Hill Reaction Research Articles

Potential role of apple wood biochar in mitigating mercury toxicity in corn (Zea mays L.)

Mercury (Hg) is a very toxic decomposition-resistant metal that can cause plant toxicity through bioaccumulation and oxidative damage. Biochar, derived from organic waste and agricultural garbage, is an on-site modification technique that can improve soil health in heavy metals-polluted regions. The present experiment was designed to explore the role of apple biochar in the management of mercury toxicity in corn (Zea mays cv. ‘PL535’). Different levels of biochar derived from apple wood (0%, 2.5%, 5.0%, and 7.5% w/w) along with different Hg concentrations (0, 20, 40, and 60 mg/L) were used in the experiment that was based on a completely randomized design. Based on the results, HgCl2 at all rates reduced root and shoot dry weight and length, tolerance index, chlorophyll a and b content, the Hill reaction, and dissolved proteins and increased shoot and root Hg content (up to 72.57 and 717.56 times, respectively), cell death (up to 58.36%), MDA level (up to 47.82%), H2O2 (up to 66.33%), dissolved sugars, and proline. The results regarding enzymatic and non-enzymatic antioxidants revealed increases in total phenol and flavonoids content (up to 71.27% and 86.71%, respectively), DPPH free radical scavenging percentage, and catalase (CAT) and ascorbate peroxidase (APX) activity (up to 185.93% and 176.87%, respectively), in corn leaves with the increase in the Hg rate applied to the culture medium. The application of biochar to the substrate of the Hg-treated corns reduced Hg bioavailability, thereby reducing Hg accumulation in the roots (up to 76.88%) and shoots (up to 71.79%). It also reduced the adverse effect of Hg on the plants by increasing their shoot and root dry weight, photosynthesizing pigments, Hill reaction, and APX activity and reducing cell death, H2O2 content, and MDA content. The results reflected the capability of apple wood biochar at all rates in reducing Hg bioavailability and increasing Hg fixation in Hg-polluted soils. However, it was most effective at the rate of 7.5%.

Cytokinins along with Osmoprotectant Trehalose Overcome the Deleterious Effect of Drought Stress on Wheat

Experiment was conducted to evaluate, how the foliar application of trehalose (tre) along with kinetin (kn) and benzyl adenine (BA) affect the wheat genotypes (HD2967, PBW660 and WH1105) under drought stress conditions. Trehalose, Kn and BA tested in laboratory studies for their best concentrations, were applied in field grown wheat under drought. Presently, significant reduction was observed in leaf area, relative growth, Hill reaction and harvest index and sharp increase was recorded in concentration of non-enzymatic antioxidants constituents at both stages except reduced ascorbic acid content showed decline at flag leaf stage along with the upsurge in the activities of enzymatic antioxidants of wheat under drought as compared to control or irrigated ones. Foliar application of growth regulators altered activities of enzymatic and non-enzymatic antioxidants at both vegetative and flag leaf stage and helps in mitigation of negative impact of drought by regulation of Hill reaction, leaf area and growth rate of wheat that tends to maintain the final harvest of wheat crop.

Experimental determination and thermodynamic calculation of phase equilibria in Ag-Zr-Y system

The phase equilibria of the Ag-Zr-Y system at 800, 600 and 500 °C were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM) with energy dispersive X-ray spectrometry (EDS) techniques. The solubilities of Y in the Ag2Zr and AgZr phases and of Zr in the Ag51Y14, Ag2Y and AgY phases were measured, and no ternary compound was found in these isothermal sections. By means of the CALPHAD method, thermodynamic parameters of the Ag-Zr-Y system were assessed based on the experimental data from the present work and the literature. Substitutional solution model was used to describe the solution phases and sublattice models were used to describe binary compounds. A set of self-consistent and accurately described thermodynamic parameters of the Ag-Zr-Y system were obtained. The representative isothermal sections and liquidus projection were calculated, and the Hill reaction scheme of the Ag-Zr-Y system was constructed. The calculated results are in agreement with the experimental data.

