Total Ascorbate Content Research Articles

The ozone sensitivity of five poplar clones is not related to stomatal conductance, constitutive antioxidant levels and morphology of leaves

Ground-level ozone (O3) is an important phytotoxic air pollutant in China. In order to compare the sensitivity of common poplar clones to O3 in China and explore the possible mechanism, five poplar clones, clone DQ (Populus cathayana), clone 84 K (P. alba × P. glandulosa), clone WQ156 (P. deltoids × P. cathayana), clone 546 (P. deltoides cv. ‘55/56’ × P. deltoides cv. ‘Imperial’) and clone 107 (P. euramericana cv. ‘74/76’) were exposed to four O3 treatments. According to the date of the initial visible O3 symptom and the slopes of O3 exposure-response relationships with the relative light-saturated rate of CO2 assimilation, we found that clone DQ and clone 546 were the most sensitive to O3, clone 84 K and clone WQ156 were the less sensitive, and clone 107 was the most tolerant, which could provide a basis to select O3 tolerant clones for poplar planting at areas with serious O3 pollution. Elevated O3 significantly reduced photosynthetic parameters, total phenols content, potential antioxidant capacity, leaf mass per area and biomass of five poplar clones, and there were significant interactions between O3 and clones for most photosynthetic parameters. Elevated O3 also significantly increased malondialdehyde content and total ascorbate content. The responses of total antioxidant capacity for poplar clones to elevated O3 were different, as indicated by the increase for clone 107 and reduction for other clones under elevated O3 treatment. Our results on the sensitivity of different poplar clones to O3 are not related to leaf stomatal conductance, leaf constitutive antioxidant levels or leaf morphology of plant grown in clean air. The possible reason is little difference in leaf traits among clones within close species, suggesting that more properties of plants should be considered for exploring the sensitivity mechanism of close species, such as mesophyll conductance, antioxidant enzyme activity and apoplastic antioxidants.

Interactive Effect of Silicon (Si) and Salicylic Acid (SA) in Maize Seedlings and Their Mechanisms of Cadmium (Cd) Toxicity Alleviation

The present study has been conducted to evaluate the impact of silicon (Si) and salicylic acid (SA) in the regulation of Cd-induced toxicity in maize seedlings. Cadmium (Cd: 100 µM) significantly reduced root and shoot fresh weight and length, photosynthetic pigments, total soluble protein content and chlorophyll fluorescence parameters. Cadmium decreased root and shoot length by 23 and 19% and fresh weight by 27 and 24%, respectively when compared to their respective controls. Similarly, total chlorophyll, carotenoids and total soluble protein were decreased by 21, 18 and 28%, respectively by Cd. In contrast, the addition of SA (500 µM) and Si (10 µM), and their combination (SA + Si) together with Cd treatment successfully ameliorated Cd-induced harmful impacts on studied parameters as SA and Si alone and in combination reduced Cd accumulation and oxidative stresses and thus refurbish the damages. Cd significantly stimulated activity of superoxide dismutase while inhibited activities of ascorbate peroxidase (APX), glutathione reductase (GR) and dehydroascorbate reductase (DHAR), and declined total ascorbate and glutathione contents. In contrast, the addition of SA and Si alone and in combination stimulated the activities of APX, GR and DHAR and significantly increased levels of total ascorbate and glutathione. In conclusion, the present study suggested that although SA and Si both alone are able to alleviate Cd-induced toxicity in maize seedlings, but their combination was the most effective in nullifying Cd-induced toxicity in maize seedlings.

The adaptation strategies of Herpetospermum pedunculosum (Ser.) Baill at altitude gradient of the Tibetan plateau by physiological and metabolomic methods

