Differences In Salinity Tolerance Research Articles

Myers' divisions revisited: Contemporary evidence for distinct trait differences among global inland fishes

AbstractEighty years ago, George S. Myers classified inland fishes in three divisions (primary, secondary and peripheral) based on their salinity tolerance and eco‐evolutionary history. Although this classification has been followed by many fish studies, it has also received considerable criticism. Here, we aim to test for differences in salinity and thermal tolerance, species traits and distribution patterns among the three divisions using data for about 21,000 species. We found that primary fishes have much less salinity tolerance than secondary and peripheral species, with some secondary fishes displaying the highest tolerances (>100 ppt). We also provide, for the first time, evidence of significant phylogenetic signal of salinity tolerance, comparable in magnitude to conservative traits, and show that studied peripheral and secondary species have maintained or even developed salinity tolerance, in contrast to primary fishes. Although peripheral fishes are the most different, and despite the large variability observed within some families, primary and secondary species also show differences in morphology and life‐history traits. The distribution ranges and genetic diversity of primary and secondary fish divisions are similar and differ from peripheral species, suggesting that although there is evidence of oceanic dispersal of a few secondary fishes at evolutionary time scales, it is a rare contemporary phenomenon. Importantly, a few findings outlined in this study, namely, differences in salinity tolerance, rely on limited data. Thus, we urge for additional empirical research on the salinity tolerance of freshwater fish, which remains largely unexplored, to help clarify differences among and within clades.

The effects of salinity on the distribution and survival of two exotic ostracods in the Iberian Peninsula

Recent research highlighted the need to include experimental estimates of tolerance limits to varying environmental conditions when investigating what factors limit species distributions. However, most niche approaches are only based on the statistical dependence between environmental and occurrence data. Here, we combined field data with survival experiments to assess the role of salinity as a limiting factor in the distribution of two species of exotic ostracods from the Iberian Peninsula. Vizcainocypria viator is a free-living species associated with rice fields and Ankylocythere sinuosa is a commensal of the red swamp crayfish (Procambarus clarkii). Experiments and field data indicate that the distribution of V. viator is limited by adult survival at low and high salinities (below electrical conductivity of 0.6 mS/cm and above 10 mS/cm). In the case of A. sinuosa, the analysis of field data shows that its prevalence is negatively affected by high salinity, whereas experiments indicate an optimal survival at high salinities (conductivity above 10.2 mS/cm), thus suggesting that high salinity may impact A. sinuosa distribution indirectly through affecting host traits (e.g. reduced activity). The habitat of close ancestors (marine versus non-marine respectively for A. sinuosa and V. viator) most likely explains the contrasting differences in salinity tolerance between both ostracod species.

Salinity and cultivar effects on alfalfa forage yield and nutritive value in a Mediterranean climate

AbstractBackgroundSoil and water salinity are increasing problems worldwide, causing significantly reduced crop yields. Alfalfa (Medicago sativa L.) is often listed as salt‐sensitive, but field testing of improved cultivars is limited. Forage systems and improved high‐quality alfalfa varieties are needed to enable crop production under high salinity (HS) conditions.MethodsThe objective of this study was to measure the yield and quality response of alfalfa to high saline conditions in the field and to document the relative saline tolerance of its varieties. HS irrigation water (electrical conductivity of water, or ECw 8.0–11.0 dS m−1) was applied to 33 nondormant alfalfa cultivars and were compared with low salinity (LS) treatments (ECw 0.5–1.2 dS m−1) over 4 years in a Mediterranean environment on a clay loam soil utilizing a split‐plot design. Crops were harvested seven to eight times per year, and the forage quality was measured on selected harvests utilizing near‐infrared spectroscopy.ResultsThe average yield loss due to HS treatment was 23.9% compared with LS treatment, but yields averaged 23.4 Mg ha−1 under HS over the 3 full years of production. This level of production is considered to be economically viable in this region. Differences in salinity tolerance between lines were identified in the field; individual cultivars lost 5%–35% of their LS yield when grown under HS conditions. Forage quality was significantly improved under HS versus LS conditions, but improvements were negatively correlated with biomass yield (R2 > 0.81), similar to responses observed in drought‐stressed alfalfa.ConclusionsThese yield results confirm greenhouse studies, indicating that alfalfa is highly salt tolerant once established in the field, with potential for further improvement with tolerant cultivars. Salinity tolerance should be chosen based on total biomass yield as well as on the salinity tolerance index (HS yield relative to LS yield). Agronomic practices to mitigate salinity and sodicity are critical, along with improved cultivars.

