Tolerance of a field grown soybean cultivar to elevated ozone level is concurrent with higher leaflet ascorbic acid level, higher ascorbate-dehydroascorbate redox status, and long term photosynthetic productivity

We examined the characteristics of ascorbic acid (ASC) level, dehydroascorbate (DHA) level, and the ASC–DHA redox status in the leaflets of two soybean cultivars grown in a field environment and exposed to elevated ozone (O₃) levels. These two cultivars, one that preliminary evidence indicated to be O₃-tolerant (cv Essex), and one that was indicated to be O₃-sensitive (cv Forrest), were grown in open-top chambers during the summer of 1997. The plants were exposed daily to a controlled, moderately high O₃ level (≈58 nl l⁻¹ air) in the light, beginning at the seedling stage and continuing to bean maturity. Concurrently, control plants were exposed to carbon-filtered, ambient air containing a relatively low O₃ level (≈24 nl l⁻¹ air) during the same period. Elevated O₃ did not affect biomass per plant, mature leaf area accretion, or bean yield per plant of cv Essex. In contrast, elevated O₃ level decreased the biomass and bean yield per plant of cv Forrest by approximately 20%. Daily leaflet photosynthesis rate and stomatal conductance per unit area did not decrease in either cultivar as a result of prolonged O₃ exposure. A 10% lower mature leaflet area in O₃-treated cv Forrest plants contributed to an ultimate limitation in long-term photosynthetic productivity (vegetative and bean yield). Possible factors causing cv Essex to be more O₃ tolerant than cv Forrest were: 1) mature leaflets of control and O₃-treated cv Essex plants consistently maintained a higher daily ASC level than leaflets of cv Forrest plants, and 2) mature leaflets of cv Essex plants maintained a higher daily ASC–DHA redox status than leaflets of cv Forrest plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

The relations between antioxidant enzymes and chlorophyll fluorescence parameters in common bean cultivars differing in sensitivity to drought stress

Effects of the antioxidant system and chlorophyll fluorescence on drought tolerance of four common bean (Phaseolus vulgaris L.) cultivars were studied. The cultivars were positioned in the order of a decrease in their drought tolerance: Yakutiye, Pinto Villa, Ozayse, and Zulbiye on the basis of changes in the water potential, stomatal conductance, photosynthetic pigment content, and lipid peroxidation. Under drought conditions, the level of H₂O₂ was not changed in cv. Pinto Villa but decreased in other cultivars. Antioxidant enzymes (superothide dismutase (SOD), guaiacol peroxidase (GPX), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)) were generally activated in all cultivars. Interestingly, CAT, APX, and GR activities were not changed in cv. Pinto Villa, APX activity decreased in cv. Yakutiye, and CAT activity was not changed in cv. Zulbiye. The increases in SOD and GPX activities in cv. Ozayse were higher than in other cultivars. Drought stress reduced the effective quantum yield of PS2 (Φ_PS2) and the photochemical quenching (q_p), while it increased nonphotochemical quenching (NPQ) in all cultivars. The reduction or increase was more pronounced in cv. Zulbiye. There were generally significant correlations between q_p, NPQ, and ROS scavenging by SOD and APX. Also, there were significant correlations between SOD and q_p in tolerant cultivars and APX and q_p in sensitive ones. The results indicate that activation of SOD and APX was closely related to the efficiency of PS2 in common bean cultivars. This interaction was essential for protection of photosystems and plant survival under drought.     

Processes hindering activation of lipid peroxidation in cold-tolerant plants under hypothermia

The reasons why the rate of lipid peroxidation (POL) associated with a long-term action of low above-zero temperature (5°C, 6 days) on 6-week-old plants of two potato (Solanum tuberosum L.) cultivars (cold-tolerant cv. Desnitsa and less tolerant cv. Desiree) did not rise were investigated. Upon a long-term action of low hardening temperatures on the plants of both cultivars, there was an equilibrium between the rate of generation of superoxide anion (O₂^·− and activity of superoxide dismutase (SOD), which inactivated it with the formation of H₂O₂. Among the enzymes breaking up hydrogen peroxide, the highest activity was observed for guaiacol peroxidases, which was an order of magnitude greater than the activity of catalase. In potato cultivars, POL processes were not considerably activated; however, activities of antioxidant enzymes (SOD, catalase, and guaiacol peroxidases) in cold-tolerant cv. Desnitsa and less tolerant cv. Desiree differed. It was concluded that, upon a long-term action of hardening temperatures, cold-tolerant plants could sup-press POL processes. Moreover, a test for tolerance to damaging temperature (−3°C, 18 h) showed that detected preservation of the prooxidant/antioxidant equilibrium not only maintained vital activities at low above-zero temperatures but also elevated tolerance to short-term frosts, with this adaptability being cultivar-specific.     

