Responses of Ceriops Roxburghiana to NaCl Stress

Responses of Ceriops roxburghiana Arn. leaves to the sodium chloride, applied at different concentrations (ranging from 100 to 600 mM), has been evaluated. Total amino acid content decreased with increasing NaCl concentration, while the protein content increased significantly up to 400 mM concentration and decreased thereafter. Total sugar content decreased at concentrations beyond 400 mM. Proline and glycine betaine were accumulated with increasing NaCl concentration. Protease and ATPase activities were increased whereas proline oxidase activity were decreased with increasing salinity. Peroxidase and malate dehydrogenase (NADH-MDH) activities did not significantly differ under various NaCl concentrations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Separate and combined effects of silicon and selenium on salt tolerance of wheat plants

Soil salinity is the leading global abiotic stress which limits agricultural production with an annual increment of 10%. Therefore; a pot experiment was conducted with the aim to alleviate the salinity effects on wheat seedlings through exogenous application of silicon (Si) and selenium (Se). Treatments included in the study were viz. (Ck) control (no NaCl nor Si and Se added), only salinity (50 mM NaCl), salinity + Si (50 mM NaCl with 40 mM Si), salinity + Se (50 mM NaCl with 40 mM Se) and salinity + Si + Se (50 mM NaCl + 40 mM Si + 40 mM Si). The salt stress impaired the growth (root and shoot dry weight, root: shoot ratio, seedlings biomass), water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings. Nonetheless, the foliar application of Si and Se alone and in combination improved the growth, water relations, photosynthetic attributes, transpiration rate and chlorophyll contents of wheat seedlings under stressed conditions. Moreover, an increase in antioxidant enzyme activity and accumulation of osmo-protectants (proline, soluble protein and soluble sugar) was noted under stressed conditions, which was more pronounced in wheat seedling which experienced combined application of Si and Se. To conclude that, foliar application of Si alone mitigated the adverse effect of salinity, while the combined application of Si and Se was proved to be even more effective in alleviating the toxic effects of salinity stress on wheat seedlings.     

Differential responses of antioxidative enzymes and lipid peroxidation to salt stress in salt-tolerant Plantago maritima and salt-sensitive Plantago media

The changes in plant growth, relative water content (RWC), stomatal conductance, lipid peroxidation and antioxidant system in relation to the tolerance to salt stress were investigated in salt-tolerant Plantago maritima and salt-sensitive Plantago media. The 60 days old P. maritima and P. media seedlings were subjected to 0, 100 and 200 mM NaCl for 7 days. Reduction in shoot length was higher in P. media than in P. maritima after exposure to 200 mM NaCl, but 100 mM NaCl treatment did not show any effect on shoot length of P. maritima. Shoot dry weight decreased in P. media and did not change in P. maritima. Two hundred millimolar NaCl treatment had no effect on leaf RWC in P. maritima, but it was reduced in P. media. Salt stress caused reduction in stomatal conductance being more pronounced in P. media than in P. maritima. Activities of superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2) decreased in P. media with increasing salinity. Ascorbate peroxidase (APX; EC 1.11.1.11) activity in leaves of P. media was increased and showed no change under 100 and 200 mM NaCl, respectively. However, activities of CAT, APX and GR increased under 200 mM NaCl while their activities did not change under 100 mM NaCl in P. maritima. SOD activity in leaves of P. maritima increased with increasing salinity. Concomitant with this, four SOD activity bands were identified in leaves of P. maritima, two bands only were observed in P. media. Peroxidase (POX; EC 1.11.1.7) activity increased under both salt concentrations in P. maritima, but only under 200 mM NaCl in P. media. Confirming this, five POX activity bands were identified in leaves of P. maritima, but only two bands were determined in P. media. Malondialdehyde levels in the leaves increased under salt stress in P. media but showed no change and decreased in P. maritima at 100 and 200 mM NaCl, respectively. These results suggest that the salt-tolerant P. maritima showed a better protection mechanism against oxidative damage caused by salt stress by its higher induced activities of antioxidant enzymes than the salt-sensitive P. media.     

