ROS homeostasis in halophytes in the context of salinity stress tolerance

The Effects of Hydro-Priming and Colonization with Piriformospora indica and Azotobacter chroococcum on Physio-Biochemical Traits, Flavonolignans and Fatty Acids Composition of Milk Thistle (Silybum marianum) under Saline Conditions

Salinity is an important challenge around the world, effecting all physiological and biochemical processes of plants. It seems that seed priming can diminish the negative impacts of salinity. To study the effects of hydro-priming and inoculation with Piriformospora indica (Pi) and Azotobacter chroococcum (Az) on physio-biochemical traits, flavonolignans and fatty acids composition of milk thistle under saline conditions, a greenhouse experiment was carried out. Our results indicated that under salinity, seed priming, especially Pi, improved physio-biochemical properties in milk thistle. Under 120 mM NaCl, inoculation with Pi increased membrane stability index (MSI) and relative water content (RWC) (by 21.86 and 33.43%, respectively). However, peroxidase (POX) (5.57- and 5.68-fold in roots and leaves, respectively), superoxide dismutase (SOD) (4.74- and 4.44-fold in roots and leaves, respectively), catalase (CAT) (6.90- and 8.50-fold in roots and leaves, respectively) and ascorbate peroxidase (APX) (5.61- and 5.68-fold in roots and leaves, respectively) activities increased with increasing salinity. Contrary to salinity, hydro-priming with Az and Pi positively altered all these traits. The highest content of the osmolytes, adenosine triphosphate (ATP) content and rubisco activity were recorded in Pi treatments under 120 mM NaCl. Stearic acid (20.24%), oleic acid (21.06%) and palmitic acid (10.48%) increased, but oil content (3.81%), linolenic and linoleic acid content (22.21 and 15.07%, respectively) decreased under saline conditions. Inoculations of Pi positively altered all these traits. The present study indicated that seed priming with Pi under 120 mM NaCl resulted in maximum silychristin, taxidolin, silydianin, isosilybin, silybin and silymarin of milk thistle seeds.

Drought and UV Radiation Stress Tolerance in Rice Is Improved by Overaccumulation of Non-Enzymatic Antioxidant Flavonoids

Drought and ultraviolet radiation (UV radiation) are the coexisting environmental factors that negatively affect plant growth and development via oxidative damage. Flavonoids are reactive, scavenging oxygen species (ROS) and UV radiation-absorbing compounds generated under stress conditions. We investigated the biosynthesis of kaempferol and quercetin in wild and flavanone 3-hydroxylase (F3H) overexpresser rice plants when drought and UV radiation stress were imposed individually and together. Phenotypic variation indicated that both kinds of stress highly reduced rice plant growth parameters in wild plants as compared to transgenic plants. When combined, the stressors adversely affected rice plant growth parameters more than when they were imposed individually. Overaccumulation of kaempferol and quercetin in transgenic plants demonstrated that both flavonoids were crucial for enhanced tolerance to such stresses. Oxidative activity assays showed that kaempferol and quercetin overaccumulation with strong non-enzymatic antioxidant activity mitigated the accumulation of ROS under drought and UV radiation stress. Lower contents of salicylic acid (SA) in transgenic plants indicated that flavonoid accumulation reduced stress, which led to the accumulation of low levels of SA. Transcriptional regulation of the dehydrin (DHN) and ultraviolet-B resistance 8 (UVR8) genes showed significant increases in transgenic plants compared to wild plants under stress. Taken together, these results confirm the usefulness of kaempferol and quercetin in enhancing tolerance to both drought and UV radiation stress.

Enhanced reactive oxygen detoxification occurs in salt-stressed soybean roots expressing GmSALT3

Soybean (Glycine max) is an important crop globally for food and edible oil production. Soybean plants are sensitive to salinity (NaCl), with significant yield decreases reported under 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, and is predominately expressed in root phloem and xylem associated cells under both saline and non-saline conditions. 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 (0 h, 6 h, and 3 days). Gene ontology (GO) analysis showed that NIL-T has greater responses aligned to oxidation reduction. ROS were less abundant and scavenging enzyme activity was greater 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.

LED spectral quality and NaCl salinity interact to affect growth, photosynthesis and phytochemical production of Mesembryanthemum crystallinum

The edible halophyte Mesembryanthemum crystallinum L. was grown at different NaCl salinities under different combined red and blue light-emitting diode (LED) light treatments. High salinity (500 mM NaCl) decreased biomass, leaf growth, and leaf water content. Interactions between LED ratio and salinity were detected for shoot biomass and leaf growth. All plants had F v /F m ratios close to 0.8 in dark-adapted leaves, suggesting that they were all healthy with similar maximal efficiency of PSII photochemistry. However, measured under the actinic light near or above the growth light, the electron transport rate (ETR) and photochemical quenching (qP) of M. crystallinum grown at 100 and 250 mM NaCl were higher than at 500 mM NaCl. Grown under red/blue LED ratios of 0.9, M. crystallinum had higher ETR and qP across all salinities indicating higher light energy utilisation. Crassulacean acid metabolism (CAM) was induced in M. crystallinum grown at 500 mM NaCl. CAM-induced leaves had much higher non-photochemical quenching (NPQ), suggesting that NPQ can be used to estimate CAM induction. M. crystallinum grown at 250 and 500 mM NaCl had higher total chlorophyll and carotenoids contents than at 100 mM NaCl. Proline, total soluble sugar, ascorbic acid, and total phenolic compounds were higher in plants at 250 and 500 mM NaCl compared with those at 100 mM NaCl. An interaction between LED ratio and salinity was detected for proline content. Findings of this study suggest that both salinity and light quality affect productivity, photosynthetic light use efficiency, and proline accumulation of M. crystallinum .

Polyamine oxidase 3 is involved in salt tolerance at the germination stage in rice

Soil salinity inhibits seed germination and reduces seedling survival rate, resulting in significant yield reductions in crops. Here, we report the identification of a polyamine oxidase, OsPAO3, conferring salt tolerance at the germination stage in rice (Oryza sativa L.), through map-based cloning approach. OsPAO3 is up-regulated under salt stress at the germination stage and highly expressed in various organs. Overexpression of OsPAO3 increases activity of polyamine oxidases, enhancing the polyamine content in seed coleoptiles. Increased polyamine may lead to the enhance of the activity of ROS-scavenging enzymes to eliminate over-accumulated H2O2 and to reduce Na+ content in seed coleoptiles to maintain ion homeostasis and weaken Na+ damage. These changes resulted in stronger salt tolerance at the germination stage in rice. Our findings not only provide a unique gene for breeding new salt-tolerant rice cultivars but also help to elucidate the mechanism of salt tolerance in rice.

Phytoglobin Expression Alters the Na+/K+ Balance and Antioxidant Responses in Soybean Plants Exposed to Na2SO4

Soybean (Glycine max) is an economically important crop which is very susceptible to salt stress. Tolerance to Na2SO4 stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin GmPgb1. Salt stress depressed several gas exchange parameters, including the photosynthetic rate, caused leaf damage, and reduced the water content and dry weights. Lower expression of respiratory burst oxidase homologs (RBOHB and D), as well as enhanced antioxidant activity, resulting from GmPgb1 overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H2O2-quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and GmPgb1-suppressing plants, overexpression of GmPgb1 attenuated the accumulation of foliar Na+ and exhibited a lower Na+/K+ ratio. These changes were attributed to the induction of the Na+ efflux transporter SALT OVERLY SENSITIVE 1 (SOS1) limiting Na+ intake and transport and the inward rectifying K+ channel POTASSIUM TRANSPORTER 1 (AKT1) required for the maintenance of the Na+/K+ balance.

Antioxidants as modulators of arsenic-induced oxidative stress tolerance in plants: An overview

Arsenic (As) is a highly toxic contaminant in the environment. Although both inorganic and organic types of arsenic exist in the environment, the most common inorganic forms of As that adversely affect plants are arsenite (As III) and arsenate (As V). Despite no evidence for As being essential for plant growth, exposure of roots to this element can cause its uptake primarily via transporters responsible for the transport of essential mineral nutrients. Arsenic exposure even at low concentrations disturbs the plant normal functioning via excessive generation of reactive oxygen species, a condition known as oxidative stress leading to an imbalance in the redox system of the plant. This is associated with considerable damage to the cell components thereby impairing normal cellular functions and activation of several cell survival and cell death pathways. To counteract this oxidative disorder, plants possess natural defense mechanisms such as chemical species and enzymatic antioxidants. This review considers how different types of antioxidants participate in the oxidative defense mechanism to alleviate As stress in plants. Since the underlying phenomena of oxidative stress tolerance are not yet fully elucidated, the potential for "Omics" technologies to uncover molecular mechanisms are discussed. Various strategies to improve As-induced oxidative tolerance in plants such as exogenous supplementation of effective growth regulators, protectant chemicals, transgenic approaches, and genome editing are also discussed thoroughly in this review.

