Activity Of Photosystem Research Articles

The Cytochrome b 6 f Complex Is Not Involved in Cyanobacterial State Transitions.

Photosynthetic organisms must sense and respond to fluctuating environmental conditions in order to perform efficient photosynthesis and to avoid the formation of dangerous reactive oxygen species. The excitation energy arriving at each photosystem permanently changes due to variations in the intensity and spectral properties of the absorbed light. Cyanobacteria, like plants and algae, have developed a mechanism, named "state transitions," that balances photosystem activities. Here, we characterize the role of the cytochrome b 6 f complex and phosphorylation reactions in cyanobacterial state transitions using Synechococcus elongatus PCC 7942 and Synechocystis PCC 6803 as model organisms. First, large photosystem II (PSII) fluorescence quenching was observed in State II, a result that does not appear to be related to energy transfer from PSII to PSI (spillover). This membrane-associated process was inhibited by betaine, Suc, and high concentrations of phosphate. Then, using different chemicals affecting the plastoquinone pool redox state and cytochrome b 6 f activity, we demonstrate that this complex is not involved in state transitions in S. elongatus or Synechocystis PCC6803. Finally, by constructing and characterizing 21 protein kinase and phosphatase mutants and using chemical inhibitors, we demonstrate that phosphorylation reactions are not essential for cyanobacterial state transitions. Thus, signal transduction is completely different in cyanobacterial and plant (green alga) state transitions.

Влияние наночастиц на физиологические характеристики и активность ферментов растений, выращенных в соленых почвах

Lately, use of nanoparticles in ecological problems solution of agriculture rouses a great interest. One of the interesting directions in nanotechnologies is nanoparticles application in agricultural plants salt-tolerance. Normal development of the plan provision in the saline soils was tried using from nanoparticles on the basis of Al2O3, CuO, Fe2O4, ZnO, TiO2 metals. For this purpose, an influence of nanoparticles on seeds hydration, soil rhizosphere, contamination and planes shooting in the normal and saline soils was investigated. In this connection before sowing the seeds were worked out by the nanoparticle dust. An impact of nanoparticles on plants shooting energy. Growth and development, photosynthetic pigments quantity. Photosystem activity and plant ferments concern future duties. The nanoparticles diffusion in seed endosperm was studied on the basis of the EPR method in the researches. Therefore, the samples were prepared from different layers of the seeds endosperm to determine EPR signal, the plant seeds were exposed to the influence of nanoparticles in dispersible solution for one day. Influence of nanoparticles on chlorophyll quantity in shooting leaves of the grown cultures in the normal and saline soils using of the spectroscopic method was determined. It was determined as a result of the experiment that nanoparticles stimulate shoots development changing a hydration character of the seeds, diffusing to the seeds, creating an opportunity for shooting in the saline soils.

Photosynthesis and organization of maize mesophyll and bundle sheath thylakoids of plants grown in various light intensities

The aim of this study was to investigate the acclimation of photosynthetic apparatus of maize to different light intensities during growth. Plants were grown at irradiance of 80 (LL), 200 (ML) and 600 (HL) μmol photons m−2 s−1. Our main interest was to understand how the light intensity influences the organization/function of thylakoid complexes in mesophyll (M) and bundle sheath (BS) chloroplasts. We have investigated several physiological parameters including rate of photosynthesis and respiration, the activity of photosystems, fluorescence in RT and at 77 K, phosphorylation of PSII proteins, level of proteins, and organization of thylakoid complexes. We suggest that BS chloroplasts are the main light target. Adjustment of the light absorption and distribution between both photosystems in BS is related to the organization of supercomplexes according to the phosphorylation level. The high rate of phosphorylation of LHCII in BS thylakoids is probably related to the absence of Lhcb3 protein and its replacement by Lhcb1 or Lhcb2 that undergo phosphorylation. In BS thylakoids, for all light conditions the LHCII proteins are bound to PSI, and a high pool of phosphorylated free trimers is present. We conclude that the investigated M and BS chloroplasts use different mechanisms of adjustment and optimization of their function, depending on the optimal or adverse irradiance conditions prevailing during the growth, and that these mechanisms are associated with different light penetration across the leaf. These changes induced by light in both types of chloroplasts are important in the regulation of chloroplast membrane flexibility and thus its function.