Salicylic acid-induced salinity tolerance in corn grown under NaCl stress

Effects of salicylic acid on some physiological and biochemical characteristics of maize ( Zea mays L.) seedlings under NaCl stress were studied. Pre-soaking treatments of NaCl (0, 50, 100 and 200 mM) were given to maize seeds in the presence as well as in the absence of 0.5 mM salicylic acid. Two-week-old maize seedlings exhibited significant decrease in dry weight, root length, shoot length and leaf area on 6 h exposure of 100 and 200 mM NaCl stress. Photosynthetic pigments and NR activity in leaves decreased sharply with increasing stress levels. Both proline content and lipid peroxidation (measured in terms of MDA) levels increased significantly under saline conditions. However, seedlings pretreated with 0.5 mM salicylic acid along with the salinity levels showed enhancement in growth parameters, photosynthetic pigments, NR activity while, free proline and MDA levels decreased. The results showed that salt-induced deleterious effects in maize seedlings were significantly encountered by the pretreatment of salicylic acid. It is concluded that 0.5 mM salicylic acid improves the adaptabilities of maize plants to NaCl stress.     

Differential sensitivity of stomatal and non-stomatal components to NaCl or Na2SO4 salinity in horsegram, Macrotyloma uniflorum (Lam.)

14CO2 assimilation rate (P), leaf diffusive conductance (gs), photosynthetic electron flow, and activities of enzymes of Calvin cycle were studied in a horsegram [Macrotyloma uniflorum (Lam.)] in response to salinity induced by NaCl or Na2SO4. A significant reduction in P and gs by both salt treatments was registered. Na2SO4 caused a greater reduction in gs than the NaCl salinity. Studies with isolated chloroplasts confirmed a greater sensitivity to NaCl than to Na2SO4. Salinity inhibited the photosynthetic electron transport. The activity of ribulose-1,5-bisphosphate carboxylase (E.C.4.1.1.39) was under salinity inhibited more than the activities of other three enzymes of the Calvin cycle, ribulose-5-phosphate kinase (E.C.2.7.1.19), ribose-5-phosphate isomerase (E.C.5.3.16), and NADP-glyceraldehyde-3-phosphate dehydrogenase (E.C.1.2.13). These inhibitions lead to a reduced capacity for ribulose-1,5-bisphosphate regeneration. Isolated chloroplasts extracted from salt stressed plants and supplemented with the substrates of Calvin cycle could elevate P, but the P was always lower than in the controls. Decreased P in horsegram exposed to high salinity can be attributed to both stomatal and non-stomatal components, however, the sensitivity to the salt source, NaCl or Na2SO4, was different.     

Salinity tolerance and antioxidant status in cotton cultures

This investigation focuses upon cell growth and antioxidant status in cultured cells of cotton (Gossypium herbaceum) cvs. Dhumad (salt-tolerant, TOL), H-14 (medium salt-tolerant, MED), and RAhs-2 (salt-sensitive, SEN) exposed to saline stress (50-200 mM NaCl). Mean (+/- SEM) callus fresh weight (f.wt.) and dry weight (d.wt.) gains were significantly (p <.05) greater on Murashige and Skoog (MS) [1]-based medium with 50 mM NaCl for the TOL cv. (62% and 16%, respectively) over NaCl-free controls (2020 +/- 45 and 166 +/- 4 mg, respectively); comparable differences were not observed for the MED cv. A significant (p <.05) decrease in mean f.wt. occurred with the SEN cv. exposed to 50 mM NaCl. For all cvs., there were (p <.05) reductions in mean f.wts. in medium with >or=100 mM NaCl. At 200 mM NaCl, mean f.wt. decreases were 52% (TOL), 89% (MED), and 91% (SEN), respectively. A strong correlation existed between antioxidant status and growth of cells with NaCl. Superoxide dismutase and glutathione reductase activities increased with increasing salinity in the TOL cv. to maximum values of 26.3 +/- 1.1 U mg(-1) protein and 1.05 +/- 0.01 AB(340 nm) min(-1) mg(-1) protein, respectively, at 150 mM NaCl; for the MED and SEN cvs., there were no changes in activities of these enzymes between control and salt treatments. Catalase activity decreased progressively with increasing salt concentration in all cvs. except for SEN with 100 mM NaCl, where mean catalase activity (1.75 +/- 0.04 AB(240 nm) min(-1) mg(-1) protein) was greater (p <.05) than control (1.13 +/- 0.08). Overall, cultured cotton cells provide an experimental system for investigating the role of antioxidants in salt tolerance at the cellular level.     

