Synergistic effects of drought and ascorbic acid on growth,mineral nutrients and oxidative defense system in canola (Brassica napus L.) plants

A study was conducted to find out the role of ascorbic acid (AsA) in modulating growth and different physio-biochemical attributes of canola plants under well-watered as well as water-deficit conditions. Drought stress imposed on 60 % field capacity significantly decreased the shoot and root fresh and dry weights, leaf chlorophyll contents, shoot and root P, root K⁺, and activity of CAT enzyme, while increased chlorophyll a/b contents, MDA, NPQ, leaf total phenolics, free proline and GB contents in both canola cultivars. Foliar-applied varying levels (50, 100 and 150 mg L^?1) of AsA enhanced shoot and root fresh and root dry weights, qN, NPQ, shoot and root P, AsA as well as the activity of POD enzyme particularly under drought stress conditions. Of both canola cultivars, cv. Dunkeld was higher in shoot fresh weights, ETR and F _v /F _m, MDA, proline and GB contents, and POD activity, however, cv. Cyclone in total phenolics and qN under well-watered and water-deficit conditions. Overall, the foliar-applied AsA had a positive effect, though not marked, on salt sensitive cv. Cyclone in terms of improved growth and other attributes, whereas exogenously applied AsA had a non-significant effect on relatively salt tolerant cv. Dunkeld.     

Exogenous application of epibrassinolide attenuated Verticillium wilt in upland cotton by modulating the carbohydrates metabolism,plasma membrane ATPases and intracellular osmolytes

Verticillium dahliae toxin (Vd toxin) was employed as pathogen free model system to induce osmotic stress on upland cotton and its amelioration is investigated using epibrassinolide (EBR). In this study, we observed the physiological and biochemical differences among Vd toxin alone and EBR + Vd toxin treated plants using different levels of root (5, 10, 15 nM) and shoot (50, 100, 200 nM) applied EBR. Results revealed that in absence of EBR, Vd toxin caused 83 % plant wilting and the levels of glycine betaine and proline were 33 and 61 % higher than non treated control, respectively. However, the accumulation of these osmolytes was decreased in EBR treated plants with minimum values at 5 and 200 nM. Furthermore, the results depicted a remarkable decline in soluble sugars, photosynthesis, transpiration, chlorophyll content and chlorophyll florescence (Fv/Fm) in Vd toxin alone treated plants than EBR + Vd toxin. Besides, the activities of sucrose synthase, sucrose phosphate synthase and acid invertase were high in Vd + EBR treated plants with increased root and shoot biomass than Vd toxin alone treated plants. Moreover, EBR remarkably regulated the levels of plasma membrane ATPases and contents of total ATPase and Na⁺ K⁺-ATPase were elevated while contents of Ca²⁺ Mg²⁺-ATPase and H⁺ K⁺-ATPase were decreased as compared to Vd toxin alone treated plants. This study broadens our understanding of Verticillium wilt and demonstrates the potential role of EBR in mediating tolerance against Vd toxin induced stress of V. dahliae in cotton.     

Epibrassinolide Application Regulates Some Key Physio-biochemical Attributes As Well As Oxidative Defense System in Maize Plants Grown Under Saline Stress