The effects of glyphosate-based herbicide formulations on Lemna minor, a non-target species

Research into plants plays an important role in evaluations of water pollution with pesticides. Lemna minor (common duckweed) is widely used as an indicator organism in environmental risk assessments. The aim of this study was to determine by biological Lemna test and chemical methods the effect of glyphosate (GlyPh) concentrations of 0–40 μM on duckweed, an important link in the food chain. There are no published data on glyphosate's effects on the activity of enzymes of the amine biosynthesis pathway: ornithine decarboxylase, S-adenosylmethionine decarboxylase, tyrosine decarboxylase, lysine decarboxylase and arginine decarboxylase, and the content of shikimic acid and glyphosate residues in the tissues of common duckweed.It was found that glyphosate was taken up by duckweed. In plants exposed to 3 μM of glyphosate for 7 days, glyphosate content exceeded the acceptable Maximum Residue Level (MRL) 10-fold. Glyphosate accumulation in plant tissues exerted toxic effects on duckweed by decreasing its growth and yield, inhibiting the synthesis of chlorophyll a and b and carotenoids, and decreasing the photochemical activity of photosystem II (PSII). However, glyphosate increased the concentration of shikimic acid in the tested plants. The activity of ornithine decarboxylase increased 4-fold in plants exposed to 20 μM of the herbicide. As a water pollutant, glyphosate increased the content of biogenic amines tyramine, putrescine, cadaverine, spermidine and spermine. The activity of peroxidase and catalase was highest in duckweed exposed to 20 μM and 7 μM of the herbicide, respectively. The predicted toxic units were calculated based on glyphosate content and the computed EC values. The mean effective concentration calculated for all morphological and biochemical parameters of duckweed was determined at EC10 = 1.55, EC25 = 3.36, EC50 = 6.62 and EC90 = 14.08 μM of glyphosate. The study demonstrated that glyphosate, the active ingredient of Roundup Ultra 360 SL herbicide, induces morphological and biochemical changes in non-target plants and exerts toxic effects on aquatic ecosystems even during short-term exposure.

