Progress in Understanding the Physiological and Molecular Responses of Populus to Salt Stress

Unraveling the lncRNA-miRNA-mRNA Regulatory Network Involved in Poplar Coma Development through High-Throughput Sequencing

Poplar coma, the fluff-like appendages of seeds originating from the differentiated surface cells of the placenta and funicle, aids in the long-distance dispersal of seeds in the spring. However, it also poses hazards to human safety and causes pollution in the surrounding environment. Unraveling the regulatory mechanisms governing the initiation and development of coma is essential for addressing this issue comprehensively. In this study, strand-specific RNA-seq was conducted at three distinct stages of coma development, revealing 1888 lncRNAs and 52,810 mRNAs. The expression profiles of lncRNAs and mRNAs during coma development were analyzed. Subsequently, potential target genes of lncRNAs were predicted through co-localization and co-expression analyses. Integrating various types of sequencing data, lncRNA-miRNA-TF regulatory networks related to the initiation of coma were constructed. Utilizing identified differentially expressed genes encoding kinesin and actin, lncRNA-miRNA-mRNA regulatory networks associated with the construction and arrangement of the coma cytoskeleton were established. Additionally, relying on differentially expressed genes encoding cellulose synthase, sucrose synthase, and expansin, lncRNA-miRNA-mRNA regulatory networks related to coma cell wall synthesis and remodeling were developed. This study not only enhances the comprehension of lncRNA but also provides novel insights into the molecular mechanisms governing the initiation and development of poplar coma.

Enhancing Salt Tolerance in Poplar Seedlings through Arbuscular Mycorrhizal Fungi Symbiosis

Poplar (Populus spp.) is a valuable tree species with multiple applications in afforestation. However, its growth in saline areas, including coastal regions, is limited. This study aimed to investigate the physiological mechanisms of arbuscular mycorrhizal fungi (AMF) symbiosis with 84K (P. alba × P. tremula var. glandulosa) poplar under salt stress. We conducted pot experiments using NaCl solutions of 0 mM (control), 100 mM (moderate stress), and 200 mM (severe stress) and evaluated the colonization of AMF and various physiological parameters of plants, including photosynthesis, biomass, antioxidant enzyme activity, nutrients, and ion concentration. Partial least squares path modeling (PLS-PM) was employed to elucidate how AMF can improve salt tolerance in poplar. The results demonstrated that AMF successfully colonized the roots of plants under salt stress, effectively alleviated water loss by increasing the transpiration rate, and significantly enhanced the biomass of poplar seedlings. Mycorrhiza reduced proline and malondialdehyde accumulation while enhancing the activity of antioxidant enzymes, thus improving plasma membrane stability. Additionally, AMF mitigated Na+ accumulation in plants, contributing to the maintenance of a favorable ion balance. These findings highlight the effectiveness of using suitable AMF to improve conditions for economically significant tree species in salt-affected areas, thereby promoting their utilization.

Ecophysiological response of Populus alba L. to multiple stress factors during the revitalisation of coal fly ash lagoons at different stages of weathering