It was aimed to investigate the ameliorative effect of exogenously applied 24-epibrassinolide (EBR) on some key growth parameters and mineral elements in two salt-stressed maize (PR 32T83 and PR 34N24) cultivars. A factorial experiment was designed with two electrical permeability (EC) levels (1.1 and 8.0 dS/m) and two levels (1.5 and 2.0 µM) of EBR supplied as a seed treatment, foliar spray, or both in combination. The foliar application of EBR was done once a week during the experiment. After 42 days of these treatments, the plants were harvested to assess growth, water relations, and oxidative and antioxidative systems. Salt stress markedly reduced plant fresh and dry weights, maximum fluorescence yield of PS-II, chlorophyll contents, leaf water potential, and leaf K and Ca, but it increased membrane permeability, the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC. 1.11.1.7), and catalase (CAT; EC. 1.11.1.6) enzymes, and the contents of proline and glycine betaine, leaf sap osmotic pressure, lipid peroxidation, hydrogen peroxide, and leaf Na and Cl. However, both seed treatment and foliar application of EBR to the maize plants exposed to saline conditions enhanced key growth attributes, water relations, and the activities of various antioxidant enzymes as well as the levels of proline, but they reduced electrolyte leakage, and H₂O₂ and MDA contents. Saline stress reduced leaf N, Ca²⁺, K⁺, and P contents as compared to those in the non-stressed plants. Both seed treatment and foliar application of EBR reduced Na⁺ and Cl^? concentrations, but increased those of N, Ca²⁺, K⁺, and P. Foliar application of EBR was more effective in increasing nutrient levels of plants grown at the high saline regime compared to the seed treatment of EBR. The study clearly indicates that both seed treatment and foliar application of EBR at the rate of 2.0 µM can overcome the detrimental effect of salinity stress on maize growth, which was found to be significantly linked to reduced concentrations of Na, Cl, MDA, and H₂O₂ as well as EL and increased activities of key antioxidant enzymes in the maize plants.     

Changes in growth,photosynthetic capacity and ionic relations in spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) due to pre-sowing seed treatment with polyamines

The influence of pre-sowing seed treatment with polyamines (2.5 mM putrescine, 5.0 mM spermidine and 2.5 mM spermine) on growth, photosynthetic capacity, and ion accumulation in two spring wheat (Triticum aestivum L.) cultivars MH-97 (intolerant) and Inqlab-91 (tolerant) was examined. The primed seeds of each treatment and non-primed seeds were sown in a field containing 15 dS m⁻¹ NaCl. Although all three polyamines were effective in improving shoot growth and grain yield in both cultivars under saline conditions, the effect of spermine was very pronounced particularly in improving grain yield. Different priming agents did not affect the net CO₂ assimilation rate and transpiration rate of either cultivar. However, pre-treatment with spermidine increased stomatal conductance (g_s) in the tolerant cultivar, whereas with spermine stomatal conductance decreased in the intolerant cultivar under salt stress. Priming agents had different effects on the accumulation of different ions in wheat plant tissues. When spermidine and distilled water were used as priming agents, they were effective in reducing shoot [Na⁺] in the tolerant and intolerant cultivars, respectively under saline conditions. Although all priming agents caused an increase in shoot [K⁺], distilled water was more effective in improving shoot [K⁺] in both cultivars under salt stress. Pre-treatment with spermidine was very effective in reducing shoot [Cl⁻] under saline conditions particularly in the tolerant cultivar. However, the pattern of accumulation of different ions in roots due to different seed priming treatments was not consistent in either cultivar except that root Na⁺ decreased due to priming with spermine and spermidine in the intolerant and tolerant cultivars under saline conditions. In conclusion, although all three priming agents, spermine, spermidine and putrescine, were effective in alleviating the adverse effect of salt stress on wheat plants, their effects on altering the concentration of different ions and growth were different in the two cultivars differing in salt tolerance.     

Amelioration of NaCl stress by triadimefon in peanut seedlings

Peanut (Arachis hypogaea L.cv. VRI-2) seeds were imbibed in distilled water(control), 30 mM NaCl (stressed) and 30 mM NaCl + 10 mg L^-1 triadimefon for 12 h and grown in a seed germinator with a day/night temperature of 30/22 °C and a photoperiod of 16 h with a PPFD of 250 µEm^-2 s_-1. Seedlings were irrigated with respective treatment solutions. Fifteen days old seedlings were harvested and used for the study. The NaCl stress decreased seedling growth, dry weight, photosynthetic pigments, protein content and the level of proline oxidase activity and it increased proline, glycine betaine content, protease and ATPase activities. Triadimefon treatment ameliorated the stress caused NaCl by increasing root growth, dry weight, chlorophyll, carotenoid, protein and glycine betaine contents and by decreasing proline accumulation, proline oxidase levels and ATPase. The stress amelioration conferred by triadimefon may be mediated by increased protein synthesis, osmoregulation and reduced energy requirement.     

