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.     

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.     

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.     

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.     

Salt stress response in tomato beyond the salinity tolerance threshold

Crop salt tolerance is generally assessed as the relative yield response to increasing root zone salinity, expressed as soil (EC_e) or irrigation water (EC_w) electrical conductivity. Alternatively, the dynamic process of salt accumulation into the shoot relative to the shoot biomass has also been considered as a tolerance index. These relationships are graphically represented by two intersecting linear regions, which identify (1) a specific threshold tolerance, at which yield begins to decrease, and (2) a declining region, which defines the yield reduction rate. Although the salinity threshold is intuitively a critical parameter for establishing plant salt tolerance, we focused our interest on physiological modifications that may occur in the plant at salinity higher than the so-called tolerance threshold. For this purpose, we exposed hydroponically grown tomato plants to eight different salinity levels (EC = 2.5 (non-salinized control); 4.2; 6.0; 7.8; 9.6; 11.4; 13.2; 15.0 dS m⁻¹). Based on biomass production, water relations, leaf ions accumulation, leaf and root abscisic acid and stomatal conductance measurements, we were able to identify a specific EC value (approximately 9.6 dS m⁻¹) at which a sharp increase of the shoot and root ABA levels coincided with (1) a decreased sensitivity of stomatal response to ABA; (2) a different partitioning of Na⁺ ions between young and mature leaves; (3) a remarkable increase of the root-to-shoot ratio. The specificity and functional significance of this response in salt stress adaptation is discussed.     

Changes in root system structure,leaf water potential and gas exchange of maize and triticale seedlings affected by soil compaction

The physiological reasons associated with differential sensitivity of C₃ and C₄ plant species to soil compaction stress are not well explained and understood. The responses of growth characteristics, changes in leaf water potential and gas exchange in maize and triticale to a different soil compaction were investigated. In the present study seedlings of triticale and maize, representative of C₃ and C₄ plants were subjected to low (L – 1.10 g cm⁻³), moderate (M – 1.34 g cm⁻³) and severe (S – 1.58 g cm⁻³) soil compaction level. Distinct differences in distribution of roots in the soil profile were observed. Plants of treatments M or S in comparison to treatment L, showed a decrease in leaf number, dry mass of stem, leaves and roots, and an increase in the shoot to root ratio. A drastic decrease in root biomass in M and S treatments in the soil profile on depth from 15 to 40 cm was observed. Any level of soil compaction did not influence the number of seminal and seminal-adventitious roots but decreased their length. The number and total length of nodal roots decreased with compaction. Changes of growth traits in M and S treatments in comparison to the L were greater for maize than for triticale and were accompanied by daily changes in water potential (ψ) and gas exchange parameters (P_N, E, g_s). Differences between M and S treatments in daily changes in ψ for maize were in most cases statistically insignificant, whereas for triticale, they were statistically significant. Differences in the responses of maize and triticale to soil compaction were found in P_N, E and g_s in particular for the measurements taken at 12:00 and 16:00. The highest correlation coefficients were obtained for the relationship between leaf water potential and stomatal conductance, both for maize and triticale, which indicates the close association between stomata behavior and changes in leaf water status.     

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.     

Effects of salt stress on ion content,antioxidant enzymes and protein profile in different tissues of Broussonetia papyrifera

Although some plant responses to salinity have been characterized, the precise mechanisms by which salt stress damages plants are still poorly understood especially in woody plants. In the present study, the physiological and biochemical responses of Broussonetia papyrifera, a tree species of the family, Moraceae, to salinity were studied. In vitro-produced plantlets of B. papyrifera were treated with varying levels of NaCl (0, 50, 100 and 150 mM) in hydroponic culture. Changes in ion contents, accumulation of H₂O₂, as well as the activities and isoform profiles of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in the leaves, stems and roots were investigated. Under salt stress, there was higher Na⁺ accumulation in roots than in stems and leaves, and Ca^2 +, Mg^2 + and P^3 + content, as well as K⁺/Na⁺ ratio were affected. NaCl treatment induced an increase in H₂O₂ contents in the tissues of B. papyrifera. The work demonstrated that activities of antioxidant defense enzymes changed in parallel with the increased H₂O₂ and salinity appeared to be associated with differential regulation of distinct SOD and POD isoenzymes. Moreover, SDS-PAGE analysis of total proteins extracted from leaves and roots of control and NaCl-treated plantlets revealed that in the leaves salt stress was associated with decrease or disappearance of some protein bands, and induction of a new protein band after exposure to 100 and 150 mM NaCl. In contrast, NaCl stress had little effect on the protein pattern in the roots. In summary, these findings may provide insight into the mechanisms of the response of woody plants to salt stress.     

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.     