增温对宁夏北部春小麦叶片光合作用的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 增温对宁夏北部春小麦叶片光合作用的影响 DOI: 10.5846/stxb201810302343 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 宁夏高等学校科学技术研究资助项目（NGY2015055）；宁夏自然科学基金资助项目（NZ16007）；国家自然科学基金项目（31660377） Effects of elevated temperature on photosynthesis of spring wheat in northern Ningxia Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为探索宁夏北部春小麦叶片光合作用应对未来气候变化的响应机制，进一步阐明气候变暖对干旱半干旱区春小麦生长的影响。采用自动控制红外线辐射器野外增温模拟气候变化的方法，以不做增温处理的春小麦冠层温度为基础温度，设置不同增温梯度（CK：0℃、T1：0.5℃、T2：1℃、T3：1.5℃、T4：2.0℃），开展气温升高对宁夏北部春小麦全生育期叶片叶面积、光合色素含量、光合特性、叶绿素荧光参数、干物重、产量等指标的影响试验。结果表明：春小麦苗期-拔节期，温度增加0.5℃时叶片叶面积、叶绿素含量、Pn（净光合速率）、WUE（叶片水分利用效率）呈上升的趋势。温度增加1.0-2.0℃时以上指标呈下降趋势，同时Ls（气孔限制值）呈上升趋势，Ci（胞间CO2浓度）呈下降的趋势，说明此时叶片Pn的下降主要是叶绿素含量的下降和气孔限制导致的。春小麦拔节期之后，叶片叶面积、叶绿素含量、Pn、WUE、Ls随温度的增加呈下降的趋势，而Ci随温度的增加呈上升的趋势，说明此时叶片Pn的下降则主要是叶绿素含量的下降和非气孔因素导致。叶绿素荧光参数表明在苗期-拔节期，春小麦对温度升高具有一定的抗逆性，能应对增温胁迫以热耗散的形式做出自我保护。拔节期以后，春小麦叶片光系统Ⅱ反应中心受温度胁迫可逆性失活，光合机构受到破坏。另外，春小麦干物重的变化趋势与叶面积等指标的变化趋势基本一致，产量及产量构成因素小穗数、穗粒数、千粒重随温度的增加显著降低，说明春小麦拔节期之前增温0.5℃有利于提高叶片光系统Ⅱ的潜在活性，增加叶片抗逆性，促进光合作用的进行，最终使光合产物累积量增多。增温梯度过大或增温时间过长则会使春小麦受高温胁迫，导致叶片光系统Ⅱ原初光能捕获、电子传递等效率降低，光合机构受到破坏，致使叶片Pn、WUE等数值下降，光合产物累积量减少，产量减少。 Abstract:In order to explore the response mechanism of photosynthesis of spring wheat leaves to climate change in northern Ningxia, the effects of warming on the growth of spring wheat in arid and semi-arid regions were further clarified. The effects of elevated temperature on leaf area, photosynthetic pigment content, photosynthetic characteristics, chlorophyll fluorescence parameters, and dry weight of spring wheat during the growth period in northern Ningxia were tested using automatic control infrared radiator for simulating climate change in the field. The method was based on the temperature of the spring wheat canopy temperature without treatment, and different temperature gradients were set (CK:0℃, T1:0.5℃, T2:1℃, T3:1.5℃, and T4:2.0℃). The results showed that leaf area, chlorophyll content, Pn (net photosynthetic rate), and WUE (leaf water use efficiency) of spring wheat had an upward trend when the temperature increased by 0.5℃ during seedling-jointing stage. The above indices indicated a downward trend when the temperature increased by 1.0-2.0℃, while Ls (stomatal limitation value) showed an upward trend and Ci (intercellular CO2 concentration) showed a downward trend, indicating that the decrease of Pn in leaves was mainly caused by the decrease of chlorophyll content and stomatal limitation. However, after the jointing stage, the leaf area, chlorophyll content, Pn, WUE, and Ls were decreased when increasing temperature, while Ci increased, which indicating that the decrease of leaf Pn was mainly caused by a decrease in chlorophyll and non-stomatal limitation. Chlorophyll fluorescence parameters showed that spring wheat was resistant to temperature rise before jointing stage, and could cope with the warming stress to protect itself in the form of heat dissipation. After the jointing stage, the photosystem II reaction center of spring wheat leaves was reversibly inactivated by temperature stress, and the photosynthetic apparatus was destroyed. In addition, the change trend of dry weight of spring wheat was basically consistent with that of leaf area and other indicators. The yield and yield components, spikelet number, grains number per spike, and 1000-grain weight decreased significantly with rising temperature. When 0.5℃ rising before jointing stage, it was beneficial to increase the potential activity of leaf photosystem II, increase leaf resistance, promote photosynthesis, and eventually increase photosynthetic product. If the temperature gradient is too large or the heating time is too long, spring wheat will be subjected to high temperature stress, which leads to the reduction of the original light energy capture and electron transfer efficiency of the leaf photosystem II, and the photosynthetic mechanism is damaged. Finally, the values of Pn and WUE in the leaves of spring wheat decreased, the accumulation of photosynthetic products and the yield decreased. 参考文献 相似文献 引证文献

Acquired tolerance of the photosynthetic apparatus to photoinhibition as a result of growing Solanum lycopersicum at moderately higher temperature and light intensity.

