Effects of 28-homobrassinolide on growth, lipid peroxidation and antioxidative enzyme activities in seedlings of Zea mays L. under salinity stress

The effects of 28-homobrassinolide (28-homoBL) on seedling growth, lipid peroxidation and antioxidative enzyme activities in the seedlings of Zea mays L. (var. Partap-1) under salt (NaCl) stress were studied. The surface-sterilized seeds were germinated in petriplates containing different concentrations of NaCl (25, 50, 75 and 100 mM) only, 28-homoBL (10⁻⁷, 10⁻⁹ and 10⁻¹¹ M) only and NaCl supplemented with 28-homoBL for 7 days. The activities of superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (POD, EC 1.11.1.7), catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APOX, EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) were analysed in 7 day-old seedlings. It was observed that 28-homoBL treatments reduced the toxicity of salt on seedling growth considerably. Lipid peroxidation level was significantly increased under saline stress, but lowered with 28-homoBL applications revealing less oxidative damage. Further 28-homoBL treatments to the seedlings showed an enhancement in activities of SOD, POD, CAT and APOX. The activities of all antioxidative enzymes were further increased in seedlings treated with solution containing 28-homoBL and salt together as compared to seedlings treated with different concentration of salt solution only.     

Effect of 24-Epibrassinolide on Antioxidative Defence System Against Lead-Induced Oxidative Stress in The Roots of <Emphasis Type="Italic">Brassica juncea</Emphasis> L. Seedlings

Lead (Pb) toxicity causes oxidative stress by increasing the production of reactive oxygen species. The aim of the present study was to investigate the role of 24-epibrassinolide (24-EBL) on the antioxidant defence system as a response to Pb stress in Brassica juncea L. Surface-sterilized seeds were exposed to Pb ion (0 and 2 mM) toxicity in Petri dishes and subsequently, the seeds were sprayed with either (i) deionized water or (ii) different concentrations (10^–12, 10^–10, and 10^–8 M) of 24-EBL on alternate days. After nine days, the roots of the B. juncea seedlings were harvested to analyze the heavy metal content, root length, hydrogen peroxide level, lipid peroxidation, total protein content and activities of the antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, glutathione reductase and glutathione-S-transferase). According to our results, the Pb ions accumulated by the B. juncea roots led to oxidative stress by increasing the level of H₂O₂ and malondialdehyde, and thus, increased the activity of the antioxidative enzymes (except for catalase) and the growth and total protein content decreased. Whereas, the 24-EBL treatment to the roots of Pb stressed seedlings was able to alleviate the Pb-induced oxidative stress. Upon the application of 24-EBL, a reduction in Pb accumulation, H₂O₂ and malondialdehyde levels as well as an increased total protein content and activity of antioxidative enzymes detoxifying hydrogen peroxide (catalase, ascorbate peroxidase and peroxidase) were observed. As a result, the stress protective properties of 24-EBL depending on concentration in B. juncea roots were revealed in this study.     

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 silicon and arbuscular mycorrhiza in modulating ascorbate-glutathione cycle and antioxidant scavenging capacity in differentially salt-tolerant <Emphasis Type="Italic">Cicer arietinum</Emphasis> L. genotypes subjected to long-term salinity

Salinity is the major environmental constraint that affects legume productivity by inducing oxidative stress. Individually, both silicon (Si) nutrition and mycorrhization have been reported to alleviate salt stress. However, the mechanisms adopted by both in mediating stress responses are poorly understood. Thus, pot trials were undertaken to evaluate comparative as well as interactive effects of Si and/or arbuscular mycorrhiza (AM) in alleviating NaCl toxicity in modulating oxidative stress and antioxidant defence mechanisms in two Cicer arietinum L. (chickpea) genotypes—HC 3 (salt-tolerant) and CSG 9505 (salt-sensitive). Plants subjected to different NaCl concentrations (0–100 mM) recorded a substantial increase in the rate of superoxide radical (O₂ ^·?), H₂O₂, lipoxygenase (LOX) activity and malondialdehyde (MDA) content, which induced leakage of ions and disturbed Ca²⁺/Na⁺ ratio in roots and leaves. Individually, Si and AM reduced oxidative burst by strengthening antioxidant enzymatic activities (superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPOX)). Si was relatively more efficient in reducing accumulation of stress metabolites, while mycorrhization significantly up-regulated antioxidant machinery and modulated ascorbate-glutathione (ASA-GSH) cycle. Combined applications of Si and AM complemented each other in reducing reactive oxygen species (ROS) build-up by further enhancing the antioxidant defence responses. Magnitude of ROS-mediated oxidative burden was lower in HC 3 which correlated strongly with more effective AM symbiosis, better capacity to accumulate Si and stronger defence response when compared with CSG 9505. Study indicated that Si and/or AM fungal amendments upgraded salt tolerance through a dynamic shift from oxidative destruction towards favourable antioxidant defence system in stressed chickpea plants.     