Effects of salt stress on volatile compounds,total phenolic content and antioxidant activities of Salvia mirzayanii

Salvia mirzayanii is a medicinal and aromatic plant belonging to the Lamiaceae family, which is an endemic plant in Iran. In this study, the effects of different salt concentrations on total phenolic content, antioxidant activities and volatile components of the aerial parts of S. mirzayanii were studied. The results showed that total phenolic content increased with the increase in salt concentration. The increase was more pronounced under moderate salinity (3.8 mg GAE g^− 1 DW at 6.8 dS m^− 1 NaCl). Plants grown at 6.8 dS m^− 1 NaCl displayed the highest DPPH˚ scavenging activity with the lowest IC₅₀ value (2.13 mg ml^− 1) compared to the control. The volatile components were identified and analyzed by HS (headspace)-GC–MS using the Combi PAL System technique. The main components of control plants were α-terpinyl acetate, 1,8-cineole and bicyclogermacrene. The proportions of these main compounds were differently affected by salinity stress. The results showed that the synthesis of both total phenolic and some important volatile components was induced by moderate salinity.     

Involvement of polyamines,abscisic acid and anti-oxidative enzymes in adaptation of Blue Panicgrass (Panicum antidotale Retz.) to saline environments

A hydroponic experiment was conducted to assess the possible involvement of polyamines (PAs), abscisic acid (ABA) and anti-oxidative enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) in adaptation of six populations of Panicum antidotale Retz. to selection pressure (soil salinity) of a wide range of habitats. Plants of six populations were collected from six different habitats with ECe ranging from 3.39 to 19.23 dS m⁻¹ and pH from 7.65 to 5.86. Young tillers from 6-month-old plants were transplanted in plastic containers each containing 10 l of half strength Hoagland's nutrient solution alone or with 150 mol m⁻³ NaCl. After 42 days growth, contents of polyamines (Put, Spd and Spm) and ABA, and the activities of anti-oxidative enzymes (SOD, POD and CAT) of all populations generally increased under salt stress. The populations collected from highly saline habitats showed a greater accumulation of polyamines and ABA and the activities of anti-oxidative enzymes as compared to those from mild or non-saline habitats. Moreover, Spm/Spd and Put/(Spd + Spm) ratios generally increased under salt stress. However, the populations from highly saline environments had significantly higher Spm/Spd and Put/(Spd + Spm) ratios as compared to those from mild or non-saline environments. Similarly, the populations adapted to high salinity accumulated less Na⁺ and Cl⁻ in culm and leaves, and showed less decrease in leaf K⁺ and Ca²⁺ under salinity stress. Higher activities of anti-oxidative enzymes and accumulation of polyamines and ABA, and increased Spm/Spd and Put/(Spm + Spd) ratios were found to be highly correlated with the degree of adaptability of Panicum to saline environment.     

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.     

Silicon supply in soilless cultivations of zucchini alleviates stress induced by salinity and powdery mildew infections

In the present study, the hypothesis was tested as to whether silicon supplied via the nutrient solution is capable of enhancing the tolerance of hydroponically grown zucchini squash (Cucurbita pepo L. cv. ‘Rival’) to salinity and powdery mildew infections. Two experiments were conducted involving a low (2.2 dS m^?1, 0.8 mM NaCl) and a high salinity level (6.2 dS m^?1, 35 mM NaCl) in combination with a low (0.1 mM) and a high (1.0 mM) Si level in the nutrient solution supplied to the crop. The exposure of the plants to high external salinity restricted significantly the vegetative growth as well as the fruit yield of zucchini due to a reduction of both the number of fruits per plant and the mean fruit weight. However, the inclusion of 1 mM of Si in the salinized nutrient solution mitigated the salinity-associated suppression of both growth and yield. Part of the growth and fruit yield suppression at high salinity was due to restriction of net photosynthesis. The stomatal conductance was also restricted by salinity, whereas the substomatal CO₂ concentration was not affected by the NaCl or Si treatments. The supply of 1 mM of Si via the nutrient solution mitigated the inhibitory effect of salinity on net photosynthesis and this effect was associated with lower Na and Cl translocation to the epigeous plant tissues. Furthermore, the supply of Si via the nutrient solution suppressed appreciably the expansion of a powdery mildew (Podosphaera xanthii) infection in the leaves at both salinity levels. These results indicate that the supply of at least 1 mM of Si via the nutrient solution is capable of enhancing both tolerance to salinity and resistance to powdery mildew in soilless cultivations of zucchini squash.     

