Fungal endophyte Penicillium janthinellum LK5 improves growth of ABA-deficient tomato under salinity

An endophytic fungus was isolated from the roots of tomato (Solanum lycopersicum Mill) and identified as Penicillium janthinellum LK5. The culture filtrate (CF) of P. janthinellum significantly increased the shoot length of gibberellins (GAs) deficient mutant waito-c and normal Dongjin-beyo rice seedlings as compared to control. The CF of P. janthinellum contained GAs (GA₃, GA₄, GA₇ and GA₁₂). To assess endophyte-growth promoting and stress-tolerance potential, the CF along with the propagules of endophyte was applied to tomato-host and abscisic acid (ABA)-deficient mutant Sitiens plants under sodium chloride (NaCl) induced salinity stress. Sitiens plants had retarded growth under normal and salinity stress however its growth was much improved during P. janthinellum-association. The endophyte inoculation reduced the membrane injury by decreasing lipid peroxidation as compared to non-inoculated control under salinity. Endophyte-associated Sitiens plants have significantly higher catalase, peroxidase and glutathione activities as compared to control. Endophyte-infected host and Sitiens plants had low level of sodium ion toxicity and high calcium contents in its root as compared to control. P. janthinellum LK5 helped the Sitiens plants to synthesis significantly higher ABA and reduced the level of jasmonic acid to modulate stress responses. The results suggest that endophytes-association can resist salinity stress by producing gibberellins and activating defensive mechanisms of host and Sitiens plants to achieve improved growth.     

Endophytic fungal pre-treatments of seeds alleviates salinity stress effects in soybean plants

In the present study, four endophytic fungi (GM-1, GM-2, GM-3, and GM-4) were tested for their ability to improve soybean plant growth under salinity stress conditions. The seed germination and plant growth were higher in seeds pretreated with endophytic fungal cultures than their controls. The positive influence of fungi on plant growth was supported by gibberellins analysis of culture filtrate (CF), which showed wide diversity and various concentrations of GAs. Specifically, GA₄, GA₇, GA₈, GA₉, GA₁₂, and GA₂₀ were found in fungal CFs. Under salinity stress conditions, GM-1 significantly enhanced the length and fresh weight of soybean plants relative to other fungal treatments. GM-1 effectively mitigated the adverse effects of salinity by limiting lipid peroxidation and accumulating protein content. GM-2, GM-3, and GM-4 also counteracted the salinity induced oxidative stress in soybean plants through reduction of lipid peroxidation and enhancement of protein content, maintaining the length and fresh weight of shoots. The activities of the antioxidant enzymes catalase, superoxide dismutase and peroxidase were inhibited in salinity exposed plants, while GM-1 significantly enhanced these antioxidant enzyme activities in plants under salt stress. GM-1 treatment also showed lower levels of abscisic acid and elevated levels of salicylic acid in plants under salinity stress. Hence, GM-1 was identified as Fusarium verticillioides (teleomorph Gibberella moniliformis) isolate RK01 based on its DNA sequence homology. These results suggest that endophytic fungal (F. verticillioides) pre-treatment of soybean seeds would be an effective method to promote soybean plant growth under salinity stress conditions.     

外源GSH对盐胁迫下番茄幼苗生长及抗逆生理指标的影响

采用营养液栽培法,研究外源谷胱甘肽(GSH)对NaCl胁迫下番茄幼苗生长、根系活力、电解质渗透率和丙二醛(MDA)、脯氨酸(Pro)、可溶性糖含量以及超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性的影响,为利用外源物质减轻盐胁迫伤害提供理论依据。结果显示:(1)NaCl胁迫显著抑制了番茄幼苗的生长、根系活力和SOD、POD、CAT活性,提高了电解质渗透率及MDA、Pro、可溶性糖含量;(2)外源喷施GSH能够诱导NaCl胁迫下番茄幼苗叶片抗氧化酶SOD、POD、CAT活性上调,电解质渗透率及MDA含量下降,Pro和可溶性糖含量恢复至对照水平;(3)外源喷施还原型谷胱甘肽抑制剂(BSO)使NaCl胁迫下番茄幼苗的根系活力以及抗氧化酶SOD、POD、CAT活性下降,脯氨酸含量提高;(4)喷施GSH可诱导BSO和NaCl共处理番茄植株的根系活力、SOD、POD、CAT活性提高,MDA和Pro含量降低。研究表明,外源GSH可通过提高促进盐胁迫下番茄幼苗植株渗透调节能力及清除活性氧的酶促系统的防御能力、降低细胞膜脂过氧化程度、保护膜结构的完整性,从而有效缓解NaCl胁迫对番茄幼苗生长的抑制,提高其耐盐性。     