BackgroundHerpetospermum pedunculosum (Ser.) Baill is annual scandent herbs. They are used in the treatment of piles, inflammation of the stomach and the intestines. It can survive the extreme environment of the Tibetan Plateau (TP). However, the underlying mechanisms of this adaptation to H. pedunculosum from TP remain unclear. Here, we combined physiological and metabolomics methods to analyze H. pedunculosum response to altitude gradient differences.ResultsAt high altitude, increases in the activities of Ascorbate peroxidase (APX), Glutathione reductase (GR), Dehydroascorbate reductase (DHAR), Monodehydroascorbate reductase (MDHAR), Superoxide dismutase (SOD) have been observed in leaves. Total Glutathion content, total Ascorbate content and the ASA (ascorbic acid)/docosahexaenoic acid (DHA) ration were highly elevated from low altitude to high altitude. In addition, high altitude induces decrease of the Anthocyanidin content (ANTH) and increase of abscisic acid content (ABA). The GC-MS analyses identified of 50 metabolites from leaves of H. pedunculosum. In addition, a metabolic network was constructed based on metabolomic datasets using a weighted correlation network analysis (WGCNA) approach. The network analysis uncovered 4 distinguished metabolic modules highly associated with I, II, III and IV respectively. Furthermore, the analysis successfully classified 50 samples into seven groups: carbohydrates, amino acids, organic acids, lipid components, polyamine, secondary metabolism and others.ConclusionsIn the present study, the content of parts of amino acid components increased in samples collected at higher altitudes, and most of metabolites, including carbohydrates and organic acids were assigned to the carbon metabolic pathway comprising reductive pentose phosphate pathway, glycolysis and TCA cycle, indicating the direct relationship between adaptability and the carbon metabolic pathway and amino acids in H. pedunculosum response to high altitude. The results of this study laid the foundation of the molecular mechanism on H. pedunculosum from high altitude.

Intraspecific variation in sensitivity of high yielding rice varieties towards UV-B radiation.

Effective screening of thirteen commonly cultivated rice (Oryza sativa L.) varieties was carried out to evaluate the varietal-specific differences in morphological, physiological and biochemical responses to various doses of UV-B irradiation (7, 14, 21 and 28 kJm-2d-1). Determination of UV-B tolerant rice varieties would be helpful in selecting a suitable variety for the areas experiencing higher influx of UV-B radiation. Based on the initial screening of thirteen rice varieties, carried out by analyzing shoot length, fresh weight, photosynthetic pigments and the rate of lipid peroxidation under various doses of UV-B, it was found that Mangalamahsuri, Aathira, Kanchana, Jyothi and Annapoorna were tolerant lines and Neeraja, Swetha, Swarnaprabha and Aiswarya were the sensitive ones. Further screening of these nine varieties was done by analyzing primary metabolites (total protein, soluble sugar and proline content) and non enzymatic antioxidants (ascorbate and glutathione) involved in free radical scavenging mechanism to mitigate the negative effects of UV-B irradiation. Based on the cumulative stress response index (CSRI), the sum of relative individual component responses (total protein, soluble sugar, proline, ascorbate and glutathione content) at each UV-B treatment and total stress response index (TSRI), the sum of CSRI of all the four UV-B treatments for each variety, nine rice varieties selected after primary screening were classified as tolerant (Mangalamahsuri, Aathira and Kanchana), intermediate (Jyothi, Annapoorna, Neeraja and Swetha) and sensitive (Swarnaprabha and Aiswarya).

Dynamic changes in common metabolites and antioxidants during Penicillium expansum-apple fruit interactions

Penicillium expansum-infected apple fruit resulted in a disrupted balance of primary metabolites and impacted the ascorbate–glutathione cycle. The initial decline in fructose, malic acid, shikimic acid and total ascorbate content (6 hpi) was followed by a significant increase in malic acid (24 hpi) and total glutathione (3 dpi). Significant increase in sucrose was accompanied by a decline in glucose and ascorbate content (5 dpi). Total glutathione and shikimic acid gradually deteriorated with symptom development. A negative correlation was found between sucrose and ascorbate-glutathione pool. Other correlations were strong amongst other metabolites and lesion size indicating that they may be involved or important for apple fruit decay.

