The response of rice to salt stress (200 mmol/L NaCl) was investigated at the transcription level in Egyptian varieties Giza 177 (salt sensitive variety) and Giza 178 (salt tolerant variety). We applied a genome-wide RNA-Seq transcriptome study at 21-day-old seedlings of both varieties, exposed or not to salt stress for 24 h. Most differentially expressed genes (DEGs) between the two varieties in response to salt stress were related to the expression of genes active at the cell wall (CW) level, including wall modification, hemicellulose/cellulose synthesis and transcripts of the peroxidase family activated in response to oxidative stress/oxidation reduction, which were significantly more represented in Giza 178. Consistently, Gene Ontology (GO) analysis showed differentially expressed transcripts, involved in response to oxidative stress and chemical stimulus, directly implicated in salt stress response and up-regulated in Giza 178, as well as oxidoreductase, peroxidase and antioxidant activities. When the two varieties were directly compared in exposed or not to salt stress conditions, Giza 177 showed a higher number of differentially expressed and unique loci than Giza 178, including transposable elements (TE). However, Giza 178 showed a higher number of transcription factors (TF) expressed, mostly involving myeloblastosis (MYB) family members and bZIP elements, with annotated elements including zinc finger domain, kinase, expansin, cellulose, sucrose synthase, peroxidase precursor, dehalogenase-like hydrolase, and sodium/ calcium exchanger protein.

Abstract Background: Halophytes are better than glycophytes at employing mechanisms to avoid salt injury, but both types of plants can undergo damage due to high soil salinity. Arbuscular mycorrhizal fungi (AMF) can mitigate the damage from salt stress in both halophytes and glycophytes by enhancing salt tolerance and improving energy efficiency. However, variations in mycorrhizal symbiotic efficiency between halophytes and glycophytes were still poorly under - stood. Therefore, we evaluated the magnitude of AMF effects on plant growth and determined the mechanisms that regulate the growth response of halophytes and glycophytes by performing a meta-analysis of 916 studies (from 182 publications). Results: Arbuscular mycorrhizal fungi significantly enhance biomass accumulation, osmolytes synthesis (soluble sugar and soluble protein), nutrients acquisition (nitrogen, phosphorus, and potassium ion), antioxidant enzyme activ- ities (superoxide dismutase and catalase), and photosynthetic capacity (chlorophyll and carotenoid contents, photo- synthetic rate, stomatal conductance, and transpiration rate). AMF also substantially decreased sodium ion acquisition and malondialdehyde levels in both halophytes and glycophytes under salt stress conditions. Mycorrhizal halophytes deploy inorganic ions (potassium and calcium ions) and limited organic osmolytes (proline and soluble sugar) to achieve energy-efficient osmotic adjustment and further promote biomass accumulation. Mycorrhizal glycophytes depend on the combined actions of soluble sugar accumulation, nutrients acquisition, sodium ion exclusion, super- oxide dismutase elevation, and chlorophyll synthesis to achieve biomass accumulation. Conclusions: Arbuscular mycorrhizal fungi inoculation is complementary to plant function under salt stress condi- tions, not only facilitating energy acquisition but also redistributing energy from stress defence to growth. Glyco- phytes are more dependent on AMF symbiosis than halophytes under salt stress conditions.

The fruticose epiphytic lichen Seirophora villosa, strictly associated with Juniperus shrublands in the Mediterranean basin, was used to investigate the role of hairiness on a lichen thallus, as a characteristic morphological trait. We evaluated the effect of hair removal on the physiological parameters of a set of samples, during desiccation and on exposure to different salt concentrations. Hairy thalli were less affected by salt, suggesting that during dehydration, the presence of hair protects the thallus from light irradiance, oxidative stresses and the lipid peroxidation generated by free radicals, and could offer passive, but selective, water control. Our results showed that hair could not only increase thallus surface and promote water absorption when availability is low, but could also repel the salt dissolved in water by activating a passive resistance mechanism, by preventing salt entering.