The effects of salt stress on growth,water relations and ion accumulation in two halophyte Atriplex species

Atriplex halimus is found in the Mediterranean Basin along the coastal areas of Sardinia, but few data are available on its adaptability to salinity. The effects of drought and salinity under controlled conditions on two clones of A. halimus, designated MOR2 and SOR4, originating from southern and northern Sardinia, respectively, were compared with those of seedlings of A. nummularia, an Australian species widely used in the restoration of arid areas. The effects of increasing NaCl salinity above seawater concentrations and of increasing the KCl concentration gradient were tested. Plants were harvested and analysed after 10 and 20 days of NaCl and KCl treatments. All plants remained alive until the end of treatment, although growth was strongly reduced, mainly for the A. halimus MOR2 clone, under increasing concentrations of KCl. The leaves and roots of both species responded positively to increasing NaCl concentrations up to 600 mM NaCl for A. halimus, whereas the optimal growth of A. nummularia was recorded at 300 mM NaCl. SOR4 was more sensitive to KCl toxicity. The Na⁺ concentration in the plants increased with increased salinity and was higher in A. halimus than in A. nummularia, suggesting that A. halimus is an ion accumulator and may be used for phytoremediation. The sodium accumulation in the roots of the A. halimus MOR2 clone was far greater than in its leaves. This suggests that MOR2 is an Na⁺ excluder, either by minimising the entry of salt into the plant or by an excretion mechanism via the vesiculated hairs that play a significant role in the removal of salt from the remainder of the leaf, thereby preventing its accumulation to toxic levels in the leaves, whereas SOR4 acted as an Na⁺ includer. Higher levels of proline were detected in the MOR2 clone under NaCl treatments, suggesting a more developed adaptative mechanism for the selection of this characteristic in the southern part of the island, which is more exposed to abiotic stresses, particularly water stress that is either generated by salinity or by other causes.     

Exogenous sodium sulfide improves morphological and physiological responses of a hybrid Populus species to nitrogen dioxide

Gaseous nitrogen dioxide (NO₂) can disturb normal plant growth and trigger complex physiological responses. NO₂-induced responses are influenced by biotic or abiotic factors. In this study, we investigated the effects of exogenous sodium sulfide (Na₂S, 5 mmol L⁻¹) on epidermis and stomata related physico-chemical responses of hybrid poplar cuttings (Pouplus alba × P. berolinensis) to gaseous NO₂ (4 μl 1⁻¹) for three time periods (0, 14 and 48 h). We also investigated hydrogen sulfide (H₂S), nitrate-nitrogen and nitrate reductase activity (NR) in control and Na₂S treated plants. Our results showed that NO₂ exposure for 48 h led to the decline of NR, maximal PSII quantum yield (F_v/F_m), net photosynthetic rate (P_n), and dark respiration rate (R_d). The maximum rate for the post-illumination carbon dioxide burst (PIB) occurred in 48-h exposed leaves 13–15 s after darkening. Moreover, NO₂ exposure resulted in a significant increase in nitrogen percentage (from 0 to 33%) and a decrease in the macro and micro-elements of leaf surface. Spraying Na₂S aqueous solution on the leaf surfaces significantly increased the thicknesses of palisade/spongy tissue and H₂S content. Na₂S pretreatment alleviated NO₂-caused toxic effects as indicated by increased NR and higher values of P_n, F_v/F_m, and actual photochemical efficiency in light (ФPSII) compared with the control. Na₂S pretreatment had no significant impacts on PIB-based photorespiration or elements composition of a leaf surface.     

The impact of arbuscular mycorrhizal fungi in mitigating salt-induced adverse effects in sweet basil (Ocimum basilicum L.)

Salinity is one of the serious abiotic stresses adversely affecting the majority of arable lands worldwide, limiting the crop productivity of most of the economically important crops. Sweet basil (Osmium basilicum) plants were grown in a non-saline soil (EC = 0.64 dS m⁻¹), in low saline soil (EC = 5 dS m⁻¹), and in a high saline soil (EC = 10 dS m⁻¹). There were differences between arbuscular mycorrhizal (Glomus deserticola) colonized plants (+AMF) and non-colonized plants (−AMF). Mycorrhiza mitigated the reduction of K, P and Ca uptake due to salinity. The balance between K/Na and between Ca/Na was improved in +AMF plants. Growth enhancement by mycorrhiza was independent from plant phosphorus content under high salinity levels. Different growth parameters, salt stress tolerance and accumulation of proline content were investigated, these results showed that the use of mycorrhizal inoculum (AMF) was able to enhance the productivity of sweet basil plants under salinity conditions. Mycorrhizal inoculation significantly increased chlorophyll content and water use efficiency under salinity stress. The sweet basil plants appeared to have high dependency on AMF which improved plant growth, photosynthetic efficiency, gas exchange and water use efficiency under salinity stress. In this study, there was evidence that colonization with AMF can alleviate the detrimental salinity stress influence on the growth and productivity of sweet basil plants.     