The Effects of Blue and Red Light on the Hill Reaction of isolated Chloroplasts, Photosynthesis and Saponin Accumulation in Fenugreek Leaves (Trigonella foenum-graecum L.)

Blue light (450 nm) and red light (660 nm) were two specific wavelengths that have essential roles in plant photosynthesis and signals to synthesize plant metabolisms. In the fenugreek plant (Trigonella foenum – graecum L.), various saponins were synthesized in leaves and were used in pharmaceuticals. This study focused on the effects of blue and red light alone or in combination with fluorescent light on isolated chloroplasts, photosynthesis activities and saponin accumulation of fenugreek leaves. The results showed that the blue light increased the Hill reaction, stomatal opening and the ratio of chlorophyll a and b (Chla/b). Otherwise, the red light promoted total chlorophyll content and increased saponin in Fenugreek leaves. In addition, the combination of blue, red and fluorescent light increased photosynthesis activities and maintained plant growth and increased saponin accumulation in Fenugreek leaves.

Ambiguous changes in photosynthetic parameters of Lemna minor L. after short-term exposure to naproxen and paracetamol: Can the risk be ignored?

Non-steroidal anti-inflammatory drugs (NSAID) are recently monitored in the aquatic environment. Naproxen (NPX), paracetamol (PCT) and their transformation products can influence the biochemical and physiological processes at the sub-cellular and cellular levels taking part in the growth and development of plants. This study aimed to compare the effects of NPX and PCT, drugs with different physico-chemical properties, on the growth and photosynthetic processes in Lemna minor during a short-term (7 days) exposure. Although duckweed took up more than five times higher amount of PCT as compared to NPX (275.88 µg/g dry weight to 43.22 µg/g when treated with 10 mg/L), only NPX limited the number of new plants by 9% and 26% under 1 and 10 mg/L, respectively, and increased their dry weight (by 18% under 10 mg/L) and leaf area per plant. A considerable (by 30%) drop in the content of photosynthetic pigments under 10 mg/L treatment by both drugs did not significantly affect the efficiency of the primary processes of photosynthesis. Values of induced chlorophyll fluorescence parameters (F0, FV/FM, ΦII, and NPQ) showed just a mild stimulation by PCT and a negative effect by NPX (by up to 10%), especially on the function of photosystem II and electron transport in both intact duckweed plants and isolated chloroplasts. Lowered efficiency of Hill reaction activity (by more than 10% under 0.1 – 10 mg/L treatments) in isolated chloroplasts suspension proved the only inhibition effect of PCT to primary photosynthetic processes. In intact plants, higher treatments (0.5 - 10 mg/L) by both NPX and PCT induced an increase in RuBisCO content. The results prove that the potential effect of various drugs on plants is hard to generalise.

Effects of Phytotoxic Nonenolides, Stagonolide A and Herbarumin I, on Physiological and Biochemical Processes in Leaves and Roots of Sensitive Plants

Phytotoxic macrolides attract attention as prototypes of new herbicides. However, their mechanisms of action (MOA) on plants have not yet been elucidated. This study addresses the effects of two ten-membered lactones, stagonolide A (STA) and herbarumin I (HBI) produced by the fungus Stagonospora cirsii, on Cirsium arvense, Arabidopsis thaliana and Allium cepa. Bioassay of STA and HBI on punctured leaf discs of C. arvense and A. thaliana was conducted at a concentration of 2 mg/mL to evaluate phenotypic responses, the content of pigments, electrolyte leakage from leaf discs, the level of reactive oxygen species, Hill reaction rate, and the relative rise in chlorophyll a fluorescence. The toxin treatments resulted in necrotic and bleached leaf lesions in the dark and in the light, respectively. In the light, HBI treatment caused the drop of carotenoids content in leaves on both plants. The electrolyte leakage caused by HBI was light-dependent, in contrast with that caused by STA. Both compounds induced light-independent peroxide generation in leaf cells but did not affect photosynthesis 6 h after treatment. STA (10 µg/mL) caused strong disorders in root cells of A. thaliana leading to the complete dissipation of the mitochondrial membrane potential one hour post treatment, as well as DNA fragmentation and disappearance of acidic vesicles in the division zone after 8 h; the effects of HBI (50 µg/mL) were much milder. Furthermore, STA was found to inhibit mitosis but did not affect the cytoskeleton in cells of root tips of A. cepa and C. arvense, respectively. Finally, STA was supposed to inhibit the intracellular vesicular traffic from the endoplasmic reticulum to the Golgi apparatus, thus interfering with mitosis. HBI is likely to have another main MOA, probably inhibiting the biosynthesis of carotenoids.

