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.     

Overexpression of <Emphasis Type="Italic">SlERF1</Emphasis> tomato gene encoding an ERF-type transcription activator enhances salt tolerance

Ethylene-responsive factors (ERFs) play an important role in plant responses to stresses. For this study, we obtained sense- and antisense-SlERF1 transgenic tomato plants to analyze the function of the SlERF1 gene in tomato plants. Overexpression of SlERF1 in tomato plants enhanced salt tolerance during tomato seedling root development. In addition, tomato seedlings overexpressing SlERF1 showed the higher relative water content and lower MDA content and electrolyte leakage; they accumulated more free proline and soluble sugars, as compared with wild-type and antisense-SlERF1 transgenic tomato plants under salt stress. Moreover, SlERF1 activated the expression of stress-related genes, including LEA, P5CS, DREB3-1, and ltpg2 in tomato plants under salt stress. Thus, SlERF1 played a positive role in the salt tolerance of tomato plants.     

Organic substances responsible for salt tolerance inEruca sativa

Responses of a salt tolerant and a normal population of an oilseed crop,Eruca sativa Mill. were assessed after four weeks growth in sand culture salinized with 0 (control), 100, 200, or 300 mol m^?3 NaCl. The salt tolerant plants produced significantly greater dry biomass than the normal population. The populations did not differ significantly in leaf osmotic potential, relative water content and leaf soluble proteins. However, the tolerant population accumulated significantly greater amounts of soluble sugars, proline and free amino acids in the leaves compared with the non-tolerant population. It is established that leaf soluble sugars, proline, and free amino acids are important components of salt tolerance inEruca sativa.     

Medicago truncatula stress associated protein 1 gene (MtSAP1) overexpression confers tolerance to abiotic stress and impacts proline accumulation in transgenic tobacco

Stress associated proteins (SAP) have been already reported to play a role in tolerance acquisition of some abiotic stresses. In the present study, the role of MtSAP1 (Medicago truncatula) in tolerance to temperature, osmotic and salt stresses has been studied in tobacco transgenic seedlings. Compared to wild type, MtSAP1 overexpressors were less affected in their growth and development under all tested stress conditions. These results confirm that MtSAP1 is involved in the response processes to various abiotic constraints. In parallel, we have performed studies on an eventual link between MtSAP1 overexpression and proline, a major player in stress response. In an interesting way, the results for the transgenic lines did not show any increase of proline content under osmotic and salt stress, contrary to the WT which usually accumulated proline in response to stress. These data strongly suggest that MtSAP1 is not involved in signaling pathway responsible for the proline accumulation in stress conditions. This could be due to the fact that the overexpression of MtSAP1 provides sufficient tolerance to seedlings to cope with stress without requiring the free proline action. Beyond that, the processes by which the MtSAP1 overexpression lead to the suppression of proline accumulation will be discussed in relation with data from our previous study involving nitric oxide.     

Transgenic Medicago truncatula plants that accumulate proline display nitrogen-fixing activity with enhanced tolerance to osmotic stress

Legume root nodule nitrogen-fixing activity is severely affected by osmotic stress. Proline accumulation has been shown to induce tolerance to salt stress, and transgenic plants over-expressing Delta(1)-pyrroline-5-carboxylate synthetase (P5CS), which accumulates high levels of proline, display enhanced osmotolerance. Here, we transformed the model legume Medicago truncatula with the P5CS gene from Vigna aconitifolia, and nodule activity was evaluated under osmotic stress in transgenic plants that showed high proline accumulation levels. Nitrogen fixation was significantly less affected by salt treatment compared to wild-type (WT) plants. To our knowledge, this is the first time that transgenic legumes have been produced that display nitrogen-fixing activity with enhanced tolerance to osmotic stress. We studied the expression of M. truncatula proline-related endogenous genes M. truncatulaDelta(1)-pyrroline-5-carboxylate synthetase 1 (MtP5CS1), M. truncatulaDelta(1)-pyrroline-5-carboxylate synthetase 2 (MtP5CS2), M. truncatula ornithine delta-aminotransferase (MtOAT), M. truncatula proline dehydrogenase (MtProDH) and a proline transporter gene in both WT and transgenic plants. Our results indicate that proline metabolism is finely regulated in response to osmotic stress in an organ-specific manner. The transgenic model allowed us to analyse some of the biochemical and molecular mechanisms that are activated in the nodule in response to high salt conditions, and to ascertain the essential role of proline in the maintenance of nitrogen-fixing activity under osmotic stress.     

