Simultaneous application of salicylic acid and calcium improves salt tolerance in two contrasting tomato (Solanum lycopersicum) cultivars

Soil salinity is one of the most important environmental factors responsible for serious agricultural problems. Tomato salt tolerance may be improved by genetic selection and by the use of adapted physiological tools. The aim of this study was to investigate the impact of exogenous application of salicylic acid (SA 0.01 mM) and calcium sulphate (CaSO₄ 5 mM), singly or in combination, on plant growth, photosynthetic pigments, nutritional behaviour and some metabolic parameters (total chlorophyll, carotenoids, soluble sugars, proline and lipid peroxidation) of two tomato cultivars (cv. Super Marmande and cv. Red River) exposed to salt stress (100 mM NaCl). Application of 100 mM NaCl reduced plant growth, total chlorophyll and carotenoid contents. Salt stress also induced an accumulation of Na⁺, a decrease in K⁺ and Ca^2 + concentration and root sugar level, an increase in malondialdehyde (MDA) and proline concentration. Deleterious impact of salinity was related to modification in ion content rather than modification in the plant water status. Exogenous application of SA or Ca alone improved plant behaviour in the presence of NaCl. Nevertheless, the best results in terms of growth, photosynthetic pigment concentrations and mineral nutrition (limitation of Na⁺ accumulation and maintenance of K⁺ and Ca^2 + content) were obtained in response to the combined SA + Ca treatment. Although the involved physiological parameters varied depending on the considered cultivar, our results suggest that Ca^2 + and SA may interact to reduce the stress experienced by the plant in the presence of NaCl.     

Effect of NaCl on growth and Cd accumulation of halophyte Spartina alterniflora under CdCl2 stress

A study quantifying the effect of NaCl on growth and Cd accumulation of Spartina alterniflora subjected to Cd stress was conducted. Seedlings were cultivated in the presence of 1 or 3 mM Cd alone, or combined with NaCl (50 or 100 mM). The results showed that NaCl magnified the phytotoxicity of moderate Cd stress (1 mM Cd) on plants due to reduced levels of plant biomass, plant height, and chlorophyll a + b, while no synergistic effects were recorded under severe Cd stress (3 mM Cd). Proline and Ca^2 + accumulated along with additional NaCl under moderate Cd stress, instead of reduced or unchanged levels under severe Cd stress owing to different adoption strategies caused by NaCl under different Cd stresses. NaCl reduced the oxidative stress in Cd-treated plants through increasing levels of antioxidative enzymes (catalase (CAT) and peroxidase (POD)) under moderate Cd stress. With NaCl addition, Cd^2 + contents in S. alterniflora increased and reduced under moderate and severe Cd stress, respectively. However, total Cd^2 + amounts increased with increasing NaCl concentration due to biological dilution. NaCl improved the increase of Cd^2 + translocation factor (TF) under moderate Cd stress, indicating that NaCl might improve Cd^2 + uptake and translocation from roots to shoots, and enhance the phytoextraction of S. alterniflora on Cd; while phytostabilization of Cd under severe Cd stress may be possible due to the reduced TF. Thus, NaCl alleviated phytotoxicity caused by Cd stress through improved management of osmotic solutes and oxidative status, and affected Cd accumulations in S. alterniflora differently under moderate and severe Cd stresses.     

Effect of high salinity on Atriplex portulacoides: Growth,leaf water relations and solute accumulation in relation with osmotic adjustment