Pseudomonas simiae augments the tolerance to alkaline bauxite residue in Atriplex canescens by modulating photosynthesis, antioxidant defense enzymes, and compatible osmolytes

In situ revegetation is effective in improving water-stable aggregation, preserving structural stability, and decreasing groundwater pollution to reduce the environmental risks posed by alkaline bauxite residue (ABR). Pseudomonas simiae, a plant growth-promoting rhizobacteria (PGPR), was used to promote Atriplex canescens growth challenged by ABR. The mechanism of P. simiae-induced plant growth promotion and tolerance against ABR stresses has been investigated. P. simiae was shown to alleviate ABR-induced stress in A. canescens by regulating photosynthesis and transpiration, inducing antioxidant defense, causing osmolyte accumulation, and altering plant morphology. Shoot dry weight, root dry weight, and root length of A. canescens were increased by 5.9%, 6.7%, and 11.5%, respectively, after inoculation with P. simiae for 60 days. Thus, it seems that P. simiae systemically regulated physiological processes in A. canescens favoring its growth under ABR treatments.

Root Na+ Content Negatively Correlated to Salt Tolerance Determines the Salt Tolerance of Brassica napus L. Inbred Seedlings

Soil salinization is a major environmental stressor that reduces the growth and yield of crops. Maintaining the balance of ions under salinity is vital for plant salt tolerance; however, little is known about the correlation between the salt tolerance of crops and the ion contents of their roots and shoots. Here, we investigated the poorly understood salt-tolerance mechanisms, particularly regarding ion contents (particularly Na+), in Brassica napus subsp. napus L., an agriculturally important species. Twenty B. napus inbred lines were randomly chosen from five salt-tolerance categories and treated with increasing concentrations of NaCl (0–200 mmol) for this work. We found that the root Na+ content is the most correlated limiting factor for the salt tolerance of B. napus; the higher the salt tolerance, the lower the root Na+ content. Correspondingly, the Ca2+/Na+ and K+/Na+ ratios of the roots were highly correlated with B. napus salt tolerance, indicating that the selective absorption ability of these ions by the roots and their translocation to the shoots play a pivotal role in this trait. These data provide a foundation for the further study of the molecular mechanisms underlying salt tolerance and for breeding salt-tolerant B. napus cultivars.

OsAPX1 Positively Contributes to Rice Blast Resistance

Ascorbate peroxidases (APXs) maintain cellular reactive oxygen species (ROS) homeostasis through their peroxidase activity. Here, we report that OsAPX1 also promotes ROS production such that a delicate cellular ROS homeostasis is achieved temporally after Magnaporthe oryzae infection. OsAPX1 specifically induces ROS production through increasing respiratory burst oxidase homologs (OsRBOHs) expression and can be inhibited by DPI, a ROS inhibitor. The time-course experiment data show that the simultaneous induction of OsAPX1 and OsRBOHs leads to ROS accumulation at an early stage; whereas a more durable expression of OsAPX1 leads to ROS scavenging at a later stage. By the temporal switching between ROS inducer and eliminator, OsAPX1 triggers an instant ROS burst upon M. oryzae infection and then a timely elimination of ROS toxicity. We find that OsAPX1 is under the control of the miR172a-OsIDS1 regulatory module. OsAPX1 also affects salicylic acid (SA) synthesis and signaling, which contribute to blast resistance. In conclusion, we show that OsAPX1 is a key factor that connects the upstream gene silencing and transcription regulatory routes with the downstream phytohormone and redox pathway, which provides an insight into the sophisticated regulatory network of rice innate immunity.

Maize Seed Germination Under Low-Temperature Stress Impacts Seedling Growth Under Normal Temperature by Modulating Photosynthesis and Antioxidant Metabolism

Spring maize is usually subjected to low-temperature stress during seed germination, which retards seedling growth later even under a suitable temperature. However, the mechanism underlying maize seed germination under low-temperature stress impacting seedling growth is still ambiguous. In this study, we used one low-temperature sensitive maize (SM) and one low-temperature resistance maize (RM) to investigate the mechanism. The results showed that the SM line had higher malondialdehyde content and lower total antioxidant capacity (TAC) and germination percentage than the RM line under low-temperature stress, indicating the vulnerability of SM line to low-temperature stress. Further transcriptome analysis revealed that seed germination under low-temperature stress caused the down-regulation of photosynthesis-related gene ontology terms in two lines. Moreover, the SM line displayed down-regulation of ribosome and superoxide dismutase (SOD) related genes, whereas genes involved in SOD and vitamin B6 were up-regulated in the RM line. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that photosynthesis and antioxidant metabolism-related pathways played essential roles in response to low-temperature stress during seed germination. The photosynthetic system displayed a higher degree of damage in the SM line. Both qRT-PCR and physiological characteristics experiments showed similar results with transcriptome data. Taken together, we propose a model for maize seed germination in response to low-temperature stress.

Impact of Nanomaterials on the Regulation of Gene Expression and Metabolomics of Plants under Salt Stress

Plant salinity resistance results from a combination of responses at the physiological, molecular, cellular, and metabolic levels. This article focuses on plant stress tolerance mechanisms for controlling ion homeostasis, stress signaling, hormone metabolism, anti-oxidative enzymes, and osmotic balance after nanoparticle applications. Nanoparticles are used as an emerging tool to stimulate specific biochemical reactions related to plant ecophysiological output because of their small size, increased surface area and absorption rate, efficient catalysis of reactions, and adequate reactive sites. Regulated ecophysiological control in saline environments could play a crucial role in plant growth promotion and survival of plants under suboptimal conditions. Plant biologists are seeking to develop a broad profile of genes and proteins that contribute to plant salt resistance. These plant metabolic profiles can be developed due to advancements in genomic, proteomic, metabolomic, and transcriptomic techniques. In order to quantify plant stress responses, transmembrane ion transport, sensors and receptors in signaling transduction, and metabolites involved in the energy supply require thorough study. In addition, more research is needed on the plant salinity stress response based on molecular interactions in response to nanoparticle treatment. The application of nanoparticles as an aspect of genetic engineering for the generation of salt-tolerant plants is a promising area of research. This review article addresses the use of nanoparticles in plant breeding and genetic engineering techniques to develop salt-tolerant crops.

GR24-mediated enhancement of salt tolerance and roles of H2O2 and Ca2+ in regulating this enhancement in cucumber

This study investigated the regulation of the exogenous strigolactone (SL) analog GR24 in enhancing the salt tolerance and the effects of calcium ion (Ca2+) and hydrogen peroxide (H2O2) on GR24's regulation effects in cucumber. The seedlings were sprayed with (1) distilled water (CK), (2) NaCl, (3) GR24, then NaCl, (4) GR24, then H2O2 scavenger, then NaCl, and (5) GR24, then Ca2+ blocker, then NaCl. The second true leaf was selected for biochemical assays. Under the salt stress, the exogenous GR24 maintained the ion balance, increased the activity of antioxidant enzymes, reduced the membrane lipid peroxidation, and increased the activities of catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), accompanied by a decrease in relative conductivity, an increase in the proline content, and elevated gene expression levels of antioxidant enzymes, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, calcium-dependent protein kinases (CDPKs), salt overly sensitive SOS1, CBL-interacting protein kinase 2 (CIPK2), and calcineurin B-like protein 3 (CBL3). Such protective effects triggered by GR24 were attenuated or almost abolished by ethylene glycol tetraacetic acid (EGTA), lanthanum chloride (LaCl3, Ca2+ channel blocker), diphenyleneiodonium (DPI, NADPH oxidase inhibitor), and dimethylthiourea (DMTU, hydroxyl radical scavenger). Our data suggest that exogenous GR24 is highly effective in alleviating salt-induced damages via modulating antioxidant capabilities and improving ionic homeostasis and osmotic balance and that H2O2 and Ca2+ are required for GR24-mediated enhancement of salt tolerance.

Physiological Adaptation of Three Wild Halophytic Suaeda Species: Salt Tolerance Strategies and Metal Accumulation Capacity

Understanding salt tolerance mechanisms in halophytes is critical for improving the world's agriculture under climate change scenarios. Herein, the physiological and metabolic responses of Suaeda monoica, Suaeda vermiculata, and Suaeda schimperi against abiotic stress in their natural saline environment on the east coast of the Red Sea were investigated. The tested species are exposed to different levels of salinity along with elemental disorders, including deficiency in essential nutrients (N&P in particular) and/or elevated levels of potentially toxic elements. The tested species employed common and species-specific tolerance mechanisms that are driven by the level of salinity and the genetic constitution of Suaeda species. These mechanisms include: (i) utilization of inorganic elements as cheap osmotica (Na+ in particular), (ii) lowering C/N ratio (S. monoica and S. schimperi) that benefits growth priority, (iii) efficient utilization of low soil N (S. vermiculata) that ensures survival priority, (v) biosynthesis of betacyanin (S. schimperi and S. vermiculata) and (vi) downregulation of overall metabolism (S. vermiculata) to avoid oxidative stress. Based on their cellular metal accumulation, S. monoica is an efficient phytoextractor of Cr, Co, Cu, Ni, and Zn, whereas S. vermiculata is a hyper-accumulator of Hg and Pb. S. schimperi is an effective phytoextractor of Fe, Hg, and Cr. These results highlight the significance of Suaeda species as a promising model halophyte and as phytoremediators of their hostile environments.

