Effects of Salinity and Relative Humidity on Two Melon Cultivars Differing in Salt Tolerance

The effects of increasing relative humidity on the growth and salt tolerance of two melon (Cucumis melo L.) cultivars, Revigal C-8 (salt sensitive) and Galia (salt tolerant) was investigated. One month after germination, the plants were exposed for 15 d to 0 (control) and 80 mM NaCl, under relative humidity (RH), 30 and 70 %. The growth of the whole plant, leaf, stem and root of cv. Revigal C-8 was increased with increasing RH. On the other hand, cv. Galia showed an increase in root growth with increasing RH only under the NaCl treatment. Under salinity, most of the Na⁺ was withheld in the stems. An increase in RH in the NaCl treatment significantly decreased Na⁺ and Cl^– concentrations in leaves of cv. Revigal C-8, while it had no effect on their concentrations in cv. Galia. In both cultivars, increasing RH under NaCl condition significantly decreased water contents in leaves and stems, and increased osmotic potential in roots. The amount of the root exudate of cv. Galia was significantly decreased with increasing RH, while it was not affected in cv. Revigal C-8. Under the NaCl treatment, cv. Galia had significantly higher leaf osmotic potential than cv. Revigal C-8 at both relative humidities and higher amount of root exudate at 30 % RH.     

Effect of paclobutrazol on wheat salt tolerance at pollination stage

The effects of paclobutrazol (PBZ) (0, 30, 60, and 90 ppm) and NaCl (0, 75, 150, and 225 mM) treatments on a salt-tolerant (Karchia-65) cultivar of wheat (Triticum aestivum L.) at the pollination stage were studied. Salt stress decreased plant height, the length and area of the flag leaf, fresh and dry weights of the shoot, roots, and flag leaf, and water content. On the background of salinity, PBZ treatment further suppressed plant height. Although plants growth was suppressed in PBZ-treated plants, PBZ treatment moderated the negative effect of salinity on some growth parameters. Under PBZ treatments, plants tissues accumulated more watersoluble carbohydrates and reducing sugars than control plants, with the exception of water-soluble carbohydrates in the roots. The Na⁺ content in roots significantly (p ≤ 0.05) increased at 150 and 225 mM NaCl, but PBZ treatment moderated the harmful effect of the highest levels of salinity. Salinity with or without PBZ treatment improved the K⁺, P, and N contents in plants. It is reasonably to suggest that the protection and increasing salt tolerance caused by PBZ was due to the mechanism nearly similar to the salt-tolerant cultivar physiological systems. These observations suggest that PBZ treatment has the potential to increase salt tolerance with a limiting damage caused by salt stress even in salt-tolerant plants. This text was submitted by the authors in English. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 2, pp. 278–284.     

Effects of paclobutrazol on cultivars of Chinese bayberry (<Emphasis Type="Italic">Myrica rubra</Emphasis>) under salinity stress

Salt stress is one of the most critical factors hindering the growth and development of plants. Paclobutrazol (PBZ) is widely used to minimize this problem in agriculture because it can induce salt stress tolerance in plants. This study investigated the effects of PBZ on salt tolerance of seedlings from two Chinese bayberry cultivars (i.e., Wangdao and Shenhong). Plants were treated with three salt concentrations (0, 0.2, and 0.4 % NaCl) and two PBZ concentrations (0 and 2.0 μmol L^–1). Application of PBZ increased a relative water content, proline content, chlorophyll (a+b) content, and antioxidant enzyme activities in both cultivars, resulting in a better acclimation to salt stress and an increase in dry matter production. We concluded that PBZ ameliorated the negative effects of salt stress in Chinese bayberry seedlings.     