The kinetics of photoinhibition in detached leaves from tomato plants (Solanium lycopersicum L. cv. M82) grown for 6 days under different combinations of optimal and moderately high temperature and optimal and high light intensity were studied. The inhibition of PSII was evaluated by changes in maximal quantum yield, the coefficient of photochemical quenching and the quantum yield of PSII. The changes of PSI activity was estimated by the redox state of P700. The involvement of different possible protective processes was checked by determination of nonphotochemical quenching and cyclic electron flow around PSI. To evaluate to what extent the photosynthetic apparatus and its response to high light treatment was affected by growth conditions, the kinetics of photoinhibition in isolated thylakoid membranes were also studied. The photochemical activities of both photosystems and changes in the energy distribution and interactions between them were evaluated by means of a Clark electrode and 77 K fluorescence analysis. The data showed an increased tolerance to photoinhibition in plants grown under a combination of moderately high temperature and light intensity, which was related to the stimulation of cyclic electron flow, PSI activity and rearrangements of pigment-protein complexes, leading to a decrease in the excitation energy delivered to PSII.

Chemical reduction of graphene enhances in vivo translocation and photosynthetic inhibition in pea plants

Reduced graphene oxide (RGO) was translocated into leaves and inhibited the activity of photosystem II by damaging the oxygen-evolving-complex on the donor side.

Exogenous alpha lipoic acid can stimulate photosystem II activity and the gene expressions of carbon fixation and chlorophyll metabolism enzymes in maize seedlings under drought

Protective compounds such as non-enzymatic antioxidants, osmolytes and signal molecules have been applied to plants exposed to various environmental stresses to increase their stress tolerance. However, there are not enough records about the response of plants to alpha lipoic acid (ALA) application with antioxidant properties. Therefore, this study was designed to evaluate the function of exogenous ALA on the photosynthetic performance of maize seedlings grown in hydroponic conditions under drought stress. Three weeks old seedlings were treated with or without ALA (12 μM) and they were subjected to drought stress induced by 10% polyethylene glycol (PEG6000) for 24 h. Chlorophyll content, gas exchange parameters, chlorophyll fluorescence and the expression levels of genes involved in CO2 fixation (ribulose-1,5-bisphosphate carboxylase (rubisco), phosphoenolpyruvate carboxylase (PEPc), Rubisco activase (RCA)) and chlorophyll metabolism (magnesium chelatase (Mg-CHLI) and chlorophyllase (Chlase)) were determined. The application of ALA increased chlorophyll content and the activity of photosystem II in comparison to the untreated seedlings under drought stress. The relative expression levels of Rubisco, PEPc, RCA and Mg-CHLI significantly increased while the Chlase gene expression decreased in seedlings to which ALA was applied in comparison those to which it was not applied under the stress. These results suggest that exogenous ALA can enhance the photosynthetic performance of maize seedlings exposed to drought by inducing photosystem II activity and the gene expressions of carbon fixation and chlorophyll metabolism enzymes.

Increased Catalase Activity and Maintenance of Photosystem II Distinguishes High-Yield Mutants From Low-Yield Mutants of Rice var. Nagina22 Under Low-Phosphorus Stress.