Arbuscular mycorrhizal influence on growth,photosynthetic pigments,osmotic adjustment and oxidative stress in tomato plants subjected to low temperature stress

The influence of the arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on characteristics of growth, photosynthetic pigments, osmotic adjustment, membrane lipid peroxidation and activity of antioxidant enzymes in leaves of tomato (Lycopersicon esculentum cv Zhongzha105) plants was studied in pot culture under low temperature stress. The tomato plants were placed in a sand and soil mixture at 25°C for 6 weeks, and then subjected to 8°C for 1 week. AM symbiosis decreased malondialdehyde (MDA) content in leaves. The contents of photosynthetic pigments, sugars and soluble protein in leaves were higher, but leaf proline content was lower in mycorrhizal than non-mycorrhizal plants. AM colonization increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in leaves. The results indicate that the AM fungus is capable of alleviating the damage caused by low temperature stress on tomato plants by reducing membrane lipid peroxidation and increasing the photosynthetic pigments, accumulation of osmotic adjustment compounds, and antioxidant enzyme activity. Consequently, arbuscular mycorrhiza formation highly enhanced the cold tolerance of tomato plant, which increased host biomass and promoted plant growth.     

Salinity up-regulates the antioxidative system in root mitochondria and peroxisomes of the wild salt-tolerant tomato species Lycopersicon pennellii

The effect of salinity on the antioxidative system of root mitochondria and peroxisomes of a cultivated tomato Lycopersicon esculentum (Lem) and its wild salt-tolerant related species L. pennellii (Lpa) was studied. Salt stress induced oxidative stress in Lem mitochondria, as indicated by the increased levels of lipid peroxidation and H(2)O(2). These changes were associated with decreased activities of superoxide dismutase (SOD) and guaiacol peroxidases (POD) and contents of ascorbate (ASC) and glutathione (GSH). By contrast, in mitochondria of salt-treated Lpa plants both H(2)O(2) and lipid peroxidation levels decreased while the levels of ASC and GSH and activities of SOD, several isoforms of ascorbate peroxidase (APX), and POD increased. Similarly to mitochondria, peroxisomes isolated from roots of salt-treated Lpa plants exhibited also decreased levels of lipid peroxidation and H(2)O(2) and increased SOD, ascorbate peroxidase (APX), and catalase (CAT) activities. In spite of the fact that salt stress decreased activities of antioxidant enzymes in Lem peroxisome, oxidative stress was not evident in these organelles.     

Exogenous salicylic acid alleviates NaCl toxicity and increases antioxidative enzyme activity in <Emphasis Type="Italic">Lycopersicon esculentum</Emphasis>

Effects of exogenous salicylic acid (SA) on plant growth, contents of Na, K, Ca and Mg, activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and contents of ascorbate and glutathione were investigated in tomato (Lycopersicon esculentum L.) plants treated with 100 mM NaCl. NaCl treatment significantly increased H₂O₂ content and lipid peroxidation indicated by accumulation of thiobarbituric acid reactive substances (TBARS). A foliar spray of 1 mM SA significantly decreased lipid peroxidation caused by NaCl and improved the plant growth. This alleviation of NaCl toxicity by SA was related to decreases in Na contents, increases in K and Mg contents in shoots and roots, and increases in the activities of SOD, CAT, GPX and DHAR and the contents of ascorbate and glutathione.     

Endophytic bacterial diversity of Avicennia marina helps to confer resistance against salinity stress in Solanum lycopersicum

The current study aimed to explore the endophytic bacterial diversity of Avicennia marina and the potential roles of these endophytes in counteracting saline conditions in tomato plants. Molecular analysis revealed strains from Paenibacillus, Bacillus, Microbacterium, Citrobacter, Lysinibacillus, Halomonas, Virgibacillus, Exiguobacterium, and Vibrio. However, Bacillus pumilus AM11 and Exiguobacterium sp. AM25 showed significantly higher growth in saline media. In response to salinity stress, tomato plants treated with AM11 and AM25 showed significantly higher (～15–23%) biomass, photosynthetic rate and pigment accumulation compared to controls. Salinity-exposed plants had significantly reduced growth and increased (three-fold) lipid peroxidation, whilst glutathione, catalase, and peroxidase activities were significantly reduced. In contrast, AM11, AM25, and methionine improved these physiochemical attributes. The study concludes that the application of bacterial endophytes from plants growing in saline conditions can offer other plants similar stress-resistance potential. Such halophytic bacterial strains can be used to improve plant growth in saline conditions.     

