Accumulation Of Organic Osmolytes Research Articles

Structural and Functional Strategies in Cenchrus Species to Combat Environmental Extremities Imposed by Multiple Abiotic Stresses.

Multiple abiotic stresses such as drought, salinity, heat, and cold stress prevailing in natural habitats affect plant growth and development. Different species modify their structural and functional traits to combat these abiotic stresses while growing in stressful environments. Cenchrus species, i.e., Cenchrus pennisetiformis, C. setiger, and C. prieurii are widely distributed grasses found growing all over the world. Samples from natural populations were collected from different ecological regions in the Punjab and Khyber Pakhtoonkhwa that were exposed to aridity, salinity, and cold, while one site was designated as normal control. In the present study, structural and functional modifications of three Cenchrus species under abiotic stresses were evaluated. It was expected that each Cenchrus species may evolve different strategies to cope with multiple abiotic stresses. All Cenchrus species responded differently whether growing in normal environment or stressful conditions. The most remarkable feature for survival in C. pennisetiformis under cold stress was increased inflorescence and increased stem and root lignification. C. prieurii showed better tolerance to saline and cold environments. C. setiger showed better development of leaf sheath anatomical traits. The structural and functional modifications in Cenchrus species such as development of mechanical tissues provided structural support, while dermal and parenchymatous tissues increased water storage capacity and minimized water loss. An increase in the concentration of organic osmolytes and ionic content aids turgor pressure maintenance and ionic content crucial for plant growth and development. It was concluded that structural and functional alterations in all Cenchrus species were very specific and critical for survival under different environmental stresses. The ecological fitness of these species relied on maintenance of growth and biomass production, and the development of mechanical, vascular, dermal and parenchyma tissues under stressful environmental conditions. Moreover, accumulation of beneficial ions (K+ and Ca2+) and organic osmolytes were critical in turgor maintenance, hence survival of Cenchrus spp.

Survival tactics of an endangered species Withania coagulans (Stocks) Dunal to arid environments.

Withania coagulans is a valuable medicinal plant with high demand, but its wild growth and local usage pose a threat to its natural habitat. This study aims to understand the plant's growth, anatomy, and physiology in different environmental conditions to aid in conservation and re-vegetation efforts. Fifteen differently adapted populations of Withania coagulans were collected from diverse ecological regions, viz., (i) along the roadside, (ii) hilly areas, (iii) barren land, and (iv) wasteland to unravel the adaptive mechanisms that are responsible for their ecological success across heterogenic environments of Punjab, Pakistan. The roadside populations had high values of photosynthetic pigments, total soluble proteins, root endodermis thickness, stem and leaf cortical thickness, and its cell area. The populations growing in hilly areas showed better growth performance such as vigorous growth and biomass production. Additionally, there was enhanced accumulation of organic osmolytes (glycine betaine and proline), chlorophyll content (chl a/b), and enlarged epidermal cells, cortical cells, vascular bundles, metaxylem vessels, and phloem region in roots. In case of stem area, epidermal thickness, cortical thickness, vascular bundle, and pith area showed improved growth. However, the barren land population showed significant increase in carotenoid contents, vascular bundle area, and metaxylem area in roots, and xylem vessels and phloem area in stems and leaves. The wasteland population surpassed the rest of the populations in having greater root dry weight, higher shoot ionic contents, increased root area, thick cortical, and vascular bundle area in roots. Likewise, cortical thickness and its cell area, and pith area in stems, whereas large vascular bundles, phloem region, and high stomatal density were recorded in leaves. Subsequently, natural populations showed the utmost behavior related to tissue organization and physiology in response to varied environmental conditions that would increase the distribution and survival of species.

Structural Determinants and Functional Significance of Dimerization for Osmosensing Transporter ProP in Escherichia coli.