An upland rice variety, Nagina22 (N22) and its 137 ethyl methanesulfonate (EMS)-induced mutants, along with a sensitive variety, Jaya, was screened both in low phosphorus (P) field (Olsen P 1.8) and in normal field (Olsen P 24) during dry season. Based on the grain yield (YLD) of plants in normal field and plants in low P field, 27 gain of function (high-YLD represented as hy) and 9 loss of function (low-YLD represented as ly) mutants were selected and compared with N22 for physiological and genotyping studies. In low P field, hy mutants showed higher P concentration in roots, leaves, grains, and in the whole plant than in ly mutants at harvest. In low P conditions, Fv/Fm and qN were 24% higher in hy mutants than in ly mutants. In comparison with ly mutants, the superoxide dismutase (SOD) activity in the roots and leaves of hy mutants in low P fields was 9% and 41% higher at the vegetative stage, respectively, but 51% and 14% lower in the roots and leaves at the reproductive stage, respectively. However, in comparison with ly mutants, the catalase (CAT) activity in the roots and leaves of hy mutants in low P fields was 35% higher at the vegetative stage and 15% and 17% higher at the reproductive stage, respectively. Similarly, hy mutants in low P field showed 20% and 80% higher peroxidase (POD) activity in the roots and leaves at the vegetative stage, respectively, but showed 14% and 16% lower POD activity at the reproductive stage in the roots and leaves, respectively. Marker trait association analysis using 48 simple sequence repeat (SSR) markers and 10 Pup1 gene markers showed that RM3648 and RM451 in chromosome 4 were significantly associated with grain YLD, tiller number (TN), SOD, and POD activities in both the roots and leaves in low P conditions only. Similarly, RM3334 and RM6300 in chromosome 5 were associated with CAT activity in leaves in low P conditions. Notably, grain YLD was positively and significantly correlated with CAT activity in the roots and shoots, Fv/Fm and qN in low P conditions, and the shoots’ P concentration and qN in normal conditions. Furthermore, CAT activity in shoots was positively and significantly correlated with TN in both low P and normal conditions. Thus, chromosomal regions and physiological traits that have a role in imparting tolerance to low P in the field were identified.

Effects of Drought Stress on the Photosynthesis in Maize

To clarify how the components of the entire photosynthetic electron transport chain in response to drought stress in maize. The activities of photosystem II (PSII), photosystem I (PSI), and the electron transport chain between PSII and PSI of maize were investigated by prompt fluorescence (PF), delayed fluorescence (DF) and 820 nm modulated reflection (MR). Maize (Zea mays L.) plants were subjected to different levels of soil water availability including control, moderate and severe drought stress. A significant decrease in ϕE0, Ψ0 and PIABS was found in maize treated with moderate drought stress. A significant increase in ABS/RC was observed, but there were no significant change in the fast MR phase and the amplitude of DF under moderate drought stress compared to the control. Under severe drought stress, the exchange capacity between QA to QB, reoxidation capacity of plastoquinol, and the oxidation and re-reduction rates of PC and P700 all decreased. These results demonstrated that moderate drought stress reduced the photochemical activity of PSII from QA to PQH2, while the photochemical activity of PSI was unscathed. However, severe drought stress inhibited the entire electron transport chain from the donor side of PSII to PSI-end electron acceptors. In addition, the photochemical activity of PSII is more sensitive to drought stress than PSI.

The characteristic pattern of multiple colored layers in coastal stratified lakes in the process of separation from the White Sea

An unusual feature of the saline stratified lakes that were formed due to ongoing postglacial uplift on the White Sea coast is the presence of several differently colored thin layers in the zone with sharp gradients. Colored layers in five lakes at various stages of separation from the sea were investigated using optical microscopy, spectrophotometry, spectrofluorimetry, and photobiology. The upper greenish colored layer located in the aerobic strata of all lakes near the compensation depth of 1% light penetration contains green algae. In the chemocline, another layer, brightly green, red or pink, is dominated by mixotrophic flagellates. Despite the very low light intensities and the presence of H2S, active photosynthesis by these algae appears to be occurring, as indicated by high values of the maximum quantum yield of primary photochemistry, electron transport activity, photosynthetic activity of photosystem II, the fraction of active centers, and low values of heat dissipation. In the reduced zone of the chemocline, a dense green or brown suspension of anoxygenic phototrophs (green sulfur bacteria) is located.

Physiological and Biochemical Responses of Cucumis melo L. Chloroplasts to Low-Phosphate Stress.