Selenium Improves Physiological Parameters and Alleviates Oxidative Stress in Shoots of Lead-Exposed <Emphasis Type="Italic">Vicia faba</Emphasis> L. <Emphasis Type="Italic">minor</Emphasis> Plants Grown Under Phosphorus-Deficient Conditions

The goal of the study was to investigate the effects of exogenous selenium (Se) on the tolerance of faba bean plants to lead (Pb) stress under P-deficient conditions. The bean plants were grown for 2 weeks on Hoagland solution supplied with Pb (0, 50 μM) and Se (0, 1.5, or 6 μM), separately or simultaneously. It was shown that Pb did not affect shoot growth but caused major damage in the leaves, which was accompanied by Pb accumulation in these tissues. The exposure of the shoots to Pb led to significant changes in the biochemical parameters: the MDA content, glutathione peroxidase (GSH-Px), guaiacol peroxidase (GPOX), and catalase (CAT) activity increased. Furthermore, Pb intensified O ₂ ^?? and H₂O₂ production. Both the Se concentrations used increased the chlorophyll b, chlorophyll a+b, and carotenoid content in the faba bean plants. Selenite also generally enhanced CAT, GPOX, and GSH-Px activities and the T-SH level. Our results imply that the degree of disturbances caused by Pb could be partially ameliorated by Se supplementation. Selenite at a lower dose alleviated Pb toxicity by decreased H₂O₂ and O ₂ ^?? production and decreased the GSH-Px, GPOX, and CAT activities. The beneficial effect of the higher selenite concentration could be related to reduction of lipid peroxidation in the shoots of the Pb-treated plants. However, the effect of Se on the Pb-stressed plants greatly depended on the selenite dose in the nutrient solution.     

Chloroplast-located <Emphasis Type="Italic">BjFer1</Emphasis> together with anti-oxidative genes alleviate hydrogen peroxide and hydroxyl radical injury in cytoplasmic male-sterile <Emphasis Type="Italic">Brassica juncea</Emphasis>

We studied how plant cell modulated redox homeostasis in cytoplasmic male-sterility (CMS) Brassica juncea. The CMS Brassica juncea was identified to be mutated in several mitochondrial genes that suggested the changes of cell redox homeostasis. We observed that it was not associated with increased oxidative stress as shown by decreased H₂O₂ and ^∙OH contents in this type of CMS. The expressions of several anti-oxidative genes were up-regulated in 5-day-old seedlings of CMS than MF lines under light and dark conditions. The mitochondrial alternative oxidase pathway was not activated, as indicated by no increased expression of AOX1a gene in CMS. Interestingly, the expression of Ferritin1 gene was markedly activated in 5-day-old seedlings of CMS than MF line under light and dark conditions. Consequently, we detected increased content of total iron in 30-day-old leaves in CMS than MF line. We isolated Ferritin1 orthologous gene from Brassica juncea, which was targeted to the chloroplast and induced by Fe-citrate and H₂O₂, not ABA. Taken together, we proposed that increased expressions of BjFer1 and several antioxidant genes protected cell from oxidative stress in CMS Brassica juncea.     

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.     

Exogenous nitric oxide protects against salt-induced oxidative stress in the leaves from two genotypes of tomato (<Emphasis Type="Italic">Lycopersicom esculentum</Emphasis> Mill.)

