Pre-treatment with H<Subscript>2</Subscript>O<Subscript>2</Subscript> induces salt tolerance in Barley seedlings

Barley seedlings were pre-treated with 1 and 5 μM H₂O₂ for 2 d and then supplied with water or 150 mM NaCl for 4 and 7 d. Exogenous H₂O₂ alone had no effect on the proline, malondialdehyde (MDA) and H₂O₂ contents, decreased catalase (CAT) activity and had no effect on peroxidase (POX) activity. Three new superoxide dismutase (SOD) isoenzymes appeared in the leaves as a result of 1 μM H₂O₂ treatment. NaCl enhanced CAT and POX activity. SOD activity and isoenzyme patterns were changed due to H₂O₂ pre-treatment, NaCl stress and leaf ageing. In pre-treated seedlings the rate of ¹⁴CO₂ fixation was higher and MDA, H₂O₂ and proline contents were lower in comparison to the seedlings subjected directly to NaCl stress. Cl⁻ content in the leaves 4 and 7 d after NaCl supply increased considerably, but less in pre-treated plants. It was suggested that H₂O₂ metabolism is involved as a signal in the processes of barley salt tolerance.     

Exogenous spermidine alleviates fruit granulation in a <Emphasis Type="Italic">Citrus</Emphasis> cultivar (<Emphasis Type="Italic">Huangguogan</Emphasis>) through the antioxidant pathway

The role of exogenous spermidine (Spd) in alleviating fruit granulation in the grafted seedlings of a Citrus cultivar (Huangguogan) was investigated. Granulation resulted in increased electrical conductivity, cell membrane permeability, and total pectin, soluble pectin, cellulose, and lignin contents. However, it decreased the activities of superoxide dismutase, peroxidase, and catalase, as well as the (Spd + Spm):Put ratio. The application of exogenous Spd onto Huangguogan seedlings significantly increased proline and ascorbate contents, but decreased the H₂O₂ and O ₂ ^?· levels, which suggested that exogenous Spd provided some protection from oxidative damage. In addition, exogenous Spd decreased cell membrane permeability and MDA content, and increased the (Spd + Spm):Put ratio. The activities of antioxidant enzymes, such as catalase, peroxidase, and superoxide dismutase, were increased in Spd-treated seedlings affected by fruit granulation, resulting in a decrease in oxidative stress levels. The protective effects of Spd were reflected by a decrease in superoxide levels through osmoregulation, increased proline and ascorbate contents, and increased antioxidant activities. Our observations reveal the importance of exogenous Spd in alleviating citrus fruit granulation.     

Interactive effects of salicylic acid and silicon on oxidative damage and antioxidant activity in spinach (<Emphasis Type="Italic">Spinacia oleracea</Emphasis> L. cv. Matador) grown under boron toxicity and salinity

We investigated individual and combined effects of salinity, soil boron (B), silicon (Si) and salicylic acid (SA) on the activities of major antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT and ascorbate peroxidase, APX) and non-enzymatic antioxidants (AA), proline, chlorophyll, anthocyanin, H₂O₂ concentration, stomatal resistance (SR), lipid peroxidation (MDA), membrane permeability (MP), and the uptake of sodium (Na), chloride (Cl), boron and Si of spinach plants. In general, salinity significantly increased H₂O₂ and proline concentrations, antioxidant activity, membrane permeability, lipid peroxidation and SR of the spinach plants, indicating that they were stressed, whereas application of B only increased proline concentration. However, plant fresh weights did not decline with either treatment. The application of Si decreased H₂O₂ and increased the activity of SOD and CAT. The application of SA increased SOD activity. Neither SA nor Si had any effect on the proline concentration, or MP. However, application of Si increased chlorophyll concentration and decreased lipid peroxidation (MDA concentration). Si treatment had no effect on SR. The concentration of B in the tissues, which was strongly increased by B treatment, was decreased by NaCl. As a result of salinity, concentrations of Na⁺ and Cl⁻ ions were increased in the plant tissues, and application of Si slightly increased these concentrations. These results indicate that exogenous Si application increases stress tolerance of spinach, a plant that is naturally reasonably resistant to combined salinity and B toxicity, by the enhancement of antioxidant mechanisms that reduce membrane damage. Exogenous SA has a less obvious effect, although the levels of salinity and boron stress applied were not sufficient in this experiment to reduce plant fresh weight.     

