Salt-tolerant Plant Species Research Articles

Paradox of plant growth promotion potential of rhizobacteria and their actual promotion effect on growth of barley (Hordeum vulgare L.) under salt stress

From the rhizosphere of two salt tolerant plant species, Hordeum secalinum and Plantago winteri growing in a naturally salt meadow, 100 strains were isolation on enrichment media for various plant growth-promoting (PGP) functions (ACC deaminase activity, auxin synthesis, calcium phosphate mobilization and nitrogen fixation). Based on the taxonomic affiliation of the isolated bacteria and their enrichment medium 22 isolates were selected to test their growth promotion effect on the crop barley (Hordeum vulgare) under salt stress in pot experiment. In parallel the isolates were characterized in pure culture for their plant growth-promoting activities. Surprisingly the best promotors did not display a promising set of PGP activities. Isolates with multiple PGP-activities in pure culture like Microbacterium natoriense strain E38 and Pseudomonas brassicacearum strain E8 did not promote plant growth. The most effective isolate was strain E108 identified as Curtobacterium flaccumfaciens, which increased barley growth up to 300%. In pure culture strain E108 showed only two out of six plant growth promoting activities and would have been neglected. Our results highlight that screening based on pure culture assays may not be suitable for recognition of best plant growth promotion candidates and could preclude the detection of both new PGPR and new plant promotion mechanisms.

Defining the next generation modeling of coastal ecotone dynamics in response to global change

Coastal ecosystems are especially vulnerable to global change; e.g., sea level rise (SLR) and extreme events. Over the past century, global change has resulted in salt-tolerant (halophytic) plant species migrating into upland salt-intolerant (glycophytic) dominated habitats along major rivers and large wetland expanses along the coast. While habitat transitions can be abrupt, modeling the specific drivers of abrupt change between halophytic and glycophytic vegetation is not a simple task. Correlative studies, which dominate the literature, are unlikely to establish ultimate causation for habitat shifts, and do not generate strong predictive capacity for coastal land managers and climate change adaptation exercises. In this paper, we first review possible drivers of ecotone shifts for coastal wetlands, our understanding of which has expanded rapidly in recent years. Any exogenous factor that increases growth or establishment of halophytic species will favor the ecotone boundary moving upslope. However, internal feedbacks between vegetation and the environment, through which vegetation modifies the local microhabitat (e.g., by changing salinity or surface elevation), can either help the system become resilient to future changes or strengthen ecotone migration. Following this idea, we review a succession of models that have provided progressively better insight into the relative importance of internal positive feedbacks versus external environmental factors. We end with developing a theoretical model to show that both abrupt environmental gradients and internal positive feedbacks can generate the sharp ecotonal boundaries that we commonly see, and we demonstrate that the responses to gradual global change (e.g., SLR) can be quite diverse.

Identification of salt tolerant Acacia species for saline land utilisation

AbstractThe deleterious effects of soil salinity on biodiversity and agricultural productivity make it essential to devise strategies that would reduce its impact and expansion. For sustainable agriculture on dryland salinity affected areas, the use of native salt-tolerant plant species of economic value could provide a solution. In this work, the salinity tolerance potential of fifteen different Australian Acacia (wattle) species, pre-selected on the basis of phylogenetic relationships, were tested. The effects of salinity stress on morphological and physiological parameters, such as shoot and root lengths, shoot and root biomass, tissue water content, tolerance indices and accumulation of major cations (sodium, potassium, magnesium, calcium), all of which are indicators of salt stress response, were investigated. The species exhibited varied responses to the various parameters, some species consistently indicative of salt tolerance. Consolidating the tolerance indices based on morphological and physiological effects of salt stress, a method was developed to arbitrarily rank the species for their tolerance. Two highly tolerant, three tolerant and six moderately tolerant species could thus be identified. The work supports use of phylogenetics for initial screening for large genera, such as Acacia, and provides an experimental methodology for identification of candidate species for environmental stress tolerance and other applications.

