Car) occurred in cucumber. A lower CO2 concentration in chloroplasts (C c) was accompanied by a decrease in the maximum rate of electron transport (J max) and the maximum rate of ribulose 1,5-bisphosphate carboxylation (V cmax), restricting CO2 utilization in Mg-deficient plants. Rice and cucumber photorespiration rate (P r) increased under Mg deficiency. Additionally, for cucumber, Car and non-photochemical quenching (NPQ) were reduced under lower Mg supply. Meanwhile, cucumber Mg deficiency significantly increased the fraction of absorbed light energy dissipated by an additional quenching mechanism (Φf,D). Under Mg deficiency, suppressed photosynthesis was attributed to comprehensive restrictions of mesophyll conductance (g m), J max, and V cmax. Cucumber was more sensitive to Mg deficiency than rice due to lower NPQ, higher rates of electron transport to alternative pathways, and subsequently, photooxidation damage.

Responses of photosynthesis and chlorophyll fluorescence during light induction in different seedling ages of Mahonia oiwakensis

BackgroundThe aim of this study was to determine the actual state of the photosynthetic apparatus and exhibit distinguishable differences in the chlorophyll fluorescence (ChlF) components in different seedling ages of M. oiwakensis plants subjected to different light intensity (LI). Potted 6-month-old greenhouse seedlings and field collected 2.4-year-old seedlings with 5 cm heights were selected and randomly separated into seven groups for photosynthesis measurements illuminated with 50, 100 (assigned as low LI), 300, 500, 1,000 (as moderate LI), 1,500 and 2,000 (as high LI) μmol m–2 s–1 photosynthetic photon flux density (PPFD) treatments.Resultsn 6-month-old seedlings, as LI increased from 50 to 2,000 PPFD, the values of non-photochemical quenching and photo-inhibitory quenching (qI) increased but potential quantum efficiency of PSII (Fv/Fm) and photochemical efficiency of photosystem II (ΦPSII) values decreased. High electron transport rate and percentage of actual PSII efficiency by Fv/Fm values were observed in 2.4-year-old seedlings at high LI conditions. Furthermore, higher ΦPSII was detected under low LI conditions, with lower energy-dependent quenching (qE) and qI values and photo-inhibition % decreased as well. However, qE and qI increased as ΦPSII decreased and photo-inhibition% increased under high LI treatments.ConclusionsThese results could be useful for predicting the changes in growth and distribution of Mahonia species grown in controlled environments and open fields with various combinations of varying light illuminations, and ecological monitoring of their restoration and habitat creation is important for provenance conservation and helps to formulate better conservation strategies for the seedlings.

Phenotyping of basil (Ocimum basilicum L.) illuminated with UV-A light of different wavelengths and intensities

The effects of light on plants depend on the energy dose and spectral characteristics. We investigated how UV-A radiation with two different wavelengths, 365 and 385 nm, combined at different intensities as supplemental light to red-blue baseline illumination affects growth and selected physiological and biochemical traits of green leaf basil (Ocimum basilicum L.). Conventional physiological measurements and biochemical analyses of photosynthetic pigments and phenolics were combined with high-throughput phenotyping. We did not detect any negative effects of UV-A on plant growth and photosynthetic functions, even at high doses of short-wave UV-A. Furthermore, thylakoid processes were enhanced under UV-A, as evidenced by higher electron transport rates and increased photochemical efficiency. The increase in anthocyanin index (ARI) indicates the UV-screening response. However, no anthocyanins were detected in the leaves, and the only phenolic compounds that responded to UV-A were hydroxycinnamic acid derivatives, which have a dual function in responding to UV-A (UV protection and antioxidants). UV-A increased the pool of xanthophyll cycle pigments and their ratio to chlorophylls. All this prevents photoinhibition and contributes to a high plasticity/efficiency of the basil's response to light environment.

Unraveling the hierarchical porous structure in natural pollen-derived Fe-containing carbon to address the shuttle effect and dead sulfur problems in lithium-sulfur batteries