Antioxidative response in different sorghum species under short-term salinity stress

Seedlings of sorghum varieties (M35-1, a drought tolerant species; SPV-839, a drought sensitive one) differing in their drought tolerance were subjected to 150 mM NaCl stress for a short duration of time (up to 72 h). Both the varieties failed to exhibit efficient ion exclusion mechanism like that of salt tolerant species, but in turn resulted in higher accumulation of Na⁺ and Cl⁻ ions over a period of 72 h salt stress. In addition, accumulation of calcium, potassium and proline in seedlings of sorghum varieties was moderate to short-term NaCl stress. The modulation of antioxidant components significantly diverged between the two varieties during seed germination, further the efficiency of antioxidant scavenging system is maintained during short-term NaCl treatments. In comparison to tolerant variety, the sensitive variety depicted higher SOD activity under control and salinity treatments but specific activity of catalase was significantly reduced. In contrast, drought tolerant variety exhibited efficient hydrogen peroxide scavenging mechanisms with higher catalase and GST activities under control and salt stress conditions, but not in the sensitive one. In conclusion, our comparative studies indicate that drought tolerant and susceptible varieties of sorghum induce efficient differential oxidative components of enzymatic machinery for scavenging ROS thereby alleviating the oxidative stress generated by salt stress during seedling growth.     

Effects of NaCl and Mycorrhizal Fungi on Antioxidative Enzymes in Soybean

The effects of different concentrations of NaCl on the activities of antioxidative enzymes in the shoots and roots of soybean (Glycine max [L.] Merr cv. Pershing) inoculated or not with an arbuscular mycorrhizal fungus, Glomus etunicatum Becker & Gerdemann, were studied. Furthermore, the effect of salt acclimated mycorrhizal fungi on the antioxidative enzymes in soybean plants grown under salt stress (100 mM NaCl) was investigated. Activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased in the shoots of both mycorrhizal (M) and nonmycorrhizal (NM) plants grown under NaCl salinity. Salinity increased SOD activity in the roots of M and NM plants, but had no effect on CAT and polyphenol oxidase activities in the roots. M plants had greater SOD, POD and ascorbate peroxidase activity under salinity. Under salt stress, soybean plants inoculated with salt pre-treated mycorrhizal fungi showed increased SOD and POD activity in shoots, relative to those inoculated with the non pre-treated fungi.     

Exogenously applied paclobutrazol modulates growth in salt-stressed wheat plants

Effect of paclobutrazol (PBZ) treatment on salinity tolerance of wheat (Triticum aestivum) was investigated on a salt-tolerant (Karchia-65) and salt-sensitive (Ghods) cultivars. Salinity significantly reduced the investigated growth parameters such as plant height, length and area of sixth leaf, root length, fresh and dry weight of shoot, roots and sixth leaf, water content (WC) of plant and seeds weight in the both cultivars. The negative effect of salinity in Ghods cultivar was more than Karchia cultivar. However, PBZ treatment reduced the growth in both cultivars, the differences in plant growth among various levels of NaCl decreased in PBZ-treated plants. Salt stress resulted in high accumulation of Na⁺ in the sixth leaf and roots in both cultivars, particularly in Ghods cultivar. Against Karchia cultivar, salt stress decreased the storage of K⁺, P and N in sixth leaf and roots in Ghods cultivar. In the both cultivars, PBZ treatment enhanced the K⁺, P and N contents in sixth leaf and roots by increasing salinity. Although PBZ treatment decreased the growth of plants, it improved the weight of seeds against stress damage. PBZ treatment reduced the accumulation of harmful Na⁺ ion in plant tissues while increased the K⁺, P and N contents. These observations suggest that PBZ treatment may increase tolerance by diminishing ionic imbalance caused by salt stress.     

The effect of 5-azacytidine on wheat seedlings responses to NaCl stress

The effect of 5-azacytidine (5-azaC) on the alleviation of damaging effects of NaCl treatment was studied in two wheat (Triticum aestivum L.) cultivars differing in salt tolerance (salt-tolerant Dekang-961 and sensitive Lumai-15). The plants were pre-treated or not with 50 μM 5-azaC and then subjected to salt stress induced by 100 or 150 mM NaCl. Salinity caused reduction in biomass accumulation and increase in malondialdehyde content in root tissues in both cultivars, but less in pre-treated seedlings. The activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) in the roots of both cultivars increased during salt stress, but the rate of increase was higher in Dekang-961. Plants treated with 5-azaC had higher root SOD, CAT and POD activities under salt stress than untreated plants. Content of 5-methylcytosine (5mC) decreased in both cultivars under salt stress, and the level of demethylation was higher in Dekang-961 than that in Lumai-15. Moreover, the degree of methylation was lower in both cultivars under salt stress after 5-azaC application compared to only salt-treated groups. These findings suggested that 5-azaC could protect plants from salt stress.     