Phosphorus (P) is a limiting plant soil nutrient. Long-term low inorganic phosphate (Pi) irreversibly damages plant cells and hinders plant growth. Plants have evolved several adaptive biochemical, physiological, and developmental responses to low-Pi stress. However, little is known about chloroplast responses to low-Pi stress. In this study, we used physiological and biochemical analyses to investigate melon chloroplast responses to low-Pi stress. The results indicated that low-Pi stress impeded melon seedling growth and reduced its dry matter content by inhibiting the photosynthesis. Low-Pi stress reduced the P content in shoots, which inhibited ATP synthase (ATP-ase) activity, and disturbed the proton and electron transport efficiency on chloroplast photosynthetic electron transport chain. In addition, low-Pi stress induced reactive oxygen species (ROS) production in the leaves, which caused membrane peroxidation. Therefore, redox homeostasis was not maintained, and the melon leaves presented with symptoms of photooxidative stress. To mitigate photoinhibition, the melon plants initiated non-photochemical chlorophyll fluorescence quenching (NPQ) initiated by acidification of the thylakoid lumen to dissipate excess excitation energy, significantly improved ROS-scavenging enzyme activity. Based on these experimental results, we concluded that low Pi inhibited photosystem activity and caused photooxidative stress and photoinhibition. To alleviate these negative effects, the plant activated its NPQ mechanism, alternative electron transport pathways, and antioxidant system to protect its chloroplasts.

Oxygenic Photoreactivity in Photosystem II Studied by Rotating Ring Disk Electrochemistry.

Protein film photoelectrochemistry has previously been used to monitor the activity of photosystem II, the water-plastoquinone photooxidoreductase, but the mechanistic information attainable from a three-electrode setup has remained limited. Here we introduce the four-electrode rotating ring disk electrode technique for quantifying light-driven reaction kinetics and mechanistic pathways in real time at the enzyme–electrode interface. This setup allows us to study photochemical H2O oxidation in photosystem II and to gain an in-depth understanding of pathways that generate reactive oxygen species. The results show that photosystem II reacts with O2 through two main pathways that both involve a superoxide intermediate to produce H2O2. The first pathway involves the established chlorophyll triplet-mediated formation of singlet oxygen, which is followed by its reduction to superoxide at the electrode surface. The second pathway is specific for the enzyme/electrode interface: an exposed antenna chlorophyll is sufficiently close to the electrode for rapid injection of an electron to form a highly reducing chlorophyll anion, which reacts with O2 in solution to produce O2•–. Incomplete H2O oxidation does not significantly contribute to reactive oxygen formation in our conditions. The rotating ring disk electrode technique allows the chemical reactivity of photosystem II to be studied electrochemically and opens several avenues for future investigation.

Adverse effects of strong light and nitrogen deficiency on cell viability, photosynthesis, and motility of the red-tide dinoflagellate Karenia mikimotoi

:The dinoflagellate Karenia mikimotoi is a red tide–forming alga that causes serious damage to aquaculture in coastal areas around the world. Its eco-physiological characteristics have been investigated extensively but conditions associated with declines of red tides of K. mikimotoi remain unknown. In the present study, we investigated the effects of light and nutrients on the viability, activity of photosystem II (PSII), and motility of K. mikimotoi. Cells were incubated under low (100 μmol photons m−2 s−1 on a 12:12 light:dark cycle of illumination) or high irradiance (1000 μmol photons m−2 s−1) for 4 h in the middle of the photoperiod, in different media. Under low light, most cells survived for about 1 month in media depleted of nitrogen (N) and phosphorus (P), similar to their survival pattern in complete medium. However, when cells that had been pre-incubated in N-depleted medium for 7 d were incubated under high light in an N-depleted medium, cell density and PSII activity declined within a few days. In P-depleted and complete media, there were no significant differences in cell density and PSII activity between low and high light, at least for 10 d. Furthermore, PSII activity was much more sensitive to photoinhibition in N-depleted than in complete medium. The rhythm of diurnal vertical migration of K. mikimotoi was observed in very low light (10 μmol photons m−2 s−1) in different media. The rhythm became obscure in N- and P-depleted media; in fact, most cells stayed in the surface layer all day in N-depleted medium. Moreover, cells accumulating in surface layers in N- and P-depleted media descended very little, even when irradiated with high light. These observations suggest that N-deficiency might trap cells in the surface layer and increase their susceptibility to photoinhibition of PSII, possibly leading to cell death. The combination of N-deficiency and high light thus appears to be an important factor that determines the decline of red tides of K. mikimotoi.