Exogenous spermidine and spermine enhance cadmium tolerance of <Emphasis Type="Italic">Potamogeton malaianus</Emphasis>

In order to investigate the effects of spermidine (Spd) and spermine (Spm) on cadmium stress, the content of chlorophyll, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), soluble protein and proline, the rate of O₂^·− generation, and activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) in Potamogeton malaianus Miq. were measured. Exogenous application of Spd or Spm significantly enhanced the level of proline, retarded the loss of chlorophyll, enhanced photosynthesis, decreased the rate of O₂^·− generation and H₂O₂ content, and prevented Cd-induced lipid peroxidation. Spd and Spm also effectively maintained the balance of antioxidant enzyme activities under Cd stress; however, GR activity was found to increase only slightly in response to polyamines (PAs). The antioxidant systems, which were modified by PAs, were able to moderate the radical-scavenging system and to lessen in this way the oxidative stress. These results suggest that both Spd and Spm can enhance Cd tolerance of P. malaianus.     

Responses of in vitro-cultured <Emphasis Type="Italic">Allium hirtifolium</Emphasis> to exogenous sodium nitroprusside under PEG-imposed drought stress

Drought stress is a major threat to plant production in semi-arid and arid areas of the world. This research was laid out to asses the effects of sodium nitroprusside (SNP) as a nitric oxide donor on growth, physiological and biochemical changes of in vitro-cultured Allium hirtifolium under polyethylene glycol (PEG) induced drought stress. Basal plate explants of A. hirtifolium were cultured on MS medium containing different levels of PEG (0, 2, 4, 8 and 16 mM) and SNP (0, 10, 40 and 70 µM). After prolonged drought, growth responses, oxidative stress indicators, and phytochemical variations of regenerated plantlets with or without PEG and/or SNP treatments were recorded. Water limitation reduced regeneration potential of explants and consequently number of shoots per explant. Relative water content, total chlorophyll and carotenoid contents of regenerated A. hirtifolium plantlets decreased, but accumulation of malondialdehyde, H₂O₂ and proline and the activities of superoxide dismutase, ascorbate peroxidase, catalase and peroxidase enzymes increased with decreasing water availability. Total phenol and allicin contents were also increased in response to drought stress. Exogenous SNP in 10 and particularly in 40 µM was effective in enhancing regeneration rate and relative water content as well as protecting photosynthetic pigments under different levels of water availability. SNP also inhibited the hydrogen peroxide (H₂O₂) accumulation and lipid peroxidation in cell membranes via increasing the activities of superoxide dismutase and ascorbate peroxidase enzymes and accumulating proline and allicin. In general, these results suggest that exogenous SNP at 40 µM not only could somewhat protect A. hirtifolium from drought stress, but also can help to improve the propagation and allicin production of that plant under in vitro condition.     

Effects of Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> stress on oxidative damage,antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants

The effects of Ca(NO₃)₂ stress on biomass production, oxidative damage, antioxidant enzymes activities and polyamine contents in roots of grafted and non-grafted tomato plants were investigated. Results showed that when exposed to 80 mM Ca(NO₃)₂ stress, the biomass production reduction in non-grafted plants was more significant than that of grafted plants. Under Ca(NO₃)₂ stress, superoxide anion radical (O₂•⁻) producing rate, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents of non-grafted plants roots were significantly higher than those of grafted plants, however, nitrate (NO₃ ⁻), ammonium (NH₄ ⁺) and proline contents, superoxide dismutase (SOD, EC1.15.1.1), peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6) and arginine decarboxylase (ADC, EC 4.1.1.19) activities of grafted plants roots were significantly higher than those of non-grafted plants. Regardless of stress, free, conjugated and bound polyamine contents in roots of grafted plants were significantly higher than those of non-grafted plants. The possible roles of antioxidant enzymes, prolines and polyamines in adaptive mechanism of tomato roots to Ca(NO₃)₂ stress were discussed. Gu-Wen Zhang and Zheng-Lu Liu contributed equally to this work.     