Promotion of growth and upregulation of thylakoid membrane proteins in the halophyte Salicornia bigelovii Torr. under saline conditions

Salicornia bigelovii is an unusually salt-tolerant plant species and is able to continue to photosynthesize and grow in saline conditions. There is an interest in understanding the mechanisms of this salt tolerance. In this study, S. bigelovii plants grown under 400 mM NaCl had higher growth and higher photosynthetic capacity than those not grown with salt. The intensities of the fluorescence emission peaks in the thylakoid membrane spectra in the salt treatment were higher than in the control. PSII and PSI peaks of the control were blue-shifted, indicating that salt deficiency affects energy transfer and structural stability in PSII and PSI. Both SDS-PAGE and western blot illustrated that the PSI proteins PsaA and PsaB and the PSII proteins CP47 and CP43 were upregulated with salt treatment, which might partly explain the change in the energy transfer process. Furthermore, Lhcb1 was also stimulated by salt treatment while Lhcb2 and Lhcb3 did not show noticeable changes. This demonstrated that salt is important in the maintenance of photosynthesis. In summary, treatment with salt led to an increased amount of PsaA/B, CP47, CP43, and Lhcb1 with a concurrent increase in antennae size. These photosystem changes may be responsible for the adaptation of S. bigelovii to saline conditions.

IMPACTS OF CLIMATE CHANGE ON VEGETATION DISTRIBUTION NO. 2 - CLIMATE CHANGE INDUCED VEGETATION SHIFTS IN THE NEW WORLD

After giving an overview of climate change induced vegetation shifts in the Palearctic region in our previous paper, in this article we review literature available in Web of Science on North and South America. We study different geographical regions such as Canada, Alaska, California, Southwestern, Eastern and Southeastern USA, the Great Lakes region, the Great Plains, intermontane basins and plateaus, Rocky Mountains and the Cascades as well as Central and South America. We summarize main results of relevant field studies, experiments and model simulations. Predicted environmental changes include temperature increases, altering precipitation patterns, droughts, permafrost thaw and ground subsidence in arctic regions, enhanced El Nino Southern Oscillation, sea level rise, increasing salinity of the vadose zone, snowpack declines and various disturbances. All vegetation types are affected by these changes, to the most important phenomena belong e.g. reduction of arctic and alpine communities, decreasing area of taiga, shrub encroachment in tundra areas, northward expansion of the tree line, reduction in wetland areas, invasion, altering forest regeneration patterns, decrease in dominance of conifer species, increased cover of salt-tolerant plant species in tidal marshes, expansion of grassland, compositional and structural changes of grasslands and forests, drying up of bogs, landward migration of mangroves, savannification of forests, expansion of chaparral as well as upward migration of species in the mountains.

English

Endophytic bacteria were isolated from leaves of four dominant halophyte and salt tolerant plant species of coastal Gujarat. The bacterial counts on nutrient agar were found to be maximum in Spharanthus indicus (40%) and were minimum in Salicornia brachiata (10%). Twenty (20) bacterial isolates were selected and were characterized through morphological characters and biochemical tests. Three were pigmented and 17 were non-pigmented and 50% isolates exhibited amylase activity and only 15% isolates showed urease activity. Six (30%) and two (10%) isolates showed positive results for ammonia production and phosphate solubilization activity. Salt tolerance of the endophytes was also tested. Of the 20 endophytic bacteria, seventeen (85%) isolates showed growth at 7.5% NaCl and fifteen (75%) tolerated upto 10% NaCl concentration. Overall, the growth rate of endophytes decreased with increasing concentration of NaCl in media. The endophytic bacteria were identified through 16S rRNA sequencing and mostly the isolated endophytic bacteria belong to genera Bacillus spp.   Key words: Endophyte, halophyte, halophilic bacteria, coastal region, salt tolerance.