Osmosensing transporter ProP forestalls cellular dehydration by detecting environments with high osmotic pressure and mediating the accumulation of organic osmolytes by bacterial cells. It is composed of 12 transmembrane helices with cytoplasmic N- and C-termini. In Escherichia coli, dimers form when the C-terminal domains of ProP molecules form homodimeric, antiparallel, α-helical coiled coils. No dominant negative effect was detected when inactive and active ProP molecules formed heterodimers in vivo. Purification of ProP in detergent dodecylmaltoside yielded monomers, which were functional after reconstitution in proteoliposomes. With other evidence, this suggests that ProP monomers function independently whether in the monomeric or dimeric state. Amino acid replacements that disrupted or reversed the coiled coil did not prevent in vivo dimerization of ProP detected with a bacterial two-hybrid system. Maleimide labeling detected no osmolality-dependent variation in the reactivities of cysteine residues introduced to transmembrane helix (TM) XII. In contrast, coarse-grained molecular dynamic simulations detected deformation of the lipid around TMs III and VI, on the lipid-exposed protein surface opposite to TM XII. This suggests that the dimer interface of ProP includes the surfaces of TMs III and VI, not of TM XII as previously suggested by crosslinking data. Homology modeling suggested that coiled-coil formation and dimerization via such an interface are not mutually exclusive. In previous work, alterations to the C-terminal coiled coil blocked co-localization of ProP with phospholipid cardiolipin at E. coli cell poles. Thus, dimerization may contribute to ProP targeting, adjust its lipid environment, and hence indirectly modify its osmotic stress response.

The nuclear factor of activated T cells 5 (NFAT5) contributes to the renal corticomedullary differences in gene expression

The corticomedullary osmotic gradient between renal cortex and medulla induces a specific spatial gene expression pattern. The factors that controls these differences are not fully addressed. Adaptation to hypertonic environment is mediated by the actions of the nuclear factor of activated T-cells 5 (NFAT5). NFAT5 induces the expression of genes that lead to intracellular accumulation of organic osmolytes. However, a systematical analysis of the NFAT5-dependent gene expression in the kidneys was missing. We used primary cultivated inner medullary collecting duct (IMCD) cells from control and NFAT5 deficient mice as well as renal cortex and inner medulla from principal cell specific NFAT5 deficient mice for gene expression profiling. In primary NFAT5 deficient IMCD cells, hyperosmolality induced changes in gene expression were abolished. The majority of the hyperosmolality induced transcripts in primary IMCD culture were determined to have the greatest expression in the inner medulla. Loss of NFAT5 altered the expression of more than 3000 genes in the renal cortex and more than 5000 genes in the inner medulla. Gene enrichment analysis indicated that loss of NFAT5 is associated with renal inflammation and increased expression of kidney injury marker genes, like lipocalin-2 or kidney injury molecule-1. In conclusion we show that NFAT5 is a master regulator of gene expression in the kidney collecting duct and in vivo loss of NFAT function induces a kidney injury like phenotype.

Intercropping induces physiological and morphological plasticity in oilseed rape and barley under drought stress

Intercropping is an agricultural practice that can improve crop yield due to better availability of resources, including water. There are few studies, however, addressing the physiological mechanisms behind this phenomenon. In this work oilseed rape (Brassica napus L.) and barley (Hordeum vulgare L.) were cultivated either as monocrop (MC) or intercrop (IC) under well-watered (WW) or drought stress (DS) conditions in a growth chamber. After eight weeks DS, the leaf relative water content was higher in the IC compared with the MC plants in both species and the DS-induced senescence of old leaves was considerably postponed in oilseed rape. Intercropped oilseed rape showed elevated levels of leaf photosynthesis rate, superior accumulation of organic osmolytes but higher water loss compared with the MC counterparts under DS conditions. In barley, less transpiration, an increased root : shoot ratio and osmolyte accumulation was observed in the IC compared with MC plants under DS conditions. The water use efficiency was higher in the IC compared to MC barley and the plants yield was higher in the IC than in the MC oilseed rape. Our data showed that intercropping is a reliable practice for cultivation of both species under arid and semi-arid regions or under rainfed conditions.