蒭雷草对盐胁迫的生理响应

该文选择从西沙东岛采集蒭雷草,通过分株繁殖挑选健壮植株作为材料,模拟热带珊瑚岛生境设置不同浓度NaCl处理,研究不同程度的盐胁迫对其植株叶片丙二醛(MDA)、抗氧化酶以及渗透调节物质的影响.结果表明:(1)短期(28 d)盐胁迫下,NaCl浓度的增加并未加速蒭雷草叶片细胞发生膜脂过氧化作用,MDA含量增加幅度较小;随着...     

Enhanced Tonoplast H+-ATPase Activity and Superoxide Dismutase Activity in the Halophyte Suaeda salsa Containing High Level of Betacyanin

In this study, high-betacyanin Suaeda salsa seedlings were developed and used to explore whether the betacyanin accumulation is related to salinity tolerance in S. salsa. After 8 days of culture, betacyanin content decreased markedly in both high-betacyanin S. salsa seedlings and the control under nonsalt stress, but the decreases were suppressed by NaCl treatments. Betacyanin content in high-betacyanin seedlings was much higher than that in the control throughout the salt treatments. Growth of S. salsa plants was significantly promoted by NaCl treatments, and the fresh weight of high-betacyanin seedlings was much higher than that of the control when grown in 400 mmol L⁻¹ NaCl. Similar cell sap osmolarity and K⁺/Na⁺ ratios were observed in high-betacyanin seedlings and the control. No obvious differences in V-ATPase (tonoplast H⁺-ATPase) activity, leaf SOD (superoxide dismutase) activity, and total chloroplast SOD (including thylakoid-bound SOD and stroma SOD) activity were detected between high-betacyanin seedlings and the control under nonsalt stress conditions. However, V-ATPase hydrolytic activity increased dramatically in S. salsa seedlings when subjected to different levels of NaCl, and the increases in V-ATPase activity in high-betacyanin seedlings were much higher than that in the control. No clear pattern was observed for NaCl-dependent activity changes of P-ATPase (plasma membrane H⁺-ATPase) and V-PPase (tonoplast H⁺-pyrophosphatase). Similar changes were demonstrated in leaf SOD activity and chloroplast SOD activity under salt stress. Both leaf SOD activity and chloroplast SOD activity were markedly enhanced with the increase of NaCl or with time, especially thylakoid-bound SOD activity. Furthermore, the increases in chloroplast SOD activity and thylakoid-bound SOD activity were much higher in high-betacyanin seedlings than that in the control at different levels of NaCl treatment. The higher V-ATPase activity, chloroplastic SOD activity, and thylakoid-bound SOD activity demonstrated in high-betacyanin seedlings, but lower in the control, suggest that high-betacyanin S. salsa seedlings may have higher potential to be energized by the electrochemical gradient for ion uptake into the vacuole and to scavenge O₂^−• in situ produced in the chloroplasts, which may lead to higher salt tolerance than the control under salt stress. Thus, betacyanin may be involved in salt tolerance of S. salsa.     

An Enhancing Effect of Exogenous Mannitol on the Antioxidant Enzyme Activities in Roots of Wheat Under Salt Stress

The role of mannitol as an osmoprotectant, a radical scavenger, a stabilizer of protein and membrane structure, and protector of photosynthesis under abiotic stress has already been well described. In this article we show that mannitol applied exogenously to salt-stressed wheat, which normally cannot synthesize mannitol, improved their salt tolerance by enhancing activities of antioxidant enzymes. Wheat seedlings (3 days old) grown in 100 mM mannitol (corresponding to −0.224 MPa) for 24 h were subjected to 100 mM NaCl treatment for 5 days. The effect of exogenously applied mannitol on the salt tolerance of plants in view of growth, lipid peroxidation levels, and activities of antioxidant enzymes in the roots of salt-sensitive wheat (Triticum aestivum L. cv. Kızıltan-91) plants with or without mannitol was studied. Although root growth decreased under salt stress, this effect could be alleviated by mannitol pretreatment. Peroxidase (POX) and ascorbate peroxidase (APX) activities increased, whereas superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) activities decreased in Kızıltan-91 under salt stress. However, activities of antioxidant enzymes such as SOD, POX, CAT, APX, and GR increased with mannitol pretreatment under salt stress. Although root tissue extracts of salt-stressed wheat plants exhibited only nine different SOD isozyme bands of which two were identified as Cu/Zn-SOD and Mn-SOD, mannitol treatment caused the appearance of 11 different SOD activity bands. On the other hand, five different POX isozyme bands were determined in all treatments. Enhanced peroxidation of lipid membranes under salt stress conditions was reduced by pretreatment with mannitol. We suggest that exogenous application of mannitol could alleviate salt-induced oxidative damage by enhancing antioxidant enzyme activities in the roots of salt-sensitive Kızıltan-91.     

