Silicon increases boron tolerance and reduces oxidative damage of wheat grown in soil with excess boron

The effect of silicon on the growth, boron concentrations, malondialdehyde (MDA) content, lipoxygenase (LOX) activity, proline (PRO) and H₂O₂ accumulation, and the activities of major antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)] and non-enzymatic antioxidants (AA) of wheat grown in soil originally with toxic B concentrations were investigated. Applied of 5.0 and 10.0 mM Si to the B toxic soil significantly increased Si concentration of the wheat and counteracted the deleterious effects of B on shoot growth. The contents of PRO, H₂O₂, MDA, and LOX activity of wheat grown in B toxic soil were significantly reduced by Si treatments. Compared with control plants, the activities of SOD, CAT, APX and content of AA were decreased by applied Si. Based on the present work, it can be concluded that Si alleviates B toxicity of wheat by preventing oxidative membrane damage and also translocation of B from root to shoot and/or soil to plant.     

Hydrogen Sulfide Maintains Good Nutrition and Delays Postharvest Senescence in Postharvest Tomato Fruits by Regulating Antioxidative Metabolism

As a signaling molecule, hydrogen sulfide (H₂S) plays an indispensable role in the modulation of ripening and senescence in fruits and vegetables. To explore the role of H₂S in regulating metabolism of postharvest tomato, ripening-related physiological parameters, activities of antioxidant enzymes and gene expression were analyzed in H₂S-fumigated tomato fruits. These results show that H₂S significantly delayed the color transition and softening of tomato fruit, and maintained higher level of flavonoids and lower level of anthocyanin during storage. Besides, H₂S could maintain higher level of nutritional-related metabolites, such as reducing sugar, ascorbic acid during postharvest storage. Moreover, H₂S decreased the rate of O₂⁻ production, inhibited the production of H₂O₂ and malondialdehyde (MDA), enhanced the activities of antioxidant enzymes including ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (POD) in tomato fruits, while reduced the activities of phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and lipoxygenase (LOX). Besides, the expression of the antioxidant-encoding genes SlCAT2, SlPOD12 was generally upregulated with H₂S fumigation. Principal component analysis (PCA) suggests that H₂S induced significant discrepancy mainly to the differences in firmness, anthocyanin, flavonoid and the activity of guaiacol peroxidase (POD), and the correlation analysis further shows that H₂S affected pigment metabolism and nutritional quality. In conclusion, H₂S could maintain better appearance and nutritional quality, and prolong the storage period of postharvest tomato fruits through activating the antioxidative system.

     

Responses to drought stress in two poplar species originating from different altitudes

Cuttings of Populus kangdingensis and Populus cathayana, originating from high and low altitudes in the eastern Himalaya, respectively, were examined during one growing season in a greenhouse to determine their responses to drought stress (soil moisture decreased from 100 to 55 or 25 % field capacity). Compared to control plants grown under 100 % field capacity, those poplars grown under 55 and 25 % field capacity possessed lower increases in height and stem diameter, and higher contents of soluble sugars, free proline, malondialdehyde (MDA) and hydrogen peroxide, and higher activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR). Compared with P. cathayana with greater leaf area, P. kangdingensis with greater root/shoot ratio exhibited lower MDA and H₂O₂ contents, higher soluble sugar and free proline contents, and higher activities of CAT, SOD, POD, APX and GR. These results suggested that P. kangdingensis was more drought tolerant than P. cathayana.     

Papaya fruit ripening: ROS metabolism,gene cloning,characterization and molecular docking of peroxidase

Climacteric fruit ripening has been characterized by oxidative burst and involve active oxidative metabolism with generation of reactive oxygen species (ROS). In the present paper, the papaya fruit ripening was found to be associated with increase in polygalacturonase (PG), pectate lyase (PEL), catalase (CAT), ascorbate peroxidase (APX), H₂O₂ and lipid peroxidation concomitant with decrease in the activities of superoxide dismutase (SOD) and guaiacol peroxidase (GPX). Furthermore, a cDNA (903 bp) of GPX from unripe papaya fruit pulp was isolated and cloned. On BLAST analysis, the deduced protein exhibited homology with various peroxidases and specific hits for plant heme peroxidase family namely heme and calcium binding domains. GPX of papaya was modeled and docked with various substrates and inhibitors among which guaiacol and cysteine were found to be the best substrate and inhibitor, respectively.     