Nitric oxide (NO) has emerged as a key molecule involved in many physiological events in plants. To characterize roles of NO in tolerance of tomato (Lycopersicom esculentum Mill.) to salt stress, the protective effects of NO against salt-induced oxidative stress in the leaves of tomato cultivar Hufan1480 (salt-tolerant) and Hufan2496 (salt-sensitive) were evaluated. Under salt stress, Hufan1480 showed higher biomass accumulation, and less oxidative damage when compared with the Hufan2496. Application of exogenous sodium nitroprusside, a NO donor, dramatically alleviated growth suppression induced by salt stress in two tomato ecotypes, reflected by decreased malondialdehyde and O₂^·− production. Furthermore, the antioxidant enzymes superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase, the antioxidant metabolites ascorbate and reduced glutathione, and the osmosis molecules proline and soluble sugar were increased in both ecotypes in the presence of NO under salt stress. Therefore, the protective effect of NO against salt-induced oxidative damages in tomato seedlings is most likely mediated through stimulation of antioxidant system.     

Effects of 28-homobrassinoloid on key physiological attributes of <Emphasis Type="Italic">Solanum lycopersicum</Emphasis> seedlings under cadmium stress: Photosynthesis and nitrogen metabolism

Heavy metal accumulation due to environmental pollution, especially in agricultural ecosystem can cause serious deterioration of crop yield and quality. In present study we assessed the effect of exogenous 28-homobrassinoloid (HBL; 10^?8 M) on growth, photosynthesis, indices of chlorophyll a fluorescence and nitrogen metabolism in Solanum lycopersicum seedlings grown under two doses (Cd₁: 3 mg kg^?1 sand and Cd₂: 9 mg kg^?1 sand) of cadmium. Accumulation of Cd in root tissues was considerably higher than shoot hence, Cd declined the growth, pigment contents, and photosynthetic O₂ yield in its concentration dependent manner. Chlorophyll a fluorescence due to Cd stress was negatively affected as shown by decreased Q_A ^? reoxidation kinetics: φP₀, ψ₀, φE₀ and PI__ABS and increased energy flux parameters: ABS/RC, TR₀/RC, ET₀/RC and DI₀/RC. HBL application under Cd stress improved the photochemistry of photosystem II (PS II) by affecting these parameters positively. Treatment of Cd in test seedlings resulted into significant decrease in nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase activities, and induced enhancing effect on ammonium content and glutamate dehydrogenase activity. Exogenous HBL treatment alleviated the negative effect of Cd on growth, photosynthesis, contents of protein, carbohydrate and inorganic nitrogen and nitrogen assimilating enzymes. The data indicate that exogenous HBL protects the test seedlings during the early growth phase against Cd phytotoxicity by regulating Cd accumulation in tissues and two key metabolic processes; photosynthesis and nitrogen metabolism.     

<Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract alleviates nickel toxicity by suppressing its uptake and modulating antioxidative defence in rice seedlings

Terminalia arjuna (Ta) bark contains various natural antioxidants and has been used to protect animal cells against oxidative stress. In the present study, we have examined alleviating effects of Ta bark aqueous extract against Ni toxicity in rice (Oryza sativa L.). When rice seedlings were raised for 8 days in hydroponics in Yoshida nutrient medium containing 200 μM NiSO₄, a decline in height, reduced biomass, increased Ni uptake, loss of root plasma membrane integrity, increase in the level of O₂˙^?, H₂O₂ and ˙OH, increased lipid peroxidation, decline in photosynthetic pigments, increase in the level of antioxidative enzymes superoxide dismutase, catalase and glutathione peroxidase and alterations in their isoenzyme profile patterns were observed. Transmission electron microscopy (TEM) showed damage to chloroplasts marked by disorganised enlarged starch granules and disrupted thylakoids under Ni toxicity. Exogenously adding Ta bark extract (3.2 mg ml^?1) to the growth medium considerably alleviated Ni toxicity in the seedlings by reducing Ni uptake, suppressing generation of reactive oxygen species, reducing lipid peroxidation, restoring level of photosynthesis pigments and ultrastructure of chloroplasts, and restoring levels of antioxidative enzymes. Results suggest that Ta bark extract considerably alleviates Ni toxicity in rice seedlings by preventing Ni uptake and reducing oxidative stress in the seedlings.     

