Photosynthesis In Cucumber Research Articles

Effects of microplastics and combined pollution of polystyrene and di-n-octyl phthalate on photosynthesis of cucumber (Cucumis sativus L.)

Photosynthesis provides carbon sources and energy for crop growth and development, and the widespread presence of microplastics and plastic plasticisers in agricultural soils affects crop photosynthesis, but the mechanism of the effect is not clear. This study aims to investigate the effects of different microplastics and plasticizers on cucumber photosynthesis. Using polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), and di-n-octyl phthalate (DOP) as representative microplastics and plasticizers, we assessed their impact on cucumber photosynthesis. Our results reveal significant alterations in key parameters: intercellular CO2 concentration (Ci) and transpiration rate (Tr) increased across all treatments, whereas stomatal limit value (Ls) and water use efficiency (WUE) decreased. Notably, PS + DOP treatment led to a significant reduction in the maximum efficiency of photosystem II (Fv/Fm) and ATP accumulation. Furthermore, PE and PS + DOP treatments decreased lycopene and ɛ-carotene synthesis rates, as well as abscisic acid (ABA) accumulation. All treatments inhibited the conversion of β-carotene into strigolactone (SL) and decreased chlorophyll synthesis rates, with PS + DOP exhibiting the most severe impact. Regarding chlorophyll degradation pathways, PVC and PE treatments reduced chlorophyll decomposition rates, whereas DOP with PS promoted degradation. PE and PS treatments also impaired light energy capture, electron transport, and the structural stability of photosystems I and II, as well as photosynthetic capacity and NADPH and ATP synthesis rates. Our findings underscore the differential impacts of microplastics and plasticizers on cucumber photosynthesis, with PS + DOP having the most detrimental effect. These results shed light on the complex interactions between microplastics and plant physiology, highlighting the urgent need for mitigation strategies in agricultural practices to safeguard crop productivity and environmental sustainability.

Effects of Bacillus subtilis on Cucumber Seedling Growth and Photosynthetic System under Different Potassium Ion Levels.

Potassium deficiency is one of the important factors restricting cucumber growth and development. This experiment mainly explored the effect of Bacillus subtilis (B. subtilis) on cucumber seedling growth and the photosynthetic system under different potassium levels, and the rhizosphere bacteria (PGPR) that promote plant growth were used to solubilize potassium in soil, providing theoretical support for a further investigation of the effect of biological bacteria fertilizer on cucumber growth and potassium absorption. "Xinjin No. 4" was used as the test material for the pot experiment, and a two-factor experiment was designed. The first factor was potassium application treatment, and the second factor was bacterial application treatment. The effects of different treatments on cucumber seedling growth, photosynthetic characteristics, root morphology, and chlorophyll fluorescence parameters were studied. The results showed that potassium and B. subtilis had obvious promotion effects on the cucumber seedling growth and the photosynthesis of leaves. Compared with the blank control, the B. subtilis treatment had obvious effects on the cucumber seedling height, stem diameter, leaf area, total root length, total root surface area, total root volume, branch number, crossing number, gs, WUE, Ci, and A; the dry weight of the shoot and root increased significantly (p ≤ 0.05). Potassium application could significantly promote cucumber growth, and the effect of B. subtilis and potassium application was greater than that of potassium application alone, and the best effect was when 0.2 g/pot and B. subtilis were applied. In conclusion, potassium combined with B. subtilis could enhance the photosynthesis of cucumber leaves and promote the growth of cucumber.