Elevated CO<Subscript>2</Subscript> ameliorated oxidative stress induced by elevated O<Subscript>3</Subscript> in <Emphasis Type="Italic">Quercus mongolica</Emphasis>

Using open top chambers, the effects of elevated O₃ (80 nmol mol⁻¹) and elevated CO₂ (700 μmol mol⁻¹), alone and in combination, were studied on young trees of Quercus mongolica. The results showed that elevated O₃ increased malondialdehyde content and decreased photosynthetic rate after 45 days of exposure, and prolonged exposure (105 days) induced significant increase in electrolyte leakage and reduction of chlorophyll content. All these changes were alleviated by elevated CO₂, indicating that oxidative stress on cell membrane and photosynthesis was ameliorated. After 45 days of exposure, elevated O₃ stimulated activities of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11), but the stimulation was dampened under elevated CO₂ exposure. Furthermore, ascorbate (AsA) and total phenolics contents were not higher in the combined gas treatment than those in elevated O₃ treatment. It indicates that the protective effect of elevated CO₂ against O₃ stress was achieved hardly by enhancing ROS scavenging ability after 45 days of exposure. After 105 days of exposure, elevated O₃ significantly decreased activities of SOD, catalase (CAT, EC 1.11.1.6) and APX and AsA content. Elevated CO₂ suppressed the O₃-induced decrease, which could ameliorate the oxidative stress in some extent. In addition, elevated CO₂ increased total phenolics content in the leaves both under ambient O₃ and elevated O₃ exposure, which might contribute to the protection against O₃-induced oxidative stress as well.     

External spermine prevents UVA-induced damage of <Emphasis Type="Italic">Synechocystis</Emphasis> sp. PCC 6803 via increased catalase activity and decreased H<Subscript>2</Subscript>O<Subscript>2</Subscript> and malonaldehyde levels

Common polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), are cationic compounds known as beneficial factors for many cellular processes including cell division, proliferation, differentiation, and stress response in all living organisms. Effects of exogenous Spm on the protective responses of Synechocystis sp. PCC 6803 exposed to UVA were investigated. The presence of 0.5 mM Spm in the culture medium significantly reduced cell growth after 60 min under white light condition but protected the cells after growing for 60 min under UVA. The stress-tolerant response of Synechocystis cells represented by the ratio of putrescine/spermidine (Put/Spd) showed about a 6-fold increase after 60 min UVA in the presence of Spm. In addition, those levels of chlorophyll a, carotenoids, and photosynthetic oxygen evolution were increased by Spm supplementation in UVA-treated cells. Exogenous Spm induced the activity of catalase but not superoxide dismutase in cells under UVA treatment. On the other hand, Spm treatment enabled cells to apparently decrease the intracellular free radical H₂O₂ and malonaldehyde (MDA) levels. Overall results suggested that Spm supplementation could protect Synechocystis sp. PCC 6803 cells via the increase of Put/Spd ratio and the reduction of both H₂O₂ and MDA levels in conjunction with the induction of catalase activity. Interestingly, UVA-treated cells as compared to non-treated cells with exogenous Spm showed a decrease of Spm with an increase of Put and no change in Spd. This suggested the back conversion of Spm to Spd and finally to Put as cellular mechanism in response to UVA.     

Induction of Oxidative Stress and Antioxidant Activity by Hydrogen Peroxide Treatment in Tolerant and Susceptible Wheat Genotypes

We induced an oxidative stress by means of exogenous hydrogen peroxide in two wheat genotypes, C 306 (tolerant to water stress) and Hira (susceptible to water stress), and investigated oxidative injury and changes in antioxidant enzymes activity. H₂O₂ treatment caused chlorophyll degradation, lipid peroxidation, decreased membrane stability and activity of nitrate reductase. Hydrogen peroxide increased the activity of antioxidant enzymes, glutathione reductase and catalase. These effects increased with increasing H₂O₂ concentrations. However, no change was observed in the activity of superoxide dismutase and proline accumulation.     

The Allelopathic Effects of Sunflower and Wheat Root Exudates on <i>Sinapis arvensis and Sinapis alba</i>