Heterologous expression and characterization of a new heme-catalase in <Emphasis Type="Italic">Bacillus subtilis</Emphasis> 168

Reactive oxygen species (ROS) is an inherent consequence to all aerobically living organisms that might lead to the cells being lethal and susceptible to oxidative stress. Bacillus pumilus is characterized by high-resistance oxidative stress that stimulated our interest to investigate the heterologous expression and characterization of heme-catalase as potential biocatalyst. Results indicated that recombinant enzyme significantly exhibited the high catalytic activity of 55,784 U/mg expressed in Bacillus subtilis 168 and 98.097 µmol/min/mg peroxidatic activity, the apparent K _m of catalytic activity was 59.6 ± 13 mM with higher turnover rate (K _cat = 322.651 × 10³ s^?1). The pH dependence of catalatic and peroxidatic activity was pH 7.0 and pH 4.5 respectively with temperature dependence of 40 °C and the recombinant heme-catalase exhibited a strong Fe²⁺ preference. It was further revealed that catalase KatX2 improved the resistance oxidative stress of B. subtilis. These findings suggest that this B. pumilus heme-catalase can be considered among the industrially relevant biocatalysts due to its exceptional catalytic rate and high stability and it can be a potential candidate for the improvement of oxidative resistance of industrially produced strains.     

Cobalt-induced oxidative stress causes growth inhibition associated with enhanced lipid peroxidation and activates antioxidant responses in Indian mustard (Brassica juncea L.) leaves

The effect of 100 μM cobalt (Co) on plant growth and on biochemical parameters indicative of oxidative stress was investigated in a hydroponic experiment. The responses of antioxidant enzymes and compounds of the ascorbate–glutathione (AsA–GSH) cycle were also assessed on the hyperaccumulating plant, Indian mustard (Brasssica juncea L.). The effect of excess Co was associated with a significant increase in the levels of proline, carbonylated protein, malondialdehyde, superoxide anion (O ₂ ^·? ), and hydrogen peroxide (H₂O₂), and resulted in the accumulation of Co. Co toxicity was associated with an increase in the volume of palisade and spongy cells, and a reduction in the number of chloroplasts per cell. Co-induced cell death was characterized by DNA fragmentation and a 36 kDa DNase activity. Despite decreased catalase activity, peroxidase, superoxide dismutase, and AsA–GSH cycle-related enzymes including monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase exhibited remarkable induction under Co stress. Furthermore, the contents of reduced and oxidized forms of ascorbate and glutathione were significantly increased with Co supplementation. Co treatment led to the activation of 44 and 46 kDa mitogen-activated protein kinase (MAPK) and indicated the role of the MAPK cascade in transducing Co-mediated signals. The present results suggest that excess Co reduces seedling growth by inducing oxidative stress related to lipid peroxidation and overproduction of O ₂ ^·? and H₂O₂. The stimulated activities of antioxidative enzymes and induction of MAPKs did not reverse the oxidative stress caused by Co-induced reactive oxygen species generation in Indian mustard seedlings.     

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.     

Exogenous 5-aminolevulinic acid alleviates the detrimental effects of UV-B stress on lettuce (<Emphasis Type="Italic">Lactuca sativa</Emphasis> L) seedlings

One of the abiotic stress factors affecting plant metabolism is ultraviolet-B (UV-B) radiation. 5-Aminolevulinic acid (ALA), a key precursor of porphyrin biosynthesis, promotes plant growth and crop yields. To investigate the alleviating effects of exogenous ALA on the damages caused by UV-B exposure, two different concentrations [10 ppm (ALA1) and 25 ppm (ALA2)] of ALA were applied to lettuce seedlings for 24 h and then they were exposed to 3.3 W m^?2 UV-B. Results showed that UV-B treatment significantly decreased chlorophyll a and b (Chl a and b) concentration, enhanced the activity of antioxidant enzymes, total phenolic concentration, soluble sugar contents, expression of phenylalanine ammonia lyase (PAL) and γ-tocopherol methyltransferase (γ-TMT) genes, the concentration of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), and the rate of superoxide radical (\({\text{O}}_{2}^{ - }\)) generation in the lettuce seedlings when compared to the control. Pre-treatment with exogenous ALA significantly enhanced UV-B stress tolerance in lettuce seedlings by decreasing the reactive oxygen species. On the other hand, ALA application caused more increases in the PAL and γ-TMT gene expression, antioxidant enzymes activities, Chl a and b concentration, total phenolic content, antioxidant capacity and the concentrations of soluble sugars. Obtained results indicated that UV-B radiation exerts an adverse effect on lettuce seedlings, and some of the negative effects of UV-B radiation can be alleviated by exogenous ALA.     

