Bedeutung einiger nichtflüchtiger carbonsäuren für die frostresistenz des halophyten Halimione portulacoides unter dem einfluß verschieden hoher kochsalzbelastung

Summary Plants of Halimione portulacoides (L.) Aellen were grown in natural temperature and light conditions but with different concentrations of NaCl in the nutrient solution. From August 1971 to April 1972 freezing tolerance, water content, succulence, accumulation of different sugars, citrate, malate, and chloride were simultaneously determined. If no NaCl was supplied the chloride content of the leaves decreased continuously within the period of investigation. During repeated and increasing addition of NaCl the chloride content of the leaves generally increased. However, there was a reversible decrease during the frost period, although no new leaves were formed and loss through leaves and dilution of the nutrient medium by precipitation was prevented (Fig. 1).In spite of being in minimum the chloride content was relatively high in winter. No regulation of the concentration by increase of succulence was observed. The concentration did, however, increase due to a diminished water uptake in the coldest period.Sugars, which are regarded as protective agents against the influence of freezing and salts, accumulated only slightly in the frost period. Predominantly sucrose, raffinose and stachyose were remarkable. Their concentration was not sufficient to compensate the salt burden and thus could not increase the freezing tolerance. The sugar content was even lowered when the salt content was higher. In contrast, citrate and to a lesser extent malate were intensively increased in the cold season (Fig. 3). Thus organic acid to chloride ratios of between 1:2 and 1:6 were established for Halimione, which expresses the effective protection of the membrane systems against freezing injury (Fig. 4), as has been shown in vitro for e.g. spinach chloroplasts by Santarius (1971). Accumulation of these acids was even enhanced by an increasing salt burden. Consequently accumulation of organic acids or their salts such as citrate and probably malate indicates an adaptation of halophytes, which enables them to survive freezing under salt stress on the sea shore and in cold desert regions during the winter.     

Sugar compartmentation in frost-hardy and partially dehardened cabbage leaf cells

In frost-hardy and partially dehardened leaves of Brassica oleracea L. var. sabellica L. the distribution of cryoprotective sugars and of chloride between chloroplasts and the nonchloroplast part of leaf cells was investigated using the nonaqueous isolation technique as a means of cell fractionation. In chloroplasts of frost-hardy leaves high concentrations of sucrose and raffinose and comparatively low concentrations of chloride have been found. The ratios between sugars and chloride were so as to ascertain complete protection of the frost-sensitive thylakoid membranes during freezing. During dehardening, sugars decreased especially in the chloroplasts. There was a conversion of sucrose and raffinose into monosaccharides. This led to a large increase in the concentration of glucose and fructose in the nonchloroplast parts of the cells. There is evidence that the sugar concentration in the vacuole increased at the expense of sugars located in chloroplasts and cytoplasm. The quantity of sugars that remained in the chloroplasts did not appear to be sufficient for complete membrane protection at very low freezing temperatures.     

On the ecophysiology of Halimione portulacoides

Growth rate and salt accumulation were investigated in experiments on Halimione portulacoides with seven sodium chloride treatments, in water culture. The growth of Halimione was found to be stimulated by moderate, 85–170 mM NaCl, levels of salinity, but increasingly depressed by salinities from 410–690 mM NaCl, which is comparable to salinities in salt marshes during the growing season. Using the same technique, growth rate, chloride and nitrogen uptake experiments at four different sodium chloride and nitrate treatment levels were conducted, in order to study the effect of nitrogen and salt. At 8 mM NaCl in the growth medium growth was depressed at 16.2 mM nitrate treatment levels. At 137 mM, 410 mM and 684 mM of NaCl growth was stimulated by increasing levels of nitrogen. The results of these experiments are discussed in relation to the nitrogen and salt conditions prevailing in Halimione portulacoides salt-marsh communities.     

