Modulation of symbiotic efficiency and nodular antioxidant enzyme activities in two <Emphasis Type="Italic">Phaseolus vulgaris</Emphasis> genotypes under salinity

To analyse nodular expression of antioxidant enzymes depending on plant genotype and salinity, two Phaseolus vulgaris genotypes, tolerant BAT477 and sensitive COCOT, were inoculated with the reference strain Rhizobium tropici CIAT899 and grown under 25 and 50 mM NaCl. Plant growth, nodulation and nitrogen fixing activity measured by the acetylene reducing activity (ARA) as an indicator of nitrogenase (E.C. 1.7.9.92) activity were more affected by salt concentrations in COCOT than in BAT477, particularly with 50 mM NaCl. Electrophoresis analysis of antioxidant enzymes in nodules, roots and free-living rhizobia showed that only catalase (CAT E.C. 1.11.1.6) isoenzymes varied with genotype. The sensitive genotype showed lower antioxidant enzyme activities than tolerant genotype and it was more affected by salinity. In the tolerant genotype catalase and ascorbate peroxidase (APX, E.C. 1.11.1.11) were inhibited by salt stress, whereas superoxide dismutase (SOD, E.C. 1.15.1.1) and peroxidase (POX, E.C. 1.11.1.7) were activated by salinity. Statistical analysis allowed suggesting that tolerance to salinity is associated with a differential regulation of distinct superoxide dismutase and peroxidase activities.     

Distribution of phenolic compounds and antioxidant activity between young and old leaves of Carthamus tinctorius L. and their induction by salt stress

In the present work, we investigated the effect of salt stress on the distribution of safflower (Carthamus tinctorius L.) antioxidant system in relation to leaf age. The study was carried out under growth chamber conditions using seedlings of three cultivars which were subjected to 0 and 50 mM NaCl for 3 weeks. Leaf growth, water content, lipid peroxidation, and phenolic compound (total polyphenols, total flavonoids, and proanthocyanidins) concentration were measured at two leaf stages (young and old leaves). Leaf growth was affected by salinity only in Kairouan cultivar that also showed a significant decrease in old leaf water content. By contrast, Gabes and Tazarka cultivars maintained their old leaf water content constant and showed a reduction in that of young leaves. This could be attributed to a higher aptitude of the latter two cultivars to use absorbed sodium and chloride for osmotic adjustment in old leaves, keeping potassium for specific functions. Salt-induced lipid peroxidation was observed only in old leaves, whereas the accumulation of the major phenolic compounds under saline conditions was higher in young leaves, except in Gabes cultivar where no significant difference was found between the two leaf stages. A significant variability was also found between the three cultivars. The better behavior of salt-challenged leaves of Gabes and Tazarka cultivars compared to that of Kairouan cultivar may be related to their higher water content and the accumulation of polyphenols, in particular flavonoids that were shown to be efficiently involved in the restriction of salt-induced oxidative damages.     

Physiological and antioxidant responses of <Emphasis Type="Italic">Mentha pulegium</Emphasis> (Pennyroyal) to salt stress

Mentha pulegium L. is a medicinal and aromatic plant belonging to the Labiatae family present in the humid to the arid bioclimatic regions of Tunisia. We studied the effect of different salt concentrations on plant growth, mineral composition and antioxidant responses. Physiological and biochemical parameters were assessed in the plant organs after 2 weeks of salt treatment with 25, 50, 75 and 100 mM NaCl. Results showed that, growth was reduced even by 25 mM, and salt effect was more pronounced in shoots (leaves and stems) than in roots. This growth decrease was accompanied by a restriction in tissue hydration and K⁺ uptake, as well as an increase in Na⁺ levels in all organs. Considering the response of antioxidant enzymes to salt, leaves and roots reacted differently to saline conditions. Leaf and root guaiacol peroxidase activity showed an increase by different concentration of NaCl, but superoxide dismutase activity in the same organs showed a slight modification in NaCl-treated leaves and roots. Moreover, polyphenol contents and antioxidant activity were analysed in M. pulegium leaves and roots under salt constraint. The analysis showed an increase of total polyphenol content (2.41–8.17 mg gallic acid equivalent g⁻¹ dry weight) in leaves. However, methanol extract of leaves at 100 mM NaCl displayed the highest DPPH· scavenging ability with the lowest IC₅₀ value (0.27 μg ml⁻¹) in comparison with control which exhibited IC₅₀ equal to 0.79 μg ml⁻¹.     

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.     