Spatial regulation of RBOHD via AtECA4-mediated recycling and clathrin-mediated endocytosis contributes to ROS accumulation during salt stress response but not flg22-induced immune response

Various environmental stresses can induce production of reactive oxygen species (ROS) to turn on signaling for proper responses to those stresses. Plasma membrane (PM)-localized respiratory burst oxidase homologs (RBOHs), in particular RBOHD, produce ROS via the post-translational activation upon abiotic and biotic stresses. Although the mechanisms of RBOHD activation upon biotic stress have been elucidated in detail, it remains elusive how salinity stress activates RBOHD. Here, we present evidence that trafficking of PM-localized RBOHD to endosomes and then its recycling back to the PM is critical for ROS accumulation upon salinity stress. ateca4 plants that were defective in recycling of proteins from endosomes to the PM and clc2-1 and chc2-1 plants that were defective in endocytosis showed a defect in salinity stress-induced ROS production. In addition, ateca4 plants showed a defect in transient accumulation of GFP:RBOHD to the PM at the early stage of salinity stress. By contrast, ateca4 plants showed no defect in the increase in the ROS level and accumulation of RBOHD to the PM upon flg22 treatment as wild-type plants. Based on these observations, we propose that factors involved in the trafficking machinery such as AtECA4 and clathrin are important players in salt stress-induced, but not flg22-induced, ROS accumulation.

The IbBBX24-IbTOE3-IbPRX17 module enhances abiotic stress tolerance by scavenging reactive oxygen species in sweet potato

Soil salinity and drought limit sweet potato yield. Scavenging of reactive oxygen species (ROS) by peroxidases (PRXs) is essential during plant stress responses, but how PRX expression is regulated under abiotic stress is not well understood. Here, we report that the B-box (BBX) family transcription factor IbBBX24 activates the expression of the class III peroxidase gene IbPRX17 by binding to its promoter. Overexpression of IbBBX24 and IbPRX17 significantly improved the tolerance of sweet potato to salt and drought stresses, whereas reducing IbBBX24 expression increased their susceptibility. Under abiotic stress, IbBBX24- and IbPRX17-overexpression lines showed higher peroxidase activity and lower H₂ O₂ accumulation compared with the wild-type. RNA sequencing analysis revealed that IbBBX24 modulates the expression of genes encoding ROS scavenging enzymes, including PRXs. Moreover, interaction between IbBBX24 and the APETALA2 (AP2) protein IbTOE3 enhances the ability of IbBBX24 to activate IbPRX17 transcription. Overexpression of IbTOE3 improved the tolerance of tobacco plants to salt and drought stresses by scavenging ROS. Together, our findings elucidate the mechanism underlying the IbBBX24-IbTOE3-IbPRX17 module in response to abiotic stress in sweet potato and identify candidate genes for developing elite crop varieties with enhanced abiotic stress tolerance.

Development of phytoremediator screening strategy and exploration of Pennisetum aided chromium phytoremediation mechanisms in soil

Screening of chromium (Cr) phytoremediators (i.e., hyperaccumulator plants and accumulation plants) is essential for the phytoremediation of Cr-contaminated soils but less tackled previously. In this study, we proposed a stepwise strategy for screening Cr phytoremediators and explored tolerance mechanism of the screened species. To achieve effective screening of Cr phytoremediators, seed germination, hydroponic, and pot experiment were performed sequentially, and an improved indicator system was established accordingly. Pennisetum was selected from nine plants, with its high growth rate and Cr remediation efficiency successfully demonstrated in the field. Antioxidant enzymes (i.e., superoxide dismutase (SOD) and catalase (CAT)) and photosynthesis under Cr stress were monitored for tracking the tolerance mechanism. Results showed that the enhanced SOD and CAT contributed to the strong tolerance of Pennisetum to Cr. The SOD and CAT were positively correlated with net photosynthetic rate (Pn), resulting in a phenomenon that Cr had no significant effect on Pn of Pennisetum even at 400 mg kg^-1. The research findings helped obtain powerful Cr phytoremediators, deepen our understanding of the tolerance mechanisms associated with phytoremediation, and eventually facilitate effective Cr removal in soil.

Functions of Redox Signaling in Pollen Development and Stress Response

Cellular redox homeostasis is crucial for normal plant growth and development. Each developmental stage of plants has a specific redox mode and is maintained by various environmental cues, oxidants, and antioxidants. Reactive oxygen species (ROS) and reactive nitrogen species are the chief oxidants in plant cells and participate in cell signal transduction and redox balance. The production and removal of oxidants are in a dynamic balance, which is necessary for plant growth. Especially during reproductive development, pollen development depends on ROS-mediated tapetal programmed cell death to provide nutrients and other essential substances. The deviation of the redox state in any period will lead to microspore abortion and pollen sterility. Meanwhile, pollens are highly sensitive to environmental stress, in particular to cell oxidative burst due to its peculiar structure and function. In this regard, plants have evolved a series of complex mechanisms to deal with redox imbalance and oxidative stress damage. This review summarizes the functions of the main redox components in different stages of pollen development, and highlights various redox protection mechanisms of pollen in response to environmental stimuli. In continuation, we also discuss the potential applications of plant growth regulators and antioxidants for improving pollen vigor and fertility in sustaining better agriculture practices.

Synergistic Association With Root Endophytic Fungi Improves Morpho-Physiological and Biochemical Responses of Chenopodium quinoa to Salt Stress

Symbiotic associations with microbes can contribute to mitigating abiotic environmental stress in plants. In this study, we investigated individual and interactive effects of two root endophytic fungal species on physiological and biochemical mechanisms of the crop Chenopodium quinoa in response to salinity. Fungal endophytes (FE) Talaromyces minioluteus and Penicillium murcianum, isolated from quinoa plants that occur naturally in the Atacama Desert, were used for endophyte inoculation. A greenhouse experiment was developed using four plant groups: (1) plants inoculated with T. minioluteus (E1+), (2) plants inoculated with P. murcianum (E2+), (3) plants inoculated with both fungal species (E1E2+), and (4) non-inoculated plants (E-). Plants from each group were then assigned to either salt (300 mM) or control (no salt) treatments. Differences in morphological traits, photosynthesis, stomatal conductance, transpiration, superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase, (POD), phenylalanine ammonia-lyase (PAL), phenolic content, and lipid peroxidation between plant groups under each treatment were examined. We found that both endophyte species significantly improved morphological and physiological traits, including plant height, number of shoots, photosynthesis, stomatal conductance, and transpiration, in C. quinoa in response to salt, but optimal physiological responses were observed in E1E2+ plants. Under saline conditions, endophyte inoculation improved SOD, APX, and POD activity by over 50%, and phenolic content by approximately 30%, with optimal enzymatic responses again observed in E1E2+ plants. Lipid peroxidation was significantly lower in inoculated plants than in non-inoculated plants. Results demonstrate that both endophyte species enhanced the ability of C. quinoa to cope with salt stress by improving antioxidative enzyme and non-enzyme systems. In general, both FE species interacting in tandem yielded better morphological, physiological, and biochemical responses to salinity in quinoa than inoculation by a single species in isolation. Our study highlights the importance of stress-adapted FE as a biological agent for mitigating abiotic stress in crop plants.

Early signalling processes in roots play a crucial role in the differential salt tolerance in contrasting Chenopodium quinoa accessions

Significant variation in epidermal bladder cell (EBC) density and salt tolerance (ST) exists amongst quinoa accessions, suggesting that salt sequestration in EBCs is not the only mechanism conferring ST in this halophyte. In order to reveal other traits that may operate in tandem with salt sequestration in EBCs and whether these additional tolerance mechanisms acted mainly at the root or shoot level, two quinoa (Chenopodium quinoa) accessions with contrasting ST and EBC densities (Q30, low ST with high EBC density versus Q68, with high ST and low EBC density) were studied. The results indicate that responses in roots, rather than in shoots, contributed to the greater ST in the accession with low EBC density. In particular, the tolerant accession had improved root plasma membrane integrity and K+ retention in the mature root zone in response to salt. Furthermore, superior ST in the tolerant Q68 was associated with faster and root-specific H2O2 accumulation and reactive oxygen species-induced K+ and Ca2+ fluxes in the root apex within 30 min after NaCl application. This was found to be associated with the constitutive up-regulation of the membrane-localized receptor kinases regulatory protein FERONIA in the tolerant accession. Taken together, this study shows that differential root signalling events upon salt exposure are essential for the halophytic quinoa; the failure to do this limits quinoa adaptation to salinity, independently of salt sequestration in EBCs.