Morpho-physiological variations play an important role in plant adaptation to salt stress. We evaluated the morpho-biochemical changes, induced by a progressive salt exposure in cvs of Brassica napus L., that may lead to adaptation to saline soil. Basing on germination test on seeds of several cvs, exposed to increasing concentration of NaCl, we selected tolerant (T) and susceptible (S) genotypes. To evaluate their adaptation ability to salinity, 15 days old seedlings of Dynastie (T) and SY Saveo (S) cvs were irrigated with Hoagland solution added with 0 (control), 160 and 320 mM NaCl for 60 days. Gradual plant exposure to salinity reduced plant growth, size and number of leaves. Treated plants had higher amounts of proline, phenolics and pigments. Photochemical activity was not particularly affected by NaCl. The activity of polyphenol oxidase, ascorbate peroxidase and superoxide dismutase were differently enhanced in the two cvs. In these cvs the salt exposure elicited responses, i.e. a genotype dependent acclimation, that improve tolerance. This work represents a starting point to enhance the knowledge of stress response mechanisms in oil seed rape to select tolerant cvs for breeding and saline soil recovery programs.

Modulation of growth in response to environmental cues is a fundamental aspect of plant adaptation to abiotic stresses. TIP41 (TAP42 INTERACTING PROTEIN OF 41 kDa) is the Arabidopsis thaliana orthologue of proteins isolated in mammals and yeast that participate in the Target-of-Rapamycin (TOR) pathway, which modifies cell growth in response to nutrient status and environmental conditions. Here, we characterized the function of TIP41 in Arabidopsis. Expression analyses showed that TIP41 is constitutively expressed in vascular tissues, and is induced following long-term exposure to NaCl, polyethylene glycol and abscisic acid (ABA), suggesting a role of TIP41 in adaptation to abiotic stress. Visualization of a fusion protein with yellow fluorescent protein indicated that TIP41 is localized in the cytoplasm and the nucleus. Abolished expression of TIP41 results in smaller plants with a lower number of rosette leaves and lateral roots, and an increased sensitivity to treatments with chemical TOR inhibitors, indicating that TOR signalling is affected in these mutants. In addition, tip41 mutants are hypersensitive to ABA at germination and seedling stage, whereas over-expressing plants show higher tolerance. Several TOR- and ABA-responsive genes are differentially expressed in tip41, including iron homeostasis, senescence and ethylene-associated genes. In yeast and mammals, TIP41 provides a link between the TOR pathway and the protein phosphatase 2A (PP2A), which in plants participates in several ABA-mediated mechanisms. Here, we showed an interaction of TIP41 with the catalytic subunit of PP2A. Taken together, these results offer important insights into the function of Arabidopsis TIP41 in the modulation of plant growth and ABA responses.

Hydrogen represents a possible alternative energy carrier to face the growing request for energy and the shortage of fossil fuels. Photofermentation for the production of H2 constitutes a promising way for integrating the production of energy with waste treatments. Many wastes are characterized by high salinity, and polluted seawater can as well be considered as a substrate. Moreover, the application of seawater for bacterial culturing is considered cost-effective. The aims of this study were to assess the capability of the metabolically versatile freshwater Rhodopseudomonas palustris 42OL of producing hydrogen on salt-containing substrates and to investigate its salt stress response strategy, never described before. R. palustris 42OL was able to produce hydrogen in media containing up to 3 % added salt concentration and to grow in media containing up to 4.5 % salinity without the addition of exogenous osmoprotectants. While the hydrogen production performances in absence of sea salts were higher than in their presence, there was no significant difference in performances between 1 and 2 % of added sea salts. Nitrogenase expression levels indicated that the enzyme was not directly inhibited during salt stress, but a regulation of its expression may have occurred in response to salt concentration increase. During cell growth and hydrogen production in the presence of salts, trehalose was accumulated as a compatible solute; it protected the enzymatic functionality against salt stress, thus allowing hydrogen production. The possibility of producing hydrogen on salt-containing substrates widens the range of wastes that can be efficiently used in production processes.