The effect of salt stress on lipid peroxidation and antioxidative enzymes in callus of two <Emphasis Type="Italic">Acanthophyllum</Emphasis> species

The changes in lipid peroxidation and the involvement of the antioxidant system in relation to salt stress tolerance were investigated in the callus of Acanthophyllum glandulosum and Acanthophyllum sordidum. The callus was subjected to NaCl stress (50–200 mM) for 40 d. The callus of A. glandulosum was less sensitive to NaCl stress than that of A. sordidum. Increasing concentrations of NaCl from 50 to 200 mM correlated to increased proline content in A. glandulosum. Total protein content was higher in extracts of A. glandulosum than in extracts of A. sordidum under both control and salinity treatments. Compared with A. sordidum, lipid peroxidation and H₂O₂ content were lower and the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase, and glutathione reductase were higher in A. glandulosum under salt stress. Activity staining of antioxidant enzymes separated by native polyacrylamide gel electrophoresis (PAGE) revealed that callus of A. sordidum had five Fe-SOD isoforms and one Mn-SOD isoform, all of which were reduced by salinity. In A. glandulosum, two Mn-SOD, three Fe-SOD, and one Cu/Zn-SOD isoforms were detected. Out of these six SOD isoforms, expression of the Mn-SOD and Fe-SOD isoforms was enhanced at 100 mM and higher NaCl concentrations. Two and six GPX isoforms were detected in A. sordidum and A. glandulosum, respectively. Expression of the single CAT isoform in A. sordidum was preferentially reduced by salinity. In A. glandulosum, the two CAT isoforms showed differential down regulation under NaCl stress, with the CAT2 isoform detected only under control condition. These results suggest that A. glandulosum callus is better protected against salinity-induced oxidative damage by maintaining higher activities of antioxidant enzymes than the callus of A. sordidum.     

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.     

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.     

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.     

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

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

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.     

Responses of salt-tolerant and intolerant wheat genotypes to sodium chloride: Photosynthesis,antioxidants activities,and yield

Physiological responses of two wheat (Triticum aestivum L.) genotypes (salt-tolerant DK961 and salt-sensitive JN17) to increased salt concentrations (50, 100, 150 mM NaCl: NaCl⁵⁰, NaCl¹⁰⁰, NaCl¹⁵⁰) were studied. Photosynthetic capacity, irradiance response curves, contents of soluble sugars, proteins, and chlorophyll (Chl), K⁺/Na⁺ ratio, and activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) in flag leaves were measured on 7 d after anthesis. In control (NaCl⁰) plants, non-significant (p>0.05) differences were found in gas exchange and saturation irradiance (SI) between salt-tolerant (ST) and salt-sensitive (SS) wheat genotypes. However, we found higher soluble sugar and protein contents, K⁺/Na⁺ ratio, and antioxidant enzyme activities, but lower Chl content and yield in ST wheat. Salinity stresses remarkably increased soluble sugar and protein contents and the antioxidant activities, but decreased K⁺/Na⁺ ratio, Chl contents, SI, photosynthetic capacities, and yield, the extent being considerably larger in JN17 than DK961. Although the soluble sugar and protein contents and the antioxidant activities of JN17 elevated more evidently under salt stresses, those variables never reached the high levels of DK961. The antioxidant enzyme activities of SS wheat increased in NaCl⁵⁰ and NaCl¹⁰⁰, but decreased rapidly when the NaCl concentration reached 150 mM. Thus the ST wheat could maintain higher grain yield than the SS one by remaining higher osmoregulation and antioxidative abilities, which led to higher photosynthetic capacity. Hence the ST wheat could harmonize the relationship between CO₂ assimilation (source) and the grain yield (sink) under the experimental conditions.     

Role of Salicylic Acid in Promoting Salt Stress Tolerance and Enhanced Artemisinin Production in Artemisia annua L.

In the present investigation, the role of salicylic acid (SA) in inducing salinity tolerance was studied in Artemisia annua L., which is a major source of the antimalarial drug artemisinin. SA, when applied at 1.00 mM, provided considerable protection against salt stress imposed by adding 50, 100, or 200 mM NaCl to soil. Salt stress negatively affected plant growth as assessed by length and dry weight of shoots and roots. Salinity also reduced the values of photosynthetic attributes and total chlorophyll content and inhibited the activities of nitrate reductase and carbonic anhydrase. Furthermore, salt stress significantly increased electrolyte leakage and proline content. Salt stress also induced oxidative stress as indicated by the elevated levels of lipid peroxidation compared to the control. A foliar spray of SA at 1.00 mM promoted the growth of plants, independent of salinity level. The activity of antioxidant enzymes, namely, catalase, peroxidase, and superoxide dismutase, was upregulated by salt stress and was further enhanced by SA treatment. Artemisinin content increased at 50 and 100 mM NaCl but decreased at 200 mM NaCl. The application of SA further enhanced artemisinin content when applied with 50 and 100 mM NaCl by 18.3 and 52.4%, respectively. These results indicate that moderate saline conditions can be exploited to obtain higher artemisinin content in A. annua plants, whereas the application of SA can be used to protect plant growth and induce its antioxidant defense system under salt stress.     