The enormous quantities of fly ash (FA) produced by thermal power plants is a global problem and safe, sustainable approaches to reduce the amount and its toxic effects are still being sought. Vegetation cover comprising long-living species can help reduce FA dump-related environmental health issues. However, the synergistic effect of multiple abiotic factors, like drought, low organic matter content, a deficit of essential nutrients, alkaline pH, and phytotoxicity due to high potentially toxic element (PTE) and soluble salt content, limits the number of species that can grow under such stressful conditions. Thus, we hypothesised that Populus alba L., which spontaneously colonised two FA disposal lagoons at the 'Nikola Tesla A' thermal power plant (Obrenovac, Serbia) 3 years (L3) and 11 years (L11) ago, has high restoration potential thanks to its stress tolerance. We analysed the basic physical and chemical properties of FA at different weathering stages, while the ecophysiological response of P. alba to multiple stresses was determined through biological indicators [the bioconcentration factor (BCF) and translocation factor (TF) for PTEs (As, B, Cr, Cu, Mn, Ni, Se, and Zn)] and by measuring the following parameters: photosynthetic efficiency and chlorophyll concentration, non-enzymatic antioxidant defence (carotenoids, anthocyanins, and phenols), oxidative stress (malondialdehyde (MDA) concentrations), and total antioxidant capacity (IC50) to neutralise DPPH free radical activity. Unlike at L3, toxic As, B, and Zn concentrations in leaves induced oxidative stress in P. alba at L11, shown by the higher MDA levels, lower vitality, and reduced synthesis of chlorophyll, carotenoids, and total antioxidant activity, suggesting its stress tolerance decreases with long-term exposure to adverse abiotic factors. Although P. alba is a fast-growing species with good metal accumulation ability and high stress tolerance, it has poor stabilisation potential for substrates with high As and B concentrations, making it highly unsuitable for revitalising such habitats.

Ion Changes and Signaling under Salt Stress in Wheat and Other Important Crops

High concentrations of sodium (Na+), chloride (Cl-), calcium (Ca2+), and sulphate (SO42-) are frequently found in saline soils. Crop plants cannot successfully develop and produce because salt stress impairs the uptake of Ca2+, potassium (K+), and water into plant cells. Different intracellular and extracellular ionic concentrations change with salinity, including those of Ca2+, K+, and protons. These cations serve as stress signaling molecules in addition to being essential for ionic homeostasis and nutrition. Maintaining an appropriate K+:Na+ ratio is one crucial plant mechanism for salt tolerance, which is a complicated trait. Another important mechanism is the ability for fast extrusion of Na+ from the cytosol. Ca2+ is established as a ubiquitous secondary messenger, which transmits various stress signals into metabolic alterations that cause adaptive responses. When plants are under stress, the cytosolic-free Ca2+ concentration can rise to 10 times or more from its resting level of 50-100 nanomolar. Reactive oxygen species (ROS) are linked to the Ca2+ alterations and are produced by stress. Depending on the type, frequency, and intensity of the stress, the cytosolic Ca2+ signals oscillate, are transient, or persist for a longer period and exhibit specific "signatures". Both the influx and efflux of Ca2+ affect the length and amplitude of the signal. According to several reports, under stress Ca2+ alterations can occur not only in the cytoplasm of the cell but also in the cell walls, nucleus, and other cell organelles and the Ca2+ waves propagate through the whole plant. Here, we will focus on how wheat and other important crops absorb Na+, K+, and Cl- when plants are under salt stress, as well as how Ca2+, K+, and pH cause intracellular signaling and homeostasis. Similar mechanisms in the model plant Arabidopsis will also be considered. Knowledge of these processes is important for understanding how plants react to salinity stress and for the development of tolerant crops.

The Euphrates Poplar Responses to Abiotic Stress and Its Unique Traits in Dry Regions of China (Xinjiang and Inner Mongolia): What Should We Know?

At the moment, drought, salinity, and low-temperature stress are ubiquitous environmental issues. In arid regions including Xinjiang and Inner Mongolia and other areas worldwide, the area of tree plantations appears to be rising, triggering tree growth. Water is a vital resource in the agricultural systems of countries impacted by aridity and salinity. Worldwide efforts to reduce quantitative yield losses on Populus euphratica by adapting tree plant production to unfavorable environmental conditions have been made in response to the responsiveness of the increasing control of water stress. Although there has been much advancement in identifying the genes that resist abiotic stresses, little is known about how plants such as P. euphratica deal with numerous abiotic stresses. P. euphratica is a varied riparian plant that can tolerate drought, salinity, low temperatures, and climate change, and has a variety of water stress adaptability abilities. To conduct this review, we gathered all available information throughout the Web of Science, the Chinese National Knowledge Infrastructure, and the National Center for Biotechnology Information on the impact of abiotic stress on the molecular mechanism and evolution of gene families at the transcription level. The data demonstrated that P. euphratica might gradually adapt its stomatal aperture, photosynthesis, antioxidant activities, xylem architecture, and hydraulic conductivity to endure extreme drought and salt stress. Our analyses will give readers an understanding of how to manage a gene family in desert trees and the influence of abiotic stresses on the productivity of tree plants. They will also give readers the knowledge necessary to improve biotechnology-based tree plant stress tolerance for sustaining yield and quality trees in China's arid regions.