Atriplex (Halimione) portulacoides is a halophyte with potential interest for saline soil reclamation and phytoremediation. Here, we assess the impact of salinity reaching up to two-fold seawater concentration (0–1000 mM NaCl) on the plant growth, leaf water status and ion uptake and we evaluate the contribution of inorganic and organic solutes to the osmotic adjustment process. A. portulacoides growth was optimal at 200 mM NaCl but higher salinities (especially 800 and 1000 mM NaCl) significantly reduced plant growth. Na⁺ and Cl⁻ contents increased upon salt exposure especially in the leaves compared to the roots. Interestingly, no salt-induced toxicity symptoms were observed and leaf water content was maintained even at the highest salinity level. Furthermore, leaf succulence and high instantaneous water use efficiency (WUE_i) under high salinity significantly contributed to maintain leaf water status of this species. Leaf pressure–volume curves showed that salt-challenged plants adjusted osmotically by lowering osmotic potential at full turgor (Ψ_π¹⁰⁰) along with a decrease in leaf cell elasticity (values of volumetric modulus elasticity (ε) increased). As a whole, our findings indicate that A. portulacoides is characterized by a high plasticity in terms of salt-response. Preserving leaf hydration and efficiently using Na⁺ for the osmotic adjustment especially at high salinities (800–1000 mM NaCl), likely through its compartmentalization in leaf vacuoles, are key determinants of such a performance. The selective absorption of K⁺ over Na⁺ in concomitance with an increase in the K⁺ use efficiency also accounted for the overall plant salt tolerance.     

In vitro salinity tolerance of two pistachio rootstocks: Pistacia vera L. and P. atlantica Desf

Seedlings of Pistacia vera L. and Pistacia atlantica Desf. were cultured on hormone-free DKW medium supplemented with NaCl. The plants were subjected to low NaCl concentrations ranging from 0 to 80 mM for 45 days or to high salt concentrations (0, 131, and 158.5 mM for P. vera and 0, 131, and 240 mM for P. atlantica) for 25 days. Toxicity symptoms were recorded for seedlings exposed to low NaCl treatments. Plant growth, survival rates, mineral content, as well as proline and soluble sugar contents were determined and evaluated at the end of the culture period. The results indicated that low NaCl treatments yielded no instances of plant death in both species. At high salt conditions, however, significant mortality rates were noted for both species, being 22.86% at 240 mM NaCl for P. atlantica and 25.8% at 158.5 mM NaCl for P. vera. With regards to salinity effects, levels of 60 and 80 mM NaCl induced significant decreases of stem elongation and leaf number in the P. vera species. Salinities between 40 and 80 mM NaCl, however, induced a decrease in the root number of both species. The fresh weights of P. vera and P. atlantica also decreased significantly after 45 days of culture at NaCl concentrations between 40 and 80 mM and after 25 days of culture at 158.5 and 240 mM NaCl, respectively. The sodium and chloride uptake in plant organs seemed to be controlled more efficiently in P. atlantica than in P. vera. In both species, the K⁺ content was noted to undergo a significant decrease when salinity increased. While the K⁺/Na⁺ ratio was maintained above 2 at low NaCl treatments, it was sharply decreased at high NaCl conditions, suggesting a failure of K–Na selectivity mechanism. The Ca²⁺/Na⁺ ratio decreased significantly at 60 and 80 mM NaCl in P. vera and at 60 mM NaCl for P. atlantica. In both Pistacia species, high NaCl treatments (131–240 mM NaCl) induced a significant increase in proline content.     

Amperometric xanthine biosensors based on electrodeposition of platinum on polyvinylferrocenium coated Pt electrode

Novel xanthine biosensors were successfully fabricated by immobilizing xanthine oxidase on polyvinylferrocenium perchlorate matrix (PVF⁺ClO₄⁻) and platinum electrodeposited polyvinylferrocenium perchlorate matrix. PVF⁺ClO₄⁻ film was coated on Pt electrode at +0.7 V vs. Ag/AgCl by electrooxidation of polyvinylferrocene (PVF). Platinum nanoparticles were deposited on PVF⁺ClO₄⁻ electrode by electrochemical deposition in 2.0 mM H₂PtCl₆ solution at −0.2 V. Xanthine oxidase was incorporated into the polymer matrix via ion exchange process by immersing modified Pt electrodes in the enzyme solution. The amperometric responses of the biosensors were measured via monitoring oxidation current of hydrogen peroxide at +0.5 V. Under the optimal conditions, the linear ranges of xanthine detection were determined as 1.73 × 10⁻³–1.74 mM for PVF⁺XO⁻ and 0.43 × 10⁻³–2.84 mM for PVF⁺XO⁻/Pt. The detection limits of xanthine were 5.20 × 10⁻⁴ mM for PVF⁺XO⁻ and 1.30 × 10⁻⁴ mM for PVF⁺XO⁻/Pt. Moreover, the effects of applied potential, electrodeposition potential, H₂PtCl₆ concentration, amount of electrodeposited Pt nanoparticles, thickness of polymeric film, temperature, immobilization time, xanthine and xanthine oxidase concentrations on the response currents of the biosensors were investigated in detail. The effects of interferents, the operational and storage stabilities of biosensors and the applicabilities to drug samples of the biosensors analysis were also evaluated.     

