Salt Tolerance in Aquatic Macrophytes: Ionic Relation and Interaction

Effects of seawater salinity (SWS) and pure NaCl on the intracellular contents of Na⁺, K⁺, Mg²⁺, Ca²⁺, chlorophylls (Chl) and carotenoids (Car) were studied in three submerged aquatic macrophytes, Hydrilla verticillata, Najas indica and Najas gramenia, which differed in their tolerance to salinity. NaCl resulted in significant increase in Chl/Car ratio in the salt-sensitive H. verticillata and moderately salt-tolerant N. indica, but not in the salt-tolerant N. gramenia. SWS treatment did not result in any significant change in the ratio. The intracellular content of Na⁺ increased significantly in all the test plants upon exposure to both NaCl and SWS. The content of K⁺ decreased significantly in these plants upon salinity treatment, except in N. gramenia. The contents of Ca²⁺ and Mg²⁺ decreased significantly upon NaCl treatment and remained unchanged or increased upon SWS treatment. No relationship between salt tolerance and K⁺/Na⁺ ratio was observed. The maintenance of a minimal level of K⁺ was observed to be the most probable requirement of salt tolerance in aquatic macrophytes.     

Mechanisms of salt stress tolerance development in barley plants under the influence of 5-aminolevulinic acid

Growing barley (Hordeum vulgare L.) plants for 7 days on NaCl solutions (20–200 mM) decreased chlorophyll (Chl) a and b content with respect to that in untreated control plants. The content of free proline and the plant ability to synthesize 5-aminolevulinic acid (ALA) started to increase in parallel at salt concentrations of 20–50 mM. The maximum amount of ALA accumulated in plants grown at 100 mM NaCl was twofold higher than in control plants grown on fresh water. In this case the proline content increased 2.8-fold. On further increase in salt concentration, the rate of ALA accumulation decreased, approaching control values at 150 mM NaCl; even lower rates were observed at 200 mM NaCl. The reduced ability to synthesize ALA was accompanied by an increase in proline content. The albino tissue of plants treated at the seed stage with the antibiotic streptomycin lost its ability to synthesize ALA needed for Chl formation. The proline content in the albino tissue was tenfold higher than in control green plants and was 30-fold higher when the plants were grown on solutions with 100 mM NaCl. No effect of NaCl on ALA-dehydratase activity was noted. As NaCl concentration was raised, there occurred the decrease in magnesium chelatase activity, accumulation of reactive oxygen species (ROS), the increase in ascorbate peroxidase activity, and a slight decrease in lipid peroxidation level. Growing plants in the presence of 150 mM NaCl and 10 or 60 mg/l exogenous ALA led to the increase in proline content (by a factor of 1.8 and 4.2, respectively) and to the decrease in ROS content, in comparison with plants grown on salt solutions without ALA. Furthermore, in the presence of exogenous ALA, the parameters of seedling growth became similar to those of NaCl-untreated plants. The role of ALA in plants as an antistress agent is considered. ALA is supposed to confer tolerance to salt stress by taking part in Chl and heme biosynthesis and also through functioning as a plant growth regulator. A hypothesis is put forward that the impairment of ALA-synthesizing ability may redirect metabolic conversions of glutamic acid from Chl and heme synthesis to the proline synthesis pathway, which would stimulate proline biosynthesis and improve salt tolerance.     

Inductive responses of some organic metabolites for osmotic homeostasis in peanut (Arachis hypogaea L.) seedlings during salt stress