In vitro selection of drought-tolerant white poplar clones based on antioxidant activities and osmoprotectant content

Introduction

In light of upcoming climate change, there is an urgent requirement for tree improvement regarding adaptability to drought-caused stress and the development of quick and reliable screening methodologies for genotypes' drought tolerance. White poplar is, despite its high adaptability, considered to be an endangered tree species in Serbia, which gives it special importance in the preservation and improvement of biodiversity of riparian ecosystems. The main goal of this research was to evaluate the tolerance of five white poplar clones to the presence of polyethylene glycol (PEG 6000 molecular weight 6000) (different concentrations (e.g. 0 g/L, 1 g/L, 10 g/L, 20 g/L, and 50 g/L) in Aspen Culture Medium (ACM).

Methods

The tolerance of the clones was evaluated by using morphological parameters (shoot fresh and dry weight, root fresh and dry weight), photosynthetic pigments (contents of chlorophyll a, chlorophyll b, carotenoids, and chlorophyll a+b), and biochemical parameters (total phenolic content, total flavonoid content, ferric reducing antioxidant power, antioxidant activities (DPPH activity and ABTS assay), free proline content and glycine betaine content.

Results and Discussion

The values of morphological and photosynthetic pigments declined with an increase in the concentration of PEG 6000. At a concentration of 50 g/L, the content of shoot fresh mass decreased by 41%, the content of Chl a by 68%, Chl b by 65%, and Car by 76% compared to the control. Also, at the same medium, there was an increase in the content of total phenols, accumulation of proline, the content of glycine betaine as well as in antioxidant activity. Based on the obtained results, it can be assumed that more drought-tolerant clones are characterized by high values for biomass, high content of photosynthetic pigments, and high content of proline and glycine betaine in conditions similar to drought in vitro. Clone L-80 showed better results in most of the tested parameters, especially compared to the reference clone Villafranca.

Phenotypic and microarray analysis reveals salinity stress-induced oxidative tolerance in transgenic rice expressing a DEAD-box RNA helicase, OsDB10

Helicases are the motor proteins not only involved in the process of mRNA metabolism but also played a significant role in providing abiotic stresses tolerance. In this study, a DEAD-box RNA helicase OsDB10 was cloned and functionally characterized. The transcript levels of OsDB10 were increased both in shoot and root upon salt, heat, cold, and ABA application and was more prominent in shoot compared to root. Genomic integration of OsDB10 in transgenic rice was confirmed by PCR, Southern blot and qRT-PCR analysis. The transgenic plants showed quicker seed germination, reduced necrosis, higher chlorophyll, more survival rate, better seedling growth, and produced more grain yield under salinity stress. Furthermore, transgenic lines also accumulated less Na+ and high K+ ions and salinity tolerance of the transgenic were also assayed by measuring different bio-physiological indices. Moreover, the OsDB10 transgenic plants showed enhanced tolerance to salinity-induced oxidative stress by scavenging ROS and increased activity of antioxidants enzymes. Microarray analysis showed upregulation of transcriptional regulations and metabolic reprogramming as OsDB10 overexpression modulates the expression of many other genes. Altogether, our results confirmed that OsDB10 is a functional DEAD-box RNA helicase and played vital roles in plant defence response against salinity stress.