Comprehensive analysis of NFAT5 associated gene expression in the renal collecting duct

BackgroundThe renal cortico‐medullary osmotic gradient is a crucial factor for the urine concentration mechanism and is mainly generated by sodium chloride and urea. Due to this, the cells in the renal inner medulla are challenged with a hypertonic environment. The adaptation of these cells is mediated by the action of the tonicity‐responsive enhancer‐binding factor (TonEBP, also known as nuclear factor of activated T cells 5, NFAT5). NFAT5 induces the expression of genes that lead to accumulation of organic osmolytes within the cells. The cortico‐medullary osmotic gradient also induces a specific spatial gene expression pattern within the kidneys. So far, a systematic analysis of the contribution of NFAT5 on gene expression in the kidneys was missing, which was accomplished here.MethodsWe performed next generation RNA sequencing (NGS) using NFAT5 deficient and wild type control primary cultivated inner medullary collecting duct (IMCD) cells. As a second approach, we used renal cortex and renal inner medulla from principal cell specific NFAT5 deficient mice and control mice for NGS analysis. Differentially expressed genes were analyzed by pathway, functional and gene enrichment analysis.ResultsIn primary IMCD cells hyperosmolality induced massive changes in gene expression. Aquaproin‐2 (Aqp2) was one of the transcripts with the highest level of induction. Loss of NFAT5 abolished hyperosmolality‐induced expression of Aqp2. Most of the hyperosmolality induced transcripts had the highest expression in the inner medulla. Loss of NFAT5 affected the expression of more than 3,000 genes in renal cortex and more than 5,000 genes in the inner medulla, compared to control kidneys. Again, loss of NFAT5 was associated with decreased expression of Aqp2. We observed increased expression of kidney injury marker genes, like lipocalin‐2 or kidney injury molecule 1. Gene enrichment analysis also indicated that loss of NFAT5 is associated with a renal inflammation‐like phenotype.ConclusionThis is the first study addressing the role of NFAT5 on hypertonicty‐induced changes in gene expression in the kidney. NFAT5 is the master regulator of osmolality induced Aqp2 gene expression and in vivoloss of function induces a kidney injury‐like phenotype through currently unknown mechanisms.

Modulation of physiological plasticity through structural and functional modifications in Stipagrostis plumosa L. for adaptability to hyper-arid environments

The role of morpho-physiological attributes along with the antioxidant potential of Stipagrostis plumosa L. populations collected from arid regions in adaptability to aridity was evaluated. Root to shoot length, chlorophyll, carotenoids, and organic osmolytes (total free amino acids, total soluble proteins, glycinebetaine, and proline) increased with more activities of antioxidant enzymes (APX, CAT, POD, and SOD). Root and shoot fresh:dry weight ratio and leaf area decreased with increasing dryness ratio (D: 8.40?30.49) and decreasing precipitation (519 mm to 143 mm). Hyperarid populations [Noorpur Thal - NpT (D: 10.90; P: 400 mm) and Cholistan - Cho (D:30.49; P: 143 mm)] relied on reduced leaf area and plant biomass, longer roots, more activities of antioxidant enzymes with higher accumulation of organic osmolytes, and better compartmentation of ions in root and shoot. Root and leaf epidermal thicknesses, epidermal cell area, the proportion of cortical parenchyma, metaxylem cell area, abaxial stomatal density and area reduced significantly while stem epidermis thickness, cortical cell area, and metaxylem cell area increased in relatively less arid populations [Neela WahnNeW (D: 8.40; P: 519 mm) and Kallar Kahar-KKr (D: 8.99; P: 485 mm)]. In conclusion, survival of S. plumosa under water deficit was directly linked to the plasticity in morpho-physiological and anatomical traits such as epidermal hairs, thick leaves, intense sclerification in roots epidermis, cortex and endodermis, and vascular bundle. These traits not only accounted for the movement of water and solutes but also help conserve water and provided mechanical strength for survival in hyperarid environments.

Functional traits for salinity tolerance in differently adapted populations of Fimbristylis complanata (Retz.)