Arbuscular mycorrhizal symbiosis regulates physiology and performance of <Emphasis Type="Italic">Digitaria eriantha</Emphasis> plants subjected to abiotic stresses by modulating antioxidant and jasmonate levels

This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.     

Effect of Arbuscular Mycorrhizal Inoculation on Salt-induced Nodule Senescence in <Emphasis Type="Italic">Cajanus cajan</Emphasis> (Pigeonpea)

Many physiological and biochemical plant processes affected by salt stress trigger premature nodule senescence and decrease their ability to fix nitrogen. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating salt-induced premature nodule senescence in Cajanus cajan (L.) Millsp. Greenhouse experiments were conducted in which the plants were exposed to salinity stress of 4, 6, and 8 dSm⁻¹. Various parameters linked to nodule senescence were assessed at 80 days after sowing. Nodulation, leghemoglobin content, and nitrogenase enzyme activity measured as acetylene-reducing activity (ARA) were evaluated. Two groups of antioxidant enzymes were studied: (1) enzymes involved in the detoxification of O₂⁻ radicals and H₂O₂, namely, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX), and (2) enzymes that are important components of the ascorbate glutathione pathway responsible for the removal of H₂O₂, namely, glutathione reductase (GR) and ascorbate peroxidase (APOX). Exposure of plants to salinity stress enhanced nodule formation; however, nodule growth suffered remarkably and a marked decline in nodule biomass, relative permeability, and lipid peroxidation was observed. Leghemoglobin content and ARA were reduced under saline conditions. AM significantly improved nodulation, leghemoglobin content, and nitrogenase activity under salt stress. Activities of SOD, CAT, APOX, POX, and GR increased markedly in mycorrhizal-stressed plants. A synthesis of the evidence obtained in this study suggests a correlation between enhanced levels of antioxidant enzyme activities, reduced membrane permeability, reduced lipid peroxidation, and improved nitrogen-fixing efficiency of AM plants under stressed and unstressed conditions. These factors could be responsible for the protective effects of mycorrhiza against stress-induced premature nodule senescence.     

Effect of sodium carbonate-induced salinity–alkalinity on some key osmoprotectants,protein profile,antioxidant enzymes,and lipid peroxidation in two mulberry (Morus alba L.) cultivars

The changes in accumulation of two potential osmoprotectants (proline and glycine betaine), lipid peroxidation appraised as malondialdehyde (MDA) level, activities of key antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), peroxidase (POD: EC 1.11.1.7), and glutathione reductase (GR: EC 1.6.4.2), and soluble protein profile in two cultivars of mulberry (S146 and Sujanpuri) differing in alkalinity (NaHCO₃) tolerance were investigated at 2-month intervals up to 6-month growth under stress conditions. Varying levels of salinity–alkalinity developed in soil were 0, 30, 40, and 50 g of NaHCO₃ kg^?1 soil with pH 7.8, 9.1, 9.8, and 10.3, respectively. Alkali stress led to a consistent accumulation of proline and glycine betaine in mulberry leaves with time. The activities of leaf SOD, CAT, POD, and GR increased with increase in external salt concentration and pH. The increase in antioxidant enzyme activities was higher in cv. S146 than cv. Sujanpuri, whereas rate of lipid peroxidation measured in terms of MDA was higher in cv. Sujanpuri as compared to cv. S146. Protein profile revealed that some unknown proteins of low molecular mass (10–32.5 kDa) were induced by NaHCO₃ stress, but differently in two cultivars.     

Contrasting Effects of GA3 Treatments on Tomato Plants Exposed to Increasing Salinity

