Effect of Salts on Growth and Pectinase Production by Halotolerant Yeast, <Emphasis Type="Italic">Debaryomyces nepalensis</Emphasis> NCYC 3413

In this study, Debaryomyces nepalensis NCYC 3413 isolated from rotten apple was studied for its halotolerance and its growth was compared with that of Saccharomyces cerevisiae in high salt medium. The specific growth rate of D. nepalensis was not affected by KCl even up to a concentration of 1 M, whereas NaCl and LiCl affected the growth of D. nepalensis. Among all tested salts, LiCl showed maximum inhibition on growth. At all conditions, halotolerance of D. nepalensis was much higher than that of S. cerevisiae. D. nepalensis showed maximum viability (80–100%) when grown in KCl, which was higher than with NaCl and LiCl. Pectinase production by D. nepalensis was noted at all high salt concentrations, namely, 2 M NaCl, 2 M KCl, and 0.5 M LiCl, and the maximum specific activity was observed when the strain was grown in 2 M NaCl.     

Ecological studies onTamarix aphylla (L.) Karst

Summary Young saplings ofTamarix aphylla were investigated for their growth intensity under saline irrigation, as well as for the lethal limits of salinity they can tolerate. The saplings were found to be quite sensitive to the addition of NaCl to the irrigation solutions and died when the concentration of the solutions was raised to about 0.7.M NaCl. Growth was depressed even by irrigation with a 0.1M NaCl solution, and no increase in the plant weight was obtained under irrigation with a 0.3M NaCl solution. It, thus, appears thatT. aphylla is not suitable for afforestation of saline habitats.Some aspects of the salt excretion ofT. aphylla were investigated. Sodium and chlorine were found to be excreted most readily and exhibit an optimum type of curve, when the excretion is plotted against the concentration of the irrigation solution. Interrelations between the various ions in the irrigation solutions and the amounts of salts excreted, were found to take place and to parallel the behaviour of these ions in their uptake by the roots. T. aphylla seems to be able to reflect the soil's salinity and the composition of its salts, by the excreted salt crystals.     

Effect of salinity on growth of four strains of Rhizobium and their infectivity and effectiveness on two species of Acacia

Two Rhizobium strains (WU1001 and WU1008) were isolated from nodules of Acacia redolens growing in saline areas of south-west Australia, and two strains selected from the University of Western Australia's culture collection (WU429 isolated from A. saligna and WU433 from A. cyclops). The growth of each in buffered, yeast extract mannitol broth culture was largely unaffected by salt up to 300 mM NaCl. A slight increase in lag time occurred at concentrations of 120 mM NaCl and above, but cell number at the static phase was not affected. Each of the four Rhizobium strains tested accumulated Na⁺ but showed decreasing levels of sugar with increasing salt in the external medium. Amino acid levels also increased, in some cases by more than tenfold. However, the relative proportion of each remained fairly constant in the bacteria, irrespective of salt treatment. Only trace quantities of proline were detected and there was no increase in this amino acid with salt. Acidic amino acids (glutamate and aspartate) remained as a constant proportion.Rhizobium strains WU429, WU1001 and WU1008 produced effective nodules on both A. cyclops and A. redolens grown in sand with up to 80 mM NaCl (added in nutrient solutions free of nitrogen). Strain WU433 was highly infective on both Acacia species tested at low salt concentrations (2–40 mM NaCl), but infection was sensitive to salt levels at 120 mM NaCl and above. Nodules formed with strain WU433 were, however, ineffective on both A. redolens and on A. cyclops and showed nil or negligible rates of acetylene reduction at all salt concentrations. Strains WU429, WU1001 and WU1008 in combination with a highly salt-tolerant provenance of A. redolens formed symbioses which did not vary significantly in nodule number and mass, specific nodule activity or total N content irrespective of salt level up to 160 mM NaCl. On a more salt sensitive provenance of A. redolens and on A. cyclops the infectivity and effectivity of the Rhizobium strains tested usually decreased as the external salt concentration increased. These data are interpreted to indicate that tolerance of the legume host was the most important factor determining the success of compatible Rhizobium strains in forming effective symbioses under conditions of high soil salinity.     