Sustainable Reuse of Expresso Coffee By-products as a Natural Fertilizer to Improve Growth and Photosynthesis in Cucumber (Cucumis sativus L.) Plants

Spent coffee grounds (SCGs), deriving from the high global coffee consumption, can have an appreciable environmental impact. One of the eco-friendly reuses of SCGs is their application as a natural fertilizer. This study adopted a soilless cultivation approach to growing Cucumis sativus seedlings using, as rooting media, different coffee solutions obtained by infusing fresh coffee powder or SCGs from mocha and pods for 7 or 30 days. Seedlings’ germination, eco-physiological and biochemical traits were evaluated and the potential toxicological risks or beneficial effects of SCGs on plants were assessed. Results indicate that, although germination was unaffected, fresh coffee medium inhibited seedling development and that 7 days mocha solution stopped seedling growth and induced leaf structural alterations. Conversely, 30 days mocha and pod suspensions promoted seedling biomass, and increased leaf area, leaf polyphenol concentration, and photochemical efficiency. In conclusion, findings indicate that fresh powder can induce toxic effects while SCGs can improve cucumber from a physiological point of view by acting as a natural fertilizer. This study opens future investigations that will help manage coffee waste released into the environment by sustainable practices.Graphical

Exogenous dopamine promotes photosynthesis and carbohydrate metabolism of downy mildew-infected cucumber

Downy mildew causes great damage to cucumber photosynthesis and is a major threat to cucumber production. The increase in drawbacks associated with chemical treatments has prompted the need for alternative protecting agents. We evaluated the physiological effects of different exogenous dopamine concentrations on the photosynthetic capacity and carbohydrate metabolism of downy mildew-infected cucumber. The results showed that applying 100 µmol L−1 exogenous dopamine significantly promoted the growth of cucumbers under downy mildew stress and decreased the disease index, thereby contributing to improved disease resistance in cucumber. Exogenous dopamine effectively increased the photosynthetic pigment content, chlorophyll fluorescence parameters, net leaf photosynthetic rate and stomatal conductance and transpiration rate but reduced the intercellular CO2 concentration. Exogenous dopamine application also increased the activity of ribulose-1,5-bisphosphate carboxylase/oxygenase during carbon assimilation, upregulated the expression of Rubisco regulatory genes (CsrbcL and CsrbcS) and downregulated the expression of chlorophyll degradation related genes (CsPAO and CsRCCR). The contents of total soluble and reducing sugars were increased, thereby maintaining the osmotic adjustment function. At the same time, applying 100 µmol L−1 dopamine significantly increased the activity of sucrose synthase, sucrose phosphate synthase, acid invertase and neutral invertase in carbohydrate metabolism. Further, dopamine application upregulated the expression of CsSUS3 and CsSPS4 and increased cucumber starch, cellulose, fructose, sucrose and glucose contents. Therefore, exogenous dopamine can effectively alleviate the damage to cucumber photosynthetic and carbohydrate metabolism rates caused by downy mildew, thereby maintaining the normal growth of cucumber under stress.

Melatonin alleviates imidacloprid phytotoxicity to cucumber (Cucumis sativus L.) through modulating redox homeostasis in plants and promoting its metabolism by enhancing glutathione dependent detoxification

Melatonin (Mel), a powerful antioxidant that has the ability to regulate physiological and biochemical processes in plants under abiotic stresses. However, its roles in pesticide detoxification is poorly understood. Herein, selecting leaf spraying insecticide imidacloprid (IMD) as the model, we demonstrated the detoxification mechanism underlying root pretreatment of Mel on IMD in cucumber. IMD treatment affected the primary light conversion efficiency of photosystem II (Fv/Fm), reduced the quantum yield, and increased hydrogen peroxide and superoxide anions contents as well as the levels of membrane lipid peroxidation, indicating that excessive IMD treatment induces oxidative stress. Nonetheless, by increasing the appropriate levels of exogenous Mel, the photosynthesis of cucumber under IMD treatment reached the control levels, effectively removing reactive oxygen species. Furthermore, the content and ratio of ascorbate (AsA) and glutathione (GSH) were decreased under IMD treatment; Mel treatment enhanced the AsA/DHA and GSH/GSSG ratios, as well as the activities of MDHAR, DHAR and GR, suggesting that Mel could alleviate oxidative stress of cucumber treated with IMD by regulating the ascorbic acid-glutathione cycle. Importantly, IMD degradation rate and glutathione S-transferase (GST) activity increased after Mel treatment. The levels of transcripts encoding antioxidant enzymes GPX and GST (GST1,2 and 3) were also increased, indicating that Mel accelerated IMD degradation. These results suggest that Mel plays an important role in the detoxification of IMD by promoting GST activity and transcription and the AsA-GSH cycle, thus providing an approach for plants to reduce IMD residue through the plant's own detoxification mechanism.