A DEAD box helicase Psp68 positively regulates salt stress responses in marker-free transgenic rice plants

Helicases are the motor proteins not only involved in transcriptional and post-transcription process but also provide abiotic stress tolerance in many crops. The p68, belong to the SF2 (DEAD-box helicase) family proteins and overexpression of Psp68 providing enhanced tolerance to transgenic rice plants. In this study, salinity tolerant marker-free transgenic rice has been developed by overexpressing Psp68 gene and phenotypically characterized. The Psp68 overexpressing marker-free transgenic rice plants were initially screened in the rooting medium containing salt stress and 20% polyethylene glycol (PEG). Stable integration and overexpression of Psp68 in marker-free transgenic lines were confirmed by molecular analyses including PCR, southern, western blot, and qRT-PCR analyses. The marker-free transgenic lines showed enhanced tolerance to salinity stress as displayed by early seed germination, higher chlorophyll content, reduced necrosis, more survival rate, improved seedling growth and more grain yield per plant. Furthermore, Psp68 overexpressing marker-free transgenics also accumulated less Na+ and higher K+ ions in the presence of salinity stress. Phenotypic analyses also revealed that marker-free transgenic rice lines efficiently scavenge ROS-mediated damages as displayed by lower H2O2 and malondialdehyde content, delayed electrolyte leakage, higher photosynthetic efficiency, membrane stability, proline content and enhanced activities of antioxidants enzymes. Overall, our results confirmed that Psp68 overexpression confers salinity stress tolerance in marker-free transgenics, hence the technique could be utilized to develop genetically modified crops without any biosafety issues.

The C2 H2 -type zinc finger transcription factor OSIC1 positively regulates stomatal closure under osmotic stress in poplar

Salt and drought impair plant osmotic homeostasis and greatly limit plant growth and development. Plants decrease stomatal aperture to reduce water loss and maintain osmotic homeostasis, leading to improved stress tolerance. Herein, we identified the C₂ H₂ transcription factor gene OSMOTIC STRESS INDUCED C₂ H₂ 1 (OSIC1) from Populus alba var. pyramidalis to be induced by salt, drought, polyethylene glycol 6000 (PEG6000) and abscisic acid (ABA). Overexpression of OSIC1 conferred transgenic poplar more tolerance to high salinity, drought and PEG6000 treatment by reducing stomatal aperture, while its mutant generated by the CRISPR/Cas9 system showed the opposite phenotype. Furthermore, OSIC1 directly up-regulates PalCuAOζ in vitro and in vivo, encoding a copper-containing polyamine oxidase, to enhance H₂ O₂ accumulation in guard cells and thus modulates stomatal closure when stresses occur. Additionally, ABA-, drought- and salt-induced PalMPK3 phosphorylates OSIC1 to increase its transcriptional activity to PalCuAOζ. This regulation of OSIC1 at the transcriptional and protein levels guarantees rapid stomatal closure when poplar responds to osmotic stress. Our results revealed a novel transcriptional regulatory mechanism of H₂ O₂ production in guard cells mediated by the OSIC1-PalCuAOζ module. These findings deepen our understanding of how perennial woody plants, like poplar, respond to osmotic stress caused by salt and drought and provide potential targets for breeding.

Genome-wide analysis of TPX2 gene family in Populus trichocarpa and its specific response genes under various abiotic stresses

Microtubules are essential for regulating cell morphogenesis, plant growth, and the response of plants to abiotic stresses. TPX2 proteins are the main players determining the spatiotemporally dynamic nature of the MTs. However, how TPX2 members respond to abiotic stresses in poplar remains largely unknown. Herein, 19 TPX2 family members were identified from the poplar genome and analyzed the structural characteristics as well as gene expression patterns. All TPX2 members had the conserved structural characteristics, but exhibited different expression profiles in different tissues, indicating their varying roles during plant growth. Additionally, several light, hormone, and abiotic stress responsive cis-acting regulatory elements were detected on the promoters of PtTPX2 genes. Furthermore, expression analysis in various tissues of Populus trichocarpa showed that the PtTPX2 genes responded differently to heat, drought and salt stress. In summary, these results provide a comprehensive analysis for the TPX2 gene family in poplar and an effective contribution to revealing the mechanisms of PtTPX2 in the regulatory network of abiotic stress.