Characterization of the Leaf Color Mutant hy and Identification of the Mutated Gene in Chinese Cabbage

Leaf color mutants play an important role in our understanding of chlorophyll biosynthesis and catabolism. In this study, we obtained a yellow-green leaf mutant hy in an ethyl methanesulfonate mutagenized population of chinese cabbage (Brassica rapa ssp. pekinensis). The hy phenotype was controlled by a recessive allele at a single locus. The intrinsic photochemical activity of photosystem II (PSII) is impaired in hy, suggesting that absorbed light energy is not efficiently transferred from the light-harvesting complexes antenna to the PSII reaction centers and dissipated as heat or fluorescence. We measured chlorophyll content and chlorophyll precursors and analyzed the expression of key genes in the chlorophyll synthetic pathway in hy and wild type. The mutation phenotype was consistent with inhibited expression of chlorophyll a oxygenase (CAO) gene in the chlorophyll synthetic pathway. In mutant hy, CAO cDNA was cloned so that a C to T mutation at 1099 bp caused a conserved proline (Pro) to serine (Ser) mutation at the 367th amino acid in C-domain, which changed the secondary structure of CAO protein. We speculate that the mutation amino acid changed in the C-domain may affect the catalytic function in mutant CAO.

Seasonal Changes in Primary Photosynthetic Events during Low Temperature Adaptation of Pinus sylvestris in Central Yakutia

The methods of chlorophyll fluorescence induction and HPLC were used to study the influence of autumnal temperature decrease on photochemical electron-transport activity of photosystem II (PSII), nonphotochemical quenching of excessive excitation energy, and the composition of pigments in the firstyear needles of Pinus sуlvestris L. trees grown naturally in Central Yakutia. In the period from the beginning of September to October 10, the chlorophyll content was reduced by half, while the Chl a/b ratio increased from 2.9 to 4.3–4.5, indicating the degradation of peripheral antenna complexes. The decrease in average daily temperature to 4.9–6.4°C led to a transient increase in the quantum yield of nonphotochemical quenching (ΔpH-dependent parameter φNPQ). These changes were accompanied by a slow accumulation of unregulated zeaxanthin fraction insensitive to illumination conditions. The further decrease in average daily temperature to near-zero levels was paralleled by a sharp increase in zeaxanthin content, while the pH-dependent quenching was replaced with the constitutive quenching (parameter φf,D) because of the supposed structural reorganization of PSII. These processes were accompanied by a fast decrease in PSII functional activity, which was mostly due to the impairment of plastoquinone photochemical reduction. Freezing temperatures (from–3.6 to–12.1) destructed the oxygen-evolving complex in PSII and completely inactivated the PSII reaction centers. It is concluded that the largest changes in the condition of photosynthetic apparatus occur at a near-zero temperature range and proceed until complete inactivation of PSII under the action of freezing temperatures.

Chlorella zofingiensis as a promising strain in wastewater treatment

This study was conducted to evaluate the efficiency of treatment by C. zofingiensis, C. vulgaris and Scenedesmus sp. in terms of nutrient loading, lipid productivity and the activity of photosystem II. Results from nutrient loading suggested that the nitrogen loading of C. zofingiensis at 0.406 mg/L/h was higher than C. vulgaris and Scenedesmus sp., and the phosphorus loading of C. zofingiensis at 0.075 mg/L/h was higher than C. vulgaris. During the treating process, C. zofingiensis accumulated lipid with higher productivity of 26.57 mg/L/d than C. vulgaris and Scenedesmus sp. In combination with photosynthetic efficiency, C. zofingiensis possessed superior trophic transfer efficiency and absorption capability, even in worse environmental conditions. C. zofingiensis, therefore, exhibited the promising application prospect in wastewater treatment.