Stomatal limitation of photosynthesis and reduced growth of the halophyte, Plantago maritima L., at high salinity

Abstract. Plantago maritima L. was grown at three levels of salinity, 50, 200, 350 mol m⁻³ NaCl, and the effects on growth, ion content and photosynthetic capacity were studied. Shoot and root dry weight, leaf production and leaf length were all substantially reduced in plants grown at high salinity. Total leaf area of plants grown at 350 mol m⁻³ NaCl was only 20% of that in plants at low salinity. Both the Na⁺ and K⁺ content of leaves and roots increased with external salinity. There was no change in the Na⁺/K⁺ ratio of leaves or roots at different salinity levels. Despite the large reductions in growth and high accumulation of Na⁺ ions, leaf photosynthetic rate was only slightly reduced by salinity stress. The reduction in photosynthesis was not caused by reduced biochemical capacity as judged by photosynthetic response to intercellular CO₂ and by ribulose-1,5-bisphosphate carboxylase activity, but was due to reduced leaf conductance and low intercellular CO₂ concentration. The increased stomatal limitation of photosynthesis resulted in higher water-use efficiency of plants grown at high salinity.     

Effect of NaCl on Biomass and Contents of Sugars, Proline and Proteins in Seedlings and Leaf Explants of Nicotiana tabacum Grown in vitro

Effects of NaCl on growth in vitro and contents of sugars, free proline and proteins in the seedlings and leaf explants of Nicotiana tabacum cv. Virginia were investigated. The fresh and dry mass of the seedlings decreased under salinity. These growth parameters in leaf explants decreased at 50 mM NaCl and increased up to 150 mM NaCl and then decreased at higher level of salinity. Free proline content in both seedlings and leaf explants increased and polysaccharide content decreased continuously with increasing of NaCl concentration. Reducing sugars, oligosaccharides, soluble sugars and total sugars contents in both seedlings and leaf explants decreased up to 150 mM NaCl and then increased at higher concentrations of NaCl.     

Photosynthetic activity and leaf antioxidative responses of Atriplex portulacoides subjected to extreme salinity

Responses of Atriplex portulacoides upon 40-day-long exposure to salinity (0?C1,000?mM NaCl) were investigated. Mother plants originated from a sabkha located in a semi-arid region of Tunisia. The plant relative growth rate and leaf expansion increased significantly at 200?mM NaCl but decreased at higher salinities. Interestingly, the plants survived salinity as high as 1,000?mM NaCl without displaying salt-induced toxicity symptoms. Despite significant increase in leaf Na⁺ and Cl^? concentrations upon salt treatment, no significant effect on leaf relative water content was registered. Chlorophyll contents and the gas exchange parameters showed a significant stimulation at the optimal salinity (200?mM NaCl) followed by a decline at higher salinities. Extreme salinity hardly impacted the maximal efficiency of photosystem II photochemistry (F _v/F _m), but a marked decrease in the relative quantum yield of photosystem II (??_PSII) was observed, along with a significant increase in non-photochemical quenching (NPQ). Leaf malondialdehyde and carotenoid contents were generally unaffected following salt exposure, whereas those of anthocyanins, polyphenols, and proline increased significantly, being maximal at 1,000?mM NaCl. Leaf superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11), and glutathione reductase (EC 1.6.4.2) activities were significantly stimulated by salinity, whereas catalase (EC 1.11.1.6) activity was maximal in the 0?C400?mM NaCl range. As a whole, protecting the photosynthetic machinery from salt-induced photodamage together with the sustained antioxidant activity may account for the performance of A. portulacoides under high salinity.     