The influence of salinity on cell ultrastructures and photosynthetic apparatus of barley genotypes differing in salt stress tolerance

A hydroponic experiment was conducted to elucidate the difference in growth and cell ultrastructure between Tibetan wild and cultivated barley genotypes under moderate (150 mM NaCl) and high (300 mM NaCl) salt stress. The growth of three barley genotypes was reduced significantly under salt stress, but the wild barley XZ16 (tolerant) was less affected relative to cultivated barley Yerong (moderate tolerant) and Gairdner (sensitive). Meanwhile, XZ16 had lower Na⁺ and higher K⁺ concentrations in leaves than other two genotypes. In terms of photosynthetic and chlorophyll fluorescence parameters, salt stress reduced maximal photochemical efficiency (F _v/F _m), net photosynthetic rate (Pn), stomatal conductance (Gs), and intracellular CO₂ concentration (Ci). XZ16 showed relatively smaller reduction in comparison with the two cultivated barley genotypes. The observation of transmission electron microscopy found that fundamental cell ultrastructure changes happened in both leaves and roots of all barley genotypes under salt NaCl stress, with chloroplasts being most changed. Moreover, obvious difference could be detected among the three genotypes in the damage of cell ultrastructure under salt stress, with XZ16 and Gairdner being least and most affected, respectively. It may be concluded that high salt tolerance in XZ16 is attributed to less Na⁺ accumulation and K⁺ reduction in leaves, more slight damage in cell ultrastructure, which in turn caused less influence on chloroplast function and photosynthesis.     

Effects of prolonged freezing stress on the photosynthetic apparatus of moderately hardy leaves as assayed by chlorophyll fluorescence kinetics

Abstract Moderately frost-hardy leaves of the wintergreen broadleaf woody shrubs Pyracantha coccinea and Ligustrum ovalifolium and the winter annual herb Spinacia oleracea were subjected to extended freezing stress up to 15 d at temperatures 2–8°C above the mean lethal temperature (LT₅₀). After thawing, the fast kinetics of in vivo chlorophyll fluorescence of photosystem II (PSII) and the potential of linear photosynthetic electron transport of isolated thylakoid membranes was measured at room temperature. The lower the minimum freezing temperature and the longer the time of exposure, the greater was the suppression of the fluorescence signals of the leaves and decrease of the electron transport capacity of the thylakoid membranes. The pattern of inactivation of PSII -mediated electron flow, i.e. inhibition of photoreaction to photochemistry and/or electron donation to the photochemical reaction, during long-term freezing at temperatures somewhat above the LT₅₀ of the leaves was similar to that observed earlier after relatively brief exposure of leaves and isolated thylakoid membranes to more severe freezing stress. As injury occurred during freezing in complete darkness, it is likely that prolonged winter stress under natural environmental conditions causes changes in the photosynthetic apparatus of moderately hardy leaves which are not due to photoinhibition.     

Phelipanche aegyptiaca parasitism impairs salinity tolerance in young leaves of tomato

The parasite Phelipanche aegyptiaca infests tomato, a crop plant that is commonly cultivated in semi‐arid environments, where tomato may be subject to salt stress. Since the relationship between the two stresses —salinity and parasitism – has been poorly investigated in tomato, the effects of P. aegyptiaca parasitism on tomato growing under moderate salinity were examined. Tomatoes were grown with regular or saline water irrigation (3 and 45 mM Cl^?, respectively) in soils infested with P. aegyptiaca . The infested plants accumulated higher levels of sodium and chloride ions in the roots, shoots and leaves (old and young) under both salinity levels vs. non‐infected plants. There was a positive linear correlation between P. aegyptiaca biomass and salt accumulation in young tomato leaves, and a negative linear correlation between parasite biomass and the osmotic potential of young tomato leaves. Concentrations of the osmoprotectants proline, myoinositol and sucrose were reduced in infected tomato plants, which impaired the host's osmotic adjustment ability. The sensitivity of P. aegyptiaca to salt stress was manifested as a decrease in biomass. In conclusion, P. aegyptiaca parasitism reduced the salt tolerance of tomato plants by promoting the accumulation of salts from the rhizosphere and impairing the host's osmotic adjustment ability.     

