La glutamine synthètase du Suaeda maritima. Action in vivo et in vitro du NaCl

The glutamine synthetase of Suaeda maritima. In vivo and in vitro action of NaCl Glutamine synthetase (GS; EC 6.3.1.2) was isolated and characterized from roots and aerial parts of the halophyte Suaeda maritima (L.) Dum. var. macrocarpa Moq. Km values of GS were identical in both types of organ and unchanged by the salinity in the medium. Addition of NaCl in the culturing solution increased the specific activity of the enzyme especially in the aerial parts, where GS is more abundant. This increase was all the more pronounced if the plant-salt contact period was extended (between 21 and 45 days). In vitro the addition of 0 to 500 m M of salt did not affect the activity of GS at satured substrate concentrations. At low glutamate concentrations in combination with 300 m M NaCl or more, a slight competitive inhibition was observed, never over 18%. – The remarkable insensibility of GS to salinity in vitro and the stimulating effect of NaCl in vivo on the synthesis of the leaf enzyme indicates that GS plays a fundamental part in the assimilation of NH4⁺ in the halophyte Suaeda maritima var. macrocarpa.     

Sensitivity of selected Frankia isolates from Casuarina, Allocasuarina and North American host plants to sodium chloride

Three experiments examined the effects of NaCl concentrations 0 to 500 mM on the growth of isolates of Frankia from Casuarinaceae and selected North American host plants. Four Casuarina isolates grew well in defined medium (pyruvate-BAP) but not in a yeast extract medium. Conversely the non-Casuarina isolates preferred the yeast-extract medium, although two of them grew in the defined medium. When grown in their preferred medium, the Casuarina isolates were little affected by NaCl concentrations up to 200 m M but did not grow at 500 m M . The non-Casuarina isolates, with the exception of an isolate from Purshia tridentata . were severely affected above 50 m M NaCl.
Nitrogenase activity (C₂H₂ reduction) by the non-Casuarina isolates could not be detected in low-N medium although protein determinations indicated that a low level of nitrogen fixation had occurred. All four Casuarina isolates showed nitrogenase activity in culture, up to 200 m M NaCl, although at that concentration of NaCl, growth was affected more than that of cultures in N-supplemented medium. All four strains showed a marked increase in nitrogenase activity up to 72 h after the addition of C₂H₂, with the magnitude of the effect and their subsequent behaviour being strain dependent.
The results indicate that the isolates of Frankia from Casuarina and Allocasuarina , and that from Purshia tridentata , are more tolerant of NaCl than isolates from species not normally growing under sodic conditions. They provide optimism that these strains could successfully establish in saline soils if introduced with species of host plants tolerant to these soils.     

Specific regulation of SOD isoforms by NaCl and osmotic stress in leaves of the C3 halophyte Suaeda salsa L

The halophyte Suaeda salsa L., exposed to different NaCl concentrations (100 and 400 mmol/L) and polyethylene glycol (isoosomotic to 100 mmol/L NaCl) containing nutrient solutions under normal or K+-deficient conditions for 7 days, was used to study effects of NaCl salinity and osmotic stress on chlorophyll content, chlorophyll fluorescence characteristics, malonedialdehyde (MDA) content, and superoxide dismutase (SOD) isoform activities. Photosynthetic capacity was not decreased by NaCl treatment, indicating that S. salsa possesses an effective antioxidative response system for avoiding oxidative damage. Seven SOD activity bands were detected in S. salsa leaf extracts, including an Mn-SOD and several isoforms of Fe-SOD and CuZn-SOD. It turned out that NaCl salinity and osmotic stress lead to a differential regulation of distinct SOD isoenzymes. This differential regulation is suggested to play a major role in stress tolerance of S. salsa.     