The role of plant hormones under saline stress is critical in modulating physiological responses that will eventually lead to adaptation to an unfavorable environment. Nevertheless, the functional level of plant hormones, and their relative tissue concentration, may have a different impact on plant growth and stress tolerance at increasing salinity of the root environment. Vigorous plant growth may counteract the negative effects of salinization. In contrast, low gibberellin (GA) levels have been associated with reduced growth in response to salinity. Based on these facts and considering that the physiological basis of the cause-effect relationship between functional growth control and stress adaptation/survival is still a matter of debate, we hypothesized that exogenous applications of the plant hormone GA₃ may compensate for the salt-induced growth deficiency and consequently facilitate tomato plant adaptation to a saline environment. GA₃ application (0 or 100 mg GA₃ l⁻¹) was compared under four salinity levels, obtained by adding equal increments of NaCl:CaCl₂ (2:1 molar basis) (EC = 2.5, 6.8, 11.7, 16.7 dS m⁻¹) to the nutrient solution. GA₃ treatment reduced stomatal resistance and enhanced plant water use at low salinity. These responses were associated with an increased number of fruit per plant at harvest. However, moderate and high salinity nullified these differences. The fruit carotenoid level was generally lower in GA₃-treated plants, indicating either an inhibitory effect of GA₃ treatment on carotenoid biosynthesis or a reduced perception of the stress environment by GA₃-treated tomato plants.     

Coronatine alleviates salinity stress in cotton by improving the antioxidative defense system and radical-scavenging activity

Coronatine (COR) is a chlorosis-inducing phytotoxin that mimics some biological activities of methyl jasmonate. This study investigated whether COR confers salinity tolerance to cotton and whether such tolerance is correlated with changes in the activity of antioxidant enzymes. COR at 0.01muM was applied hydroponically to cotton seedlings at the two-leaf stage for 24h. A salinity stress of 150mM NaCl was imposed after completion of COR treatment for 15d. Salinity stress reduced biomass of seedlings and increased leaf superoxide radicals, hydrogen peroxide, lipid peroxidation, and electrolyte leakage. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione reductase (GR), and of the stable free radical, 1,1-diphenyl-2-picrylhydrazyl (DPPH), scavenging activity were altered by salinity to varying degrees. Pretreatment with COR increased the activities of CAT, POD, GR, and DPPH scavenging activity in leaf tissues of salinity-stressed seedlings. Thus, COR might reduce the production of reactive oxygen species by activating antioxidant enzymes and DPPH-radical scavenging, thereby preventing membrane peroxidation and denaturation of bio-molecules.     

Exogenous application of mannitol and thiourea regulates plant growth and oxidative stress responses in salt-stressed maize (Zea mays L.)

Abstract

The mechanism of growth amelioration in salt-stressed maize (Zea mays L. cv., DK 647 F1) by exogenously applied mannitol (M) and thiourea (T) was investigated. Maize seedlings were planted in pots containing perlite and subjected to 0 or 100 mM NaCl in full strength Hoagland's nutrient solution. Two levels of M (15 and 30 mM) or T (3.5 and 7.0 mM) were sprayed to the leaves of maize seedlings 10 days after germination. Salinity stress caused considerable reduction in plant dry biomass, chlorophyll content, and relative water content in the maize plants. However, it increased the activities of catalase (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1), and polyphenol oxidase (PPO; EC 1.10.3.1), and levels of hydrogen peroxide (H₂O₂) and electrolyte leakage, but it did not change peroxidase (POD; EC 1.11.1.7) activity. Foliar application of M or T was found to be effective in checking salt-induced shoot growth inhibition. Exogenously applied M or T reduced the activities of CAT, SOD, POD, and PPO in the salt-treated maize plants compared to those in the plants not fed with these organic compounds. Salinity increased Na⁺ contents but decreased those of K⁺, Ca^{2 +}, and P in the leaves and roots of the maize plants. Foliar-applied M or T increased the contents of K⁺, Ca^{2 +}, and P, but decreased that of Na⁺ in the salt-stressed maize plants with respect to those of the salt-stressed plants not supplied with mannitol or thiourea. Mannitol was found to be more effective than thiourea in improving salinity tolerance of maize plants in terms of growth and physiological attributes measured in the present study.     

Salinity induced the changes of root growth and antioxidative responses in two wheat cultivars

This study aimed to investigate the inhibitory mechanism of root growth and to compare antioxidative responses in two wheat cultivars, drought-tolerant Ningchun and drought-sensitive Xihan, exposed to different NaCl concentrations. Ningchun exhibited lower germination rate, seedling growth, and lipid peroxidation than Xihan when exposed to salinity. The loss of cell viability was correlated with the inhibition of root growth induced by NaCl stress. Moreover, treatments with H₂O₂ scavenger dimethylthiourea and catalase (CAT) partly blocked salinity-induced negative effects on root growth and cell viability. Besides, the enhancement of superoxide radical and H₂O₂ levels, and the stimulation of CAT and diamine oxidase (DAO) as well as the inhibition of glutathione reductase (GR) were observed in two wheat roots treated with salinity. However, hydroxyl radical content increased only in Xihan roots under NaCl treatment, and the changes of soluble peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), and cell-wall-bound POD activities were different in drought-tolerant Ningchun and drought-sensitive Xihan exposed to different NaCl concentrations. In conclusion, salinity might induce the loss of cell viability via a pathway associated with extracellular H₂O₂ generation, which was the primary reason leading to the inhibition of root growth in two wheat cultivars. Here, it was also suggested that increased H₂O₂ accumulation in the roots of drought-tolerant Ningchun might be due to decreased POD and GR activities as well as enhanced cell-wall-bound POD and DAO ones, while the inhibition of APX and GR as well as the stimulation of SOD and DAO was responsible for the elevation of H₂O₂ level in drought-sensitive Xihan roots.     