Effect of salt stress on physiological and antioxidative responses in two species of <Emphasis Type="Italic">Salicornia</Emphasis> (<Emphasis Type="Italic">S. persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>)

The effects of salt stress on growth parameters, free proline content, ion accumulation, lipid peroxidation, and several antioxidative enzymes activities were investigated in S. persica and S. europaea. The seedlings were grown for 2 months in half-strength Hoagland solution and treated with different concentrations of NaCl (0, 85, 170, 340, and 510 mM) for 21 days. The fresh and dry weights of both species increased significantly at 85 and 170 mM NaCl and decreased at higher concentrations. Salinity increased proline content in both the species as compared to that of control. Sodium (Na⁺) content in roots and shoots increased, whereas K⁺ and P_i content in both organs decreased. At all NaCl concentrations, the total amounts of Na⁺ and K⁺ were higher in shoots than in roots. Malondialdehyde (MDA) content declined at moderate NaCl concentrations (85 and 170 mM) and increased at higher levels. With increased salinity, superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPX) activities also increased gradually in both species. In addition, it seems that GPX, CAT, and SOD activities play an essential protective role in the scavenging reactive oxygen species (ROS) in both species. Native polyacrylamide gel electrophoresis (PAGE) indicated different isoform profiles between S. persica and S. europaea concerning antioxidant enzymes. These results showed that S. persica exhibits a better protection mechanism against oxidative damage and it is more salt-tolerant than S. europaea possibly by maintaining and/or increasing growth parameters, ion accumulation, and antioxidant enzyme activities.     

Provenance variation in tolerance of Melaleuca cajuputi trees to interactive effects of aluminum and salt

A future rise in sea level will expand areas of salt-affected acid sulfate soil, calling for studies on plant tolerance to combined aluminum (Al) and salt (NaCl) stress. We investigated random amplified polymorphic DNA (RAPD) profiles and tolerance to Al and NaCl alone and in combination in 14 Melaleuca cajuputi Powell provenances. Two-month-old seedlings were grown with or without 10 mM Al and/or 50 mM NaCl at pH 3.8 for 3 months. Plant growth was reduced mostly by combined Al and NaCl stress and then by NaCl and least by Al. Moreover, Al enhanced the effect of NaCl on growth and vice versa. There were significant differences in plant growth among provenances under all treatments; however, positive relationships were found among Al tolerance, NaCl tolerance, and combined Al and NaCl tolerance. Provenance variation in stress tolerance increases with the increasing levels of stress effect. Furthermore, NaCl tolerance tended to have a positive relationship with osmotic potential. Leaf sap K concentration was decreased by NaCl and increased by Al; however, provenances that were more tolerant to NaCl tended to have lower K concentrations. RAPD analysis also revealed genetic variation among provenances. These results suggest that the low tolerance to combined Al and NaCl stress in M. cajuputi is largely due to low tolerance to NaCl and the effect of interaction between Al and NaCl. Provenance variation in stress tolerance was significant and could be partly explained by the variation in genetic material and the ability of plants to reduce ion excess stress in their shoots.     

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

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

     

Phenolic nature,occurrence and polymerization degree as marker of environmental adaptation in the edible halophyte Mesembryanthemum edule

Mesembryanthemum edule is an edible medicinal halophyte traditionally used to treat several human diseases. In this study, particular importance was attached to the influence of environmental conditions on phenolic composition and antioxidant activities of two M. edule provenances from contrasting climatic regions (Djerba and Monastir sampled from arid and superior semi-arid bioclimatic stages, respectively). Shoot phenolic content was evaluated using colorimetric method and its composition was identified by HPLC analysis with or without thiolysis. Antioxidant activities were assessed by five in vitro antioxidant systems. Results showed that the two M. edule provenances were significantly different according to their antioxidant activity as well as their polyphenol profiles. Indeed, plants from Djerba (lack of rainfall and long light hour periods) exhibited stronger antioxidant activity together with higher phenolic content. For instance, Djerba provenance shoots showed much lower IC₅₀ (4.8 μg ml⁻¹) and EC₅₀ (80 μg ml^− 1) values for DPPH and Fe-reducing tests, respectively. In addition, the superiority of this provenance (Djerba) was more marked as compared to positive controls (BHT, BHA, and VitC). HPLC identification revealed also an important difference between the two provenances on major flavonoid components. This difference was confirmed by the mean degrees of tannin polymerization (DPn) which was higher in Djerba plants. These data suggest that M. edule adaptation to environmental stresses proceeds through induced particular phenol quality and DPn for the improvement of their antioxidant capacities to protect plant tissues against oxidative stress.     

