Halophytes and other molecular strategies for the generation of salt-tolerant crops

Structural characterization and potential anti-tumor activity of a polysaccharide from the halophyte Salicornia bigelovii Torr

Plant polysaccharides are highly potent bioactive molecules. Clarifying the structural composition and bioactivities of plant polysaccharides will provide insights into their structure-activity relationships. Therefore, herein, we identified a polysaccharide produced by Salicornia bigelovii Torr. and analyzed the structure and anti-tumor activity of its component, SabPS-1. SabPS-1 was 3.24 × 104 Da, primarily composed of arabinose (24.96 %), galactose (30.39 %), and galacturonic acid (23.20 %), rhamnose (6.21 %), xylose (4.99 %), glucuronic acid (3.12 %), mannuronic acid (1.75 %), mannose (1.69 %), glucose (1.54 %), fucose (1.12 %), and guluronic acid (1.03 %). The backbone of SabPS-1 was a → 4)-β-D-GalpA-(1→, →5)-α-L-Araf-(1→, and→4)-β-D-Galp-(1 → molecule with a branched chain of α-L-Araf-(1 → connected to sugar residues of →3,6)-β-D-Galp-(1 → in the O-3 position. SabPS-1 induced apoptosis and inhibited the growth of HepG-2 cells, with viability of 47.90 ± 4.14 (400 μg/mL), indicating anti-tumor activity. Apoptosis induced by SabPS-1 may be associated with the differential regulation of caspase 3, caspase 8, Bax, and Bcl-2. To the best of our knowledge, this is the first study to investigate the principal structures and anti-tumor biological activities of SabPS-1. Our findings demonstrated the excellent anti-tumor properties of SabPS-1, which will aid in the development of anti-tumor drugs utilizing Salicornia bigelovii Torr.

Exogenous application of salicylic acid ameliorates salinity stress in barley (Hordeum vulgare L.)

Barley (Hordeum vulgare L.) is a significant cereal crop belonging to Poaceae that is essential for human food and animal feeding. The production of barley grains was around 142.37 million tons in 2017/2018. However, the growth of barley was influenced by salinity which was enhanced by applying a foliar spray of salicylic acid. The current study investigated to evaluated the potential effect of SA on the barley (Hordeum vulgare L.) plants under salinity stress and its possible effects on physiological, biochemical, and growth responses. The experiment was conducted at Postgraduate Research Station (PARS), University of Agriculture; Faisalabad to assess the influence of salicylic acid on barley (Hordeum vulgare L.) under highly saline conditions. The experiment was conducted in a Completely Randomized Design (CRD) with 3 replicates. In plastic pots containing 8 kg of properly cleaned sand, two different types of barley (Sultan and Jau-17) were planted. The plants were then watered with a half-strength solution of Hoagland's nutritional solution. After the establishment of seedlings, two salt treatments (0 mM and 120 mM NaCl) were applied in combining three levels of exogenously applied salicylic acid (SA) (0, 0.5, and 1 mg L-1). Data about morphological, physiological, and biochemical attributes was recorded using standard procedure after three weeks of treatment. The morpho-physiological fresh weight of the shoot and root (48%), the dry mass of the shoot and root (66%), the plant height (18%), the chlorophyll a (30%), the chlorophyll b (22%), and the carotenoids (22%), all showed significant decreases. Salinity also decreased yield parameters and the chl. ratio (both at 29% and 26% of the total chl. leaf area index). Compared to the control parameters, the following data was recorded under salt stress: spike length, number of spikes, number of spikelets, number of tillers, biological yield, and harvest index. Salicylic acid was used as a foliar spray to lessen the effects of salinity stress, and 1 mg L-1 of salicylic acid proved more effective than 0.5 mg L-1. Both varieties show better growth by applying salicylic acid (0 mg L-1) as a control, showing normal growth. By increasing its level to (0.5 mg L-1), it shows better growth but maximized growth occurred at a higher level (1 mg L-1). Barley sultan (Hordeum vulgare L.) is the best variety as compared to Jau-17 performs more growth to mitigate salt stress (0mM and 120mM NaCl) by improving morpho-physiological parameters by enhancing plan height, Root and shoot fresh and dry weights, as well as root and shoot lengths, photosynthetic pigments, area of the leaves and their index, and yield attributes and reduce sodium ions.

Balancing growth amidst salt stress - lifestyle perspectives from the extremophyte model Schrenkiella parvula

Schrenkiella parvula, a leading extremophyte model in Brassicaceae, can grow and complete its lifecycle under multiple environmental stresses, including high salinity. Yet, the key physiological and structural traits underlying its stress-adapted lifestyle are unknown along with trade-offs when surviving salt stress at the expense of growth and reproduction. We aimed to identify the influential adaptive trait responses that lead to stress-resilient and uncompromised growth across developmental stages when treated with salt at levels known to inhibit growth in Arabidopsis and most crops. Its resilient growth was promoted by traits that synergistically allowed primary root growth in seedlings, the expansion of xylem vessels across the root-shoot continuum, and a high capacity to maintain tissue water levels by developing thicker succulent leaves while enabling photosynthesis during salt stress. A successful transition from vegetative to reproductive phase was initiated by salt-induced early flowering, resulting in viable seeds. Self-fertilization in salt-induced early flowering was dependent upon filament elongation in flowers otherwise aborted in the absence of salt during comparable plant ages. The maintenance of leaf water status promoting growth, and early flowering to ensure reproductive success in a changing environment, were among the most influential traits that contributed to the extremophytic lifestyle of S. parvula.