Transformation of Arabidopsis thaliana with the codA gene for choline oxidase; accumulation of glycinebetaine and enhanced tolerance to salt and cold stress

Glycinebetaine is one of the compatible solutes that accumulate in the chloroplasts of certain halotolerant plants when these plants are exposed to salt or cold stress. The codA gene for choline oxidase, the enzyme that converts choline into glycinebetaine, has previously been cloned from a soil bacterium, Arthrobacter globiformis. Transformation of Arabidopsis thaliana with the cloned codA gene under the control of the 35S promoter of cauliflower mosaic virus enabled the plant to accumulate glycinebetaine and enhanced its tolerance to salt and cold stress. At 300 mM NaCl, considerable proportions of seeds of transformed plants germinated well, whereas seeds of wild-type plants failed to germinate. At 100 mM NaCl, transformed plants grew well whereas wild-type plants did not do so. The transformed plants tolerated 200 mM NaCl, which was lethal to wild-type plants. After plants had been incubated with 400 mM NaCl for two days, the photosystem II activity of wild-type plants had almost completely disappeared, whereas that of transformed plants remained at more than 50% of the original level. When exposed to a low temperature in the light, leaves of wild-type plants exhibited symptoms of chlorosis, whereas those of transformed plants did not. These observations demonstrate that the genetic modification of Arabidopsis thaliana that allowed it to accumulate glycinebetaine enhanced its ability to tolerate salt and cold stress.     

Population differentiation within Festuca rubra L. with regard to soil salinity and soil water

Summary Seed and transplanted adult plants from populations of Festuca rubra, collected from inland, salt-marsh and sand-dune sites were grown on culture solution with added sodium chloride. The growth of the populations of the three habitats was reduced differentially by salt. The salt marsh ecotype Festuca rubra ssp. litoralis was only slightly affected and the inland ecotype F. rubra ssp. rubra was severely retarded at 60 mM NaCl. The dune ecotype F. rubra ssp. arenaria had an intermediate tolerance. The tolerant ecotypes accumulated less sodium chloride as compared to the sensitive ecotype, suggesting that salt tolerance is caused in part by salt exclusion.In addition, the dune ecotype F.r. arenaria appeared to be more drought tolerant than the salt marsh ecotype. Abscission of salt-saturated leaves does not function as an adaptation to salinity in Festuca rubra.All three ecotypes accumulated proline with increased salinity. The response was most pronounced in the drought tolerant F.r. arenaria, indicating that proline accumulation is a response to osmotic stress rather than to ion-specific effects of salinity. The observed differences in salt tolerance may be explained by differential sensitivity to toxic effects of sodium chloride.The occurrence on a beach plain of closely adjacent populations of F.r. arenaria and F.r. litoralis, differing markedly in salt tolerance, is briefly discussed.     

Sodium and Chloride Sensitivity in Alfalfa (Medicago sativa L.): Growth,Photosynthesis, and Tissue Ion Regulation in Contrasting Genotypes

Alfalfa (Medicago sativa L.) is a moderately salt-tolerant plant. This study was conducted to evaluate responses of two contrasting alfalfa genotypes (OMA-84-salt sensitive and OMA-285-salt-tolerant) to components (Na⁺, and/or Cl^?) of salt stress. Alfalfa genotypes were exposed to Na⁺???salts (without chloride), Cl^????salts (without sodium), and NaCl (sodium chloride) stresses with two concentrations (30 and 150 mM). The treatments, involving macronutrients, with the same osmotic potentials, were taken as control. Salt stress, irrespective of type and intensity, caused a significant reduction in plant biomass, physiological (net photosynthetic rate, photosystem II efficiency, chlorophyll fluorescence, water use efficiency, maximum yield of primary photochemistry, and electron transport rate), and shoot mineral (calcium, magnesium, phosphorus, and potassium) contents compared to control; however, this reduction was in the order of NaCl (150 mM)?>?Na⁺ (150 mM)?>?Cl^? (150 mM). The alfalfa genotype OMA-285 sustained growth under both types of salt stresses than the genotype OMA-84 due to less accumulation of Na⁺ and Cl^? ions, maintenance of higher K⁺/Na⁺ ratio, and better photosynthetic activities. In conclusion, salt stress caused a significant reduction in alfalfa growth, this reduction was more under NaCl stress and the effect was mainly additive. The alfalfa genotype OMA-285 sustained growth under salt stresses than the genotype OMA-84 due to ionic homeostasis. However, the tested genotypes were more sensitive to Na⁺ toxicity than the Cl^? toxicity, and the contrasting genotypes differed in tissue tolerance of high Na⁺ and Cl^?. Further research is needed to evaluate tissue tolerance in a diverse and large group of alfalfa genotypes to elucidate the general salt tolerance mechanism in alfalfa.