Ferulic acid confers tolerance against excess boron by regulating ROS levels and inducing antioxidant system in wheat leaves (Triticum aestivum)

Ferulic acid (FA; 3-methoxy-4-hydroxycinnamic acid) is a candidate for improving plant tolerance to stress conditions through improving water solubility and antioxidant activity. To our knowledge, no study has thus far explored the potential for exogenous FA application to improve tolerance against excess boron (B) in plants. For this purpose, wheat seedlings grown in hydroponic culture were treated with FA (25 and 75 μM) alone or in combination with B (4 and 8 mM). The results showed that B caused a decrease in water content (RWC), osmotic potential (ΨΠ) and proline content (Pro). FA application prevented decreases of these parameters. 8 mM B increased superoxide dismutase (SOD) activity. Superoxide anion radical (O2―) and hydrogen peroxide (H2O2) increased during B exposure, while catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities did not. However, due to increased SOD activity, FA under stress successfully decreased O2― content. Additionally, exogenously applied FA under 4 mM B stress increased the activities of CAT and POX. While excess B in wheat leaves did not induce activities of APX, GR, monodehydroascorbate reductase (MDHAR) or dehydroascorbate reductase (DHAR) or increase total ascorbate (tAsA) or dehydroascorbate (DHA) contents, FA with stress did. 25 μM FA with B remarkably maintained regeneration of ascorbate and induced contents of tAsA and GSH (including the ascorbate-glutathione cycle) and induced CAT activity. Taken together, stress-induced H2O2 content significantly decreased and the scavenging of OH increased in wheat with FA application through the activation of antioxidant enzymes. Consequently, FA prevented lipid peroxidation (TBARS) caused by stress due to increased radical scavenging activity.

Abscisic acid enhances lead translocation from the roots to the leaves and alleviates its toxicity in Populus × canescens.

To shed light on physiological mechanisms underlying abscisic-acid (ABA)-mediated lead (Pb) uptake, translocation and detoxification, we exposed Populus × canescens saplings to either 0 or 3 mM Pb2+ in combination with either 0 or 10 μM exogenous ABA. Pb was taken up by the roots and accumulated mainly in the cortex. A fraction of the Pb in the roots was translocated to the leaves, thereby resulting in decreased photosynthesis and biomass. Pb accumulation caused a burst of reactive oxygen species (ROS), with higher concentrations of total thiols, glutathione, and ascorbate in the roots and/or leaves. Exogenous ABA stimulated Pb uptake, decreased Pb deposition in the cortex, and enhanced Pb vascular loading in the roots. Exogenous ABA alleviated the Pb-induced reductions in photosynthesis and root biomass, and decreased Pb-triggered ROS overproduction in the roots and/or leaves. Correspondingly, exogenous ABA stimulated the mRNA levels of a few genes involved in Pb uptake, transport, and detoxification, including NRAMP1.4, ABCG40, FRD3.1, PCS1.1, and ABCC1.1. These results suggest that exogenous ABA enhances Pb uptake and translocation, and alleviates Pb toxicity in poplars through the ABA-induced movement of Pb from the root cortex to the vascular stele, and transcriptionally regulated key genes involved in Pb tolerance.

Physiological responses of date palm (Phoenix dactylifera) seedlings to acute ozone exposure at high temperature

Vegetation in the Arabian Peninsula is facing high and steadily rising tropospheric ozone pollution. However, little is known about the impacts of elevated ozone on date palms, one of the most important indigenous economic species. To elucidate the physiological responses of date palm to peak levels of acute ozone exposure, seedlings were fumigated with 200 ppb ozone for 8 h. Net CO2 assimilation rate, stomatal conduction, total carbon, its isotope signature and total sugar contents in leaves and roots were not significantly affected by the treatment and visible symptoms of foliar damage were not induced. Ozone exposure did not affect hydrogen peroxide and thiol contents but diminished the activities of glutathione reductase and dehydroascorbate reductase, stimulated the oxidation of ascorbate, and resulted in elevated total ascorbate contents. Total nitrogen, soluble protein and lignin contents remained unchanged upon ozone exposure, but the abundance of low molecular weight nitrogen (LMWN) compounds such as amino acids and nitrate as well as other anions were strongly diminished in leaves and roots. Other nitrogen pools did not benefit from the decline of LMWN, indicating reduced uptake and/or enhanced release of these compounds into the soil as a systemic response to aboveground ozone exposure. Several phenolic compounds, concurrent with fatty acids and stearyl alcohol, accumulated in leaves, but declined in roots, whereas total phenol contents significantly increased in the roots. Together these results indicate that local and systemic changes in both, primary and secondary metabolism contribute to the high tolerance of date palms to short-term acute ozone exposure.

Comparative compositional analysis of transgenic potato resistant to potato tuber moth (PTM) and its non-transformed counterpart.