Effect of NaCl on fatty acids, phenolics and antioxidant activity of Nigella sativa organs

The objective of this study was to investigate the effect of salinity on growth, fatty acid composition, phenol content and antioxidant activity of Nigella sativa organs. Plants were grown hydroponically under NaCl stress (0, 20 40 and 60 mM). The results indicated that salinity affected N. sativa growth. The fatty acid composition of the leaves and the roots was investigated for the first time and major fatty acids were linolenic acid (58.1%) in the leaves and linoleic (43.9%) and palmitic (33.3%) acids and in the roots. Total fatty acid (TFA) content of the leaves decreased at 60 mM NaCl while root TFA increased at 20 and 40 mM NaCl. Moreover, the fatty acid composition was affected by NaCl; in leaves, the double bond index (DBI) decreased accompanied by a decrease of the level of linolenic acid which reached 14% at 60 mM NaCl. However, root DBI degree increased at 40 at 60 mM NaCl provoked mainly by the increase of the amount of linoleic acid by 15 and 8%, respectively, and the decrease of the amount of palmitic acid by 20 and 14%, respectively. Salt stress increased total polyphenol and individual phenolic acid contents in shoots. Moreover, the antiradical activity of the shoots (DPPH) increased at 60 mM NaCl. However, in roots, the total polyphenol content and the antiradical activity decreased sharply with increasing NaCl doses. Data reported here revealed the variation of fatty acids and phenolic compound contents in different organs of N. sativa, and the possible role of theses changes in the plant salt response were discussed.     

Antioxidative enzymatic protection in leaves of two contrasting cowpea cultivars under salinity

The aim of this work was to investigate the role of the antioxidant enzymes in salt tolerance comparing the salt-sensitive (Pérola) and a salt-tolerant (Pitiúba) cultivar of cowpea [Vigna unguiculata (L.) Walp.]. Salt stress (100 mM NaCl for 8 d) reduced the leaf growth rate more in the sensitive cultivar. The salt-induced decrease in the relative water content, Na⁺ accumulation and increase in leaf electrolyte leakage was similar in both cultivars. Salt stress induced a higher increase in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and phenol peroxidase (POX) in the tolerant cultivar than in sensitive one.     

Growth,photosynthesis, and ion distribution in hydroponically cultured <Emphasis Type="Italic">Populus alba</Emphasis> L. cuttings grown under various salinity concentrations

Growth, photosynthesis, and Na⁺, K⁺, and Ca²⁺ distributions were investigated in 2-year-old hydroponically cultured Populus alba L. cuttings exposed to salt stresses (0, 0.85, 8.5, 17, and 85 mM NaCl in experiment 1 and 0, 50, 100, 150, and 200 mM in experiment 2) for 4 weeks in 2/5 Hoagland solution. Salt did not markedly inhibit height growth and diameter increment in 150 and 100 mM NaCl, respectively. The 85 mM NaCl treatment increased the dry weights of roots and total dry weight of plants, while 150 mM NaCl significantly reduced the dry weights of leaves, stems, and total plant weight. The decline in the photosynthetic rate lagged 2 weeks behind that of stomatal conductance in the 50 and 100 mM salt solutions. Different ions exhibited different distributions in different parts of the plant. Most Na⁺ ions were excluded and/or compartmentalized in roots at low and moderate salt stress (≤50 mM). K⁺ content in leaves increased with the increase in the salt concentration in the growth solutions.     

Roots volatiles and fatty acids of coriander (<Emphasis Type="Italic">Coriandrum sativum</Emphasis> L.) grown in saline medium

An hydroponic culture was conducted to investigate the effect of saline stress on the essential oil and fatty acid composition of Tunisian coriander (Coriandrum sativum L.) roots. Ten days old coriander seedlings were treated during 3 weeks with different NaCl concentrations (0, 25, 50 and 75 mM). Roots volatile components and fatty acids were analyzed. The essential oil yield was 0.06% in the control, on the basis of dry matter weight, and did not changed at low concentration (25 mM), while it increased significantly with increasing NaCl concentrations to reach 0.12 and 0.21% at 50 and 75 mM NaCl, respectively. The major volatile component was (E)-2-dodecenal with 52% of total essential oil constituents, followed by decanal, dodecanal, (E)-2-tridecenal and (E)-2-dodecenal. Further, the amount of these compounds was affected differently by the NaCl level. Total fatty acid amount of coriander roots increased significantly only with 50 and 75 mM NaCl. Three major fatty acids: linoleic (43%), oleic (25.5%) and palmitic (21.6%) were identified. Linoleic acid amount remains unchanged at 25 mM, while it increased with raising NaCl concentrations. However, oleic acid amount decreased only at 25 mM and no effect was observed at 50 and 75 mM. Fatty acid percentages were differently affected by salt. The oleic/linoleic ratio was reduced with raising NaCl concentrations.