De novo assembly provides new insights into the evolution of Elaeagnus angustifolia L

BACKGROUND

Elaeagnus angustifolia L. is a deciduous tree in the family Elaeagnaceae. It is widely used to study abiotic stress tolerance in plants and to improve desertification-affected land because of its ability to withstand diverse types of environmental stress, such as drought, salt, cold, and wind. However, no studies have examined the mechanisms underlying the resistance of E. angustifolia to environmental stress and its adaptive evolution.

METHODS

Here, we used PacBio, Hi-C, resequencing, and RNA-seq to construct the genome and transcriptome of E. angustifolia and explore its adaptive evolution.

RESULTS

The reconstructed genome of E. angustifolia was 526.80 Mb, with a contig N50 of 12.60 Mb and estimated divergence time of 84.24 Mya. Gene family expansion and resequencing analyses showed that the evolution of E. angustifolia was closely related to environmental conditions. After exposure to salt stress, GO pathway analysis showed that new genes identified from the transcriptome were related to ATP-binding, metal ion binding, and nucleic acid binding.

CONCLUSION

The genome sequence of E. angustifolia could be used for comparative genomic analyses of Elaeagnaceae family members and could help elucidate the mechanisms underlying the response of E. angustifolia to drought, salt, cold, and wind stress. Generally, these results provide new insights that could be used to improve desertification-affected land.

Role of lncRNAs in cis- and trans-regulatory responses to salt in Populus trichocarpa

Long non-coding RNAs (lncRNAs) are emerging as versatile regulators in diverse biological processes. However, little is known about their cis- and trans-regulatory contributions in gene expression under salt stress. Using 27 RNA-seq data sets from Populus trichocarpa leaves, stems and roots, we identified 2988 high-confidence lncRNAs, including 1183 salt-induced differentially expressed lncRNAs. Among them, 301 lncRNAs have potential for positively affecting their neighboring genes, predominantly in a cis-regulatory manner rather than by co-transcription. Additionally, a co-expression network identified six striking salt-associated modules with a total of 5639 genes, including 426 lncRNAs, and in these lncRNA sequences, the DNA/RNA binding motifs are enriched. This suggests that lncRNAs might contribute to distant gene expression of the salt-associated modules in a trans-regulatory manner. Moreover, we found 30 lncRNAs that have potential to simultaneously cis- and trans-regulate salt-responsive homologous genes, and Ptlinc-NAC72, significantly induced under long-term salt stress, was selected for validating its regulation of the expression and functional roles of the homologs PtNAC72.A and PtNAC72.B (PtNAC72.A/B). The transient transformation of Ptlinc-NAC72 and a dual-luciferase assay of Ptlinc-NAC72 and PtNAC72.A/B promoters confirmed that Ptlinc-NAC72 can directly upregulate PtNAC72.A/B expression, and a presence/absence assay was further conducted to show that the regulation is probably mediated by Ptlinc-NAC72 recognizing the tandem elements (GAAAAA) in the PtNAC72.A/B 5' untranslated region (5'-UTR). Finally, the overexpression of Ptlinc-NAC72 produces a hypersensitive phenotype under salt stress. Altogether, our results shed light on the cis- and trans-regulation of gene expression by lncRNAs in Populus and provides an example of long-term salt-induced Ptlinc-NAC72 that could be used to mitigate growth costs by conferring plant resilience to salt stress.