In this study, we aimed to investigate the allelopathic effects of sunflower and wheat root exudates on the common weeds such as wild mustard and white mustard in our region. The root exudates which were obtained by soaking 8 weeks old sunflower and wheat seedlings (20 or 40 seedlings) in 100 mL of distilled water for 3 days were applied to the leaves of wild mustard and white mustard. In order to compare the allelopathic effect, the recommended dose (1 g.da^-1 ) and twice the recommended dose (2 g.da^-1 ) of Gromstor (Tribenuron-methyl), a herbicide preferred by farmers for the chemical control of these weeds was also applied. The allelopathy was performed for wild mustard and white mustard seedlings by the measurement of different physiological and biochemical parameters, such as chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, proline, total protein amounts and superoxide dismutase enzyme activity. The amounts of total chl and carotenoid in wild mustard leaves decreased in all treatment groups compared to control. The highest decrease in total chl (50.93%) and carotenoid (46.69%) was oberved in the treatment of 40 wheat seedlings. 100 mL^-1 distilled water. In the white mustard leaves, the amount of total chl in all treatment groups except the treatment group of Gromstor 2 g.da^-1 and carotenoid in all treatment groups increased compared to the control. The highest increases again were observed in 40 wheat seedlings. 100 mL^-1 distilled water treatment. The proline amounts in wild mustard and white mustard increased in all treatment groups. The highest increase was observed for the treatment of 20 wheat seedlings. 100 mL^-1 distilled water in wild mustard (459.69%) and 40 sunflower seedlings. 100 mL^-1 distilled water in white mustard plant (104.70%). In superoxide dismutase enzyme activities, treatments decreased activity except treatment of 40 sunflower seedling root exudate in wild mustard, while increased activity outside commercial herbicide treatment in white mustard. The results showed that sunflower and wheat root exudates have allelopathic effects on wild mustard and white mustard weeds. It is thought that the study will be a reference for new studies that will enable the use of plant root exudates as bioherbicides or foliar fertilizers and will contribute to the fight against weeds in organic agriculture.     

hCG treatment raises H<Subscript>2</Subscript>O<Subscript>2</Subscript> levels and induces germ cell apoptosis in rat testis

The clinical significance of exogenous hCG treatment is to stimulate steroidogenesis and spermatogenesis in the testis. However, the pathogenesis of detrimental effects on the testis arising out of chronic hCG treatment is yet to be clearly ascertained. In the present study we have shown that hCG treatment (100 IU/day) to rats for 30 days raises testicular oxidative stress leading to germ cell apoptosis and impairment of spermatogenesis. The treatment raises testicular H₂O₂ levels along with increase in lipid peroxidation and concomitant decrease in the enzymatic antioxidant activities like superoxide dismutase, catalase and glutathione-s-transferase. The rise in the number of apoptotic germ cells was associated with up regulation of Fas protein expression and caspase-3 activity in the testis. However, serum testosterone which was elevated by 15 days of hCG treatment declined to pretreatment levels by 30 days. No significant alteration in serum gonadotropins was observed. The above findings indicate that the pathogenesis of deleterious effects following chronic hCG treatment is due to increase in testicular oxidative stress with high H₂O₂ availability leading to apoptosis among germ cells.     

Pellino-1 Protects Periodontal Ligament Stem Cells Against H<Subscript>2</Subscript>O<Subscript>2</Subscript>-Induced Apoptosis via Activation of NF-κB Signaling

To determine the protective effects of Pellino-1 against H₂O₂-induced apoptosis in periodontal ligament stem cells (PDLSC). We demonstrated that H₂O₂ decreases PDLSC viability by 40 and 50% with the concentrations of 400 and 500 μM, respectively, with an observed downregulation of Pellino-1 mRNA and protein; we further concluded that overexpression of Pellino-1 significantly lowers 8-hydroxy-2′-deoxyguanosine levels by 10% and upregulates superoxide dismutase 1, glutathione peroxidase levels, and catalase mRNA levels by 200, 40, and 250%, respectively. More importantly, we found that overexpression of Pellino-1 inhibited H₂O₂-induced cellular apoptosis through the activation of the NF-κB signaling pathway. Pellino-1 may be critically important for cell survival in the presence of oxidative elements; activation of the NF-κB signaling cascade was required for the overexpression of Pellino-1 to protect the cells from H₂O₂-induced apoptosis.     

Tomato Jasmonic Acid-Deficient Mutant <Emphasis Type="Italic">spr2</Emphasis> Seedling Response to Cadmium Stress