The influence of cold acclimation on antioxidative enzymes and antioxidants in sensitive and tolerant barley cultivars

In order to better understand the role of cold acclimation in alleviating freezing injury, two barley cultivars with different cold tolerance, i.e. a sensitive cv. Chumai 1 and a tolerant cv. Mo 103, were used. The freezing treatment increased leaf soluble protein content more in the tolerant cultivar than in the sensitive one. Cold acclimation increased H₂O₂ content of the two cultivars during freezing treatment, especially in Mo 103. Glutathione and ascorbate contents during freezing and recovery were significantly higher in cold-acclimated plants than in non-acclimated ones. Activities of peroxidase, ascorbate peroxidase and glutathione reductase were also higher in cold-acclimated plants than non-acclimated plants during freezing treatment. However, there was no significant difference between cold-acclimated plants and the control plants in catalase activity. It may be assumed that cold acclimation induced H₂O₂ production, which in turn enhanced activities of antioxidative enzymes and synthesis of antioxidants, resulting in alleviation of oxidative stress caused by freezing.     

Relationship of antioxidant enzymes to ozone tolerance in branches of mature ponderosa pine (Pinus ponderosa) trees exposed to long-term, low concentration, ozone fumigation and acid precipitation

Seasonal activity of superoxide dismutase (SOD, EC 1.15.1.1). ascorbate peroxidase (APOD, EC 1.11.1.11) and guaiacol-oxidizing enzymes (GPODs, EC 1.11.1.7) was examined in needles of 12- to 15-year-old ponderosa pine (Pinus ponderosa Laws.) trees which received ozone (O₃) and acid precipitation treatment. Individual branches were enclosed in branch exposure chambers delivering either charcoal-filtered (O₃-reduced) air, ambient air, or air with twice ambient (2 x ambient) concentrations of O₃. Acid precipitation treatments were rain of pH 3.0 or 5.1 or no rain. Changes in antioxidant enzyme activity were not a consistent response to O₃ fumigation or acid precipitation, but when observed, they occurred most often in the O₃-sensitive clone and in symptomatic, fumigated branches. In the second year of fumigation. O₃ fleck symptoms appeared on needles of the sensitive clone as early as July and APOD activities were significantly increased by O₃ at all sampling dates. In the tolerant clone, antioxidant enzyme activities were not significantly changed by O₃ in the first season of fumigation (March to December 1990), not even during an episode when ambient O₃ concentrations reached 125 nl 1^?1 (240 nl 1^?1 in 2x ambient chambers). No foliar symptoms were observed on needles of the tolerant clone during this year. However, in the second year of fumigation (1992), O₃ fleck symptoms were observed on the tolerant clone and APOD activities were significantly increased in previous-year needles. The tolerant clone had SOD, APOD, and GPOD activities at least 40% higher than those of the sensitive clone before fumigation and 65, 178, and 119% higher, respectively, during both years of fumigation. The higher constitutive levels of these enzymes may have protected against foliar injury in 1990, however in 1992 we concluded that the stimulations in antioxidant enzyme activities observed in symptomatic branches of both clones were a consequence of O₃ injury. Total (intra- and extracellular) activities of the antioxidant enzymes did not appear to be good indicators of O₃ tolerance. Phenotypically, the O₃-tolerant clone was much more vigorous and in both years of fumigation, gas exchange rates were 30 to 71% higher than in the sensitive clone (P. D. Anderson, unpublished data). The greater vigor of the tolerant clone may allow more carbon allocation to protective and repair processes which include, but are not restricted to, the turnover of antioxidant enzymes and metabolites.     