Development of NaCl-tolerant line in Chrysanthemum morifolium Ramat. through shoot organogenesis of selected callus line

Plants were regenerated successfully through shoot organogenesis of a NaCl-selected callus line of Chrysanthemum morifolium Ramat. cv. Maghi Yellow (a salt sensitive cultivar), developed through stepwise increase in NaCl concentration (0-100mM) in the MS medium. The stepwise increase in NaCl concentration from a relatively low level to cytotoxic level was found to be a better way to isolate NaCl-tolerant callus line, since direct transfer of callus to high saline medium was detrimental to callus survival and growth. The selected callus line exhibited significant increase in superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and glutathione reductase (EC 1.6.4.2) activities compared to control callus (grown in medium devoid of NaCl). Stability of salt tolerance character of the selected callus line was checked by growing the calli in NaCl-free medium for 3 consecutive months followed by re-exposure to higher salinity stress (120mM NaCl). Among different growth regulator treatments, a combination of 5mgl(-1) TDZ (Thidiazuron) along with 0.25mgl(-1) NAA and 0.5mgl(-1) GA(3) was found to be the most effective for shoot organogenesis in selected callus line. The regeneration potential of the NaCl-tolerant callus ranged from 20.8% to 0% against 62.4% to 0% in control callus line. Under elevated stress condition (medium supplemented with 250mM NaCl), selected calli derived regenerants (S1 plants) exhibited significantly higher SOD and APX activities over both PC (positive control: control callus derived plants grown on MS medium devoid of NaCl) and NC (negative control: control callus derived plants subjected to 250mM NaCl stress) plants. In addition, the NC plants showed stunted growth, delayed root initiation, and had lesser number of roots as compared to S1 plants. Based on growth performance and antioxidant capacity, the S1 plants could be considered as NaCl-tolerant line showing all positive adaptive features towards the salinity stress. Further study on agronomic performance of these S1 plants under saline soil condition need to be undertaken to check the genetic stability of the induced salt-tolerance.     

Combination Effect of NaCl Salinity and Nitrogen Form on Mineral Composition of Sunflower Plants

The effect of two N-forms (NH₄ ⁺ and NO₃ ^–) and NaCl on pattern of accumulation of some essential inorganic nutrients was examined in sunflower (Helianthus annuus L.) cv. Hisun 33. Eight-day-old plants of were subjected for 21 d to Hoagland's nutrient solution containing 8 mM N as NH₄ ⁺ or NO₃ ^·, and salinized with and addition of NaCl to the growth medium had no significant effect on total leaf N. However, root N of NH₄-supplied plants decreased significantly with increase in NaCl concentration, whereas that of NO₃-supplied plants remained unaffected. There was no significant effect of NaCl on leaf or root P, but the NO₃-supplied plants had significa concentration of leaf P than that of NH₄-supplied plants at varying salt treatments. Salinity of the rooting med did not show any significant effect on Na⁺ concentrations of leaves or roots of plants subjected to two differen N. NH₄-treated plants generally had greater concentrations of Cl^– in leaves and roots and lower K⁺ content in leaves than NO₃-supplied plants. Ca²⁺ concentrations of leaves and roots and Mg²⁺ concentrations of leaves decreased in NH₄-supplied plants due to NaCl, but they remained unaffected in NO₃-treated plants.     