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

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

盐胁迫下囊果碱蓬出苗状况及苗期抗盐性

研究了盐胁迫对囊果碱蓬出苗、幼苗生长、离子积累以及光合放氧速率的影响.囊果碱蓬生长的最适盐浓度在200 mmol/L NaCl左右.高浓度NaCl(400 mmol/L和600 mmol/L)没有显著降低其出苗率,200 mmol/L NaCl对出苗率具有促进作用.400 mmol/L和600 mmol/L NaCl显著降低了光合放氧速率.囊果碱蓬在高浓度NaCl处理下能够维持叶片较高的K+/Na+ 及含水量可能是其适应高盐生境的重要机制.     

Growth, photosynthesis and respiration in Plantago coronopus as affected by salinity

Plantago coronopus was grown in a non-saline culture solution and in a culture solution containing 50 m M NaCl. The rates of dry matter accumulation in both roots and shoots were not affected by 50 m M NaCl. Photosynthesis, expressed per shoot, was also the same in both environments. Neither the rate of shoot respiration nor that of root respiration was affected by salinity. In both environments the alternative respiratory pathway contributed to the same extent in root respiration. The activity of the alternative pathway decreased with increasing age. Since the respiratory activities were the same in plants grown under both saline and non-saline conditions and since the alternative respiratory pathway was also equally active in roots under both environmental conditions, it is concluded that respiratory costs involved in growth in 50 m M NaCl are negligible in terms of the plant's total energy costings.     

NaCl‐induced accumulation of glycinebetaine in four subtropical halophytes from Pakistan

Variation in both the total content and the concentration of glycinebetaine in response to increasing soil salinity was studied in the salt‐secreting Atriplex griffithii Moq., the leaf succulent Suaeda fruticosa (L.) Forssk., the stem succulent Haloxylon recurvum Bunge ex Boiss. and the osmotically adjusting desert grass Halopyrum mucronatum (L.) Stapf. collected from a subtropical maritime desert in Pakistan. Glycinebetaine content (mmol kg⁻¹ dry weight) increased with increasing NaCl in Atriplex griffithii, Haloxylon recurvum and Halopyrum mucronatum , but peaked at 600 m M NaCl for Suaeda fruticosa and declined thereafter. Glycinebetaine concentration (mmol l⁻¹ tissue water) increased with increasing salinity in all four halophyte species and was sufficiently high to serve as an osmoticum in all cases.     

Salt tolerance of the reed plant Phragmites communis

Reed plants ( Phragmites communis Trinius) were grown at NaCl concentrations up to 500 m M and their growth, mineral contents and leaf blade osmotic potential were determined. Addition of NaCl up to 300 m M did not affect growth significantly. Sucrose, Cl^-and Na⁺ concentrations in the shoots increased with the salinity of the medium and the shoot water content decreased. K⁺ always contributed most to the leaf osmotic potential. Even in the presence of 250 m M NaCl in the rooting medium, the leaf blade contained only 50 mM Na⁺, suggesting that the plants have an efficient mechanism for Na⁺ exclusion. ²²Na⁺ uptake experiments suggested that the retranslo-cation of absorbed Na⁺ from shoots to the rooting medium lowered the uptake of Na⁺.     

Nitrogen fixation (C2H2 reduction) by Medicago nodules and bacteroids under sodium chloride stress