Differential responses to salinity of two Atriplex halimus populations in relation to organic solutes and antioxidant systems involving thiol reductases

Atriplex halimus L. is a xero-halophyte species widespread in the Mediterranean basin. The tolerance to water stress and high salinity of two Atriplex populations from semi-arid (Djelfa) and arid saline (Laghouat) Algerian regions has been investigated in relation with organic solutes and antioxidant systems. Whereas no noticeable difference was observed between the two populations under water stress resulting from withholding watering or PEG treatment, Laghouat plants display significantly higher fresh and dry weights than Djelfa plants when exposed to high salinity. At 300mM NaCl, Laghouat plants exhibit higher concentrations in Na(+), proline and quaternary ammonium compounds, and a higher catalase activity than Djelfa plants. We then analysed the involvement of recently characterized plastidial thiol reductases, peroxiredoxins (Prxs) and methionine sulphoxide reductases (MSRs), key enzymes scavenging organic peroxides and repairing oxidized proteins, respectively. Upon salt treatment (300mM NaCl), we observed higher amounts of PrxQ and over-oxidized 2-Cys Prx in Laghouat than in Djelfa. An increased abundance of plastidial MSRA and a higher total MSR activity were also noticed in Laghouat plants treated with 300mM NaCl compared to Djelfa ones. We propose that mechanisms based on organic solutes and antioxidant enzymes like catalases, peroxiredoxins and MSRs party underlie the better tolerance of the Laghouat population to high salt.     

Salt-induced lipid changes in Catharanthus roseus cultured cell suspensions

Salt treatment strongly affected cell growth by decreasing dry weight. Exposure of Catharanthus roseus cell suspensions to increasing salinity significantly enhanced total lipid (TL) content. The observed increase is mainly due to high level of phospholipids (PL). Hundred mM NaCl treatment increased phospholipid species phosphatidylcholine (PC) and phosphatidylethanolamine (PE), whereas it reduced glycolipid ones monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) but not sulfoquinovosyldiacylglycerol (SQDG). Moreover, fatty acid composition was clearly modified when cells were cultured in the presence of 100 mM NaCl, whereas only few changes occurred at 50 mM. Salt treatment decreased palmitic acid (16:0) level and increased that of linolenic acid (18:2). Such effect was observed in phospholipid species PC and PE and in glycolipid DGDG. Double bond index (DBI) was enhanced more than 2-fold in fatty acids of either glycolipids or phospholipids from cells submitted to 100 mM NaCl. Free sterol content was also significantly enhanced, especially at 100 mM NaCl, whereas free sterols/phospholipids (St/PL) ratio was slightly decreased. All these salt-induced changes in membrane lipids suggest an increase in membrane fluidity of C. roseus cells.     

Effect of salt stress on growth parameters, enzymatic antioxidant system, and lipid peroxidation in wild chicory (Cichorium intybus L.)

Efficient utilization of saline land for food cultivation can increase agricultural productivity and rural income. To obtain information on the salt tolerance/susceptibility of wild chicory (Cichorium intybus L.), the influence of salinity (0–260 mM NaCl) on chicory seed germination and that of two salinity levels of irrigation water (100 and 200 mM NaCl) on plant growth, antioxidative enzyme activity, and accumulation of proline and malondialdehyde (MDA) were investigated. The trials were performed outdoors, in pots placed under a protective glass covering, for two consecutive years. Seeds showed a high capacity to germinate in saline conditions. The use of 100 mM NaCl solution resulted in 81 % germination, whereas seed germinability decreased below 40 % using salt concentrations above 200 mM NaCl. Wild chicory showed tolerance to medium salinity (100 mM NaCl), whereas a drastic reduction in biomass was observed when 200 mM NaCl solution was used for irrigation. MDA, present in higher amounts in leaves than in roots, decreased in both tissues under increasing salinity. Proline content increased remarkably with the level of salt stress, more so in roots than in leaves. In salt stress conditions, the activity of antioxidant enzymes (APX, CAT, POD, SOD) was enhanced. The electrophoretic patterns of the studied enzymes showed that the salinity of irrigation water affected only the intensity of bands, but did not activate new isoforms. Our results suggest that wild chicory is able to grow in soil with moderate salinity by activating antioxidative responses both in roots and leaves.     