Short-term Thermal Acclimation Increases Ribulose 1, 5 Bisphosphate Carboxylase/Oxygenase Activity and Content and Enhances Heat Stress Tolerance of Photosynthesis in Cucumber

Short-term Thermal Acclimation Increases Ribulose 1, 5 Bisphosphate Carboxylase/Oxygenase Activity and Content and Enhances Heat Stress Tolerance of Photosynthesis in Cucumber

Hydrogen sulfide acted as a downstream signal was involved in the regulation of salicylic acid on photosynthesis of cucumber seedlings under low temperature and low light intensity

Both salicylic acid (SA) and hydrogen sulfide (H2S) play an important role in regulating plant growth and development and physiological metabolism under abiotic stresses. As signal molecules, the interaction between them in regulating cucumber photosynthesis under low temperature and low light is still unclear. Here, we examined the regulation and interaction of SA and H2S on photosynthesis in cucumber seedlings under low temperature (8 ℃/5 ℃, day/night) and low light (100 μmol·m-2·s-1). Seedlings were foliar-sprayed with SA, sodium sulfide (NaHS, H2S donor), and their scavenger or biosynthesis inhibitors, respectively. Seedlings treated with deionized water at suitable temperature and light condition were used as the control. The results showed that SA increased the L-/D-cysteine desulfhydrase (LCD, DCD) activities and relative mRNA expression, and consequently promoted the endogenous H2S production. However, NaHS did not affect the activities and gene expressions of phenylalnine ammonialyase and isochorismate and endogenous SA level. Compared with the H2O-treated seedlings under low temperature and low light, SA- and NaHS-treated seedlings showed an increase in the photosynthetic rate, stomatal conductance and transpiration rate, while a decrease in intercellular CO2 concentration. SA and NaHS increased the CO2 assimilation, which mainly attributed to the increases in the activities of the ribulose-1, 5-bisphosphate carboxylase, rubisco activase, sedoheptulose-1, 7-bisphosphatase and fructose-1, 6-bisphosphatase, as well as their mRNA expression. Meanwhile, SA and NaHS improved the actual photochemical efficiency and maximal photochemical efficiency of PSII, and therefore alleviated the damage in photosynthetic apparatus and negative effect on growth from low temperature and low light stress. The SA-induced higher photosynthesis and growth in stressed seedlings were suppressed by addition of H2S scavenger hypotaurine. However, the H2S-induced tolerance of photosynthetic apparatus to low temperature and low light was not affected by SA biosynthesis inhibitor paclobutrazol and 2-aminoindan-2-phosphonic acid. Our results suggested that H2S, as a downstream signal of SA, was involved in regulating photosynthesis in cucumber seedlings under low temperature and low light.

Comparation of the phytotoxicity between chemically and green synthesized silver nanoparticles

Green synthesis of silver nanoparticles (Ag NPs) by using plants extracts has provided an eco-friendly alternation for industry and agriculture application. Here, we prepared Ag NPs by using the cucumber leaves and rice husk extracts, and further assessed the antimicrobial activity and phytotoxicity of green synthesized Ag NPs (g-Ag NPs) comparing with chemically synthesized Ag NPs (chem-Ag NPs). The chem-Ag NPs had strong antibacterial activity on the growth of Escherichia coli, while g-Ag NPs by rice husks (gr-Ag NPs) exhibited long-term antibacterial effects. In terms of phytotoxicity, the chem-Ag NPs induced over-generation of ROS and activated plant antioxidant defense systems, thus resulting in the upregulation of MDA and Zn contents and downregulation of antioxidant capacity, carotenoid, globulin and Mo contents. However, g-Ag NPs significantly promoted cucumber photosynthesis by increasing chlorophyll contents. Besides, the green synthesized Ag NPs by cucumber extracts (gc-Ag NPs) increased protein contents and gr-Ag NPs stimulated the upregulation of Mn and the downregulation of Al, which were all positive effects. Overall, compared with chem-Ag NPs, g-Ag NPs exhibited long-tern antimicrobial properties and attenuated toxicity to plants, which could be used as potential nanopesticide or nanoscale growth regulator in agriculture.