Examination of Antioxidative System’s Responses in the Different Phases of Drought Stress and During Recovery in Desert Plant <Emphasis Type="Italic">Reaumuria soongorica</Emphasis> (Pall.) Maxim

The aim of this study was to test the protective roles of superoxide dismutases (SODs), guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) against oxidative damage and their activities in different phases of the dry down process in Reaumuria soongorica (Pall.) Maxim. leaves. Drought stress was imposed during 100 consecutive days and rewatering after 16, 72, and 100 days. The concentration of hydrogen peroxide (H₂O₂), malondialdehyde, and SODs activities were elevated significantly with progressing drought stress. POD and CAT activities increased markedly in the early phase of drought and decreased significantly with further drought stress continuation, and POD activity was unable to recover after rewatering. Ascorbate, reduced glutathione, APX, and GR activities declined in the initial stages of drought process, elevated significantly with further increasing water deficit progression and recovered after rewatering. These results indicate that: (1) iron SODs-removing superoxide anion is very effective during the whole drought stress; (2) CAT scavenges H₂O₂ in the early phase of drought and enzymes of ascorbate–glutathione cycle scavenge H₂O₂ in further increasing drought stress; and (3) POD does not contribute to protect against oxidative damage caused by H₂O₂ under drought stress.     

Postharvest chilling induces oxidative stress response in the dwarf tomato cultivar Micro-Tom

Oxidative stress is involved in the response of Lycopersicon esculentum fruits (cultivar Micro-Tom) to chilling. Changes in activated oxygen scavenging enzymes, superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and glutathione reductase (GR, EC 1.6.4.2) were examined during ripening after postharvest chilling. Also, lipid peroxidation, respiration, and pigment contents were determined. These parameters were affected by chilling, especially the lycopene content and the respiration rate that showed a high value when the fruits were transferred to higher temperatures. CAT activity increased the day after the fruits were re-warmed, while the activity of GR was higher in the chilled than in the non-chilled green fruits. Lipid peroxidation was more evident at the 'pre-chilled' yellow and red fruits. APX and SOD were not affected by previous chilling in ripening fruits. These results indicate that oxidative stress is generated by conservation at 4°C. The antioxidant response of tomato fruit could be mediated by CAT and GR but not by SOD or APX. Moreover, CAT seemed to respond to the increase in the respiration rate.     

Ecophysiological adaptation of <Emphasis Type="Italic">Calligonum roborovskii</Emphasis> to decreasing soil water content along an altitudinal gradient in the Kunlun Mountains,central Asia

To understand the ecophysiological adaptation mechanisms of Calligonum roborovskii to altitude variation, this study analyzed chlorophyll a (Chl a), chlorophyll b (Chl b), Chl (a + b), carotenoid (Car), malondialdehyde (MDA), ascorbate (AsA), proline (Pro), membrane permeability (MP), reactive oxygen species (ROS), specific leaf area (SLA), leaf mass per area (LMA), leaf nitrogen content based on mass (N_mass), and the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX) in leaves of plants inhabiting different altitudes (A1: 2100 m, A2: 2350 m, A3: 2600 m) on the northern slope of the Kunlun Mountains. The results showed that Chl a, Chl b, Chl (a + b), SLA, N_mass, and the activity of CAT increased with increasing altitude. LMA, MP, MDA, Car, Pro, AsA, O₂⁻, H₂O₂ and the activities of SOD, POD, and APX decreased with increasing altitude. The test results also showed that, changes in venvironmental factors along an altitudinal gradient are not obvious. Soil water content is the main ecological factor. With increasing altitude, soil water content increased significantly. More non-enzymatic and enzymatic antioxidants played an important role in eliminating intracellular ROS. They kept the cell membrane in a stable state and ensured the normal growth of C. roborovskii.     

Heat shock-mediated H2O2 accumulation and protection against Cd toxicity in rice seedlings

Rice (Oryza sativa L.) seedlings stressed with CdCl₂ (0.5 mM or 50 μM) showed typical Cd toxicity (leaf chlorosis, decrease in chlorophyll content, or increase in H₂O₂ and malondialdehyde contents). Rice seedlings pretreated with heat shock at 45°C (HS) for 2 or 3 h were protected against subsequent Cd stress. Rice seedlings pretreated with HS had similar Cd concentration in leaves caused by CdCl₂ as those non-HS. The content of H₂O₂ increased in leaves 1 h after HS exposure. However, APX and GR activities were higher in HS-treated leaves than their respective control, and it occurred after 2 h of HS treatment. Pretreatment of rice seedlings with H₂O₂ under non-HS conditions resulted in an increase in APX, GR, and CAT activities and protected rice seedlings from subsequent Cd stress. HS-induced H₂O₂ production and protection against subsequent Cd stress can be counteracted by imidazole, an inhibitor of NADPH oxidase complex. Results of the present study suggest that early accumulation of H₂O₂ during HS signals the increase in APX and GR activities, which in turn prevents rice seedlings from Cd-caused oxidative damage.     