How salt stress-responsive proteins regulate plant adaptation to saline conditions

An overview is presented of recent advances in our knowledge of candidate proteins that regulate various physiological and biochemical processes underpinning plant adaptation to saline conditions. Salt stress is one of the environmental constraints that restrict plant distribution, growth and yield in many parts of the world. Increased world population surely elevates food demands all over the globe, which anticipates to add a great challenge to humanity. These concerns have necessitated the scientists to understand and unmask the puzzle of plant salt tolerance mechanisms in order to utilize various strategies to develop salt tolerant crop plants. Salt tolerance is a complex trait involving alterations in physiological, biochemical, and molecular processes. These alterations are a result of genomic and proteomic complement readjustments that lead to tolerance mechanisms. Proteomics is a crucial molecular tool that indicates proteins expressed by the genome, and also identifies the functions of proteins accumulated in response to salt stress. Recently, proteomic studies have shed more light on a range of promising candidate proteins that regulate various processes rendering salt tolerance to plants. These proteins have been shown to be involved in photosynthesis and energy metabolism, ion homeostasis, gene transcription and protein biosynthesis, compatible solute production, hormone modulation, cell wall structure modification, cellular detoxification, membrane stabilization, and signal transduction. These candidate salt responsive proteins can be therefore used in biotechnological approaches to improve tolerance of crop plants to salt conditions. In this review, we provided comprehensive updated information on the proteomic data of plants/genotypes contrasting in salt tolerance in response to salt stress. The roles of salt responsive proteins that are potential determinants for plant salt adaptation are discussed. The relationship between changes in proteome composition and abundance, and alterations observed in physiological and biochemical features associated with salt tolerance are also addressed.

Defense mechanisms promoting tolerance to aggressive Phytophthora species in hybrid poplar

Poplars are among the fastest-growing trees and significant resources in agriculture and forestry. However, rapid growth requires a large water consumption, and irrigation water provides a natural means for pathogen spread. That includes members of Phytophthora spp. that have proven to be a global enemy to forests. With the known adaptability to new hosts, it is only a matter of time for more aggressive Phytophthora species to become a threat to poplar forests and plantations. Here, the effects of artificial inoculation with two different representatives of aggressive species (P. cactorum and P. plurivora) were analyzed in the proteome of the Phytophthora-tolerant hybrid poplar clone T-14 [Populus tremula L. 70 × (Populus × canescens (Ait.) Sm. 23)]. Wood microcore samples were collected at the active necrosis borders to provide insight into the molecular processes underlying the observed tolerance to Phytophthora. The analysis revealed the impact of Phytophthora on poplar primary and secondary metabolism, including carbohydrate-active enzymes, amino acid biosynthesis, phenolic metabolism, and lipid metabolism, all of which were confirmed by consecutive metabolome and lipidome profiling. Modulations of enzymes indicating systemic response were confirmed by the analysis of leaf proteome, and sampling of wood microcores in distal locations revealed proteins with abundance correlating with proximity to the infection, including germin-like proteins, components of proteosynthesis, glutamate carboxypeptidase, and an enzyme that likely promotes anthocyanin stability. Finally, the identified Phytophthora-responsive proteins were compared to those previously found in trees with compromised defense against Phytophthora, namely, Quercus spp. and Castanea sativa. That provided a subset of candidate markers of Phytophthora tolerance, including certain ribosomal proteins, auxin metabolism enzymes, dioxygenases, polyphenol oxidases, trehalose-phosphate synthase, mannose-1-phosphate guanylyltransferase, and rhamnose biosynthetic enzymes. In summary, this analysis provided the first insight into the molecular mechanisms of hybrid poplar defense against Phytophthora and identified prospective targets for improving Phytophthora tolerance in trees.

OsCYP714D1 improves plant growth and salt tolerance through regulating gibberellin and ion homeostasis in transgenic poplar

Cytochrome P450 monooxygenases (CYP450s) play crucial roles in the regulation of plant growth and response to abiotic stress. However, their functions in woody trees are still largely unknown. Previously, we reported that expression of the rice cytochrome P450 monooxygenase gene OsCYP714D1 increased gibberellic acid (GA) accumulation and shoot growth in transgenic poplar. In this work, we demonstrate that expression of OsCYP714D1 improved the salt tolerance of transgenic poplar plants. Compared to wild type, plant height and K⁺ content were significantly higher, whereas plant growth inhibition and Na⁺ content were significantly lower, in transgenic plants grown under high salt stress condition. Transcriptomic analyses revealed that OsCYP714D1 expression up-regulated the expressions of GA biosynthesis, signaling and stress responsive genes in transgenic plants under both normal and high salt stress conditions. Further gene ontology (GO) analyses indicated that genes involved in plant hormone and ion metabolic activities were significantly enriched in transgenic plants. Our findings imply that OsCYP714D1 participated in the regulation of both shoot growth and salt resistance through regulating gibberellin and ion homeostasis in transgenic poplar, and it can be used as a candidate gene for the engineering of new tree varieties with improved biomass production and salt stress resistance.