The salt tolerance of peanut (Arachis hypogaea L.) seedlings was evaluated by analyzing growth, nutrient uptake, electrolyte leakage, lipid peroxidation and alterations in levels of some organic metabolites under NaCl stress. The plant height, leaf area and plant biomass decreased significantly in salt-treated seedlings as compared with control. The relative water content (RWC %) of leaf decreased by 16 % at high concentrations of NaCl. There was an increase in the lipid peroxidation level and decrease in the electrolyte leakage at high concentrations of NaCl. The total free amino acid and proline contents of leaf increased by 5.5- and 43-folds, respectively in 150 mM NaCl-treated plants as compared with control. Total sugar and starch content increased significantly at high concentrations of NaCl. Chl a, Chl b, total chlorophyll and carotenoid contents decreased significantly at high salinity. Na⁺ contents of leaf, stem and root increased in dose-dependent manner. K⁺ content remained unaffected in leaf and root and decreased in stem by salinity. The results from present study reveal that the peanut plants have an efficient adaptive mechanism to tolerate high salinity by maintaining adequate leaf water status associated with growth restriction. In order to circumvent the stress resulting from high salinity, the levels of some organic metabolites such as total free amino acids, proline, total sugars and starch were elevated. The elevated levels of the organic metabolites may possibly have some role in maintenance of osmotic homeostasis, nutrient uptake and adequate tissue water status in peanut seedlings under high-salinity conditions.     

盐胁迫对竹柳幼苗生理响应及结构解剖的研究

为了解盐胁迫对竹柳(Salix spp.)幼苗生长的影响,采用土培方法,对NaCl胁迫下半年生竹柳扦插苗的成活率、生理响应和根叶部结构进行研究。结果表明,在0.25%Na Cl胁迫(轻度盐胁迫)下竹柳能正常生长,而在0.5%NaCl(中度、重度盐胁迫)下生长受到抑制,推断竹柳的耐盐阈值是0.5%。随着NaCl浓度的增大,叶片相对含水量、叶绿素a含量、叶绿素总含量和叶绿素a/b均呈下降趋势;但叶绿素b含量、脯氨酸含量和MDA含量呈升高趋势。在轻度盐胁迫下,叶片SOD活性和可溶性蛋白含量均升高,在中、重度盐胁迫下显著下降。从根叶解剖结构来看,叶片、角质层、栅栏组织厚度和根部周皮和直径在轻度盐胁迫时最大,但在中度盐胁迫时叶片栅栏组织细胞长度减小且排列越来越疏松,根部输导组织细胞不正常。这表明竹柳在轻度胁迫时具有一定的耐盐性,但在中高度盐胁迫下生长不良。     

转AtNHX1基因杨树Tr品系的耐盐性研究

以不同盐分强度处理欧美107杨(Populus × euramericana ‘Neva’) (Wt)和转拟南芥液泡膜Na⁺/H⁺逆向转运蛋白基因AtNHX1欧美107杨新品系(Tr)幼苗, 揭示Tr和Wt两品系幼苗耐盐性的差异, 探索拟南芥液泡膜Na⁺/H⁺逆向转运蛋白基因AtNHX1对提高杨树耐盐能力的效应。结果表明: 低盐处理下, Wt植株生长明显受到抑制, 其干重显著低于对照, 盐分强度加大后, 抑制作用更大, 其干重只有对照的50%; 而Tr植株在低盐处理下干重与对照差异不显著, 高盐处理时其干重为对照的74%。同时, 不同盐度处理下, Tr的干重均显著高于Wt, 且随着盐度升高, 两品系间植株干重差异增大。盐处理后, Tr植株叶片叶绿素和类胡萝卜素的含量均显著高于Wt, 并能维持较高的净光合速率(P_n)和PSII最大光化学效率(F_v/F_m); 在盐处理下虽然Tr叶片和根系均较Wt积累了更多的Na⁺, 但同时也维持了更高的K⁺和K⁺/Na⁺比率, 而且叶片对K⁺选择性的运输明显高于Wt; 同时, Tr叶片MDA含量和电解质渗漏率显著低于Wt。可见, 在盐处理下转AtNHX1植株较未转基因植株维持了更高的生长量、光合色素、光合能力和叶片质膜稳定性, 说明AtNHX1的转入能够显著提高欧美107杨的耐盐性。     

Physiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritima

Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco‐physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance‐ and salt‐dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose‐dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na⁺ and Cl^?, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt‐challenged.     