Special issue in honour of Prof. Reto J. Strasser - Dorsoventral variation in photosynthesis during leaf senescence probed by chlorophyll a fluorescence induction kinetics in cucumber and maize plants

Although photosynthesis has been intensively studied during leaf senescence, it is unclear whether the changes of photosynthetic function in various mesophyll tissues can be detected using chlorophyll a fluorescence induction kinetics (CFI) in vivo. To clarify this question, leaf structure and CFI were carefully examined in senescent leaves. The results showed declines in chlorophyll content and photosynthetic rate in both cucumber and maize plants as leaves aged. In cucumber leaves, the number of chloroplasts decreased more rapidly in the palisade tissue compared to the sponge tissue as senescence progressed. Under various pulse light intensities, the enhancement of the relative variable fluorescence in the CFI curves measured on the adaxial side was larger than that on the abaxial side of senescent cucumber leaves, indicating senescence in the palisade tissue progressed more quickly than that in the sponge tissue. JIP-test parameters further showed that the loss of photosynthetic electron transport activity in palisade tissue was faster than that in sponge tissue. However, during leaf senescence in maize, there were no such dorsoventral differences. We therefore propose that the decline of photosynthesis in cucumber leaves is largely determined by the senescence of palisade tissue. The changes in photosynthesis in palisade and sponge tissues with leaf aging can be probed effectively by CFI measured on both sides of cucumber leaves in vivo.

Inhibition of photosynthesis in cucumber leaves by oxybenzone

Oxybenzone (OBZ), a popular additive in sunscreen, can protect human skin by blocking ultraviolet (UV) rays from the sun (Baker et al. 2015). In addition to being used in sunscreens, OBZ is also widely used in perfumes, shampoos, lip balms, and other pharmaceuticals and personal care products (PPCPs) (Aguirre et al. 1992, Emonet et al. 2001, Kasichayanula et al. 2007). OBZ can enter rivers, lakes, groundwater, sewage, and so on through human activities and was identified as an 'emerging environmental pollutant' by the Environmental Protection Agency of the USA (Rodil et al. 2012, Aguera et al. 2013). With the rise in coastal tourism, a large number of coral reefs in coastal areas are being exposed to water containing OBZ (Baron et al. 2013, Tashiro and Kameda 2013). OBZ, as a pseudo-persistent pollutant, has a long-term toxic effect on the environment (Vione et al. 2013).

Effect of Short-Term Treatment of Roots with Melatonin on Photosynthesis of Cucumber Leaves

Effect of a short-term (15, 30, 60, and 120 min) root treatment with melatonin (0.1 pM and 1.0 µM) on physiological parameters of the leaf was studied in 21-day-old cucumber (Cucumis sativus L.) plants, early cv. Izyashchnyi, grown on Murashige-Skoog nutrient medium. Experimental data concerning kinetics of melatonin influence have shown that the duration of the aftereffect necessary for activation of photosynthesis, transpiration, and stomatal conductance of cucumber leaves decreased when the concentration of the exogenous melatonin used for root treatment rose. A similar pattern was observed in respect to intensification of lipids’ peroxidation, content of proline, and activation of guaiacol-dependent peroxidase (ЕС 1.11.1.7). Under the effect of melatonin, antiradical activity in the leaf decreased in 120 min, which was preceded by a reduction in the content of total flavonoids. Regulation in activity of antioxidant enzymes superoxide dismutase (ЕС 1.15.1.1) and catalase (ЕС 1.11.1.6) was more intricate. Possible mechanisms of the influence of melatonin on parameters of photosynthesis in cucumber leaves are discussed.