The involvement of jasmonic acid (JA) in the plant response to cadmium (Cd) stress has been addressed in some publications by application experiments or analysis of endogenous contents of JA. In this study, we comparatively investigated the response of tomato wild type (WT) and its JA-deficient mutant spr2 to Cd stress aimed at clarifying the role of JA. One-month-old potted plants were exposed to CdCl₂ at final concentrations of 5, 25, and 50 mg kg^?1 in soil, respectively, for 15 days. The root and leaf Cd contents were dramatically increased, especially in the spr2 plants, in a CdCl₂ dose-effect manner. In the Cd dose-dependent inhibitory effect on plant growth, spr2 plants were more obvious than WT plants. This was also reflected by certain physiological and biochemical metabolisms. We analyzed photosynthesis-related parameters including total chlorophyll, actual efficiency of PS2, ratio of variable to maximum chlorophyll fluorescence, and net photosynthetic rate; relative water content, soluble sugar and proline contents, and starch accumulation; oxidative stress and antioxidative defense including malondialdehyde production, electrolyte leakage, H₂O₂ levels, activities of superoxide dismutase, peroxidase, and catalase, and their isoform expression profiles. The Cd-induced changes in all these parameters supported the conclusion that endogenous JA deficiency enhanced tomato seedling sensitivity to Cd. This implies that JA positively regulates the tomato plant response to Cd stress.     

Effects of exposure of callus cells of two wheat varieties to silver nanoparticles and silver salt (AgNO<Subscript>3</Subscript>)

Metal nanoparticles significantly affect the physiological properties of plants, e.g., seed germination, growth and metabolism. In the present study, the toxic effects of silver nanoparticles (AgNPs) and silver ions were studied on callus cells of two varieties of wheat (Triticum aestivum L.): stress tolerant—Parabola; stress sensitive—Raweta. Stress induced by silver particles or ions (0, 20, 40, 60 ppm) was investigated using different parameters such as morphological characteristics, lipid peroxidation and mobilization of defense system which was determined by analyzing the activity of antioxidant enzymes, glutathione (GSH) and proline contents. Microscopic observations revealed deformation of cells after treatment by sol of higher silver concentrations. An increase in malondialdehyde content in both studied varieties was observed. Tested varieties showed an increased proline content in the silver-treated cells. There was no effect of silver on the superoxide dismutases activity, while the activity of catalase was significantly decreased. The changes in the activity of peroxidases in both varieties were opposite. The highest content of intracellular GSH was noticed at a concentration of 20 ppm of both AgNPs and silver ions. The presented results demonstrate a significant similarity of the effects caused by the studied stressors: silver nanoparticles and silver ions. The results characterized the mechanism of action of nanosilver on wheat callus: morphology disorder, damage to cell membranes, severe oxidative stress and in consequence intensification of production of non-enzymatic antioxidants.     

Role of glycolysis and antioxidant enzymes in the toxicity of amyloid beta peptide Aβ<Subscript>25–35</Subscript> to erythrocytes

The role of glycolysis and antioxidant enzymes in amyloid beta peptide Aβ_25–35 toxicity to human and rat erythrocytes was studied. The erythrotoxicity of Aβ_25–35 was shown to increase two-to fourfold both in the absence of glucose in the incubation medium and upon the addition of sodium fluoride, an enolase inhibitor. Potassium cyanide, a Cu,Zn-superoxide dismutase inhibitor, abolishes the toxic effect of Aβ_25–35 to erythrocytes, whereas mercaptosuccinate, a glutathione peroxidase inhibitor, and ouabain, a Na⁺,K⁺-ATPase inhibitor, promote it. Sodium azide, a catalase inhibitor, did not affect the cell lysis under the action of Aβ_25–35. The results support the hypothesis that H₂O₂, Cu,Zn superoxide dismutase, and glutathione peroxidase are involved in the toxicity mechanism rather than superoxide radical. Glycolysis and Na⁺,K⁺-ATPase play a substantial protective role. Fullerene C₆₀ nanoparticles are toxic to erythrocytes of both types; their toxicity is not related to enhanced oxidative stress and the mechanism of toxicity differs from that of Aβ_25–35.     

Oxidative processes at initial stages of interaction of nodule bacteria (<Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis>) and pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.): A review

A possible physiological mechanism of legume-Rhizobium symbiosis, consisting in regulation of the intensity of oxidative processes by the macrosymbiont in response to infection with Rhizobium, was analyzed using our own and published data. The results used in the analysis included data on the content of reactive oxygen species (O ₂ ^·? and H₂O₂), activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), and intensity of lipid peroxidation proceeding with the involvement of lipophilic phenolic compounds of the microsymbiont.     