Reactive oxygen species, ascorbate–glutathione pool, and enzymes of their metabolism in drought-sensitive and tolerant indica rice (Oryza sativa L.) seedlings subjected to progressing levels of water deficit

Water deficit for rice is a worldwide concern, and to produce drought-tolerant varieties, it is essential to elucidate molecular mechanisms associated with water deficit tolerance. In the present study, we investigated the differential responses of nonenzymatic antioxidants ascorbate (AsA), glutathione (GSH), and their redox pool as well as activity levels of enzymes of ascorbate–glutathione cycle in seedlings of drought-sensitive rice (Oryza sativa L.) cv. Malviya-36 and drought-tolerant cv. Brown Gora subjected to water deficit treatment of ?1.0 and ?2.1 MPa for 24–72 h using PEG-6000 in sand cultures. Water deficit caused increased production of reactive oxygen species such as O₂?^?, H₂O₂, and HO? in the tissues, and the level of production was higher in the sensitive than the tolerant cultivar. Water deficit caused reduction in AsA and GSH and decline in their redox ratios (AsA/DHA and GSH/GSSG) with lesser decline in tolerant than the sensitive seedlings. With progressive level of water deficit, the activities of monodehydroascorbate reductase, dehydroascorbate reductase, ascorbate peroxidase (APX), and glutathione transferase increased in the seedlings of both rice cultivars, but the increased activity levels were higher in the seedlings of drought-tolerant cv. Brown Gora compared to the sensitive cv. Malviya-36. Greater accumulation of proline was observed in stressed seedlings of tolerant than the sensitive cultivar. In-gel activity staining of APX revealed varying numbers of their isoforms and their differential expression in sensitive and tolerant seedlings under water deficit. Results suggest that an enhanced oxidative stress tolerance by a well-coordinated cellular redox state of ascorbate and glutathione in reduced forms and induction of antioxidant defense system by elevated activity levels of enzymes of ascorbate–glutathione cycle is associated with water deficit tolerance in rice.     

Pathways of ROS homeostasis regulation in Mesembryanthemum crystallinum L. calli exhibiting differences in rhizogenesis

A comparison of the hydrogen peroxide (H₂O₂) content, proline and betacyanin concentration and activities of some antioxidant enzymes (catalase, superoxide dismutase, guaiacol and ascorbate peroxidases) was made in Mesembryanthemum crystallinum L. calli differing in rhizogenic potential. Callus was induced from hypocotyls of 10-day-old seedlings on a medium containing 1?mg?l^?1 2,4-dichlorophenoxyacetic acid and 0.2?mg?l^?1 kinetin, which was either supplemented with 40?mM NaCl (CIM-NaCl medium) or did not contain any salt (CIM medium). The callus obtained on CIM-NaCl was rhizogenic, whereas the callus induced on the medium without salt was non-rhizogenic throughout the culture. The rhizogenic callus differed from the non-rhizogenic callus in lower betacyanin and H₂O₂ content, but the rhizogenic callus displayed a higher proline level. The activity of H₂O₂ scavenging enzymes, such as catalase (CAT), ascorbate peroxidase (APX) and guaiacol peroxidase (POD), was markedly higher in the rhizogenic callus than in the non-rhizogenic callus, but the total activity of superoxide dismutase (SOD) was higher in the non-rhizogenic callus than in the rhizogenic callus. Aminotriazole (CAT inhibitor) and diethyldithiocarbamate (SOD inhibitor) were added solely to the CIM and CIM-NaCl media to manipulate the concentration of reactive oxygen species (ROS) in the cultured tissues. Both CAT and SOD inhibitors brought about an increase in H₂O₂ content in calli cultured on CIM-NaCl and the loss of rhizogenic potential. Conversely, the addition of inhibitors to the medium without salt led to a decrease in H₂O₂ content. This corresponded with a significant decrease in the endogenous concentration of betacyanins, but did not change the lack of rhizogenic ability.     