Poly(L–lysine)–DNA interactions in NaCl solutions: B → C and B → ψ Transitions

Thermal denaturation and circular dichroism (CD) properties of poly(L -lysine)–DNA complexes vary greatly when these complexes are prepared differently, that is, whether by NaCl-gradient dialysis starting from 2.0 M NaCl or by direct mixing at low salt. These differing properties were investigated in more detail by examining complexes, made by direct mixing in the presence of various concentrations of NaCl, both before and after the NaCl was dialyzed out of the complex solution. The precipitation curves of DNA due to polylysine binding indicate that such binding is noncooperative at zero salt; from 0.1 up to 1.0 M NaCl they exhibit varying degrees of cooperatively. Starting from zero salt, as the NaCl concentration used for complex formation is increased, both the CD and the melting properties of the complexes are shifted from those of directly mixed at zero salt to those of reconstitution: in the CD spectra there is a gradual shift from a B → C transition to a B → ψ transition; thermal denaturation results show a gradual increase in the melting temperatures of both free DNA (t_m) and polylysine-bound DNA (t′_m). The progressive shift from B → C to B → ψ suggests a close relationship between these two transitions. Large aggregates of the complexes do not warrant the appearance of ψ-type CD spectra: ψ-spectra have been obtained in the supernatants of polylysine–DNA complexes made and measured at 1.0 M NaCl while slightly perturbed CD spectra in B → C transition have been observed in turbid solutions of fully covered complexes made at very low salt. If the complexes are made at intermediate salts and dialyzed to a very low salt, although up to 60% of the DNA is still bound by polylysine, the CD spectra of the complexes are shifted back to the B-type CD characteristic of pure DNA.     

Effects of temperature and gibberellic acid on phospholipid composition of Avena sativa stem segments

Stem segments taken from Avena sativa plants grown at 10°, 20° or 30° varied in their phospholipid composition depending on the growth temperature; as temperature was lowered, there was a shift towards a greater proportion of unsaturated fatty acids. A significant increase was observed in the concentration of linolenic acid (18:3) as growth temperature was lowered. Although prolonged treatment of oat plants with GA₃ produced marked changes in phospholipid composition of stem segments, these changes did not always accompany the GA₃-induced growth response of segments. Treatment of stem segments with GA₃ for only 20 hr produced a significant growth response with little or no effect on phospholipid composition over this time. The data support the hypothesis that GA₃-induced growth in Avena stem segments can occur without a concomitant change in phospholipid composition.     

The role of osmotic effects in haloadaptation of Vibrio costicola

Growth rates of Vibrio costicola showed a broad optimum between 0.8 and 1.5 M-NaCl, and there was no growth above 3.3 M-NaCl in a peptone-based medium. The minimum requirement of 0.5 M-NaCl for growth in NaCl alone was reduced to 0.3 M-NaCl when the total solute concentration was raised to 0.5 to 1.0 M equivalent with sucrose or glycerol. Compared with equivalent NaCl concentrations, higher concentrations of sucrose were more inhibitory to growth, whereas glycerol had less effect. Increasing the medium NaCl concentration suddenly by 2- or 3-fold with either a constant starting, or final, salt concentration showed that, after the shift-up, the lag in growth, the rate of growth, and the inhibition of phospholipid synthesis depended both on the final NaCl concentration and the magnitude of the shift in salinity. The time-courses of phospholipid synthesis following a 2- or 3-fold shift-up in NaCl or sucrose media were very similar and exhibited a relative increase in phosphatidylglycerol synthesis over that of phosphatidylethanolamine. This 'switch-over' was not seen following shift-up in glycerol media when there was also a stimulation, rather than inhibition, of phospholipid synthesis. It is concluded that during phenotypic haloadaptation of V. costicola, osmotic effects play a significant part in the sensing of and response to raised external salinity.     

Salt resistance of chickpea genotypes in solutions salinized with NaCl or Na2SO4

Summary To assess the potential for developing a salt resistant cultivar of chickpea (Cicer arietinum L.) 160 genotypes were screened for percent survival after 9 weeks in greenhouse solution cultures, with 50 mM NaCl or 25 mM Na₂SO₄. All plants grew well in the sulfate treatment but only cv. L-550 survived the chloride treatment. Salt damage appeared and developed slowly. To check these apparent effects of cultivar and kind of anion, three genotypes including cv. L-550 were then grown in solutions with isoosmotic NaCl or Na₂SO₄ at three levels (−0.044, −0.088, and −0.132 MPa), and in a separate experiment cv. L-550 was grown with NaCl and Na₂SO₄ at four levels: 10, 20, 30 and 50 mM Na. Salt composition affected shoot weight less than salt level or cultivar did. Shoot dry weight was only slightly less in chloride treatments than in isoosmotic sulfate, and for the least sensitive cultivar (L-550) this held only at the highest salt level, corresponding to that in the screening trial. Further, sensitivity to sulfate and to chloride was equal when sodium concentrations in shoots were equal, regardless of anion compositions of media. Shoot Na concentration was a useful negative indicator of growth under salt stress regardles of cultivar, and may be a useful tolerance indicator also for other species that neither accumulate nor efficiently exclude Na.     