Assimilate Partitioning and Photosynthetic Parameters of Rice (Oryza sativa L.) in Response to Salicylic Acid Application

Salicylic acid (SA), a signaling molecule is known to affect various physiological processes like growth and development, photosynthesis, absorption and translocation of assimilates etc. Therefore, an experiment was conducted to study the effect of salicylic acid on assimilate partitioning and yield of rice. The experiment comprised of 14 treatments replicated thrice in Randomized Complete Block Design (RCBD). Foliar application of SA @ 50, 100, 150 & 200 µg ml-1 was done at boot leaf stage (BL), one week after boot leaf stage (1WABL) and at BL + 1WABL. Treatment of water spray and unsprayed (control) were also included. Findings reveal that application of 100 µg ml-1 SA at BL + 1WABL resulted in the highest grain yield, which was statistically similar to 150 µg ml-1 SA at BL + 1WABL. The higher productivity under respective treatments can be ascribed to higher crop growth rate, relative growth rate, net assimilation rate and improvement in partitioning of dry matter from vegetative parts to grains due to improved vascularization. Also there was improvement in photosynthetic efficiency in terms of total chlorophyll content; carotenoid content and Hill reaction activity under SA treated plots. Thus, the productivity enhancement in rice can be achieved through 2 foliar sprays of salicylic acid @ 100 µg ml-1 each at boot leaf stage + one week after boot leaf stage.

Trigonella foenum-graecum (fenugreek) differentially regulates antioxidant potential, photosynthetic, and metabolic activities under arsenic stress

Arsenic (As) contamination is continuously increasing in the groundwaters and soils around the world causing toxicity in the plants with a detrimental effect on physiology, growth, and yield. In a hydroponic system, thirty-day-old plants of Trigonella foenum-graecum were subjected to 0, 50, or 100 µM NaHAsO40.7 H2O for 10 days. The magnitude of oxidative stress increased, whereas growth indices and photosynthetic parameters decreased in a dose-dependent manner. The efficiency of photosystem II in terms of Hill reaction activity (HRA) or chlorophyll-a was adversely affected by As stress. The antioxidant potential of plants regarding ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays was enhanced, indicating the augmented resistance mechanism in plants to counter As stress. The metabolite analysis of leaf extracts revealed many As responsive metabolites including amino acids, organic acids, sugars/polyols, and others. Phenylalanine and citrulline were highly accumulated at 50 or 100 µM As, salicylic acid accumulated more at 50 µM of As while ascorbic acid notably increased at 100 µM of As. At 50 or 100 µM As, the glucose and fructose contents increased while the sucrose content decreased. At both As doses, tagatose and glucitol contents were 13 times higher than controls. Varied accumulation of metabolites could be associated with the different As doses that represent the range of tolerance in T. foenum-graecum towards As toxicity. Pathway analysis of metabolites revealed that amino acid and carbohydrate metabolism and the citrate cycle play important roles under As stress. This study helps in a better metabolomic understanding of the dose-dependent toxicity and response of As in T. foenum-graecum.

Biochar-based nutritional nanocomposites: a superior treatment for alleviating salt toxicity and improving physiological performance of dill (Anethum graveolens).

