The activity of antioxidative enzymes in three strawberry cultivars related to salt-stress tolerance

Effects of salt stress on the time course of stomatal behaviors and the activity of antioxidative enzymes such as catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APX) (EC 1.11.1.11), and glutathione reductase (GR) (EC. 1.6.4.2) were studied in three strawberry cultivars. The responses of the cultivars ‘Camarosa’, ‘Tioga,’ and ‘Chandler’ were compared when they were irrigated with nutrient solution containing 0, 8.5, 17.0, and 34.0 mM sodium chloride (NaCl) for 30 days. A significant reduction in stomatal conductance (g_s) was seen particularly on the 30th day of the salt treatments only in Camarosa, which is parallel to transpiration rate (E). CAT activities decreased in all of the salt treatments only in Tioga, while it remained almost unchanged or slightly increased depending on the period in Camarosa and Chandler. APX activity sharply increased in 17.0 and 8.5-mM NaCl treatments for 30 days in Camarosa and Tioga, respectively, whereas it linearly increased based on the NaCl treatments in Chandler. On the other hand, only Camarosa demonstrated a sharp increase in GR activity induced by salinity applied for 30 days. All the data indicated that control of the stomatal behavior, the higher salt-stress tolerance (LT₅₀) and higher constitutive activity of antioxidant enzymes made Camarosa and Tioga relatively salt-tolerant cultivars.     

Varied tolerance to NaCl salinity is related to biochemical changes in two contrasting lettuce genotypes

Salt stress perturbs a multitude of physiological processes such as photosynthesis and growth. To understand the biochemical changes associated with physiological and cellular adaptations to salinity, two lettuce varieties (Verte and Romaine) were grown in a hydroponics culture system supplemented with 0, 100 or 200 mM NaCl. Verte displayed better growth under 100 mM NaCl compared to Romaine, but both genotypes registered relatively similar reductions in growth under 200 mM NaCl treatment. Both varieties showed differences in net photosynthetic activity in the absence of salt and 8 days after salt treatment. These differences diminished subsequently under prolonged salt stress (14 days). Verte showed enhanced leaf proline and restricted total cations especially Na⁺, lesser malondialdehyde (MDA) formation and lignification in the roots under 100 mM NaCl salinity. Membrane damage estimated by electrolyte leakage increased with elevated salt concentrations in roots of both varieties, but Verte had significantly lower electrolyte leakage relative to Romaine under 100 mM NaCl. Moreover, Verte also accumulated greater levels of carotenoids under increasing NaCl concentrations compared to Romaine. Taken together, these findings suggest that the greater tolerance of Verte to 100 mM NaCl is related to the more restricted accumulation of total cations and toxic Na⁺ in the roots and enhanced levels of antioxidative metabolites in root and leaf tissue.     

Amelioration of salt-induced oxidative stress in eggplant by application of 24-epibrassinolide

The effects of exogenous 24-epibrassinolide (EBR) on the growth, oxidative damage, antioxidant system and ion contents in eggplant (Solanum melongena L.) seedlings under salt stress were investigated. Eggplant seedlings were exposed to 90 mM NaCl with 0, 0.025, 0.05, 0.10 and 0.20 mg dm⁻³ EBR for 10 d. EBR, especially at concentration 0.05 mg dm⁻³, alleviated growth suppression caused by NaCl stress, decreased electrolyte leakage, superoxide production and content of malondialdehyde and H₂O₂ in NaCl-treated plants. EBR also increased activities of superoxide dismutase, guaiacol peroxidase, catalase and ascorbate peroxidase and the contents of ascorbic acid and reduced glutathione. Furthermore, we also found that Na⁺, Cl⁻ contents were decreased, K⁺, Ca²⁺ contents and K⁺/Na⁺, Ca²⁺/Na⁺ ratios were increased in the presence of EBR under salt stress.     