The effects of pine wood vinegar on the germination, growth and photosynthetic characteristics of cucumber

Wood vinegar is a substance, derived from cooling black carbon fire, which could be used instead of chemical materials in the agriculture industry as an organic compound. In order to study the effectiveness of pine wood vinegar on physiological and photosynthesis traits of cucumber, two experiments were conducted based on a completely randomized design with six treatments including 0, 1250, 2000, 2500, 3333 and 5000 mgL-1 of wood vinegar with four replications. The first experiment was designed in the laboratory in order to study the effect of pine wood vinegar priming on cucumber seeds and the second one was conducted in a greenhouse condition to investigate the effect of wood vinegar on seedlings of cucumber in Isfahan University of Technology. The highest flower number and yield in cucumber was observed in 2500 mgL-1 pine wood vinegar trearment. Photosynthesis in cucumber increased in 2000 mgL-1 pine wood vinegar trearment. The lowest transpiration in cucumber was 1.54 mmolm–2s–1 in 2000 mgL-1 pine wood vinegar treatment. 1250 mgL-1 wood vinegar treatment increased germination percentage and speeded up the germination process compare to control. The highest root length, volume and surface were observed at 1250 mgL-1 treatment. The concentration of nitrogen (5.5% DW) in the treatment of 3333 mgL-1 Pine wood vinegar, the potassium concentration in the treatment of 5000 mgL-1 and calcium and iron concentrattions in the treatment of 1250 mgL-1 were at the highest levels compared to other treatments. The highest amount of chlorophyll and photosynthesis was observed at 2000 mgL-1 treatment. The wood vinegar with 2500 mgL-1 pine wood vinegar concentration showed the highest flower and fruit yield in cucumber, but the best quality of fruit was produced by 2000 mgL-1 treatment.

Calcium is involved in exogenous NO-induced enhancement of photosynthesis in cucumber (Cucumis sativus L.) seedlings under low temperature

The present study explored the role of calcium ion (Ca2+) in nitric oxide (NO)-induced tolerance to low temperature in cucumber (Cucumis sativus L.) seedlings. Low temperature (11 °C/7 °C) induced a raise in NO accumulation and caused significant damages to photosynthetic processes in cucumber leaves, as evidenced by the decreased net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), chlorophyll content, maximal photochemical efficiency of photosystem II (PSII) (Fv/Fm), maximal fluorescence (Fm) photochemical quantum yield [Y (II)], relative apparent electron transport rate (ETR), quantum yield of PSII electron transport (Fm/Fo) and latent PSII quantum yield (Fv/F0), and the increased intercellular CO2 concentration (Ci), parameters of quantum yield of regulated energy dissipation [Y (NPQ)], and quantum yield of non-regulated energy dissipation [Y (NO)]. However, exogenous sodium nitroprusside (SNP), a donor of NO, ameliorated the negative effects of low temperature. Furthermore, the content of starch, sucrose, glucose, fructose, soluble sugar and reducing sugar, as well as the transcript levels of subunit of magnesium chelatase (ChlD, ChlI, ChlH), chlorophyll a-b binding protein (Chl), original chlorophyll redox enzymes (POR) and cytochrome b6/f complex (Cytb6f) genes were elevated by the treatment with SNP alone, whereas the inhibition of Ca2+ with EGTA (Ca2+ chelating agent), LaCl3 (Ca2+ channel blocker), TFP and W-7 (calmodulin antagonists) attenuated or almost abolished the aforementioned effects of SNP under low temperature. Taken together, our findings demonstrated that Ca2+ participated in the NO-induced tolerance to low temperature by modulating the leaf gas exchange, processes of PSII, carbohydrate metabolism and expression of chlorophyll synthesis-related genes in cucumber leaves.