Changes of pollen viability after preservation of Paeonia lactiflora in different provenances

Pollen contains all the haploid genetic information of species and is of great significance to preserve germplasm resources safely and effectively. The acquisition of high quality materials is a very important step in germplasm preservation. This study compared the viability and physiological condition of Paeonia lactiflora pollen from several provenances after preservation, to explore the effect of provenance difference on pollen viability and physiological responses after preservation. The results showed that: the pollen viability of two cultivars were significantly different in provenances after preserved at -20 °C or liquid nitrogen (LN) for 3 months, the pollen viability of 'Fen Yu Nu' showed Lanzhou > Beijing > Luoyang > Heze, while the pollen viability of 'Zi Feng Chao Yang' showed Luoyang > Beijing > Heze. Similarly, the oxidative stress levels of the Paeonia lactiflora pollen after preservation with LN or -20 °C were also significantly different among the provenances, and there was a relationship between the viability and the oxidative stress levels produced by the provenances differences. Reactive oxygen species (ROS) content, malondialdehyde (MDA) content, superoxide dismutase (SOD) activity and glutamate reductase (GR) activity in pollen from different provenances were contrary to the changes of viability; while catalase (CAT), ascorbic acid peroxidase (APX), ascorbic acid (AsA) and glutathione (GSH) were consistent with the changes of viability. The results indicated that the responses of antioxidant systems of two cultivars pollen to preservation with LN or -20 °C were different in provenances, and this difference was one of the reasons for the different viability of pollen after preservation with LN or -20 °C.

Rewilding staple crops for the lost halophytism: Toward sustainability and profitability of agricultural production systems

Abiotic stress tolerance has been weakened during the domestication of all major staple crops. Soil salinity is a major environmental constraint that impacts over half of the world population; however, given the increasing reliance on irrigation and the lack of available freshwater, agriculture in the 21st century will increasingly become saline. Therefore, global food security is critically dependent on the ability of plant breeders to create high-yielding staple crop varieties that will incorporate salinity tolerance traits and account for future climate scenarios. Previously, we have argued that the current agricultural practices and reliance on crops that exclude salt from uptake is counterproductive and environmentally unsustainable, and thus called for a need for a major shift in a breeding paradigm to incorporate some halophytic traits that were present in wild relatives but were lost in modern crops during domestication. In this review, we provide a comprehensive physiological and molecular analysis of the key traits conferring crop halophytism, such as vacuolar Na⁺ sequestration, ROS desensitization, succulence, metabolic photosynthetic switch, and salt deposition in trichomes, and discuss the strategies for incorporating them into elite germplasm, to address a pressing issue of boosting plant salinity tolerance.

Genome-wide characterization and functional analysis of class III peroxidase gene family in soybean reveal regulatory roles of GsPOD40 in drought tolerance

Class III peroxidases (PODs) are plant-specific glycoproteins, that play essential roles in various plant physiological processes and defence responses. To date, scarce information is available about the POD gene family in soybean. Hence, the present study is the first comprehensive report about the genome-wide characterization of GmPOD gene family in soybean (Glycine max L.). Here, we identified a total of 124 GmPOD genes in soybean, that are unevenly distributed across the genome. Phylogenetic analysis classified them into six distinct sub-groups (A-F), with one soybean specific subgroup. Exon-intron and motif analysis suggested the existence of structural and functional diversity among the sub-groups. Duplication analysis identified 58 paralogous gene pairs; segmental duplication and positive/Darwinian selection were observed as the major factors involved in the evolution of GmPODs. Furthermore, RNA-seq analysis revealed that 23 out of a total 124 GmPODs showed differential expression between drought-tolerant and drought-sensitive genotypes under stress conditions; however, two of them (GmPOD40 and GmPOD42) revealed the maximum deregulation in all contrasting genotypes. Overexpression (OE) lines of GsPOD40 showed considerably higher drought tolerance compared to wild type (WT) plants under stress treatment. Moreover, the OE lines showed enhanced photosynthesis and enzymatic antioxidant activities under drought stress, resulting in alleviation of ROS induced oxidative damage. Hence, the GsPOD40 enhanced drought tolerance in soybean by regulating the key physiological and biochemical pathways involved in the defence response. Lastly, the results of our study will greatly assist in further functional characterization of GsPODs in plant growth and stress tolerance in soybean.

Genetic and Molecular Mechanisms Conferring Heat Stress Tolerance in Tomato Plants

Climate change is a major threat to global food security. Changes in climate can directly impact food systems by reducing the production and genetic diversity of crops and their wild relatives, thereby restricting future options for breeding improved varieties and reducing the ability to adapt crops to future challenges. The global surface temperature is predicted to rise by an average of 0.3°C during the next decade, and the Paris Agreement (Paris Climate Accords) aims to limit global warming to below an average of 2°C, preferably to 1.5°C compared to pre-industrial levels. Even if the goal of the Paris Agreement can be met, the predicted rise in temperatures will increase the likelihood of extreme weather events, including heatwaves, making heat stress (HS) a major global abiotic stress factor for many crops. HS can have adverse effects on plant morphology, physiology, and biochemistry during all stages of vegetative and reproductive development. In fruiting vegetables, even moderate HS reduces fruit set and yields, and high temperatures may result in poor fruit quality. In this review, we emphasize the effects of abiotic stress, especially at high temperatures, on crop plants, such as tomatoes, touching upon key processes determining plant growth and yield. Specifically, we investigated the molecular mechanisms involved in HS tolerance and the challenges of developing heat-tolerant tomato varieties. Finally, we discuss a strategy for effectively improving the heat tolerance of vegetable crops.

Abscisic Acid Mediates Grafting-Induced Cold Tolerance of Watermelon via Interaction With Melatonin and Methyl Jasmonate

Grafting is widely used to increase plant defense responses to various stresses. Grafting-induced cold tolerance is associated with the increase of the antioxidant potential of plants; however, the underlying mechanisms remain unclear. Here, we found that pumpkin rootstocks promote antioxidant enzyme activities and alleviate cold-induced oxidative damage, accompanied by increased abscisic acid (ABA), melatonin, and methyl jasmonate (MeJA) levels in leaves. Increased ABA accumulation in leaves was attributed partly to the increased ABA levels in rootstocks. ABA induced antioxidant enzymes activities and the accumulation of melatonin and MeJA, while inhibition of ABA synthesis blocked the rootstock-induced antioxidant activity and the accumulation of melatonin and MeJA under cold stress. Melatonin and MeJA application also enhanced ABA accumulation in leaves after cold exposure, whereas inhibition of melatonin or MeJA synthesis attenuated the rootstock-induced increase of ABA. Moreover, melatonin and MeJA application alleviated cold-induced oxidative stress, but inhibition of melatonin or MeJA synthesis lowered the rootstock- or ABA-induced antioxidant potential and tolerance to cold. These findings indicate that ABA plays an important role in the grafting-induced cold tolerance by promoting the accumulation of melatonin and MeJA, which in turn, promote ABA accumulation, forming a positive feedback loop.

Genome-Wide Identification, Characterization and Expression Analysis of the CIPK Gene Family in Potato (Solanum tuberosum L.) and the Role of StCIPK10 in Response to Drought and Osmotic Stress

The potato (Solanum tuberosum L.), one of the most important food crops worldwide, is sensitive to environmental stresses. Sensor–responder complexes comprising calcineurin B-like (CBL) proteins and CBL-interacting protein kinases (CIPKs) not only modulate plant growth and development but also mediate numerous stress responses. Here, using a Hidden Markov Model and BLAST searches, 27 CIPK genes were identified in potato and divided into five groups by phylogenetic analysis and into two clades (intron-poor and intron-rich) by gene structure analysis. Quantitative reverse-transcription PCR (qRT-PCR) assays revealed that StCIPK genes play important roles in plant growth, development and abiotic stress tolerance. Up-regulated expression of StCIPK10 was significantly induced by drought, PEG6000 and ABA. StCIPK10 enhances both the ability of potato to scavenge reactive oxygen species and the content of corresponding osmoregulation substances, thereby strengthening tolerance to drought and osmotic stress. StCIPK10 is located at the intersection between the abscisic acid and abiotic stress signaling pathways, which control both root growth and stomatal closure in potato. In addition, StCIPK10 interacts with StCBL1, StCBL4, StCBL6, StCBL7, StCBL8, StCBL11 and StCBL12, and is specifically recruited to the plasma membrane by StCBL11.

Oxidative damage, antioxidant mechanism and gene expression in tomato responding to salinity stress under in vitro conditions and application of iron and zinc oxide nanoparticles on callus induction and plant regeneration

BACKGROUND

Salinity is one of the most challenging abiotic stresses restricting the growth of plants. In vitro screening will increase the efficiency and speed of salinity tolerant genotypes identifications. The response of four tomato cultivars under salinity was analyzed in vitro to evaluate the seedlings growth, biochemical, and gene expression responses as well as the effect of nano zinc and iron on callus induction and plant regeneration.

RESULTS

The results showed that an increase in salinity stress in the medium decreased the germination percentage, fresh and dry weight of shoot, root length, chlorophyll a, b and carotenoids content, K and Ca content, and on the other hand, Na content was increased. MDA content ('Nora', 'PS-10', 'Peto' and 'Roma': 1.71, 1.78, 1.66 and 2.16 folds, respectively), electrolyte leakage ('PS-10': 33.33%; 'Roma': 56.33%), were increased with salinity of 100 mM compared to control. Proline content was increased in 50 mM NaCl (10.8 fold). The most activity of antioxidant enzymes including CAT, SOD, APX, GPX, and GR was observed in the 'PS-10' cultivar, and the lowest activity of these enzymes was observed in 'Roma' under salinity stress. The AsA and GSH were decreased and DHA and GSSG were increased with the increased intensity of salinity. The relative expression of SOD, APX, and GR genes varied in different cultivars at different salinity concentrations. The most percentage of callus induction was observed with applying iron oxide nanoparticles, and the most regeneration rate was recorded using zinc oxide nanoparticles.

