Ascorbate–Glutathione Oxidant Scavengers, Metabolome Analysis and Adaptation Mechanisms of Ion Exclusion in Sorghum under Salt Stress

Salt stress is one of the major significant restrictions that hamper plant development and agriculture ecosystems worldwide. Novel climate-adapted cultivars and stress tolerance-enhancing molecules are increasingly appreciated to mitigate the detrimental impacts of adverse stressful conditions. Sorghum is a valuable source of food and a potential model for exploring and understanding salt stress dynamics in cereals and for gaining a better understanding of their physiological pathways. Herein, we evaluate the antioxidant scavengers, photosynthetic regulation, and molecular mechanism of ion exclusion transporters in sorghum genotypes under saline conditions. A pot experiment was conducted in two sorghum genotypes viz. SSG 59-3 and PC-5 in a climate-controlled greenhouse under different salt concentrations (60, 80, 100, and 120 mM NaCl). Salinity drastically affected the photosynthetic machinery by reducing the accumulation of chlorophyll pigments and carotenoids. SSG 59-3 alleviated the adverse effects of salinity by suppressing oxidative stress (H2O2) and stimulating enzymatic and non-enzymatic antioxidant activities (SOD, APX, CAT, POD, GR, GST, DHAR, MDHAR, GSH, ASC, proline, GB), as well as protecting cell membrane integrity (MDA, electrolyte leakage). Salinity also influenced Na+ ion efflux and maintained a lower cytosolic Na+/K+ ratio via the concomitant upregulation of SbSOS1, SbSOS2, and SbNHX-2 and SbV-Ppase-II ion transporter genes in sorghum genotypes. Overall, these results suggest that Na+ ions were retained and detoxified, and less stress impact was observed in mature and younger leaves. Based on the above, we deciphered that SSG 59-3 performed better by retaining higher plant water status, photosynthetic assimilates and antioxidant potential, and the upregulation of ion transporter genes and may be utilized in the development of resistant sorghum lines in saline regions.

Ion-Exclusion/Cation-Exchange Chromatography Using Dual-Ion-Exchange Groups for Simultaneous Determination of Inorganic Ionic Nutrients in Fertilizer Solution Samples for the Management of Hydroponic Culture

In this study, ion-exclusion/cation-exchange chromatography (IEC/CEC) using dual-ion-exchange groups (carboxy and sulfo groups) for the simultaneous determination of anions (SO42−, Cl−, NO3−, and HPO42−) and cations (Na+, NH4+, K+, Mg2+, and Ca2+) was developed. By using the combination of dual-ion-exchange groups, simultaneous separation of inorganic ions with HPO42− was achieved that was impossible by the conventional IEC/CEC based on the single-ion-exchange group (carboxy group). This method was applied to the monitoring of inorganic ionic nutrients in fertilizer solution samples in hydroponic culture. As a result, a higher peak resolution of inorganic anions and cations with phosphate ion using IEC/CEC with dual-ion-exchange groups was achieved in the absence of matrix effects. In addition, the developed method helps to understand the behavior of ionic nutrients in fertilizer solution during hydroponic cultivation and is potentially useful for the individual fertilization of ionic nutrients.

Supported MXene/GO Composite Membranes with Suppressed Swelling for Metal Ion Sieving

Novel two-dimensional (2D) membranes have been utilized in water purification or seawater desalination due to their highly designable structure. However, they usually suffer from swelling problems when immersed in solution, which limits their further applications. In this study, 2D cross-linked MXene/GO composite membranes supported on porous polyamide substrates are proposed to improve the antiswelling property and enhance the ion-sieving performance. Transition-metal carbide (MXene) nanosheets were intercalated into GO nanosheets, where the carboxyl groups of GO combined the neighboring hydroxyl terminal groups of MXene with the formation of -COO- bonds between GO and MXene nanosheets via the cross-linking reaction (−OH + −COOH = −COO− + H2O) after heat treatment. The permeation rates of the metal ions (Li+, Na+, K+, Al3+) through the cross-linked MXene/GO composite membrane were 7–40 times lower than those through the pristine MXene/GO membrane. In addition, the cross-linked MXene/GO composite membrane showed excellent Na+ rejection performance (99.3%), which was significantly higher than that through pristine MXene/GO composite membranes (80.8%), showing improved ion exclusion performance. Such a strategy represents a new avenue to develop 2D material-derived high-performance membranes for water purification.