In this study, the compositions of transgenic potatoes (TPs) resistant to potato tuber moth (Phthorimaea operculella) were compared with those of its non-transgenic (NTP) counterparts. The light inducible promoter, phosphoenolpyruvate carboxylase led to the expression of Cry1Ab only in the leaves and light-treated tubers of the TPs. No significant differences were found in the moisture, ash, dry weight, total soluble protein, carbohydrate, starch, fiber, ascorbate, cations, anions, fatty acids, and glycoalkaloids contents of TP and NTP. Moreover, light treatment significantly affected the contents of ascorbate, acetate and nitrite anions, palmitic, stearic and linolenic fatty acids, α-haconine and α-solanine glycoalkaloids in TP and NTP tubers. While, significant differences were observed in the amino acid contents in light-treated tubers of TPs than the NTP ones. Although, light treatment in potato tubers resulted in marked metabolic changes, all the variations observed in the metabolites compositions were found to be within the desired reference ranges for potato plants. In conclusion, the results indicated that the TPs were substantially and nutritionally equivalent to the NTP counterparts.

Susceptibility of an ascorbate-deficient mutant of Arabidopsis to high-light stress

Ascorbate is an important antioxidant involved in both enzymatic and nonenzymatic reactions in plant cells. To reveal the function of ascorbate associated with defense against photo-oxidative damage, responses of the ascorbate-deficient mutant vtc2-1 of Arabidopsis thaliana to high-light stress were investigated. After high-light treatment at 1,600 μmol(photon) m–2 s–1 for 8 h, the vtc2-1 mutant exhibited visible photo-oxidative damage. The total ascorbate content was lower, whereas accumulation of H2O2 was higher in the vtc2-1 mutant than that in the wild type. The chlorophyll (Chl) content and PSII Chl fluorescence parameters, such as maximal quantum yield of PSII photochemistry, yield, and electron transport rate, in vtc2-1 mutant decreased more than that in the wild type, whereas the nonphotochemical quenching coefficient increased more in the wild type than that in vtc2-1 mutant. Therefore, the vtc2-1 mutant was more sensitive to high-light stress than the wild type. Accumulation of reactive oxygen species was mainly responsible for the damage of PSII in the vtc2-1 mutant under high light. The results indicate that ascorbate plays a critical role in maintaining normal photosynthetic function in plants under high-light stress.

Evaluation of barnyard millet diversity in central Himalayan region for environmental stress tolerance

SUMMARYThe mountain ecosystem of the Central Himalayan Region is known for its diversity of crops and their wild relatives. In spite of adverse climatic conditions, this region is endowed with a rich diversity of millets. Hence, the aim of the present study was to explore, collect, conserve and evaluate the diversity of barnyard millet (Echinochloa frumentacea) to find out the extent of diversity available in different traits and the traits responsible for abiotic stress tolerance, and to identify trait-specific accessions for crop improvement and also for the cultivation of millets in the region as well as in other similar agro-ecological regions. A total of 178 accessions were collected and evaluated for a range of morpho-physiological and biochemical traits. Significant variability was noted in days to 50% flowering, days to 80% maturity, 1000 seed weight and yield potential of the germplasm. These traits are considered to be crucial for tailoring new varieties for different agro-climatic conditions. Variations in biochemical traits such as lipid peroxidation (0·552–7·421 nmol malondialdehyde formed/mg protein/h), total glutathione (105·270–423·630 mmol/g fresh weight) and total ascorbate (4·980–9·880 mmol/g fresh weight) content indicate the potential of collected germplasm for abiotic stress tolerance. Principal component analysis also indicated that yield, superoxide dismutase activity, plant height, days to 50% flowering, catalase activity and glutathione content are suitable traits for screening large populations of millet and selection of suitable germplasm for crop improvement and cultivation. Trait-specific accessions identified in the present study could be useful in crop improvement programmes, climate-resilient agriculture and improving food security in areas with limited resources.

The influence of pulsed light exposure mode on quality and bioactive compounds of fresh-cut mangoes.