JcLEA, a Novel LEA-Like Protein from Jatropha curcas, Confers a High Level of Tolerance to Dehydration and Salinity in Arabidopsis thaliana

Jatropha curcas L. is a highly drought and salt tolerant plant species that is typically used as a traditional folk medicine and biofuel crop in many countries. Understanding the molecular mechanisms that underlie the response to various abiotic environmental stimuli, especially to drought and salt stresses, in J. curcas could be important to crop improvement efforts. In this study, we cloned and characterized the gene for a late embryogenesis abundant (LEA) protein from J. curcas that we designated JcLEA. Sequence analyses showed that the JcLEA protein belongs to group 5, a subgroup of the LEA protein family. In young seedlings, expression of JcLEA is significantly induced by abscisic acid (ABA), dehydration, and salt stress. Subcellular localization analysis shows that that JcLEA protein is distributed in both the nucleus and cytoplasm. Moreover, based on growth status and physiological indices, the overexpression of JcLEA in transgenic Arabidopsis plants conferred increased resistance to both drought and salt stresses compared to the WT. Our data suggests that the group 5 JcLEA protein contributes to drought and salt stress tolerance in plants. Thus, JcLEA is a potential candidate gene for plant genetic modification.

Finite element approximation of a surface–subsurface coupled problem arising in forest dynamics

We propose a finite element approximation for an evolution model describing the spatial population distribution of two salt tolerant plant species, such as mangroves, which are affected by inter- and intra-specific competition (Lotka–Volterra), population pressure (cross-diffusion) and environmental heterogeneity (environmental potential). The environmental potential and the Lotka–Volterra terms are assumed to depend on the salt concentration in the roots region, which may change as a result of mangroves ability for uptaking fresh water and leave the salt of the solution behind, in the saturated porous medium. Consequently, partial differential equations modeling the population dynamics on the surface are coupled with Darcy-transport equations modeling the salt and pressure–velocity distribution in the subsurface. We provide a numerical discretization based on a stabilized mixed finite element method for the transport-Darcy flow problem coupled to a finite element method for a regularized version of the cross-diffusion population model, which we use to numerically demonstrate the behavior of the system.

Application of Molecular Markers for Identification of Potential Salt Tolerant Plant Species for use in Agroforestry and Saline Land Reclamation

In this paper, a novel approach for preliminary identification of salt tolerance in Acacia species is presented, based on molecular phylogenetic analysis using nuclear ribosomal DNA markers (ITS and ETS). Four species of Acacia, i.e., A. pendula, A. salicina, A. victoriae and A. stenophylla, had been initially identified as salt tolerant and were being used for a land reclamation project of a salinity degraded area in Victoria, Australia. Using molecular techniques, a phylogenetic tree was constructed to identify additional Acacia species closest to the four candidate salt tolerant species. These data could be potentially used to identify and select additional salt tolerant genotypes that can be used for land revegetation projects for salinity-affected areas. Since these species are native to Australian landscape, employing them in preventing the expansion of salinity will also help with biodiversity conservation.

Physiological and proteomic characterization of salt tolerance in a mangrove plant, Bruguiera gymnorrhiza (L.) Lam

Salinity is a major abiotic stress that is responsible for growth reduction in most higher plants. Bruguiera gymnorrhiza (L.) Lam., a mangrove plant, is a halophyte and is one of the most salt-tolerant plant species. Physiological and proteomic characteristics of B. gymnorrhiza were investigated under three NaCl concentrations (0, 200 and 500 mM) in this study. Maximum seedling growth occurred at 200 mM NaCl. Leaf osmotic potential was more negative as salt levels increased further. Physiological results revealed that inorganic ions (especially Na(+) and Cl(-)) played a key role in osmotic adjustment of B. gymnorrhiza leaves under salinity treatments. Comparative proteomic analysis revealed 23 salt-responsive proteins in B. gymnorrhiza leaves, which were differentially expressed under salt treatment compared with control. Ten protein spots were analyzed by liquid chromatography-tandem mass spectrometry, leading to identification of proteins involved in photosynthesis, antioxidation, protein folding, cell organization and metabolism. Salt-responsive mechanism was different between 200 and 500 mM NaCl-treated plants on the basis of the physiological and proteomic analyses. Salt tolerance under 200 mM NaCl treatment was due to effective osmotic adjustment, accumulation of inorganic ions (especially Na(+) and Cl(-)) as well as increased expression of photosynthesis-related proteins and antioxidant enzymes, which improved the salt tolerance of B. gymnorrhiza, and furthermore promoted plant growth. On the other hand, 500 mM NaCl reduced the growth of B. gymnorrhiza, which appears to have been caused by the accumulation of NaCl (ionic effect) and energy consumption by organic solute synthesis. Moreover, the repressed expression of photosynthesis-related proteins and antioxidant enzymes led to the reduction of growth. Protein folding and degradation-related proteins and cell organization-related protein were up-regulated and played important roles in salt tolerance of B. gymnorrhiza under severe salt stress.