Salt stress affects water relations,photosynthesis, and oxidative defense mechanisms in Solanum melongena L.

Abstract

A greenhouse experiment was conducted to examine the salt-induced changes in some key physio-biochemical attributes in eggplant (cv. New Noble) plants. Eggplant plants were grown under varying levels (0, 50, 100, and 150 mM) of sodium chloride under greenhouse conditions supplied with natural light and other climatic conditions. Varying saline regimes in growth medium significantly reduced the shoot and root fresh and dry weights, shoot and root lengths, relative water content, chlorophyll a and b pigments, photosynthetic rate (A), water-use efficiency, stomatal conductance (g _s ), leaf and root K⁺, total phenolics, total soluble proteins, activity of superoxide dismutase (SOD), and leaf water and osmotic potentials in all eggplant plants. However, in contrast, saline regimes of the root growing medium did not affect transpiration rate (E), internal CO₂ concentration (C _i ), C _i /C _a ratio, photochemical quenching (qP), non-photochemical quenching, efficiency of photosystem-II (F _v /F _m ), leaf and root Ca²⁺ as well as ascorbic acid (AsA) contents in eggplant. A significant increase was observed in leaf turgor potential, free proline and glycinebetaine contents, leaf and root Na⁺ contents, malondialdehyde and hydrogen peroxide (H₂O₂) contents and activities of peroxidase (POD) and catalase (CAT) in eggplant plants under varying saline regimes. Overall, salt-induced growth reduction in eggplant plants was found to be associated with high accumulation of Na⁺ in both roots and shoots, which adversely affected photosynthetic capacity, chlorophyll pigments, K⁺ and Ca²⁺ contents, H₂O₂ and AsA levels and activities of SOD, POD, and CAT.     

Seeds of Kosteletzkya virginica (Malvaceae): their structure,germination, and salt tolerance. II. Germination and salt tolerance

Kosteletzkya virginica (L.) Presl. (Malvaceae) is a perennial that grows in saline or brackish water, and is salt-tolerant in its mature state, but less tolerant during germination. The seeds show a very low permeability to water that increases during storage. The permeability to water differs in seeds harvested in different years. Optimal temperature for germination is 28–30 C. The effect of salinity on imbibition is largely osmotic, but germination is inhibited, apparently, by the combined osmotic and “ionic” effects, especially at high NaCl concentrations. Inhibition of germination by high NaCl concentrations is relatively more severe in scarified than in intact seeds, indicating that the seed coat acts as a partial barrier to Na⁺ influx. External application of proline or betaine did not improve germination under saline conditions. Dry seeds contain a significant amount of betaine and low levels of proline, but during germination and in the presence of NaCl the betaine content decreased while the proline content increased. Thus, the likely compatible solute in the germinating seed seems to be proline.     

La Dendrologia di Ulisse Aldrovandi

Abstract

Legume-Rhizobium symbiotic nitrogen (N₂) fixation plays a critical role in sustainable nitrogen management in agriculture. The nitrogen fixed by the root nodules not only affects the nitrogen cycle of nature, but is also of great economic importance. A number of physiological and biochemical processes in the nodules are affected by salt stress. The objective of this study was to evaluate the role of arbuscular mycorrhiza (AM) in moderating toxic effects of salt stress on nodular metabolism in Cajanus cajan (L.) Millspaugh (pigeonpea) cv. Manak. Exposure of plants to salinity stress (4, 6 and 8 dSm^?1) caused ionic imbalance, which resulted in increased Na⁺ and reduced K⁺ and Ca²⁺ contents in the nodules. Salinity induced increased synthesis and accumulation of proline and glycine betaine. Salt stress significantly increased the antioxidant enzyme activities in the nodules of all plants. Nodular growth suffered remarkably and a marked decline in nodule biomass was observed under salt stress. Leghemoglobin content and acetylene reduction activity (ARA) also declined under saline conditions. AM could significantly improve nodule dry mass, leghemoglobin content and nitrogenase activity, and phosphorus content under salt stress. Activities of antioxidant enzymes increased markedly in nodules of mycorrhizal-stressed plants. This study suggested a correlation between improved functional efficiency of nodules and higher osmolyte accumulation and enhanced antioxidant enzyme activities of AM plants under stressed conditions relative to the nodules of uninoculated plants.     