Physiological and Growth Responses of Tomato Progenies Harboring the Betaine Alhyde Dehydrogenase Gene to Salt Stress

The responses of five transgenic tomato （Lycopersicon esculentum Mill） lines containing the betaine aldehyde dehydrogenase （BADH） gene to salt stress were evaluated. Proline, betaine （N, N, N-trimethylglycine, hereafter betalne）, chlorophyll and ion contents, BADH activity, electrolyte leakage （EL）, and some growth parameters of the plants under 1.0% and 1.5% NaCl treatments were examined. The transgenic tomatoes had enhanced BADH activity and betaine content, compared to the wild type under stress conditions. Salt stress reduced chlorophyll contents to s higher extent in the wild type than in the transgenic plants. The wild type exhibited significantly higher proline content than the transgenic plants at 0.9% and 1.3% NaCh Cell membrane of the wild type was severely damaged as determined by higher EL under salinity stress. K^＋ and Ca^2＋ contents of all tested lines decreased under salt stress, but the transgenic plants showed a significantly higher accumulation of K^＋ and Ca^2＋ than the wild type. In contrast, the wild type had significantly higher CI- and Na^2＋ contents than the transgenic plants under salt stress. Although yield reduction among various lines varied, the wild type had the highest yield reduction. Fruit quality of the transgenic plants was better in comparison with the wild type as shown by a low ratio of blossom end rot fruits. The results show that the transgenic plants have improved salt tolerance over the wild type.     

Response of barley seedlings to UV-B radiation as affected by NaCl

The response of barley seedlings, subjected to 150 mmol/L NaCl for 4 days at different light regimes (4 d in the light, 4 d in darkness and a 12 h light/dark cycle) before UV-B radiation was investigated. NaCl treatment resulted in a decrease of total chlorophyll content and an increase in H2O2, free proline and lipid peroxidation, as quantified by measurement of malondialdehyde. Significantly more proline was accumulated in the light than in darkness. The combination of UV-B and NaCl treatment produced an additive effect on most of the parameters studied. UV-B radiation reduced the chlorophyll/carotenoids ratio and photochemical efficiency of PSII as estimated by chlorophyll fluorescence. NaCl pre-exposure decreased H2O2 generation and lipid peroxidation and alleviated the inhibitory effect of UV-B on PSII activity. Proline accumulated under salt stress conditions might be one of the reasons for the observed tolerance of barley seedlings to UV-B radiation.     

Changes in water relations,photosynthetic activity and proline accumulation in one-year-old olive trees (<Emphasis Type="Italic">Olea europaea</Emphasis> L. cv. Chemlali) in response to NaCl salinity

The comparative responses of young olive trees (Olea europaea L. cv “Chemlali”) to different NaCl salinity levels were investigated over 11 months. One-year-old own rooted plants were grown in 10-L pots containing sand and perlite mixture (1:3 v/v). Trees were subjected to three irrigation treatments: CP (control plants that were irrigated with fresh water); SS1 (salt stressed plants irrigated with water containing 100 mM NaCl) and SS2 plants (salt stressed plants irrigated with water containing 200 mM NaCl). Shoot elongation rate, relative water content, leaf water potential and net carbon dioxide exchange rates decreased significantly with increased NaCl salinity level. Under stressed conditions, the increase of Na⁺ and Cl⁻ ions in both leaves and roots was accompanied with that of proline and soluble sugars. The above results show that the accumulation of proline and sugars under stressed conditions could play a role in salt tolerance. The absence of toxicity symptoms under both stress treatments and the superior photosynthetic activity recorded in SS1-treated plants suggest that cv Chemlali is better able to acclimatize to 100 mM NaCl than at 200 mM NaCl. Our findings indicate that saline water containing 100 mM NaCl, the most available water in arid region in Tunisia, can be recommended for the irrigation of cv Chemlali in the arid south of Tunisia.     

Influence of exogenous application of glycinebetaine on antioxidative system and growth of salt-stressed soybean seedlings (Glycine max L.)