Evaluation of zinc tolerance and accumulation potential of the coastal shrub Limoniastrum monopetalum (L.) Boiss.

The coastal shrub Limoniastrum monopetalum is capable of growth in soil containing extremely high concentrations of heavy metals. A greenhouse experiment was conducted in order to investigate the effects of a range of Zn concentrations (0–130 mmol l⁻¹) on growth and photosynthetic performance, by measuring relative growth rate, total leaf area, plant height, gas exchange, chlorophyll fluorescence parameters and photosynthetic pigment concentrations. We also determined the total zinc, nitrogen, phosphorus, sulphur, calcium, magnesium, sodium, potassium, iron and copper concentrations in the plant tissues. The study species demonstrated hypertolerance to Zn stress, since survival was recorded with leaf concentrations of up to 1700 mg Zn kg⁻¹ dry mass when treated with 130 mmol Zn l⁻¹. L. monopetalum exhibited little overall effects on photosynthetic function at Zn levels of up to 90 mmol l⁻¹. At greater external Zn concentration, plant growth was negatively affected, due in all probability to the recorded decline in net photosynthetic rate, which may be linked to the adverse effect of the metal on photosynthetic electron transport. Growth parameters were virtually unaffected by leaf tissue concentrations as high as 1400 mg Zn kg⁻¹ dry mass thus indicating that this species could play an important role in the phytoremediation of Zn-polluted areas.     

Stomatal,biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment

The effect of salinity on leaf area and the relative accumulation of Na⁺ and K⁺ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities ≥ 40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities ≤ 30‰ were negatively correlated with the total leaf area per plant (r² = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r² = 0.94). Selective uptake of K⁺ over Na⁺ declined sharply with increasing salinity, where K⁺/Na⁺ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis V_c,max (from 50.4 to 18.4 μmol m⁻² s^-1), J_max (from 118.0 to 33.8 μmol photons m⁻² s⁻¹), and V_TPU (from 6.90 to 2.30 μmol m⁻² s⁻¹), while stomatal limitation to gas phase conductance (S_L) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (S_L) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.     

Thiourea mediated regulation in the expression profile of aquaporins and its impact on water homeostasis under salinity stress in Brassica juncea roots

Bioregulatory molecules such as thiourea (TU) play an important role in imparting stress tolerance to crops. However, the molecular mechanism involved in the TU-mediated tolerance has not been elucidated. Towards this endeavour, the expression profile of various PIPs (plasma membrane intrinsic proteins) was studied under salt stress (NaCl; 700 mM) with/without thiourea (TU; 6.5 mM) at different time periods in roots of Brassica juncea. Various aquaporin isoforms demonstrated an upregulation upon salinity stress imposition, whereas they were downregulated upon TU supplementation. TU treatment also led to a decrease in the accumulation of reactive oxygen species and delimited the need for an enhanced accumulation of osmolytes. The vacuolar pH was also maintained in NaCl + TU treatment as demonstrated by in vivo ³¹P NMR of roots. In conclusion, TU supplementation to salt stressed seedlings was found to maintain the water homeostasis of roots through coordinated regulation of different PIP isoforms.     

