A novel in vitro tissue culture approach to study salt stress responses in citrus

In citrus, a major crop throughout the world, growth and yield are seriously affected by salinity. Different approaches, including agronomical, physiological and molecular methods, have been used to address this problem. In this work, an in vitro experimental system has been developed to study the toxic effect of NaCl on three citrus genotypes, avoiding the ion filter that represents the root system. To carry out the experiments, shoots were obtained from nodal segments of Cleopatra mandarin, Carrizo citrange and citrumelo CPB4475 plants growing in a greenhouse. Shoots were cultured in control or NaCl-supplemented media. After testing several salt concentrations, 60 mM NaCl was selected as saline treatment. Shoots accumulated similar levels of chloride when cultured without roots and exhibited similar leaf damage. No increases in malondialdehyde levels were observed in any genotype (as a measure of oxidative stress). Similar patterns of hormonal signalling (in terms of abscisic acid and salicylic acid contents) were exhibited in the three genotypes, despite their different tolerance under field conditions. All data together indicate that, without root system, all genotypes had the same behaviour under salt stress. The in vitro culture system has been proved as a useful tool to study biochemical processes involved in the response of citrus to salt stress.     

Salt-induced oxidative stress in rosemary plants: Damage or protection?

Mechanisms of photoprotection and antioxidant protection, including changes in chlorophylls, xanthophyll cycle components and levels of low-molecular-weight chloroplastic antioxidants (lutein, β-carotene and α-tocopherol) were studied together with levels of malondialdehyde, a product of lipid peroxidation, in the response of rosemary (Rosmarinus officinalis L.) plants to salt stress. Plants were exposed to increasing NaCl concentrations (50, 100 and 150 mM) for 6 weeks, and two concentrations of the following chloride salts: KCl, CaCl₂, MgCl₂ and FeCl₃, were used together with 100 mM NaCl to explore the extent to which these salts can alter the mechanisms of photoprotection, antioxidant protection and malondialdehyde accumulation in leaves. Increasing concentrations of NaCl decreased leaf water contents and photosynthetic pigment levels, while the contents of α-tocopherol and malondialdehyde increased, but with completely different kinetics. α-Tocopherol levels increased in a dose-dependent manner as stress progressed, while malondialdehyde levels increased at the highest dose (150 mM NaCl) but only during early phases of stress. Furthermore, although the addition of chloride salts to NaCl-treated plants apparently improved leaf physiological status, in terms of water and chlorophyll contents, plants showed an increased photoprotective demand and increased oxidative stress, particularly in FeCl₃-treated plants. It is concluded that (i) rosemary plants can withstand moderate doses of NaCl in the medium (at least 150 mM NaCl for 6 weeks), (ii) oxidative stress may be a mechanism for protecting plants from moderate doses of salt stress rather than causing damage to plants, and (iii) the addition of chloride salts to NaCl-treated plants may dramatically increase the photoprotective demand and oxidative stress of leaves, while plant growth is not negatively affected.     

Silicon and Nitric Oxide-Mediated Regulation of Growth Attributes,Metabolites and Antioxidant Defense System of Radish (<i>Raphanus sativus</i> L.) under Arsenic Stress

Arsenic (As) contaminated food chains have emerged as a serious public concern for humans and animals and are known to affect the cultivation of edible crops throughout the world. Therefore, the present study was designed to investigate the individual as well as the combined effects of exogenous silicon (Si) and sodium nitroprusside (SNP), a nitric oxide (NO) donor, on plant growth, metabolites, and antioxidant defense systems of radish (Raphanus sativus L.) plants under three different concentrations of As stress, i.e., 0.3, 0.5, and 0.7 mM in a pot experiment. The results showed that As stress reduced the growth parameters of radish plants by increasing the level of oxidative stress markers, i.e., malondialdehyde and hydrogen peroxide. However, foliar application of Si (2 mM) and pretreatment with SNP (100 µM) alone as well as in combination with Si improved the plant growth parameters, i.e., root length, fresh and dry weight of plants under As stress. Furthermore, As stress also reduced protein, and metabolites contents (flavonoids, phenolic and anthocyanin). Activities of antioxidative enzymes such as catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POD), and polyphenol oxidase (PPO), as well as the content of non-enzymatic antioxidants (glutathione and ascorbic acid) decreased under As stress. In most of the parameters in radish, As III concentration showed maximum reduction, as compared to As I and II concentrations. However, the individual and combined application of Si and NO significantly alleviated the As-mediated oxidative stress in radish plants by increasing the protein, and metabolites content. Enhancement in the activities of CAT, APX, POD and PPO enzymes were recorded. Contents of glutathione and ascorbic acid were also enhanced in response to co-application of Si and NO under As stress. Results obtained were more pronounced when Si and NO were applied in combination under As stress, as compared to their individual application. In short, the current study highlights that Si and NO synergistically regulate plant growth through lowering the As-mediated oxidative stress by upregulating the metabolites content, activity of antioxidative enzymes and non-enzymatic antioxidants in radish plants.