Effects of salicylic acid and salinity on apoplastic antioxidant enzymes in two wheat cultivars differing in salt tolerance

The effects of salicylic acid (SA) and salinity on the activity of apoplastic antioxidant enzymes were studied in the leaves of two wheat (Triticum aestivam L.) cultivars: salt-tolerant (Gerek-79) and salt-sensitive (Bezostaya). The leaves of 10-d-old seedlings grown at nutrient solution with 0 (control), 250 or 500 mM NaCl were sprayed with 0.01 or 0.1 mM SA. Then, the activities of catalase (CAT), peroxidase (POX) and superoxide dismutase (SOD) were determined in the fresh leaves obtained from 15-d-old seedlings. The NaCl applications increased CAT and SOD activities in both cultivars, compared to those of untreated control plants. In addition, the NaCl increased POX activity in the salt-tolerant while decreased in the salt-sensitive cultivar. In control plants of the both cultivars, 0.1 mM SA increased CAT activity, while 0.01 mM SA slightly decreased it. SA treatments also stimulated SOD and POX activity in the salt-tolerant cultivar but significantly decreased POX activity and had no effect on SOD activity in the saltsensitive cultivar. Under salinity, the SA treatments significantly inhibited CAT activity, whereas increased POX activity. The increases in POX activity caused by SA were more pronounced in the salt-tolerant than in the salt-sensitive cultivar. SOD activity was increased by 0.01 mM SA in the salt-tolerant while increased by 0.1 mM SA treatment in the salt-sensitive cultivar.     

<Emphasis Type="Italic">Piriformospora indica</Emphasis> Alleviates Salinity by Boosting Redox Poise and Antioxidative Potential of Tomato

More than 20% of irrigated land has been influenced by salt stress, decreasing crop production. In this research, we investigated the effect of different levels of salinity (0, 50, 100 and 150 mM NaCl) and the efficiency of Piriformospora indica on growth, biochemical traits, antioxidative defense system in tomato (Solanum lycopersicum L.). NaCl stress reduced chlorophyll content, height and biomass of plants. Higher level of salinity (150 mM) declined the plant height by 22.65%, total dry weight by 56.44% and total chlorophyll by 44.34%, however, P. indica inoculation raised plant height by 43.47%, dry weight by 69.23% and total chlorophyll content by 48.09%. Salinity stress increased H₂O₂, malondialdehyde (MDA), superoxide anion and 1,1-diphenyl-2-picrylhydrazyl (DPPH) level in leaves and roots tomato seedlings. However, P. indica inoculation reduced H₂O₂, MDA and superoxide anion and enhanced DPPH compared to non-inoculated plants at all NaCl levels. The total phenol and flavonoids increased with NaCl treatment. On the other hand, the total phenolic and flavonoid increased more in P. indica inoculated plants compared to non-inoculated ones. Moreover, inoculation of P. indica implicated noteworthy improvement of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) activity in tomato upon salinity. Notably, colonization with P. indica significantly improved the content of reduced ascorbic acid (AsA), glutathione (GSH) and redox ratio in the tomato plants under salinity resulting in reduced redox state. Our findings confirmed that salinity had negative effect on tomato seedling; however, P. indica inoculation increased tolerance to salinity by improving the content of phenolic compounds, non-enzymatic antioxidants, and increasing the activity of antioxidant enzymes.     

Growth and Fatty Acid Composition of Borage (Borago officinalis L.) Leaves and Seeds Cultivated in Saline Medium

The effects of salinity on growth and fatty acid composition of borage (Borago officinalis L.) leaves and seeds grown in hydroponic medium were investigated. Three different levels of NaCl (25, 50, and 75 mM) were applied. The first results showed that salinity significantly reduced plant growth by 56.5 % at 75 mM compared with the control, suppressed seed yield at 50 and 75 mM, and increased lipid peroxidation. Raising NaCl concentrations led to an important decrease in total fatty acid (TFA) content by 77 % at 75 mM NaCl. Moreover, the polyunsaturated fatty acid (PUFA) content decreased, whereas the saturated fatty acids increased with respect to increasing salinity. The 25 mM NaCl level did not modify the fatty acid composition of seeds and their contents.     

5-Aminolevulinic acid improves photosynthetic gas exchange capacity and ion uptake under salinity stress in oilseed rape (Brassica napus L.)