Salicylic acid-mediated changes in photosynthesis,nutrients content and antioxidant metabolism in two mustard (<Emphasis Type="Italic">Brassica juncea</Emphasis> L.) cultivars differing in salt tolerance

Mustard (Brassica juncea L.) cultivars Alankar (salt-tolerant) and PBM16 (salt-sensitive) plants were grown with 50 mM NaCl and were sprayed with 0.1, 0.5, and 1.0 mM salicylic acid (SA) to study the physiological processes determining salt tolerance and to observe the influence of SA application on the alleviation of NaCl-induced adverse effects. The content of leaf Na⁺, Cl⁻, H₂O₂, TBARS, and electrolyte leakage and the activity of SOD were higher in PBM16 than Alankar. In contrast, nutrients content, activity of APX and GR, glutathione content, photosynthetic and growth characteristics were higher in Alankar. Treatment of 50 mM NaCl resulted in increase of Na⁺ and Cl⁻, oxidative stress, activity of antioxidant enzymes and glutathione content, while nutrients content, photosynthetic, and growth characteristics decreased in both the cultivars. Application of 0.5 mM SA alleviated the negative effects of 50 mM NaCl maximally, but 1.0 mM SA proved inhibitory. The effect of SA was more conspicuous in Alankar than PBM16. It is concluded that the higher tolerance of Alankar was due to its lower leaf Na⁺ and Cl⁻ content, higher nutrients content, and efficient antioxidant metabolism. The application of 0.5 mM SA substantially alleviated salt-induced adverse effects in Alankar.     

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.     

Osmolytes in salinity-stressed Iris hexagona

We characterize the salinity stress response of Iris hexagona, a freshwater species, by measuring three putative osmolytes, betaine, proline, and dimethylsulphonio-propionate (DMSP) in plants after short (3 days) and long-term (4–5 months) exposure to NaCl. HPLC analyses show that untreated control leaves contained 2.1, 0.2 and 3.2 mg g⁻¹ DW of betaine, proline, and DMSP, respectively, and establish the presence of these compounds in the Iridaceae. Within 4 days of salinity stress (200 mM NaCl) betaine, proline and DMSP increased significantly. Among vegetative tissues, the highest level of proline occurred in roots; betaine and DMSP were highest in leaves. Analyses of generative tissue (flowers and flower stalks) after long-term exposure showed the highest levels (>10 mg g⁻¹ DW) of all examined compounds in petals but only proline and betaine increased with salinity. All three substances showed a basipetal gradient in flower stalks. Although the examined compounds responded to salinity, the osmometry of the sap indicated that they comprise less than 10% of the osmotically active solutes. The temporal and spatial changes in the distribution of the analyzed compounds indicate complex responses to salinity.     

Influence of exogenously applied nitric oxide on strawberry (Fragaria × ananassa) plants grown under iron deficiency and/or saline stress

A study was carried out to assess the protective effects of exogenously applied nitric oxide (NO) in the form of its donor sodium nitroprusside (SNP) to strawberry seedlings (Fragaria × ananassa cv. Camarosa) grown under iron deficiency (ID), salinity stress or combination of both. The experimental design contained control, 0.1 mM FeSO₄ (ID, Fe deficiency); 50 mM NaCl (S, Salinity) and ID + S. Plants were sprayed with 0.1 mM SNP or 0.1 mM sodium ferrocyanide, an analogue of SNP containing no NO. The deleterious effects of ID + S treatments on plant fresh and dry matters, total chlorophyll and chlorophyll fluorescence were more striking than those caused by the ID or S treatment alone. Furthermore, combination of salinity and iron stress exacerbated electrolyte leakage (EL) and the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in plant leaves compared to those in plants grown with either of the single stresses. NO treatment effectively reduced EL, MDA and H₂O₂ in plants grown under stress conditions applied singly or in combination. Salt stress alone and with ID reduced the superoxide dismutase (EC1.15.1.1) and catalase (EC 1.11.1.6) activities but increased that of POD (EC 1.17.1.7). Exogenously applied NO led to significant changes in antioxidant enzyme activities in either ID or S than those by ID+S. Overall, exogenously applied NO was more effective in mitigating the stress‐induced adverse effects on the strawberry plants exposed to a single stress than those due to the combination of both stresses.     