Medicago ciliaris (L.) All., a salt-tolerant legume, was not nodulated by Rhizobium meliloti (2011), a strain commonly used for field inoculation of alfalfas. A strain of Rhizobium meliloti (ABS7) was isolated from saline Algerian soils. It is generally more salt-resistant than strain 2011, exhibits a higher rate of growth and induces the formation of nodules on M. ciliaris . C₂H₂ reduction activity of M. ciliaris nodules was inhibited by 50% in the presence of 200 m M NaCl in the culture medium. whereas 100 m M NaCl was sufficient to inhibit the activity of nodules of M. sativa (L. cv. Europe). C₂H₂ reduction by bacteroids, isolated from nodules of the two species of alfalfa, was directly inhibited by the presence of NaCl in the incubation medium. In both cases, glucose could support bacteroid nitrogen fixation, but only in a narrow range of O₂ tensions. Bacteriods from M. ciliaris were more tolerant to salt than M. sativa ones. The salt resistance of bacteroids from nodules of plants watered with NaCl solutions was not improved in either species. Salt directly added to the incubation mixture of bacteroids or to the culture medium of plants inhibited O₂ uptake of bacteroids isolated from nodules of both M. ciliaris and M. sativa . The depressive effect of NaCl on bacteroid C₂H₂ reduction could be directly related to the drop in bacteroid respiration. The nitrogen fixation capacity of the M. ciliaris-Rhizobium meliloti (ABS7) symbiosis under saline conditions leads us to recommend the introduction of this association in salt-troubled areas.     

Wachstum und photosyntheseleistung der halophyten Mesembryanthemum nodiflorum L. und Suaeda maritima (L.) Dum. bei variierter NaCl-Salinität des anzuchtmediums

Summary The effect of various concentrations of NaCl in the culture solution (up to 400 mM) on growth (fresh weight, dry weight, chlorophyll content) and net CO₂ gas exchange was studied in two halophytes, Mesembryanthemum nodiflorum L. and Suaeda maritima (L.) Dum. Mesembryanthemum nodiflorum reaches optimal growth at concentrations of 100 to 200 mM NaCl in the culture medium, whereas growth of Suaeda maritima is stimulated up to concentrations of 400 mM NaCl. Independent of this stimulated plant growth, net CO₂ uptake in the light appears to be decreased with increased salinity when net CO₂ assimilation is calculated on a fresh weight or dry weight basis. However, expressed per mg chlorophyll, net CO₂ uptake is clearly correlated with plant productivity at different levels of salinity.     

Effects of NaCl on the properties of phosphoenolpyruvate carboxylase from Suaeda monoica and Chloris gayana

The effects of NaCl on the kinetic properties of desalted phosphoenolpyruvate carboxylase (PEP carboxylase, EC 4.1.1.31) from two halophytes, Suaeda monoica Forssk. ex. J.F. Gmel and Chloris gayana Kunth. were investigated. The tolerance of PEP carboxylase to NaCl in the reaction medium depends on the enzyme pre-conditioning as well as on the concentration of its substrate PEP in the assay medium. Addition of PEP to the extraction and the storage medium, stabilizes the enzyme. Such a pre-treated enzyme is inhibited by NaCl in the presence of low concentrations of PEP in the assay medium but is activated by NaCl in the presence of PEP at concentrations above 1.0 m M . NaCl modifies the n_H value, K' and V_max, and seems to act as an allosteric effector.     

Osmoregulation of the salt-tolerant yeast Debaryomyces hansenii grown in a chemostat at different salinities.

The intracellular solute composition of the salt-tolerant yeast Debaryomyces hansenii was studied in glucose-limited chemostat cultures at different concentrations of NaCl (4 mM, 0.68 M, and 1.35 M). A strong positive correlation between the total intracellular polyol concentration (glycerol and arabinitol) and medium salinity was demonstrated. The intracellular polyol concentration was sufficient to balance about 75% of the osmotic pressure of the medium in cultures with 0.68 and 1.35 M NaCl. The intracellular concentration of K+ and Na+, which at low external salinity gave a considerable contribution to the intracellular water potential, was only slightly enhanced with raised medium salinity. However, the ratio of intracellular K+ to Na+ decreased; but this decrease was less drastic in the cells than in the surrounding medium, i.e., the cells were able to select for K+ in favor of Na+. The turgor pressure, which was estimated on the basis of intracellular solute concentrations, was 2,200 kPa in cultures with 4 mM NaCl and decreased when the external salinity was raised, resulting in a value of about 500 kPa in cultures with 1.35 M NaCl. The maintenance of a positive turgor pressure at high salinity was mainly due to an increased production and accumulation of glycerol.     

