Comparison of antioxidant responses to cadmium and lead in Bruguiera gymnorrhiza seedlings

Seedlings of mangrove plant Bruguiera gymnorrhiza cultured in sand with Hoagland’s nutrient solution were treated with 1 to 30 mM Cd(NO₃)₂ or Pb(NO₃)₂ for 2 months. In all Cd/Pb treatments, the malondialdehyde content increased while the chlorophyll content declined. Peroxidase (POD) and superoxide dismutase (SOD) activities in roots increased at moderate Cd/Pb concentrations (1–10 mM), whereas decreased at higher concentrations (20–30 mM). Catalase (CAT) activity in roots was inhibited by 1–10 mM Cd but enhanced by 1–10 mM Pb. The activities of POD, SOD and CAT in leaves were less affected by Cd and Pb than in roots. A new SOD and three CAT isoenzymes were induced by Pb. In contrast, no additional SOD and CAT isoenzymes were induced by Cd.     

Scots pine as a model plant for studying the mechanisms of conifers adaptation to heavy metal action: 2. Functioning of antioxidant enzymes in pine seedlings under chronic zinc action

Functioning of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APO), and guaiacol peroxidases (GPO)) and low-molecular organic ROS scavengers (proline and phenolic compounds) in various organs (roots, cotyledons, stem, and needle) of 6-week-old seedlings of pine (Pinus sylvestris L.) developing in the chronic presence of ZnSO₄ (50, 100, and 150 μM). Pine seedlings were grown in water culture in the climate-controlled chamber at an irradiance of 37.6 W/m² with a 16-h photoperiod, an air temperature of 23 ± 1/15 ± 1°C (day/night), and a relative humidity of 55/70% (day/night). Endogenous Zn content was a key factor determining SOD activity decomposing superoxide into H₂O₂ and O₂. Hydrogen peroxide produced is efficiently destroyed by CAT and also by APO and GPO. At the same time, the content of proline increased (especially at 150 μM ZnSO₄), but the content of phenolic compounds remained unchanged. All these processes help to maintain stable intracellular levels of O₂^⊙− and H₂O₂ at elevated zinc concentrations and to prevent generation of hydroxyl radical and development of oxidative stress.     

镉诱导萝卜幼苗活性氧产生、脂质过氧化和抗氧化酶活性的变化

通过水培试验,研究Cd2+胁迫对萝卜幼苗活性氧的产生、脂质过氧化和抗氧化酶活性的影响。超氧 阴离子(O 2)的产生速率和丙二醛(MDA)的含量与对照相比有不同程度的增加,表明Cd2+胁迫能导致萝卜体 内的氧化胁迫;超氧化物歧化酶(SOD)的活性,随着Cd2+浓度提高,首先明显上升,然后逐渐下降,甚至低于 对照,叶片过氧化氢酶(CAT)的活性明显增加,根系CAT活性则减少,根系以及较高浓度Cd2+处理后期叶片 谷胱甘肽还原酶(GR)的活性均显著增加。推测:胁迫初期可能主要由SOD和CAT发挥抗氧化作用;后期由 于抗坏血酸—谷胱甘肽(AsA GsH)循环途径的激活,以及还原型谷胱甘肽(GSH)和植物络合素(Phytochela tins,PCs)的合成,可能在清除活性氧或者直接鏊合Cd2+中起作用。     

Nickel-induced Inhibition of Wheat Root Growth is Related to H2O2 Production, but not to Lipid Peroxidation