Halophyte crop cultivation: The case for Salicornia and Sarcocornia

Increasing soil salinization and the growing scarcity of fresh water dictate the need for a creative solution to attain sustainable crop production. To accomplish this aim, the domestication of inherently salt tolerant plant species with economic value is proposed as a straightforward methodology. Most studies investigating salt tolerance mechanisms are linked to small, experimental systems that cannot be generalized to the real agricultural context. The crops Salicornia and Sarcocornia, however, with their extreme salt tolerance and long history of consumption by humans, make the ideal model plants on which to base a halophyte growth strategy. New applied technologies were developed for leafy vegetable production using small-scale greenhouse and in-field studies. Several cultivation systems adapted to the irrigation water salinity and the available soil conditions are described. Daylength manipulation and a repetitive harvest regime partially elucidated the flowering patterns of Salicornia and Sarcocornia and showed that flowering should be prevented for maximal vegetable production. Additionally, the beneficial effect of saline irrigation on quality parameters via the enhancement of stress-induced secondary metabolites with antioxidant capacity should be considered during cultivation. This review summarizes the recent developments in growing halophytes for food production with saline irrigation, using Salicornia and Sarcocornia as a case study.

Plasma membrane permeability as an indicator of salt tolerance in plants

There is evidence that the plasma membrane (PM) permeability alterations might be involved in plant salt tolerance. This review presents several lines of evidence demonstrating that PM permeability is correlated with salt tolerance in plants. PM injury and hence changes in permeability in salt sensitive plants is brought about by ionic effects as well as oxidative stress induced by salt imposition. It is documented that salinity enhances lipid peroxidation as well as protein oxidative damage, which in turn induces permeability impairment. PM protection, and thus retained permeability, in tolerant plants under salt imposition could be achieved through increasing antioxidative systems and thereby reducing lipid peroxidation and protein oxidative damage of PM. It appears that specific membrane proteins and/or lipids are constitutive or induced under salinity, which may contribute to maintenance of membrane structure and function in salt tolerant plant species. Furthermore, protecting agents (e.g., glycinebetaine, proline, polyamines, trehalose, sorbitol, mannitol) accumulated in salt tolerant species/cultivars may also contribute to PM stabilization and protection under salinity. Based on the presented evidence that PM permeability correlates with plant salt tolerance, we suggest that PM permeability is an easy and useful parameter for selection of genotypes of agriculture crops adapted to salt stress.

Photosynthesis and antioxidant activity in Jatropha curcas L. under salt stress

Biodiesel is an alternative to petroleum diesel fuel. It is a renewable, biodegradable, and nontoxic biofuel. Interest in the production of biodiesel from Jatropha curcas L. seeds has increased in recent years, but the ability of J. curcas to grow in salt-prone areas, such as the Caatinga semiarid region, has received considerably meager attention. The aim of this study was to identify the main physiological processes that can elucidate the pattern of responses of J. curcas irrigated with saline water, which commonly occurs in the semiarid Caatinga region. This study measured the activity of the antioxidant enzymes involved in the scavenging of reactive oxygen species, which include catalase (CAT) and ascorbate peroxidase (APX), as well as malondialdehyde (MDA) levels. The levels of chlorophyll (Chl), carotenoids, amino acids, proline, and soluble proteins were also analyzed. The net carbon assimilation rate (P N), stomata conductance (g s), and transpiration rate (E) decreased with salt stress. The activities of CAT and APX were decreased, while H2O2 and MDA levels as well as electrolyte leakage were significantly increased in salt-stressed plants compared to the untreated ones. These observations suggest that the ability of J. curcas plants resist to salt stress is associated with the activities of protective enzymes and their defensive functions. However, our results indicate that the reactive oxygen species scavenging system is not sufficient to protect J. curcas leaves against oxidative damage caused by salt stress, and, therefore, it cannot be treated as a salt tolerant plant species.