Effects of saline and osmotic stress on proline and sugar accumulation in Populus euphratica in vitro

The use of in vitro shoot cultures to evaluate osmotic and salt tolerance and the effects of salt and mannitol in the medium on proline and sugar accumulation were investigated in two poplar species, P. euphratica and P. alba cv. Pyramidalis × P. tomentosa. Shoot length, leaf number, whole plant dry weight, and the accumulation of proline and total soluble sugars in leaves were quantified after 2 weeks. All P. euphratica plantlets survived at all levels of mannitol and NaCl, while the mortality of P. alba cv. Pyramidalis × P. tomentosa increased both at the mannitol and the NaCl treatments. A significant increase in proline accumulation was observed in both young and mature P. euphratica leaves at 200 mM mannitol and above, and at 150 mM NaCl and above. The total soluble sugar content increased in young P. euphratica leaves at 250 mM NaCl; however, it decreased in the mature leaves. Similar increases of the total soluble sugar content were not seen in P. alba cv. Pyramidalis × P. tomentosa plants in response to either mannitol or NaCl treatment. Our results suggest that accumulated proline and sugars promote osmotic and salt tolerance. The effects of accumulated proline and total soluble sugars on leaves are discussed in relation to growth and osmotic adjustment. This revised version was published online in August 2006 with corrections to the Cover Date.     

星星草耐盐碱生理机制的初步研究

对盐碱胁迫下星星草幼苗光全特性,蒸腾速率,水分利用效率,电解质外渗率,Ｎａ＾＋和Ｋ＾＋含量,可溶性盐含量,游离脯氨酸含量和可溶性糖含量的研究结果表明,在低浓度盐碱胁迫下,星星草幼苗的抗起因三性是以其具有一定的耐盐光合蒸腾特性,和较强的渗透调节能为基础。     

Overexpression of a TFIIIA-type zinc finger protein gene ZFP252 enhances drought and salt tolerance in rice (Oryza sativa L.)

We previously identified a salt and drought stress-responsive TFIIIA-type zinc finger protein gene ZFP252 from rice. Here we report the functional analysis of ZFP252 using gain- and loss-of-function strategies. We found that overexpression of ZFP252 in rice increased the amount of free proline and soluble sugars, elevated the expression of stress defense genes and enhanced rice tolerance to salt and drought stresses, as compared with ZFP252 antisense and non-transgenic plants. Our findings suggest that ZFP252 plays an important role in rice response to salt and drought stresses and is useful in engineering crop plants with enhanced tolerance to salt and drought stresses.     

Leaf water relations and net gas exchange responses of salinized Carrizo citrange seedlings during drought stress and recovery

BACKGROUND AND AIMS: Since salinity and drought stress can occur together, an assessment was made of their interacting effects on leaf water relations, osmotic adjustment and net gas exchange in seedlings of the relatively chloride-sensitive Carrizo citrange, Citrus sinensis x Poncirus trifoliata. METHODS: Plants were fertilized with nutrient solution with or without additional 100 mm NaCl (salt and no-salt treatments). After 7 d, half of the plants were drought stressed by withholding irrigation water for 10 d. Thus, there were four treatments: salinized and non-salinized plants under drought-stress or well-watered conditions. After the drought period, plants from all stressed treatments were re-watered with nutrient solution without salt for 8 d to study recovery. Leaf water relations, gas exchange parameters, chlorophyll fluorescence, proline, quaternary ammonium compounds and leaf and root concentrations of Cl(-) and Na(+) were measured. KEY RESULTS: Salinity increased leaf Cl(-) and Na(+) concentrations and decreased osmotic potential (Psi(pi)) such that leaf relative water content (RWC) was maintained during drought stress. However, in non-salinized drought-stressed plants, osmotic adjustment did not occur and RWC decreased. The salinity-induced osmotic adjustment was not related to any accumulation of proline, quaternary ammonium compounds or soluble sugars. Net CO(2) assimilation rate (A(CO2)) was reduced in leaves from all stressed treatments but the mechanisms were different. In non-salinized drought-stressed plants, lower A(CO2) was related to low RWC, whereas in salinized plants decreased A(CO2) was related to high levels of leaf Cl(-) and Na(+). A(CO2) recovered after irrigation in all the treatments except in previously salinized drought-stressed leaves which had lower RWC and less chlorophyll but maintained high levels of Cl(-), Na(+) and quaternary ammonium compounds after recovery. High leaf levels of Cl(-) and Na(+) after recovery apparently came from the roots. CONCLUSIONS: Plants preconditioned by salinity stress maintained a better leaf water status during drought stress due to osmotic adjustment and the accumulation of Cl(-) and Na(+). However, high levels of salt ions impeded recovery of leaf water status and photosynthesis after re-irrigation with non-saline water.     