Overexpression of AtNHX5 improves tolerance to both salt and water stress in rice (Oryza sativa L.)

Overexpression of NHX genes has been previously shown to improve salt tolerance of transgenic plants. In this study, transgenic rice plants overexpressing AtNHX5 showed not only high salt tolerance, but also high drought tolerance. Measurements of ion levels indicated that Na⁺ and K⁺ contents were all higher in AtNHX5 overexpressing shoots than in wild type (WT) shoots in high saline conditions. After exposure to water deficiency and salt stress, the WT plants all died, while the AtNHX5 overexpressing rice plants had a higher survival rate, dry weight, leaf water content, and leaf chlorophyll contents, accumulated more proline, and had less membrane damage than the WT plants. In addition, seeds of both transgenic and WT plants germinated on 1/2 MS medium supplemented with 250 mM mannitol, but overexpression of AtNHX5 improved the shoot growth of the seedlings. Taken together, the results indicate that AtNHX5 gene could enhance the tolerance of rice plants to multiple environmental stresses by promoting the accumulation of more effective osmolytes (ions or proline) to counter the osmotic stress caused by abiotic factors.     

Exogenous proline effects on water relations and ions contents in leaves and roots of young olive

The ability of exogenous compatible solutes, such as proline, to counteract salt inhibitory effects was investigated in 2-year-old olive trees (Olea europaea L. cv. Chemlali) subjected to different saline water irrigation levels supplied or not with exogenous proline. Leaf water relations [relative water content (RWC), water potential], photosynthetic activity, leaf chlorophyll content, and starch contents were measured in young and old leaves. Salt ions (Na⁺, K⁺, and Ca²⁺), proline and soluble sugars contents were determined in leaf and root tissues. Supplementary proline significantly mitigated the adverse effects of salinity via the improvement of photosynthetic activity (Pn), RWC, chlorophyll and carotenoid, and starch contents. Pn of young leaves in the presence of 25 mM proline was at 1.18 and 1.38 times higher than the values recorded under moderate (SS1) and high salinity (SS2) treatments, respectively. Further, the proline supply seems to have a more important relaxing effect on the photosynthetic chain in young than in old leaves of salt-stressed olive plants. The differential pattern of proline content between young and old leaves suggests that there would be a difference between these tissues in distinguishing between the proline taken from the growing media and that produced as a result of salinity stress. Besides, the large reduction in Na⁺ accumulation in leaves and roots in the presence of proline could be due to its interference in osmotic adjustment process and/or its dilution by proline supply. Moreover, the lower accumulation of Na⁺ in proline-treated plants, compared to their corresponding salinity treatment, displayed the improved effect of proline on the ability of roots to exclude the salt ions from the xylem sap flowing to the shoot, and thus better growth rates.     

Physiological and biochemical adaptations of Cynodon dactylon (L.) Pers. from the Salt Range (Pakistan) to salinity stress