     

Combined effect of salicylic acid and salinity on some antioxidant activities,oxidative stress and metabolite accumulation in <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis>

It has been shown that salicylic acid (SA) acts as an endogenous signal molecule responsible for inducing abiotic stress tolerance in plants. The effect of SA and sodium chloride (NaCl) on growth, metabolite accumulation, oxidative stress and enzymatic and non-enzymatic antioxidant responses on common bean plants (Phaseolus vulgaris, cv. F-15) was studied. Results revealed that either SA or NaCl decrease, shoot, root and total plant dry weights. SA treatments decreased the contents of proline, and reduced forms of ascorbate and glutathione, however, the content of soluble sugars (TSS), thiobarbituric acid-reactive substances (TBARs) and oxidized ascorbate remained unaffected. On the other hand, salinity significantly reduced the levels of endogenous SA but increased the content of proline, soluble sugars, TBARs, ascorbate and glutathione, as well as all increasing the levels of antioxidant enzyme activities assayed, except CAT. The application of SA improved the response of common bean plants to salinity by increasing plant dry weight and decreasing the content of organic solutes (proline and TSS) and damage to the membrane (TBARs). Moreover, SA application under saline conditions decreased the levels of antioxidant enzyme activities POX, APX and MDHAR which could indicate successful acclimatization of these plants to saline conditions.     

Ammonium enhances resistance to salinity stress in citrus plants

In this work, we demonstrate that NH?? nutrition in citrange Carrizo plants acts as an inducer of resistance against salinity conditions. We investigated its mode of action and provide evidence that NH?? confers resistance by priming abscisic acid and polyamines, and enhances H?O? and proline basal content. Moreover, we observed reduced Cl? uptake as well as enhanced PHGPx expression after salt stress. Control and N-NH?? plants showed optimal growth. However, N-NH?? plants displayed greater dry weight and total lateral roots than control plants, but these differences were not observed for primary root length. Our results revealed that N-NH?? treatment induces a similar phenotypical response to the recent stress-induced morphogenetic response (SIMRs). The hypothesis is that N-NH?? treatment triggers mild chronic stress in citrange Carrizo plants, which might explain the SIMR observed. Moreover, we observed modulators of stress signaling, such as H?O? in N-NH?? plants, which could acts as an intermediary between stress and the development of the SIMR phenotype. This observation suggests that NH?? treatments induce a mild stress condition that primes the citrange Carrizo defense response by stress imprinting and confers protection against subsequent salt stress.     

Carbohydrate Depletion in Roots and Leaves of Salt-Stressed Potted <Emphasis Type="Italic">Citrus clementina</Emphasis> L.

In citrus, damage produced by salinity is mostly due to toxic ion accumulation, since this salt-sensitive crop adjusts osmotically with high efficiency. In spite of this observation, the putative role of sugars as osmolites under salinity remains unknown. In this work, we have studied carbohydrate contents (total hexoses, sucrose and starch) in leaves and roots of citrus grown under increasing salinity. The experimental system was characterized through the analyses of several parameters known to be strongly affected by salinity in citrus, such as chloride accumulation, photosynthetic rate, ethylene production and leaf abscission. Three-year-old plants of the Clementina de Nules cultivar grafted on Carrizo citrange rootstock were watered with three different levels of salinity (NaCl was added to the watering solutions to achieve final concentrations of 30, 60 and 90 mM). Data indicate that salt stress caused an accumulation of chloride ions in a way proportional to the external increase in NaCl. The adverse conditions reduced CO₂ assimilation, increased ethylene production and triggered abscission of the injured leaves. Data also show that salinity induced progressive depletions of carbohydrates in leaves and roots of citrus plants. This observation clearly indicates that sugar accumulation is not a main component of the osmotic adjustment machinery in citrus.     