Effects of exogenous nickel (Ni: 10 and 200 μM) on growth, mitotic activity, Ni accumulation, H₂O₂ content and lipid peroxidation as well as the activities of various antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione peroxidase (GSH-Px) were investigated in wheat roots. A considerable Ni accumulation in the roots occurred at both the concentrations. Although Ni at 10 μM did not have any significant effect on root growth, it strongly inhibited the root growth at 200 μM. Mitotic activity in the root tips was not significantly affected by exposure of the seedlings to 10 μM Ni; however, it was almost completely inhibited at 200 μM treatment. Ni stress did not result in any significant changes in CAT and APX activities as well as lipid peroxidation. However, H₂O₂ concentration increased up to 82% over the control in the roots of seedlings exposed to 200 μM Ni. There was a significant decline in both SOD (50%) and GSH-Px (20–30%) activities in the roots when the seedlings were treated with 200 μM Ni. The results indicated that a strong inhibition of wheat root growth caused by Ni stress was not due to enhanced lipid peroxidation, but might be related to the accumulation of H₂O₂ in root tissue.     

AtMTM1, a novel mitochondrial protein,may be involved in activation of the manganese-containing superoxide dismutase in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Mtm1p is essential for the posttranslational activation of manganese-containing superoxide dismutase (SOD2) in Saccharomyces cerevisiae; however, whether the same holds true for Arabidopsis thaliana is unknown. In this study, by using the yeast mtm1 mutant complementation method, we identified a putative MTM gene (AtMTM1, At4g27940) that is necessary for SOD2 activation. Further, analysis of SOD activity revealed that an SOD2 defect is rescued in the yeast mutant Y07288 harboring the AtMTM1 gene. Related mRNA-level analysis showed the AtMTM1 gene is induced by paraquat but not by hydrogen peroxide, which indicates that this gene is related to the superoxide scavenger SOD. In addition, an AtMTM1::GFP fusion construct was transiently expressed in the protoplasts, and it was localized to the mitochondria. Furthermore, sequence deletion analysis of AtMTM1 revealed that the code region (amino acid (aa) 60–198) of Mtm1p plays an important role in localization of the protein to the mitochondria. Regulation of AtMTM1 gene expression was analyzed using a fusion construct of the 1,766 bp AtMTM1 promoter and the GUS (β-glucuronidase) reporter gene. The screen identified GUS reporter gene expression in the developing cotyledons, leaves, roots, stems, and flowers but not in the siliques. Our results suggest that AtMTM1 encodes a mitochondrial protein that may be playing an important role in activation of MnSOD1 in Arabidopsis.     

Effect of low above-zero temperature on the content of low-molecular antioxidants and activities of antioxidant enzymes in green barley leaves

We studied the effect of low above-zero temperature (2°C) on the content of low-molecular antioxidants (ascorbic acid, glutathione, and carotenoids) and also activities of antioxidant enzymes (ascorbate peroxidase, APO; catalase, CAT; glutathione reductase, GR; and superoxide dismutase, SOD) in green barley (Hordeum vulgare L.) seedlings. Under stress conditions, the content of low-molecular antioxidants, especially that of reduced ascorbate form, increased. Low-temperature stress activated APO, CAT, GR, and SOD. First enzymes responding to the action of stress factor were APO and CAT, i.e., enzymes neutralizing hydrogen peroxide in plant cells, which indicated H₂O₂ active generation at low temperature. Cytoplasmic SOD was more active than its chloroplast isoforms. This indicates that oxidative process initiation under low-temperature stress occurred more active in the cytosol. After termination of stress-factor action, the content of total ascorbate, glutathione, and carotenoids reduced rapidly to the level close to the initial one. During post-stress period, the amount of reduced ascorbate declined as well; however, it remained at the level higher than the initial one. Activities of APO and CAT dropped sharply; activities of GR and SOD reduced gradually. Thus, reduced ascorbate, APO, and CAT play an important role in plant cell defense against above-zero temperatures close to zero; reduced ascorbate, GR, and SOD are especially important during post-stress period.     