Exogenous proline alleviates the effects of H2O2-induced oxidative stress in wild almond species

The effect of proline on the antioxidant system in the leaves of eight species of wild almond (Prunus spp.) exposed to H₂O₂-mediated oxidative stress was studied. The levels of endogenous proline (Pro) and hydrogen peroxide, and the activities of total superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and guaiacol peroxidase (POD) were measured. The degradation of chlorophyll but not carotenoids occurred in leaves in the solution of 5 mM H₂O₂. An increase in membrane lipid peroxidation was observed in H₂O₂ treatment, as assessed by MDA level and percentage of membrane electrolyte leakage (EL). Significant increases in total SOD and CAT activities, as well as decreases in APX and POD activities, were detected in H₂O₂-treated leaves. The three SOD isoforms showed different behavior, as Mn-SOD activity was enhanced by H₂O₂, whereas Fe-SOD and Cu/Zn-SOD activities were inhibited. In addition, Pro accumulation up to 0.1 ??mol/g fr wt, accompanied by significant decreases in ascorbate and glutathione levels, was observed in H₂O₂-treated leaves. After two different treatments with 10 mM Pro + 5 mM H₂O₂, total SOD and CAT activities were similar to the levels in control plants, while POD and APX activities were higher if compared to the leaves exposed only to H₂O₂. Pro + H₂O₂ treatments also caused a strong reduction in the cellular H₂O₂ and MDA contents and EL. The results showed that Pro could have a key role in protecting against oxidative stress injury of wild almond species by decreasing membrane oxidative damage.     

Accumulation, subcellular localization and ecophysiological responses to copper stress in two Daucus carota L. populations

Copper accumulation, subcellular localization and ecophysiological responses to excess copper were investigated using pot culture experiments with two Daucus carota L. populations, from a copper mine and an uncontaminated field site, respectively. Significant differences of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) concentrations and antioxidant enzyme [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX)] activities of leaves under Cu treatment were observed between the two populations. At high Cu concentrations (400 and 800 mg kg⁻¹), a significant increase in contents of MDA and H₂O₂ but a significant decrease in activities of SOD, CAT and APX were observed in uncontaminated population. Contrarily, the population from copper mine maintained a lower level of MDA and H₂O₂ but higher activities of SOD, CAT and APX. Copper accumulation in roots and shoots increased significantly with the increase of copper concentrations in soils in the two populations. No significant difference of the total Cu in roots and shoots was found between the two populations at same copper treatment. There were also no striking differences of cell wall-bound Cu and protoplasts Cu of leaves between the two populations. The difference was that Cu concentration in vacuoles of leaves was 1.5-fold higher in contaminated site (CS) population than in uncontaminated site population. Hence, more efficient vacuolar sequestration for Cu and maintaining high activities of SOD, CAT and APX in the CS population played an important role in maintaining high Cu tolerance.     

Recovery of bean plants from boron-induced oxidative damage by zinc supply

The effects of zinc on growth, boron uptake, lipid peroxidation, membrane permeability (MP), lypoxygenase (LOX) activity, proline and H₂O₂ accumulation, and the activities of major antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) in bean plants were investigated under greenhouse conditions. Treatments consisted of control, 20 mg/kg B, and 20 mg/kg B plus 20 mg/kg Zn. When the plants were grown with 20 mg/kg Zn, B toxicity was less severe. Zinc supplied to soil counteracted the deleterious effects of B on root and shoot growth. Excess B significantly increased and Zn treatment reduced B concentrations in shoot and root tissues. Applied Zn increased the Zn concentration in the roots and shoots. While the concentrations of H₂O₂ and proline were increased by B toxicity, their concentrations were decreased by Zn supply. Boron toxicity increased the MP, malondialdehyde content, and LOX activity in excised bean leaves. Applied Zn significantly ameliorated the membrane deterioration. Compared with control plants, the activity of SOD was increased while that of CAT was decreased and APX remained unchanged in B-stressed plants. However, application of Zn decreased the SOD and increased the CAT and APX activities under toxic B conditions. It is concluded that Zn supply alleviates B toxicity by preventing oxidative membrane damage. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 555–562. This text was submitted by the authors in English.     