Functional modifications in three populations of Fimbristylis complanata collected from differently salt effected habitats were evaluated. The populations were established in pots and treated with five NaCl levels (0, 100, 200, 300, and 400 mM). Population SH (collected from the highest salinities, ECe 37.94 dS m−1) exhibited better osmotic adjustment because of the higher accumulation of organic osmolytes under high salinities and was ranked as highly tolerant. Other features like an increased concentration of chlorophyll pigments ensured maintenance of photosynthetic capability, and accumulated higher K+ and Ca2+ contents that minimized the toxic effect of Na+ and maintained ion homeostasis. Salinity tolerance in the Lillah–Khewra foothills (LR) population (collected from moderately saline site, ECe 31.36 dS m−1) relied on the maintenance of shoot dry weight (SDW) and shoot and root length (RL) with a parallel accumulation of organic osmolytes and shoot Ca2+. This species is a stem succulent and can store excessive amount of salt in storage parenchyma, as indicated by the accumulation of high concentration of Na+ in shoot. The SH population, in particular, can be rated as the best for phytoremediation of salt-affected soils that accumulated more Na+ than other populations and concentration of osmolytes for turgor maintenance under high salinities. Novelty statement Fimbristylis is less explored, particularly no information available on salt tolerance of F. complanata exists in the literature.

Simultaneous Biochemical and Physiological Responses of the Roots and Leaves of Pancratium maritimum (Amaryllidaceae) to Mild Salt Stress.

Pancratium maritimum (Amaryllidaceae) is a bulbous geophyte growing on coastal sands. In this study, we investigated changes in concentrations of metabolites in the root and leaf tissue of P. maritimum in response to mild salt stress. Changes in concentrations of osmolytes, glutathione, sodium, mineral nutrients, enzymes, and other compounds in the leaves and roots were measured at 0, 3, and 10 days during a 10-day exposure to two levels of mild salt stress, 50 mM NaCl or 100 mM NaCl in sandy soil from where the plants were collected in dunes near Cuma, Italy. Sodium accumulated in the roots, and relatively little was translocated to the leaves. At both concentrations of NaCl, higher values of the concentrations of oxidized glutathione disulfide (GSSG), compared to reduced glutathione (GSH), in roots and leaves were associated with salt tolerance. The concentration of proline increased more in the leaves than in the roots, and glycine betaine increased in both roots and leaves. Differences in the accumulation of organic osmolytes and electron donors synthesized in both leaves and roots demonstrate that osmoregulatory and electrical responses occur in these organs of P. maritimum under mild salt stress.

Silicon Alleviate Hypoxia Stress by Improving Enzymatic and Non-enzymatic Antioxidants and Regulating Nutrient Uptake in Muscadine Grape (Muscadinia rotundifolia Michx.).

Flooding induces low oxygen (hypoxia) stress to plants, and this scenario is mounting due to hurricanes followed by heavy rains, especially in subtropical regions. Hypoxia stress results in the reduction of green pigments, gas exchange (stomatal conductance and internal CO2 concentration), and photosynthetic activity in the plant leaves. In addition, hypoxia stress causes oxidative damage by accelerating lipid peroxidation due to the hyperproduction of reactive oxygen species (ROS) in leaf and root tissues. Furthermore, osmolyte accumulation and antioxidant activity increase, whereas micronutrient uptake decreases under hypoxia stress. Plant physiology and development get severely compromised by hypoxia stress. This investigation was, therefore, aimed at appraising the effects of regular silicon (Si) and Si nanoparticles (SiNPs) to mitigate hypoxia stress in muscadine (Muscadinia rotundifolia Michx.) plants. Our results demonstrated that hypoxia stress reduced muscadine plants’ growth by limiting the production of root and shoot dry biomass, whereas the root zone application of both Si and SiNP effectively mitigated oxidative and osmotic cell damage. Compared to Si, SiNP yielded better efficiency by improving the activity of enzymatic antioxidants [including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)], non-enzymatic antioxidants [ascorbic acid (AsA) and glutathione contents], and accumulation of organic osmolytes [proline and glycinebetaine (GB)]. SiNP also regulated the nutrient profile of the plants by increasing N, P, K, and Zn contents while limiting Mn and Fe concentration to a less toxic level. A negative correlation between antioxidant activities and lipid peroxidation rates was observed in SiNP-treated plants under hypoxia stress. Conclusively, SiNP-treated plants combat hypoxia more efficiently stress than conventional Si by boosting antioxidant activities, osmoprotectant accumulation, and micronutrient regulation.