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.

Physiological and Molecular Analysis Reveals the Differences of Photosynthesis between Colored and Green Leaf Poplars

Leaf coloration changes evoke different photosynthetic responses among different poplar cultivars. The aim of this study is to investigate the photosynthetic difference between a red leaf cultivar (ZHP) and a green leaf (L2025) cultivar of Populus deltoides. In this study, ‘ZHP’ exhibited wide ranges and huge potential for absorption and utilization of light energy and CO₂ concentration which were similar to those in ‘L2025’ and even showed a stronger absorption for weak light. However, with the increasing light intensity and CO₂ concentration, the photosynthetic capacity in both ‘L2025’ and ‘ZHP’ was gradually restricted, and the net photosynthetic rate (Pn) in ‘ZHP’ was significantly lower than that in ‘L2025’under high light or high CO₂ conditions, which was mainly attributed to stomatal regulation and different photosynthetic efficiency (including the light energy utilization efficiency and photosynthetic CO₂ assimilation efficiency) in these two poplars. Moreover, the higher anthocyanin content in ‘ZHP’ than that in ‘L2025’ was considered to be closely related to the decreased photosynthetic efficiency in ‘ZHP’. According to the results from the JIP-test, the capture efficiency of the reaction center for light energy in ‘L2025’ was significantly higher than that in ‘ZHP’. Interestingly, the higher levels of light quantum caused relatively higher accumulation of Q_A^- in ‘L2025’, which blocked the electron transport and weakened the photosystem II (PSII) performance as compared with ‘ZHP’; however, the decreased capture of light quantum also could not promote the utilization of light energy, which was the key to the low photosynthetic efficiency in ‘ZHP’. The differential expressions of a series of photosynthesis-related genes further promoted these specific photosynthetic processes between ‘L2025’ and ‘ZHP’.

Seed biostimulant Bacillus sp. MGW9 improves the salt tolerance of maize during seed germination

Crop performance is seriously affected by high salt concentrations in soils. To develop improved seed pre-sowing treatment technologies, it is crucial to improve the salt tolerance of seed germination. Here, we isolated and identified the strain Bacillus sp. MGW9 and developed the seed biostimulant MGW9. The effects of seed biopriming with the seed biostimulant MGW9 in maize (Zea mays L.) under saline conditions were studied. The results show that the strain Bacillus sp. MGW9 has characteristics such as salt tolerance, nitrogen fixation, phosphorus dissolution, and indole-3-acetic acid production. Seed biopriming with the seed biostimulant MGW9 enhanced the performance of maize during seed germination under salinity stress, improving the germination energy, germination percentage, shoot/seedling length, primary root length, shoot/seedling fresh weight, shoot/seedling dry weight, root fresh weight and root dry weight. Seed biostimulant MGW9 biopriming also alleviated the salinity damage to maize by improving the relative water content, chlorophyll content, proline content, soluble sugar content, root activity, and activities of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, while decreasing the malondialdehyde content. In particular, the field seedling emergence of maize seeds in saline-alkali soil can be improved by biopriming with the seed biostimulant MGW9. Therefore, maize seed biopriming with the seed biostimulant MGW9 could be an effective approach to overcoming the inhibitory effects of salinity stress and promoting seed germination and seedling growth.