Mesoporous carbon–metal composites with the merits of strong adsorption ability over soluble lithium polysulfides (LiPSs), excellent sulfur dispersion, high conductivity, low cost, and rapid catalytic conversion rate to suppress the shuttle effect are promising in lithium-sulfur batteries. However, their application is usually limited by structural collapse and fast fading because of the poorly dispersed metal-based compounds in the mesoporous carbon host during high-temperature synthesis. Herein, a 3D rape pollen-derived carbon (RPDC) containing Fe-based compounds as the sulfur host is prepared through the solid-state reaction of simultaneous carbonization between natural rape pollen and ferrous oxalate. Characterizations confirm that Fe-RPDC composites have stronger physiochemical adsorption and catalytic ability than pure RPDC, Fe-doped commercial activated carbon, and pure Fe3O4. Then, soluble LiPSs are adsorbed, fixed on the surface of the Fe-RPDC composites and catalyzed by Fe-based compounds to reduce the “dead sulfur”. Finally, a mature natural structure-derived hollow carbon-iron compound system is developed. The lithium-sulfur battery assembled using Fe-RPDC as host showed excellent long-term stability and a high electron transport rate. The Fe-RPDC@S composite with 69.6 wt% sulfur content exhibits the highest initial discharge capacity of 955.7 mA h g−1 at a rate of 1 C and can be maintained at 556.3 mA h g−1 even after 150 cycles. The decay rate is only 0.03 % per cycle, and the average Coulomb efficiency is approximately 98 %. Hence, the reasonable design of Fe-RPDC composites is of great significance for promoting the transformation of polysulfide intermediates and chemically anchoring soluble LiPSs to restrain “dead sulfur” and can be used to realize low-cost, green and large-scale production.

Superior Fenton-like and photo-Fenton-like activity of MoS2@TiO2/N-doped carbon nanofibers with phase-regulated and vertically grown MoS2 nanosheets

Molybdenum disulfide (MoS2) nanosheets were recently found to have great potential in heterogeneous Fenton-like reactions, but the synergistic effects of its phase and vertical structure on activating hydrogen peroxide (H2O2) remain ambiguous. Herein, a series of 1 T/2H MoS2@TiO2/NCNFs were constructed by vertically growing trigonal phase (1 T)/hexagonal phase (2H) MoS2 on self-supported titanium dioxide/nitrogen-doped carbon nanofibers (TiO2/NCNFs) for Fenton-like and photo-Fenton-like degradation of tetracycline (TC). It was found that metallic 1 T phase MoS2 favors the dark-Fenton-like reaction, but proper biphase 1 T/2H MoS2 benefit the photo-Fenton-like reaction. This depends on the high electron transport rate of 1 T MoS2 and the photocatalytic effect of 2H MoS2. Significantly, the vertical structure MoS2 nanosheets were much more effective in promoting H2O2 activation than phase regulation. In dark, the reaction rate constant for the optimized vertical 1 T/2H MoS2@TiO2/NCNFs was 0.0246 min−1, which was 16.4 times that for stacked MoS2 (0.0015 min−1). Quenching experiments indicated that •O2–, •OH and h+ were all involved in the photo-Fenton-like reaction, whereas •OH predominated the dark-Fenton-like reaction. The probable TC degradation pathways were investigated and proposed. Besides, the optimized 1 T/2H MoS2@TiO2/NCNFs demonstrated excellent stability, recyclability and adaptability. This work is instructive for designing highly efficient MoS2-based Fenton-like or photo-Fenton-like catalysts.

Seasonal ecophysiology of Fucus vesiculosus (Phaeophyceae) in the Northern Baltic Sea

ABSTRACT The brown macroalga Fucus vesiculosus is a foundation species in temperate rocky shores, subjected to seasonally fluctuating environmental conditions. To obtain a more complete picture of the seasonality of F. vesiculosus ecophysiology in the northern Baltic Sea, in situ photochemistry, elemental ratios and chlorophyll a and c content of the alga were investigated in field campaigns conducted in different months throughout the year during 2017. Carbon, nitrogen, carbon to nitrogen ratio and chlorophyll a and c content of the alga varied substantially throughout the year, with highest carbon content observed in summer, and highest nitrogen content in winter. C:N ratio in F. vesiculosus apical tissue ranged from 8.6 in February to 48.3 in July. Chlorophyll a and c content followed inversely the seasonal patterns of ambient irradiance. High chlorophyll a and c content in winter was associated with higher maximum photosynthetic efficiency of energy conversion (Fv/Fm), but not with efficiency of photosynthetic energy conversion under light limitation (α). Electron transport rate correlated strongly with seawater temperature, and the highest electron transport rates were observed in summer and correlated with highest internal carbon content of the alga. Redundancy analysis conducted on measured environmental variables against physiological responses identified day of year, temperature and macronutrients in seawater as the most important variables driving the observed seasonal patterns in F. vesiculosus ecophysiology. The results suggest elevated temperatures may increase Fucus growth and photosynthesis rates in the study area. Highlights Two distinct physiological states of Fucus vesiculosus were identified. The most important variables driving responses were season, temperature and macronutrients. Fucus ecophysiology shows substantial seasonality in the northern Baltic Sea.

Physiological and Proteomic Responses of Cassava to Short-Term Extreme Cool and Hot Temperature.