Biochar-supported metal oxide nanocomposites as functional materials could help to improve the production and stress tolerance of plants by enhancing the physicochemical properties of biochar. This experiment was carried out to assess the effects of unmodified biochar (30gkg-1 soil) and biochar-based nanocomposites (BNCs) of iron (30g BNC-FeOkg-1 soil), zinc (30g BNC-ZnO kg-1 soil), and a combined form (15g BNC-FeO + 15g BNC-ZnOkg-1 soil) on dill (Anethum graveolens L.) plants under various salinity levels (non-saline, 6 and 12dSm-1). The biochar-related treatments reduced sodium content of the plants, leading to a decline in osmolytes, antioxidant enzymes activities, reactive oxygen species (ROS), lipid peroxidation, NADP reduction, abscisic acid, jasmonic acid, and salicylic acid in dill leaf tissues. The combined form of BNCs reduced sodium content of leaf tissue by about 22% and 26% under 6 and 12dSm-1 salinities, respectively. In contrast, addition of biochar, particularly biochar-based nanocomposites to the saline soil, enhanced potassium, iron, and zinc contents of leaf tissue, photosynthetic pigments, leaf water content, oxygen evolution rate, hill reaction and ATPase activities, endogenous indole-3-acetic acid, plant organs biomass, and consequently essential oil yield of plant organs. The combined form of BNCs in comparison with unmodified biochar improved vegetative, inflorescence, and seed biomass under 12dSm-1 salinity by about 33%, 25%, and 6%, respectively. These findings revealed that BNCs with novel structure can potentially enhance salt tolerance, plant biomass, and essential oil yield of different organs in salt-stressed dill plants through decreasing leaf sodium content and ROS generation and increasing nutrient availability, water status, and photosynthetic pigments.

Natural xylose-derived carbon dots towards efficient semi-artificial photosynthesis

Photosynthesis by plants stores sunlight into chemicals and drives CO2 fixation into sugars with low biomass conversion efficiency due to the unoptimized solar spectrum utilization and various chemical conversion possibilities that follow H2O oxidation. Expanding the solar spectrum utilization and optimizing the charge transfer pathway of photosynthesis is critical to improving the conversion efficiency. Here, a group of carbon dots (CDs) with distinct content of sp2 CC domain are prepared by one-step carbonization of natural xylose, which penetrated natural chloroplasts and integrated with the grana thylakoid to promote in vitro photosynthesis. Structural characterization and electrochemical results reveal the positive impact of graphitization degree on the electron transport capacity of CDs. Classic Hill reaction and ATP production demonstrate the enhanced photosynthetic activity resulting from the CDs-mediated electron transfer of photosystem II. In-depth studies of the structure–function relationship prove the synergistic effect of intensified biotic-abiotic interaction between CDs and chloroplast, lower charge transfer resistance, and extended light absorption. This work posts a promising method to optimize electron transport and improve natural photosynthesis using artificial interventions.

Mechanisms of cerium-induced stress in plants: A meta-analysis

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca2+, K+, and K+/Na+, indicating an important role of K+ and Na+ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (gs), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. gs), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1–25 mg L−1 commonly enhance chlorophyll a and b, gs, A, and plant biomass, whereas concentrations >50 mg L−1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg−1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Effect of Enhanced Ultraviolet-B Radiation on Fruit Maturity and Quality and Leaf Photosynthesis in ‘Guifei’ Mango

To investigate the characteristics of photosynthetic physiological changes in leaves of Mangifera indica L. cv. Guifei under enhanced ultraviolet (UV)-B radiation, natural light-exposed trees were used as controls and 96 kJ·m−2·d−1 enhanced UV-B radiation was artificially simulated in the field. The changes in fruit maturity and quality, the leaf net photosynthetic rate (Pn), photosynthetic pigment contents, photochemical reactions, the activities of photosynthetic enzymes and related gene expression levels were determined. Compared with the control, the percentage of mature fruits under the treatment significantly increased, and fruit quality improved. The net photosynthetic rate (Pn), photosynthetic pigment content, Hill reaction activity, and photochemical quenching coefficient (qP) of the treated leaves showed significantly higher values than those of the control leaves. The activities of Rubisco and Rubisco activating enzyme (RCA) and the expression levels of the Rubisco large subunit and Rubisco small subunit were significantly increased. Treatment with 96 kJ·m−2·d−1 enhanced ultraviolet-B radiation improved Rubisco activity by increasing the expression of the Rubisco large and small subunit genes, thereby enhancing the CO2-fixing capacity and dark reaction capacity of leaves. Thus, the net photosynthetic rate of leaves increased, which promoted the early maturity of ‘Guifei’ mango by the rapid accumulation of photosynthetic products.