Alleviation of salt stress in lemongrass by salicylic acid

Soil salinity is one of the key factors adversely affecting the growth, yield, and quality of crops. A pot study was conducted to find out whether exogenous application of salicylic acid could ameliorate the adverse effect of salinity in lemongrass (Cymbopogon flexuosus Steud. Wats.). Two Cymbopogon varieties, Krishna and Neema, were used in the study. Three salinity levels, viz, 50, 100, and 150 mM of NaCl, were applied to 30-day-old plants. Salicylic acid (SA) was applied as foliar spray at 10^?5 M concentration. Totally, six SA-sprays were carried out at 10-day intervals, following the first spray at 30 days after sowing. The growth parameters were progressively reduced with the increase in salinity level; however, growth inhibition was significantly reduced by the foliar application of SA. With the increase in salt stress, a gradual decrease in the activities of carbonic anhydrase and nitrate reductase was observed in both the varieties. SA-treatment not only ameliorated the adverse effects of NaCl but also showed a significant improvement in the activities of these enzymes compared with the untreated stressed-plants. The plants supplemented with NaCl exhibited a significant increase in electrolyte leakage, proline content, and phosphoenol pyruvate carboxylase activity. Content and yield of essential oil was also significantly decreased in plants that received salinity levels; however, SA overcame the unfavorable effects of salinity stress to a considerable extent. Lemongrass variety Krishna was found to be more adapted to salt stress than Neema, as indicated by the overall performance of the two varieties under salt conditions.     

Alleviation of NaCl toxicity in the cyanobacterium <Emphasis Type="Italic">Synechococcus</Emphasis> sp. PCC 7942 by exogenous calcium supplementation

Salinity (NaCl) is one of the major problems associated with irrigated agricultural lands, especially rice fields. Being the common inhabitants of rice fields, cyanobacteria frequently experience high concentration of NaCl which in turn causes cellular damage. Therefore, mitigation of NaCl stress in cyanobacteria, plant growth-promoting microorganisms, is of utmost importance. The present study was designed to investigate the role of calcium in the alleviation of NaCl stress-induced cellular in Synechococcus sp. PCC 7942. The cyanobacterium was subjected to sub-lethal concentration of NaCl (800 mM) with and without the supplementation of calcium (1 mM CaCl₂) for 8 days. The results showed a drastic reduction in growth due to excess NaCl, but supplementation of CaCl₂ reduced the salt stress damage and partially restored growth. Application of calcium increased pigment contents, photosynthetic efficiency, antioxidative enzyme activity, osmolyte contents and reduced the intracellular sodium ion concentration, MDA content, electrolyte leakage and free oxygen radical generation. Furthermore, proteins involved in photosynthesis, respiration, ATP synthesis and protein synthesis along with two hypothetical proteins were also observed to be upregulated in the cyanobacterium in presence of calcium. Furthermore, proteins related to oxidative stress defence, nitrogen metabolism, carbohydrate metabolism, fatty acid metabolism and secondary metabolism were found to be upregulated by several fold. Therefore, our study suggests that calcium suppresses salt toxicity in Synechococcus sp. PCC 7942 by restricting the entry of Na⁺ into the cell, increasing osmolyte production and upregulating defence-related proteins.     

Ultrastructural evidence for AMF mediated salt stress mitigation in Trigonella foenum-graecum

The study unveils that inoculation with arbuscular mycorrhizal fungus (Glomus intraradices Schenck and Smith) prevents salt-induced ultrastructural alterations in fenugreek (Trigonella foenum-graecum L.) plants. Mycorrhizal (M) and non-mycorrhizal (NM) fenugreek plants were subjected to four levels of NaCl (0, 50, 100, and 200 mM NaCl). Salt-induced ultrastructural changes were captured using a Transmission Electron Microscope. Effects of salt on the ultrastructure of cells include shrinkage of protoplasm, widening apoplastic space between cell wall and cell membrane, disorganization of grana in chloroplast—swelling and reduction in the number of thylakoids, disintegration of chloroplast membrane, accumulation of plastoglobules, dilation of cristae and denser matrix in mitochondria, and aggregation of chromatin in nucleus. However, the extent of salt-induced ultrastructural damage was less in M plants as compared to NM plants. Lower lipid peroxidation and electrolyte leakage in M plants also indicated less membrane damage. This reduction of ultrastructure damage is a demonstration of enhanced tolerance in M plants to salt stress. The AMF-mediated lesser damage may be due to higher osmolyte (glycinebetaine, sugars) and polyamines concentration, and more and bigger plastoglobules (higher α-tocopherol concentration) in M plants as compared to NM plants. While lower Na⁺ and Cl^? ions assures less ionic toxicity, higher osmolytes and tocopherols ensure osmotic adjustment and better capacity to scavenge free radicals generated due to salt stress, respectively.     