Endophytic bacterium Bacillus subtilis (BERA 71) improves salt tolerance in chickpea plants by regulating the plant defense mechanisms

Plant growth-promoting endophytic bacteria can stimulate the growth, nutrient acquisition, symbiotic performance and stress tolerance of chickpea plants under saline soil conditions. The aim of this study was to investigate the stress-adaptive mechanisms of chickpea plants mediated by Bacillus subtilis (BERA 71) under saline conditions. Inoculation with BERA 71 enhanced plant biomass and the synthesis of photosynthetic pigments and reduced the levels of reactive oxygen species (ROS) and lipid peroxidation in plants under conditions of stress. Furthermore, the activities of ROS-scavenging antioxidant enzymes (superoxide dismutase, peroxidase, catalase and glutathione reductase), the levels of non-enzymatic antioxidants (ascorbic acid and glutathione) and the total phenol content were increased in stressed plants during bacterial association. The bacteria decreased sodium accumulation and enhanced the nitrogen, potassium, calcium and magnesium content in the plants. The suppression of ROS generation and of lipid peroxidation and the accumulation of proline in BERA-71-inoculated plants enhanced the membrane stability under salinity stress and non-stress conditions.     

Response of the cultivated tomato and its wild salt-tolerant relative Lycopersicon pennellii to salt-dependent oxidative stress: increased activities of antioxidant enzymes in root plastids

Root plastids of the cultivated tomato Lycopersicon esculentum (Lem) exhibited salt-induced oxidative stress as indicated by the increased H 2 O 2 and lipid peroxidation levels which were accompanied with increased contents of the oxidized forms of ascorbate and glutathione. In contrast, H 2 O 2 level decreased, lipid peroxidation level slightly decreased and the levels of the reduced forms of ascorbate and glutathione increased in plastids of L. pennellii (Lpa) species in response to salinity. This better protection of Lpa root plastids from salt-induced oxidative stress was correlated with increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (POD), monodehydroascorbate reductase (MDHAR), glutathione peroxidase (GPX), glutathione- S -transferase (GST) and phospholipid hydroperoxide glutathione peroxidase (PHGPX). In the plastids of both species, activities of SOD, APX, and POD could be resolved into several isozymes. In Lem plastids two Cu/ZnSOD isozymes were found whereas in Lpa an additional FeSOD type could also be detected. In response to salinity, activities of selected SOD, APX, and POD isozymes were increased in Lpa, while in Lem plastids the activities of most of SOD and POD isozymes decreased. Taken together, it is suggested that plastids play an important role in the adaptation of Lpa roots to salinity.     

Response of antioxidant enzymes in rice (<Emphasis Type="Italic">Oryza sauva</Emphasis> L. cv. Dongjin) under mercury stress

We studied the effects of different concentrations of mercury (0.0 to 100 μM) on growth and photosynthetic efficiency in rice plants treated for 21 d. In addition, we investigated how this metal affected the malondialdehyde (MDA) content as well as the activity of five antioxidant enzymes — superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), guaiacol peroxidase (POD), and catalase (CAT). Photosynthetic efficiency (Fμ/F_m) and seedling growth decreased as the concentration of Hg was increased in the growth media. Plants also responded to Hg-induced oxidative stress by changing the levels of their antioxidative enzymes. Enhanced lipid peroxidation was observed in both leaves and roots that had been exposed to oxidative stress, with leaves showing higher enzymatic activity. Both SOD and APX activities increased in treatments with up to 50 μM Hg, then decreased at higher concentrations. In the leaves, both CAT and POD activities increased gradually, with CAT levels decreasing at higher concentrations. In the roots, however, CAT activity remained unchanged while that of POD increased a bit more than did the control for concentrations of up to 10 μM Hg. At higher Hg levels, both CAT and POD activities decreased. GR activity increased in leaves exposed to no more than 0.25 μM Hg, then decreased gradually. In contrast, its activity was greatly inhibited in the roots. Based on these results, we suggest that when rice plants are exposed to different concentrations of mercury, their antioxidative enzymes become involved in defense mechanisms against the free radicals that are induced by this stress.     