Naturally adapted salt tolerant populations provide a valuable material for exploring the adaptive components of salt tolerance. Under this aspect, two populations of Cynodon dactylon (L.) Pers. were subjected to salt stress in hydroponics. One was collected from a heavily salt-affected soil in the vicinity of a natural salt lake, Uchhali Lake, in the Salt Range of the Punjab province of Pakistan, and the other from a normal non-saline habitat from the Faisalabad region. The NaCl treatments in Hoagland's nutrient solution were: Control (no salt), 50, 100, 150 and 200 mM of NaCl. After 8 weeks of growth in hydroponics produced biomass, ion relations, and photosynthetic capacity were measured in the differently adapted ecotypes. In the ecotype of C. dactylon from the Salt Range, shoot dry weight was only slightly affected by varying levels of salt. However, in contrast, its root weight was markedly increased. On the other hand, the ecotype from Faisalabad (non-saline habitat) showed a marked decrease in shoot and root dry weights under saline regimes. The ecotype from the Salt Range accumulated relatively less amount of Na⁺ in the shoot than did that from Faisalabad, particularly at higher salt levels. Shoot or root K⁺ and Ca²⁺ contents varied inconsistently in both ecotypes under salt stress. All the photosynthetic parameters, leaf water potential and osmotic potential, and chlorophyll content in both ecotypes were adversely affected by salt stress, but all these physiological attributes except turgor potential and soluble sugars were less affected at high salinities in the salt tolerant ecotype from Salt Range. This ecotype accumulated significantly higher organic osmotica (total free amino acids, proline, total soluble proteins, and total soluble sugars) under saline conditions than its intolerant counterpart. Overall, the salt tolerant ecotype of C. dactylon from the Salt Range showed high salt tolerance due to its restricted uptake of Na⁺ accompanied by an increased uptake of K⁺ and Ca²⁺ in the roots as well as shoot due to its higher photosynthetic capacity and accumulation of organic osmotica such as free amino acids and proline under saline conditions.     

Exogenously applied paclobutrazol modulates growth in salt-stressed wheat plants

Effect of paclobutrazol (PBZ) treatment on salinity tolerance of wheat (Triticum aestivum) was investigated on a salt-tolerant (Karchia-65) and salt-sensitive (Ghods) cultivars. Salinity significantly reduced the investigated growth parameters such as plant height, length and area of sixth leaf, root length, fresh and dry weight of shoot, roots and sixth leaf, water content (WC) of plant and seeds weight in the both cultivars. The negative effect of salinity in Ghods cultivar was more than Karchia cultivar. However, PBZ treatment reduced the growth in both cultivars, the differences in plant growth among various levels of NaCl decreased in PBZ-treated plants. Salt stress resulted in high accumulation of Na⁺ in the sixth leaf and roots in both cultivars, particularly in Ghods cultivar. Against Karchia cultivar, salt stress decreased the storage of K⁺, P and N in sixth leaf and roots in Ghods cultivar. In the both cultivars, PBZ treatment enhanced the K⁺, P and N contents in sixth leaf and roots by increasing salinity. Although PBZ treatment decreased the growth of plants, it improved the weight of seeds against stress damage. PBZ treatment reduced the accumulation of harmful Na⁺ ion in plant tissues while increased the K⁺, P and N contents. These observations suggest that PBZ treatment may increase tolerance by diminishing ionic imbalance caused by salt stress.     

Glycine betaine aldehyde dehydrogenase from Bacillus subtilis: characterization of an enzyme required for the synthesis of the osmoprotectant glycine betaine

Production of the compatible solute glycine betaine from its precursors choline or glycine betaine aldehyde confers a considerable level of tolerance against high osmolarity stress to the soil bacterium Bacillus subtilis. The glycine betaine aldehyde dehydrogenase GbsA is an integral part of the osmoregulatory glycine betaine synthesis pathway. We strongly overproduced this enzyme in an Escherichia coli strain that expressed a plasmid-encoded gbsA gene under T7φ10 control. The recombinant GbsA protein was purified 23-fold to apparent homogeneity by fractionated ammonium sulfate precipitation, ion-exchange chromatography on Q-Sepharose, and subsequent hydrophobic interaction chromatography on phenyl-Sepharose. Molecular sieving through Superose 12 and sedimentation centrifugation through a glycerol gradient suggested that the native enzyme is a homodimer with 53.7-kDa subunits. The enzyme was specific for glycine betaine aldehyde and could use both NAD⁺ and NADP⁺ as cofactors, but NAD⁺ was strongly preferred. A kinetic analysis of the GbsA-mediated oxidation of glycine betaine aldehyde to glycine betaine revealed K _m values of 125 μM and 143 μM for its substrates glycine betaine aldehyde and NAD⁺, respectively. Low concentrations of salts stimulated the GbsA activity, and the enzyme was highly tolerant of high ionic conditions. Even in the presence of 2.4 M KCl, 88% of the initial enzymatic activity was maintained. B. subtilis synthesizes high levels of proline when grown at high osmolarity, and the presence of this amino acid strongly stimulated the GbsA activity in vitro. The enzyme was stimulated by moderate concentrations of glycine betaine, and its activity was highly tolerant against molar concentrations of this osmolyte. The high salt tolerance and its resistance to its own reaction product are essential features of the GbsA enzyme and ensure that B. subtilis can produce high levels of the compatible solute glycine betaine under conditions of high osmolarity stress. Received: 2 May 1997 / Accepted: 2 July 1997     