不同海拔青海云杉与祁连圆柏叶片抗氧化系统

以祁连山寺大隆林区连续海拔梯度(2 665~3 365 m)上青海云杉(Picea crassifolia)和祁连圆柏(Sabina przewalskii)为材料, 测定叶片中抗氧化保护系统的变化, 探讨常绿木本植物抗氧化系统对高山极端环境的适应机制。结果显示, 祁连圆柏和青海云杉叶片中丙二醛(MDA)含量均与海拔高度呈正相关, 相同海拔上青海云杉MDA含量极显著高于祁连圆柏(p＜0.01)。随海拔升高, 两树种抗氧化保护酶超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性和非酶促抗氧化剂脯氨酸(Pro)、抗坏血酸(AsA)、还原性谷胱甘肽(GSH)含量均呈明显增加趋势。青海云杉叶片的AsA水平高于祁连圆柏, 但对海拔变化的敏感性较低; 祁连圆柏的GSH、Pro水平及其对海拔变化的敏感性均高于青海云杉。结果表明, 研究区青海云杉所受过氧化伤害较祁连圆柏更严重, 但两树种清除O₂^-·的能力相当而主要负责分解H₂O₂的酶种有所不同: 祁连圆柏中为POD, 青海云杉中则为CAT、APX和GR, AsA-GSH循环系统在青海云杉活性氧清除中的作用强于在祁连圆柏中, 祁连圆柏的活性氧清除物质可能以Pro为主。     

Exogenous H<Subscript>2</Subscript>O<Subscript>2</Subscript> improves the chilling tolerance of manilagrass and mascarenegrass by activating the antioxidative system

The effect of foliar pretreatment by hydrogen peroxide (H₂O₂) at low concentrations of 0, 5, 10, and 15 mM on the chilling tolerance of two Zoysia cultivars, manilagrass (Zoysia matrella) and mascarenegrass (Zoysia tenuifolia), was studied. The optimal concentration for H₂O₂ pretreatment was 10 mM, as demonstrated by the lowest malondialdehyde (MDA) content and electrolyte leakage (EL) levels and higher protein content under chilling stress (7°C/2°C, day/night). Prior to initiation of chilling, exogenous 10 mM H₂O₂ significantly increased catalase (CAT), ascorbate peroxidase (APX), glutathione-dependent peroxidases (GPX), and glutathione-S-transferase (GST) activities in manilagrass, and guaiacol peroxidase (POD), APX, and glutathione reductase (GR) activities in mascarenegrass, suggesting that H₂O₂ may act as a signaling molecule, inducing protective metabolic responses against further oxidative damage due to chilling. Under further stress, optimal pretreatments alleviated the increase of H₂O₂ level and the decrease of turfgrass quality, and improved CAT, POD, APX, GR, and GPX activities, with especially significant enhancement of APX and GPX activities from the initiation to end of chilling. These antioxidative enzymes were likely the important factors for acquisition of tolerance to chilling stress in the two Zoysia cultivars. Our results showed that pretreatment with H₂O₂ at appropriate concentration may improve the tolerance of warm-season Zoysia grasses to chilling stress, and that manilagrass had better tolerance to chilling, as evaluated by lower MDA and EL, and better turfgrass quality, regardless of the pretreatment applied.     

Changes in expression of the cytosolic ascorbate peroxidase gene,ca-capx1, during germination and development of hot pepper seedlings

Ascorbate peroxidase (APX), an antioxidant enzyme, scavenges H₂O₂ that is produced by normal metabolism and cellular oxidative stresses. To investigate its role during germination and seedling growth, we isolated a cDNA encoding cytosolic APX (cAPX) in hot pepper(Capsicum annuum L). The full-length clone,Ca- cAPX1, is 1011 bp long and has an ORF encoding 249 amino acid residues. During seedling development, cAPX activity and expression levels were higher at Days 5 and 6 post-imbibition, respectively, whereas those of catalase (CAT) increased at Days 8 and 10. The increased amount of H₂O₂ in that early developmental stage (Day 5) may have been counteracted mainly by APX, and further removed by CAT in cooperation with APX. To determine whether the accumulation of H₂O₂ via suppression ofcAPX expression might be a factor in stimulating germination, we constructed a transformant ofCaAPX1. Compared with the wild type, the germination rate for the antisense-suppressedArabidopsis increased by 26%, while its H₂O₂ content rose by 50%. Therefore, we propose that the pre-germination suppression ofcAPX expression stimulates seed germination by promoting the accumulation of H₂O₂.     