On the mechanism of salt tolerance in olive (Olea europaea L.) under low- or high-Ca2+ supply

The effect of changes in Ca²⁺/Na⁺ ratios at the root zone has been reported in Olea europaea, a species mostly cultivated in calcareous soils. Plants were exposed to low (2.0 mM, low-Ca) or high-Ca²⁺ supply (9.0 mM, high-Ca) and supplied with 0 or 200 mM NaCl. Measurements were performed on water relations, gas exchange and photosynthetic performances, ion fluxes at whole-plant and leaf level, Na⁺ allocation at organismal level, the elemental and soluble carbohydrate concentration in the leaf. Most parameters were also measured during a period of relief from salinity stress, as Olea europaea suffers from fluctuating root zone NaCl concentrations over the whole growing season. High-Ca²⁺ supply decreased stomatal conductance, especially during the first two weeks of treatment. In response to salinity stress (i) leaf turgor potential was more severely depressed in high-Ca than in low-Ca plants, whereas net CO₂ assimilation rate and relative growth rate were unaffected by root zone Ca²⁺ concentrations (ii) high-Ca plants had a markedly superior ability to both exclude Na⁺ from the shoot and to selectively transport K⁺ over Na⁺ than low-Ca plants; (iii) both CO₂ carboxylation efficiency and maximal efficiency of PSII photochemistry (F_v/F_m) were significantly smaller in low-Ca than in high-Ca plants, likely as a result of a greater accumulation of toxic ions. Consistently, when osmotic stress was relieved by supplying plants with good quality water (relief period), both photosynthetic (+44%) and growth rates (+65%) recovered to a markedly superior degree in high-Ca than in low-Ca plants which had been previously treated with 200 mM NaCl. We conclude that (1) high-Ca²⁺ supply expose olive leaves to a more severe dehydration, but allowed to restrict both the entry and the allocation of potentially toxic ions to sensitive shoot organs; (2) a transient restriction of water-mass flow to the shoot during salinization may be of relatively minor significance in Olea europaea, which is very tolerant to drought; (3) overall salt tolerance in Olea europaea, as in most evergreen sclerophylls inhabiting Mediterranean areas, tightly depends upon the ability to reduce water uptake and transpiration during the dry/warm period and to recover photosynthetic and growth rates when low-salinity flood water is available. Therefore, data from the present experiment allow conclude that an increase in root zone Ca²⁺ concentration enhances tolerance to salinity stress in olive plants.     

24-Epibrassinolide ameliorates the saline stress and improves the productivity of wheat (Triticum aestivum L.)

Two wheat (Triticum aestivum L.) cultivars, Sids 1 and Giza 168, were grown under non-saline or saline conditions (4.7 and 9.4 dS m⁻¹) and were sprayed with 0.00, 0.05 and 0.10 mg l⁻¹ 24-epibrassinolide (EBL). Salt stress considerably decreased plant productivity, membrane stability index, photochemical reactions of photosynthesis, the content of relative water, chlorophyll and nitrate, the activity of nitrate reductase and carbonic anhydrase and the level of carbohydrate and protein. The reduction was more pronounced in Giza 168. The follow-up treatment with 0.1 mg l⁻¹ EBL detoxified the stress generated by salinity and significantly improved the above parameters, especially in Sids 1. Glycinebetaine concentration was sharply elevated by salt stress and/or EBL treatments, particularly in Sids 1. Salinity increased putrescine level in Sids 1 and Giza 168, however, spermidine and spermine increased in Sids 1 and decreased in Giza 168. Exogenously applied EBL had a varying effect on polyamines pool under saline condition, an increase in putrescine level associated with low contents of spermidine and spermine in Giza 168 was observed, while Sids 1 showed a decrease in putrescine and high increase in spermidine and spermine. EBL prevented diamine oxidase and polyamine oxidase inhibition, indicating a positive correlation between salt tolerance and polyamines accumulation. Obviously, EBL can be a practical strategy toward generating high-yielding plants under saline condition by enhancing carbon and nitrogen metabolisms. This is the first report dealing with EBL effect on polyamines pool under salt stress.     