Analysis of genes related to chlorophyll metabolism under elevated CO2 in cucumber (Cucumis sativus L.)

Cucumber is a vegetable crop with a large area of protected cultivation. The application of CO2 can promote photosynthesis in cucumber and increase yield. However, as an important photosynthetic pigment, and the molecular mechanisms of chlorophyll action are still unclear. It is therefore of great theoretical and practical significance to discover CO2-sensitive genes and analyze metabolic pathways to clarify the mechanisms of promoting photosynthesis by RNA sequencing. In this study, the photosynthetic correlation index and chlorophyll content under elevated CO2 and control conditions were compared. It was found that the application of CO2 expanded the effective light utilization range and promoted the biosynthesis of chlorophyll in cucumber. Seventeen genes related to chlorophyll were discovered in 380 differentially expressed genes (DEGs) obtained by RNA-Seq and they were involved in chlorophyll biosynthesis, chlorophyll-binding protein and chloroplast development. These genes were suggested to be related to increasing photosynthetic rate under enriched CO2 in cucumber. With fold change (FC) > 1.5 at false discovery rate (FDR) <0.05 as the selection criteria, the key enzymes in the chlorophyll metabolism pathway were analyzed, and expression of Csa4G165920 and Csa4G056670 encoding two enzymes were corresponded to the chlorophyll content, indicating that these two genes are also directly involved in chlorophyll metabolism and photosynthesis. These results clarified the molecular mechanism of increased photosynthetic rate caused by increased chlorophyll content and thus which increased carbon source after CO2 enrichment, which laid a foundation for further research on molecular mechanism of CO2 fertilization in cucumber.

Optimization and control of the light environment for greenhouse crop production

Optimization and control of the greenhouse light environment is key to increasing crop yield and quality. However, the light saturation point impacts the efficient use of light. Therefore, the dynamic acquisition of the light saturation point that is influenced by changes in temperature and CO2 concentration is an important challenge for the development of greenhouse light environment control system. In view of this challenge, this paper describes a light environment optimization and control model based on a crop growth model for predicting cucumber photosynthesis. The photosynthetic rate values for different photosynthetic photon flux densities (PPFD), CO2 concentration, and temperature conditions provided to cucumber seedlings were obtained by using an LI-6400XT portable photosynthesis system during multi-factorial experiments. Based on the measured data, photosynthetic rate predictions were determined. Next, a support vector machine(SVM) photosynthetic rate prediction model was used to obtain the light response curve under other temperatures and CO2 conditions. The light saturation point was used to establish the light environment optimization and control model and to perform model validation. The slope of the fitting straight line comparing the measured and predicted light saturation point was 0.99, the intercept was 23.46 and the coefficient of determination was 0.98. The light control model was able to perform dynamic acquisition of the light saturation point and provide a theoretical basis for the efficient and accurate control of the greenhouse light environment.

Study of the physiological mechanism of delaying cucumber senescence by wheat intercropping pattern

This paper investigates the physiological mechanism of the effect of delaying cucumber senescence on protein levels under the experimental model of monoculture and wheat intercropping. We analyzed cucumber roots for differential protein expression, and protein types were identified by core technology of proteomics. 45 differential proteins were identified as being differentially expressed between monoculture and intercropping of wheat, which were involved in carbohydrate metabolism, antioxidant and stress response, growth and development regulation, biological information transfer, and nucleic acid biosynthesis. The results showed the rate of photosynthesis of cucumber was increased under wheat intercropping pattern due to three enzymes being up-regulated. The respiration of cucumber was reduced when five enzymes were down-regulated. The antioxidant and resistant capacity of cucumber was enhanced significantly under wheat intercropping pattern because two enzymes were down-regulated while the activity of four other antioxidant enzymes was up-regulated. Intercropping wheat could delay the senescence of cucumber leaves by increasing the expression of IPT gene, reducing the expression of PAO and ETR2 gene, and inhibiting the expression of Cu/Zn-SOD and GS1 gene in later stages. Two proteins related to growth and development in cucumber were up-regulated, and one was down-regulated, while two proteins related to nucleic acid biosynthesis and chaperonin showed obvious down-regulation under wheat intercropping. Therefore, the growth and development was improved and senescence of cucumber could be delayed. Under intercropping pattern, the fresh weight, chlorophyll content, photosynthetic rate, and peroxidase activity of cucumber plants were higher than those of cucumber monoculture groups.Thus, the senescence of cucumber could be delayed under wheat intercropping by regulating its physiological mechanisms, such as by improving photosynthesis, reducing respiratory consumption, slowing the cell apoptosis rate, and enhancing the antioxidant and resistant capacity significantly, etc.