A high-quality de novo genome assembly for clapper rail (Rallus crepitans).

The clapper rail (Rallus crepitans), of the family Rallidae, is a secretive marsh bird species that is adapted for high salinity habitats. They are very similar in appearance to the closely related king rail (R. elegans), but while king rails are limited primarily to freshwater marshes, clapper rails are highly adapted to tolerate salt marshes. Both species can be found in brackish marshes where they freely hybridize, but the distribution of their respective habitats precludes the formation of a continuous hybrid zone and secondary contact can occur repeatedly. This system, thus, provides unique opportunities to investigate the underlying mechanisms driving their differential salinity tolerance as well as the maintenance of the species boundary between the 2 species. To facilitate these studies, we assembled a de novo reference genome assembly for a female clapper rail. Chicago and HiC libraries were prepared as input for the Dovetail HiRise pipeline to scaffold the genome. The pipeline, however, did not recover the Z chromosome so a custom script was used to assemble the Z chromosome. We generated a near chromosome level assembly with a total length of 994.8 Mb comprising 13,226 scaffolds. The assembly had a scaffold N50 was 82.7 Mb, L50 of four, and had a BUSCO completeness score of 92%. This assembly is among the most contiguous genomes among the species in the family Rallidae. It will serve as an important tool in future studies on avian salinity tolerance, interspecific hybridization, and speciation.

New insights into differential salinity tolerance between autotrophic and heterotrophic partial nitrification

Autotrophic (R1) and heterotrophic (R2) partial nitrification showed considerable differences under salinity free conditions, however, their response to salinity stress remains elusive. In this study, R2 (87.29%) outperformed the R1 (79.56%) by achieving higher ammonia removal efficiency (ARE) at 0 g/L NaCl. A subsequent increase in salinity load gradually diminished the comparative nitrification advantages held by R2. Moreover, ARE of R1 surpassed R2 at 45 g/L NaCl (about 70.00%), and ARE disparity between two reactors widened with an elevation in load. Biofilm morphology analysis revealed that R1 biofilm was disrupted at a faster rate by salinity than R2. Successive peeling of β-polysaccharide and protein layer resulted in loose biofilm structures in R1. These loose biofilms structures and coping mechanisms, such as increased polysaccharide production in the tightly bound extracellular polymeric substances (TB-EPS), could improve the efficiency of R1's ability to transmit nutrients under salinity stress. In contrast, R2 retained higher total EPS and its biofilm was covered by proteins even at 70 g/L NaCl. Whereas, a change in load (50–70 g/L NaCl) resulted in a substantial loss of important AOB like Nitrosococcus accounted for its inferior ARE during this period, indicating that the higher amount of EPS had limited protective roles under high salinity stress. In a nut shell, the results of this study demonstrated the significance of controlling organic inflow while treating high saline wastewater.

Deciphering microbial community dynamics along the fermentation course of soy sauce under different temperatures using metagenomic analysis.

Fermented soy sauce consists of microorganisms that exert beneficial effects. However, the microbial community dynamics during the fermentation course is poorly characterized. Soy sauce production is classified into the stages of mash fermentation with koji (S0), brine addition (S1), microbial transformation (S2), flavor creation (S3), and fermentation completion (S4). In this study, microbial succession was investigated across stages at different temperatures using metagenomics analyses. During mash fermentation, Aspergillus dominated the fungal microbiota in all stages, while the bacterial composition was dominated by Bacillus at room temperature and by a diverse composition of enriched lactic acid bacteria (LAB) at a controlled temperature. Compared with a stable fungal composition, bacterial dynamics were mostly attributable to fluctuations of LAB, which break down carbohydrates into lactic acid. After adding brine, increased levels of Enterococcus and decreased levels of Lactococcus from S1 to S4 may reflect differences in salinity tolerance. Staphylococcus, as a fermentation starter at S0, stayed predominant throughout fermentation and hydrolyzed soybean proteins. Meanwhile, Rhizopus and Penicillium may improve the flavor. The acidification of soy sauce was likely attributable to production of organic acids by Bacillus and LAB under room temperature and controlled temperature conditions, respectively. Metagenomic analysis revealed that microbial succession was associated with the fermentation efficiency and flavor enhancement. Controlled temperature nurture more LAB than uncontrolled temperatures and may ensure the production of lactic acid for the development of soy sauce flavor.