Alfalfa (Medicago sativa L.) clones tolerant to salt stress: in vitro selection

In order to quickly and efficiently evaluate the salt tolerance of alfalfa, salinity tests were conducted on Medicago sativa L. var. australis, var. icon, var. loi, and var. gea, under in vitro conditions. Pregerminated seeds of four varieties were subjected to five different NaCl concentrations (0, 50, 100, 150, 200 mM). The influence of saline stress was estimated on the basis of survival percentage, growth parameters, and electrolyte leakage. The seedlings surviving on the medium enriched with salt at the highest concentration were presumed to be tolerant and represented the mother plants for the production of in vitro clones. In the following step, the clones were evaluated in vitro to confirm the salt tolerance. The influence of mild salt stress (75 mM NaCl) on the growth parameters of selected clones was examined. At the end of this trial, the proline accumulation and sodium content in alfalfa shoots were also quantified. The results suggest an increased level of proline promotes salt tolerance. Medicago sativa L. var. icon is highly tolerant in comparison with the other varieties tested. In vitro selection of M. sativa L. varieties on salt-containing media allowed us to obtain clones with increased salinity tolerance.     

Understanding Saline and Osmotic Tolerance of Populus euphratica Suspended Cells

Tolerance of Populus euphratica suspended cells to ionic and osmotic stresses implemented respectively by NaCl and PEG (6000) was characterized by monitoring cell growth, morphological features, ion compartmentation and polypeptide patterns. The cells grew and proliferated when submitted to stresses of 137 mM NaCl or 250 g l⁻¹ PEG, and survived at 308 mM of NaCl, showing tolerance to saline and particularly osmotic stress. They were resistant to plasmolysis and had dense cytoplasms, large nuclei and nucleoli, and evident cytoplasmic strands under high saline and osmotic stress. The sequestration of Cl⁻ into the vacuoles was observed in the cells stressed with 137 and 223 mM NaCl. The cellular protein profile was modified by high salt and osmotic stress and showed 28 kDa polypeptides up-regulated by both NaCl and PEG, and 66 and 25 kDa polypeptides up-regulated only by high NaCl stress. The salt tolerance of P. euphratica cells might be related to their capacity of adapting to higher osmotic stress by maintaining cell integrity, sequestrating Cl⁻ into vacuoles and modulating polypeptides that reflect cellular metabolic adaptations.     

Two-stage culture for producing berberine by cell suspension and shoot cultures of <Emphasis Type="Italic">Berberis buxifolia</Emphasis> Lam

In vitro cultures of Berberis buxifolia were established using thidiazuron (4.5, 23 and 45 mM) or picloram (4 and 40 mM) as plant growth regulators for sustaining growth. For producing berberine, a two-stage culture was performed. In the first step, thidiazuron or picloram were used for biomass production followed by the production stage where benzylaminopurine (4.4 mM) was added as a plant growth regulator. Berberine yields (102 mg g⁻¹ DW) and in vitro shoot cultures (200 mg g⁻¹ DW) were significantly lower than those of whole plants in the field (416 mg g⁻¹ DW). The highest productivity (0.18 mg 1⁻¹ day⁻¹) was attained using picloram (either 4 on 40 mM) in the first stage for producing biomass.     

Fatty acid desaturase-6 (Fad6) is required for salt tolerance in Arabidopsis thaliana

Fatty acid desaturases play important role in plant responses to abiotic stresses including cold, high temperature, drought, and osmotic stress. In this work, we provide the evidence that Fad6, a chloroplast desaturase, is required for salt tolerance during the early seedling development of Arabidopsis. Expression of Fad6 was responsive to salt and osmotic stress. Compared with the wild-type plants, the fad6 mutant showed reduced tolerance to salt stress, and accumulated more Na⁺ and less K⁺ under high NaCl stress condition. Furthermore, cellular oxidative damage was more severe in fad6 when treated with high concentrations of NaCl, as indicated by increased electrolyte leakage rate and malondialdehyde production, as well as by decreased activities of anti-oxidative enzymes. All these results suggest that Fad6 is required for salt resistance in Arabidopsis.     