Comparison of resistance to drought of three bean cultivars

The aim of the present work was to evaluate oxidative stress and plant antioxidant system of three contrasting bean (Phaseolus vulgaris L.) genotypes in the response to drought. Drought was imposed 14 d after emergence, by withholding water, until leaf relative water content reached 65 %. Water stress increased lipid peroxidation (LPO), membrane injury index, H₂O₂ and OH^⋅ production in leaves of stressed plants. Activities of the antioxidative enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APOX) increased significantly under water stress in all the studied cultivars, while catalase (CAT) increased in cvs. Plovdiv 10 and Prelom, but decreased in cv. Dobrudjanski ran. Furthermore cv. Plovdiv 10 which had the highest APOX and CAT activities also showed the lowest increase in H₂O₂ and OH^⋅ production and LPO while cv. Dobrudjanski ran showed the lowest increases (and often the lowest values) in the antioxidant enzyme activities and the highest increases of H₂O₂ and OH^⋅ production, and LPO. On the basis of the data obtained we could specify cv. Plovdiv 10 and cv. Prelom as drought tolerant and cv. Dobrudjanski ran as a drought sensitive.     

Water deficit and aluminum tolerance are associated with a high antioxidative enzyme capacity in Indica rice seedlings

Plant growth and productivity are greatly affected due to changes in the environmental conditions. In the present investigation, the interactive effects of two important abiotic stresses, i.e., water deficit and Al toxicity, were examined in the seedlings of two rice (Oryza sativa L.) cvs. Malviya-36 (water deficit/Al sensitive) and Vandana (water deficit/Al tolerant). When 15 days grown seedlings were exposed to water deficit (created with 15 % polyethylene glycol 6000) or Al (1 mM AlCl₃) treatment or both the treatments together for 48 h, the lengths of root/shoot, relative water content, and chlorophyll greatly declined in the seedlings of the sensitive cultivar, whereas in the tolerant seedlings, either little or insignificant decline in these parameters was observed due to the treatments. Seedlings subjected to water deficit or Al treatment alone or in combination showed increased intensity of the isoenzyme activity bands of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) in in-gel activity staining studies. Water deficit caused decrease in intensity of catalase (CAT) activity bands; however, when seedlings were exposed to AlCl₃ alone or in combination with water deficit, the intensity of the CAT isoforms increased in both the rice cultivars. The level of expression of the activity bands of SOD, CAT, GPX, and APX was always higher in the seedlings of tolerant cv. Vandana compared to the sensitive cv. Malviya-36 under both controls as well as stress treatments. Higher intensity of isozymes representing higher activity levels of antioxidative enzymes in the rice seedlings and their further increase under water deficit, Al exposure, or in combination of both the stresses appears to serve as useful marker for specifying a combination of water deficit and Al tolerance in rice.     

Antioxidative enzymes in cultivars of pepper plants with different sensitivity to cadmium

The effect of growing five different cultivars of pepper plants (Capsicum annuum L.) with CdCl₂ concentrations ranging from 0.125 to 0.5 mM on different physiological parameters, and antioxidative enzyme activities of leaves was studied. On the basis of growth parameters, pepper plants were relatively tolerant to cadmium, although metal concentrations higher than 0.125 mM produced a significant inhibition of growth, net photosynthesis, and water use efficiency. Different sensitivities to Cd⁺⁺ ions were observed among cultivars, Abdera being the most resistant to cadmium stress, while Mondo and Herminio were the most sensitive cultivars. Cadmium concentrations of 0.5 mM produced an increase in the activity of glutathione reductase, and guaiacol peroxidase in most cultivars, while catalase and superoxide dismutase (SOD) were slightly depressed. The analysis of the SOD activity pattern by native-PAGE showed the presence in most cultivars of four SODs which were identified as Mn–SOD, Fe–SOD, CuZn–SOD I and CuZn–SOD II. However, the two CuZn–SODs were absent in the Cd-sensitive cv. Herminio. The growth of pepper plants with 0.5 mM cadmium inhibited the activity of CuZn–SODs in all cultivars, while the activity of Mn- and Fe–SOD was enhanced. The activity of NADPH-dehydrogenases (glucose-6-P-dehydrogenase, 6-phosphogluconate dehydrogenase, NADP–isocitrate dehydrogenase and malic enzyme) showed a Cd-dependent enhancement in most cultivars, the highest increase being observed in the tolerant cv. Abdera. These results suggest that in pepper plants the tolerance to Cd toxicity is more dependent on the availability of NADPH than on its antioxidant capacity.     