CONCLUSION

The results showed that salt-tolerant cultivars such as 'PS-10' with better osmotic adjustment, are suitable candidates for the future production and breeding programs. The use of nutrient nanoparticles under salinity stress for different tomato cultivars increased their performance.

Gene regulation at transcriptional and post-transcriptional levels to combat salt stress in plants

Soil salinity is a major challenge that will be faced more and more by human population in the near future. Higher salt concentrations in the soil limit the growth and production of crops, which poses serious threats to global food production. Various plant breeding approaches have been followed in the past which are reported to reduce the effect of salt stress by inducing the level of protective metabolites like osmolytes and antioxidants. Conventional breeding approaches are time-consuming and not cost-effective. In recent times, genetic engineering has been largely followed to confer salt tolerance through introgressions of single transgenes or stacking multiple transgenes. However, most of such works are limited only at the laboratory level and field trials are still awaited to prove the long-term efficacy of such transgenics. In this review, we attempt to present a broad overview of the current strategies undertaken to develop halophytic and salt-tolerant crops. The salt-induced damages in the plants are highlighted, followed by representing the novel traits, associated with salt stress, which can be used for engineering salt tolerance in glycophytic crops. Additionally, the role of transcriptional and epigenetic regulation in plants for amelioration of salt-induced damages has been reviewed. The role of post-transcriptional mechanisms such as microRNA regulation, genome editing and alternative splicing, during salt stress, and their implications in the development of salt-tolerant crops are also discussed. Finally, we present a short overview about the role of ion transporters and rhizobacteria in the engineering of salt tolerance in crop species.

The halophyte gene ScVTC2 confers resistance to oxidative stress via AsA-mediated photosynthetic enhancement

Various abiotic stresses commonly cause excessive production of reactive oxygen species (ROS) and result in oxidative stress, which challenges the physiological homeostasis of plants. Maintaining a delicate balance between ROS generation and removal is critical for plants to cope with stressful environments. Suaeda corniculata is a typical euhalophyte with strong tolerance to salt stress, but its mechanism of ROS detoxification to prevent oxidative stress is unknown. Here, a combined analysis of RNA-Seq and photosynthetic assays was performed on S. corniculata under oxidative stress to uncover the underlying mechanism that modulates oxidative tolerance. Our results showed that all genes involved in the pathway of ROS scavenging, especially the AsA-GSH pathway, were highly enriched under oxidative stress. Notably, VTC2 (GGPase), which functions in the L-galactose pathway of AsA synthesis, was significantly upregulated. Arabidopsis transgenic plants with heterologous expression of ScVTC2 showed elevated AsA and increased tolerance to oxidative stress. Furthermore, ScVTC2 also established better photosynthetic capacity in these plants upon oxidative treatment. Thus, ScVTC2 not only functioned as an effective ROS scavenger but also as a protector of the photosynthetic apparatus in S. corniculata and allowed plants to respond to and tolerate oxidative stress.

Biosurfactant production by halophilic yeasts isolated from extreme environments in Botswana

Nine morphologically distinct halophilic yeasts were isolated from Makgadikgadi and Sua pans, as pristine and extreme environments in Botswana. Screening for biosurfactant production showed that Rhodotorula mucilaginosa SP6 and Debaryomyces hansenii MK9 exhibited the highest biosurfactant activity using Xanthocercis zambesiaca seed powder as a novel and alternative inexpensive carbon substrate. Chemical characterization of the purified biosurfactants by Fourier Transform Infra-Red spectroscopy suggested that the biosurfactant from R. mucilaginosa SP6 was a rhamnolipid-type whereas the biosurfactant from D. hansenii MK9 was a sophorolipid-type. The two biosurfactants exhibited antimicrobial activities against eight pathogenic bacteria and fungal strains (Proteus vulgaris, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Micrococcus luteus, Cryptococcus neoformans, Candida albicans and Aspergilus niger). The sophorolopid-type biosurfactant was found to be the most potent among the antimicrobial drug resistant strains tested. The findings open up prospects for the development of environmentally friendly antimicrobial drugs that use an inexpensive source of carbon to reduce the costs associated with the production of biosurfactants.

Analysis of Salinity Tolerance in Tomato Introgression Lines Based on Morpho-Physiological and Molecular Traits

The development of salt-tolerant tomato genotypes is a basic requirement to overcome the challenges of tomato production under salinity in the field or soil-free farming. Two groups of eight tomato introgression lines (ILs) each, were evaluated for salinity tolerance. Group-I and the group-II resulted from the following crosses respectively: Solanum lycopersicum cv-6203 × Solanum habrochaites and Solanum lycopersicum M82 × Solanum pennellii. Salt tolerance level was assessed based on a germination percentage under NaCl (0, 75, 100 mM) and in the vegetative stage using a hydroponic growing system (0, 120 mM NaCl). One line from group I (TA1648) and three lines from group II (IL2-1, IL2-3, and IL8-3) were shown to be salt-tolerant since their germination percentages were significantly higher at 75 and 100 mM NaCl than that of their respective cultivated parents cvE6203 and cvM82. Using the hydroponic system, IL TA1648 and IL 2-3 showed the highest value of plant growth traits and chlorophyll concentration. The expression level of eight salt-responsive genes in the leaves and roots of salt-tolerant ILs (TA1648 and IL 2-3) was estimated. Interestingly, SlSOS1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated in leaves of both TA1648 and IL 2-3 genotypes under NaCl stress. While SlHKT1.1, SlNHX2, SlNHX4, and SlERF4 genes were upregulated under salt stress in the roots of both TA1648 and IL 2-3 genotypes. Furthermore, SlSOS2 and SlSOS3 genes were upregulated in TA1648 root and downregulated in IL 2-3. On the contrary, SlSOS1 and SlHKT1.2 genes were upregulated in the IL 2-3 root and downregulated in the TA1648 root. Monitoring of ILs revealed that some of them have inherited salt tolerance from S. habrochaites and S. pennellii genetic background. These ILs can be used in tomato breeding programs to develop salt-tolerant tomatoes or as rootstocks in grafting techniques under saline irrigation conditions.

BpTCP3 Transcription Factor Improves Salt Tolerance of Betula platyphylla by Reducing Reactive Oxygen Species Damage

The plant-specific transcription factors TEOSINTE BRANCHED1/CYCLO IDEA/PROLIFERATING CELL FACTOR1 (TCP) act as developmental regulators that have many roles in the growth and development processes throughout the entire life span of plants. TCP transcription factors are responsive to endogenous and environmental signals, such as salt stress. However, studies on the role of the TCP genes in salt stress response have rarely focused on woody plants, especially forest trees. In this study, the BpTCP3 gene, a CYC/TB1 subfamily member, isolated from Betula platyphylla Sukaczev, was significantly influenced by salt stress. The β-glucuronidase (GUS) staining analysis of transgenic B. platyphylla harboring the BpTCP3 promoter fused to the reporter gene GUS (pBpTCP3::GUS) further confirmed that the BpTCP3 gene acts a positive regulatory position in salt stress. Under salt stress, we found that the BpTCP3 overexpressed lines had increased relative/absolute high growth but decreased salt damage index, hydrogen peroxide (H2O2), and malondialdehyde (MDA) levels versus wild-type (WT) plants. Conversely, the BpTCP3 suppressed lines exhibited sensitivity to salt stress. These results indicate that the BpTCP3 transcription factor improves the salt tolerance of B. platyphylla by reducing reactive oxygen species damage, which provides useful clues for the functions of the CYC/TB1 subfamily gene in the salt stress response of B. platyphylla.

Integrated de novo Analysis of Transcriptional and Metabolic Variations in Salt-Treated Solenostemma argel Desert Plants

Solenostemma argel (Delile) Hayne is a desert plant that survives harsh environmental conditions with several vital medicinal properties. Salt stress is a major constraint limiting agricultural production around the globe. However, response mechanisms behind the adaptation of S. argel plants to salt stress are still poorly understood. In the current study, we applied an omics approach to explore how this plant adapts to salt stress by integrating transcriptomic and metabolomic changes in the roots and leaves of S. argel plants under salt stress. De novo assembly of transcriptome produced 57,796 unigenes represented by 165,147 transcripts/isoforms. A total of 730 differentially expressed genes (DEGs) were identified in the roots (396 and 334 were up- and down-regulated, respectively). In the leaves, 927 DEGs were identified (601 and 326 were up- and down-regulated, respectively). Gene ontology and Kyoto Encyclopedia of Genes And Genomes pathway enrichment analyses revealed that several defense-related biological processes, such as response to osmotic and oxidative stress, hormonal signal transduction, mitogen-activated protein kinase signaling, and phenylpropanoid biosynthesis pathways are the potential mechanisms involved in the tolerance of S. argel plants to salt stress. Furthermore, liquid chromatography-tandem mass spectrometry was used to detect the metabolic variations of the leaves and roots of S. argel under control and salt stress. 45 and 56 critical metabolites showed changes in their levels in the stressed roots and leaves, respectively; there were 20 metabolites in common between the roots and leaves. Differentially accumulated metabolites included amino acids, polyamines, hydroxycinnamic acids, monolignols, flavonoids, and saccharides that improve antioxidant ability and osmotic adjustment of S. argel plants under salt stress. The results present insights into potential salt response mechanisms in S. argel desert plants and increase the knowledge in order to generate more tolerant crops to salt stress.