The effects of calcium sulphate on growth,membrane stability and nutrient uptake of tomato plants grown under salt stress

A pot experiment was carried out with tomato (Lycopersicon esculentum Mill.) cv. “Target F1” in a mixture of peat, perlite, and sand (1:1:1) to investigate the effects of supplementary calcium sulphate on plants grown at high NaCl concentration (75 mM). The treatments were: (i) control (C), nutrient solution alone; (ii) salt treatment (C + S), 75 mM NaCl; (iii) salt plus calcium treatment 1 (C + S + Ca1), 75 mM NaCl plus additional mixture of 2.5 mM CaSO₄ in nutrient solution; (iv) salt plus calcium treatment 2 (C + S + Ca2), 75 mM NaCl plus additional mixture of 5 mM CaSO₄ in nutrient solution. The plants grown under salt stress produced low dry matter, fruit weight, and relative water content than those grown in standard nutrient solution. Supplemental calcium sulphate added to nutrient solution containing salt significantly improved growth and physiological variables affected by salt stress (e.g. plant growth, fruit yield, and membrane permeability) and also increased leaf K⁺, Ca²⁺, and N in tomato plants. The effects of supplemental CaSO₄ in maintaining membrane permeability, increasing concentrations of Ca²⁺, N, and K⁺ and reducing concentration of Na⁺ (because of cation competition in root zone) in leaves could offer an economical and simple solution to tomato crop production problems caused by high salinity.     

Interactive effects of salinity and water depth on the growth of Melaleuca ericifolia Sm. (Swamp paperbark) seedlings

Melaleuca ericifolia Sm. (Swamp paperbark) is a common tree species in freshwater and brackish wetlands in southern and eastern Australia. The survival of this species in many wetlands is now threatened by increased salinity and inappropriate water regimes. We examined the response of 5-month-old M. ericifolia seedlings to three water depths (exposed, waterlogged and submerged) at three salinities (2, 49 and 60 dS m⁻¹). Increasing water depth at the lowest salinity did not affect survival, but strongly inhibited seedling growth. Total biomass, leaf area and maximum root length were highest in exposed plants, intermediate in waterlogged plants and lowest in submerged plants. Although completely submerged plants survived for 10 weeks at the lowest salinity, they demonstrated negative growth rates and were unable to extend their shoots above the water surface. At the higher salinities, M. ericifolia seedlings were intolerant of waterlogging and submergence: all plants died after 9 weeks at 60 dS m⁻¹. Soil salinities increased over time, and by Week 10, exceeded external water column salinities in both the exposed and waterlogged treatments. In exposed sediment, ∼90% of plants survived for 10 weeks at 60 dS m⁻¹ even though soil salinities reached ∼76 dS m⁻¹. No mortality occurred in the exposed plants at 49 dS m⁻¹, and small but positive relative growth rates were recorded at Week 10. We conclude that at low salinities M. ericifolia seedlings are highly tolerant of sediment waterlogging, but are unlikely to tolerate prolonged submergence. However, at the higher salinities, M. ericifolia seedlings are intolerant of waterlogging and submergence and died rapidly after 5 weeks exposure to this combination of environmental stressors. This research demonstrates that salinity may restrict the range of water regimes tolerated by aquatic plants.     

Physiology of acclimation to salinity stress in pea (Pisum sativum)

Pea (Pisum sativum L.) seedlings were grown in half strength Hoagland solution and exposed to 0, 10, 25 mM NaCl and 2.5% PEG 6000 for 1 week (pre-treatment). Thereafter plants were exposed to 0 and 80 mM NaCl for 2 weeks (main treatment). The control plants were maintained in half strength Hoagland solution without NaCl. Various physiological parameters were recorded from control, pretreated and non-pretreated plants. There was no negative effect of the pre-treatments on growth (total fresh and dry matter production), and plants pre-treated with 10 mM NaCl had biomass accumulation equal to control plants. The beneficial effect of salt acclimation was also evident in the prevention of K⁺ leakage and Na⁺ accumulation, primary in roots, suggesting that here the physiological processes play the major role. 2.5% PEG 6000 was not as efficient as salt in enhancing salt tolerance and acclimation appears to be more related to ion-specific rather than osmotic component of stress. We also recorded an increase of the xylem K/Na in the salt acclimated plants. Therefore, the present study reveals that short-term exposure of the glycophyte P. sativum species activates a set of physiological adjustments enabling the plants to withstand severe saline conditions, and while acclimation takes place primary in the root tissues, control of xylem ion loading and efficient Na⁺ sequestration in mesophyll cells are also important components of this process.     