HKT transporters are Na+-permeable membrane proteins, which mediate Na+ and K+ homeostasis in K+-depleted and saline environments in plants. Class II HKT transporters, a distinct subgroup found predominantly in monocots, are known to mediate Na+-K+ co-transport in principle. Here we report features of ion transport functions of No-OsHKT2;2/1, a class II transporter identified in a salt tolerant landrace of indica rice, Nona Bokra. We profiled No-OsHKT2;2/1 expression in organs of Nona Bokra plants with or without salinity stress. Dominant accumulation of the No-OsHKT2;2/1 transcript in K+-starved roots of Nona Bokra plants largely disappeared in response to 50 mM NaCl. We found that No-OsHKT2;2/1 expressed in the high-affinity K+ uptake deficient mutant of Saccharomyces cerevisiae and Xenopus laevis oocytes shows robust K+ selectivity even in the presence of a large amount of NaCl as reported previously. However, No-OsHKT2;2/1-expressing yeast cells exhibited Na+ hypersensitive growth under various concentrations of K+ and Na+ as the cells expressing Po-OsHKT2;2, a similar class II transporter from another salt tolerant indica rice Pokkali, when compared with the growth of cells harboring empty vector or cells expressing OsHKT2;4. The OsHKT2;4 protein expressed in Xenopus oocytes showed strong K+ selectivity in the presence of 50 mM NaCl in comparison with No-OsHKT2;2/1 and Po-OsHKT2;2. Together with apparent plasma membrane-localization of No-OsHKT2;2/1, these results point to possibilities that No-OsHKT2;2/1 could mediate destructive Na+ influx over K+ uptake in Nona Bokra plants upon salinity stress, and that a predominant physiological function of No-OsHKT2;2/1 might be the acquisition of Na+ and K+ in K+-limited environments

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The halophyte Mesembryanthemum crystallinum adapts to salt stress by salt uptake and switching from C3 photosynthesis to CAM (crassulacean acid metabolism). An important role in this process is played by transport proteins in the tonoplast of the central vacuole. In the present study we examine dynamic changes in the protein composition during salt-stress adaptation in microsomes from M. crystallinum leaves. Plants challenged with 400 mM NaCl accumulate salt by day 4 of treatment and malic acid only at day 12; a switching to CAM hence follows any initial steps of salt adaptation with a delay. Using a label-free and semiquantitative approach, we identified the most dramatic changes between the proteome of control plants and plants harvested after 12 days of the treatment; the abundance of 14 proteins was significantly affected. The proteomic data revealed that the majority of the subunits of V-ATPase (vacuolar H+-ATPase) holoenzyme. The salt treatment somewhat decreased the abundance of all subunits in the short term (4 days). Long-term adaptation, including the switching to CAM, goes together with a strong increase in the representation of all detectable subunits. Because this increase is subunit-specific,with the highest rise occurring for subunits E and c, the data suggest that long-term adaptation to salt stress correlates with a change in V-ATPase subunit stoichiometry and highlight the structural plasticity of this holoenzyme. © 2013 Biochemical Society.

The effects of reduced water potential ( ) in NaCl and pre-osmopriming in PEG, on seed germination and early radicle growth at different temperatures were assessed in the laboratory for sweet sorghum [Sorghum bicolor (L.) Moench] cv. Roce. Five salt solutions (with a of 0-control, -0.22, -0.42, -0.82 or -1.23MPa) and four temperatures of 10, 15, 25 or 35 oC were used for germination tests. Daily and final germination, seed moisture at 4 and 24 h of imbibition and radicle length 2 days after initial germination were recorded. Sorghum seeds seem to be more tolerant to reduced at optimum temperature. Indeed, at 25 oC, downto-0.82MPa seed germinationwas not affected. The increase in incubation temperature to 35 oC determined a greater seedwater content and a faster germination than at 25 oC at all s, despite the lower final germination percentage. With the lowering of temperature to 15 oC, germination percentage significantly declined with the decrease of and at -0.82MPa it reduced to less than 50%. At 10 oC seeds failed to germinate at <-0.22MPa due to combined depressive effects of reduced and low temperature. Seed priming enhanced germination and shortened the delay in germination time due to the increase in saline stress, at suboptimal temperatures only. This effect could be explained by the faster water absorption occurring in primed seeds as compared to those unprimed, at these temperatures, regardless of salt concentration of the solution. Root growth was more sensitive than germination to salt stress. Indeed, the increase in NaCl concentration adversely affected root elongation at all temperatures. The beneficial effects of PEG-osmopriming were evident on root growth at all temperatures except the optimal one. From a practical point of view, when early sowings of sweet sorghum are requested, the use of primed seeds is suggested, as PEG-osmopriming is helpful in overcoming the negative effect imposed by reduced water potential upon seed germination under suboptimal thermal conditions. When salinewater is available for irrigation at sowing, it may be useful to sow when optimal or nearly optimal temperature may be encountered in the soil in order to avoid the combined stress of temperature and salinity.