GmSALT3 expression improves reactive oxygen species detoxification in salt-stressed soybean roots

Soybean plants are salinity (NaCl) sensitive, with their yield significantly decreased under moderately saline conditions. GmSALT3 is the dominant gene underlying a major QTL for salt tolerance in soybean. GmSALT3 encodes a transmembrane protein belonging to the plant cation/proton exchanger (CHX) family. It is currently unknown through which molecular mechanism(s) the ER-localised GmSALT3 contributes to salinity tolerance, as its localisation excludes direct involvement in ion exclusion. In order to gain insights into potential molecular mechanism(s), we used RNA-seq analysis of roots from two soybean NILs (Near Isogenic Lines); NIL-S (salt-sensitive, Gmsalt3) and NIL-T (salt-tolerant, GmSALT3), grown under control and saline conditions (200 mM NaCl) at three time points (0h, 6h, and 3 days). Gene ontology (GO) analysis showed that NIL-T has greater responses aligned to oxidation reduction. ROS were shown less abundant and scavenging enzyme activity was higher in NIL-T, consistent with the RNA-seq data. Further analysis indicated that genes related to calcium signalling, vesicle trafficking and Casparian strip (CS) development were upregulated in NIL-T following salt treatment. We propose that GmSALT3 improves the ability of NIL-T to cope with saline stress through preventing ROS overaccumulation in roots, and potentially modulating Ca2+ signalling, vesicle trafficking and formation of diffusion barriers.

Up Regulation in Transcript Abundance of Plastidic Isoforms of Antioxidant Enzymes and Accumulation of Compatible Osmolytes Impart Tissue Tolerance to Salinity Stressed Wheat Plants

The response of salt tolerant wheat genotype (Kharchia 65), and sensitive cultivars (HD2687, HD2009, WL711) to vegetative stage salinity stress (for 4 weeks) were studied at 1.1 (control), 9.1 (S1) and 14.2 (S2) dSm-1 salinity levels. Based on relative change in Membrane stability, PSII efficiency, retention of chlorophyll and carotenoid contents, Kharchia 65 showed better tolerance to salinity than other genotypes considered. To understand the role of different component mechanisms, expression of genes involved in ion exclusion, antioxidant defence and compatible osmolyte synthesis were analysed. Expression of SOS1 (plasma membrane Na+/H+ antiporter), NHX (vacuolar Na+/H+ antiporter), Ionic (sodium exclusion) and tissue tolerance (Sodium compartmentation, compatible solute accumulation and antioxidant defence) mechanisms were analysed in leaves of the genotypes after 4 weeks of salinity stress. Expression assay and the content of respective constituents indicated that apart from the well-known ion exclusion ability, Kharchia 65 also showed high level of tissue tolerance resulting in high early vigour and maintenance of growth rate afterwards. In Kharchia 65, sensing of salinity stress at plasma membrane activates NADPH Oxidase (RBOH) genes and generate ROS at apoplast. Apoplastic ROS triggers calcium influx and activates calcium signaling genes of SOS pathway (SOS1 and NHX). ROS generated from organelles chloroplast, peroxisome and mitochondria triggers cellular oxidative burst. ROS and calcium activates MAPK genes and downstream transcription factors, NAC and bZIP. MAPK signaling induces cellular antioxidant and compatible osmolyte biosynthesis and imparts tissue tolerance to salinity.

Ion Pairing and Dielectric Decrement in Glycosaminoglycan Brushes

<p>Cell-surface polysaccharides are essential to many aspects of physiology, serving as a highly-conserved evolutionary feature of life and as an important part of the innate immune system in mammals. Here, as simplified biophysical models of these sugar-coatings, we present results of molecular dynamics simulations of hyaluronic acid and heparin brushes that show important effects of ion-pairing, water dielectric decrease, and co-ion exclusion. As in prior studies of macromolecular crowding under physiologically-relevant salt concentrations, our results show equilibria with electroneutrality attained through screening and pairing of brush anionic charges by monovalent cations at atomistic detail. Most surprising is the reversal of the Donnan potential obtained from both nonpolarizable and Drude polarizable force fields, in contrast to what would be expected based on electrostatic Boltzmann partitioning alone. Water dielectric decrement within the brush domain is also associated with Born hydration-driven cation exclusion from the brush. We observe that the primary partition energy attracting cations to attain brush electroneutrality is the ion-pairing or salt-bridge energy. Potassium and sodium pairing to glycosaminoglycan carboxylates and sulfates show similar abundance of contact-pairing and solvent-separated pairing. We conclude that in these crowded macromolecular brushes, ion-pairing, Born-hydration, and electrostatic potential energies all contribute to attain electroneutrality and should therefore contribute in mean-field models to accurately represent brush electrostatics. </p>