Effects of salt stress in relation to osmotic adjustment on sugarcane (<Emphasis Type="Italic">Saccharum officinarum</Emphasis> L.) callus cultures

In vitro responses of embryogenic sugarcane (Saccharum officinarum L.; cv. CoC-671) calli stressed with different levels of NaCl (0.0, 42.8, 85.6, 128.3, 171.1, 213.9 or 256.7 mM) were studied. The results showed that a significant decrease in callus growth and cell viability occurred with ≥85.6 mM NaCl. Higher amounts of free proline and glycine betaine were accumulated in NaCl-stressed calli. Although the leached and retained Na⁺ contents increased, the retained K⁺ content decreased with increasing levels of NaCl. Such a mechanism implies that sugarcane can be considered as a Na⁺-excluder. The accumulation of salt ions and osmolytes could play an important role in osmotic adjustment in sugarcane cells under salt stress.     

Physiological responses of three soybean species (<Emphasis Type="Italic">Glycine soja,G. gracilis</Emphasis>, and <Emphasis Type="Italic">G. max</Emphasis> cv. Melrose) to salinity stress

Understanding the mechanism for salt tolerance in wild soybean (Glycine soja) can help researchers improve that trait in cultivated soybean lines. We analyzed the effects of excess NaCl on the growth, physiology, and ion distribution in three soybean species: wild G. soja (W8), semi-wild G. gracilis (SW18), and the cultivated salt-sensitive G. max (cv. Melrose). These comparisons revealed that, under salt stress, shoot and root lengths and biomass (either shoot or root dry weights) were significantly higher for the W8 genotype than for the other two. Most of the morphological parameters for roots from the W8 plants were also increased, including total length, specific root length, and surface area. However, the average root diameter for W8 was significantly lower than that of either SW18 or ‘Melrose’ soybeans. In response to salinity, photosynthesis was suppressed to a greater extent in ‘Melrose’ than in W8. The relatively higher tolerance shown by W8 plants was also associated with lower levels of malondialdehyde, hydrogen peroxide, and relative electrical conductivity, but higher activities by superoxide dismutase and peroxidase, as well as more free proline and glycine betaine. In addition, the W8 plants contained less Na⁺ and Cl^?, but more K⁺, and they had a higher K⁺/Na⁺ ratio in their leaves and roots when compared with either SW18 or ‘Melrose’ plants. Therefore, the W8 genotype performs better in terms of seedling growth, photosynthetic characteristics, and physiological indexes. These findings provide guidance for developing new soybean cultivars with improved tolerance to salt stress. Our data also contribute to the knowledge base for plant salt tolerance as a tool for increasing the yields of other crops in high-salinity soils.     