Changes in leaf ecophysiological traits and proteome profile provide new insights into variability of salt response in the succulent halophyte Cakile maritima

Natural variability of stress tolerance in halophytic plants is of significance both ecologically and in view of identifying molecular traits for salt tolerance in plants. Using ecophysiological and proteomic analyses, we address these phenomena in two Tunisian accessions of the oilseed halophyte, Cakile maritima Scop., thriving on arid and semi-arid Mediterranean bioclimatic stages (Djerba and Raoued, respectively), with a special emphasis on the leaves. Changes in biomass, photosynthetic gas exchange and pigment concentrations in C. maritima plants treated with three salinity levels (0, 100 and 300mM NaCl) were monitored for 1month. Comparative two-dimensional gel electrophoresis (2-DE) revealed 94 and 56 proteins of differential abundance in Raoued and Djerba accessions, respectively. These salinity-responsive proteins were mainly related to photosynthesis and oxidative phosphorylation (OXPHOS). Although Djerba accession showed a lower biomass productivity, it showed a slightly higher CO2 assimilation rate than Raoued accession when salt-treated. Photosynthesis impairment in both accessions under salinity was also suggested by the lower abundance of proteins involved in Calvin cycle and electron transfer. A significant increase of protein spots involved in the OXPHOS system was found in Djerba accession, suggesting an increase in mitochondrial respiration for increased ATP production under saline conditions, whereas a lesser pronounced trend was observed for Raoued accession. The latter showed in addition higher abundance of proteins involved in photorespiration. Salt-challenged plants of Djerba also likely developed mechanisms for scavenging ROS in leaves as shown by the increase in superoxide dismutase and thioredoxin, while an opposite trend was found in Raoued.

Effect of Salinity on Growth, Ion Accumulation and Mineral Nutrition of Different Accessions of a Crop Wild Relative Legume Species, Trifolium fragiferum

Crop wild relatives represent a valuable resource for the breeding of new crop varieties suitable for sustainable productivity in conditions of climate change. The aim of the present study was to assess salt tolerance of several wild accessions of T. fragiferum from habitats with different salinity levels in controlled conditions. Decrease of plant biomass and changes in partitioning between different organs was a characteristic response of plants with increasing substrate salinity, but these responses were genotype-specific. In several accessions, salinity stimulated reproductive development. The major differences in salinity responses between various T. fragiferum genotypes were at the level of dry biomass accumulation as well as water accumulation in plant tissues, resulting in relatively more similar effect on fresh mass. Na⁺ and Cl^- accumulation capacity were organ-specific, with leaf petioles accumulating more, followed by leaf blades and stolons. Responses of mineral nutrition clearly were both genotype- and organ-specific, but several elements showed a relatively general pattern, such as increase in Zn concentration in all plant parts, and decrease in Ca and Mg concentration. Alterations in mineralome possibly reflect a reprogramming of the metabolism to adapt to changes in growth, morphology and ion accumulation resulting from effect of NaCl. High intraspecies morphological and physiological variability in responses of T. fragiferum accessions to salinity allow to describe them as ecotypes.

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants

Soil salinization, which is aggravated by climate change and inappropriate anthropogenic activities, has emerged as a serious environmental problem, threatening sustainable agriculture and future food security. Although there has been considerable progress in developing crop varieties by introducing salt tolerance-associated traits, most crop cultivars grown in saline soils still exhibit a decline in yield, necessitating the search for alternatives. Halophytes, with their intrinsic salt tolerance characteristics, are known to have great potential in rehabilitating salt-contaminated soils to support plant growth in saline soils by employing various strategies, including phytoremediation. In addition, the recent identification and characterization of salt tolerance-related genes encoding signaling components from halophytes, which are naturally grown under high salinity, have paved the way for the development of transgenic crops with improved salt tolerance. In this review, we aim to provide a comprehensive update on salinity-induced negative effects on soils and plants, including alterations of physicochemical properties in soils, and changes in physiological and biochemical processes and ion disparities in plants. We also review the physiological and biochemical adaptation strategies that help halophytes grow and survive in salinity-affected areas. Furthermore, we illustrate the halophyte-mediated phytoremediation process in salinity-affected areas, as well as their potential impacts on soil properties. Importantly, based on the recent findings on salt tolerance mechanisms in halophytes, we also comprehensively discuss the potential of improving salt tolerance in crop plants by introducing candidate genes related to antiporters, ion transporters, antioxidants, and defense proteins from halophytes for conserving sustainable agriculture in salinity-prone areas.

Cation/Ca2+ Exchanger 1 (MdCCX1), a Plasma Membrane-Localized Na+ Transporter, Enhances Plant Salt Tolerance by Inhibiting Excessive Accumulation of Na+ and Reactive Oxygen Species

High salinity causes severe damage to plant growth and significantly reduces crop yields. The CCX family proteins can facilitate the transport of multiple ions to prevent toxicity. CCX proteins play an important role in regulating plant salt tolerance, but no detailed studies on CCX proteins in apples have been reported. Here, the CCX family gene MdCCX1 was cloned from apple (Malus domestica). It is constitutively expressed in various apple tissues and is significantly induced by salt stress. As a plasma membrane-localized protein, MdCCX1-overexpression could complement the Na⁺-sensitive phenotype of yeast mutants and reduce the Na⁺ content in yeast cells under NaCl treatment, suggesting that MdCCX1 could be a plasma membrane-localized Na⁺ transporter. To identify the function of MdCCX1 in salt response, we transformed this gene into Arabidopsis, apple calli, and apple plants. Overexpression of MdCCX1 significantly improved the salt tolerance of these transgenic materials. The significantly reduced Na⁺ content under NaCl treatment indicated that MdCCX1 overexpression could enhance plant salt tolerance by inhibiting the excessive accumulation of Na⁺. Besides, MdCCX1 overexpression could also enhance plant salt tolerance by promoting ROS scavenging. These findings provide new insight and rich resources for future studies of CCX proteins in plant species.