Salinity is one of the major constraints in oilseed rape (Brassica napus L.) production. One of the means to overcome this constraint is the use of plant growth regulators to induce plant tolerance. To study the plant response to salinity in combination with a growth regulator, 5-aminolevulinic acid (ALA), oilseed rape plants were grown hydroponically in greenhouse conditions under three levels of salinity (0, 100, and 200 mM NaCl) and foliar application of ALA (30 mg/l). Salinity depressed the growth of shoots and roots, and decreased leaf water potential and chlorophyll concentration. Addition of ALA partially improved the growth of shoots and roots, and increased the leaf chlorophyll concentrations of stressed plants. Foliar application of ALA also maintained leaf water potential of plants growing in 100 mM salinity at the same level as that of the control plants, and there was also an improvement in the water relations of ALA-treated plants growing in 200 mM. Net photosynthetic rate and gas exchange parameters were also reduced significantly with increasing salinity; these effects were partially reversed upon foliar application with ALA. Sodium accumulation increased with increasing NaCl concentration which induced a complex response in the macro-and micronutrients uptake and accumulation in both roots and leaves. Generally, analyses of macro- (N, P, K, S, Ca, and Mg) and micronutrients (Mn, Zn, Fe, and Cu) showed no increased accumulation of these ions in the leaves and roots (on dry weight basis) under increasing salinity except for zinc (Zn). Foliar application of ALA enhanced the concentrations of all nutrients other than Mn and Cu. These results suggest that under short-term salinity-induced stress (10 days), exogenous application of ALA helped the plants improve growth, photosynthetic gas exchange capacity, water potential, chlorophyll content, and mineral nutrition by manipulating the uptake of Na⁺.     

Effect of salinity on germination,phytase activity and phytate content in lettuce seedling

Seeds of four lettuce (Lactuca sativa L.) varieties (Romaine, Augusta, Vista and Verte) differing in their salt sensitivity were sown at 0 (Control), 50, 100 and 150 mM NaCl. The final germination percentage decreased with the increasing salinity and was annulated at the highest salt concentration in Vista and Verte, the most sensitive varieties. However, in the less sensitive ones, Romaine and Augusta, it was slightly modified at 50 and 100 mM NaCl and then decreased by 50% compared with the control, at 150 mM. The effects of NaCl 100 mM on seedling growth, phytase activities, phytate and inorganic phosphorus contents were studied in Romaine and Vista showing different behaviours towards salinity. Radicle and hypocotyl length and fresh and dry weights were reduced by salt treatment in both varieties. In addition, radicle phytase activity exhibited an increase in Romaine (less sensitive) and a decrease in Vista (more sensitive). In hypocotyl, this activity showed no difference with the control in the two varieties. However, in cotyledons, and during early hours after germination, salinity decreased phytase activity in both varieties whereas in the later hours (72–96 h) this activity reached the value of the control in Romaine. The enhancement of phytase activity was concomitant with an increase in orthophosphate content and a decrease in phytate reserve. These results suggest that salt presence in the medium delays Pi remobilization from phytate stock, but stimulates assimilation of phosphorus more than its accumulation in the organs of the two lettuce varieties.     

Salinity-induced Physiological Modification in the Callus from Halophyte Nitraria tangutorum Bobr.

Little is known about the physiological adaptation mechanisms of the desert halophyte Nitraria tangutorum Bobr. to the environment. In this study, callus from Nitraria tangutorum Bobr. was used to investigate physiological responses to salinity and the regulatory function of nitric oxide (NO) on catalase (CAT) activity. Increased dry weight and soluble proteins were observed in the callus exposed to lower salinity (50 and 100 mM NaCl), whereas 200 mM NaCl led to significant decreases of these two growth parameters, and the levels of proline and soluble carbohydrates also were enhanced under NaCl treatment. In addition, short-term stress from 50 mM NaCl and the application of lower sodium nitroprusside (SNP, a NO donor) concentration resulted in decreased levels of malondialdehyde (MDA). In contrast, higher concentrations of NaCl and SNP induced significant oxidative damage in Nitraria tangutorum Bobr. callus. Analysis based on the fluorescent probe DAF-FM DA revealed that NaCl and SNP treatment led to enhanced levels of NO in the callus cells. Moreover, the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) reduced endogenous NO concentrations and abolished the enhancement in dry weight and the decrease in MDA level under 50-mM-NaCl treatment. CAT activity increased under salt stress, and the 50-mM-NaCl effect was alleviated by treatment with c-PTIO or the nitric oxide synthase inhibitor N^ω-nitro-l-arginine. We suggest that Nitraria tangutorum Bobr. callus exhibited tolerance to lower-salinity stress. We also showed that increased NO generation in response to salinity might be associated with regulation of growth, protection against oxidative damage, and excitation of CAT activity in Nitraria tangutorum Bobr. callus under salt stress.     