Light-Dark Changes in Proline Content of Barley Leaves under Salt Stress

Proline accumulation in leaves of barley (Hordeum vulgare L. cv. Alfa) seedlings treated with 150 mM NaCl was promoted in the light and suppressed in the dark. The light/dark changes of proline content was enhanced with each 12 h light/12 h dark cycle and the proline content increased steadily. Root and shoot concentrations of Na⁺ and Cl^– in salt treated plants increased about 10 to 25 times as compared to the control. The content of these ions and the content of malondialdehyde were higher in the shoot of seedlings exposed to salt stress for 4 d in the light in comparison with the seedlings exposed to NaCl for 4 d in darkness. Light stimulated both ions and proline accumulation in the leaves and has no effect in the roots. Oxygen uptake was higher in the seedlings kept 4 d in the light which have higher endogenous free proline content. Chlorophyll fluorescence measurements showed that the photochemical activity of PS 2 slightly decreased as a result of salt stress and was not influenced by light regimes during plant growth.     

Interactive effects of triadimefon and salt stress on antioxidative status and ajmalicine accumulation in Catharanthus roseus

The ability of triadimefon (TDM), a triazole group of fungicide, to ameliorate salinity stress was studied in Catharanthus roseus (L.) G. Don. plants subjected to sodium chloride (NaCl) treatment. NaCl treatment at 80 mM level decreased overall growth of this plant and reduced the chlorophyll contents, protein, antioxidant enzymes such as peroxidase (POX), superoxide dismutase (SOD) and polyphenol oxidase (PPO). The root alkaloid ajmalicine got increased under salt treatment. When these stressed plants were treated with TDM at 15 mg l⁻¹ concentration minimized the inhibitory effects of NaCl stress by increasing the root, shoot growth and leaf area and increased dry weight (DW), chlorophyll, protein contents and the activities of antioxidant enzymes like POX, SOD and PPO, thereby paved the way to overcome the salinity injury. The quantity of ajmalicine was again increased with the TDM treatment when compared to both control and NaCl treated plants. From these results, it is proved that the fungicide TDM have great role in the enhancement of plant antioxidative enzymes and the enhanced scavenging of potentially harmful free radicals, as a mechanism of protecting plants against noxious oxidative stress from the environment and also in the enhancement of active principles.     

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.     

Grafting raises the salt tolerance of tomato through limiting the transport of sodium and chloride to the shoot

With the aim of determining whether grafting could improve salinity tolerance of tomato (Lycopersicon esculentum Mill.), and what characteristics of the rootstock were required to increase the salt tolerance of the shoot, a commercial tomato hybrid (cv. Jaguar) was grafted onto the roots of several tomato genotypes with different potentials to exclude saline ions. The rootstock effect was assessed by growing plants at different NaCl concentrations (0, 25, 50, and 75 mM NaCl) under greenhouse conditions, and by determining the fruit yield and the leaf physiological changes induced by the rootstock after 60 d and 90 d of salt treatment. The grafting process itself did not affect the fruit yield, as non-grafted plants of cv. Jaguar and those grafted onto their own root showed the same yield over time under non-saline conditions. However, grafting raised fruit yield in Jaguar on most rootstocks, although the positive effect induced by the rootstock was lower at 25 mM NaCl than at 50 and 75 mM NaCl. At these higher levels, the plants grafted onto Radja, Pera and the hybrid VolgogradskijxPera increased their yields by approximately 80%, with respect to the Jaguar plants. The tolerance induced by the rootstock in the shoot was related to ionic rather than osmotic stress caused by salinity, as the differential fruit yield responses among graft combinations were mainly related to the different abilities of rootstocks to regulate the transport of saline ions. This was corroborated by the high negative correlation found between fruit yield and the leaf Na(+) or Cl(-) concentrations in salt-treated plants after 90 d of salt treatment. In conclusion, grafting provides an alternative way to enhance salt tolerance, determined as fruit yield, in the tomato, and evidence is reported that the rootstock is able to reduce ionic stress.     