Effect of Japanese foxtail (Alopecurus japonicus) at varying densities on the physiological characteristics of wheat

To evaluate the effect of Japanese foxtail (Alopecurus japonicus Steud.) at different densities on the photosynthetic physiology of wheat, “Yangmai 16” wheat was cultivated in a field using two sowing rates (150 kg ha−1, conventional seeding rate; 225 kg ha−1, high seeding rate) and with different densities of A. japonicus for two years. A. japonicus affected the physiological characteristics of wheat, such as its leaf photosynthetic rate, fluorescence parameters, Hill reaction activity, Rubisco activity, yield and yield components, to varying degrees. However, the physiological responses of wheat at different seeding rates varied; the effect of A. japonicus on wheat was more severe at the conventional seeding rate than at the high seeding rate. A. japonicus affected wheat leaf morphology and inhibited photosynthetic processes, leading to decreased PSII electron transport, energy metabolism and photosynthate accumulation, ultimately reducing wheat yield. An appropriate increase in the wheat seeding rate could improve specific leaf weight, maintain Rubisco activity, reduce photoinhibition, and alleviate the stress caused by A. japonicus.

Anacardic Acid Derivatives Affect the in Vitro Reactions of Photosynthesis.

The dichloromethane extract of the cashew nuts from Anacardium occidentale was fractionated by rotation locular countercurrent chromatography aimed at discovering metabolites that could be useful as new models for photosynthesis inhibitors. The chemical fractionation afforded a complex mixture of anacardic acids, which upon catalytic hydrogenation yielded anacardic acid (1). Methylation of 1 via reaction with diazomethane afforded an ester 2. Both compounds were evaluated using polarographic approaches and fluorescence studies of chlorophyll a (ChL a). The in vitro assays informed the decision for the classification of 1 and 2 as Hill reaction inhibitors. Besides that, 1 inhibited the donor side of the PSII, while 2 acted as an energy transfer inhibitor. Therefore, this study is important for the development of herbicides.

Hazardous Impact of Nickel in Alteration of Antioxidative Mechanism and Inhibition of Growth and Biomass Yield in Rice (Oryza sativa L.)

Many anthropogenic activities (smelters, mines and municipal waste) enhance the heavy metal toxicity in soil and water and it is gradually accumulated in plants, and finally through food chain it reaches to human beings. To investigate hazardous impact of excess nickel on growth, biomass, yield and metabolism of rice (Oryza sativa L) the plants were grown in refined sand at 0.0001mM (control), 0.05, 0.10, 0.20, 0.40, and 0.50 mM nickel (Ni) supply. After 16 days of treatment the excess supply of Ni(&gt;0.50mM) reduced biomass, photosynthetic pigments (both chlorophyll a and b), Hill reaction activity, water soluble proteins, activity of catalase (CAT), and enhanced the activity of peroxidase (POX), ribonuclease and acid phosphatase in rice leaves. The antioxidative regulation was inhibited through CAT, although increased activity of POX supported the plants in overcoming the toxic effect of nickel. At 112 days (70 days after Ni treatment) the accumulation of iron in shoot and root was reduced. Phosphorus was significantly increased in both shoot and root. Sulphur accumulation was increased in panicle, leaves, shoot and root. Nickel accumulation in different plant parts was increased many fold (as in leaves it was increased about 25 times, in stem 18 times and in roots it was 17 times) in 0.50 mM Ni supply in comparision to control. Rice appeared very prone to nickel toxicity as Ni supply beyond 0.050 mM resulted into complete loss of economic yield due to inhibited flowering and poor panicle numbers.