Glycinebetaine is one of the most competitive compounds which play an important role in salt stress in plants. In this study, the enhanced salt tolerance in soybean (Glycine max L.) by exogenous application of glycinebetaine was evaluated. To improve salt tolerance at the seedling stage, GB was applied in four different concentrations (0, 5, 25 and 50 mM) as a pre-sowing seed treatment. Salinity stress in the form of a final concentration of 150 mM sodium chloride (NaCl) over a 15 day period drastically affected the plants as indicated by increased proline, MDA and Na⁺ content of soybean plants. In contrast, supplementation with 50 mM GB improved growth of soybean plants under NaCl as evidenced by a decrease in proline, MDA and Na⁺ content of soybean plants. Further analysis showed that treatments with GB, resulted in increasing of CAT and SOD activity of soybean seedlings in salt stress. We propose that the role of GB in increasing tolerance to salinity stress in soybean may result from either its antioxidant capacity by direct scavenging of H₂O₂ or its role in activating CAT activity which is mandatory in scavenging H₂O₂.     

The effect of NaCl on proline accumulation in potato seedlings and calli

The effects of salt stress were studied on the accumulation and metabolism of proline and its correlation with Na⁺ and K⁺ content in shoots and callus tissue of four potato cultivars, viz., Agria, Kennebec (relatively salt tolerant), Diamant and Ajax (relatively salt sensitive). Na⁺ and proline contents increased in all cultivars under salt stress. However, K⁺ and protein contents decreased in response to NaCl treatments. The activities of enzymes involved in proline metabolism, Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) increased and decreased, respectively, in response to elevated NaCl concentrations. The changes of P5CS and ProDH activities in more salt sensitive cultivars (Diamant, Ajax) were more than those in the tolerant ones. Then the stimulation of synthesis in combination with a partially increase of protein proteolysis, a decrease in proline utilization and inhibition of oxidation resulted in high proline contents in seedlings and calli under salt stress. In callus tissue, reduced growth and cell size may be partially responsible for high proline accumulation in response to high NaCl levels. However, although the basic proline contents in the seedlings of more salt tolerant cultivars were higher than the sensitive ones, a clear relationship was not generally observed between accumulation of proline and salt tolerance in potato.     

Gamma radiation and hormone treatment as tools to reduce salt stress in rice (Oryza sativa L.)

We investigated the effects of jasmonic acid (JA) and gamma irradiation on the growth and metabolic responses to salt stress in rice (Oryza sativa L.) plants. The relative growth rate (RGR), relative water content (RWC), and chlorophyll (Chl) content were lower in NaCI-treated plants than in the control, whereas the malondialdehyde content (MDA), electrolyte leakage (EL), and contents of proline and abscisic acid (ABA) were higher in the treated plants. When induced by the salt stress, those effects, however, were somewhat alleviated by the application of JA or gamma irradiation. The most significant response was manifested by the proline content, with relatively lower values for alleviation being recorded for the contents of RGR, RWC, Chl, and MDA, as well as EL. Moreover, although total Chl content was not significantly influenced by JA or gamma irradiation in plants under salt stress, an increase in the level of Chl a resulted in a markedly changed ratio of Chl a/b. The degree of alleviation, in terms of growth and metabolic responses, was more extensive for JA-treated plants than for those exposed to gamma irradiation.     

2种补血草属植物幼苗对NaCl胁迫的生理响应

以盐生植物大叶补血草和黄花补血草为实验材料,研究了NaCl胁迫对其幼苗叶绿素、可溶性蛋白、丙二醛含量等的影响,探讨这些生理指标的变化与补血草耐盐性的关系。结果表明,150mmol/LNaCl胁迫均使大叶补血草和黄花补血草幼苗叶片的叶绿素a(Chla)、叶绿素b(Chlb)和叶绿素总量降低,而过氧化氢(H2O2)和丙二醛(MDA)含量增加,且这种胁迫效应随处理时间的延长而增强,在相同胁迫时间段,大叶补血草各指标的减少或增加幅度明显大于黄花补血草;NaCl胁迫使大叶补血草叶片可溶性蛋白含量降低,却使黄花补血草可溶性蛋白含量增加。表明,NaCl胁迫对大叶补血草的伤害更大,黄花补血草的耐盐性可能强于大叶补血草。     

Comparative lipid peroxidation,antioxidant defense systems and proline content in roots of two rice cultivars differing in salt tolerance