Salinity induced oxidative stress and antioxidant system in salt-tolerant and salt-sensitive cultivars of rice (Oryza sativa L.)

Indices of oxidative stress viz., superoxide radical and H₂O₂ content increased in leaves of all the cultivars with the rise in salinity level, the increase was more pronounced and significant in salt-sensitive varieties and non-significant in resistant cultivars. Except for glutathione reductase (GR), basal activities of all other antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) were significantly higher in leaves of all the resistant cultivars as compared to the sensitive ones. A differential response of salinity was observed on various enzymatic and non-enzymatic components of antioxidant system in leaves of salt-tolerant and salt-sensitive cultivars of rice (Oryza sativa L.). Activities of superoxide dismutase and glutathione reductase enhanced in all the tolerant cultivar while declined in the sensitive cultivars with increasing salinity from 0 to 100 mM. Salt-stress induced the activities of catalase and peroxidase in all the cultivars but the magnitude of increase was more pronounced in the sensitive cultivars than in the tolerant cultivars. Contrarily, APX activity increased in the salt-sensitive cultivars but showed no significant change in the salt-tolerant cultivars. The amount of ascorbic acid content, reduced glutathione (GSH), reduced/oxidized glutathione (GSSG) ratio was higher in leaves of the tolerant cultivars than that of the sensitive cultivars under saline conditions. It is inferred that leaves of salt-tolerant cultivars tend to attain greater capacity to perform reactions of antioxidative pathway under saline conditions to combat salinity-induced oxidative stress.     

Effect of jasmonic acid on the pro-/antioxidant system of wheat coleoptiles as related to hyperthermia tolerance

The effects of treatment with jasmonic acid (JA) of wheat (Triticum aestivum L, cv. Elegia) coleoptiles on the generation of superoxide anion-radical (O ₂ ^·? ), the activity of extracellular peroxidase, enzymatic and non-enzymatic components of the antioxidant system were studied. During the first hour after the start of coleoptile treatment with 1 μM JA, the generation of O ₂ ^·? was enhanced and the extracellular peroxidase was activated. During following 23 h, these effects were gradually reduced. JA-enhanced O ₂ ^·? generation was partially suppressed by coleoptile treatment with the inhibitor of peroxidase salicylhydroxamic acid, the inhibitor of NADPH-oxidase imidazol, and also the calcium chelator EGTA. Under the influence of JA treatment, antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and soluble guaiacol peroxidase) in wheat coleoptiles were activated. Treatment with JA improved coleoptile tolerance to damaging heating (10 min at 43°C); it favored the maintenance of the pools of enzymatic and non-enzymatic antioxidants. The inhibitors of NADPH-oxidase and peroxidase, and also calcium chelator reduced a positive JA influence on coleoptile thermotolerance. The role of changes in the pro-/antioxidant balance in plant tissues for the realization of stress-defensive JA effects is discussed.     

Antioxidant defense mechanism under salt stress in wheat seedlings

The present study was carried out to study the effect of salt stress on cell membrane damage, ion content and antioxidant enzymes in wheat (Triticum aestivum) seedlings of two cultivars salt-tolerant KRL-19 and salt-sensitive WH-542. Seedlings (4-d-old) were irrigated with 0, 50 and 100 mM NaCl. Observations were recorded on the 3^rd and 6^th day after salt treatment and 2^nd day after salt removal. The relative water content declined with induction of salt stress, more in WH-542 than in cv. KRL-19. K⁺/Na⁺ ratio in KRL-19 was higher than in WH-542. WH-542 suffered greater damage to cellular membranes due to lipid peroxidation as indicated by higher accumulation of H₂O₂, MDA and greater leakage of electrolytes than KRL-19. The activities of catalase, peroxidase and ascorbate peroxidase and glutathione reductase increased with increase in salt stress in both the cultivars, however, superoxide dismutase activity declined. Upon desalanization, partial recovery in the activities of these enzymes was observed in KRL-19 and very slow recovery in WH-542.     

