Photosystem II photochemistry and physiological parameters of three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis> under salt stress

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Salt stress caused a marked decrease in osmotic potential and a significant accumulation of Na⁺ and Cl⁻ in leaves of both species. Moderate salinity had a stimulating effect on growth rate, net CO₂ assimilation, transpiration and stomatal conductance for the xero-halophytic species. At higher salinities, these physiological parameters decreased significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea they decreased linearly with salinity. Nitraria retusa PSII photochemistry and carotenoid content were unaffected by salinity, but a reduction in chlorophyll content was observed at 800 mM NaCl. Similar results were found in A. halimus, but with a decrease in the efficiency of PSII (F′v/F′m) occurred at 800 mM. Conversely, in M. arborea plants we observed a significant reduction in pigment concentrations and chlorophyll fluorescence parameters. The marked toxic effect of Na⁺ and/or Cl⁻ observed in M. arborea indicates that salt damage effect could be attributed to ions’ toxicity, and that the reduction in photosynthesis is most probably due to damages in the photosynthetic apparatus rather than factors affecting stomatal closure. For the two halophyte species, it appears that there is occurrence of co-limitation of photosynthesis by stomatal and non-stomatal factors. Our results suggest that both N. retusa and A. halimus show high tolerance to both high salinity and photoinhibition while M. arborea was considered as a slightly salt tolerant species.     

Salt stress effects on growth,pigments, proteins and lipid peroxidation in <Emphasis Type="Italic">Salicornia persica</Emphasis> and <Emphasis Type="Italic">S. europaea</Emphasis>

The effects of NaCl stress on growth, water status, contents of protein, proline, malondialdehyde (MDA), various sugars and photosynthetic pigments were investigated in seedlings of Salicornia persica and S. europaea grown in vitro. Seeds were germinated under NaCl (0, 100, 200, 300, 400, 500 and 600 mM) on Murashige and Skoog medium for 45 d. The shoot growth of both species increased under low NaCl concentration (100 mM) and then decreased with increasing NaCl concentrations. In contrast to S. persica, root length in S. europaea reduced steadily with an increase in salinity. Proline content in S. persica was higher than in S. europaea at most NaCl concentrations. Proline, reducing saccharide, oligosaccharide and soluble saccharide contents increased under salinity in both species. In contrast, contents of proteins and polysaccharides reduced in both species under salt stress. MDA content remained close to control at moderate NaCl concentrations (100 and 200 mM) and increased at higher salinities. MDA content in S. europaea was significantly higher than S. persica at higher salinities. Salt treatments decreased K⁺ and P contents in seedlings of both species. Significant reduction in contents of chlorophylls and carotenoids due to NaCl stress was also observed in seedlings of both species. Some differences appeared between S. persica and S. europaea concerning proteins profile. On the basis of the data obtained, S. persica is more salt-tolerant than S. europaea.     

UV effects on photosynthesis and DNA in propagules of three Antarctic seaweeds (<Emphasis Type="Italic">Adenocystis utricularis</Emphasis>, <Emphasis Type="Italic">Monostroma hariotii</Emphasis> and <Emphasis Type="Italic">Porphyra endiviifolium</Emphasis>)

Ozone depletion is highest during spring and summer in Antarctica, coinciding with the seasonal reproduction of most macroalgae. Propagules are the life-stage of an alga most susceptible to environmental perturbations therefore, reproductive cells of three intertidal macroalgal species Adenocystis utricularis (Bory) Skottsberg, Monostroma hariotii Gain, and Porphyra endiviifolium (A and E Gepp) Chamberlain were exposed to photosynthetically active radiation (PAR), PAR + UV-A and PAR + UV-A + UV-B radiation in the laboratory. During 1, 2, 4, and 8 h of exposure and after 48 h of recovery, photosynthetic efficiency, and DNA damage were determined. Saturation irradiance of freshly released propagules varied between 33 and 83 μmol photons m⁻² s⁻¹ with lowest values in P. endiviifolium and highest values in M. hariotii. Exposure to 22 μmol photons m⁻² s⁻¹ PAR significantly reduced photosynthetic efficiency in P. endiviifolium and M. hariotii, but not in A. utricularis. UV radiation (UVR) further decreased the photosynthetic efficiency in all species but all propagules recovered completely after 48 h. DNA damage was minimal or not existing. Repeated exposure of A. utricularis spores to 4 h of UVR daily did not show any acclimation of photosynthesis to UVR but fully recovered after 20 h. UVR effects on photosynthesis are shown to be species-specific. Among the tested species, A. utricularis propagules were the most light adapted. Propagules obviously possess good repair and protective mechanisms. Our study indicates that the applied UV dose has no long-lasting negative effects on the propagules, a precondition for the ecological success of macroalgal species in the intertidal.     