The changes in the activity of antioxidant enzymes such as superoxide dismutase (SOD: EC 1.15.1.1), catalase (CAT: EC 1.11.1.6), peroxidase (POX: EC 1.11.1.7), ascorbate peroxidase (APOX: EC 1.11.1.11) and glutathione reductase (GR: EC 1.6.4.2), free proline content, and the rate of lipid peroxidation level in terms of malondialdehyde (MDA) in roots of two rice cultivars (cvs.) differing in salt tolerance were investigated. Plants were subjected to three salt treatments, 0, 60, and 120 mol m⁻³ NaCl for 7 days. The results showed that activated oxygen species may play a role in cellular toxicity of NaCl and indicated differences in activation of antioxidant defense systems between the two cvs. The roots of both cultivars showed a decrease in GR activity with increase in salinity. CAT and APOX activities increased with increasing salt stress in roots of salt-tolerant cultivar Pokkali but decreased and showed no change, respectively, in roots of IR-28 cultivar. POX activity decreased with increasing NaCl concentrations in salt-tolerant Pokkali but increased in IR-28. SOD activity showed no change in roots of both cultivars under increasing salinity. MDA level in the roots increased under salt stress in sensitive IR-28 but showed no change in Pokkali. IR-28 produced higher amount of proline under salt stress than in Pokkali. Increasing NaCl concentration caused a reduction in root fresh weight of Pokkali and root dry weight of IR-28. The results indicate that improved tolerance to salt stress in root tissues of rice plants may be accomplished by increased capacity of antioxidative system.     

In vitro selection of mung bean and tomato for improving tolerance to NaCl

Mung bean and tomato were in vitro selected from cotyledons on MS medium for improved tolerance to NaCl. The growth responses; the Na, K, proline and anthocyanin contents; and activities of phenylalanine ammonia lyase (PAL, EC 4.3.1.5), tyrosine ammonia lyase (TAL, EC 4.3.1) and chalcone isomerase (CI, EC 5.5.1.5) of the selected plants were characterised and compared with those of the original plants in relation to treatment with NaCl. The treatments significantly reduced fresh and dry weights of shoots and roots; the reduction was least pronounced in selected plants. Meanwhile, Na content was significantly increased; however, K was decreased, a trend that was obvious in original plants but withdrawn following in vitro selection with a consequent lowering in Na/K ratio. In addition, proline was greatly induced by NaCl; the induction was most pronounced in selected plants. Moreover, NaCl significantly increased anthocyanin and activities of PAL, TAL and CI in shoots and roots of both species; the increase was lesser in the selected than in the original plants. These findings indicated that selection of mung bean and tomato resulted in a recovery of growth, overproduction of proline and K and withdrawal of Na and secondary metabolism parameters relative to original plants pointing out to an improved tolerance to NaCl following in vitro selection.     

Brassinosteroid seed priming with nitrogen supplementation improves salt tolerance in soybean

This study was conducted to evaluate the influence of brassinosteroid (24-epibrassinolide, EBL) seed priming and optimal nitrogen (N) supply in improving salt tolerance in soybean. The experimental treatments were (a) control (nutrient solution without N and without EBL priming), (b) nutrient solution without N and EBL seed priming, (c) N supplemented nutrient solution without EBL priming and (d) EBL seed priming + N supplemented nutrient solution under optimal (0 mM NaCl) and salt stress (0 mM NaCl) conditions. Salt stress caused significant reduction in growth and biomass accumulation of soybean. However, EBL seed priming and application of N improved the soybean performance under optimal and salt stress conditions. In this regard, treatments receiving both EBL and N were more effective. EBL priming and N, alone and in combination, triggered the accumulation of osmolytes including proline, glycine betaine and sugars resulting in better photo-protection through maintenance of tissue water content. Antioxidant activity and osmolyte accumulation significantly increased due to combined treatment of N and EBL under normal as well as salt stress conditions. In conclusion, salt stress caused reduction in growth and biomass soybean due to oxidative damage and osmotic stresses. However, soybean performance was improved by seed priming with EBL. Supplementation of N further improved the effectiveness of EBL treatment in improving salt tolerance in soybean.     