The Distribution and Cooperation of Antioxidant (Iso)enzymes and Antioxidants in Different Subcellular Compartments in Maize Leaves during Water Stress

The effects of mild water stress induced by polyethylene glycol (PEG) on the activities of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)] and their isoenzymes and the antioxidant content [ascorbate (ASC) and glutathione (GSH)] of different subcellular compartments were investigated in maize. For each subcellular compartment, the activities of almost all isoenzymes resolved on native PAGE increased after 4–12 h of exposure to water stress and declined after that, showing concomitant changes with the activities of their respective total enzymes and the antioxidant content. For each subcellular compartment, at least one isoform for the detected antioxidant enzymes was resolved, but different kinds of antioxidant isoenzymes in different subcellular compartments had different responses to water stress. The relative contribution of Fe–SOD in chloroplasts and Mn–SOD in mitochondria was higher than that in other subcellular compartments. However, in apoplasts the activities of Mn–SOD and Fe–SOD declined during the process of water stress, in contrast to those located in other subcellular compartments. The results from the activities of antioxidant (iso)enzymes demonstrated that all antioxidant enzymes in all subcellular compartments were mobilized in cooperation and responded synchronously under mild water stress, with the same trend of changes in their activity. This indicated their orchestrated effects in scavenging reactive oxygen species (ROS) in situ. Additionally, the results suggested that mitochondria and apoplasts, responding most actively, might be targets for improving plant performance under mild water stress.     

Reactive Oxygen Species and Relative Enzyme Activities in the Development of Aerial Roots of Chinese Banyan (Ficus microcarpa)

Although previous research has indicated that reactive oxygen species (ROS) regulate cell extension and tissue ontogenesis, the functions of ROS in aerial roots have not been previously studied. This research evaluated ROS production and dissipation in aerial roots of Chinese banyan (Ficus microcarpa). Aerial root segments (4 cm long) were cut from trees and divided into developmental zones 1, 2, and 3 (0–5, 5–15, and 15–25 mm from root tip, respectively). According to histochemical and biochemical determinations, production of the superoxide radical (O ₂ ^·– ), hydrogen peroxide (H₂O₂), and the hydroxyl radical (^·OH) decreased from zone 1 to zone 3. The detected ROS increased with the application of exogenous stimulators of ROS generation and decreased with the application of exogenous inhibitors of ROS generation. Based on protein content, superoxide dismutase (SOD) activity increased but peroxidase (POD) and catalase (CAT) activities decreased from zone 1 to zone 3, whereas based on root segment fresh weight, SOD and CAT activities did not differ among the zones but POD activity decreased from zone 1 to 3. We conclude that ROS are generated mainly in the rapidly developing zones of aerial roots and suggest that NADPH oxidase, POD, and SOD control ROS generation. POD activity and the hydroxyl cycle seem particularly important in ROS generation in aerial roots.     

Genotype-Dependent Effect of Exogenous Nitric Oxide on Cd-induced Changes in Antioxidative Metabolism, Ultrastructure, and Photosynthetic Performance in Barley Seedlings (Hordeum vulgare)

A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O₂^•−, H₂O₂, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P _n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD) and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover, Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced damage to leaf/root ultrastructure, and increased chlorophyll content and P _n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments. Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular structure.     

Effect of La(III) on the growth and aging of root of loquat plantlet in vitro

The effect of lanthanum on the adventitious root growth, activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), O₂ production rate, MDA content, and the relative plasma membrane permeability in roots of loquat test-tube plantlet were studied. Addition of lanthanum chloride (0.5 μmol/L) to the culture medium significantly increased the length of roots, increased the dry weight, enhanced the activities of SOD, CAT, and POD, decreased O₂ production rate, malondialdehyde (MDA) contents, and the relative plasma membrane permeability. The relatively stable membrane structure of cell could defer the root aging of the plantlet in vitro. There are important theory meaning and practical value in applying LaCl₃ in the rooting medium to raise the rate of rooting and transplant for wood plant.     

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.     