Semiconducting quantum dots for artificial photosynthesis

Sunlight is our most abundant, clean and inexhaustible energy source. However, its diffuse and intermittent nature makes it difficult to use directly, suggesting that we should instead store this energy. One of the most attractive avenues for this involves using solar energy to split H2O and afford H2 through artificial photosynthesis, the practical realization of which requires low-cost, robust photocatalysts. Colloidal quantum dots (QDs) of IIB–VIA semiconductors appear to be an ideal material from which to construct highly efficient photocatalysts for H2 photogeneration. In this Review, we highlight recent developments in QD-based artificial photosynthetic systems for H2 evolution using sacrificial reagents. These case studies allow us to introduce strategies — including size optimization, structural modification and surface design — to increase the H2 evolution activities of QD-based artificial photosystems. Finally, we describe photocatalytic biomass reforming and unassisted photoelectrochemical H2O splitting — two new pathways that could make QD-based solar-to-fuel conversion practically viable and cost-effective in the near future.

Exogenous melatonin enhances salt stress tolerance in maize seedlings by improving antioxidant and photosynthetic capacity.

Melatonin (N-acetyl-5-methoxytryptamine) is an important biological hormone in many abiotic stress responses and developmental processes. In this study, the protective roles of melatonin were investigated by measuring the antioxidant defense system and photosynthetic characteristics in maize under salt stress. The results indicated that NaCl treatment led to the decrease in plant growth, chlorophyll contents and photochemical activity of photosystem II (PSII). However, the levels of reactive oxygen species increased significantly under salt stress. Meanwhile, we found that application of exogenous melatonin alleviated reactive oxygen species burst and protected the photosynthetic activity in maize seedlings under salt stress through the activation of antioxidant enzymes. In addition, 100 μM melatonin-treated plants showed high photosynthetic efficiency and salinity. Immunoblotting analysis of PSII proteins showed that melatonin application alleviated the decline of 34 kDa PSII reaction center protein (D1) and the increase of PSII subunit S protein. Taken together, our study promotes more comprehensive understanding in the protective effects of exogenous melatonin in maize under salt stress, and it may be involved in activation of antioxidant enzymes and regulation of PSII proteins.

Effects of 1-butyl-3-methylimidazolium chloride on the photosynthetic system and metabolism of maize (Zea mays L.) seedlings

Ionic liquids (ILs) are widely used in various chemical processes. However, a growing number of studies have found that ILs are potentially toxic to different types of living organisms, including crops. The present study analysed the effects of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) on the photosynthetic system and metabolism of maize seedlings. Results showed that [C4mim]Cl could significantly reduce maize leaf chlorophyll level and cause extensive leaf bleaching. The activity of photosystem II (PSII) was significantly inhibited when seedlings exposed to higher concentration of [C4mim]Cl. The maximum quantum yield of PSII and the potential efficiency of PSII were reduced by 63% and 88% under 800 mg/L [C4mim]Cl treatment in comparison with the control treatment. The RNA sequencing analysis performed to examine gene expression profiles of maize leaves under [C4mim]Cl treatment revealed 639 differentially expressed genes (DEGs), 115 of which were categorized into different metabolic pathways. Among these DEGs, the seven genes involved in the photosynthetic Calvin cycle were down-regulated by [C4mim]Cl exposure. For carbohydrates and amino acids metabolism, the genes for starch synthesis were down-regulated, while the genes for amino acids and protein degradation were up-regulated. The changes observed in these major metabolic pathways might be an important reason for [C4mim]Cl toxicity.