Recent (1975–2004) Vegetation Change in the San Francisco Estuary, California, Tidal Marshes

Abstract WATSON, E.B. and BYRNE, R., 2012. Recent (1975–2004) vegetation change in the San Francisco Estuary, California, tidal marshes. The establishment and monitoring of vegetation plots provide unique information on the spatiotemporal dynamics of plant distributions. In 1975, U.S. Geological Survey (USGS) scientists Atwater and Hedel established vegetation transects at six tidal marshes spanning the salinity gradient of the San Francisco Estuary, California, to establish a baseline against which future vegetation changes could be measured. Since 1975, estuarine salinity has increased because of water diversion, whereas sea level has risen at rates that exceed late-Holocene background levels. During the summers of 2003–04, we reoccupied these transects and measured plant composition to better understand the response of marsh vegetation to these hydrologic changes. Our results indicate that during the past 30 years, Sarcocornia pacifica, the most salt-tolerant plant species, increased in cover, whereas ...

Difference in miRNA expression profiles between two cotton cultivars with distinct salt sensitivity

MicroRNAs (miRNAs) are a class of endogenous, non-coding small RNAs that play important roles in many developmental processes and stress responses in plants and animals. Cotton (Gossypium hirsutum L.) is considered a relatively salt-tolerant non-halophytic plant species. To study the role of miRNAs in salt adaptation, a salt-tolerant cotton cultivar SN-011 and a salt-sensitive cultivar LM-6 were used to detect differentially expressed miRNAs. Using miRNA microarray analysis and a computational approach, 17 cotton miRNAs belonging to eight families were identified. Although they are conserved, 12 of them showed a genotype-specific expression model in both the cultivars. Under salt stress treatment, miR156a/d/e, miR169, miR535a/b and miR827b were dramatically down-regulated in SN-011, while miR167a, miR397a/b and miR399a were up-regulated. Only miR159 was found to be down-regulated in LM-6 under salt stress. To gain insight into their functional significance, 26 target genes were predicted and their functional similarity was further analyzed. Quantitative real-time PCR showed that the expression of seven target genes showed a significant inverse correlation with corresponding miRNAs. These differentially expressed miRNAs can help in further study into the role of transcriptome homeostasis in the adaptation responses of cotton to salt.

Use of constructed wetland systems with Arundo and Sarcocornia for polishing high salinity tannery wastewater

Treatment of tannery wastewater is problematic due to high and variable concentrations of complex pollutants often combined with high salinity levels. Two series of horizontal subsurface flow constructed wetlands (CWs) planted with Arundo donax and Sarcocornia fruticosa were set up after a conventional biological treatment system operating at a tannery site. The aim of the CWs was polishing organics and nitrogen from the high salinity effluent (2.2-6.6g Cl(-)L(-1)). Both plant species established and grew well in the CW. Arundo, however, had more vigorous growth and a higher capacity to take up nutrients. The CWs were efficient in removing COD and BOD(5) with removal efficiencies varying between 51 and 80% for COD (inlet: 68-425mgL(-1)) and between 53 and 90% for BOD(5) (inlet: 16-220mgL(-1)). Mass removal rates were up to 615kg COD ha(-1)d(-1) and 363 BOD(5) kgha(-1)d(-1). Removal efficiencies were 40-93% for total P, 31-89% for NH(4)(+) and 41-90% for Total Kjeldahl Nitrogen. CW systems planted with salt tolerant plant species are a promising solution for polishing saline secondary effluent from the tannery industry to levels fulfilling the discharge standards.