Superoxide dismutase of plant cell vacuoles

Metal-dependent superoxide dismutases (SOD; EC 1.15.1.1) are present in many cell compartments (mitochondria, plastids, nuclei, peroxisomes, endoplasmic reticulum, cell wall and cytosol). We have established that SOD is also localized in the central vacuole. Cyanide-sensitive Cu, Zn-SOD was found in the fraction of isolated vacuoles of red beet roots (Beta vulgaris L.). The enzyme was represented by three isoforms. Comparison of isoenzyme composition and the level of SOD activity in vacuoles, nuclei, plastids and mitochondria isolated from root cells has shown that Cu, Zn-SOD is present in vacuoles and nuclei, two SOD forms (Cu, Zn- and Fe-SOD) are present in plastids, and two SOD forms (Cu, Zn- and Mn-SOD) are present in mitochondria. Cu, Zn-SOD of organelles, unlike vacuolar Cu, Zn-SOD, had only one isoform. The level of enzyme activity from the vacuolar fraction was twice higher than the level of SOD activity from the fractions of isolated organelles. Previously it has been suggested that Cu, Zn-SOD may be localized on the vacuolar membrane or in the near-membrane space from the side of cytoplasm. Our tests have revealed the Cu, Zn-SOD activity in water-soluble extracts of isolated vacuole fractions in the absence of detergent, which may confirm localization of the enzyme inside the organelles.     

Excess copper induces accumulation of hydrogen peroxide and increases lipid peroxidation and total activity of copper–zinc superoxide dismutase in roots of Elsholtzia haichowensis

The effects of excess copper (Cu) on the accumulation of hydrogen peroxide (H₂O₂) and antioxidant enzyme activities in roots of the Cu accumulator Elsholtzia haichowensis Sun were investigated. Copper at 100 and 300 μM significantly increased the concentrations of malondialdehyde and H₂O₂, and the activities of catalase (E.C. 1.11.1.6), ascorbate peroxidase (E.C. 1.11.1.11), guaiacol peroxidase (GPOD, E.C. 1.11.1.7) and superoxide dismutase (SOD, E.C. 1.15.1.1). Isoenzyme pattern and inhibitor studies showed that, among SOD isoforms, only copper–zinc superoxide dismutase (CuZn–SOD) increased. Excess Cu greatly increased the accumulation of superoxide anion (O₂ ^·−) and H₂O₂ in E. haichowensis roots. This study also provides the first cytochemical evidence of an accumulation of H₂O₂ in the root cell walls as a consequence of Cu treatments. Experiments with diphenyleneiodonium as an inhibitor of NADPH oxidase, 1,2-dihydroxybenzene-3,5-disulphonic acid as an O₂ ^·− scavenger, and N-N-diethyldithiocarbamate as an inhibitor of SOD showed that the source of H₂O₂ in the cell walls could partially be NADPH oxidase. The enzyme can use cytosolic NADPH to produce O₂ ^·−, which rapidly dismutates to H₂O₂ by SOD. Apoplastic GPOD and CuZn–SOD activities were induced in roots of E. haichowensis with 100 μM Cu suggesting that these two antioxidant enzymes may be responsible for H₂O₂ accumulation in the root apoplast.     

Reactive oxygen species production and antioxidative defense in pea (Pisum sativum L.) root nodules after short-term aluminum treatment

Pea plants (Pisum sativum L.) were treated with 50???M aluminum chloride at pH 4.5 for 2 or 24?h at room temperature. Following treatment, root nodule Al uptake, the generation of reactive oxygen species (ROS, O ₂ ^?· and H₂O₂), and the activities of the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD) and peroxidase (POX) were investigated. Aluminum accumulation was found chiefly in the apoplast of the nodule cortex, endodermis and meristem, while the formation of peroxide was detected in the nodule cortex, infection threads and bacteroidal tissue. Further, there were increased levels of superoxide in the meristem and bacteroidal tissue. The activity of SOD (EC 1.15.1.1) and POX (EC 1.11.1.7) increased in the Al-treated nodules and the roots of pea plants, whereas CAT (EC 1.11.1.6) activity decreased. The Al absorbed by the nodules induced ROS production. The POX and SOD are important ROS-scavengers in Al-stressed nodules.     