Oil and Flower Production in Rosa damascena trigintipetala Dieck under Salinity Stress in Taif Region, Saudi Arabia

The flower industry depends on oil and fragrance, which is addressed in the current work. Different concentrations of NaCl (0, 250, 500, 1000, and 1500 ppm) were applied to Taif rose plants (Rosa damascena var. trigintipetala Dieck) to evaluate their effects on growth and essential oil content. Results clearly indicated the highest survival percentage (98.3%) was seen in untreated plants compared to plants under salinity stress. Moreover, increasing the NaCl levels induced an adverse effect on the growth parameters of Taif rose plants, while some essential oil contents were increased to the maximum degree of their tolerance to salinity stress. The extracted essential oils were analyzed using GC/MS. The essential oils of Taif rose plants treated with 500 ppm NaCl recorded the highest values of citronellol, geraniol and phenylethyl alcohol contents (16.56, 8.67 and 9.87%), respectively. NaCl at 250 ppm produced the highest values of heneicosane (13.12%), and then decreased to the lowest value (7.79%) with the increase of NaCl to 1500 NaCl, compared to the control and other NaCl levels. The current results could highlight the impact of salinity stress on Rosa damascena Miller var. trigintipetala Dieck for better economic and industrial applications.

The PalERF109 transcription factor positively regulates salt tolerance via PalHKT1;2 in Populus alba var. pyramidalis

Salinity restricts the growth of trees to varying extents, but the regulatory mechanisms involved in their varying salt tolerance are largely unknown. In an effort to elucidate these mechanisms, we identified a total of 99 genes in the Ethylene Responsive Factor (ERF) family of transcription factors and examined their expression patterns under salt stress in Populus alba var. pyramidalis. We found that a B4 group gene, PalERF109, was rapidly induced by salt treatment and preferentially expressed in stems and petioles, where it is probably involved in transport of ions and water in xylem. Overexpression of PalERF109 enhanced the salt tolerance of the poplar, and further analysis showed that it directly upregulated a high-affinity K+transporter (HKT) gene, PalHKT1;2. The results clearly indicate that PalERF109 enhances salt tolerance at least partially through direct activation of PalHKT1;2 and extends understanding of the roles of ERF genes in tree stress responses.

Effect of Overexpression of JERFs on Intracellular K+/Na+ Balance in Transgenic Poplar (Populus alba × P. berolinensis) Under Salt Stress

Salt stress is one of the main factors that affect both growth and development of plants. Maintaining K⁺/Na⁺ balance in the cytoplasm is important for metabolism as well as salt resistance in plants. In the present study, we monitored the growth (height and diameter) of transgenic Populus alba × P. berolinensis trees (ABJ01) carrying JERF36s gene (a tomato jasmonic/ethylene responsive factors gene) over 4 years, which showed faster growth and significant salt tolerance compared with non-transgenic poplar trees (9#). The expression of NHX1 and SOS1 genes that encode Na⁺/H⁺ antiporters in the vacuole and plasma membranes was measured in leaves under NaCl stress. Non-invasive micro-test techniques (NMT) were used to analyse ion flux of Na⁺, K⁺, and H⁺ in the root tip of seedlings under treatment with100 mM NaCl for 7, 15, and 30 days. Results showed that the expression of NHX1 and SOS1 was much higher in ABJ01 compared with 9#, and the Na⁺ efflux and H⁺ influx fluxes of root were remarkable higher in ABJ01 than in 9#, but K⁺ efflux exhibited lower level. All above suggest that salt stress induces NHX1 and SOS1 to a greater expression level in ABJ01, resulting in the accumulation of Na⁺/H⁺ antiporter to better maintain K⁺/Na⁺ balance in the cytoplasm of this enhanced salt resistant variety. This may help us to better understand the mechanism of transgenic poplars with improving salt tolerance by overexpressing JERF36s and could provide a basis for future breeding programs aimed at improving salt resistance in transgenic poplar.

Salinity Tolerance in Plants: Trends and Perspectives

Salinity stress is one of the more prevailing abiotic stresses which results in significant losses in agricultural crop production, particularly in arid and semi-arid areas [...].