Salicylic acid ameliorates salinity tolerance in maize by regulation of phytohormones and osmolytes

Salinity is one of the most widespread stresses responsible for water and soil pollution across the globe. Salicylic acid (SA) has a major role in defence responses against various abiotic stresses. In the current study, SA (0.05 mmol) influences were evaluated in mitigation of the negative impact of salinity (40 and 80 mmol NaCl) in the maize plant. NaCl stress-induced significant accumulation of organic osmolytes (total soluble sugars (TSS), total soluble protein (TSP), and proline) by 35.6, 66.2, and 89.2%, respectively, with 80 mmol NaCl. In addition, salinity is also responsible for the elevated accumulation of inorganic osmolytes (Na<sup>+</sup> and Na<sup>+</sup>/K<sup>+</sup> ratio) by 202.4% and 398.8%, respectively, and for the reduction in the K<sup>+</sup> and Ca<sup>2+</sup> levels by 48.6% and 58.9%, respectively, with 80 mmol NaCl. Moreover, salinity stress reduced phytohormones (indoleacetic acid (IAA) and gibberellic acid (GA3)) by 48.8% and 59.8%, respectively, with 80 mmol NaCl; however, abscisic acid (ABA) was increased by 340.5% with 80 mmol NaCl. Otherwise, SA application caused an additional enhancement in TSS, TSP, proline, K<sup>+</sup>, Ca<sup>2+</sup>, IAA, and GA3 contents but decreased the Na<sup>+</sup>, Na<sup>+</sup>/K<sup>+</sup> ratio, and ABA to an appreciable level. In conclusion, SA pre-soaking mitigates the negative impact of NaCl toxicity in maize through the regulation of phytochromes and various organic and inorganic osmolytes, which may ameliorate salinity tolerance in maize.

RETRACTED ARTICLE: Screening and differential physiological responses of tomato (Solanum lycopersicum L.) to drought stress

Water deficit stress remains an important agricultural threat worldwide, thereby identifying germplasm with proven tolerance to drought stress is imperative. Tomato (Solanum lycopersicum L.) is a prominent fruit vegetable whose growth is considerably hampered by drought stress. This study evaluated physiological responses of 14 commercial tomato cultivars subjected to drought stress. Multivariate analysis and drought susceptibility index were employed to assess differential drought tolerance among cultivars, resulting into selection of Star 9003 and Rodede as tolerant and sensitive cultivars respectively. Subsequent physiological experiments showed that cultivar Star 9003 maintained better photosynthetic parameters as opposed to Rodede under drought stress, but had lower intercellular carbon dioxide concentration indicating that available CO2 was efficiently assimilated as also shown by its higher carboxylation and instantaneous transpiration efficiencies (CE and ITE). Lower stomatal limitation values in sensitive cultivar Rodede hint at a possibility that the major photosynthetic limiting factors were non-stomatal such as oxidative stress-induced photoinhibitory damage. The present study reports that tolerance in Star 9003 was unrelated to avoidance in stomatal water losses, but in part through development of morphologically thicker leaves, accumulation of organic osmolytes for osmotic adjustment and attainment of higher efficiencies in photosynthetic water use and carbon assimilation.

Mannose regulates water balance, leaf senescence, and genes related to stress tolerance in white clover under osmotic stress