Antioxidant enzymatic activity is linked to waterlogging stress tolerance in citrus

Soil flooding constitutes a seasonal factor that negatively affects plant performance and crop yields. In this work, the relationship between oxidative damage and flooding sensitivity was addressed in three citrus genotypes with different abilities to tolerate waterlogging. We examined leaf visible damage, oxidative damage in terms of malondialdehyde (MDA) concentration, leaf proline concentration, leaf and root ascorbate and glutathione contents and the antioxidant enzyme activities superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6) and glutathione reductase (EC 1.8.1.7). No differences in the extent of oxidative damage relative to controls were found among genotypes. However, a different ability to delay the apparition of oxidative damage was associated to a higher tolerance to waterlogging. This ability was linked to an enhanced activated oxygen species' scavenging capacity in terms of an increased antioxidant enzyme activity and higher content in polar antioxidant compounds. Therefore, the existence of a direct relationship between stress sensitivity and the early accumulation of MDA is proposed. In addition, data indicate that the protective role of proline has to be considered minimal as its accumulation was inversely correlated with tolerance to the stress. The positive antioxidant response in Carrizo citrange ( Poncirus trifoliata L. Raf. ×  Citrus sinensis L. Osb.) and Citrumelo CPB 4475 ( Poncirus trifoliata L. Raf. ×  Citrus paradisi L. Macf.) might be responsible for a higher tolerance to flooding stress, whereas in Cleopatra mandarin ( Citrus reshni Hort. Ex Tan.), the early accumulation of MDA seems to be associated to an impaired ability for H₂O₂ scavenging.     

Upregulation of antioxidant and glyoxalase systems mitigates NaCl stress in Brassica juncea by supplementation of zinc and calcium

Possible involvement of calcium (Ca) and zinc (Zn) in mitigation of salt (NaCl) stress-induced oxidative damage in Brassica juncea was investigated. Salt stress (200?mM NaCl) reduced leaf pigment synthesis and some key photosynthetic attributes including stomatal conductance and internal CO₂ concentration. Exogenous application of Ca and Zn resulted in enhanced growth possibly by induction of the antioxidant defense system, resulting in improved redox state thereby favoring growth improvement. Proline accumulation (3.39-fold) was stimulated by exogenous application of Zn and Ca causing improvement in growth through enhancement in relative water content (78.46%) and increased flavonoid accumulation (86.19%). NaCl stress enhanced the hydrogen peroxide (H₂O₂), malondialdehyde and methylglyoxal content by 3-fold, 1.51-fold, and 2.98-fold, respectively, however, supplementation of Ca and Zn individually as well as in combination reduced the accumulation to an appreciable level. Ca and Zn treatment helped Brassica juncea plants to strengthen the antioxidant system and glyoxalase system and also enzymes of ascorbate-glutathione (AsA-Glu) cycle for better protection to membranes from reactive oxygen species. Moreover, Ca and Zn supplementation reduced the salt-induced damage by maintaining Na/K ratio through improved K uptake.     

Antioxidant and photosynthetic response of a purple-leaved and a green-leaved cultivar of sweet basil (Ocimum basilicum) to boron excess