Coastal erosion is a widespread phenomenon on sandy coasts throughout the Mediterranean region; along the Thyrrenian coast of Tuscany (Italy), stone pine (Pinus pinea L.) stands originally planted for the protection of agricultural crops further inland are often damaged. In the present study, a pairwise comparison of stands at different distance from the sea at eroded and control sites highlighted the effects of coastal erosion alone on pine growth and function. Dendroecological analyses made it possible to determine the temporal dynamics of the phenomenon since 1930 and the interactions with climate, whilst additional structural (LAI, sapwood area) and functional (carbon isotope discrimination) measurements were used to discriminate between stress mechanisms. Salty winds, exacerbated by the removal of dunal vegetation, were found to be the most likely cause of the observed growth decline. The presence and, in more recent times, the reduction of surfactants in sea water played an important synergistic effect. The intrusion of salty water in the water table, on the contrary, played a marginal role at the site. Finally, stressed trees were more sensitive to the inter-annual variability in precipitation; at all sites, growth was stimulated by June, November and December precipitation in the current and two preceding years. (C) 2008 Elsevier B.V. All rights reserved.

Salinity is a widespread environmental stress for crop plants. It is common in arid, semiarid, and coast regions. In those environments, seawater infiltrations can occur or the sea provides the only source of water for irrigation. The effects of 10% and 20% seawater in nutrient solutions were studied in 30 day-old plants of sunflower (Helianthus annuus L.) ecotype Katharina Piacenza. Growth parameters, ascorbate and glutathione contents, and the activities of ascorbate peroxidase and glutathione reductase were determined in shoots and roots. The results showed antioxidative responses of the ecotype to both salt treatments. The different activity patterns of antioxidant molecules and enzymes in the leaves and roots suggested a different kind of reaction to the two seawater concentrations.

The kinetic response of photosystem II (PS II) photochemistry in Spirulina platensis(Norstedt M2 ) to high salinity (0.75 M NaCl) was found to consist of two phases. The first phase, which was independent of light, was characterized by a rapid decrease (15-50%) in the maximal efficiency of PS II photochemistry (Fv /Fm), the efficiency of excitation energy capture by open PS II reaction centres (Fv?/Fm?), photochemical quenching (qp) and the quantum yield of PS II electron transport (? PS II) in the first 15 min, followed by a recovery up to about 80-92% of their initial levels within the next 2 h. The second phase took place after 4 h, in which further decline in above parameters occurred. Such a decline occurred only when the cells were incubated in the light, reaching levels as low as 45-70% of their initial levels after 12 h. At the same time, non-photochemical quenching (qN) and Q B -non-reducing PS II reaction centres increased significantly in the first 15 min and then recovered to the initial level during the first phase but increased again in the light in the second phase. The changes in the probability of electron transfer beyond QA (?o) and the yield of electron transport beyond QA (&phiv; Eo), the absorption flux (ABS/RC) and the trapping flux (TRo /RC) per PS II reaction centre also displayed two different phases. The causes responsible for the decreased quantum yield of PS II electron transport during the two phases are discussed.