Population transcriptomics reveals the effect of gene flow on the evolution of range limits

One of the most important questions in evolutionary biology is how the spatial distribution of species is limited. Asymmetric gene flow from core populations is suggested to increase the number of poorly adapted immigrants in the populations at the range edge. Genetic load due to migration, i.e., migration load, should prevent adaptation to the local habitat, leading to decreases in distribution range via local extinction or the limiting range expansion. However, few experimental studies have examined the effects of immigration on fitness and natural selection within recipient populations. To investigate the influence of migration load on the evolution of distribution range, we performed field and laboratory observations as well as population transcriptomics for the common river snail, Semisulcospira reiniana. This species meets the conditions that migration from source populations can prevent local adaptation in a sink population because they inhabit the broader range of environments, including middle/upper reaches of a river and estuaries within a single river and they may be more vulnerable to being swept away by water currents due to lowered spontaneous (upward) locomotion activity. We found that river steepness was related to the lower distribution limit of S. reiniana, with a narrower distribution range in the steeper river. Population transcriptomic analysis showed that gene flow was heavily asymmetric from the upstream populations to downstream ones in the steep river, suggesting a greater migration load in the steep river. The number of genes putatively involved in adaptation to the local habitat was lower in the steep river than in the gentle river. Gene expression profiles suggested that individuals achieve better local adaptation in the gentle river. Laboratory experiments suggested that evolutionary differences in salinity tolerance among local populations were only found in the gentle river. Our results consistent with the hypothesis that migration load owing to asymmetric gene flow disturbs local adaptation and restricts the distribution range of river snails.

Fine-mapping and characterisation of genes on barley (Hordeum vulgare) chromosome 2H for salinity stress tolerance during germination

Salinity causes a detrimental impact on plant growth, particularly when the stress occurs during germination and early development stages. Barley is one of the most salt-tolerant crops; previously we mapped two quantitative trait loci (QTL) for salinity tolerance during germination on the short arm of chromosome 2H using a CM72/Gairdner doubled haploid (DH) population. Here, we narrowed down the major QTL to a region of 0.341 or 0.439 Mb containing 9 or 24 candidate genes belonging to 6 or 20 functional gene families according to barley reference genomes v1 and v3 respectively, using two DH populations of CM72/Gairdner and Skiff/CM72, F2 and F3 generations of CM72/Gairdner/*Spartacus CL. Two Receptor-like kinase 4 (RLPK4) v1 or Receptor-like kinase (RLK) v3 could be the candidates for enhanced germination under salinity stress because of their upregulated expression in salt-tolerant variety CM72. Besides, several insertion/deletion polymorphisms were identified within the 3rd exon of the genes between CM72 and Gairdner. The sequence variations resulted in shifted functional protein domains, which may be associated with differences in salinity tolerance. Two molecular markers were designed for selecting the locus with receptor-like protein kinase 4, and one was inside HORVU2Hr1G111760.1 or HORVU.MOREX.r3.2HG0202810.1. The diagnostic markers will allow for pyramiding of 2H locus in barley varieties and facilitate genetic improvement for saline soils. Further, validation of the genes to elucidate the mechanisms involved in enhancing salinity tolerance at germination and designing RLPK4 specific markers is proposed. For this publication, all the analysis was based on barley reference genome of 2017 (v1), and it was used throughout for consistence. However, the positions of the markers and genes identified were updated according to new genome (v3) for reference.