Differential tolerance to combined salinity and O2 deficiency in the halophytic grasses Puccinellia ciliata and Thinopyrum ponticum: The importance of K+ retention in roots

Saline environments of terrestrial halophytes are often prone to waterlogging, yet the effects on halophytes of combined salinity and waterlogging have rarely been studied. Either salinity or hypoxia (low O₂) alone can interfere with K⁺ homeostasis, therefore the combination of salinity or hypoxia is expected to impact significantly on K⁺ retention in roots. We studied mechanisms of tolerance to the interaction of salinity with hypoxia in Puccinellia ciliata and Thinopyrum ponticum, halophytic grasses that differ in waterlogging tolerance. Plants were exposed to aerated and stagnant saline (250 mM NaCl) treatments with low (0.25 mM) and high (4 mM) K⁺ levels; growth, net ion fluxes and tissue ion concentrations were determined. P. ciliata was more tolerant than T. ponticum to stagnant-saline treatment, producing twice the biomass of adventitious roots, which accumulated high levels of Na⁺, and had lower shoot Na⁺. After 24 h of saline hypoxic treatment, MIFE measurements revealed a net uptake of K⁺ (∼40 nmol m⁻² s⁻¹) for P. ciliata, but a net loss of K⁺ (∼20 nmol m⁻² s⁻¹) for the more waterlogging sensitive T. ponticum. NaCl alone induced K⁺ efflux from roots of both species, with channel blocker tests implicating GORK-like channels. P. ciliata had constitutively a more negative root cell membrane potential than T. ponticum (−150 versus −115 mV). Tolerance to salinity and hypoxia in P. ciliata is related to increased production of adventitious roots, regulation of shoot K⁺/Na⁺, and a superior ability to maintain negative membrane potential in root cells, resulting in greater retention of K⁺.     

Gibberellic acid mediated induction of salt tolerance in wheat plants: Growth,ionic partitioning,photosynthesis, yield and hormonal homeostasis

In order to elucidate the GA₃-priming-induced physiochemical changes responsible for induction of salt tolerance in wheat, the primed and non-primed seeds of two spring wheat (Triticum aestivum L.) cultivars, namely, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were sown in a field treated with 15 dS m⁻¹ NaCl salinity. Although all the three concentrations (100, 150 and 200 mg L⁻¹) of GA₃ were effective in improving grain yield in both cultivars, the effect of 150 mg L⁻¹ GA₃ was much pronounced particularly in the salt intolerant cultivar when under salt stress. Seed priming with GA₃ altered the pattern of accumulation of different ions between shoots and roots in the adult plants of wheat under saline conditions. Treatment with GA₃ (150 mg L⁻¹) decreased Na⁺ concentrations both in the shoots and roots and increased Ca²⁺ and K⁺ concentrations in the roots of both wheat cultivars. GA₃-priming did not show consistent effect on gaseous exchange characteristics and the concentrations of auxins in the salt stressed plants of both wheat cultivars. However, all concentrations of GA₃ reduced leaf free ABA levels in the salt intolerant, while reverse was true in the salt tolerant cultivar under saline conditions. Priming with GA₃ (150 mg L⁻¹) was very effective in enhancing salicylic acid (SA) concentration in both wheat cultivars when under salt stress. Treatment with GA₃ (100–150 mg L⁻¹) lowered leaf free putrescine (Put) and spermidine (Spd) concentrations in the plants of both wheat cultivars. The decrease in polyamines (Put and Spd) and ABA concentrations in the salt stressed plants of the salt intolerant cultivar treated with GA₃ suggested that these plants might have faced less stress compared with control. Thus, physiologically, GA₃-priming-induced increase in grain yield was attributed to the GA₃-priming-induced modulation of ions uptake and partitioning (within shoots and roots) and hormones homeostasis under saline conditions.     