Improving Glycyrrhiza uralensis salt tolerance with N+ ion irradiation

Low energy (25 keV) N⁺ ions were implanted into liquorice (Glycyrrhiza uralensis) seeds at a fluency of either zero (control) or 900 × (2.6 × 10¹³) ions/cm². After irradiation, all the seeds were planted in the plastic pots for a growth period of one month. Thereafter, the seedlings in the pot were subjected to saline stress at 600 mM for about 3 days. The morphological and physiological characteristics such as total chlorophyll content, proline level, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ATPase, and triphenyl tetrazolium chloride (TTC) reduction in seedling roots were investigated. Our results indicated that ion irradiation significantly increased the shoot height, leaflet number, taproot lenght, lateral root number, and shoot and root weights of liquorice seedlings with or without saline stress. Furthermore, the total chlorophyll content, proline level, SOD, POD, CAT, ATPase activities, and root TTC reduction vigor of seedlings were all found to be significantly increased under saline stress by ion irradiation compared with their corresponding controls. These results indicated that ion irradiation can strengthen the resistance of liquorice seedlings to saline stress and may have a potential application for the improvement of plants in sand areas.     

Proline betaine is a highly effective osmoprotectant for Staphylococcus aureus

Proline betaine is an osmoprotectant that is at least as effective as glycine betaine, and more effective than L-proline, for various strains of Staphylococcus aureus, and Staphylococcus epidermidis and Staphylococcus saprophyticus. ¹³C NMR studies revealed that proline betaine accumulated to high levels in osmotically stressed S. aureus, but was also detected in organisms grown in its presence in the absence of osmotic stress. Competition experiments indicated that proline betaine was taken up by the proline transport systems of S. aureus, but not by the high affinity glycine betaine transport system.Abbreviations PYK Peptode - Yeast extract K₂HPO₄     

Solute levels and osmoregulatory enzyme activities in reed plants adapted to drought and saline habitats

The pattern of solute accumulation and the activities of key enzymes involved in metabolism of proline and betaine were investigated in three ecotypes of reed from different habitats: swamp reed (SR), dune reed (DR), and heavy salt meadow reed (HSR). The two terrestrial reed ecotypes, DR and HSR, exhibited a higher capacity for osmotic adjustment; they accumulated higher contents of K⁺ and Ca²⁺ in the leaves in comparison with SR. DR also had the highest soluble sugar content in its leaves. HSR has higher levels of Na⁺ in its root environment and this was reflected by considerable accumulation of Na⁺ in the HSR rhizome. However, the different zones of its leaf lamina (upper, middle and lower) did not exhibit increased levels of Na⁺, suggesting that HSR has the ability to accumulate Na⁺ in the rhizome to protect the shoots from excessive Na⁺ toxicity. DR and HSR had higher levels of proline and betaine in the leaves than did SR. This difference was consistent with the activities of the various biosynthetic enzymes: betaine aldehyde dehydrogenase (BADH), pyrroline-5-carboxylate reductase (P5CR) and ornithine--aminotransferase (OAT) were enhanced in DR and HSR as compared to SR, whereas proline oxidase (PO) activities were inhibited. These findings suggest that changes in the activities of enzymes involved in osmotregulation might play important roles in the adaptation of reed, a hydrophilic plant, to more extreme dune and saline habitats. The relative contributions of the various proline synthetic pathways are also discussed.     

不同强度盐胁迫下AM真菌对羊草生长的影响

不同浓度NaCl盐处理下,AM真菌对羊草(Leymus chinensis)的侵染能力和对植物生长的影响,从植物形态和离子含量角度探讨了AM真菌提高羊草耐盐性的作用机理。结果表明,在高盐胁迫下,AM真菌显著降低了盐胁迫效应,提高了羊草生物量,菌根效应明显。菌根化羊草的根茎比显著增加,并且N、P浓度较高,Na~+和Cl~-离子浓度较低,表明AM真菌即促进羊草对营养元素的吸收,又减少了离子毒害。菌根化羊草的Ca~(2+)和K~+离子浓度,以及P/Na~+和K~+/Na~+比高于非菌根化羊草,表明AM真菌可通过调节渗透势以避免或减缓盐胁迫造成的生理缺水。随着盐胁迫的增加,菌根化羊草对磷的依赖性逐渐转换为对钾的依赖性。研究结果有助于揭示AM真菌提高植物耐盐能力的作用机理,并对应用菌根技术修复盐化草地具有理论指导意义。