Change in antioxidant enzymes activity and some morpho-physiological characteristics of strawberry under long-term salt stress

The effects of long term salinity on some morpho-physiological characteristics were studied in strawberry Kurdistan and Queen elisa cultivars. Vegetative and biochemical traits were measured in strawberry cultivars subjected to three levels of salinity including 0, 40 and 80 mM at 20, 40 and 60th days after NaCl addition. Results showed that in both cultivars the dry weight of plant organs decreased in response to NaCl, except of crown weight in cv. Kurdistan. Root to shoot ratio increased due to a greater reduction in above ground biomass under salinity. Strawberry cultivars tended to decrease their stomatal conductance, RWC, proline, soluble carbohydrates and proteins during the different evaluation periods. Compared to the 20th day, peroxidase activity decreased at 80 mM during 40 and 60 days in cv. Queen elisa. On the contrary, ascorbate peroxidase activity elevated until the 40th day and decreased afterwards, in addition application of 40 and 80 mM NaCl increased the ascorbate peroxidase activity of both studied cultivars. Catalase activity increased from 20th until 60th days in cv. Queen elisa, while showed increase in cv. Kurdistan until day 40 and then decreased again at day 60. Application of 40 and 80 mM NaCl resulted in an increase in peroxidase, ascorbate peroxidase and catalase activities of both cultivars. The Queen elisa cv. showed lower tolerance index (45.88%) compared with cv. Kurdistan (67.97%). Finally, higher salinity resistance of cv. Kurdistan is probably associated with its ability to maintain higher RWC and higher activity of antioxidant enzymes.     

The modulation of various physiochemical changes in <Emphasis Type="Italic">Bruguiera cylindrica</Emphasis> (L.) Blume affected by high concentrations of NaCl

Bruguiera cylindrica is a major mangrove species in the tropical mangrove ecosystems and it grows in a wide range of salinities without any special features for the excretion of excess salt. Therefore, the adaptation of this mangrove to salinity could be at the physiological and biochemical level. The 3-month-old healthy plantlets of B. cylindrica, raised from propagules were treated with 0 mM, 400 mM, 500 mM and 600 mM NaCl for 20 days under hydroponic culture conditions provided with full strength Hoagland medium. The modulation of various physiochemical changes in B. cylindrica, such as chlorophyll a fluorescence, total chlorophyll content, dry weight, fresh weight and water content, Na⁺ accumulation, oxidation and antioxidation (enzymatic and non-enzymatic) features were studied. Total chlorophyll content showed very minute decrease at 500 mM and 600 mM NaCl treatment for 20 days and the water content percentage was decreased both in leaf and root tissues with increasing concentration. A significant increase of Na⁺ content of plants from 84.505 mM/plant dry weight in the absence of NaCl to 543.38 mM/plant dry weight in plants treated with 600 mM NaCl was recorded. The malondialdehyde and the metabolites content associated with stress tolerance (amino acid, total phenols and proline) showed an increasing pattern with increasing NaCl concentration as compared to the control in both leaf and root tissues but the increase recorded in plantlets subjected to 500 mM was much less, indicating the tolerance potential of this species towards 500 mM NaCl. The significant decrease of sugar content was found only in 600 mM NaCl on 20 days of treatment, showing that the process of sugar synthesis was negatively affected but the same process remains less affected at 500 mM NaCl. A slight reduction in ascorbate and glutathione content and very less increase in carotenoid content were observed at 500 mM and 600 mM NaCl stress. Antioxidant enzymes (APX, GPX, SOD and CAT) showed an enhanced activity in all the treatments and the increased activity was more significant in 600 mM treated plants. The result establishes that B. cylindrica tolerates high NaCl concentration, to the extent of 500 mM NaCl without any major inhibition on photosynthesis and metabolite accumulation. Understanding the modulation of various physiological and biochemical changes of B. cylindrica at high levels of NaCl will help us to know the physiochemical basis of tolerance strategy of this species towards high NaCl.