The oxidative stress caused by NaCl in Azolla caroliniana is mitigated by nitrate

In order to assess the role of the antioxidant defense system against salt treatment, the activities of some antioxidative enzymes and levels of some nonenzymatic antioxidants were estimated in Azolla caroliniana subjected to NaCl treatment (50 mM) for 10 days in absence or presence of nitrate. In A. caroliniana, salt treatment in absence of nitrate preferentially enhanced electrolyte leakage, lipid peroxidation, and H₂O₂ content. Also, the specific activitiy of guaiacol peroxidase (POX), glutathione reductase (GR), catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) increased. In addition, reduced glutathione level increased and consequently, glutathione/oxidized glutathione (GSH/GSSG) ratio increased. Accumulation of Na⁺ increased significantly by salinity stress which resulted in a significant decrease in K⁺ accumulation, accordingly, K⁺/Na⁺ ratio decreased. Replacement of potassium chloride by potassium nitrate in nutrient solution under salt stress (50 mM NaCl) exhibited a reduction in electrolyte leakage, lipid peroxidation, and H₂O₂ contents. Conversely, the specific activity of APX, POX, GR, CAT, and SOD increased. The content of total ascorbate decreased, in contrast, reduced and GSSG increased and the ratio of GSH/GSSG increased 2.3-fold compared to the control value. Sodium ion accumulation was minimized in the presence of nitrate, potassium ion accumulation increased and as a result, K⁺/Na⁺ ratio increased when compared with the corresponding salinized plants. The differential changes in the specific activity of antioxidant enzymes due to NaCl treatment and nitrate may be useful as markers for recognizing salt tolerance in A. caroliniana.     

The effect of calcium on the antioxidant systems in the halophyte <Emphasis Type="Italic">Cakile maritima</Emphasis> under salt stress

The purpose of the current investigation was to study the effect of Ca²⁺ (0, 3.5 and 20 mM concentrations) on the antioxidant systems in the halophyte Cakile maritima under NaCl stress (0, 100, 200 and 400 mM NaCl). Plants treated with both moderate calcium (3.5 mM) and salt levels (100 mM) showed the maximum growth, and the addition of 20 mM calcium to the nutrient media did not significantly reduce the growth under the moderate salt treatment. The absence of calcium associated with high salt concentration induced a strong reduction of biomass production. The tolerance of C. maritima at moderate salinity and calcium was related with the lowest values of the parameters indicative of oxidative stress (malondialdehyde, electrolyte leakage and hydrogen peroxide concentration). This was accompanied with a higher peroxidase, superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase activities. In contrast, in the absence of calcium, those enzymes showed the lowest activities under all salt treatments. As a whole, it can be noticed that salt tolerance was improved by moderate calcium concentration; however, the absence of calcium has a drastic effect on C. maritima.     

Characterization of <Emphasis Type="Italic">Brassica juncea</Emphasis> antioxidant potential under salinity stress

Present study characterizes the anti-oxidative defense potential of four Brassica juncea varieties, Pusa Jaikisan, Varuna, RLM-198, and CS-52, differing in their ability to withstand salinity stress. 7-day-old seedlings raised in MS medium supplemented with 0, 50, 100, and 150 mM NaCl were used to monitor changes in the growth profile, level of stress marker molecules, and activities of important antioxidant enzymes. Increasing NaCl concentration resulted in a significant (P ≤ 0.05) reduction of shoot fresh and dry mass and vigor index in all the varieties tested. Maximum reduction in growth was recorded for RLM-198 while CS-52 maintained better growth characteristics. Varuna and RLM-198 exhibited a limited increase in superoxide dismutase, ascorbate peroxidase, and total peroxidase activity under increasing salinity. These varieties also recorded maximum salt stress-induced damage in terms of increased lipid peroxidation, H₂O₂ content, and electrolyte leakage. On the other hand, CS-52 recorded maximum proline accumulation with minimum levels of H₂O₂, electrolyte leakage, and malondialdehyde contents. With increasing salinity stress, CS-52 recorded maximal increase in the activity of antioxidant enzymes. However, catalase activity did not correlate with alterations in H₂O₂ levels under stress. Interestingly, a lower superoxide dismutase:ascorbate peroxidase ratio in CS-52 correlated with stress tolerance trait, while a comparatively higher superoxide dismutase:ascorbate peroxidase ratio in RLM-198 marked the susceptible nature of the variety. Our results propose that superoxide dismutase:ascorbate peroxidase ratio is the critical factor, determining the degree of stress tolerance in Brassica juncea.     