Characteristics of Mango Leaf Photosynthetic Inhibition by Enhanced UV-B Radiation

To investigate the photosynthetic change characteristics of mango leaves under enhanced UV-B radiation, adult ‘Tainong No. 1′ mango (Mangifera indica) trees were treated (N = nine individuals) with simulated enhanced UV-B radiation [24 and 96 kJ/(m2·d)] in the field, and the photochemical reactions, activities of key enzymes in carbon assimilation, and the expression of genes were observed. The results showed that compared with the control, there was a decrease in tree yield, soluble sugar, sugar–acid ratio, and vitamin C of the fruits under the 96 kJ/(m2·d) treatment, while no significant changes were observed under 24 kJ/(m2·d). After 20 or 40 days, the leaves’ net photosynthetic rate (Pn), stomatal conductance (Sc), transpiration rate (Tr), intercellular CO2 concentration (Ci), and chlorophyll a/b under exposure to 96 kJ/(m2·d) of UV-B were significantly lower than in the control, whereas chlorophyll a, chlorophyll b, carotenoids, Hill reaction activity, photochemical quenching coefficient (qP), and Rubisco activities were significantly higher. In contrast, the Hill activity and Rubisco activity under 24 kJ/(m2·d) were significantly higher than the control, and increased by 350% and 30.8%, respectively, while Pn, Sc, Tr, Ci, and the content of photosynthetic pigments were similar to the control. The expression of gene coding the Rubisco big subunit (rbcL) was inhibited by the 96 kJ/(m2·d) treatment. We conclude that stomatal limitation was directly induced by 96 kJ/(m2·d), resulting in the inhibition of photosynthesis and the reduction in yield and deterioration of the quality of mango.

Defining date palm leaf pruning line in bearing status by tracking physiological markers and expression of senescence-related genes

The physiological and molecular markers were evaluated for defining leaf pruning line in bearing status of date palm (Phoenix dactylifera cv. Mazafati). Our results showed that the higher expression of the chlorophyllase (Chlase) gene was concomitant with lower expression of chlorophyll synthase (ChlG) and oxygen-evolving enhancer protein (PSBO) genes in the 6-year-old leaf line. In addition, the 6-year-old leaf line resulted in a lower Hill reaction rate, chlorophyll a/b ratio, photosystem Ⅱ quantum efficiency, and photosynthesis rate. Also, lower expression and activities of catalase (CAT), ascorbate peroxidase (APX), and glutathione peroxidase (GPX) was associated with higher malondialdehyde (MDA) and hydrogen peroxide (H2O2) accumulation in 6-year-old leaf line. These results suggested that the physiological maturity termination, senescence stage initiation, and source to sink transition could occur in 6-year-old leaves. Furthermore, delayed 5-year-old leaf pruning line adjustment in consecutive years could increase quantitative and qualitative yield loss, decrease water use efficiency, and promote alternate bearing and fruit abscission, which is considered a common problem of date growing areas. Further, the senescence-related markers in the alternate bearing trees pruned in pruning line 5 showed a tendency to normal trees. The five-year-old pruning line also resulted in the balance of bunching and loading the alternate bearing trees.

Using some growth stimuli, a comparative study of salt tolerance in two tomatoes cultivars and a related wild line with special reference to superoxide dismutases and related micronutrients.