Differential responses of antioxidant enzymes to aluminum toxicity in two rice (Oryza sativa L.) cultivars with marked presence and elevated activity of Fe SOD and enhanced activities of Mn SOD and catalase in aluminum tolerant cultivar

Seedlings of two Indica rice (Oryza sativa L.) cvs. HUR-105 and Vandana, differing in Al-tolerance were used to identify the key mechanisms involved in their differential behaviour towards Al toxicity. Cv. HUR-105 appeared to be Al sensitive by showing significant reduction (p ≤ 0.01) in root/shoot length, fresh weight, dry weight and water content in presence of 421 μM Al³⁺ in growth medium whereas cv. Vandana appeared to be fairly Al³⁺ tolerant. A conspicuous and significant reduction in dry weight of root and shoot was observed in Al sensitive cv. HUR-105 with 178 μM Al³⁺ treatment for 3 days. Al was readily taken up by the roots and transported to shoots in both the rice cultivars. Localization of absorbed Al was always greater in roots than in shoots. Our results of the production of reactive oxygen species (ROS) H₂O₂ and O₂ ^.? and activities of major antioxidant enzymes such as total superoxide dismutase (SOD), Cu/Zn SOD, Mn SOD, Fe SOD, catalase (CAT) and guaiacol peroxidase revealed Al induced higher oxidative stress, greater production of ROS and lesser capacity to scavenge ROS in cv. HUR-105 than Vandana. With Al treatment, higher oxidative stress was noted in shoots than in roots. Greatly enhanced activities of SOD (especially Fe and Mn SOD) and CAT in Al treated seedlings of cv. Vandana suggest the role of these enzymes in Al tolerance. Furthermore, a marked presence of Fe SOD in roots and shoots of the seedlings of Al tolerant cv. Vandana and its significant (p ≤ 0.01) increase in activity due to Al-treatment, appears to be the unique feature of this cultivar and indicates a vital role of Fe SOD in Al-tolerance in rice.     

Assessment of changes in physiological and biochemical traits in four pistachio rootstocks under drought,salinity and drought + salinity stresses

In this study, 7-month-old UCB-1, Badami, Ghazvini and Kale-Ghouchi pistachio rootstocks were exposed to control, drought, salinity and drought + salinity environments for 60 d. Total chlorophyll and total carotenoid contents decreased in all cultivars under drought, salinity and drought + salinity stresses. Under drought and salinity stresses, alone or in combination, Na⁺ and Cl⁻ ions increased in all four pistachio rootstocks, while K⁺ ion decreased only in Ghazvini and Kaleh-Ghouchi cultivars. The enzyme activities of ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase increased in all cultivars when subjected to all three stresses with the exception of the ascorbate peroxidase activity in Kale-Ghouchi cultivar during drought stress. Oxidative stress parameters including electrolyte leakage, malondialdehyde, other aldehydes and hydrogen peroxide increased under all three stress conditions in all genotypes. The content of proline, total free amino acids and total soluble carbohydrates were enhanced under drought, salinity and drought + salinity stresses, whereas the protein content decreased in all pistachio rootstocks. In all evaluated traits, except for the K⁺ ion content and APX activity, the highest impacts was seen for drought + salinity > salinity > drought stresses, respectively. For the first time, we have proven that K⁺ ion content has a positive correlation with the ascorbate peroxidase, polyphenol oxidase, catalase and guaiacol peroxidase enzymes activities under drought + salinity stress. Finally, based on the bi-plot and cluster analyses, we have selected the UCB-1 > Badami > Ghazvini > Kale-Ghouchi cultivars as the most tolerant pistachio rootstocks under drought + salinity stress, respectively.     