Effect of sodium chloride-induced stress on growth, proline, glycine betaine accumulation, antioxidative defence and bacoside A content in in vitro regenerated shoots of Bacopa monnieri (L.) Pennell

Growth, osmotic adjustment, antioxidant enzyme defense and the principle medicinal component bacoside A were studied in the in vitro raised shoot cultures of Bacopa monnieri, a known medicinal plant, under different concentrations of NaCl [0.0 (control), 50, 100, 150 or 200 mM]. A sharp increase in Na⁺ content was observed at 50 mM NaCl level and it was about 6.4-fold higher when compared with control. While Na⁺ content increased in the shoots with increasing levels of NaCl in the medium, both K⁺ and Ca²⁺ concentrations decreased. Significant reduction was observed in shoot number per culture; shoot length, fresh weight (FW), dry weight (DW) and tissue water content (TWC) when shoots were exposed to increasing NaCl concentrations (50–200 mM) as compared with the control. Decrease in TWC was not significant at higher NaCl level (150 and 200 mM). At 200 mM NaCl, growth of shoots was adversely affected and microshoots died under prolonged stress. Minimum damage to the membrane as assessed by malondialdehyde (MDA) content was noticed in the controls in contrast to sharp increase of it in NaCl-stressed shoots. Higher amounts of free proline, glycinebetaine and total soluble sugars (TSS) accumulated in NaCl-stressed shoots indicating that it is a glycinebetaine accumulator. About 2.11-fold higher H₂O₂ content was observed at 50 mM NaCl as compared with control and it reached up to 7.1-folds more at 200 mM NaCl. Antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase) also increased with a rise in NaCl level. Increase in bacoside A, a triterpene saponin content was observed only up to 100 mM NaCl level. Higher salt concentrations inhibited the accumulation of bacoside A. It appears from the data that accumulation of osmolytes, ions and elevated activities of antioxidant enzymes play an important role in osmotic adjustment in shoot cultures of Bacopa under salt stress.     

Effects of optimal and supra-optimal salinity stress on antioxidative defence,osmolytes and in vitro growth responses in <Emphasis Type="Italic">Sesuvium portulacastrum</Emphasis> L.

The effect of optimal and supra-optimal concentrations (0, 200, 400 or 600 mM) of NaCl on the growth, osmotic adjustment and antioxidant enzyme defence was studied in the in vitro cultures of Sesuvium portulacastrum. A significant increase in growth, tissue water content (TWC) and fresh to dry weight ratio (FW/DW) was observed in the shoots exposed to 200 mM salt. Minimum damage to the membrane in terms of low relative electrolytic leakage (REL) and malondialdehyde (MDA) content and better osmotic adjustment at 200 mM salt stress was coupled with the higher accumulation of sodium ions and total soluble sugars as against low proline and glycine betaine contents. A fine tuning of antioxidant enzyme activities (superoxide dismutase, catalase and ascorbate peroxidase) was also found to be responsible for the optimum growth of shoots. In contrast, sub-optimal (0 mM) and supra-optimal concentrations (400–600 mM) of NaCl significantly affected the growth, water status and increased the REL as well as MDA content of the shoots due to the accumulation of toxic concentrations of saline ions. The highest accumulation of proline and glycine betaine in addition to antioxidant enzyme activities exhibited higher osmotic adjustment and survival of the shoots under sub- or supra-optimal concentrations of NaCl as a penalty to reduced growth.     

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

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