盐胁迫对沙拐枣光合生理特性的影响

以采自甘肃民勤一年生的沙拐枣幼苗为试材,对不同NaCl浓度(0、50、100、200、300mmol·L~(-1))处理下沙拐枣光合生理特性进行分析,并对各生理指标与地上生物量进行灰色关联度分析,以探讨荒漠植物沙拐枣的抗盐机理,为沙拐枣的保护及其恢复荒漠生态系统稳定提供理论依据。结果显示:随着NaCl浓度的升高,沙拐枣同化枝内脯氨酸含量逐渐增大,而其可溶性糖含量逐渐减小;在低浓度NaCl(50mmol·L~(-1) NaCl)处理下,同化枝光合参数均增加,且净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)均达到最大值,比对照分别显著增加了33.3%、68.0%、60.8%;与50mmol·L~(-1) NaCl相比,处理浓度超过50mmol·L~(-1) NaCl时,Pn、Gs、Tr均降低;同化枝叶绿素b含量随着NaCl浓度的增加而降低,而叶绿素a和总叶绿素含量均呈先增加后降低的趋势。灰色关联度分析发现,同化枝的Tr、Gs、Ci以及叶绿素b与地上生物量的关联度较大。研究表明,低盐浓度NaCl激活了沙拐枣的某些生理机制,有利于植株的光合作用和生长,而植物在高盐浓度胁迫时能通过调节脯氨酸和可溶性糖的含量,减少叶绿素含量、Pn和Tr等维持自身的生长。     

Effects of CaSO4 and NaCl on growth and nitrogen fixation ofLeucaena leucocephala

Effects and interactions of varying CaSO₄ and NaCl levels on growth and nitrogen fixation ofLeucaena leucocephala K8 were examined. Leucaena was grown in nutrient solution at four levels of CaSO₄ (0.5, 1.0, 2.5 and 5.0 mM) and NaCl (1, 25, 50 and 100 mM) in randomized blocks with five replications. While NaCl significantly reduced plant growth, additions of CaSO₄ increased plant height, leaf number, and biomass of salt treated plants. For the nonsaline treatments, high CaSO₄ levels slightly depressed growth, which contradicts suggestions that Leucaena has a high calcium requirement. A significant calcium/sodium interaction was not seen for nodule number or weight. Nodule number was significantly depressed by 100 mM NaCl and nodule weight of the salt stressed plants significantly increased as CaSO₄ concentration increased from 0.5 to 2.5 mM. Effects of NaCl and CaSO₄ on nitrogen content of plant parts were inconclusive. The promotion of Leucaena salinity tolerance by addition of CaSO₄ may be attributed to the effect of calcium in maintaing the selective permeability of membranes.     

Cell envelope phospholipid changes in a moderate halophile during phenotypic adaptation to altered salinity and osmotic stress

Abstract The increased content of negatively-charged phospholipids in membranes of Vibrio costicola grown at high salinities is mediated by increased phospholipid synthesis of phosphatidylglycerol relative to phosphatidylethanolamine. This phenomenon provides a system for investigating the factors involved in triggering and controlling haloadaptation in this moderately halophilic bacterium. We review recent experiments, which show that when subjected to sudden increases in external salinity, V. costicola senses both the absolute NaCl concentration and the magnitude of the salt shift. We show that the latter is sensed at least in part via osmotic pressure effects, since shift-up into sucrose-containing media triggers comparable changes in growth and in phospholipid composition and synthesis.     