به‌گزینی تحمل به شوری ژنوتیپ‌های نخود کابلی در شرایط مزرعه

IntroductionChickpea (Cicer arietinum L.) is one of the important legume crops and Globally, after beans )Phaseolus spp(., chickpea is ranked as a second important legume crop (Roy et al., 2010). Chickpea is an important source of proteins for human consumption, especially in the developing countries where people cannot provide animal protein or vegetarian by choice (Zaccardelli et al., 2013). Chickpea plays an important role in the maintenance of soil fertility through nitrogen fixation (Roy et al., 2010). Plants are exposed to wide range of environmental stresses. In among, Salinity is one of the major abiotic stresses causing severe impact on crop production worldwide(Rasool et al., 2012).chickpea is a salt sensitive pulse crop and its yield is seriously affected mainly by salts (Turner et al., 2013). Salinity stress in chickpea adversely affects several morphological features and physiological processes like reduction in growth and ion balance, water status, photosynthesis, increase in hydrogen peroxide, which causes lipid per oxidation and consequently membrane injury. Also proline and carbohydrates are accumulated in plant tissue (Flowers et al., 2010; Ashraf and Harris, 2004). This study is designed to determine the effect of salt stress on physiological and biochemical parameters in chickpea genotypes exhibiting differences in salinity tolerance. The results of this study could provide information on potential physiological and biochemical parameters and could also provide deeper intelligence into tolerance mechanisms than the stresses caused by salinity. Materials and methodsThis experiment was conducted as split-plot based on randomized complete block design with three replications in 2018 at Ferdowsi University of Mashhad, Mashhad, Iran. Salinity with two levels of 0.5 and 8 dSm-1 (NaCl) was considered as main plot and chickpea genotype (17 Kabuli-type genotypes) as sub-plot. The characteristics such as soluble carbohydrates, proline, osmotic potential, MDA, DPPH, relative water content, MSI%, were evaluated in 50% of flowering. At the end of the growing season, crop was harvested and seed yield were determined. Results and discussionThe highest proline and carbohydrates content was observed in MCC65, MCC92 and MCC95 genotypes, and the lowest in MCC12 genotype. Result salinity stress caused increased 24, 19 and 19 % in the amount of osmotic potential, MDA and DPPH. Relative leaf water content and membrane stability was showen respectively 10 and 13 % reduction by use salinity stress. Survival percentage, number of branches and canopy height had reduction 6, 22 and 57. MCC65, MCC92 and MCC95 genotypes respectively by 0.183, 0.193 and 0.181 (Kg.m-2) had the highest seed yield and MCC98 and MCC298 had the lowest seed yield. The MCC65, MCC95 and MCC92 genotypes had superior traits, including performance in stress conditions compared to other genotypes, and on the other hand, the MCC98 and MCC298 genotypes had the lowest performance. Among 17 chickpea genotypes, the highest sodium content belonged to MCC95 genotype with 9.5 (mg.g.dw-1) weight and the lowest sodium MCC65 genotype with 5.8 (mg.g-1dw). MCC65 had the highest potassium in non-stress and MCC95 had the highest potassium in salinity stress. ConclusionsThe MCC65, MCC95 and MCC92 genotypes had superior traits, including performance in stress conditions compared to other genotypes, and on the other hand, the MCC98 and MCC298 genotypes had the lowest performance. Finally, further study in relation to the top three genotypes in salinity stress conditions is proposed to identify stress tolerance mechanisms as well as infrastructure as breeding programs.

Comparative transcriptomics reveals osmotic and ionic stress key genes contributing to the difference in the salinity tolerance of two pak choi cultivars

Pak choi is an important leafy vegetable crop. Salinity is among the most harmful agents that negatively influence the pak choi yield. However, the mechanism of salinity tolerance in pak choi has not been well understood. In this study, the root transcriptomics of two cultivars differing in salinity tolerance, i.e., Shanghaijimaocai (S, tolerant to salinity) and Te’aiqing (T, sensitive to salinity), were investigated under 0 and 100 mM NaCl treatments. A total of 6765, 2454, 2451 and 5798 differentially expressed unigenes (DEUs) were identified in comparison of S100/S0, T100/T0, S0/T0 and S100/T100, respectively. In Shanghaijimaocai is more sensitive to NaCl stress than Te’aiqing in terms of root transcriptomics. Based on GO and KEGG pathway analyses, the expression levels of several osmotic and ionic stress-related genes, including MP3K18, PYL8, PP2C15/16/49, ARF2, bHLH112, bZIP43, COL5, CDF1/3, ERF25/60, HSFA6, MYBS3/59/92/CCA1/PHL5, POD21, GOLS7, CIPK4/7/12, NHX7, SLAH1 and ALMT13, in Shanghaijimaocai were higher than those in Te’aiqing. Therefore, these genes might contribute to the difference in salinity tolerance. Moreover, the physiological shift of peroxidase activity was in accordance with the dynamic transcript profile of relevant unigenes. These findings would be useful for further functional analysis as potential targets to improve resistance to salinity stress via genetic engineering.