Mannose (MAN), an important monosaccharide, contributes to coping with abiotic stresses in plants. Objectives of this study were to examine whether exogenous MAN (30 mM) could significantly increase drought tolerance and further to reveal MAN-regulated tolerance mechanism in white clover under osmotic stress induced by 18 % (m/v) polyethylene glycol 6000 for 10 d in controlled growth chambers. Results show that the application of MAN significanlty alleviated stress damage and the inhibition of growth and photosynthesis in white clover under osmotic stress. The MAN-induced increase in endogenous MAN content and the accumulation of organic osmolytes (proline and water soluble sugars) could be responsible for a lower osmotic potential (OP) in white clover. The exogenous application of MAN also enhanced antioxidant enzyme (superoxide dismutase, peroxidase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase) activities and maintained ascorbic acid content in white clover during osmotic stress. As concern chlorophyll (Chl) metabolism, the MAN-treated plants showed significantly higher transcription of genes involved in Chl synthesis Mg-chelatase and protochlorophyllide reductase and lower transcription of pheophorbide a oxygenase and chlorophyllase related to Chl degradation and also a senescence associated gene 101 than untreated plants. In addition, the MAN application increased transcription of SK2-, Y2K-, and Y2SK-type dehydrin genes, and dehydrin b in leaves of white clover under osmotic stress. These results indicate that MAN plays important roles in drought tolerance not only acting as a compatible solute for OP but also delaying leaf senescence through enhancing antioxidant metabolism, decreasing Chl degradation, and increasing transcription of dehydrin genes contributing to enhanced drought tolerance in white clover.

Indicators of Osmotic and Ion Regulation in the Fish of the White Sea

The osmotic concentration; the concentrations of sodium and potassium; the content of total, free, attached water fractions in plasma; and the content of interstitial and cerebrospinal fluid, in the brain, muscles, liver, and erythrocytes typical for the fish in the native environment were determined for cod Gadus morhua. Under stress, a protective reaction is implemented, it prevents tissue dehydration by increasing the osmotic concentration in the interstitial fluid in the European flounder Platichthys flesus, spotted wolffish Anarhichas minor, lumpsucker Cyclopterus lumpus, and short-horn sculpin Myoxocephalus scorpius. The osmotic concentration preconditioned by inorganic ions in the muscles, liver, and erythrocytes of cod is significantly lower compared to the internal environment. The lack of ions in the tissues is compensated by the accumulation of organic osmolytes. Similar patterns are observed in euryhaline species when acclimated to the marine environment and in freshwater fish in the zone of critical salinity. Values of the osmotic concentration and sodium and potassium content in the blood plasma and tissues of the White Sea fish refer to the corresponding regulation ranges obtained for euryhaline and freshwater fish in the salinity range compatible with life activity.

Root physiological and biochemical responses of seashore paspalum and centipedegrass exposed to iso‐osmotic salt and drought stresses

AbstractDrought and salt are two major stresses of turfgrass. Both damage the plant root system by disrupting osmotic balance at the root–soil interface. The objectives of our hydroponic experiments were to understand root physiological and biochemical responses in two turfgrass species (seashore paspalum [Paspalum vaginatum Swartz] and centipedegrass [Eremochloa ophiuroides (Munro) Hack.]) with distinct salinity tolerance exposed to iso‐osmotic drought and salt stresses. Two seashore paspalum genotypes, ‘Seastar’ and ‘UGP113’, and a centipedegrass genotype, ‘TifBlair’, were exposed to three treatments: control, salt stress (−0.4 MPa by adding NaCl), and drought stress (−0.4 MPa by adding polyethylene glycol). Although equal in osmotic potential, drought stress damage was more evident compared with salt stress in terms of lipid peroxidation and decreased root viability in all three turfgrass genotypes. Salt stress reduced root viability only in the centipedegrass genotype, indicating ion toxicity effects in this turfgrass genotype. Seashore paspalum genotypes had greater total accumulation of Na+ and K+ for greater root osmotic adjustment than centipedegrass under salt stress. Seashore paspalum genotypes also had greater activities of root antioxidant enzymes such as superoxide dismutase, peroxidase, and glutathione reductase compared with centipedegrass under salt stress. In contrast, centipedegrass had greater total accumulation of total soluble sugar and proline for greater osmotic adjustment compared with seashore paspalum genotypes under drought stress. Despite greater accumulation of organic osmolytes, activities of superoxide dismutase, catalase, peroxidase, and glutathione reductase in centipedegrass were either lower or similar to those in seashore paspalum genotypes, and therefore centipedegrass accumulated similar oxidative damage as seashore paspalum genotypes under drought stress.