盐分对碱蓬幼苗离子含量,甜菜碱水平和BADH活性的效应

研究了盐生植物碱蓬（Ｓｕａｅｄａ ｓａｌｓａ）生长在不同浓度的ＮａＣｌ和ＫＣｌ溶液中体内Ｎａ＋ 、Ｋ＋ 含量、甜菜碱水平和甜菜碱醛脱氢酶（ＢＡＤＨ）活性的动态变化。ＮａＣｌ处理９６ 小时后,碱蓬地上部Ｋ＋ 含量低于对照,而Ｎａ＋ 明显高于对照,并分别随外界盐度增加而升、降;ＫＣｌ处理的植株,Ｋ＋ 、Ｎａ＋ 含量变化与ＮａＣｌ处理的相反;甜菜碱水平和ＢＡＤＨ 活性随外界ＮａＣｌ浓度增加而升高,甜菜碱水平随处理时间延长而增大,ＫＣｌ对甜菜碱水平和ＢＡＤＨ 活性的效应类似ＮａＣｌ。证明ＮａＣｌ和ＫＣｌ均能促进盐生植物碱蓬体内甜菜碱的积累,初步证明ＢＡＤＨ 与甜菜碱的积累有关     

Relationship between the photosynthetic activity and the performance of Cakile maritima after long-term salt treatment

Cakile maritima is a halophyte with potential for ecological, economical and medicinal uses. We address here the impact of salinity on its growth, photosynthesis and seed quality. Whole plant growth rate and shoot development were stimulated at moderate salinity (100–200 m M NaCl) and inhibited at higher salt concentrations. Although diminished in the presence of salt, potassium and calcium uptake per unit of root biomass was maintained at relatively high value, while nutrient-use efficiency (NUE) was improved in salt-treated plants. Chl and carotenoid concentrations decreased at extreme salinities, but anthocyanin concentration continuously grew with salinity. Net photosynthetic rate (A), stomatal conductance, maximum quantum efficiency of PSII and quantum yield were stimulated in the 100–200 m M NaCl range. Higher salinity adversely affected gas exchange and changed PSII functional characteristics, resulting in a reduction of A per leaf area unit. This phenomenon was associated with increased non-photochemical quenching. Harvest index, silique number and seeds per fruit valve were maximal at 100 m M NaCl. Despite the decreasing salt accumulation gradient from the vegetative to the reproductive organs, high salinities were detrimental for the seed viability and increased the proportion of empty siliques. Overall, the salt-induced changes in the plant photosynthetic activity resulted into analogous responses at the vegetative and reproductive stages. The enhancement of NUE, the absence of pigment degradation, the reduction of water loss and the concomitant PSII protection from photodamage through thermal dissipation of excess excitation significantly accounted for Cakile survival capacity at high salinity.     

盐旱互作对不同生境盐地碱蓬种子萌发和幼苗生长的影响

研究了盐旱互作对潮间带和盐碱地生境盐地碱蓬棕色种子萌发、地上部生长和离子积累的影响。不同盐浓度预处理后,未萌发的种子风干后复水,其萌发率与对照相比没有降低,说明两种生境盐地碱蓬种子萌发期间都耐干湿交替。400mmol/LNaCl溶液浇灌的潮间带生境盐地碱蓬幼苗在第3次干旱处理后萎蔫幼苗的百分比高于盐碱地生境的,而复水后正常幼苗的百分比却相反。400mmol/LNaCl溶液处理下,第3次干旱处理复水后,盐碱地生境盐地碱蓬幼苗地上部离子含量(主要是Na+和Cl-)高于潮间带生境的。表明在干旱情况下,盐碱地生境盐地碱蓬幼苗能积累更多的无机离子,降低渗透势,提高根系吸收水分的能力。上述结果说明,盐碱地生境盐地碱蓬幼苗较潮间带生境盐地碱蓬幼苗更耐盐与干旱的交互作用。     