Comparative Genomics and Transcriptomics of the Extreme Halophyte Puccinellia tenuiflora Provides Insights Into Salinity Tolerance Differentiation Between Halophytes and Glycophytes.

Halophytes and glycophytes exhibit clear differences in their tolerance to high levels of salinity. The genetic mechanisms underlying this differentiation, however, remain unclear. To unveil these mechanisms, we surveyed the evolution of salinity-tolerant gene families through comparative genomic analyses between the model halophyte Puccinellia tenuiflora and glycophytic Gramineae plants, and compared their transcriptional and physiological responses to salinity stress. Under salinity stress, the K+ concentration in the root was slightly enhanced in P. tenuiflora, but it was greatly reduced in the glycophytic Gramineae plants, which provided a physiological explanation for differences in salinity tolerance between P. tenuiflora and these glycophytes. Interestingly, several K+ uptake gene families from P. tenuiflora experienced family expansion and positive selection during evolutionary history. This gene family expansion and the elevated expression of K+ uptake genes accelerated K+ accumulation and decreased Na+ toxicity in P. tenuiflora roots under salinity stress. Positively selected P. tenuiflora K+ uptake genes may have evolved new functions that contributed to development of P. tenuiflora salinity tolerance. In addition, the expansion of the gene families involved in pentose phosphate pathway, sucrose biosynthesis, and flavonoid biosynthesis assisted the adaptation of P. tenuiflora to survival under high salinity conditions.

Rhizophora zonation, salinity, and nutrients in the western atlantic

AbstractRhizophora is the dominant genus of mangrove forests on the Atlantic coast of northern South America. What determines the zonation frequently observed in sympatric populations of the two neotropical species, R. mangle and R. racemosa, and their hybrids, R. × harrisonii, is an open question. The most widely held hypothesis is that differences in salinity tolerance among the taxonomic groups explain the observed zonation. To address this question, we analyzed the elemental composition of soils and canopy leaves from 60 Rhizophora spp. trees distributed in different intertidal zones of an estuarine site of the Paria Gulf, Venezuela. The low intertidal zone showed lower salinity, organic matter, C, N, S, and Na, and higher bulk density, Al, Fe, and Mn concentrations compared with the higher intertidal zones. Using morphological characters and microsatellite molecular markers, we identified 39 pure R. mangle, 19 hybrids, and only two pure R. racemosa. We found that both intertidal position and taxonomic groups explained most of the differences in leaf variables measured across trees. The ratio Mg/Ca, however, was higher in R. mangle than in R. racemosa and hybrids regardless of intertidal position. Moreover, at some specific intertidal position, R. mangle differed from R. racemosa and hybrids in the values of C, N, K, Mg, Fe, Mn, C/N, K/Ca, S/Ca, and δ13C. We conclude that despite the scarcity of R. racemosa and the absence of a clear species zonation, our results suggest that R. mangle copes with salinity differently than R. racemosa and R. × harrisonii.

Effect of Selection for Pyrethroid Resistance on Abiotic Stress Tolerance in Aedes aegypti from Merida, Yucatan, Mexico.