Temperature is one of the most critical factors affecting cassava metabolism and growth. This research was conducted to investigate the effects of short-term exposure to extreme cool (15 °C) and hot (45 °C) temperature on photosynthesis, biochemical and proteomics changes in potted plants of two cassava cultivars, namely Rayong 9 and Kasetsart 50. One-month-old plants were exposed to 15, 30, and 45 °C for 60 min in a temperature chamber under light intensity of 700 μmol m−2 s−1. Compared to the optimum temperature (30 °C), exposure to 15 °C resulted in 28% reduction in stomatal conductance (gs) and 62% reduction in net photosynthesis rate (Pn). In contrast, gs under 45 °C increased 2.61 folds, while Pn was reduced by 50%. The lower Pn but higher electron transport rate (ETR) of the cold-stressed plants indicated that a greater proportion of electrons was transported via alternative pathways to protect chloroplast from being damaged by reactive oxygen species (ROS). Moreover, malondialdehyde (MDA) contents, a marker related to the amount of ROS, were significantly higher at low temperature. Proteomics analysis revealed some interesting differentially expressed proteins (DEPs) including annexin, a multi-functional protein functioning in early events of heat stress signaling. In response to low-temperature stress, AP2/ERF domain-containing protein (a cold-related transcription factor) and glutaredoxin domain-containing protein (a component of redox signaling network under cold stress) were detected. Taken together, both cultivars were more sensitive to low than high temperature. Moreover, Rayong 9 displayed higher Pn under both temperature stresses, and was more efficient in controlling ROS under cold stress than Kasetsart 50.

Palmelloid formation in the Antarctic psychrophile, Chlamydomonas priscuii, is photoprotective.

Cultures of the obligate, Antarctic psychrophile, Chlamydomonas priscuii grown at permissive low temperature (8°C) are composed of flagellated, single cells, as well as non-motile, multicellular palmelloids. The relative proportions of the two cell types are temperature dependent. However, the temperature dependence for palmelloid formation is not restricted to psychrophilic C. priscuii but appears to be a general response of mesophilic Chlamydomonas species (C. reinhardtii and C. raudensis) to non-permissive growth temperatures. To examine potential differences in photosynthetic performance between single cells versus palmelloids of the psychrophile, a cell filtration technique was developed to separate single cells from palmelloids of C. priscuii grown at 8°C. Flow cytometry was used to estimate the diameter of isolated single cells (≤5 μm) versus isolated palmelloids of varying size (≥8 μm). Compared to single cells, palmelloids of C. priscuii showed a decrease in the abundance of light-harvesting complex II (LHCII) proteins with a 2-fold higher Chl a/b ratio. A decrease in both lutein and β-carotene in palmelloids resulted in carotenoid pools which were 27% lower in palmelloids compared to single cells of the psychrophile. Chlorophyll fluorescence analyses of the isolated fractions revealed that maximum photochemical efficiency of PSII (Fv/Fm) was comparable for both single cells and palmelloids of C. priscuii. However, isolated palmelloids exhibited lower excitation pressure, measured as 1 - qL, but higher yield of PSII (ΦPSII) and 50% higher rates of electron transport (ETR) than single cells exposed to high light at 8°C. This decreased sensitivity to high light in isolated palmelloids compared to single cells was associated with greater non-regulated dissipation of excess absorbed energy (ΦNO) with minimal differences in ΦNPQ in C. priscuii in response to increasing irradiance at low temperature. The ratio ΦNO/ΦNPQ observed for isolated palmelloids of C. priscuii developed at 8°C (1.414 ± 0.036) was 1.38-fold higher than ΦNO/ΦNPQ of isolated single cells (1.021 ± 0.018) exposed to low temperature combined with high light (1,000 μmol m−2 s−1). The differences in the energy quenching capacities between palmelloids and single cells are discussed in terms of enhanced photoprotection of C. priscuii palmelloids against low-temperature photoinhibition.

Enhanced abundance and activity of the chloroplast ATP synthase in rice through the overexpression of the AtpD subunit

ATP, produced by the light reactions of photosynthesis, acts as the universal cellular energy cofactor fuelling all life processes. Chloroplast ATP synthase produces ATP using the proton motive force created by solar energy-driven thylakoid electron transport reactions. Here we investigate how increasing abundance of ATP synthase affects leaf photosynthesis and growth of rice, Oryza sativa variety Kitaake. We show that overexpression of AtpD, the nuclear-encoded subunit of the chloroplast ATP synthase, stimulates both abundance of the complex, confirmed by immunodetection of thylakoid complexes separated by Blue Native-PAGE, and ATP synthase activity, detected as higher proton conductivity of the thylakoid membrane. Plants with increased AtpD content had higher CO2 assimilation rates when a stepwise increase in CO2 partial pressure was imposed on leaves at high irradiance. Fitting of the CO2 response curves of assimilation revealed that plants overexpressing AtpD had a higher electron transport rate (J) at high CO2, despite having wild-type-like abundance of the cytochrome b6f complex. A higher maximum carboxylation rate (Vcmax) and lower cyclic electron flow detected in transgenic plants both pointed to an increased ATP production compared with wild-type plants. Our results present evidence that the activity of ATP synthase modulates the rate of electron transport at high CO2 and high irradiance.