This study investigated the effect of pulsed light (PL) on the respiratory rate, quality (firmness, color and soluble solid content), bioactive compounds (ascorbate and carotenoid) and total antioxidant activity of fresh-cut "Tommy Atkins" mangoes. Fresh-cut mangoes were subjected to PL treatments: control (0P), 1 pulse (1P; 0.7Jcm-2), 4 successive pulses (4P; 2.80Jcm-2) and 1 pulse per day for 4days (1P4D; 2.80Jcm-2) before storage for 7days at 6°C. The 1P and the 4P treatments reduced fresh mass loss during storage, while 4P-treated samples also showed a slower decline of yellow color, as shown by parameter b and overall better visual appearance. After 7days of storage, total ascorbate content was 40% higher in the 1P4D treatment than in control, whereas total carotenoid content (0.894mgg-1 FM) and total antioxidant activity (144μmol trolox 100g-1 FM) were the highest in the 4P-treated samples. Results suggest that PL mode of application is more important than the fluence or final dose received by fresh-cut mangoes; moreover, 4P is an effective method to preserve, or even improve quality of fresh-cut mangoes.

Exogenous hydrogen peroxide up-regulates the contents of ascorbate and glutathione in the leaves of Vigna radiata (Linn.) Wilczek. exposed to salt stress

In this paper, the effect of exogenous hydrogen peroxide (H2O2) on the contents of ascorbate and glutathione in Vigna radiata (Linn.) Wilczek. leaves exposed to salt stress was determined. The findings showed that salt stress increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), gamma-glutamylcysteine synthetase (γ-ECS), electrolyte leakage (EL) and the contents of reduced ascorbate (AsA), reduced glutathione (GSH), total ascorbate, total glutathione and malondialdehyde (MDA). Exogenous H2O2 increased the contents of AsA, total ascorbate, GSH and total glutathione through APX, GR, DHAR and γ-ECS in leaves exposed to salt stress. Above increases were also induced by exogenous H2O2 alone, compared with control. Exogenous H2O2 had no effect on the activities of l-galactono-1,4-lactone dehydrogenase (GalLDH) and MDHAR and total ascorbate content. Exogenous H2O2 significantly reduced MDA content and EL induced by salt stress. Above results indicated that exogenous H2O2 could enhance the salt tolerance of V. radiata by regulating the ascorbate and glutathione metabolism.

Significance of sulfur in heat stressed cluster bean (Cymopsis tetragonoloba L. Taub) genotypes: responses of growth, sugar and antioxidative metabolism

ABSTRACTA sand culture experiment was carried out to study the effects of sulfur deprivation on heat stress tolerance of two cluster bean (Cymopsis tetragonoloba L. Taub) cultivars (GC-1 and Pusa Nau Bahar (PNB)). Three weeks old sulfur-starved and sulfur-supplemented plants were subjected to heat stress (45°C/35°C) treatment for 24 h. Total dry weight, chlorophyll content, Chlorophyll a:b ratio, electrolyte leakage, malondialdehyde (MDA) accumulation, H2O2 content, sugar, glucose-6-phosphate (G-6-P), fructose-6-phosphate (F-6-P), ascorbate and glutathione concentrations and antioxidant enzyme activity (superoxide dismutase (SOD) and catalase (CAT)) were monitored, at the end of the heat stress treatment. Heat stress enhanced and sulfur starvation depleted the contents of sugar metabolites, but the accumulation of sugar, G-6-P and F-6-P were not related with heat stress tolerance. Antioxidant enzyme activities of SOD and CAT were influenced significantly more by sulfur starvation than heat stress. The results showed that under heat stress, the addition of sulfur helps to mitigate the oxidative damage in both the cultivars. However, GC-1 was more heat tolerant as it was characterized by significantly higher total dry weight, chlorophyll content, ascorbate and glutathione content and lower H2O2, MDA, electrolyte leakage than PNB.