Multiple compartmentalization of sodium conferred salt tolerance in Salicornia europaea

Euhalophyte Salicornia europaea L., one of the most salt-tolerant plant species in the world, can tolerate more than 1000 mM NaCl. To study the salt tolerance mechanism of this plant, the effects of different NaCl concentrations on plant growth, as well as Na(+) accumulation and distribution at organ, tissue, and subcellular levels, were investigated. Optimal growth and an improved photosynthetic rate were observed with the plant treated with 200-400 mM NaCl. The Na(+) content in the shoots was considerably higher than that in the roots of S. europaea. The Na(+) in S. europaea cells may act as an effective osmotic adjuster to maintain cell turgor, promoting photosynthetic competence and plant growth. The results from the SEM-X-ray and TEM-X-ray microanalyses demonstrate that Na(+) was compartmentalized predominantly into the cell vacuoles of shoot endodermis tissues. Accordingly, the transcript amounts of SeNHX1, SeVHA-A, and SeVP1 increased significantly with increased NaCl concentration, suggesting their important roles in Na(+) sequestration into the vacuoles. Therefore, a multiple sodium compartmentalization mechanism is proposed to enhance further the salt tolerance of S. europaea.

Competing through altering the environment: A cross-diffusion population model coupled to transport–Darcy flow equations

We consider an evolution model describing the spatial population distribution of two salt tolerant plant species, such as mangroves, which are affected by inter- and intra-specific competition (Lotka–Volterra), population pressure (cross-diffusion) and environmental heterogeneity (environmental potential). The environmental potential and the Lotka–Volterra terms are assumed to depend on the salt concentration in the root region, which may change as a result of mangroves’ ability to uptake fresh water and leave the salt of the solution behind, in the saturated porous medium. Consequently, partial differential equations modelling the population dynamics on the surface are coupled with Darcy–transport equations modelling the salt and pressure-velocity distribution in the subsurface. We prove the existence of weak solutions of the coupled problem and provide a numerical discretization based on a stabilized mixed finite element method, which we use to numerically demonstrate the behaviour of the system.

Comparative Proteomic Analysis of Differentially Expressed Proteins in Shoots of Salicornia europaea under Different Salinity

Soil salinity is a major abiotic stress that limits agriculture productivity worldwide. Salicornia europaea is a succulent annual euhalophyte and one of the most salt tolerant plant species. The elucidation of its salt tolerance mechanism is of significance for generating salt-tolerant crops. In this study, we provided high resolution of proteome reference maps of S. europaea shoot and obtained evidence on the salt tolerance mechanism by analyzing the proteomic responses of this plant to high salinity. Our results demonstrated significant variations existed in 196 out of 1880 protein spots detected on CBB stained 2-DE gels. Of these, 111 proteins were identified by mass spectrometry. Among them, the majority was energy production and conversion related proteins, followed by photosynthesis and carbohydrate metabolism associated enzymes. Analysis of protein expression patters revealed that energy production and ion homeostasis associated proteins played important roles for this plant salt tolerance ability. Hierarchical clustering results revealed many proteins were involved in S. europaea salt tolerance mechanism as a dynamic network. Finally, based on our proteomic results, we brought forward a possible schematic representation of mechanism associated with the systematic salt tolerance phenotype in S. europaea.

Salt Uptake by Acacia biflora Saplings from Saline Root Zone

Waterlogging and subsequent soil salinization are the two major causes of degradation of irrigated agricultural lands. Subsurface Drainage Technology (SSDT) is an effective control measure for both. However, this technology is expensive and has an associated problem of safe disposal of the drainage effluents. These features have limited its large-scale adoption in India. Biodrainage is considered by some as an alternative, in which water and salt tolerant plant species are grown to remove the salt solutions from saline and waterlogged lands in an eco-friendly and economical manner. A pot experiment was conducted with saplings of Acacia biflora to determine the plant's salt uptake capacity from the root zone that was made saline by irrigation with water of different salt concentrations for a period of 6 months. The consequent plant sap salinity was measured and salt balance analysis was carried out to ascertain salt migration from the soil to the plant. The study revealed that the plants irrigated with the water of highest salinity removed 28.7 g of salt in comparison to the plant under control, which removed 8.4 g of salts. Even the highest salt removal by Acacia biflora saplings was negligible as compared to that by conventional subsurface drainage system. To portray bio-drainage as a land reclamation option, confirmation of salt uptake from saline lands having established plantation needs to be carried out.