Simple SummaryAedes aegypti is the principal vector of major human pathogens, including dengue, Zika, chikungunya, and yellow fever viruses. Vector control relies mostly on the use of pyrethroid insecticides that kill mosquitoes by disabling the nervous system through binding to the voltage-gated sodium channel (vgsc). Resistance mechanisms have evolved most commonly as mutations in the vgsc gene or in genes associated with detoxification. These mutations are thought to associate with fitness costs, such that the frequency of resistant genotypes should decrease in the absence of insecticide use, and this assumption is critical to managing resistance through insecticide rotation strategies. While most studies to date have investigated life history parameters such as fecundity, we sought to investigate whether environmental stress resistance traits might also vary with insecticide resistance. We found, contrary to our expectations, that a strain selected for enhanced insecticide resistance had higher thermotolerance than its sister insecticide susceptible counterpart. Overall, our results indicate that abiotic resistance traits can correlate with insecticide resistance in surprising and variable ways, potentially complicating the management of insecticide resistance in the field.The study of fitness costs of insecticide resistance mutations in Aedes aegypti has generally been focused on life history parameters such as fecundity, mortality, and energy reserves. In this study we sought to investigate whether trade-offs might also exist between insecticide resistance and other abiotic stress resistance parameters. We evaluated the effects of the selection for permethrin resistance specifically on larval salinity and thermal tolerance. A population of A. aegypti originally from Southern Mexico was split into two strains, one selected for permethrin resistance and the other not. Larvae were reared at different salinities, and the fourth instar larvae were subjected to acute thermal stress; then, survival to both stresses was compared between strains. Contrary to our predictions, we found that insecticide resistance correlated with significantly enhanced larval thermotolerance. We found no clear difference in salinity tolerance between strains. This result suggests that insecticide resistance does not necessarily carry trade-offs in all traits affecting fitness and that successful insecticide resistance management strategies must account for genetic associations between insecticide resistance and abiotic stress resistance, as well as traditional life history parameters.

Morphological and physiological traits reveal differential salinity tolerance of two contrasting Glandularia cultivars

In view of the current, continuous decrease of water availability, the need to explore new mitigation alternatives has given focus to salt-tolerant genotypes. The aim of this work was to study salt tolerance of two ornamental cultivars of Glandularia (Glandularia x hybrida) of contrasting vigor, Dulce Coral and Extrema Violeta, breeded at the Floriculture Institute of INTA. A greenhouse experiment was carried out with potted plants. Plants were subjected to four salt treatments 1.2, 2.4, 3.5, 4.4 dS m−1 (EC), and a control (0.03 dS m−1). Shoot dry weight of Dulce Coral was not affected by salinity. In contrast, the dry weight of Extrema Violeta decreased sharply as salinity increased. The root:shoot ratio was always higher for Extrema Violeta than Dulce Coral. The leaves of Dulce Coral accumulated less Na+ and Cl− than Extrema Violeta. Moreover, Extrema Violeta exhibited severe foliar salt damage, but Dulce Coral showed only a few, without compromising its commercial value. Besides, Dulce Coral had a higher assimilation rate than Extrema Violeta at all treatments. All these features could suggest Na+ and Cl− exclusion as salt-tolerant mechanism for Dulce Coral. Other mechanisms adopted by Dulce Coral to cope with salinity was the maintenance of a higher K+/Na+ and Ca2+/Na+ ratio in its leaves, a lower root:shoot ratio and the maintenance of photosynthesis. Therefore, Dulce Coral could be proposed as a parent for breeding programs with the objective of improving salt tolerance in Glandularia. In this exploratory study, we distinguish some of the most important physiological (K+/Na+ and Ca2+/Na+) and morphological (root:shoot ratio) traits related to salinity tolerance in Glandularia.

Implications of acute temperature and salinity tolerance thresholds for the persistence of intertidal invertebrate populations experiencing climate change.