Roots and leaves display contrasting oxidative response during salt stress and recovery in cowpea

In this study, we compare some antioxidative responses of leaves and roots associated to growth reduction in cowpea plants (Vigna unguiculata) during short-term salt stress and recovery. The salt treatment was imposed (200 mM NaCl) for six consecutive days and the salt withdrawal after 3 d. The salt treatment caused an almost complete cessation in the relative growth rate of both leaves and roots. Although NaCl withdrawal has induced an intense reduction in the Na(+) content from the leaves and roots, the growth recovery was slight, after 3 d. The leaf lipid peroxidation was increased in salt-stressed plants and slightly reduced in recovered plants after 3 d. Surprisingly, in the salt-stressed roots it decreased markedly after 3 d treatment and in the pre-stressed/recovered roots it was restored to levels near to the control. In leaves, catalase (CAT) activity showed a rapid and prominent decrease after 1 d of NaCl treatment and salt withdrawal had no effect on its recovery. In contrast, the root CAT activity was not changed by effects of both NaCl and salt withdrawal, over time interval. Leaf superoxide dismutase (SOD) activity did not change in all treatments, whereas in roots it significantly decreased after 3 d of salt treatment and recovered after NaCl withdrawal. Contrasting to the other enzymes, the guaiacol-peroxidase activity increased in leaves and roots, reaching almost 200% of control values and it significantly decreased in both organs from the pre-stressed/recovered plants. In conclusion, cowpea roots and leaves present distinct mechanisms of response to lipid peroxidation and CAT and SOD activities during salt stress and recovery. However, these responses and/or the oxidative damages caused by reactive oxygen species were not related with the growth reduction.     

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.     

Superoxide dismutase activity in salt stressed wheat seedlings

We investigated the effect of salt stress on enzymatic activity of superoxide dismutase (SOD) isozymes in shoot and root tissues of salt tolerant and sensitive wheat (Triticum aestivum L. and Triticum durum Defs.) cultivars. Ten day old seedlings were subjected to 0.7 M NaCl stress for 3 and 5 days. Seedlings treated in the same manner without salt stress served as controls. Activity of SOD isozymes in root and shoot extracts was determined by activity staining of native polyacrylamide gels. In both shoot and root extracts of examined cultivars two isozymes of SOD, namely MnSOD and Cu/ZnSOD were identified. Cu/ZnSOD activity comprised 90 % of total SOD activity in both root and shoot tissues. Salt stress caused 1–1.5 fold increase in MnSOD activity of shoots in tolerant cultivars when compared with non-stressed controls. Under stress conditions, compared to controls all cultivars exhibited reduced MnSOD activity in root tissues. Cu/ZnSOD activity, on the other hand, was remarkably enhanced (3–4 fold) in root extracts of the tolerant cultivars, whereas it was reduced in the sensitive ones.     

Expression levels of the Na + /K + transporter OsHKT2;1 and vacuolar Na + /H + exchanger OsNHX1 , Na enrichment,maintaining the photosynthetic abilities and growth performances of indica rice seedlings under salt stress

Salt affected soil inhibits plant growth, development and productivity, especially in case of rice crop. Ion homeostasis is a candidate defense mechanism in the salt tolerant plants or halophyte species, where the salt toxic ions are stored in the vacuoles. The aim of this investigation was to determine the OsNHX1 (a vacuolar Na+/H+ exchanger) and OsHKT2;1 (Na+/K+ transporter) regulation by salt stress (200 mM NaCl) in two rice cultivars, i.e. Pokkali (salt tolerant) and IR29 (salt susceptible), the accumulation of Na+ in the root and leaf tissues using CoroNa Green® staining dye and the associated physiological changes in test plants. Na+ content was largely increased in the root tissues of rice seedlings cv. Pokkali (15 min after salt stress) due to the higher expression of OsHKT2;1 gene (by 2.5 folds) in the root tissues. The expression of OsNHX1 gene in the leaf tissues was evidently increased in salt stressed seedlings of Pokkali, whereas it was unchanged in salt stressed seedlings of IR29. Na+ in the root tissues of both Pokkali and IR29 was enriched, when subjected to 200 mM NaCl for 12 h and easily detected in the leaf tissues of salt stressed plants exposed for 24 h, especially in cv. Pokkali. Moreover, the overexpression of OsNHX1 gene regulated the translocation of Na+ from root to leaf tissues, and compartmentation of Na+ into vacuoles, thereby maintaining the photosynthetic abilities in cv. Pokkali. Overall growth performance, maximum quantum yield (Fv/Fm), photon yield of PSII (ΦPSII) and net photosynthetic rate (Pn) was improved in salt stressed leaves of Pokkali than those in salt stressed IR29.