CAT and MDH improve the germination and alleviate the oxidative stress of cryopreserved <Emphasis Type="Italic">Paeonia</Emphasis> and <Emphasis Type="Italic">Magnolia</Emphasis> pollen

Researches have reported that reactive oxygen species (ROS)-induced oxidative stress plays an important role in cell cryodamage during cryopreservation. In the current study, pollen from Magnolia denudata and Paeonia lactiflora ‘Zi Feng Chao Yang’ was cryopreserved and incubated with exogenous catalase (CAT) and malate dehydrogenase (MDH) immediately after thawing. The effect of CAT and MDH on the germination of cryopreserved pollen was measured. Based on that, the ROS level, lipid peroxidation and antioxidants activities in fresh pollen, cryopreserved pollen added with or without CAT or MDH were determined to investigate their relationship with oxidative stress. Pollen from Magnolia and Paeonia showed a significant loss of germination, but marked increase of ROS and malondialdehyde (MDA) production after cryostorage. Antioxidant profiles in them were also enhanced. CAT and MDH addition increased the post-LN pollen germination of Magnolia and Paeonia significantly. Their germination rate achieved the highest with 100 IU ml^?1 MDH and 400 IU ml^?1 CAT application, respectively. Compared to their untreated controls, ROS and MDA accumulation reduced significantly in cryopreserved Magnolia pollen treated with 100 IU ml^?1 MDH, while superoxide dismutase (SOD) activity improved markedly. In the case of Paeonia, significantly lower level of ROS and MDA, but higher activity of CAT and SOD were observed in cryopreserved pollen treated with 400 IU ml^?1 CAT. In conclusion, pollen deterioration after cryopreservation is associated with ROS-induced oxidative stress. Exogenous CAT and MDH can reduce the oxidative damage through the activity stimulation of antioxidant enzymes, and play a protective role in the pollen during cryopreservation.     

Action of antioxidant enzymes and cytochrome P-450 monooxygenases in the cabbage looper in response to plant phototoxins

Effects of two biosynthetically distinct plant phototoxins—xanthototoxin, a furanocoumarin, and harmine, a β-carboline alkaloid, which are known to produce toxic oxygen species—on the food utilization efficiencies and enzymatic detoxification systems of the polyphagous cabbage looper. Trichoplusia ni (Lepidoptera: Noctuidae), were studied. Newly molted fifth-instar larvae were allowed 36 h to ingest diets containing these two phototoxins at 0.15% wet weight in the presence of near ultraviolet (UVA). The growth and development of the larvae, as well as the corresponding activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPOX), and glutathione reductase (GR) and the detoxification enzyme cytochrome P-450, were measured. Xanthotoxin reduced rates of relative growth and consumption and efficiencies of conversion of ingested and digested food to biomass. Harmine reduced rates of growth and consumption without affecting efficiencies of conversion. Specific activities of SOD, CAT, GPOX, and GR of whole-body homogenates in the absence of compounds were 0.88 units, 153μmol H₂O₂ decomposed·mg protein^?1·min—¹, 38.3 nmol NADPH oxidized·mg protein^?1·min^?1, and 0.56 nmol NADPH oxidized·mg protein^?1·min^?1, respectively. SOD activity was induced 2.9-fold and 3.8-fold by dietary xanthotoxin and harmine, respectively. CAT and GPOX activities were induced 1.2-fold by harmine only, and GR activity was not changed by either chemical. The P-450 activity toward xanthotoxin in the microsomal fraction of midguts was low (0.15 nmol xanthotoxin metabolized·mg protein^?1·min^?1) and was not induced by xanthotoxin ingestion. These studies indicate that P-450 and antioxidant enzyme systems may be independent but consequential, the induction of antioxidant enzymes by phototoxins occurring when low P-450 activity toward the phototoxin permits the accumulation of oxidative stress from unmetabolized phototoxin, which in turn induces antioxidant enzymes.     

Effect of 28-homobrassinolide on antioxidant capacity and photosynthesis in Brassica juncea plants exposed to different levels of copper

A sand culture experiment was conducted to study ameliorative role of 28-homobrassinolide (HBL) in Brassica juncea seedlings raised from the seeds treated with water, or 10⁻¹⁰, 10⁻⁸ and 10⁻⁶ M 28-homobrassinolide (HBL) and grown in the presence of copper (50, 100 and 150 mg kg⁻¹ sand) and sampled at 30 days after sowing. The plants grown in the presence of copper exhibited a significant decline in growth, chlorophyll and photosynthetic parameters. However, the activity of antioxidant enzymes: catalase (E.C. 1.11.1.6), peroxidase (E.C. 1.11.1.7) and superoxide dismutase (E.C. 1.15.1.1) and the content of proline increased in the plants grown under copper stress and/or raised from treatment with HBL. However, H₂O₂ content increased significantly in copper-treated plants and decreased in plants given HBL treatment. Treatment of seeds with HBL improved the growth, photosynthetic parameters and antioxidant enzymes and also improved in the plants grown under copper stress. The elevated antioxidant enzyme and proline might be responsible to overcome the toxic effects of copper in B. juncea.     