Proline as a biochemical marker in relation to the ecology of two halophytic Juncus species

Aims Osmolytes, used for maintaining osmotic balance and as 'osmoprotectants', are synthesized in plants as a general, conserved response to abiotic stress, although their contribution to stress-tolerance mechanisms remains unclear. Proline, the most common osmolyte, accumulates in many plant species in parallel with increased external salinity and is considered a reliable biochemical marker of salt stress. We have measured proline levels in two halophytic, closely related Juncus species under laboratory and field conditions to assess the possible relevance of proline biosynthesis for salt tolerance and therefore for the ecology of these two taxa.Methods Proline was quantified in plants treated with increasing NaCl concentrations and in plants sampled in two salt marshes located in the provinces of Valencia and Alicante, respectively, in southeast Spain. Electrical conductivity, pH, Na + and Cl ? concentrations were measured in soil samples collected in parallel with the plant material.Important findings Treatment with NaCl inhibited growth of J. acutus plants in a concentration-dependent manner, but only under high salt conditions for J. maritimus. Salt treatments led to proline accumulation in both species, especially in the more salt-tolerant J. maritimus. The results, obtained under laboratory conditions, were confirmed in plants sampled in the field. In all the samplings, proline contents were significantly lower in J. acutus than in the more tolerant J. maritimus growing in the same area. No direct correlation between soil salinity and proline levels could be established, but seasonal variations were detected, with increased proline contents under accentuated water deficit conditions. Our results suggest that proline biosynthesis is not only an induced, general response to salt stress but also an important contributing factor in the physiological mechanisms of salt tolerance in Juncus, and that it therefore correlates with the ecology of both species.     

Interactive role of nitric oxide and calcium chloride in enhancing tolerance to salt stress

Nitric oxide (NO), a small diffusible, ubiquitous bioactive molecule, acts as prooxidant as well as antioxidant, and also regulates remarkable spectrum of plant cellular mechanisms. The present work was undertaken to investigate the role of nitric oxide donor sodium nitroprusside (SNP) and/or calcium chloride (CaCl(2)) in the tolerance of excised mustard leaves to salt stress. After 24h, salt stressed leaves treated with SNP and/or CaCl(2), showed an improvement in the activities of carbonic anhydrase (CA) and nitrate reductase (NR), and leaf chlorophyll (Chl) content, leaf relative water content (LRWC) and leaf ion concentration as compared with the leaves treated with NaCl only. Salinity stress caused a significant increase in H(2)O(2) content and membrane damage which is witnessed by enhanced levels of thiobarbituric acid reactive substances (TBARS) and electrolyte leakage. By contrast, such increases were blocked by the application of 0.2mM SNP and 10mM CaCl(2) to salt stressed leaves. Application of SNP and/or CaCl(2) alleviated NaCl stress by enhancing the activities of antioxidative enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase (GR) and by enhancing proline (Pro) and glycinebetaine (GB) accumulation with a concomitant decrease in H(2)O(2) content, TBARS and electrolyte leakage, which is manifested in the tolerance of plants to salinity stress. Moreover, application of SNP with CaCl(2) was more effective to reduce the detrimental effects of NaCl stress on excised mustard leaves. In addition to this, ameliorating effect of SNP was not effective in presence of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide]. To put all these in a nut shell, the results advocate that SNP in association with CaCl(2) plays a role in enhancing the tolerance of plants to salt stress by improving antioxidative defence system, osmolyte accumulation and ionic homeostasis.     

Over-expression of Osmotin Induces Proline Accumulation and Confers Tolerance to Osmotic Stress in Transgenic Tobacco

Osmotin has been implicated in conferring tolerance to drought and salt stress in plants. We have over-expressed the osmotin gene under the control of constitutive CaMV 35S promoter in transgenic tobacco, and studied involvement of the protein in imparting tolerance to salinity and drought stress. The transgenic plants exhibited retarded leaf senescence and improved germination on a medium containing 200mM NaCl. Further, the transgenics maintained higher leaf relative water content (RWC), leaf photosynthesis and free proline content than the wild type plants during water stress and after recovery from stress. When subjected to salt stress (200mM NaCl), the transgenic plants accumulated significantly more proline than the wild type plants. These results suggest the involvement of the osmotin-induced increase in proline in imparting tolerance to salinity and drought stress in transgenic plants over-expressing the osmotin gene.