Boron (B) toxicity induces oxidative stress and alterations in the photosynthetic process. The occurrence of visible symptoms depends on plant species and even on cultivar. However, limited information is available concerning antioxidant responses to B toxicity; therefore a study was carried out to assess the role of antioxidants in hydroponically grown sweet basil submitted to B excess. Two cultivars were compared: the purple-leaved ‘Red Rubin’ that shown scarce symptoms of B-induced toxicity and the green-leaved ‘Tigullio’ in which they were evident.Sweet basil plants were grown in “floating raft system” for 20 days with 0.2 (control), 2 and 20 mg L⁻¹ of B in the nutrient solution. At the end of treatments visible symptoms of damage were evaluated and some parameters were measured: growth, leaf B accumulation, gas exchange and chlorophyll fluorescence, pigment, phenols and malondialdehyde (MDA) concentrations, total non-enzymatic antioxidant ability, antioxidant molecules and enzymes.B excess negatively affected growth and photosynthesis in both cultivars but differential mechanisms were recorded. ‘Tigullio’ exhibited a larger B accumulation in leaves as compared to ‘Red Rubin’. Moreover, in ‘Red Rubin’ plants a greater constitutive content of ascorbic acid, glutathione, anthocyanins and, consequently, a stronger antioxidant ability than ‘Tigullio’ were recorded. MDA test confirmed that the extent of oxidative stress was larger in ‘Tigullio’ than in ‘Red Rubin’. A general stimulation of antioxidant enzymes occurred by increasing B concentration in the growth medium. Notable, anthocyanins were likely involved in the B tolerance shown by ‘Red Rubin’ in consideration of their antioxidant properties and because of the role of these compounds in photoprotection. This paper represents a contribution to understanding the role of antioxidant compounds in plant tolerance to B toxicity.     

Exogenous Selenium Mitigates Salt Stress in Soybean by Improving Growth,Physiology, Glutathione Homeostasis and Antioxidant Defense

The mechanism of selenium (Se)-induced salt tolerance was studied in moderately sensitive soybean (Glycine max L.) plants. To execute this view, soybean plants were imposed with salt stress (EC 6 dS m⁻¹ ) applying NaCl. In other treatments, Se (0, 25, 50 and 75 µM Na₂SeO₄) was sprayed as co-application with that level of salt stress. Plant height, stem diameter, leaf area, SPAD value decreased noticeably under salt stress. Altered proline (Pro) level, together with decreased leaf relative water content (RWC) was observed in salt-affected plants. Salt stress resulted in brutal oxidative damage and increased the content of H₂O₂, MDA level and electrolyte leakage. Exogenous Se spray alleviated oxidative damage through boosting up the antioxidant defense system by increasing the activity of antioxidant enzymes such as catalase (CAT), peroxidase (POD) and glutathione reductase (GR), as well as by improving non-enzymatic antioxidants like glutathione (GSH) and GSH/glutathione disulfide (GSSG). The upregulated antioxidant defense system, restored Pro and leaf RWC, higher SPAD value conferred better growth and development in Se-sprayed salt-affected soybean plants which altogether put forth for the progressive yield contributing parameters and finally, seed yield. Among different doses of Se, soybean plants sprayed with 50 µM Na₂SeO₄ showed better salt tolerance.     

Response of antioxidant systems to NaCl stress in the halophyte Cakile maritima

The effects of salt stress on antioxidative activities were investigated in a coastal halophyte, Cakile maritima . Two Tunisian accessions, Jerba and Tabarka, were compared. Plants were subjected to 100, 200, or 400 m M NaCl for 20 days. Parameters of oxidative stress [malondialdehyde (MDA), electrolyte leakage (EL), and hydrogen peroxide (H₂O₂) concentration], activities of several enzymes [superoxide dismutase (SOD), catalase (CAT), peroxydase (POD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR)], and antioxidant molecules (ascorbate, ASC, and glutathione, GSH) were determined. Growth of Jerba plants was improved at 100 m M NaCl as compared to that of control. Tabarka growth was inhibited by salt at all NaCl concentrations. The relative salt tolerance of Jerba was associated with high antioxidant enzyme activities and glutathione content, together with low MDA content, EL, and H₂O₂ concentration. Lower antioxidant activities and higher MDA content, EL, and H₂O₂ concentration were found in Tabarka. As a whole, these data suggest that the capacity to limit oxidative damage is important for salt tolerance of C. maritima .     