The effect of exogenous calcium on cucumber fruit quality, photosynthesis, chlorophyll fluorescence, and fast chlorophyll fluorescence during the fruiting period under hypoxic stress

BackgroundPlants often suffer from hypoxic stress during waterlogging and hydroponic culturing. This study investigated the response of cucumber (Cucumis sativus L.) plant growth parameters, leaf photosynthesis, chlorophyll fluorescence, fast chlorophyll a fluorescence transient (OJIP), and fruit quality parameters to hypoxic stress alleviated by exogenous calcium. During the fruiting period, cucumber plants were exposed to hypoxia and hypoxia + Ca2+ treatment (4 mM Ca2+) for 9 d.ResultExogenous calcium application enhanced the biomass and fruit quality of hypoxic stressed cucumber and also increased the net photosynthesis rate, stomatal conductance, intercellular CO2 concentration, maximum quantum efficiency of photosystem II photochemistry, actual photochemical efficiency of PSII, photochemical quenching coefficient, and non-photochemical quenching coefficient. Additionally, measurement of chlorophyll a fluorescence transients showed the positive K- and L-bands were more pronounced in leaves treated with hypoxia compared with those with hypoxia + Ca2+, indicating that hypoxic treatment induced uncoupling of the oxygen-evolving complex and inhibited electron transport beyond plastoquinone pool (Qa, Qb) including possible constraints on the reduction of end electron acceptors of photosystem I. Exogenous calcium can reduce these stress-induced damages in cucumber.ConclusionThis research focused the effect of exogenous calcium on cucumber photosynthesis during the fruiting period under hypoxic stress. Hypoxic stress might impair the photosynthetic electron-transport chain from the donor side of PSII up to the reduction of end acceptors of PSI, and exogenous calcium enhanced electron transport capacity and reduced hypoxic damage of cucumber leaves.

5-Aminolevulinic Acid (ALA) Alleviated Salinity Stress in Cucumber Seedlings by Enhancing Chlorophyll Synthesis Pathway.

5-Aminolevulinic acid (ALA) is a common precursor of tetrapyrroles as well as a crucial growth regulator in higher plants. ALA has been proven to be effective in improving photosynthesis and alleviating the adverse effects of various abiotic stresses in higher plants. However, little is known about the mechanism of ALA in ameliorating the photosynthesis of plant under abiotic stress. In this paper, we studied the effects of exogenous ALA on salinity-induced damages of photosynthesis in cucumber (Cucumis sativus L.) seedlings. We found that the morphology (plant height, leave area), light utilization capacity of PS II [qL, Y(II)] and gas exchange capacity (Pn, gs, Ci, and Tr) were significantly retarded under NaCl stress, but these parameters were all recovered by the foliar application of 25 mg L-1 ALA. Besides, salinity caused heme accumulation and up-regulation of gene expression of ferrochelatase (HEMH) with suppression of other genes involved in chlorophyll synthesis pathway. Exogenously application of ALA under salinity down-regulated the heme content and HEMH expression, but increased the gene expression levels of glutamyl-tRNA reductase (HEMA1), Mg-chelatase (CHLH), and protochlorophyllide oxidoreductase (POR). Moreover, the contents of intermediates involved in chlorophyll branch were increased by ALA, including protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX, protochlorophyllide (Pchlide), and chlorophyll (Chl a and Chl b) under salt stress. Ultrastructural observation of mesophyll cell showed that the damages of photosynthetic apparatus under salinity were fixed by ALA. Collectively, the chlorophyll biosynthesis pathway was enhanced by exogenous ALA to improve the tolerance of cucumber under salinity.