Growth,fluorescence, photosynthetic O<Subscript>2</Subscript> production and pigment content of salt adapted cultures of <Emphasis Type="Italic">Arthrospira</Emphasis> (<Emphasis Type="Italic">Spirulina</Emphasis>) <Emphasis Type="Italic">platensis</Emphasis>

The effect of salt concentration (NaCl) on growth, fluorescence, photosynthetic activities and pigment content of the cyanobacterium Arthrospira platensis has been investigated over 15 days. It has been observed that high NaCl concentration induces an increase of the growth, photosynthetic efficiency (α), phycobilin/chlorophyll ratio and a slight decrease of dark respiration and compensation points. Moreover, high NaCl concentration enhances photosystem II (PSII) activity compared to photosystem I (PSI). Results show that the phycobilin-PSII energy transfer compared to the chlorophyll-PSII (F_695,600/F_695,440) increases. However, data obtained about the maximal efficiency of PSII photochemistry are controversial. Indeed, the Fv/Fm ratio decreases in salt adapted cultures, while at the same time the trapping flux per PSII reaction center (TR₀/RC) and the probability of electron transport beyond Q_A (₀) remain unchanged at the level of the donor and the acceptor sites of PSII. This effect can be attributed to the interference of phycobilin fluorescence with Chl a when performing polyphasic transient measurements.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

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.     

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.     

Time Course of <Emphasis Type="Italic">c-fos</Emphasis>, <Emphasis Type="Italic">vasopressin</Emphasis> and <Emphasis Type="Italic">oxytocin</Emphasis> mRNA Expression in the Hypothalamus Following Long-Term Dehydration

Summary 1. This study presents a time course analysis of the messenger RNA (mRNA) levels of c-fos, vasopressin (VP), and oxytocin (OT) in the paraventricular (PVN) and supraoptic nucleus (SON), following acute and chronic dehydration by water deprivation. 2. Male Wistar rats were separated into five groups: nondehydrated (control group) and dehydrated for 6, 24, 48 and 72 h. Following water deprivation, animals were decapitated, their blood was collected for hematocrit, osmolality, and plasma sodium measurements, and brains were removed for dissection of both PVN and SON. 3. As expected, the hematocrit, osmolality, plasma sodium, and weight loss were increased after water deprivation. In SON, a significant increase in both VP and OT mRNA expression was observed 6 h after dehydration reaching a peak at 24 h and returning to basal levels of expression at 72 h. In the PVN, an increase in both VP and OT mRNA expression occurred 24 h after dehydration. At 72 h the VP and OT mRNA expression levels had decreased but they were still at higher levels than those detected in control animals. 4. These results suggest that SON is the first nucleus to respond to the dehydration stimulus. Additionally, we also observed an increase in c-fos mRNA expression in both PVN and SON 6 h after water deprivation, which progressively decreased 24, 48, and 72 h after the onset of water deprivation. Therefore, it is possible that c-fos may be involved in the modulation of VP and OT genes, regulating the mRNA expression levels on a temporally distinct basis within the PVN and SON.     