Nitric oxide alleviates silver nanoparticles (AgNps)-induced phytotoxicity in Pisum sativum seedlings

Understanding the adverse impact of nanoparticles in crop plants has emerged as one of the most interesting fields of plant research. Therefore, this study has been conducted to investigate the impact of silver nanoparticles (AgNps) on Pisium sativum seedlings. Besides this, we have also tested whether nitric oxide (NO) is capable of reducing toxicity of AgNps or not. NO has been found as one of the most fascinating molecules, capable of enhancing plant tolerance to different environmental stresses. The results of the present study showed that AgNps treatments (1000 μM and 3000 μM) significantly declined growth parameters, photosynthetic pigments and chlorophyll fluorescence of pea seedlings, which could be correlated with increased accumulation of Ag in root and shoot of pea seedlings. In contrast, addition of SNP (100 μM; a donor of NO) successfully ameliorated AgNp-induced adverse effects on these parameters as it reduced accumulation of Ag and repaired damaged tissues. Levels of oxidative stress markers (SOR, H2O2 and MDA) were enhanced while their levels significantly reduced under SNP addition. AgNps (1000 μM and 3000 μM) significantly stimulated the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) while inhibited activities of glutathione reductase (GR) and dehydroascorbate reductase (DHAR). AgNps also considerably declined the total ascorbate and glutathione contents and severely damaged leaf and root anatomical structures. On the other hand, addition of SNP further increased the level of SOD, APX, GR and DHAR and significantly increased the decreased levels of total ascorbate and glutathione contents, and repaired anatomical structures. In conclusion, this study suggests that AgNps treatments adversely decreased growth, pigments and photosynthesis due to enhanced level of Ag and oxidative stress. However, SNP addition successfully ameliorates adverse impact of AgNps on pea seedlings by regulating the Ag uptake, antioxidant system, oxidative stress and anatomical structures of root and shoot.

Barley yellow dwarf virus infection and elevated CO2 alter the antioxidants ascorbate and glutathione in wheat

Plant antioxidants ascorbate and glutathione play an important role in regulating potentially harmful reactive oxygen species produced in response to virus infection. Barley yellow dwarf virus is a widespread viral pathogen that systemically infects cereal crops including wheat, barley and oats. In addition, rising atmospheric CO2 will alter plant growth and metabolism, including many potential but not well understood effects on plant-virus interactions. In order to better understand the wheat-BYDV interaction and any potential changes under elevated CO2, the total concentration and oxidised fraction of ascorbate and glutathione was measured in leaves of a susceptible wheat cultivar (Triticum aestivum L. ‘Yitpi’) infected with Barley yellow dwarf virus-PAV (Padi Avenae virus) and grown under elevated CO2 in controlled environment chambers. Virus infection decreased total leaf ascorbate and glutathione concentrations and increased the fraction of oxidised ascorbate (dehydroascorbate). Elevated CO2 decreased the fraction of oxidised ascorbate. In this work, we demonstrate that systemic infection by a phloem-restricted virus weakens the antioxidant pools of ascorbate and glutathione. In addition, elevated CO2 may decrease oxidative stress, for example, from virus infection, but there was no direct evidence for an interactive effect between treatments.

Redox regulation of ascorbate and glutathione by a chloroplastic dehydroascorbate reductase is required for high-light stress tolerance in Arabidopsis.

Chloroplasts are a significant site for reactive oxygen species production under illumination and, thus, possess a well-organized antioxidant system involving ascorbate. Ascorbate recycling occurs in different manners in this system, including a dehydroascorbate reductase (DHAR) reaction. We herein investigated the physiological significance of DHAR3 in photo-oxidative stress tolerance in Arabidopsis. GFP-fused DHAR3 protein was targeted to chloroplasts in Arabidopsis leaves. A DHAR3 knockout mutant exhibited sensitivity to high light (HL). Under HL, the ascorbate redox states were similar in mutant and wild-type plants, while total ascorbate content was significantly lower in the mutant, suggesting that DHAR3 contributes, at least to some extent, to ascorbate recycling. Activation of monodehydroascorbate reductase occurred in dhar3 mutant, which might compensate for the lack of DHAR3. Interestingly, glutathione oxidation was consistently inhibited in dhar3 mutant. These findings indicate that DHAR3 regulates both ascorbate and glutathione redox states to acclimate to HL.