Physiological Mechanisms for High Salt Tolerance in Wild Soybean (Glycine soja) from Yellow River Delta,China: Photosynthesis,Osmotic Regulation,Ion Flux and antioxidant Capacity

Glycine soja (BB52) is a wild soybean cultivar grown in coastal saline land in Yellow River Delta, China. In order to reveal the physiological mechanisms adapting to salinity, we examined photosynthesis, ion flux, antioxidant system and water status in Glycine soja under NaCl treatments, taking a cultivated soybean, ZH13, as control. Upon NaCl exposure, higher relative water content and water potential were maintained in the leaf of BB52 than ZH13, which might depend on the more accumulation of osmotic substances such as glycinebetaine and proline. Compared with ZH13, activities of antioxidant enzymes including superoxide dismutase, catalase, ascorbate peroxidase and contents of ascorbate, glutathione and phenolics were enhanced to a higher level in BB52 leaf under NaCl stress, which could mitigate the salt-induced oxidative damage in BB52. Consistently, lipid peroxidation indicated by malondialdehyde content was lower in BB52 leaf. Photosynthetic rate (Pn) was decreased by NaCl stress in BB52 and ZH13, and the decrease was greater in ZH13. The decreased Pn in BB52 was mainly due to stomatal limitation. The inhibited activation of rubisco enzyme in ZH13 due to the decrease of rubisco activase content became an important limiting factor of Pn, when NaCl concentration increased to 200 mM. Rubisco activase in BB52 was not affected by NaCl stress. Less negative impact in BB52 derived from lower contents of Na⁺ and Cl^- in the tissues, and non-invasive micro-test technique revealed that BB52 roots had higher ability to extrude Na⁺ and Cl^-. Wild soybean is a valuable genetic resource, and our study may provide a reference for molecular biologist to improve the salt tolerance of cultivated soybean in face of farmland salinity.     

Plant growth and responses of antioxidants of <Emphasis Type="Italic">Chenopodium album</Emphasis> to long-term NaCl and KCl stress

The effects of long-term NaCl and KCl treatment on plant growth and antioxidative responses were investigated in Chenopodium album, a salt-resistant species widely distributed in semi-arid and light-saline areas of Xinjiang, China. Growth parameters [plant height, branch number, leaf morphology and chlorophyll (Chl) content], the level of oxidative stress [superoxide anion radical (O₂ ⁻), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations], activity of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX)], the contents of non-enzymatic antioxidants [carotenoids (Car) and ascorbic acid (AsA)] and expression of selected genes were investigated. Plants were grown in the presence of 0, 50, and 300 mM NaCl or KCl for 2 months. Growth was stimulated by 50 mM NaCl or KCl, maintained stable at 300 mM NaCl, but was inhibited by 300 mM KCl. Three hundred mM NaCl did not affect O₂ ⁻, H₂O₂, MDA, Car and AsA, but increased the activities of SOD, CAT and POX compared to the controls. RT-PCR analysis suggested that expression of some genes encoding antioxidant enzymes could be induced during long-term salt stress, which was consistent with the enzyme activities. Treatment with 300 mM KCl was associated with elevated oxidative stress, and significantly decreased Car and AsA contents. These results suggest that an efficient antioxidant machinery is important for overcoming oxidative stress induced by treatment with high NaCl concentrations in C. album. Other strategies of ion regulation may also contribute to the differential tolerance to Na and K at higher concentrations.     

Manganese-induced salt stress tolerance in rice seedlings: regulation of ion homeostasis,antioxidant defense and glyoxalase systems

Hydroponically grown 12-day-old rice (Oryza sativa L. cv. BRRI dhan47) seedlings were exposed to 150 mM NaCl alone and combined with 0.5 mM MnSO₄. Salt stress resulted in disruption of ion homeostasis by Na⁺ influx and K⁺ efflux. Higher accumulation of Na⁺ and water imbalance under salinity caused osmotic stress, chlorosis, and growth inhibition. Salt-induced ionic toxicity and osmotic stress consequently resulted in oxidative stress by disrupting the antioxidant defense and glyoxalase systems through overproduction of reactive oxygen species (ROS) and methylglyoxal (MG), respectively. The salt-induced damage increased with the increasing duration of stress. However, exogenous application of manganese (Mn) helped the plants to partially recover from the inhibited growth and chlorosis by improving ionic and osmotic homeostasis through decreasing Na⁺ influx and increasing water status, respectively. Exogenous application of Mn increased ROS detoxification by increasing the content of the phenolic compounds, flavonoids, and ascorbate (AsA), and increasing the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD), and catalase (CAT) in the salt-treated seedlings. Supplemental Mn also reinforced MG detoxification by increasing the activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) in the salt-affected seedlings. Thus, exogenous application of Mn conferred salt-stress tolerance through the coordinated action of ion homeostasis and the antioxidant defense and glyoxalase systems in the salt-affected seedlings.     