Conformational change of poly-N epsilon-glutaryl-L-lysine and poly-N epsilon-succinyl-L-lysine in aqueous salt solutions

The conformational changes of poly-N^ε-glutaryl-L -lysine (PGL) and poly-N^ε-succinyl-L -lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0–2 M, CsCl < KCl < LiCl < NaCl; and at 2–3 M, LiCl < CsCl < KCl ～ NaCl. The preferential binding of the solvent components with various alkali metal salts of PGL or PSL was measured in LiCl, NaCl, and KCl solutions by means of equilibrium dialysis and differential refractometry. It was found that with increasing salt concentration, the polymers were preferentially hydrated in NaCl and KCl soultions; however the salt was preferentially bound to the polymers in LiCl solution. Such preferential binding was suggested to be closely related to conformational change. The addition of CaCl₂ to polymer solutions led to the stabilization of the helical structure of PGL or PSL.     

Osmoregulatory responses of bacteria isolated from fresh or composted,olive-mill waste-waters

Halotolerant bacteria isolated from raw, olive-mill waste-waters (alpechin) and from composted alpechin could grow on solid medium containing up to 10% (w/v) NaCl. Most (70%) of these halotolerant isolates could also grow in liquid minimal medium with the same NaCl concentration and three isolates from this group were chosen for further study. When grown in tryptic soy broth (TSB), two isolates responded to lowering of water activity (a _w) by addition of NaCl or sucrose in the expected manner: by increasing the proportion of membrane anionic lipids diphosphatidylglycerol or phosphatidylglycerol. Some solute-specific differences were observed. In contrast, the third isolate did not alter its membrane phospholipid composition significantly in response to growth in NaCl, whereas in sucrose there was an increase in phosphatidylethanolamine. This response is contrary to the accepted interpretation of the function of such a _w-dependent changes, as being a mechanism for preserving the membrane lipid-bilayer phase. When all three isolates were grown in the presence of alpechin, there was a decrease in the proportion of phosphatidylglycerol and a rise in the level of phosphatidylethanolamine. Quantitative and qualitative differences in compatible solute composition were observed when the three isolates were grown in TSB with NaCl or sucrose added to lower a _w. The major compatible solutes in two of the isolates were proline and betaine, whereas in the third they were proline, betaine and ectoine; one isolate also contained some trehalose when NaCl but not sucrose was the osmolyte.     

四翅滨藜生理生化特征对盐胁迫的响应

采用温室盆栽试验研究四翅滨藜(Atriplex canescens)幼苗株高、地径、生物量、净光合速率、蒸腾速率、气孔导度、叶绿素含量、抗氧化酶活性及丙二醛含量对不同浓度NaCl和Na_2SO_4(0、100、200、300和400mmol·L~(-1))胁迫的响应,以探讨四翅滨藜对不同种类及不同浓度盐渍环境的适应机制及其耐盐机理。结果显示:(1)随着盐分浓度的升高,四翅滨藜幼苗的株高、地径及生物量增量呈现出先升高后降低的趋势,低盐浓度下2种盐均促进幼苗生长,盐浓度超过400mmol·L~(-1)时,NaCl对幼苗生长具有明显抑制作用。(2)2种盐处理下,四翅滨藜幼苗净光合速率(Pn)和叶绿素含量(Chl)随盐浓度增大而升高,即2种盐均对幼苗Pn和Chl含量具有促进作用,且Na_2SO_4的促进效果大于NaCl;而幼苗蒸腾速率(Tr)和气孔导度(Gs)随盐浓度升高呈先增大后减小的趋势,且Na_2SO_4的促进作用强于NaCl。(3)与对照相比,四翅滨藜幼苗的丙二醛、SOD、POD酶活性在NaCl和Na_2SO_42种盐处理下,随着盐浓度的升高均呈现出不同程度的增大,且增大幅度总体表现为NaClNa_2SO_4。研究表明,四翅滨藜在NaCl和Na_2SO_4胁迫下,叶绿素的分解速率以及发挥作用的渗透调节物质均有差异,使得幼苗叶片健康程度不同,导致叶片光合能力大小的差异,最终表现为植株的生长差异;四翅滨藜具有较强的耐盐能力,而且对Na_2SO_4的适应能力强于NaCl。     

Effects of osmotic shock and calcium on growth and solute composition of Phaseolus vulgaris plants