     

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 treatment induces frost hardiness in leaves and isolated thylakoids from spinach

Frost hardiness of spinach (Spinacia oleracea L.) leaves was increased by high concentrations of NaCl in the hydroponic culture medium. Freezing damage was determined by measurement of slow chlorophyll fluorescence quenching after freezing of leaves. Both the osmolality of the leaf sap and forst hardiness of the leaves were linearly correlated with the salt concentration in the hydroponic culture medium. Freezing damage occurred, irrespective of the extent of frost hardening, when dehydration of cells during extracellular ice formation decreased cellular volume to approximately 14% of the volume of unfrozen cells. The resistance of isolated, washed thylakoids against mechanical and chemical damage by freezing was investigated. Chemical damage by freezing caused by salt accumulation was measured as release of chloroplast coupling factor (CF1; EC 3.6.1.3), and mechanical damage was measured as release of the lumenal protein plastocyanin from the membranes during an in-vitro freeze-thaw cycle. Isolated thylakoids from salt-treated frost-hardy spinach and those from plants hardened under natural conditions did not exhibit improved tolerance against chemical freezing stress exerted by high salt concentrations. They were, however, more hardy than thylakoids from unhardened control leaves against mechanical damage by freezing.Abbreviation CF1 peripheral part of chloroplast coupling factor ATPase     

Isolation of a cDNA clone (PcSrp) encoding serine-rich-protein from Porteresia coarctata T. and its expression in yeast and finger millet (Eleusine coracana L.) affording salt tolerance

A 1.4 Kb cDNA clone encoding a serine-rich protein has been isolated from the cDNA library of salt stressed roots of Porteresia coarctata, and designated as P. coarctata serine-rich-protein (PcSrp) encoding gene. Northern analysis and in situ mRNA hybridization revealed the expression of PcSrp in the salt stressed roots and rhizome of P. coarctata. However, no such expression was seen in the salt stressed leaves and in the unstressed tissues of root, rhizome and leaf, indicating that PcSrp is under the control of a salt-inducible tissue-specific promoter. In yeast, the PcSrp conferred increased NaCl tolerance, implicating its role in salinity tolerance at cellular level. Further, PcSrp was cloned downstream to rice Actin-1 promoter and introduced into finger millet through particle-inflow-gun method. Transgenic plants expressing PcSrp were able to grow to maturity and set seed under 250 mM NaCl stress. The untransformed control plants by contrast failed to survive under similar salt stress. The stressed roots of transgenic plants invariably accumulated higher Na⁺ and K⁺ ion contents compared to roots of untransformed plants; whereas, shoots of transgenics accumulated lower levels of both the ions than that of untransformed plants under identical stress, clearly suggesting the involvement of PcSrp in ion homeostasis contributing to salt tolerance.     

Hypersalinity effects on leaf ultrastructure and physiology in the mangrove Avicennia marina

The effects of hypersalinity on leaf ultrastructure and physiology in the mangrove, Avicennia marina, were investigated by comparing leaves of adult trees growing naturally in the field under seawater and hypersalinity conditions in Richards Bay, South Africa. We tested the hypothesis that hypersalinity has a deleterious effect on membranes and cellular organelles such as chloroplasts and mitochondria, which would impact negatively physiological processes, such as ion and water relations, and photosynthetic performance. Soil ψ and soil salinity were −2.96 ± 0.07 MPa and 35 ± 2.8 psu in the seawater salinity site, compared to −5.91 ± 0.42 MPa and 58 ± 3.6 psu respectively, in the hypersaline site. In the hypersaline site, leaves were smaller and thicker, with thicker cuticles, while chloroplasts, mitochondria and nuclei exhibited swelling and disintegration, compared to those at seawater salinity. Multivesicular structures and vesicles, observed in vacuoles, chloroplasts, mitochondria, and along cell walls and plasma membranes, were more abundant in leaves from the hypersaline than the seawater site, and were probably indicative of greater plant salt uptake in the former site. Leaf concentrations of total chlorophyll and chlorophylls a and b were lower in trees from the hypersaline site by 33%, 29%, and 45% respectively, compared to those at seawater salinity. Midday minimum xylem ψ was −3.82 ± 0.33 MPa in the seawater site and −6.47 ± 0.45 MPa in the hypersaline site. In the hypersaline site, the concentration of leaf Na⁺ was 40% higher, while those of K⁺, Ca²⁺, and Mg²⁺ were lower by 45%, 44%, and 54% respectively, than those in the seawater site. CO₂ exchange and the intrinsic photochemical efficiency of PS II were significantly lower in trees from the hypersaline site by 48 and 19% respectively. The ultrastructural evidence supported the physiological data that A. marina trees in the hypersaline site are under extreme salinity stress and that this species is growing there at the upper limit of its salt tolerance.     