Copper-induced changes in the growth, oxidative metabolism, and saponin production in suspension culture roots of Panax ginseng in bioreactors

Roots of Panax ginseng exposed to various concentrations of Cu (0.0, 5, 10.0, 25.0, and 50.0 μM) accumulated high amounts of Cu in a concentration-dependent and duration-dependent manner. Roots treated with 50 μM Cu resulted in 52% and 89% growth inhibition after 20 and 40 days, respectively. Saponin synthesis was stimulated at a Cu concentration between 5 and 25 μM but decreased at 50 μM Cu. Malondialdehyde content (MDA), lipoxygenase activity (LOX), superoxide ion (O₂ ^•−) accumulation, and H₂O₂ content at 5 and 10 μM Cu-treated roots were not increased but strongly increased at 50 μM Cu resulting in the oxidation of ascorbate (ASC) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively indicating a clear oxidative stress. Seven well-resolved bands of superoxide dismutase (SOD) were detected in the gel and an increase in SOD activity seemed to be mainly due to the induction of Fe-SOD 3. Five to 10 μM Cu slightly induced activity of ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR), guaiacol peroxidase (G-POD) but inhibited monodehydroascorbate reductase (MDHAR) and glutathione reductase (GR) enzyme activities. No changes in catalase (CAT) activity and in activity gel were found up to 25 μM Cu, but both G-POD and CAT activities were inhibited at 50 μM Cu. Glutathione metabolism enzymes such as γ-glutamylcysteine synthetase (γ-GCS), glutathione-S-transferase (GST), and glutathione peroxidase activities (GPx) were activated at 5 and 10 μM Cu but were strongly inhibited at 50 μM Cu due to the Cu accumulation in root tissues. The strong depletion of GSH at 50 μM Cu was associated to the strong induction of γ-glutamyltranspeptidase (γ-GGT) activity. These results indicate that plant could grow under Cu stress (5–25 μM) by modulating the antioxidant defense mechanism for combating Cu induced oxidative stress.     

An Enhancing Effect of Exogenous Mannitol on the Antioxidant Enzyme Activities in Roots of Wheat Under Salt Stress

The role of mannitol as an osmoprotectant, a radical scavenger, a stabilizer of protein and membrane structure, and protector of photosynthesis under abiotic stress has already been well described. In this article we show that mannitol applied exogenously to salt-stressed wheat, which normally cannot synthesize mannitol, improved their salt tolerance by enhancing activities of antioxidant enzymes. Wheat seedlings (3 days old) grown in 100 mM mannitol (corresponding to −0.224 MPa) for 24 h were subjected to 100 mM NaCl treatment for 5 days. The effect of exogenously applied mannitol on the salt tolerance of plants in view of growth, lipid peroxidation levels, and activities of antioxidant enzymes in the roots of salt-sensitive wheat (Triticum aestivum L. cv. Kızıltan-91) plants with or without mannitol was studied. Although root growth decreased under salt stress, this effect could be alleviated by mannitol pretreatment. Peroxidase (POX) and ascorbate peroxidase (APX) activities increased, whereas superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) activities decreased in Kızıltan-91 under salt stress. However, activities of antioxidant enzymes such as SOD, POX, CAT, APX, and GR increased with mannitol pretreatment under salt stress. Although root tissue extracts of salt-stressed wheat plants exhibited only nine different SOD isozyme bands of which two were identified as Cu/Zn-SOD and Mn-SOD, mannitol treatment caused the appearance of 11 different SOD activity bands. On the other hand, five different POX isozyme bands were determined in all treatments. Enhanced peroxidation of lipid membranes under salt stress conditions was reduced by pretreatment with mannitol. We suggest that exogenous application of mannitol could alleviate salt-induced oxidative damage by enhancing antioxidant enzyme activities in the roots of salt-sensitive Kızıltan-91.     