To predict whether populations of marine animals will persist in the face of changing climate conditions, it is informative to understand how past climate conditions have shaped present‐day tolerance thresholds. We examined 4 species of intertidal invertebrates (Nucella lamellosa, Littorina scutulata, Littorina sitkana, and Balanus glandula) inhabiting the coasts of Vancouver Island, Canada, where the east coast experiences historically warmer sea surface temperature (SST), warmer low tide (i.e., emersion) rock surface temperature (RST), and lower sea surface salinity (SSS) than the west coast. To determine if east coast populations have higher tolerance thresholds to acute stress than west coast populations, animals from 3 sites per coast were exposed to stressful temperatures and salinities in common garden experiments. Emersion temperature tolerance differed between populations only in N. lamellosa and B. glandula, tolerance thresholds being 1.4–1.5°C higher on the east coast. Water temperature tolerance differed between populations only in B. glandula and L. scutulata but was highest on the west coast. No differences in salinity tolerance were observed within any species. Thus, there is limited evidence of divergence among east and west coast populations in tolerance of acute stress despite the substantial historical differences in extreme temperature and salinity conditions between coasts. However, based on present‐day summertime SST and RST and known rates of change in these parameters, we predict present‐day tolerance thresholds would be sufficient to allow adults of these populations to tolerate extreme temperatures predicted for the next several hundred years, and that even a slow rate of change in acute tolerance thresholds might suffice to keep up with future temperature extremes.

Hydrotime analysis of Amaranthus spp. seed germination under salinity condition

Amaranth (Amaranthus spp.) have gained interest as crop family to be grown under diverse soil conditions such as drought and heat stress. However, the presence of salinity affects crop’s germination process due to reduction in water availability for seeds to germinate. In this study, germination behaviour of Amaranthus hybridus L., Amaranthus viridis L., Amaranthus tricolor L. and Amaranthus giganticus L. under salinity condition were analysed through hydrotime model analysis. Five water potentials in NaCl solution to induce salinity condition (0, −0.3, −0.6, −0.9, and −1.2 MPa) were used in the germination tests. Differences in salinity tolerance were determined in the different species during germination. A. giganticus recorded a lower θH (40.30) and more negative Ψb(50) (−1.55) as well as higher germination rate as compared to the other species. The hydrotime modelling approach applied in this study for the analysis of amaranth species which might help to identify crop salt tolerance at seed germination stage.

Physiological responses and tolerance mechanisms of seashore paspalum and centipedegrass exposed to osmotic and iso-osmotic salt stresses

Osmotic stresses caused by reduced water availability or the accumulation of salts in the soil can be highly damaging to plants. The objective of this study was to investigate physiological responses and tolerance mechanisms of two turfgrass species (seashore paspalum and centipedegrass) with distinct differences in salinity tolerance exposed to osmotic and iso-osmotic salt stresses. Three turfgrass genotypes including seashore paspalums ‘Seastar’ and ‘UGP113’, and centipedegrass ‘TifBlair’ were grown in ½ strength Hoagland’s solution with three different treatment conditions; control (no external addition), salt stress (-0.4 MPa by adding NaCl) and osmotic stress [-0.4 MPa by adding polyethylene glycol (PEG)]. Osmotic stress damages were more severe with greater reductions in turf quality, photochemical efficiency (Fv/Fm), relative water content (RWC) and leaf water potential (Ψw) compared to iso-osmotic salt stress in both seashore paspalum and centipedegrass. Greater osmotic adjustment (OA) with greater accumulation of metabolically inexpensive inorganic osmolytes (Na+) helped turfgrasses to lessen damages in salt stress compared to osmotic stress. However, such accumulation of Na+ resulted ion-toxicity and triggered some damages in terms of increased electrolyte leakage (EL) and reduced total protein in salt-sensitive centipedegrass. Seashore paspalum had better ion regulation and also maintained greater antioxidant enzyme activities compared to centipedegrass; therefore it was able to avoid ion-specific damages under salt stress. Differences in the utilization of specific solutes for osmotic adjustment and antioxidant metabolism are partially responsible for the differences in salt versus osmotic stress responses in these species; the regulation of these defense mechanisms requires further investigation.

Inter-population differences in salinity tolerance of adult wild Sacramento splittail: osmoregulatory and metabolic responses to salinity.