Effects of exposure to sublethal propiconazole on intestine-related biochemical responses in rainbow trout,Oncorhynchus mykiss

The effect of long-term (30 days) exposure to PCZ (0.2, 50, and 500 μg l^?1) on intestine-related biochemical markers in rainbow trout was investigated. Multiple biomarkers were measured, including digestive enzymes (proteolytic enzymes and amylase), antioxidant responses (TBARS, CP, SOD, CAT, GR and GPx) and energy metabolic parameters (RNA/DNA ratio, Na⁺-K⁺-ATPase). Exposure to 500 μg l^?1 PCZ led to significantly inhibited (p < 0.01) proteolytic enzyme and amylase activity. Activities of the antioxidant enzymes SOD, CAT, and GPx gradually increased at lower PCZ concentrations (0.2 and 50 μg l^?1). At the highest concentration (500 μg l^?1), oxidative stress was apparent as significant higher (p < 0.05) lipid peroxidation and protein carbonyls, associated with an inhibition of antioxidant enzymes activity. Moreover, energy metabolic parameters (RNA/DNA ratio, Na⁺-K⁺-ATPase) were significantly inhibited (p < 0.01) in the intestines of fish exposed to 500 μg l^?1 PCZ, compared with controls. We suggest that long-term exposure to PCZ could result in several responses in intestine-related biochemical markers, which potentially could be used as indicators for monitoring residual PCZ present in the aquatic environment.     

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.     

Biochemical indicators of salt stress in Plantago maritima: Implications for environmental stress assessment

Our study is focused on native spontaneous species of saline ecosystems Plantago maritima. Plants were cultivated at several salt concentrations (0, 50, 100, 200, 300, 400 and 500 mM NaCl) in a glass greenhouse under semi-controlled conditions. Growth parameters, water parameters and ionic status were determined and they were used as criteria to assess the response of P. maritima under a salinity gradient. Catalase, guaiacaol and ascobate peroxidase activities, total protein and proline were also determined. Our results show that P. maritima is a facultative halophyte capable of expressing its maximum growth potential at relatively low concentrations of salt (less than 3 g l⁻¹ NaCl). At high doses of salt (concentrations > 200 mM), the decrease in the growth of P. maritima is associated to a decrease in the uptake of K⁺. There is a disruption of the water intake of their organs and therefore results an invasion of the cytoplasm by Na⁺ toxic ion. However, stressed plants use K⁺ more sparingly. They invest especially in the production of biomass expressed by the dry weight of the shoots, and they use Na⁺ and proline for osmotic adjustment. The halophyte studied is able to accumulate high levels of proline in response to increasing salt concentration. The accumulation of the amino compound, mainly in roots, is interpreted as an indicator of salt tolerance. Additionally, a significant correlation between the tolerance of the plants to salinity and the activity of several antioxidant enzymes has been observed. Hence, we suggest the possibility of using these activities as a biochemical indicator for salt tolerance in P. maritima. Our study points out two types of biomarkers of salt exposure: enzymatic biomarkers in the leaves and proline content in the roots. Both did show very good correlation with salt exposure, and thus may be considered good biomarkers of exposure with a very good dose–response relationship.     

Chloride salinity reduces cadmium accumulation by the Mediterranean halophyte species Atriplex halimus L.

Soil salinity usually increases bioavailability of Cd on heavy metal polluted soils but its impact on Cd absorption and accumulation by plants remains largely unknown. Plants from the halophyte species Atriplex halimus were therefore exposed for 12 and 14 days to nutrient solution containing 50 μM CdCl₂ in the presence of NaCl, KCl or NaNO₃ 50 mM. Most Cd present in solution remained as Cd–EDTA and salinity had no impact on Cd speciation. Chloride salinity (NaCl and KCl) reduced Cd accumulation in shoots and roots while NaNO₃ increased Cd accumulation in leaves. More than 30% of accumulated Cd was found at the leaf surface and accumulated in trichomes but all tested salts decreased the proportion of excreted Cd. Cadmium induced a decrease in the leaf water content. External NaCl and KCl mitigated the deleterious impact of Cd by inducing osmotic adjustment while NaNO₃ and synthesis of protecting compounds such as soluble sugars and glycinebetaine. Free polyamines (putrescine, spermidine and spermine) increased in response to Cd, Cd + NaCl and Cd + KCl while only putrescine increased in response to Cd + NaNO₃. Proline exhibited maximal concentration in the leaves of Cd + NaCl and Cd + KCl-treated plants and was correlated with osmotic adjustment. Our results suggest that chloride salinity improved the resistance of A. halimus to Cd toxicity both by decreasing the absorption of heavy metal and by improving tissular tolerance through an increase in the synthesis of osmoprotective compounds.