Changes of antioxidative enzymes,lipid peroxidation and chlorophyll content in chickpea types colonized by different <Emphasis Type="Italic">Glomus</Emphasis> species under drought stress

In order to investigate the effects of Glomus species on some physiological characteristics of two chickpea types (Pirouz cultivar of Desi type and ILC-482 of Kabuli type) under non-stress (NS) and drought stress, an experiment was conducted using a factorial arrangement based on completely randomized design with three replications. Drought stress decreased shoot and total dry weight in plants. However inoculation of plants with mycorrhiza improved these traits. Leaf chlorophyll content was decreased, but leaf proline content and guaiacol peroxidases (EC 1.11.1.7) (POD), catalase (EC 1.11.1.6) (CAT), and ascorbate peroxidase (EC 1.11.1.11) (APX) activities were increased as a result of drought stress. Drought stress had no significant effect on soluble protein content and polyphenol oxidase (EC 1.10.3.1) (PPO) enzymatic activity in chickpea plants. In general, drought stress and especially severe drought stress increased membrane lipid peroxidation (MDA) in chickpea plants, which was more evident in non-inoculated than in inoculated plants. Inoculation of chickpea by AM significantly increased POD and PPO activities compared with non-inoculated chickpea, but had no effect on CAT activity and proline content of leaves. The reaction of chickpea cultivars to inoculation by AM species and irrigation levels were different. ILC-482 showed that antioxidant enzymes activities were more and thus less MDA compared with Pirouz cultivar. In general, the most POD and PPO activities were recorded for inoculated plants with G. etunicatum and G. versiform species, and the most APX activity was observed in plants inoculated with G. intraradices.     

Exogenous Salicylic Acid Alleviates Growth Inhibition and Oxidative Stress Induced by Hypoxia Stress in <Emphasis Type="Italic">Malus robusta</Emphasis> Rehd

Salicylic acid (SA) as a signal molecule mediates many biotic and environmental stress-induced physiologic responses in plants. In this study we investigated the role of SA in regulating growth and oxidative stress in Malus robusta Rehd under both normoxic and hypoxic conditions. Hypoxia stress inhibited plant growth and dramatically reduced biomass. Addition of SA significantly alleviated the plant growth inhibition. The amounts of superoxide radicals (O₂ ⁻) and hydrogen peroxide (H₂O₂) significantly increased in leaves of the plants exposed to hypoxia stress and resulted in oxidative stress, which was indicated by accumulated concentration of malondialdehyde (MDA) and electrolyte leakage. Addition of SA significantly decreased the level of O₂ ⁻, electrolyte leakage, and lipid peroxidation and enhanced the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) under hypoxia stress. As important antioxidants, ascorbate (AsA) and glutathione (GSH) contents in the plant leaves were slightly increased by SA treatment compared to hypoxia stress treatment alone. It was concluded that SA could alleviate the detrimental effects of hypoxia stress on plant growth and of oxidative stress by enhancing the antioxidant defense system in leaves of M. robusta Rehd.     

Redox and nitric oxide homeostasis are affected in tomato (Solanum lycopersicum) roots under salinity-induced oxidative stress

The nicotinamide adenine dinucleotide phosphate (NADPH) and reduced glutathione (GSH) molecules play important roles in the redox homeostasis of plant cells. Using tomato (Solanum lycopersicum) plants grown with 120 mM NaCl, we studied the redox state of NADPH and GSH as well as ascorbate, nitric oxide (NO) and S-nitrosoglutathione (GSNO) content and the activity of the principal enzymes involved in the metabolism of these molecules in roots. Salinity caused a significant reduction in growth parameters and an increase in oxidative parameters such as lipid peroxidation and protein oxidation. Salinity also led to an overall decrease in the content of these redox molecules and in the enzymatic activities of the main NADPH-generating dehydrogenases, S-nitrosoglutathione reductase and catalase. However, NO content as well as gluthahione reductase and glutathione peroxidase activity increased under salinity stress. These findings indicate that salinity drastically affects redox and NO homeostasis in tomato roots. In our view, these molecules, which show the interaction between ROS and RNS metabolisms, could be excellent parameters for evaluating the physiological conditions of plants under adverse stress conditions.