Effects of elevated ozone on physiological, anatomical and ultrastructural characteristics of four common urban tree species in China

Fast urbanization has led to ozone (O3) being the main pollutant in summer in most of China. To assess future ground-level O3 effects on the service of urban greening species and clarify the underlying mechanism of O3 damage, four common urban greening species, Ailanthus altissima (AA), Fraxinus chinensis (FC), Platanus orientalis (PO) and Robinia pseudoacacia (RP) were exposed to non-filtered air (NF) and to elevated O3 (E-O3) in open-top chambers. E-O3 induced visible injury in all species as well as microscopic alterations such as collapse of the palisade parenchyma cells, callose accumulation, or chloroplast and mitochondrial accelerated senescence. E-O3 significantly reduced light-saturated CO2 assimilation (Asat), the maximum activity of Rubisco (Vcmax), the maximum electron transport rate (Jmax), and fluorescence parameters such as the quantum yield of noncyclic electron transport (ϕPSII), and the quenching of photochemical efficiency of PSII (qP). It also increased total antioxidant capacity, phenolics and ascorbate contents. No significant interaction between O3 and species was found in photosynthetic performance and antioxidant systems, suggesting that the four species selected were sensitive to O3. Of all four species, AA was the most sensitive species due to a combination of earlier injury onset, anatomical features, lower antioxidant responses and higher stomatal conductance. The sensitivity of tree species to O3 is a factor to be considered for urban greening. Ozone may affect important urban forest ecosystem services by reducing CO2 assimilation.

Enhancing cytokinin synthesis by overexpressing ipt alleviated drought inhibition of root growth through activating ROS-scavenging systems in Agrostis stolonifera.

Drought stress limits root growth and inhibits cytokinin (CK) production. Increases in CK production through overexpression of isopentenyltransferase (ipt) alleviate drought damages to promote root growth. The objective of this study was to investigate whether CK-regulated root growth was involved in the alteration of reactive oxygen species (ROS) production and ROS scavenging capacity under drought stress. Wild-type (WT) creeping bentgrass (Agrostis stolonifera L. 'Penncross') and a transgenic line (S41) overexpressing ipt ligated to a senescence-activated promoter (SAG12) were exposed to drought stress for 21 d in growth chambers. SAG12-ipt transgenic S41 developed a more extensive root system under drought stress compared to the WT. Root physiological analysis (electrolyte leakage and lipid peroxidation) showed that S41 roots exhibited less cellular damage compared to the WT under drought stress. Roots of SAG12-ipt transgenic S41 had significantly higher endogenous CK content than the WT roots under drought stress. ROS (hydrogen peroxide and superoxide) content was significantly lower and content of total and free ascorbate was significantly higher in S41 roots compared to the WT roots under drought stress. Enzymatic assays and transcript abundance analysis showed that superoxide dismutase, catalase, peroxidase, and dehydroascorbate reductase were significantly higher in S41 roots compared to the WT roots under drought stress. S41 roots also maintained significantly higher alternative respiration rates compared to the WT under drought stress. The improved root growth of transgenic creeping bentgrass may be facilitated by CK-enhanced ROS scavenging through antioxidant accumulation and activation of antioxidant enzymes, as well as higher alternative respiration rates when soil water is limited.

Dynamic responses of photosynthesis and the antioxidant system during a drought and rehydration cycle in peanut plants

Drought stress is one of the most important environmental factors that adversely affect the productivity and quality of crops. Most studies focus on elucidating plant responses to this stress but the reversibility of these effects is less known. The aim of this work was to evaluate whether drought-stressed peanut (Arachis hypogaea L.) plants were capable of recovering their metabolism upon rehydration, with a focus on their antioxidant system. Peanut plants in the flowering phase (30 days after sowing) were exposed to drought stress by withholding irrigation during 14 days and subsequent rehydration during 3 days. Under these conditions, physiological status indicators, reactive oxygen species production and antioxidant system activity were evaluated. Under drought stress, the stomatal conductance, photosynthetic quantum yield and 13C:12C ratio of the peanut plants were negatively affected, and also they accumulated reactive oxygen species. The antioxidant system of peanut plants showed increases in superoxide dismutase-, ascorbate peroxidase- and glutathione reductase-specific activities, as well as the total ascorbate content. All of these responses were reversed upon rehydration at 3 days. The efficient and dynamic regulation of variables related to photosynthesis and the antioxidant system during a drought and rehydration cycle in peanut plants was demonstrated. It is suggested that the activation of the antioxidant system could mediate the signalling of drought stress responses that enable the plant to survive and recover completely within 3 days of rehydration.