Physiological and cellular responses to fluoride stress in tea (<Emphasis Type="Italic">Camellia sinensis</Emphasis>) leaves

Tea (Camellia sinensis (L.) O. Kuntze) hyper-accumulates fluoride (F), mainly in the leaves. To understand how tea copes with the stress caused by F, we tracked photosynthesis, antioxidant defense, and cell ultrastructure under different F concentrations (0–50 mg L^?1). High F (≥5 mg L^?1) caused decreases in photosynthetic and chlorophyll fluorescence parameters. Activated oxygen metabolism was altered by F, as manifested in increasing lipid peroxidation, electrolyte leakage (EL), and accumulation of H₂O₂. The activities of ascorbate peroxidase (APX, EC 1.11.1.1) and catalase (CAT, EC 1.11.1.6) increased at 0–5 mg L^?1 F, but sharply decreased less than 10–50 mg L^?1 F. The activity of manganese superoxide dismutase (Mn-SOD, EC 1.15.1.1) decreased with increasing F concentration. Expression of genes encoding antioxidant enzymes were in accordance with their measured activities. The results suggest that the antioxidant enzymes in the tea plant can eliminate reactive oxygen species (ROS) at <5 mg L^?1 F, but not at 20–50 mg L^?1 F. High F increased the number of epidermal hairs on tea leaves and decreased the stomatal aperture, reducing water loss. The leaf cellular structure appeared normal under 1–50 mg L^?1 F, although starch grains in chloroplast increased with increasing F. Proline and betaine play important roles in osmotic regulation in tea plant tolerating F stress. ROS scavenging and greater number of epidermal hairs are likely parts of the tea plant F-tolerance mechanism.     

Aminolevulinic acid and nitric oxide regulate oxidative defense and secondary metabolisms in canola (<Emphasis Type="Italic">Brassica napus</Emphasis> L.) under drought stress

To minimize the damaging effects of stresses, plant growth regulators (PGRs) are widely used to sustain the plant life under stress-prone environments. So, a study was carried out to evaluate the response of two canola (Brassica napus L.) cultivars, Dunkeld and Cyclone, to foliar-applied two potential PGRs, nitric oxide (NO) and 5-aminolevulinic acid, under water deficit conditions. In this study, the levels of NO and ALA used were 0.02 and 0.895 mM, respectively. Plants of both canola cultivars were subjected to control (100% field capacity) and water deficit (60% field capacity). Drought stress significantly decreased growth, chlorophyll pigments, relative water contents (RWC), and soluble proteins, while it increased relative membrane permeability (RMP), proline, glycinebetaine (GB), malondialdehyde (MDA), total phenolics, and activities of catalase (CAT) and peroxidase (POD) enzymes in both cultivars. Foliar application of PGRs improved growth, chlorophyll a, GB, total phenolics, CAT activity, and total soluble proteins, while it decreased RMP, MDA, and POD activity in both canola cultivars. Other physio-biochemical attributes such as chlorophyll b, RWC, hydrogen peroxide (H₂O₂) and proline contents as well as superoxide dismutase (SOD) activity remained unaffected due to application of PGRs. So, the results of the present study suggest that exogenous application of NO and ALA could be useful to enhance the drought tolerance of canola plants by up-regulating the oxidative defense system, osmoprotectant accumulation, and minimizing the lipid peroxidation.     

Early plant growth and biochemical responses induced by <Emphasis Type="Italic">Azospirillum brasilense</Emphasis> Sp245 lipopolysaccharides in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) seedlings are attenuated by procyanidin B2

This study analyzes the effects of procyanidin B2 on early wheat plant growth and plant biochemical responses promoted by lipopolysaccharides (LPS) derived from the rhizobacteria Azospirillum brasilense Sp245. Measurements of leaf, root length, fresh weight, and dry weight showed in vitro plant growth stimulation 4 days after treatment with A. brasilense as well as LPS. Superoxide anion (O₂ ^·?) and hydrogen peroxide (H₂O₂) levels increased in seedling roots treated with LPS (100 μg mL^?1). The chlorophyll content in leaf decreased while the starch content increased 24 h after treatment in seedling roots. The LPS treatment induced a high increase in total peroxidase (POX) (EC 1.11.1.7) activity and ionically bound cell wall POX content in roots, when compared to respective controls. Early plant growth and biochemical responses observed in wheat seedlings treated with LPS were inhibited by the addition of procyanidin B2 (5 μg mL^?1), a B type proanthocyanidin (PAC), plant-derived polyphenolic compound with binding properties of LPS. All results suggest first that the ionically bound cell wall POX enzymes could be a molecular target of A. brasilense LPS, and second that the recognition or association of LPS by plant cells is required to activate plant responses. This last event could play a critical role during plant growth regulation by A. brasilense LPS.