Identification of the primary response to salinity is of great importance in order to develop salt tolerant species. In this work the effect of a NaCl osmotic shock on leaf elongation of Phaseolus vulgaris L. cv. Contender has been studied. After establishing an osmotic shock by adding NaCl to the root medium, three consecutive events could be distinguished. First, there was a sudden interruption of leaf growth, followed by a period of retardation of growth, and then by a restoration of growth to reach the steady-state growth rate. High calcium (5 mM) in the growth medium diminished the initial loss of water in the roots and kept the water content higher upon restoration of leaf growth, as compared to low calcium levels (0.5 mM). During the low calcium treatment, leaf malate started to increase already 3 h after the start of the osmotic treatment, showing a maximum concentration at around 9 h, then decreasing and approaching the value of control plants. At high calcium, malate concentration remained unchanged with time. Plants grown in the presence of low calcium showed an increase in the concentration of total amino acids upon NaCl shock. It is estimated that organic metabolites, if confined to the cell cytoplasm, contribute significantly to the osmotic adjustment, together with inorganic ions. Our results support the hypothesis that water shortage in the roots is responsible for the initial inhibition of leaf elongation. The beneficial effect of calcium on restoration of growth after the NaCl shock is a consequence of short-term, energetically expensive osmotic adjustment, in which mainly organic metabolites are involved. Under steady state conditions, high calcium treatment results in a faster growth rate than low calcium. In a process of osmotic adjustment, in which inorganic ions are principally involved, this is the result of a decrease in leaf Na⁺ concentration in expanding leaves, together with an increase in K⁺ and Ca²⁺.     

Effect of NaCl on the in vitro Activity of Malate Dehydrogenase in Salt Marsh Halophytes of the U.S.

The in vitro effect of NaCl on NAD-malate dehydrogenase (E.C. 1.1.1.37; MDH) from desalted extracts of roots and leaves of six salt marsh halophytes was investigated. The plants, all native and important constituents of the salt marshes of the east coast of the U.S., included Spartina alterniflora Loisel., Spartina patens (Aiton) Muhl., Distichlis spicata (L.) Greene, Juncus roemerianus Schleele, Salicornia virginica L., and Borrichia frutescens (L.) DC. In the leaf extracts of all species except Borrichia frutescens, the MDH activity was slightly stimulated by NaCl at concentrations around 0.05 M at optimal pH (8.0–8.5) and was reduced by NaCl in higher concentrations. MDH activity in the leaf extract of Borrichia frutescens was more salt-tolerant and maximal activity occurred around 0.25 M NaCl at optimal pH (7.0). Even though similar pH optimums for activity were exhibited in the root and leaf extracts of each species, the MDH activity in the root extract was more salt-tolerant than that in the leaf extract. NaCl at concentrations up to 0.1 M stimulated the MDH activity in the root extracts of all species except that of Borrichia frutescens, which had an optimal activity in 0.5 M NaCl. In the root and leaf extracts of Borrichia frutescens, the activity of cytosol MDH was much more salt-tolerant than that of the mitochondrial MDH. A shift of the optimal pH to more acidic values with increasing concentrations of NaCl was noted in the extracts of all the species except Borrichia frutescens. The action of NaCl on MDH activity appeared to be a general ionic effect as judged by the response of the enzyme activity in the presence of iso-ionic concentrations of other salts and isoosmotic mannitol. Thus, the response of the MDH from five of the salt marsh plants to NaCl is similar to that of glycophytes. However, Borrichia frutescens possesses a salt-tolerant MDH that has optimal activity in a salt concentration as high as that of the environment.     

Interactive effects of salt concentration and temperature on growth and lipid composition in the moderately halophilic bacterium Vibrio costicola.

The interactive effects of NaCl concentration and growth temperature on the growth and lipid composition of the moderately halophilic eubacterium Vibrio costicola have been investigated. Vibrio costicola was shown to be capable of growth over the temperature range 4-37 degrees C. Maximum growth yields were obtained at 30 degrees C when the optimum NaCl concentration was 1.0 M NaCl. In contrast with some previous studies, at higher or lower growth temperatures both the optimum and lower limit of NaCl concentration were higher, but there was no change in the upper limit of NaCl concentration for growth. There were no differences between the lipid compositions of cultures grown in 1 M NaCl at 30 or 37 degrees C, but as the growth temperature was lowered from 30 to 10 or 4 degrees C, the ratio of phosphatidylethanolamine to phosphatidylglycerol increased significantly as a result of the conversion of phosphatidylglycerol to diphosphatidylglycerol; in addition, at the lower growth temperatures the phospholipid fatty acyl composition became more unsaturated and the mean acyl chain length was shorter. It is suggested that the altered salt dependence of V. costicola at temperatures below the optimum for growth is due to a modification in membrane lipid phase behavior and stability brought about by changes in lipid composition, whereas a different mechanism operates above the growth temperature optimum.     