Stress-inducible expression of barley Hva1 gene in transgenic mulberry displays enhanced tolerance against drought, salinity and cold stress

Coping with different kinds of biotic and abiotic stresses is the foundation of sustainable agriculture. Although conventional breeding and marker-assisted selection are being employed in mulberry (Morus indica L.) to develop better varieties, nonetheless the longer time periods required for these approaches necessitates the use of precise biotechnological approaches for sustainable agriculture. In an attempt to improve stress tolerance of mulberry, an important plant of the sericulture industry, an encoding late embryogenesis abundant gene from barley (HVA1) was introduced into mulberry plants by Agrobacterium-mediated transformation. Transgenic mulberry with barley Hva1 under a constitutive promoter actin1 was shown to enhance drought and salinity tolerance. Here, we report that overexpression of barley Hva1 also confers cold tolerance in transgenic mulberry. Further, barley Hva1 gene under control of a stress-inducible promoter rd29A can effectively negate growth retardation under non-stress conditions and confer stress tolerance in transgenic mulberry. Transgenic lines display normal morphology to enhanced growth and an increased tolerance against drought, salt and cold conditions as measured by free proline, membrane stability index and PSII activity. Protein accumulation was detected under stress conditions confirming inductive expression of HVA1 in transgenics. Investigations to assess stress tolerance of these plants under field conditions revealed an overall better performance than the non-transgenic plants. Enhanced expression of stress responsive genes such as Mi dnaJ and Mi 2-cysperoxidin suggests that Hva1 can regulate downstream genes associated with providing abiotic stress tolerance. The investigation of transgenic lines presented here demonstrates the acquisition of tolerance against drought, salt and cold stress in plants overexpressing barley Hva1, indicating that Arabidopsis rd29A promoter can function in mulberry.     

Growth,physiological, biochemical and ionic responses of pistachio seedlings to mild and high salinity

Key message

Depending on salt concentrations, different mechanisms are involved in the tolerance of pistachio and an acclimation to salinity conditions occurs in the leaves that develop in the presence of salt.

Abstract

Pistachio (Pistacia vera L.) is a salt tolerant species that is considered an alternative crop for cultivation in salinzied orchard soils. In this work, 12-week-old pistachio seedlings cultivated in soil under greenhouse conditions were treated with five levels of salinity including control (0.63 dSm^?1), low (2 and 4 dSm^?1) and high (8 and 10 dSm^?1) salt concentrations for further 12 weeks. Plant growth parameters were not affected by mild salinity; a significant reduction was only observed from 8 dSm^?1. Considerable differences were observed between the young and mature leaves regarding osmotic and ionic stress effects of salt. Main compatible solutes were proline in mature leaves, proline and soluble sugars in young leaves, and soluble sugars and amino acids, other than proline, in roots. Concentration and content of Na in the leaves were not significantly increased at low levels of salinity and the K:Na and Ca:Na ratio of leaves were affected only by higher salt concentrations. Using the sequential extraction procedure for cell wall isolation, we observed that both absolute and relative amounts of Na in the cell wall fraction increased under low salinity, while decreased under higher levels of salt supply. Stable water relations, photochemistry and CO₂ assimilation rates particularly of young leaves, as well as ion homeostasis were mechanisms for maintenance of plants growth under mild salinity. Under severe saline conditions, the impaired ability of mature leaves for synthesis of assimilates, preferent allocation of carbohydrates to roots for maintenance of osmotic homeostasis and finally, reduction of protein synthesis caused growth inhibition in pistachio.     