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.

Na2SO4 and NaCl salts differentially modulate the antioxidant systems in the highly stress tolerant halophyte Prosopis strombulifera

Prosopis strombulifera (Lam.) Benth. is a halophytic shrub abundant in high-salinity areas in central Argentina, with high tolerance against NaCl but strong growth inhibition by Na₂SO₄. In the present study, the modulation of the antioxidant systems (enzymatic and non-enzymatic components) was analyzed under different salt treatments (NaCl, Na₂SO₄ and the iso-osmotic mixture) in hydroponic cultivation. Na₂SO₄-treated plants showed strong indications of oxidative stress (H₂O₂ and O₂-• increase). Modifications in antioxidant enzymes activities were observed mainly under Na₂SO₄ treatment, where CAT seems to play an important role in early detoxification of H₂O₂ in roots, whereas SOD and APX have a predominant role in leaves. As part of the non-enzymatic system, 21 compounds were identified in leaves, being polyphenols the most abundant. Control plants contained the major variety of detected phytochemicals (14). Na₂SO₄-treated plants contained 10 compounds and NaCl-treated plants nine compounds, but with a different profile. NaCl-treated plants showed the highest antioxidant capacity. Our findings confirm that different types of salt treatments provoke a differential modulation of the antioxidant systems. Polyphenols and other ROS-detoxifying compounds, in a joint action with the enzymatic antioxidant system, are proposed to have a fundamental role in the cellular protection of P. strombulifera plants under severe oxidative stress. Our findings also highlight the potential of this halophyte as a valuable source of bioactive compounds with high antioxidant activity and health benefits.

Rapid Accumulation of Proline Enhances Salinity Tolerance in Australian Wild Rice Oryza australiensis Domin

Proline has been reported to play an important role in helping plants cope with several stresses, including salinity. This study investigates the relationship between proline accumulation and salt tolerance in an accession of Australian wild rice Oryza australiensis Domin using morphological, physiological, and molecular assessments. Seedlings of O. australiensis wild rice accession JC 2304 and two other cultivated rice Oryza sativa L. cultivars, Nipponbare (salt-sensitive), and Pokkali (salt-tolerant), were screened at 150 mM NaCl for 14 days. The results showed that O. australiensis was able to rapidly accumulate free proline and lower osmotic potential at a very early stage of salt stress compared to cultivated rice. The qRT-PCR result revealed that O. australiensis wild rice JC 2304 activated proline synthesis genes OsP5CS1, OsP5CS2, and OsP5CR and depressed the expression of proline degradation gene OsProDH as early as 1 h after exposure to salinity stress. Wild rice O. australiensis and Pokkali maintained their relative water content and cell membrane integrity during exposure to salinity stress, while the salt-sensitive Nipponbare failed to do so. An analysis of the sodium and potassium contents suggested that O. australiensis wild rice JC 2304 adapted to ionic stress caused by salinity by maintaining a low Na+ content and low Na+/K+ ratio in the shoots and roots. This demonstrates that O. australiensis wild rice may use a rapid accumulation of free proline as a strategy to cope with salinity stress.

Differential Regulation of NAPDH Oxidases in Salt-Tolerant Eutrema salsugineum and Salt-Sensitive Arabidopsis thaliana

Reactive oxygen species (ROS) signalling is crucial in modulating stress responses in plants, and NADPH oxidases (NOXs) are an important component of signal transduction under salt stress. The goal of this research was to investigate whether the regulation of NOX-dependent signalling during mild and severe salinity differs between the halophyte Eutrema salsugineum and the glycophyte Arabidopsis thaliana. Gene expression analyses showed that salt-induced expression patterns of two NOX genes, RBOHD and RBOHF, varied between the halophyte and the glycophyte. Five days of salinity stimulated the expression of both genes in E. salsugineum leaves, while their expression in A. thaliana decreased. This was not accompanied by changes in the total NOX activity in E. salsugineum, while the activity in A. thaliana was reduced. The expression of the RBOHD and RBOHF genes in E. salsugineum leaves was induced by abscisic acid (ABA) and ethephon spraying. The in silico analyses of promoter sequences of RBOHD and RBOHF revealed multiple cis-acting elements related to hormone responses, and their distribution varied between E. salsugineum and A. thaliana. Our results indicate that, in the halophyte E. salsugineum, the maintenance of the basal activity of NOXs in leaves plays a role during acclimation responses to salt stress. The different expression patterns of the RBOHD and RBOHF genes under salinity in E. salsugineum and A. thaliana point to a modified regulation of these genes in the halophyte, possibly through ABA- and/or ethylene-dependent pathways.

Assessment of phytoremediation capacity of three halophytes: Suaeda monoica, Tamarix indica and Cressa critica

Halophyte is a distinctive group of plants that can survive, even well flourish, at a concentration of Na⁺ and Cl^- ions along with heavy metals that would be lethal to most of the agricultural crop species. These capabilities make certain halophytes good contenders for phytoremediation through phytoextraction or phytostabilization of the salt and heavy metals (HMs) in polluted soils. Thus, the present study elucidates the phytoextraction capacity of three halophytes (Suaeda monoica, Tamarix indica and Cressa critica) growing in saline soil (EC 112 ds m^-1), with higher level of HMs rather than a cultivated soil. The accumulation of ions in above-ground tissue was determined in the all three studied plants, considering the fact that maintaining a stable cytosolic Na⁺/K⁺ ratio has become a crucial salinity tolerance mechanism. The higher salinity of soil resulted in high level of Na⁺ ions in leaves, increased synthesis of osmolyte components and robust antioxidant activities to combat the oxidative stress. As whole, changes in cellular metabolites were determined by using FT-IR spectroscopy, evident as differential FT-IR profiles in both leaves and stem specific to these metabolites. The considerable amounts of HMs accumulation including Zn, Fe, Mn, Cu, Cr, and Cd with highest being Fe in above-ground tissue of all three studied halophytes were obtained. These preliminary findings represent S. monoica, T. indica and C. cretica as potent phytoremediation plant using phytosequestration to accumulate HMs. The present study project a light on the use of these three plants in reclamation of degraded saline soils.

Increasing salinity leads to differential growth and H2O2 homeostasis in plants produced from heteromorphic seeds of the succulent halophyte Arthrocnemum indicum

Information about responses of plants grown from heteromorphic seeds is limited and inconclusive. This is especially true of subtropical halophytes where such studies have yet to be published. Therefore, growth, water-relations, and oxidative stress mitigation of plants germinated from the heteromorphic seeds of the succulent halophyte Arthrocnemum indicum under increasing (0, 300, and 900 mM NaCl) salinity were studied. Growth of plants from only small seeds was stimulated in moderate (300 mM NaCl) salinity. High (900 mM NaCl) salinity inhibited the growth of plants emerged from both small and large sized seeds. Plants germinating from both seed sizes demonstrated similar patterns of osmotic adjustment and did not develop signs of oxidative damage under increasing salinity. However, the magnitude of hydrogen peroxide and antioxidant responses differed between plant types. Under moderate salinity, plants from small seeds showed constitutive activities of most antioxidant enzymes (except superoxide dismutase) and levels of non-enzymatic antioxidants (except ascorbate). Conversely, a decline in activities of most antioxidant enzymes and levels of most non-enzymatic antioxidants occurred in plants from large seeds. While under high salinity, increased ascorbate peroxidase, glutathione, and polyphenol levels, along with unaffected ascorbate and superoxide dismutase levels, occurred in plants from small seeds. In plants from large seeds, there were increased ascorbate and polyphenol levels, but changes to the ascorbate peroxidase levels were not observed. These results thus indicate differential growth and hydrogen peroxide homeostasis in A. indicum plants emerged from heteromorphic seeds.