Isolation of hexavalent chromium resistant bacteria from industrial saline effluents and their ability of bioaccumulation

The mixed cultures has been isolated from industrial saline wastewater contaminated with chromium(VI), using enrichment in the presence of 50 mg l⁻¹ chromium(VI) and 4% (w/v) NaCl at pH 8. In this study, the molasses (M) medium was selected a suitable medium for the effective chromium bioaccumulation by the mixed cultures. Eleven pure isolates obtained from mixed cultures and some of them showed high bioaccumulation in the M media containing about 100 mg l⁻¹ chromium(VI) and 4% NaCl. The strain 8 (99.3%) and 10 (99.1%) were able to bioaccumulate more efficient than the mixed culture (98.9%) in this media. But the highest specific Cr uptake was obtained by the mixed cultures followed by strain 8 and 10 with 56.71, 33.14 and 21.7 mg g⁻¹, respectively. Bioaccumulation of chromium(VI) ions by the strain 8 growing in the media with chromium(VI) and NaCl was studied in a batch system as a function of initial chromium(VI) (86.6–547.6 mg l⁻¹) and NaCl (0, 2, 4, 6% w/v) concentrations. During all the experiments, the uptake yield of the strain 8 was highly affected from NaCl concentrations in the medium at high initial chromium(VI) concentrations. But at low chromium(VI) concentration, strain 8 was not affected from NaCl concentrations in the medium. The maximum uptake yield were obtained in the M media with 2% NaCl as 98.8% for 110.0 mg l⁻¹, 98.6% for 217.1 mg l⁻¹, 98.6% for 381.7 mg l⁻¹ and 98.2% for 547.6 mg l⁻¹ initial chromium(VI) concentrations. The strain 8 tolerated a 6% (w/v) NaCl concentration was able to bioaccumulate more than 95% of the applied chromium(VI) at the 97.6–224.4 mg l⁻¹ initial chromium(VI) concentrations. The results presented in this paper was shown that these pure and mixed cultures might be of use for the bioaccumulation of chromium(VI) from saline wastewater.     

Influence of ionic interactions on essential oil and phenolic diterpene composition of Dalmatian sage (Salvia officinalis L.)

The potential of four essential cations (K⁺, Ca²⁺, Mg²⁺ and Fe²⁺) to alleviate salt toxicity was studied in sage (Salvia officinalis L.) plants grown in pots. Two concentrations of the following chloride salts: KCl, CaCl₂, MgCl₂ and FeCl_3, were used together with 100 mM NaCl to study the effects of these nutrients on plant growth, leaf essential oils (EOs) and phenolic diterpenes composition. The sage plants accumulated Na⁺ in their leaves (includers); this has affected secondary metabolites’ biosynthesis. Treatment with 100 mM NaCl slightly decreased borneol and viridiflorol, while increased manool concentrations. Addition of KCl, CaCl₂ and MgCl₂ increased considerably in a dose-dependent manner the oxygen-containing monoterpenes (1.8-cineole, camphor, β-thujone and borneol) in 100 mM NaCl-treated sage. Whereas, the contents of viridiflorol decreased further with the addition of KCl in 100 mM NaCl-treated sage. Our results suggest that the changes in EOs composition were more related to K⁺ and Ca²⁺ availability than to Na⁺ toxicity. Furthermore, treatment with NaCl decreased by 50% carnosic acid (CA), a potent antioxidant, content in the leaves. K⁺ and Ca²⁺ promoted the accumulation of CA and its methoxylated form (MCA) in the leaves. The concentration of CA was positively correlated with leaf K⁺ (r = 0.56, P = 0.01) and Ca²⁺ (r = 0.44, P = 0.05) contents. It appears that different salt applications in combination with NaCl treatments had a profound effect on EOs and phenolic diterpene composition in sage. Therefore, ionic interactions may be carefully considered in the cultivation of this species to get the desired concentrations of these secondary metabolites in leaf extracts.     

Stomatal,biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment

The effect of salinity on leaf area and the relative accumulation of Na⁺ and K⁺ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30‰ substrate salinity. At salinities ≥ 40‰, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities ≤ 30‰ were negatively correlated with the total leaf area per plant (r² = 0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r² = 0.94). Selective uptake of K⁺ over Na⁺ declined sharply with increasing salinity, where K⁺/Na⁺ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30‰, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30‰ has significantly reduced the values of the intrinsic components of photosynthesis V_c,max (from 50.4 to 18.4 μmol m⁻² s^-1), J_max (from 118.0 to 33.8 μmol photons m⁻² s⁻¹), and V_TPU (from 6.90 to 2.30 μmol m⁻² s⁻¹), while stomatal limitation to gas phase conductance (S_L) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30‰ treatment. Under arid leaf conditions, the stomatal factor (S_L) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30‰). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.     