Biochemical responses of the ethylene-insensitive Never ripe tomato mutant subjected to cadmium and sodium stresses

In order to further address the known interaction between ethylene and components of the oxidative system, we have used the ethylene-insensitive Never ripe (Nr) tomato (Solanum lycopersicum L.) mutant, which blocks ethylene responses. The mutant was compared to the control Micro-Tom (MT) cultivar subjected to two stressful situations: 100 mM NaCl and 0.5 mM CdCl₂. Leaf chlorophyll, lipid peroxidation and antioxidant enzyme activities in roots, leaves and fruits, and Na and Cd accumulation in tissues were determined. Although we verified a similar growth pattern and Na and Cd accumulation for MT and Nr, the mutant exhibited reduced leaf chlorophyll degradation following stress. In roots and leaves, the patterns of catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), superoxide dismutase (SOD) enzyme activity as well as malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) production under the stressful conditions tested were very similar between MT and Nr mutant. However, Nr fruits showed increased H₂O₂ production, reduced and enhanced APX activity in NaCl and CdCl₂, respectively, and enhanced GPOX in NaCl. Moreover, through non-denaturing PAGE, a similar reduction of SOD I band intensity in both, control MT and Nr mutant, treated with NaCl was observed. In leaves and fruits, a similar SOD activity pattern was observed for all periods, genotypes and treatments. Overall the results indicate that the ethylene signaling associated with NR receptor can modulate the biochemical pathways of oxidative stress in a tissue dependent manner, and that this signaling may be different following Na and Cd exposure.     

Changes in the isozyme composition of antioxidant enzymes in response to aminotriazole in leaves ofArabidopsis thaliana

The changes in isozyme profiles of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) during severe deactivation of total CAT activity by aminotriazole (AT) treatment were investigated in the leaves ofArabidopsis thaliana (Columbia ecotype) in relation to H₂O₂-mediated oxidative stress. In spite of striking deactivation of total CAT activity by 0.1 mM AT, there were no significant differences in H₂O₂ levels or total leaf soluble protein contents including a Rubisco in both the control and AT-treated leaves. On the other hand, one specific protein band (molecular mass, 66 kD) was observed on the SDS-gel from leaf soluble proteins whose staining intensity was strikingly enhanced by AT treatment for 6 h. However, this band disappeared at 12 h. In the native-gel assays of CAT, POD, APX and GR isozymes, AT remarkably inhibited the expression of the CAT1 isozyme with no effects on CAT2 and CAT3, and generally had no effect on POD isozyme profiles. However, AT stimulated the intensity of activities of pre-existing APX1 and GR1 isozymes. In particular, it induced a new synthesis of one GR isozyme. Therefore, these results collectively suggest that a striking deactivation of total CAT activity by AT inA. thaliana leaves largely results from the suppression of CAT1 isozyme, and that APX1, GR1, and a newly synthesized GR isozyme could complement the role of CAT1 to metabolize H₂O₂ into non-toxic water.     

Antioxidative defense system in pigeonpea roots under waterlogging stress

Pigeonpea [Cajanus cajan (L.) Millsp.] is a waterlogging-sensitive legume crop. We studied the effect of waterlogging stress on hydrogen peroxide (H₂O₂) content, lipid peroxidation and antioxidant enzyme activities in two pigeonpea genotypes viz., ICPL-84023 (waterlogging resistant) and MAL-18 (waterlogging susceptible). In a pot experiment, waterlogging stress was imposed for 6 days at early vegetative stage (20 days after sowing). Waterlogging treatment significantly increased hydrogen peroxide accumulation and lipid peroxidation, which indicated the extent of oxidative injury posed by stress conditions. Enzyme activities of peroxidase (POX), catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD) and polyphenol oxidase (PPO) increased in pigeonpea roots as a consequence of waterlogged conditions, and all the enzyme activities were significantly higher in waterlogged ICPL-84023 than in MAL-18. POX activity was the maximum immediately after imposing stress, therefore, it was suggested to be involved in early scavenging of H₂O₂, while rest of the enzymes (CAT, APX, SOD and PPO) were more important in late responses to waterlogging. Present study revealed that H₂O₂ content is directly related to lipid peroxidation leading to oxidative damage during waterlogging in pigeonpea. Higher antioxidant potential in ICPL-84023 as evidenced by enhanced POX, CAT, APX, SOD and PPO activities increased capacity for reactive oxygen species (ROS) scavenging and indicated relationship between waterlogging resistance and antioxidant defense system in pigeonpea.