Effects of exogenous nitric oxide on photosynthesis,antioxidative ability,and mineral element contents of perennial ryegrass under copper stress

A hydroponics experiment was conducted to test the effects of sodium nitroprusside (SNP, a donor of NO) supplied with different concentrations on copper (Cu) toxicity in ryegrass seedlings (Lolium perenne L.). Excess Cu (200 µM) reduced chlorophyll content, resulting a decrease in photosynthesis. Cu stress induced the production of hydrogen peroxide (H₂O₂) and superoxide anion (O₂^{? ?}), leading to malondialdehyde (MDA) accumulation. Furthermore, activities of antioxidant enzymes in Cu-treated seedlings such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were decreased. In addition, Cu stress inhibited the uptake of K, Mg, Fe, and Zn and increased Ca content in roots. Moreover, in leaves of Cu-stressed seedlings, K, Fe, and Zn contents were decreased and the contents of Ca and Mg were not affected significantly. In Cu-treated seedlings, Cu concentration in roots was higher than in leaves. Addition of 50, 100, 200 µM SNP in Cu-mediated solutions increased chlorophyll content and photosynthesis, improved antioxidant enzyme activities, reduced Cu-induced oxidative damages, kept intracellular ion equilibrium under Cu stress, increased Cu concentration in roots and inhibited Cu accumulation in leaves. In particular, addition of 100 µM SNP had the best effect on promoting growth of ryegrass seedlings under Cu stress. However, the application of 400 µM SNP had no obvious alleviating effect on Cu toxicity in ryegrass seedlings.     

Exogenous sodium nitroprusside and glutathione alleviate copper toxicity by reducing copper uptake and oxidative damage in rice (Oryza sativa L.) seedlings

Nitric oxide (NO) and glutathione (GSH) regulate a variety of physiological processes and stress responses; however, their involvement in mitigating Cu toxicity in plants has not been extensively studied. This study investigated the interactive effect of exogenous sodium nitroprusside (SNP) and GSH on Cu homeostasis and Cu-induced oxidative damage in rice seedlings. Hydroponically grown 12-day-old seedlings were subjected to 100 μM CuSO₄ alone and in combination with 200 μM SNP (an NO donor) and 200 μM GSH. Cu exposure for 48 h resulted in toxicity symptoms such as stunted growth, chlorosis, and rolling in leaves. Cu toxicity was also manifested by a sharp increase in lipoxygenase (LOX) activity, lipid peroxidation (MDA), hydrogen peroxide (H₂O₂), proline (Pro) content, and rapid reductions in biomass, chlorophyll (Chl), and relative water content (RWC). Cu-caused oxidative stress was evident by overaccumulation of reactive oxygen species (ROS; superoxide (O₂ ^?–) and H₂O₂). Ascorbate (AsA) content decreased while GSH and phytochelatin (PC) content increased significantly in Cu-stressed seedlings. Exogenous SNP, GSH, or SNP?+?GSH decreased toxicity symptoms and diminished a Cu-induced increase in LOX activity, O₂ ^?–, H₂O₂, MDA, and Pro content. They also counteracted a Cu-induced increase in superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and glyoxalase I and glyoxalase II activities, which paralleled changes in ROS and MDA levels. These seedlings also showed a significant increase in catalase (CAT), glutathione peroxidase (GPX), dehydroascorbate reductase (DHAR), glutathione S-transferase (GST) activities, and AsA and PC content compared with the seedlings stressed with Cu alone. Cu analysis revealed that SNP and GSH restricted the accumulation of Cu in the roots and leaves of Cu-stressed seedlings. Our results suggest that Cu exposure provoked an oxidative burden while reduced Cu uptake and modulating the antioxidant defense and glyoxalase systems by adding SNP and GSH play an important role in alleviating Cu toxicity. Furthermore, the protective action of GSH and SNP?+?GSH was more efficient than SNP alone.