Effects of silicon on H+-ATPase and H+-PPase activity,fatty acid composition and fluidity of tonoplast vesicles from roots of salt-stressed barley (Hordeum vulgare L.)

We investigated the effects of silicon (Si) on time-dependent changes in root tonoplast H⁺-ATPase and H⁺-PPase activities, membrane fatty acid compositions and tonoplast fluidity in two barley (Hordeum vulgare L.) cultivars differing in salt tolerance. Plants were grown in NaCl-free (control) and NaCl-supplied (60 and 120 mM, respectively) nutrient solutions with or without 1.0 mM Si. Plant roots were harvested to isolate tonoplast vesicles for assay of H⁺-ATPase and H⁺-PPase activities at days 2, 4, and 6 after treatment in the first experiment and for analysis of membrane fatty acid composition and fluidity at day 4 after treatment in the second experiment. The results showed that tonoplast H⁺-ATPase and H⁺-PPase activities in roots of salt-treated plants increased at day 2, which was more obvious at 60 mM NaCl in the salt-tolerant cultivar than in the salt-sensitive cultivar, and then decreased at day 4 and onward. These enzyme activities decreased consistently from days 2 to 6 for treatment with 120 mM NaCl. However, inclusion of 1.0 mM Si significantly enhanced both H⁺-ATPase and H⁺-PPase activities in roots of salt stressed barley, which was irrespective of NaCl level or cultivar used. The ratio of unsaturated to saturated fatty acids (U/S) increased under salt stress for both cultivars. Addition of Si to salt treatment increased the ratio of U/S in salt-tolerant cultivar but it did not in salt-sensitive cultivar compared to non-Si-amended salt treatment. Salt treatment decreased tonoplast fluidity of roots of barley significantly compared with control treatment. However, root tonoplast fluidity was significantly lower in the Si-amended salt treatment than in the non-Si-amended salt treatment. These results were in line with the previous findings that Si could help increase antioxidative defense and reduce membrane lipid oxidative damage in barley under salt stress. The possible mechanisms involved in Si-enhanced salt tolerance were discussed with respect to cell membrane integrity, stability and function in barley.     

Salt tolerance in the halophyte Salicornia dolichostachya Moss: Growth,morphology and physiology

Salinization of agricultural land is an increasing problem. Because of their high tolerance to salinity, Salicornia spp. could become models to study salt tolerance; they also represent promising saline crops. The salinity-growth response curve for Salicornia dolichostachya Moss was evaluated at 12 salt concentrations in a hydroponic study in a greenhouse and at 5 different seawater dilutions in an outside setting. Salt concentrations ranged between 0 mM and 500 mM NaCl (≈seawater salinity). Plants were grown for six weeks and morphological and physiological adaptations in different tissues were evaluated.S. dolichostachya had its growth optimum at 300 mM NaCl in the root medium, independent of the basis on which growth was expressed. The relative growth rate (RGR) in the greenhouse experiment was comparable with RGR-values in the outdoor growth experiment. Leaf succulence and stem diameter had the highest values at the growth optimum (300 mM NaCl). Carbon isotope discrimination (δ¹³C) decreased upon salinity. S. dolichostachya maintained a lower leaf sap osmotic potential relative to the external solution over the entire salinity range, this was mainly accomplished by accumulation of Na⁺ and Cl⁻. Glycine betaine concentrations did not significantly differ between the treatments. Na⁺:K⁺-ratio and K⁺-selectivity in the shoots increased with increasing salinity, both showed variation between expanding and expanded shoot tissue. We conclude that S. dolichostachya was highly salt tolerant and showed salt requirement for optimal growth. Future growth experiments should be done under standardized conditions and more work at the tissue and cellular level needs to be done to identify the underlying mechanisms of salt tolerance.