The Sacramento splittail (Pogonichthys macrolepidotus) is composed of two genetically distinct populations endemic to the San Francisco Estuary (SFE). The allopatric upstream spawning habitat of the Central Valley (CV) population connects with the sympatric rearing grounds via relatively low salinity waters, whereas the San Pablo (SP) population must pass through the relatively high-salinity Upper SFE to reach its allopatric downstream spawning habitat. We hypothesize that if migration through SFE salinities to SP spawning grounds is more challenging for adult CV than SP splittail, then salinity tolerance, osmoregulatory capacity, and metabolic responses to salinity will differ between populations. Osmoregulatory disturbances, assessed by measuring plasma osmolality and ions, muscle moisture and Na+-K+-ATPase activity after 168 to 336h at 11‰ salinity, showed evidence for a more robust osmoregulatory capacity in adult SP relative to CV splittail. While both resting and maximum metabolic rates were elevated in SP splittail in response to increased salinity, CV splittail metabolic rates were unaffected by salinity. Further, the calculated difference between resting and maximum metabolic values, aerobic scope, did not differ significantly between populations. Therefore, improved osmoregulation came at a metabolic cost for SP splittail but was not associated with negative impacts on scope for aerobic metabolism. These results suggest that SP splittail may be physiologically adjusted to allow for migration through higher-salinity waters. The trends in interpopulation variation in osmoregulatory and metabolic responses to salinity exposures support our hypothesis of greater salinity-related challenges to adult CV than SP splittail migration and are consistent with our previous findings for juvenile splittail populations, further supporting our recommendation of population-specific management.

Tissue-Specific Regulation of Na+ and K+ Transporters Explains Genotypic Differences in Salinity Stress Tolerance in Rice.

Rice (Oryza sativa) is a staple food that feeds more than half the world population. As rice is highly sensitive to soil salinity, current trends in soil salinization threaten global food security. To better understand the mechanistic basis of salinity tolerance in rice, three contrasting rice cultivars—Reiziq (tolerant), Doongara (moderately tolerant), and Koshihikari (sensitive)—were examined and the differences in operation of key ion transporters mediating ionic homeostasis in these genotypes were evaluated. Tolerant varieties had reduced Na+ translocation from roots to shoots. Electrophysiological and quantitative reverse transcription PCR experiments showed that tolerant genotypes possessed 2-fold higher net Na+ efflux capacity in the root elongation zone. Interestingly, this efflux was only partially mediated by the plasma membrane Na+/H+ antiporter (OsSOS1), suggesting involvement of some other exclusion mechanisms. No significant difference in Na+ exclusion from the mature root zones was found between cultivars, and the transcriptional changes in the salt overly sensitive signaling pathway genes in the elongation zone were not correlated with the genetic variability in salinity tolerance amongst genotypes. The most important hallmark of differential salinity tolerance was in the ability of the plant to retain K+ in both root zones. This trait was conferred by at least three complementary mechanisms: (1) its superior ability to activate H+-ATPase pump operation, both at transcriptional and functional levels; (2) reduced sensitivity of K+ efflux channels to reactive oxygen species; and (3) smaller upregulation in OsGORK and higher upregulation of OsAKT1 in tolerant cultivars in response to salt stress. These traits should be targeted in breeding programs aimed to improve salinity tolerance in commercial rice cultivars.

Differential regulation of select osmoregulatory genes and Na+/K+-ATPase paralogs may contribute to population differences in salinity tolerance in a semi-anadromous fish

The Sacramento splittail (Pogonichthys macrolepidotus) is a species of special concern that is native to the San Francisco Estuary, USA. Two genetically distinct populations exist and differ in maximal salinity tolerances. We examined the expression of 12 genes representative of osmoregulatory functions in the gill over a 14 day time course at two different salinities [11 or 14 PSU (Practical Salinity Units)] and revealed that each population showed distinct patterns of gene expression consistent with population differences in response to osmotic regimes. The relatively more salinity-tolerant San Pablo population significantly upregulated nine out of the 12 transcripts investigated on day 1 of 11 PSU salinity exposure in comparison to the day zero freshwater control. Three transcripts (nka1a, nka1b, and mmp13) were differentially expressed between the populations at 7 and 14 days of salinity exposure, suggesting a reduced ability of the relatively salinity-intolerant Central Valley population to recover. Additionally, a phylogenetic analysis of several Sacramento splittail Na+/K+-ATPase α1 sequences resulted in grouping by proposed paralog rather than species, suggesting that different paralogs of this gene may exist. These findings, together with prior research conducted on the Sacramento splittail, suggest that the San Pablo population may be able to preferentially regulate select osmoregulatory genes, including different Na+/K+-ATPase α1 paralogs, to better cope with salinity challenges.