Enhancement of the salt tolerance of Triticum turgidum L. by the Kna1 locus transferred from the Triticum aestivum L. chromosome 4D by homoeologous recombination

Durum wheat, Triticum turgidum L. (2n= 4x=28, genome formula AABB) is inferior to bread wheat, T. aestivum L. (2n=6x=42, genome formula AABBDD), in the ability to exclude Na⁺ under salt strees, in the ratio of the accumulated K⁺ to Na⁺ in the leaves under salt stress, and in tolerance of salt stress. Previous work showed that chromosome 4D has a major effect on Na⁺ and K⁺ accumulation in the leaves of bread wheat. The 4D chromosome was recombined with chromosome 4B in the genetic background of durum wheat. The recombinants showed that Na⁺ exclusion and enhanced K⁺/Na⁺ ratio in the shoots were controlled by a single locus, Kna1, in the long arm of chromosome 4D. The recombinant families were grown in the field under non-saline conditions and two levels of salinity to determine whether Kna1 confers salt tolerance. Under salt stress, the Kna1 families had higher K⁺/Na⁺ ratios in the flag leaves and higher yields of grain and biomass than the Kna1 ^- families and the parental cultivars. Kna1 is, therefore, one of the factors responsible for the higher salt tolerance of bread wheat relative to durum wheat. The present work provides conceptual evidence that tolerance of salt stress can be transferred between species in the tribe Triticeae.     

Effects of NaCl Stress on the Structure,Pigment Complex Composition,and Photosynthetic Activity of Mangrove Bruguiera parviflora Chloroplasts

Exposure of two-month-old seedlings of Bruguiera parviflora to NaCl stress (0 to 400 mM) for 45 d under hydroponic culture caused notable disorganisation of the thylakoid structure of chloroplasts in NaCl-treated leaves as revealed from transmission electron microscopy. The absorption spectra of treated and control thylakoid samples were similar having a red peak at 680 nm and Soret peaks at 439 and 471 nm in the blue region of the spectrum. The spectra of treated samples differed from control samples by gradual decrease in absorbance of 100, 200, and 400 mM NaCl treated samples at 471 and 439 nm, which could be due to scattering of radiation in these samples. Thus, absorption characteristics of thylakoid membranes indicated no major alterations in the structural integrity of the photosynthetic membranes during salt stress in B. parviflora. Analysis of pigment protein complexes of thylakoids on non-denaturing gel showed that CP1 complex consisting of photosystem (PS) 1 reaction centre decreased marginally by 19% and the CP47 constituting the core antenna of PS2 declined significantly by 30% in 400 mM NaCl treated samples in respect to control. This decrease in structural core antenna might cause inefficient photon harvesting capacity. However, CP43 content did not alter. An increase in CP2/CP1 ratio from 3.2 in control to 4.0 in 400 mM NaCl treated samples indicated significant structural changes in the thylakoids of salt treated plants. Haem staining of thylakoids revealed significant losses in cytochrome (Cyt)f and Cyt b ₆ contents by NaCl stress. However, Cyt b ₅₅₉ content remained nearly constant in both control and NaCl treated samples. SDS-PAGE of thylakoid proteins showed that the intensity of many of Coomassie stained polypeptide bands ranging from 15–22 and 28–66 kDa regions decreased significantly in NaCl treated samples as compared to control. Electron transport activity of thylakoids, measured in terms of DCPIP photoreduction, was 22% lower in 400 mM NaCl treated plants than in the control ones. Hence, NaCl induces oxidative stress in chloroplasts causing structural alterations in thylakoids. These structural alterations might be responsible for declined efficiency of photosystems and reduced electron transport activity. This revised version was published online in August 2006 with corrections to the Cover Date.     