Tissue-specificity of ROS-induced K+ and Ca2+ fluxes in succulent stems of the perennial halophyte Sarcocornia quinqueflora in the context of salinity stress tolerance

The ability of halophytes to thrive under saline conditions implies efficient ROS detoxification and signalling. In this work, the causal relationship between key membrane transport processes involved in maintaining plant ionic homeostasis and oxidative stress tolerance was investigated in a succulent perennial halophyte Sarcocornia quinqueflora. The flux responses to oxidative stresses induced by either hydroxyl radicals (OH^•) or hydrogen peroxide (H₂O₂) were governed largely by (1) the type of ROS applied; (2) the tissue-specific origin and function (parenchymatic or chlorenchymatic); and (3) the tissue location in respect to the suberized endodermal barrier. The latter implied significant differences in responses between outer (water storage-WS; palisade tissue-Pa) and inner (internal photosynthetic layer-IP; stele parenchyma-SP) stem tissues. The ability of the cell to retain K⁺ under OH^• stress varied between different tissues and was ranked in the following descending order: WS>Pa>IP>SP. OH^• always led to Ca²⁺ influx in all stem tissues, while treatment with H₂O₂ induced tissue-specific Ca²⁺ "signatures". The inner/outer K⁺ ratio was the highest (~2.6) under the optimum NaCl dosage (200 mM) in comparison to non-saline (~0.4) and severe (800 mM; ~0.7) conditions, implying that a higher K⁺ concentration in the inner tissues is important for optimum growth. The overall results demonstrate a clear link between plant anatomical structure and ability of its tissues to maintain ionic homeostasis, via modulating their ROS sensitivity.

Heavy metal stress in rice: Uptake, transport, signaling, and tolerance mechanisms

Heavy metal contamination of agricultural fields has become a global concern as it causes a direct impact on human health. Rice is the major food crop for almost half of the world population and is grown under diverse environmental conditions, including heavy metal-contaminated soil. In recent years, the impact of heavy metal contamination on rice yield and grain quality has been shown through multiple approaches. In this review article, different aspects of heavy metal stress, that is uptake, transport, signaling and tolerance mechanisms, are comprehensively discussed with special emphasis on rice. For uptake, some of the transporters have specificity to one or two metal ions, whereas many other transporters are able to transport many different ions. After uptake, the intercellular signaling is mediated through different signaling pathways involving the regulation of various hormones, alteration of calcium levels, and the activation of mitogen-activated protein kinases. Heavy metal stress signals from various intermediate molecules activate various transcription factors, which triggers the expression of various antioxidant enzymes. Activated antioxidant enzymes then scavenge various reactive oxygen species, which eventually leads to stress tolerance in plants. Non-enzymatic antioxidants, such as ascorbate, metalloids, and even metal-binding peptides (metallothionein and phytochelatin) can also help to reduce metal toxicity in plants. Genetic engineering has been successfully used in rice and many other crops to increase metal tolerance and reduce heavy metals accumulation. A comprehensive understanding of uptake, transport, signaling, and tolerance mechanisms will help to grow rice plants in agricultural fields with less heavy metal accumulation in grains.

Modulation of salinity impact on early seedling stage via nano-priming application of zinc oxide on rapeseed (Brassica napus L.)

Salinity stress negatively affects the plant's developmental stages through micronutrient imbalance. As an essential micronutrient, ZnO can substitute Na⁺ absorption under saline conditions. Therefore, nanoparticles as technological innovation, improve the plant growth efficiency under biotic and abiotic stresses. Nano-priming has become widely applicable in agricultural research during the last decade. The current study was conducted to highlight the impact of ZnONPs priming on seedling biological processes under 150 mM of NaCl using two rapeseed cultivars during the early seedling stage. All concentrations of ZnONPs increased the germination parameters i.e., FG%, GR, VI (I), and VI (II). Meanwhile, the high concentration (ZnO 100%) showed the highest increase in shoot length (9.60% and 25.63%), root length (41.64% and 48.17%) for Yang You 9 and Zhong Shuang 11 over hydro-priming, respectively, as well as biomass. Additionally, nano-priming improved the proline, soluble sugar, and soluble protein contents as a result of osmotic protection modulation. Moreover, nano-priming alleviated ROS and biosynthesis pigments through the reduction of accumulated (H₂O₂) and (O₂^-), and chlorophyll degradation, respectively, also enhanced antioxidant adjustment via improving the plant defense system. Nano-priming substituted the Na⁺ by Zn²⁺, K⁺, and Ca²⁺, and compensated the deficit of micronutrients, thus reduced the Na⁺ toxicity in the cell cytosol. To track the effects of priming during seed imbibition, it noticed that ZnO 100% and ZnO 100%+S increased the Linoleic and Linolenic acids among the studied fatty acids composition by 12.02%, 7.59%, 13.27%, and 10.38% (Yang You 9), 7.42%, 2.77%, 2.93%, and 1.49% (Zhong Shuang 11) over the hydro-priming, respectively. Moreover, the gene expression patterns of BnCAM and BnPER reflected the enhancement of germination levels, notably under the influence of ZnO 100% priming, which increased the level of BnCAM by 70.42% and 111.9% in Yang You 9 and Zhong Shuang 11, respectively. Consequently, ZnO nano-priming enhanced the seedling development through the biosynthesis of pigments, osmotic protection, reduction of ROS accumulation, adjustment of antioxidant enzymes, and improvement of the nutrient absorption, thus enhancing the economic yield under saline conditions.

Chemical Profile, Antioxidant, Antimicrobial, and Anticancer Activities of the Water-Ethanol Extract of Pulicaria undulata Growing in the Oasis of Central Saudi Arabian Desert

Pulicaria undulata (L.) C. A. Mey has multiple uses as part of the traditional medicament, and several biological activities of the plant have been corroborated in the scientific literature. The current work evaluates the phytochemical constituents and biological properties of the water-ethanol extract of the P. undulata growing in Qassim, the central arid regions of the Kingdom of Saudi Arabia. Qualitative UPLC-ESIQ-TOF analysis identified 27 compounds belonging to the phenolics, flavonoids, triterpenes, coumarins, and of fatty acids chemical classes. The quantitative analysis exhibited 33.3 mg/g GAE (Gallic Acid Equivalents), and 10.8 mg/g QE (Quercetin Equivalents) of the phenolics and flavonoids in the plant’s concentrated (to dryness) water-ethanol extract. The trace elements analysis of the plant’s dry powder established the presence of copper (20.13 µg/kg), and zinc (68.2 µg/kg) in the higher levels of occurrences. In terms of the antioxidant potential of the plant’s extract, the ferric-reducing, and free-radicals scavenging activities were recorded at 47.11 mg/g, and 19.13 mg/g equivalents of the concentrated to dryness water-ethanol extract of the plant. The water-ethanol extract of P. undulata also exhibited antimicrobial activity against the tested Gram-positive bacteria, while no activity was observed against the tested Gram-negative bacteria, or the fungi. The MIC (minimum inhibitory concentration) values were in the range of 49 to 1563 µg/mL, whereas the MBC (minimum bactericidal concentration) values ranged from 49 to 3125 µg/mL, against the tested Gram-positive bacteria. The P. undulata water-ethanol extract also exhibited potent cytotoxic effects with the IC₅₀ value at 519.2 µg/mL against the MCF-7 breast cancer cell-lines, followed by the anticancer activity of erythroleukemic cell-lines, K562 at 1212 µg/mL, and pancreatic cell-lines, PANC-1, at 1535 µg/mL, as compared to the normal fibroblast cells (4048 µg/mL). The Annexin-V assay demonstrated that, as the P. undulata extract’s dose increased from IC₅₀ to twice of the IC₅₀, the percentage of the necrosis was found to be increased in the late apoptosis stage of the cancer cells. These data confirmed the P. undulata extract’s ability to inhibit several human cancer cell lines’ growth in comparison to other local halophytes. The antimicrobial activity of the plant was also confirmed.

Regulation of Reactive Oxygen Species and Antioxidant Defense in Plants under Salinity

The generation of oxygen radicals and their derivatives, known as reactive oxygen species, (ROS) is a part of the signaling process in higher plants at lower concentrations, but at higher concentrations, those ROS cause oxidative stress. Salinity-induced osmotic stress and ionic stress trigger the overproduction of ROS and, ultimately, result in oxidative damage to cell organelles and membrane components, and at severe levels, they cause cell and plant death. The antioxidant defense system protects the plant from salt-induced oxidative damage by detoxifying the ROS and also by maintaining the balance of ROS generation under salt stress. Different plant hormones and genes are also associated with the signaling and antioxidant defense system to protect plants when they are exposed to salt stress. Salt-induced ROS overgeneration is one of the major reasons for hampering the morpho-physiological and biochemical activities of plants which can be largely restored through enhancing the antioxidant defense system that detoxifies ROS. In this review, we discuss the salt-induced generation of ROS, oxidative stress and antioxidant defense of plants under salinity.

Expression of cyanobacterial genes enhanced CO2 assimilation and biomass production in transgenic Arabidopsis thaliana

Background

Photosynthesis is a key process in plants that is compromised by the oxygenase activity of Rubisco, which leads to the production of toxic compound phosphoglycolate that is catabolized by photorespiratory pathway. Transformation of plants with photorespiratory bypasses have been shown to reduce photorespiration and enhance plant biomass. Interestingly, engineering of a single gene from such photorespiratory bypasses has also improved photosynthesis and plant productivity. Although single gene transformations may not completely reduce photorespiration, increases in plant biomass accumulation have still been observed indicating an alternative role in regulating different metabolic processes. Therefore, the current study was aimed at evaluating the underlying mechanism (s) associated with the effects of introducing a single cyanobacterial glycolate decarboxylation pathway gene on photosynthesis and plant performance.