Comparative effects of osmotic-, salt- and alkali stress on growth,photosynthesis, and osmotic adjustment of cotton plants

In this study, cotton seedlings were subjected to osmotic-, salt- and alkali stresses. The growth, photosynthesis, inorganic ions, and organic acids in the stressed seedlings were measured, to compare the mechanisms by which plants adapt to these stresses and attempt to probe the mechanisms by which plants adapt to high pH stress. Our results indicated that, at high stress intensity, both osmotic and alkali stresses showed a stronger injurious effect on growth and photosynthesis than salt stress. Cotton accumulated large amount of Na+ under salt and alkali stresses, but not under osmotic stress. In addition, the reductions of K⁺, NO₃ ⁻, and H₂PO₄ ⁻ under osmotic stress were much greater than those under salt stress with increasing stress intensity. The lack of inorganic ions limited water uptake and was the main reason for the higher injury from osmotic-compared to salt stress on cotton. Compared with salt- and alkali stresses, the most dramatic response to osmotic stress was the accumulation of soluble sugars as the main organic osmolytes. In addition, we found that organic acid metabolism adjustment may play different roles under different types of stress. Under alkali stress, organic acids might play an important role in maintaining ion balance of cotton; however, under osmotic stress, malate might play an important osmotic role.     

基于叶片生理指标的小麦芽期耐盐性评价

土壤盐渍化严重影响小麦生产,提高小麦耐盐性是应对土壤盐渍化的主要生物途径之一.小麦芽期亦是对盐分较为敏感的时期,小麦芽期耐盐性的强弱对盐碱地小麦种植至关重要.为探讨利用叶片生理指标进行小麦芽期耐盐性评价的可行性,该文以沧麦6005及其73个叠氮化钠诱变家系为试验材料,在超纯水和40％人工海水条件下,对芽期叶片中脯氨酸、...     

Changes in the water status and osmotic solute contents in response to drought and salicylic acid treatments in four different cultivars of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis>)

Salicylic acid (SA) controls growth and stress responses in plants. It also induces drought tolerance in plants. In this paper, four wheat (Triticum aestivum L.) cultivars with different drought responses were treated with SA in three levels of drain (90, 60, 30% of maximum field capacity) to examine its interactive effects on drought responses and contents of osmotic solutes that may be involved in growth and osmotic adjustment. Under drought condition, the cultivars Geza 164 and Sakha 69 had the plant biomass and leaf relative water content (LRWC) greater than the cultivars Gemaza 1 and Gemaza 3. In all cultivars, drought stress decreased the biomass, LRWC, and the contents of inorganic solutes (Ca, K, Mg) and largely increased the contents of organic solutes (soluble sugars and proline). By contrast, SA increased the biomass, LRWC and the inorganic and organic solute contents, except proline. Correlation analysis revealed that the LRWC correlated positively with the inorganic solute contents but negatively with proline in all cultivars. SA caused maximum accumulations of soluble sugars in roots under drought. These results indicated that SA-enhanced tolerance might involve solute accumulations but independently of proline biosynthesis. Drought-sensitive cultivars had a trait lowering Ca and K levels especially in shoots. Possible functions of the ions and different traits of cultivars were discussed.     

Overexpression of OsHsp17.0 and OsHsp23.7 enhances drought and salt tolerance in rice

Heat shock proteins (Hsps) play an important role in plant stress tolerance. We previously reported that expression of OsHsp17.0 and OsHsp23.7 could be enhanced by heat shock treatment and/or other abiotic stresses. In this paper, stress tolerance assays of transgenic rice plants overexpressing OsHsp17.0 and OsHsp23.7 have been carried out. Both OsHsp17.0-OE and OsHsp23.7-OE transgenic lines demonstrated higher germination ability compared to wild-type (WT) plants when subjected to mannitol and NaCl. Phenotypic analysis showed that transgenic rice lines displayed a higher tolerance to drought and salt stress compared to WT plants. In addition, transgenic rice lines showed significantly lower REC, lower MDA content and higher free proline content than WT under drought and salt stresses. These results suggest that OsHsp17.0 and OsHsp23.7 play an important role in rice acclimation to salt and drought stresses and are useful for engineering drought and salt tolerance rice.