Anatomical changes induced by increasing NaCl salinity in three fodder shrubs, <Emphasis Type="Italic">Nitraria retusa</Emphasis>, <Emphasis Type="Italic">Atriplex halimus</Emphasis> and <Emphasis Type="Italic">Medicago arborea</Emphasis>

Nitraria retusa and Atriplex halimus (xero-halophytes) plants were grown in the range 0–800 mM NaCl while Medicago arborea (glycophyte) in 0–300 mM NaCl. Plants were harvested after 120 days of salt-treatment. The present study was designed to study the effect of salinity on root, stem and leaf anatomy, water relationship, and plant growth in greenhouse conditions. Salinity induced anatomical changes in the roots, stems and leaves. The cuticle and epidermis of N. retusa and A. halimus stems were unaffected by salinity. However, root anatomical parameters (root cross section area, cortex thickness and stele to root area ratio), and stem anatomical parameters (stem cross section area and cortex area) were promoted at 100–200 mM NaCl. Indicating that low to moderate salinity had a stimulating effect on root and stem growth of these xero-halophytic species. At higher salinities, root and stem structures were altered significantly, and their percentages of reduction were higher in A. halimus than in N. retusa whereas, in M. arborea, they were strongly altered as salinity rose. NaCl (100–300 mM) reduced leaf water content by 21.2–56.2% and specific leaf area by 51–88.1%, while increased leaf anatomical parameters in M. arborea (e.g. increased thickness of upper and lower epidermis, palisade and spongy mesophyll, entire lamina, and increased palisade to spongy mesophyll ratio). Similar results were evidenced in A. halimus leaves with salinity exceeding 100 mM NaCl. Leaves of N. retusa were thinner in salt-stressed plants while epidermis thickness and water content was unaffected by salinity. The size of xylem vessel was unchanged under salinity in the leaf’s main vein of the three species while we have increased number in M. arborea leaf main vein in the range of 200–300 mM NaCl. A longer distance between leaf vascular bundle, a reduced size and increased number of xylem vessel especially in stem than in root vascular system was evidenced in M. arborea treated plants and only at (400–800 mM) in the xero-halophytic species. The effects of NaCl toxicity on leaf, stem and root ultrastructure are discussed in relation to the degree of salt resistance of these three species. Our results suggest that both N. retusa and A. halimus show high tolerance to salinity while M. arborea was considered as a salt tolerant species.     

Prolonged salt stress alters the ratios of protochlorophyllide spectral forms in dark-grown wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>) and influences chlorophyll <Emphasis Type="Italic">a</Emphasis> accumulation following irradiation

To examine the effects of salt stress on dark-grown wheat (Triticum aestivum), seedlings of the salt-tolerant cultivar Sids 1 and the susceptible cultivar Giza 168 were grown in darkness for 14 days in nutrient solution with and without 200 mM of supplementary salt (100 mM of NaCl and 100 mM of KCl). During this time, we monitored their protochlorophyllide (Pchlide) contents, ratios of photoactive to non-photoactive forms of Pchlide (from 655/633-nm emission ratios in their 77 K fluorescence emission spectra) and (following flash irradiation) ratios of newly formed chlorophyllide (Chlide) to non-photoactive Pchlide. In addition, the accumulation of chlorophyll a in leaf sections was monitored during prolonged (24 h) irradiation. The results depended on the developmental state of the seedlings. However, the salt stress treatment caused marked increases in both Pchlide contents in dark-grown leaves and in Chlide contents following irradiation of leaf sections of both cultivars. The ratio of phototransformable to non-phototransformable Pchlide and the abundance of newly formed Chlide were also increased by the salt stress. Further, leaves of salt-stressed seedlings consistently accumulated more chlorophyll a than leaves of unstressed seedlings when floating on the nutrient solution (with or without supplementary salt) in continuous white light. The findings are consistent with the hypothesis that increased levels of the long-wavelength form of Pchlide contribute to protective mechanisms against salt stress.     

Ethanol production by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> and <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> in the presence of orange-peel oil

Summary Two ethanologenic yeasts, Saccharomyces cerevisiae and Kluyveromyces marxianus, were used to ferment sugar solutions modeling hydrolyzed Valencia orange peel waste at 37°C. Orange stripper oil produced from orange peel was added in various amounts to determine its effect on ethanol production. The minimum peel oil concentration that inhibited ethanol production was determined after 24, 48 and 72 h and the two yeasts were compared to one another in terms of ethanol yield. Minimum inhibitory peel oil concentrations for ethanol production were 0.05% at 24 h, 0.10% at 48 h, and 0.15% at 72 h for both yeasts. S. cerevisiae produced more ethanol than K. marxianus at each time point.     