Methods

Transgenic Arabidopsis thaliana plants (GD, HD, OX) expressing independently cyanobacterial decarboxylation pathway genes i.e., glycolate dehydrogenase, hydroxyacid dehydrogenase, and oxalate decarboxylase, respectively, were utilized. Photosynthetic, fluorescence related, and growth parameters were analyzed. Additionally, transcriptomic analysis of GD transgenic plants was also performed.

Results

The GD plants exhibited a significant increase (16%) in net photosynthesis rate while both HD and OX plants showed a non-significant (11%) increase as compared to wild type plants (WT). The stomatal conductance was significantly higher (24%) in GD and HD plants than the WT plants. The quantum efficiencies of photosystem II, carbon dioxide assimilation and the chlorophyll fluorescence-based photosynthetic electron transport rate were also higher than WT plants. The OX plants displayed significant reductions in the rate of photorespiration relative to gross photosynthesis and increase in the ratio of the photosynthetic electron flow attributable to carboxylation reactions over that attributable to oxygenation reactions. GD, HD and OX plants accumulated significantly higher biomass and seed weight. Soluble sugars were significantly increased in GD and HD plants, while the starch levels were higher in all transgenic plants. The transcriptomic analysis of GD plants revealed 650 up-regulated genes mainly related to photosynthesis, photorespiratory pathway, sucrose metabolism, chlorophyll biosynthesis and glutathione metabolism.

Conclusion

This study revealed the potential of introduced cyanobacterial pathway genes to enhance photosynthetic and growth-related parameters. The upregulation of genes related to different pathways provided evidence of the underlying mechanisms involved particularly in GD plants. However, transcriptomic profiling of HD and OX plants can further help to identify other potential mechanisms involved in improved plant productivity.

The Alkali Tolerance of Broomcorn Millet (Panicum miliaceum L.) at the Germination and Seedling Stage: The Case of 296 Broomcorn Millet Genotypes

Broomcorn millet (BM), one of the earliest domesticated cereal crops originating in northern China, can tolerate extreme conditions, such as drought and high temperatures, which are prevalent in saline-alkali, arid, and barren landscapes. However, its adaptive mechanism to alkali stress is yet to be comprehensively understood. In this study, 80 and 40 mM standard alkali stress concentrations were used to, respectively, evaluate the alkali tolerance at the germination and seedling stages of 296 BM genotypes. Principal component analysis (PCA), Pearson's correlation analysis, and F-value comprehensive analysis were performed on the germination parameters (germination potential, germination index, germination rate, vigor index, root length/weight, sprout length/weight, and alkali damage rate). Based on their respective F-values, the BM genotypes were divided into five categories ranging from highly alkali resistant to alkali sensitive. To study the response of seedlings to alkaline stress, we investigated the phenotypic parameters (plant height, green leaf area, biomass, and root structure) of 111 genotypes from the above five categories. Combining the parameters of alkali tolerance at the germination and seedling stages, these 111 genotypes were further subdivided into three groups with different alkali tolerances. Variations in physiological responses of the different alkali-tolerant genotypes were further investigated for antioxidant enzyme activity, soluble substances, malondialdehyde (MDA) content, electrolyte leakage rate, and leaf structure. Compared with alkali-sensitive genotypes, alkali-tolerant genotypes had high antioxidant enzyme activity and soluble osmolyte content, low MDA content and electrolyte leakage rate, and a more complete stomata structure. Taken together, this study provides a comprehensive and reliable method for evaluating alkali tolerance and will contribute to the improvement and restoration of saline-alkaline soils by BM.

Supplemental Effects of Biochar and Foliar Application of Ascorbic Acid on Physio-Biochemical Attributes of Barley (Hordeum vulgare L.) under Cadmium-Contaminated Soil

Biochar, prepared from organic waste materials, can improve the quality of contaminated soil areas. Biochar can be used as an economic centerpiece over other available resources and can properly utilize large amounts of waste. Soil contaminated with cadmium (Cd) is a worldwide problem that poses potential agricultural and human health hazards. Moreover, Cd toxicity causes serious problems for sustainable food production, especially in food crops like barley. High cadmium concentration in soil is phytotoxic and decreases plant growth and ultimately yields. Biochar and ascorbic acid in ameliorating Cd stress are economically compatible and consistent approaches in agriculture. The present study aimed to evaluate biochar’s and foliar-applied ascorbic acid’s influence on some growth and biochemical characteristics of barley (Hordeum vulgare L.) to Cd stress. The soil was supplemented with biochar 2% w/w and 20 mg Cd kg−1. The foliar application of 30 mM ascorbic acid was done on plants. The results revealed that Cd stress decreased chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids. It also increased oxidative stress indicators, i.e., APX, COD, POD, flavonoids, anthocyanin, phenolics, and electrolyte leakage, in barley with Cd-contamination. A significant enhancement in root and shoot length, gas exchange attributes, and chlorophyll contents validated the effectiveness of Bio + Asa treatments over all other treatments under Cd contamination. In conclusion, the sole applications of biochar and Asa in Cd contamination are also effective, but Bio + Asa is a better amendment for Cd stress alleviation in barley plants.

Crucial Cell Signaling Compounds Crosstalk and Integrative Multi-Omics Techniques for Salinity Stress Tolerance in Plants

In the era of rapid climate change, abiotic stresses are the primary cause for yield gap in major agricultural crops. Among them, salinity is considered a calamitous stress due to its global distribution and consequences. Salinity affects plant processes and growth by imposing osmotic stress and destroys ionic and redox signaling. It also affects phytohormone homeostasis, which leads to oxidative stress and eventually imbalances metabolic activity. In this situation, signaling compound crosstalk such as gasotransmitters [nitric oxide (NO), hydrogen sulfide (H2S), hydrogen peroxide (H2O2), calcium (Ca), reactive oxygen species (ROS)] and plant growth regulators (auxin, ethylene, abscisic acid, and salicylic acid) have a decisive role in regulating plant stress signaling and administer unfavorable circumstances including salinity stress. Moreover, recent significant progress in omics techniques (transcriptomics, genomics, proteomics, and metabolomics) have helped to reinforce the deep understanding of molecular insight in multiple stress tolerance. Currently, there is very little information on gasotransmitters and plant growth regulator crosstalk and inadequacy of information regarding the integration of multi-omics technology during salinity stress. Therefore, there is an urgent need to understand the crucial cell signaling crosstalk mechanisms and integrative multi-omics techniques to provide a more direct approach for salinity stress tolerance. To address the above-mentioned words, this review covers the common mechanisms of signaling compounds and role of different signaling crosstalk under salinity stress tolerance. Thereafter, we mention the integration of different omics technology and compile recent information with respect to salinity stress tolerance.

Effects of Salinity Stress on Chloroplast Structure and Function

Salinity is a growing problem affecting soils and agriculture in many parts of the world. The presence of salt in plant cells disrupts many basic metabolic processes, contributing to severe negative effects on plant development and growth. This review focuses on the effects of salinity on chloroplasts, including the structures and function of these organelles. Chloroplasts house various important biochemical reactions, including photosynthesis, most of which are considered essential for plant survival. Salinity can affect these reactions in a number of ways, for example, by changing the chloroplast size, number, lamellar organization, lipid and starch accumulation, and interfering with cross-membrane transportation. Research has shown that maintenance of the normal chloroplast physiology is necessary for the survival of the entire plant. Many plant species have evolved different mechanisms to withstand the harmful effects of salt-induced toxicity on their chloroplasts and its machinery. The differences depend on the plant species and growth stage and can be quite different between salt-sensitive (glycophyte) and salt-tolerant (halophyte) plants. Salt stress tolerance is a complex trait, and many aspects of salt tolerance in plants are not entirely clear yet. In this review, we discuss the different mechanisms of salt stress tolerance in plants with a special focus on chloroplast structure and its functions, including the underlying differences between glycophytes and halophytes.

Halophytes as source of bioactive phenolic compounds and their potential applications

Halophytes are salt-tolerant plants that inhabit environments in which they are exposed to extreme stress, wherefore they exhibit conserved and divergent metabolic responses different from those of conventional plants. Thus, the synthesis and accumulation of metabolites, especially of those oxidative stress-related such as phenolic compounds, should be investigated. The potential of halophytes as a source of phenolics and their prospective industrial applications are evaluated based on a comprehensive review of the scientific literature on the phenolic compounds of more than forty halophytes and their biological activities. Additionally, an overview of the analytical methodologies adopted for phenolics determination in halophytes is provided. Finally, the prospective uses and beneficial effects of the phenolic preparations from these plants are discussed. Halophytes are complex matrices, exhibiting a wide variety of phenolics in their composition, wherefore the results can be greatly affected depending on the organ plant under analysis and the extraction methodology, especially the extraction solvent used. High-performance liquid chromatography, coupled with diode array detection (HPLC-DAD) or mass spectrometry (HPLC-MS), are the most used technique. Halophytes biosynthesize phenolics in concentrations that justify the remarkable antioxidant and antimicrobial activities shown, making them ideal sources of bioactive molecules to be employed in a multitude of sectors.