Mitigation of Arsenic Toxicity in Wheat by the Exogenously Applied Salicylic Acid, 24-Epi-Brassinolide and Silicon

A greenhouse investigation was performed to examine the influence of salicylic acid (SA; 0, 0.5, and 1 mM), 24-epi-brassinolide (BR; 0, 0.5, and 0.75 μM), and silicon (Si; 0, 6, and 12 mM) in alleviating arsenic (As) toxicity in wheat under different As levels (0, 50, and 100 μM). Arsenic stress enhanced electrolyte leakage (EL), activities of some critical antioxidant enzymes, and the concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) as well as raised the accumulation of key organic osmolytes in wheat leaves. Indeed, application of Si and also of SA and BR considerably elevated the activities of antioxidant enzymes and the concentrations of osmolytes, and decreased the levels of H2O2 and MDA as well as EL in As-stressed plants. Arsenic toxicity resulted in reduced relative water content (RWC), photosynthetic rate, stomatal conductance, transpiration, and chlorophyll content of wheat. In contrast, Si, SA, and BR improved RWC and gas exchange characteristics under varying As regimes; however, the positive effects of SA and BR were high when applied with Si. The adverse effect of As on wheat was: root > leaf > grain. Under As-stress, supplementation with Si, SA, and BR applied separately or in combination caused a significant reduction in arsenic concentration in wheat, but the effect of Si + SA and especially of Si + BR was greater than that of Si, BR, or SA applied separately. Overall, SA, BR, and Si application proved to have a great potential in improving growth and quality of wheat and reducing As content in different parts of the wheat plant under high levels of As.

Acetylcholine mechanism of action to enhance tolerance to salt stress in Nicotiana benthamiana

Acetylcholine (ACh) is one of the important neurotransmitters, involved in signal transduction function in human and animal brain. However, the influence of ACh treatment on salt-stress tolerance in plants is yet unknown. Salt stress caused a reduction in gas-exchange parameters, chlorophyll content, antioxidant enzyme activities, and leaf relative water content of Nicotiana benthamiana plants. However, the above inhibitions could be significantly alleviated by application of leaf spray or root application of ACh. Exogenous ACh reduced the accumulation of malondialdehyde by enhancing activities of antioxidant enzymes such as peroxidase and superoxide dismutase. In addition, enhanced accumulation of organic osmolytes including soluble sugars and proline possibly regulated the signal mechanisms related to stress. Application of ACh could also improve gas-exchange parameters and photosynthetic pigment accumulation in leaves of salt-stressed plants. These effects of ACh were beneficial for maintaining better water status in plants, the concentration of 10 µM ACh applied both in the form of leaf spray or root application was the most effective. Therefore, our findings provided a stronger evidence for a physiological role of ACh and its potential use at optimal concentration by leaf or root application to alleviate damage caused by salt-stress in plants.

Regulatory mechanisms underlying the maintenance of homeostasis in Pyropia haitanensis under hypersaline stress conditions

Intertidal macroalgae are highly resistant to hypersaline stress conditions. However, the underlying mechanism remains unknown. In the present study, the mechanism behind Pyropia haitanensis responses to two hypersaline stress conditions [100‰ (HSS_100) and 110‰ (HSS_110)] was investigated via analyses of physiological and transcriptomic changes. We observed that the differences between the responses of Py. haitanensis to HSS_100 and HSS_110 conditions involved the following three aspects: osmotic regulation, ionic homeostasis, and adjustment to secondary stresses. First, the water retention of Py. haitanensis was maintained through increased expansin production under HSS_100 conditions, while cell wall pectin needed to be protected from hydrolysis via the increased abundance of a pectin methylesterase inhibitor under HSS_110 conditions. Meanwhile, Py. haitanensis achieved stable and rapid osmotic adjustments because of the coordinated accumulation of inorganic ions (K+, Na+, and Cl−) and organic osmolytes (glycine betaine and trehalose) under HSS_100 conditions, but not under HSS_110 conditions. Second, Py. haitanensis maintained a higher K+/Na+ ratio under HSS_100 conditions than under HSS_110 conditions, mainly via the export of Na+ into the apoplast rather than compartmentalizing it into the vacuoles, and the enhanced uptake and retention of K+. However, K+/Na+ homeostasis was not completely disrupted during a short-term exposure to HSS_110 conditions. Finally, the Py. haitanensis antioxidant system scavenged more ROS and synthesized more heat shock proteins under HSS_100 conditions than under HSS_110 conditions, although thalli may have been able to maintain a certain redox balance during a short-term exposure to HSS_110 conditions. These differences may explain why Py. haitanensis can adapt to HSS_100 conditions rather than HSS_110 conditions, and also why the thalli exposed to HSS_110 conditions can recover after being transferred to normal seawater. Thus, the data presented herein may elucidate the mechanisms enabling Pyropia species to tolerate the sudden and periodic changes in salinity typical of intertidal systems.