Higher CO2 Assimilation in Selected Rice Recombinant Inbred Lines Is Driven by Higher CO2 Diffusion and Light Use Efficiency Related to Leaf Anatomy and Mesophyll Cell Density.

Leaf anatomy determining the light distribution within the leaf and exerting influence on CO2 diffusion is considered to have dramatic potential for photosynthesis performance increase. In this study, we observed that two rice recombinant inbred lines, H138 and H217 (RILF11 plants from Sasanishiki × IRAT10), have higher net CO2 assimilation (An) than their parent Sasanishiki due mainly to the improvement of leaf anatomy. Our results showed that An positively correlated with anatomy traits’ mesophyll cell number per cross-sectional area (NO.mescell/Acros) and mesophyll area (Ames). NO.mescell/Acros exert direct and indirect effects on An. Compared to Sasanishiki flag leaves, IRAT10, H138, and H217 have higher mesophyll cell numbers. Simultaneously, higher chlorophyll content and expression of genes encoding the light-harvesting protein of PSII and PSI (Lhcb1, 2, 3 and Lhca1, 2, 3) were recorded in IRAT10, H138, and H217, which facilitates light use efficiency. Higher electron transport rate and RuBP concentration were recorded in IRAT10, H138, and H217 flag leaves. Retinoblastoma-related gene (OsRBR1), exerting effects on mesophyll cell density, can be used to modify leaf anatomy for improving leaf photosynthesis. Additionally, higher stomatal conductance and mesophyll conductance were also recorded in H138 and H217 than in Sasanishiki. Furthermore, we modeled mesophyll conductance through anatomical traits, and the results revealed that chloroplast thickness was the dominant factor restricting CO2 diffusion within mesophyll cells rather than cell wall thickness. Higher RuBP content accompanied by higher CO2 concentration within the carboxylation set in H138 and H217 flag leaves contributed to higher CO2 assimilation.

Leaf structure and photosynthesis in Populus alba under naturally fluctuating environments

The ability to modulate photosynthesis is essential for plants to adapt to fluctuating growing conditions. Populus species show high tolerance to various and highly variable environments. To understand their response strategies against fluctuating environments, this study investigated the morphological and physiological differences of white poplar (Populus alba) leaves when grown in a phytotron, glasshouse, and field. Our results show that the palisade cells were elongated in the field, which would enhance intercellular CO2 exchange. Photosynthetic capacity was the highest in the field leaves, as shown by higher electron transport rates (1.8 to 6.5 times) and carbon assimilation rates (2.7 to 4.2 times). The decrease of PSI acceptor-side limitation and increase of PSI donor-side limitation suggests changes in PSI redox status may contribute to photoprotection. This plasticity of white poplar allows adjusting its structure and photosynthesis under fluctuating conditions, which may partly enable its outstanding tolerance against environmental changes.

Seasonal changes in photosynthesis, phenolic content, antioxidant activity, and anatomy of apical and basal leaves of Aristotelia chilensis

Aristotelia chilensis (Mol.) Stuntz is an evergreen species endemic to Chile. It grows in open areas or under tree canopy, and its leaves emerge in early spring and summer. The objective of this study was to determine changes in photosynthetic parameters, total phenol content (TPC), antioxidant activity, and anatomy of apical and basal leaves of A. chilensis during the year. Photosynthesis performance was determined by measuring electron transport rate (ETR), the quantum efficiency of photosystem II (Fv/Fm), photochemical quenching (qP), and non-photochemical quenching (NPQ) with a fluorimeter. Leaf extracts were analysed to determine TPC and antioxidant activity. The maximum ETR and qP were recorded in spring and summer when the photosynthetically active radiation (PAR) at midday was higher (1901 and 1968 µmol m-2 s-1, respectively) than in other parts of a year. The Fv/Fm had typical physiological values in both types of leaves (about 0.8 in all the seasons). Also the NPQ was not influenced by the kind of leaves and season of the year. In concordance, the basal spring leaves had the highest TPC values. In contrast, the highest values of antioxidant activity were recorded in basal winter leaves followed by basal spring leaves. The results suggested that an increase in PAR (spring) positively affected the antioxidant activity and TPC, which correlated with higher ETR and qP values. The apical leaves showed morphological adaptations during the year and areas of intercellular spaces and palisade parenchyma were larger than in the basal leaves.