Boron and calcium increasePisum sativum seed germination and seedling development under salt stress

A beneficial effect of B and Ca application on symbiotic interaction between legume and rhizobia under saline conditions has recently been shown, suggesting conventional agricultural practices to increase crop salt tolerance. However, nothing is known about application of both nutrients on early events of legume development under salt stress, prior to the establishment of a symbiotic interaction. Therefore, the effects of different levels of B (from 9.3 to 93μM B) and Ca (from 0.68 to 5.44 mM Ca) on seed germination, root elongation, plant development, and mineral composition of pea (Pisum sativum L. cv. Argona) grown under 0 to 150 mM NaCl, were analysed. Development of plants previously germinated in the presence of salt was more impaired than that of plants put under salt stress once seeds were germinated. A NaCl concentration of 75 mM and 150 mM inhibited pea seed germination and seedling growth. The addition of either extra B or extra Ca to the germination solution prevented the reduction caused by 75 mM NaCl but not that of 150 mM NaCl. However, root elongation and plant development under salt stress (75 mM NaCl) was enhanced only by addition of both B and Ca. When plants were cultivated in the absence of external N, N content in roots and shoots originating from seeds was diminished by salt and enhanced by B and Ca, suggesting a role of these nutrients in remobilisation of seed nutrient stores. Salinity also led to an extremely high concentration of Na⁺ ions, and to a decrease of B and Ca concentrations. This can be overcome by addition of both nutrients, increasing salt tolerance of developing pea plants. The necessity of nutritional studies to increase crop production in saline soils is discussed and proposed.     

Increasing NaCl and CaCl<Subscript>2</Subscript> concentrations in the growth medium of quince leaves: I. Effects on somatic embryo and root regeneration

Summary The effects of increasing concentrations of NaCl and CaCl₂ on quince (Cydonia oblonga Mill. BA 29 clone) somatic embryogenesis and adventitious root regeneration were investigated. Leaves collected from in vitro-grown shoots were used as explants and induced for 2d in liquid Murashige and Skoog medium containing 11.3 μM 2,4-dichlorophenoxyacetic acid. Explants were then cultured on semisolid Murashige and Skoog medium enriched with 4.7 μM kinetin and 0.5 μM naphthaleneacetic acid under red light for 25 d and under white light for another 25 d. Two experiments were performed: in the first, NaCl was used at 0,25, 50, 100, and 200 mM in factorial combination with CaCl₂ at 3, 9, and 27 mM; in the second, NaCl was applied at 0, 5, 10, 20, 40, and 80 mM in combination with CaCl₂ at 0.3, 1.0, and 3.0 mM. Quince leaves revealed the capacity to regenerate somatic embryos and/or adventitious roots. Quantitative and qualitative regeneration from leaves was affected by NaCl treatments: increasing NaCl concentrations, in combination with CaCl₂ at 1 mM, led to an increase in the proportion of leaves producing somatic embryos only, and to a decrease of both leaves regenerating roots only and leaves simultaneously producing somatic embryos and adventitious roots. This suggests a beneficial effect of salt stress on the embryogenic process. The regeneration response decreased with increasing salt concentrations and was almost totally inhibited above 50 mM NaCl and 9 mM CaCl₂. The presence of CaCl₂ in the culture medium apparently mitigated the effects of salt stress, but only when NaCl was applied at 40 mM. NaCl at 5 mM, in the presence of 0.3 or 1 mM CaCl₂, was favorable both to somatic embryo and root production. No value of the ratio Na⁺/Ca²⁺ was found to be optimal for the regeneration processes.     

The effects of salinity on growth,nodulation and nitrogen fixation ofCasuarina equisetifolia

The growth, nodulation and nitrogen fixation ofCasuarina equisetifolia were compared at six levels (0–500mM NaCl) of salinity in sand culture. Dry weight of nodules, shoots and roots and N content of shoots increased at intermediate levels of salinity (50–100 mM) but decreased at 500 mM NaCl. Nodulation occurred at all NaCl levels, but at 500mM NaCl level, the nodule dry weight declined by 50% from the control. Increasing NaCl concentration of up to 200mM had little effect on the N₂-fixation rate, but at 500mM NaCl level the rate decreased to 40% of the control value.