GA signaling and <Emphasis Type="Italic">CO/FT</Emphasis> regulatory module mediate salt-induced late flowering in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Flowering timing is very important for the reproductive success of higher plants. However, effects of salt on plant flowering and the underlying molecular mechanisms are largely unknown. Here, we show that salt stress delays flowering in Arabidopsis in a dose-dependent manner. Mild salt stress (≤50 mM NaCl) promoted and prolonged the vegetative growth, whereas high salinity (≥100 mM NaCl) largely delayed or inhibited the transition from vegetative growth to reproductive development. The gibberellin (GA)-pathway plays an important role in this phenotype, and application of exogenous GA could restore late flowering induced by salt. In addition, the CONSTANS (CO)/FLOWERING LOCUS T (FT) module may also play a critical role in mediating the effects of salt on flowering. The mRNA abundance of CO was significantly reduced by salt stress in a dose-dependent manner. The constans (co-2) mutants did not respond to moderate salt stress, whereas over-expressing CO manifested no delay in flowering time in response to salinity. Expression of FT, SOC1 and LFY in the downstream of the pathways was also reduced by salt according to dose. Moreover, salt-sensitive mutant salt overly sensitive3 (sos3) exhibited greater sensitivity in flowering, further suggesting that ion disequilibrium mediates salt-induced late flowering. Kexue Li and Youning Wang contributed equally to this report.     

Toxic effect of methyl <Emphasis Type="Italic">tert</Emphasis>-butyl ether on growth of soil isolate <Emphasis Type="Italic">Pseudomonas veronii</Emphasis> T1/1

The toxic and growth inhibiting effects of methyl tert-butyl ether (MTBE) on the hydrocarbon-degrading Pseudomonas veronii T1/1 strain (isolated from gasoline contaminated soil) were studied. In our experiments, the MIC of MTBE was found to be 60 mM and the EC₅₀ was 51.7 mM. In the concentration range 0–30 mM, MTBE did not significantly influence the growth parameters of this bacterium, but at concentrations over 30 mM MTBE exerted a significant growth inhibiting effect. In the presence of 70 mM MTBE, the specific growth rate dropped from 0.4731 to 0.1201 h⁻¹, while the length of the lag period increased from 5.41 to 17.01 h and the yield coefficient declined from 0.2652 to 0.0718 g g⁻¹. MTBE at 100 mM inhibited the growth of this strain completely. These findings may have important environmental implications, as high concentrations of MTBE could influence the efficiency of soil and groundwater bioremediation processes significantly.     

Biosynthesis of intracellular 5-aminolevulinic acid by a newly identified halotolerant <Emphasis Type="Italic">Rhodobacter sphaeroides</Emphasis>

Of 23 strains of halotolerant (up to 12% w/v NaCl) photosynthetic bacteria isolated from various sources, one isolate, SH5, accumulated intracellular 5-aminolevulinic acid (ALA) at 0.45 μg/g dry cell wt (DCW) growing aerobically in the dark. The strain was identified as Rhodobacter sphaeroides using 16S rDNA sequencing. Biosynthesis of ALA was enhanced to 14 μg/g DCW using modified glutamate/glucose (50 mM) medium with the addition of 10 mM levulinic acid after 24 h cultivation. Addition of 30 μM Fe²⁺ to this medium increased the yield to 226 μg/g DCW.     

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.     

Fusion of carbohydrate binding modules from <Emphasis Type="Italic">Thermotoga neapolitana</Emphasis> with a family 10 xylanase from <Emphasis Type="Italic">Bacillus halodurans</Emphasis> S7

Xylanase A of Thermotoga neapolitana contains binding domains both at the N- and C-terminal ends of the catalytic domain. In the N-terminal position it contains two carbohydrate-binding modules (CBM) which belong to family 22. These CBMs bind xylan but not to cellulose. The gene encoding the mature peptide of these CBMs was fused with an alkaline active GH10 xylanase from Bacillus halodurans S7 and expressed in Escherichia coli. The (His)₆ tagged hybrid protein was purified by immobilized metal affinity chromatography and characterized. Xylan binding by the chimeric protein was influenced by NaCl concentration and pH of the binding medium. Binding increased with increasing salt concentration up to 200 mM. Higher extent of binding was observed under acidic conditions. The fusion of the CBM structures enhanced the hydrolytic efficiency of the xylanase against insoluble xylan, but decreased the stability of the enzyme. The optimum temperature and pH for the activity of the xylanase did not change.     