NaCl胁迫对宁夏枸杞叶和幼根显微及超微结构的影响

以宁夏枸杞为材料,采用超薄切片技术制备样品,应用光学显微镜和透射电镜分析了不同浓度NaCl胁迫条件下宁夏枸杞叶和幼根显微及超微结构的变化。结果表明：随着NaCl胁迫的加重,(1)叶片上表皮细胞增厚,栅栏组织细胞出现缩短现象,排列疏松且紊乱;幼根的初生结构无明显变化。(2)叶片栅栏组织中叶绿体不再紧靠在细胞膜上,叶绿体双层膜破坏,基粒片层松散排列,杂乱无章,出现膨胀和空泡现象,淀粉粒和嗜锇颗粒增多,叶肉细胞中线粒体发生轻微变化;幼根中皮层薄壁细胞线粒体形状发生改变,结构破坏,内膜和外膜模糊甚至破裂,大多数嵴模糊,出现空泡现象;细胞核解体,基质外溢。研究表明, 不同浓度的NaCl胁迫对宁夏枸杞叶片和幼根细胞的显微及超微结构影响不同,NaCl浓度大于200 mmol/L时,宁夏枸杞叶片和幼根细胞的显微及超微结构发生了明显变化,且叶肉细胞中线粒体的变化没有叶绿体的变化显著,推测叶肉细胞中线粒体的耐盐性比叶绿体强。     

Growth and ion relations in response to combined salinity and waterlogging in the perennial forage legumes Lotus corniculatus and Lotus tenuis

Lotus tenuis (Wadst. & Kit.) is a perennial legume widely grown for pasture in the flood-prone and salt affected Pampa region of Argentina. The physiology of salt and waterlogging tolerance in L. tenuis (four cultivars) was evaluated, and compared with Lotus corniculatus (three cultivars); the most widely cultivated Lotus species. Overall, L. tenuis cultivars accumulated less Na⁺ and Cl⁻, and more K⁺ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 days in aerated or in stagnant solutions. Root porosity was higher in L. tenuis cultivars due to greater aerenchyma formation. In a NaCl dose–response experiment (0–400 mM NaCl in aerated solution), L. tenuis (cv. Chaja) accumulated half as much Cl⁻ in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na⁺ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl. L. tenuis (cv. Chaja) again accumulated about half as much Cl⁻ in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na⁺ concentrations in the various shoot tissues. The higher root porosity, and maintenance of lower shoot Cl⁻ and Na⁺ concentrations in L. tenuis, compared with L. corniculatus, contributes to the greater tolerance to combined salt and waterlogging stress in L. tenuis. Moreover, significant variation for tolerance to combined salinity and waterlogging stress was identified within both L. tenuis and L. corniculatus.     

Responses to nonaeration and/or salinity stress in hydroponically cultured <Emphasis Type="Italic">Populus nigra</Emphasis> and <Emphasis Type="Italic">Populus alba</Emphasis> cuttings

Growth, photosynthesis, and Na⁺, K⁺, Ca²⁺, and Mg²⁺ distributions were examined in two-year-old hydroponically cultured Populus nigra and Populus alba cuttings exposed to salt stress (0, 50, or 100 mM NaCl) for four or six weeks and to nonaeration stress for one or three weeks, followed by a three-week aeration period in 2/5 Hoagland solution. Salt stress with 100 mM NaCl totally inhibited height increase in P. nigra cuttings. Combined salinity and nonaeration inhibited height increase to a greater degree than either stress alone in both species. Simple salt stress did not affect diameter increase in P. alba, whereas combined high salinity (100 mM NaCl) and nonaeration inhibited diameter increase. Growth and biomass accumulation were more sensitive to salt stress in P. nigra cuttings than in P. alba, although P. alba showed a more rapid decrease in photosynthesis in response to nonaeration stress. Ion distributions in the leaves and roots differed between species. P. alba was superior to P. nigra in terms of Na⁺ exclusion capacity, such that most of the absorbed Na⁺ was confined to the root system, with little reaching the leaves. The distributions of K⁺, Ca²⁺, and Mg²⁺ in the leaves and roots of each species under the two stressors were also analyzed. The lower Na⁺/K⁺ ratio in leaves indicated that P. alba was more tolerant to salt stress than P. nigra.