Effects of exogenous spermidine and arbuscular mycorrhizal fungi on plant growth of cucumber

Effects of spermidine (Spd) and arbuscular mycorrhizal fungi (AMF) on the growth and photosynthesis of cucumber (Cucumis sativus L., cv. Jinchun 2) seedlings, fruit yield and quality, microorganism and enzymatic activity in rhizosphere were investigated. The results showed that combined Spd and AMF addition significantly promoted the growth of cucumber seedlings, increased the root activity, fruit production and quality, enhanced nutrients absorption of seedlings. Net photosynthetic rate, actual photochemical efficiency, light quantum efficiency, carboxylation efficiency and light respiration rate of cucumber seedlings were increased by combined addition of Spd and AMF. The abundance of bacteria and actinomycetes in the rhizosphere of cucumber seedlings were increased, but that of fungi was decreased. The activities of enzymes, including sucrase, neutral phosphatase, catalase, and urease, were enhanced. These results suggested that the light utilization efficiency of cucumber seedlings was improved by combined addition of Spd and AMF. The growth substrate has been changed from a low-fertility type caused by fungi to a high-fertility one caused by bacteria. The decomposition and transformation of organic phosphorus and nitrogen in substrate were increased by combined addition of Spd and AMF, and thus could provide more N and P for the growth and development of cucumber, which further led to enhanced seedling growth, higher yield and quality of fruits. Moreover, Spd could increase the infection rate of AMF in cucumber roots, and together they had a synergistic effect on the growth of cucumber. Our results suggest that it is an effective method to enhance the infection rate of AMF by using Spd.

Exogenous spermidine maintains the chloroplast structure of cucumber seedlings and inhibits the degradation of photosynthetic protein complexes under high-temperature stress

Cucumbers (Cucumis sativus L.) are thermophilic horticulture crop but do not tolerate high temperature. The photosynthesis of cucumber under high temperature is highly susceptible to damage. To study the physiological mechanism of exogenous spermidine (Spd) on cucumber photosynthesis under heat stress, the sensitive cucumber cultivar ‘Jinchun no. 2’ was grown in substrate culture at a high temperature in an artificial climate box and treated with 1.0 mmol L−1 Spd under high-temperature stress (42/32 °C). The results showed that exogenous Spd alleviated the photosynthetic damage caused by heat shock, added the chlorophyll content and maintained the chloroplast structures relatively intact. Western blotting analysis showed that exogenous Spd inhibited the degradation of photosynthetic proteins, slowed the dissociation of the protein complexes, and maintained the stability of light-harvesting complexes (LHCs) in cucumber leaves under high-temperature stress. Twenty-two differentially expressed thylakoid membrane proteins involved in different photosynthetic processes were successfully authenticated by sodium dodecyl sulphate (SDS)-urea-PAGE and Blue native-polyacrylamide gel electrophoresis (BN-PAGE). The results showed that exogenous Spd regulated the expression of photosynthetic and bursal somatic membrane proteins, which resulted in adaptive changes under high-temperature stress at the transcriptional and translational levels, inhibited the degradation of thylakoid membrane proteins in cucumber leaves, and maintained the stable structure of the thylakoid membrane. Collectively, these results suggested that exogenous Spd alleviated high temperature-induced photosynthesis damage by improving the expression and synthesis of thylakoid membrane proteins, mitigating the dissociation of LHCII–Chl and thylakoid membrane protein complexes and maintaining the integrity and functional stability of the photosynthetic organ structure.