Enhancement of NaCl tolerance in Arabidopsis thaliana by exogenous L-asparagine and D-asparagine

The tolerances of Columbia Arabidopsis thaliana (L.) Heynh. to NaCl, L-asparagine (L-Asn) and D-asparagine (D-Asn) during seedling establishment on sterile agar medium were determined. Germination and the establishment of upright seedlings with expanded green cotyledons were increasingly inhibited by NaCl concentrations from 20 to 180 m M and radicle growth was prevented at 225 m M NaCl. Tolerance of established seedlings to NaCl was similar at these concentrations. Seedling establishment was prevented at 20 m M L-Asn and 60 m M D-Asn, but L-Asn was not toxic to established seedlings. At lower concentrations, exogenous L- and D-Asn enhanced NaCl tolerance during germination and seedling establishment. Inhibition of seedling establishment by NaCl concentrations below 225 m M was reduced by the addition of L- and D-Asn to the medium. Maximal reduction of NaCl inhibition occurred between 2 and 4 m M for both L- and D-Asn. Higher concentrations of NaCl prevented establishment whether exogenous Asn was present or not. Reduction of NaCl inhibition occurred to the same extent whether L-Asn was presented simultaneously with the NaCl or preloaded for up to 24 h. The total seedling content of Na⁺ increased about 4-fold to 55 μg (mg dry weight)⁻¹ as the medium concentration of NaCl was increased from 9 μ M to 150 m M NaCl. Total K⁺ content declined about 80% from about 34 μg (mg dry weight)⁻¹ over the same range of NaCl concentrations. The Na⁺ uptake and K⁺ efflux by whole seedlings were similar whether or not NaCl tolerance was increased by exogenous Asn.     

Motility of Mugil cephalus L. spermatozoa in coelomic fluid, seminal fluid and saline media

The aim of this study was to assess the motility duration of Mugil cephalus when exposed to seminal fluid, coelomic fluid and saline media. Hypo-osmotic activation medium (distilled water containing bovine serum albumin 10 or 30 mg ml⁻¹) did not trigger sperm motility. Saline solution containing 500 m m NaCl, 3.1 m m KCl, 0.2 m m Tris, 3.4 m m CaCl₂, pH 7.5 initiated the sperm activation and the motility lasted for more than 2 min. Coelomic fluid showed an inhibitory effect for triggering the motility of spermatozoa. Higher salinity increases the motility duration of sperm. The optimum motility duration was shown in salinity 32 psu.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

Comparison of Distichlis spicata and Suaeda aegyptiaca in response to water salinity: Candidate halophytic species for saline soils remediation

Distichlis spicata and Suaeda aegyptiaca are two potential halophytic plant species for bioremediation of salt degraded soils, and development of saline agriculture. The physiological responses of the species to different levels of salinity (EC 0, 12, 24, 36, and 48 dS/m) in a controlled environment experiment were studied. Both species showed a high level of tolerance to elevated concentrations of salt in the irrigation water. The shoot fresh and dry weights in S. aegyptiaca increased till 36 dS/m and were sustained under 48 dS/m while in D. spicata, both parameters decreased as salinity increased. Glycine betaine accumulation did not change in D. spicata with increasing salinity, whereas proline content revealed a marked increase of 7.13 fold in 48 dS/m salinity compared to the control, which showed its critical osmoprotection role in the plant. In S. aegyptiaca, both osmolytes content significantly increased at high salinity levels (36 and 48 dS/m) up to 3.22 and 2.0 folds, respectively. Overall, S. aegyptiaca had a better potential of Na⁺ phytoremediation, and tolerated higher salinity compared to D. spicata. In contrast, the vigorous root and rhizome growth in D. spicata made it a proper solution for protecting the soils against further erosion under saline conditions.