Antioxidative responses and their relation to salt tolerance in <Emphasis Type="Italic">Echinochloa oryzicola</Emphasis> Vasing and <Emphasis Type="Italic">Setaria virdis</Emphasis> (L.) Beauv.

Two gramineous species among wild plants, Echinochloa oryzicola Vasing and Setaria viridis (L.) Beauv., and Oryza sativa L. cv. Nipponbare were subjected to salt stress. The relative growth rate (RGR), Na content, photosynthetic rate, antioxidant enzymes activity (superoxide disumutase (SOD), catalase (CAT), ascorbate peroxidase (APx) and glutathione reductase (GR)), and malondialdehyde (MDA) content in leaves after NaCl treatment were studied. RGR significantly decreased in O. sativa more than in E. oryzicola and S. viridis. Comparatively salt-tolerant S. viridis showed higher growth rate, lower Na accumulation rate in leaves, higher photosynthetic rate, and induced more SOD, CAT, APx, and GR activity and lower increase of MDA content as compared to the salt-sensitive O. sativa. At the same time, the comparatively salt-tolerant E. oryzicola also showed higher growth rate, much lower Na accumulation and no observable increase of MDA content, even though the CAT and APx activities were not induced by salinity. These results suggested that the scavenging system induced by H₂O₂-mediated oxidative damage might, at least in part, play an important role in the mechanism of salt tolerance against cell toxicity of NaCl in some gramineous plants     

Photosynthesis and photosystem 2 efficiency of two salt-adapted halophytic seashore <Emphasis Type="Italic">Cakile maritima</Emphasis> ecotypes

The effects of salinity (0–400 mM NaCl, marked S₀, S₁₀₀, S₂₀₀, and S₄₀₀) on growth, photosynthesis, photosystem 2 (PS2) efficiency, ion relations, and pigment contents were studied in two seashore Cakile maritima ecotypes (Tabarka and Jerba, respectively, sampled from humid and arid bioclimatic areas). Growth of Jerba plants was improved at S₁₀₀ as compared to S₀. Tabarka growth was inhibited by salinity at all NaCl concentrations. Leaf sodium and chloride concentrations increased with medium salinity and were higher in Jerba than in Tabarka plants. Chlorophyll content, net photosynthetic rate, stomatal conductance (g _s), and intracellular CO₂ concentration were stimulated at moderate salinity (S₁₀₀) in Jerba plants and inhibited at higher salt concentrations in both ecotypes: g _s was the most reduced parameter. The maximum quantum efficiency of PS2 (F_v/F_m), quantum yield, linear electron transport rate, and efficiency of excitation energy capture by open PS2 reaction centres showed no significant changes with increasing salt concentration in Jerba plant and were decreased in Tabarka subjected to S₄₀₀. However, the efficiency of dissipation of excess photon energy in the PS2 antenna was maintained in Jerba and was increased in Tabarka plants challenged with S₄₀₀. Hence the relative salt tolerance of Jerba was associated with a better ability to use Na⁺ and Cl⁻ for osmotic adjustment, the absence of pigment degradation, and the concomitant PS2 protection from photodamage.     

Growth and ion uptake in <Emphasis Type="Italic">Annona muricata</Emphasis> and <Emphasis Type="Italic">A. squamosa</Emphasis> subjected to salt stress

The effects of treatment with NaCl (3, 100 and 300 mM) for 1, 2, 3 and 7 d on plant growth and ion accumulation were analyzed in 2-week and 8-week-old Annona muricata and A. squamosa plants. Fresh mass and root growth inhibition were directly related to the increase in salinity, particularly for A. squamosa. Two-weeks old seedlings were sensitive to 100 and 300 mM NaCl particularly after 7 d, whereas 8-week-old plants were shown to be more resistant to NaCl even at 300 mM NaCl. Na⁺ and Cl^– mostly accumulated in young leaves. Our results suggest that A. squamosa is more sensitive than A. muricata to salt stress and that older seedlings of both species are more tolerant than younger seedlings.