A16057 Tonicity responses by TonEBP and SMIT in human primary term cytotrophoblasts

Objectives: Previously, we and others have demonstrated that in pregnancy enhanced intake of salt (NaCl) lowers maternal blood pressure and improves pregnancy outcome; the reasons why are unknown. It has been shown in non-renal tissues such as the skin interstitium, that in response to high salt, macrophages upregulate tonicity-responsive enhancer binding protein (TonEBP), which regulates transcription of sodium-myo-inositol cotransporter (SMIT). We hypothesised that human primary term cytotrophoblasts (CTBs) are able to respond to salt in a similar manner. Methods: CTBs were incubated with 3 different salt concentrations (110, 140 and 170 mM NaCl) for 6 or 24 hours. mRNA expression of TonEBP and SMIT were measured by RT-PCR and normalised to the geometric mean of the reference genes Cyclophilin A, HPRT1 and YWHAZ. Results: After 6 h incubation with high salt (170 mM NaCl), TonEBP and SMIT mRNA levels were upregulated (p < 0.05) compared to 110 mM NaCl. After 24 h incubation with high salt, TonEBP mRNA was no longer upregulated in CTBs. However, SMIT mRNA levels stayed upregulated also after 24 h incubation with high salt (p < 0.05). Conclusion: The results of this study indicate that TonEBP regulates transcription of SMIT in human primary term cytotrophoblasts and that this regulation can be enhanced following treatment with NaCl. The TonEBP response enables cells to survive hypertonic conditions via the accumulation of organic osmolytes. The results of the CTBs confirm our results in three human trophoblast cell lines (HTR8/SVneo, JEG3, BeWo).

107. Tonicity responses by TonEBP and SMIT in human primary term cytotrophoblasts

Introduction Previously, we and others have demonstrated that in pregnancy enhanced intake of salt (NaCl) lowers maternal blood pressure and improves pregnancy outcome; the reasons why are unknown. It has been shown in non-renal tissues such as the skin interstitium, that in response to high salt, macrophages upregulate tonicity-responsive enhancer binding protein (TonEBP), which regulates transcription of sodium-myo-inositol cotransporter (SMIT). We hypothesised that placental trophoblasts are able to respond to salt in a similar manner. Objectives To use human primary term cytotrophoblasts (CTBs) to evaluate how the placenta responds to hypertonicity. Methods CTBs were incubated with 3 different salt concentrations (110, 140 and 170 mM NaCl) for 6 or 24 h. mRNA expression of TonEBP and SMIT were measured by RT-PCR and normalised to the geometric mean of the reference genes Cyclophilin A, HPRT1 and YWHAZ. Results After 6 h incubation with high salt (170 mM NaCl), TonEBP and SMIT mRNA levels were upregulated (p Conclusion The results of this study indicate that TonEBP regulates transcription of SMIT in human primary term cytotrophoblasts and that this regulation can be enhanced following treatment with NaCl. The TonEBP response enables cells to survive hypertonic conditions via the accumulation of organic osmolytes. The results of the CTBs confirm our results in three human trophoblast cell lines (HTR8/SVneo, JEG3, BeWo).