Cadmium effects on growth and antioxidant enzymes activities in Miscanthus sinensis

Plants of Miscanthus sinensis (cv. Giganteus) were grown in hydroponics for three months in nutrient solution with 0, 2.2, 4.4 and 6.6 μM CdNO₃. Growth parameters, catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities were analysed in leaves and roots collected after 1-and 3-month exposure. Dry biomass of all miscanthus organs was affected by Cd concentration both after 1-and 3-month exposure. No visible symptoms of Cd toxicity were observed in shoots and rhizomes of plants grown in presence of Cd. In contrast, roots became shorter and thicker and the whole root system more dense and compact already after one month of treatment with 6.6 μM Cd. The lower Cd concentration increased the enzymes activities after 3 months in leaves and only after 1-month in roots, while a decrease in activity was observed at higher Cd concentrations.     

Treatment of Paenibacillus illinoisensis suppresses the activities of antioxidative enzymes in pepper roots caused by Phytophthora capsici infection

Summary The activity of antioxidative enzymes after inoculation of pepper (Capsicum annuum L. Chungok) with a pathogen, Phytophthora capsici (P), the causal agent of Phytophtora blight and dual inoculation of pathogen and an antagonist, Paenibacillus illinoisensis KJA-424 (P+A), were measured and compared with that of non-inoculated (C) roots. Root mortality was significantly reduced by about 84% in P+A treatment compared with P treatment alone. When compared to the non-inoculated (C) roots, malondialdehyde (MDA) concentration gradually decreased by 52.4% in 7 days only in P-treated roots and hydrogen peroxide (H₂O₂) was not significantly affected by the treatment for 5 days but significantly decreased in the P+A-treated roots at day 7. P-treatment continuously induced peroxidase (POD) and superoxide dismutase (SOD), resulting in significant increases of 36.7% and 27.7% at day 7, respectively, compared to the control. In P+A-treated roots, the activities of POD and SOD also increased for 5 days but returned to the control level at day 7. Catalase activity fluctuated but again increased over the 7-day period following P+A inoculation. These results indicate that an antagonist P. illinoisensis KJA-424 alleviated root mortality and suppressed the elevated activities of POD and SOD in the root of pepper plant root caused by P.␣capsici infection.     

Scavenger Enzyme Activities in Subcellular Fractions of White Clover (Trifolium repens L.) under PEG-induced Water Stress

Scavenger enzyme activities in subcellular fractions under polyethylene glycol (PEG)-induced water stress in white clover (Trifolium repens L.) were studied. Water stress decreased ascorbic acid (AA) content and catalase (CAT) activity and increased the contents of hydrogen peroxide (H₂O₂), thiobarbituric acid reactive substances (TBARS) (measure of lipid peroxidation), and activities of superoxide dismutase (SOD), its various isozymes, ascorbate peroxidase (APOX), and glutathione reductase (GR) in cellular cytosol, chloroplasts, mitochondria, and peroxisomes of Trifolium repens leaves. In both the PEG-treated plants and the control, chloroplastic fractions showed the highest total SOD, APOX, and GR activities, followed by mitochondrial fractions in the case of total SOD and GR activities, whereas cytosolic fractions had the second greatest APOX activity. However, CAT activity was the highest in peroxisomes, followed by the cytosol, mitochondria, and chloroplasts in decreasing order. Although Mn-SOD activity was highest in mitochondrial fractions, residual activity was also observed in cytosolic fractions. Cu/Zn-SOD and Fe-SOD were observed in all subcellular fractions; however, the activities were the highest in chloroplastic fractions for both isoforms. Total Cu/Zn-SOD activity, the sum of activities observed in all fractions, was higher than other SOD isoforms. These results suggest that cytosolic and chloroplastic APOX, chloroplastic and mitochondrial GR, mitochondrial Mn-SOD, cytosolic and chloroplastic Cu/Zn-SOD, and chloroplastic Fe-SOD are the major scavenger enzymes, whereas cellular CAT may play a minor role in scavenging of O₂⁻ and H₂O₂ produced under PEG-induced water stress in Trifolium repens.