Methyl jasmonate and salicylic acid elicitation induces ginsenosides accumulation, enzymatic and non-enzymatic antioxidant in suspension culture Panax ginseng roots in bioreactors

The effects of methyl jasmonate (MJ) and salicylic acid (SA) on changes of the activities of major antioxidant enzymes, superoxide anion accumulation (O₂ ⁻), ascorbate, total glutathione (TG), malondialdehyde (MDA) content and ginsenoside accumulation were investigated in ginseng roots (Panax ginseng L.) in 4 l (working volume) air lift bioreactors. Single treatment of 200 μM MJ and SA to P. ginseng roots enhanced ginsenoside accumulation compared to the control and harvested 3, 5, 7 and 9 days after treatment. MJ and SA treatment induced an oxidative stress in P. ginseng roots, as shown by an increase in lipid peroxidation due to rise in O₂ ⁻ accumulation. Activity of superoxide dismutase (SOD) was inhibited in MJ-treated roots, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), SOD, guaiacol peroxidase (G-POD), glutathione peroxidase (GPx) and glutathione reductase (GR) were induced in SA-treated roots. A strong decrease in the activity of catalase (CAT) was obtained in both MJ- and SA-treated roots. Activities of ascorbate peroxidase (APX) and glutathione S transferase (GST) were higher in MJ than SA while the contents of reduced ascorbate (ASC), redox state (ASC/(ASC+DHA)) and TG were higher in SA- than MJ-treated roots while oxidized ascorbate (DHA) decreased in both cases. The result of these analyses suggests that roots are better protected against the O₂ ⁻ stress, thus mitigating MJ and SA stress. The information obtained in this work is useful for efficient large-scale production of ginsenoside by plant-root cultures.     

Effect of thiocyanate on the peroxidase and pseudocatalase activities of Leishmania major ascorbate peroxidase

We report here that the Leishmania major ascorbate peroxidase (LmAPX), having similarity with plant ascorbate peroxidase, catalyzes the oxidation of suboptimal concentration of ascorbate to monodehydroascorbate (MDA) at physiological pH in the presence of added H₂O₂ with concurrent evolution of O₂. This pseudocatalatic degradation of H₂O₂ to O₂ is solely dependent on ascorbate and is blocked by a spin trap, α-phenyl-n-tert-butyl nitrone (PBN), indicating the involvement of free radical species in the reaction process. LmAPX thus appears to catalyze ascorbate oxidation by its peroxidase activity, first generating MDA and H₂O with subsequent regeneration of ascorbate by the reduction of MDA with H₂O₂ evolving O₂ through the intermediate formation of O₂⁻. Interestingly, both peroxidase and ascorbate-dependent pseudocatalatic activity of LmAPX are reversibly inhibited by SCN⁻ in a concentration dependent manner. Spectral studies indicate that ascorbate cannot reduce LmAPX compound II to the native enzyme in presence of SCN⁻. Further kinetic studies indicate that SCN⁻ itself is not oxidized by LmAPX but inhibits both ascorbate and guaiacol oxidation, which suggests that SCN⁻ blocks initial peroxidase activity with ascorbate rather than subsequent nonenzymatic pseudocatalatic degradation of H₂O₂ to O₂. Binding studies by optical difference spectroscopy indicate that SCN⁻ binds LmAPX (Kd = 100 ± 10 mM) near the heme edge. Thus, unlike mammalian peroxidases, SCN⁻ acts as an inhibitor for Leishmania peroxidase to block ascorbate oxidation and subsequent pseudocatalase activity.     

5-Aminolevulinic acid ameliorates salinity-induced metabolic, water-related and biochemical changes in Brassica napus L.

A number of studies have established that plant growth and development in oilseed rape (Brassica napus L.) are hampered by salinity stress. Nowadays, researchers have focused on the use of plant growth regulators to increase plant tolerance against salinity. An experiment was performed to evaluate the effects of 5-aminolevulinic acid (ALA, 30 mg l^?1) on Brassica napus L. (cv. ??ZS 758??) plants under NaCl (100, 200 mM) salinity. Data presented here were recorded on two different leaf positions (first and third) to have a better understanding of the ameliorative role of ALA on NaCl-stressed oilseed rape plants. Results have shown that increasing salinity imposed negative impact on relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), whereas enhanced the level of relative conductivity, malondialdehyde (MDA) content, osmolytes (soluble sugar, soluble protein, free amino acid and proline) concentration, reactive oxygen species (ROS), and enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in two different leaf position samples. Foliar application of ALA improved relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), and also triggered the further accumulation of osmolytes (soluble sugar, soluble protein, free amino acid and proline) as well as enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in both leaf samples, whereas decreased the membrane permeability, MDA content and ROS production. Our results also indicate that osmolytes are preferentially accumulated in younger tissues.