Study of interaction effect between triacontanol and nitric oxide on alleviating of oxidative stress arsenic toxicity in coriander seedlings

In this study, triacontanol (TRIA) and nitric oxide (NO) interaction on arsenic (As)-induced oxidative stress tolerance in coriander (Coriandrum sativum L.) plants was investigated. The results showed that As had a significant adverse effect on the plant’s biomass. The seedlings pretreated with TRIA and NO significantly increased growth reduction induced by the metalloid. The obtained results indicated that the application of TRIA and sodium nitroprusside (SNP) generally reduced oxidative markers such as of electrolyte leakage percentage, malondialdehyde and H₂O₂ contents under As toxicity, while application of As treatment without TRIA?+?SNP increased these oxidative parameters compared to the control. The non-enzymatic antioxidant contents such as total phenol, anthocyanin, carotenoid, ascorbic acid and reduced glutathione (GSH) were extracted and assayed from both control and treated plants. It was found that TRIA?+?SNP treatments have a profound effect on the antioxidant metabolism and caused an enhancement in non-enzymatic antioxidant potentials under As toxicity in coriander. Moreover, the results revealed a mutually amplifying reaction between TRIA and NO in reducing As-induced damages.     

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.     

Salt Stress Induces Increase in Starch Accumulation in Duckweed (Lemna aequinoctialis,Lemnaceae): Biochemical and Physiological Aspects

In this study, antioxidant processes were searched for in macrophyte duckweed to investigate tolerance mechanisms in this species against oxidative damage caused by salinity stress. Biochemical and histological analyses were performed on four Lemna aequinoctialis clones grown in Schenk-Hildebrandt medium, 0.5 × SH, supplemented with 1% sucrose liquid medium containing or not containing NaCl in different NaCl concentrations (0, 25 and 50 mM). For most clones, the salt stress effects caused growth inhibition and antioxidant responses at 50 mM NaCl. Also, starch and reducing sugar accumulations were increased with salt, whereas the photosynthetic pigment content was reduced in clone L. aequinoctialis 5569. The plant growth inhibition reflects the oxidative stress shown by the significant increase in malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) content. In the L. aequinoctialis 5568 clone, with the highest MDA levels, no antioxidant enzymatic activity was observed. The L. aequinoctialis 5570 clone presented higher ascorbate peroxidase and catalase activities in parallel, indicating that the efficiency of the defence mechanism relies on synchrony between such enzyme activities toward successive elimination of reactive oxygen species and resulting in the assurance of some level of protection of the metabolism from oxidative damage. Considering the moderate salt stress (25 mM), the maintenance of MDA content and small growth inhibition associated with the high starch production suggested the acclimation efficiency of L. aequinoctialis 5570 and 5567 clones, indicating that they may be suitable for cultivation under moderate saline conditions, serving as biofuel feedstock. In addition, this study demonstrates great intraspecific phenotypic plasticity of duckweed, L. aequinoctialis, from closely related clones.

     

Assessment of Salinity-Induced Antioxidative Defense System of Diazotrophic Cyanobacterium Nostoc muscorum

The present study examines the salinity-induced oxidative damage and differential response of enzymatic and non-enzymatic antioxidants of Nostoc muscorum. As compared to carotenoid content which showed induction the chlorophyll and phycocyanin contents were inhibited after salt stress. Acceleration of lipid peroxidation and peroxide production suggested onset of oxidative damage. The activities of all studied enzymatic antioxidants were significantly increased by salt stress with maximum induction of superoxide dismutase (154.8% at 200 mM NaCl treatment). Interestingly under severe stress condition (250 mM NaCl) ascorbate peroxidase seems to be more crucial than catalase for peroxide scavenging. Among the studied non-enzymatic antioxidants alpha-tocopherol was induced maximally (56.0%), however, ascorbate and reduced glutathione were increased by only 8.9% after 250 mM NaCl treatment as compared to control cells. Therefore, salinity was found to induce antioxidative defense system of N. muscorum.     

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

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