Salinity is a major global problem that threatens the agricultural sector, especially in areas that suffer from a shortage of water. It motivates ionic toxicity, osmotic and oxidative stresses, which greatly inhibits plant performances and crop productivites. However, micronutrients (MNs) or plant extracts, like germinated maize grain extract (gMGE), have been reported to minimize the effects of salt stress on plant growth and returns. Therefore, this study aimed at evaluating the influences of MNs or gMGE applied as foliar sprays on growth, physio-biochemical indices, and antioxidative system components in three genotypes of tomato plants stressed by 9 dS m−1 NaCl. This salinity level markedly increased Na+ content, lipid peroxidation, ion leakage, and markers related to oxidative stress (superoxide; O2•− and hydrogen peroxide; H2O2). Besides, marked increases in activities of enzymatic (especially different forms of superoxide dismutase; SODs) and non-enzymatic antioxidants and osmoprotectant compounds were also observed. In contrast, growth, photosynthetic capacity including hill reaction activity (HRA), K+/Na+ ratio, tissue cell integrity (e.g., cell water content and membrane stability), and K+ and MNs contents decreased significantly under stress. However, compared to MNs, gMGE significantly improved the activities of the antioxidative system components (particularly SODs) and osmoprotectants, which were reflected in reduced Na+ accumulation, lipid peroxidation, ion leakage, and oxidative stress. These results were coupled with remarkable elevations in photosynthetic capacity including HRA, K+/Na+ ratio, tissue cell integrity, K+ content, and MNs contents, all of which were reflected in the enhancement of plant growth. Compared to local tomato cultivars (e.g., Castle Rock and C10), the wild line “0043-1” had better results. The interaction of three factors; salt stress, promoters, and tomato genotypes was significant. The wild tomato line “0043-1” as the best salt-tolerant is a good candidate for implication in breeding programs for tolerance to salinity to produce salt-tolerant cultivars for use to maximize tomato growth and productivity in saline environments.

Effects of heat stress on photosystem II activity and antioxidant enzymes in two maize cultivars.

The main reason for the maize genotype "DKC7221" to be heat tolerant is to have higher photosynthetic activity under heat stress conditions. The genotype "P3167" is sensitive to high temperature because of the heat-induced inhibition in photosynthetic electron transport reactions. In the present study, the effect of heat stress (45ºC for 20min) on some physiological changes was investigated through a chlorophyll afluorescence technique, and some endogenous resistance mechanisms (activities of some antioxidant enzymes, free proline, and reduced ascorbate contents) in two maize cultivars (Zea mays L. cvs. P3167 and DKC7221). Chlorophyll fluorescence measurements demonstrated that heat stress led to the reduction in the efficiency of the Hill reaction, accumulation of inactive reaction centers, inhibition of electron flow from reaction centers to the plastoquinone pool, and induction of non-photochemical dissipation of absorbed light energy. Changes in Φo/(1 - Φo), SFIABS and PIABS indicated that electron transport reactions in P3167 were almost completely inhibited by heat stress. In DKC7221, however, photosynthetic electron transport reactions were maintained under heat stress conditions. As a result of impairment in the photosynthetic efficiency in P3167 under heat stress, oxidative stress appeared as shown by lower antioxidant activity, accumulation of H2O2, malondialdehyde, and formazon and photooxidative injuries in chlorophyll pigments in the leaf tissue. DKC7221, on the other hand, had a higher antioxidant efficiency and lower oxidative damage under heat stress. FeSOD activity was found to be responsible for the dismutation of superoxide radicals in both maize genotypes under heat stress. As a result, it may be concluded that the genotype DKC7221 is more tolerant to heat stress than P3167.

Mitigation of Salinity Effects by Salicylic Acid Priming on Germination and Physiological Characteristics of Bitter Vetch (Vicia ervilia L.)

Salinity is one of the most important environmental stresses affecting the growth and yield of the plants. The effect of salicylic acid (SA) on growth, germination, and some physiological traits of bitter vetch (Vicia ervilia L.) exposed to salinity was studied in a factorial experiment based on a randomized complete block design with three replications. The experimental treatments were composed of salinity at three levels of 0, 50 and 100 mM and SA priming at three rates of 0, 0.1 and 0.2 mM. The results showed that as salinity was increased, germination and the related traits, seedling growth, and the Hill reaction rate were declined, but mean germination time and cell death were increased. SA application at the rates of 0.1 and 0.2 mM improved these parameters as compared to control. At the salinity levels of 50 and 100 mM, SA rates of 0.2 and 0.1 mM imposed the strongest effect on germination parameters and plant growth. At the salinity level of 100 mM, SA rate of 0.2 mM was more effective on leaf relative water content, seedling fresh weight, root and stem length, and root and stem fresh weight. At different levels of salinity, 0.2 mM SA increased the Hill reaction rate and cell death of bitter vetch. The application of SA under salinity stress for improvement of germination parameters, seedling growth, and physiological traits of bitter vetch could be recommended.