Saline-alkaline stress is a common problem in Akebia trifoliata cultivation. In this study, the enhancing effects of 5-azacytidine (5-AzaC) on the resistance of A. trifoliata to saline-alkaline stress and the underlying mechanisms were investigated. Plant height, stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio of 6-month-old A. trifoliata seedlings were measured after saline-alkaline stress with or without 5-AzaC treatment. Moreover, the contents of photosynthetic pigments, malondialdehyde (MDA), H2O2, sodium, soluble sugar, and proline; activities of superoxide dismutase, peroxidase (POD), and catalase (CAT); and anatomical structures of root, stem, and leaf were assessed. Furthermore, comparative transcriptome sequencing was performed. The results demonstrated that growth and development of A. trifoliata were severely inhibited under saline-alkaline stress, suggesting that the seedlings were exposed to severe oxidative and osmotic stresses. Treatment with exogenous 5-AzaC could significantly relieve the symptoms of saline-alkaline stress in A. trifoliata. Under saline-alkaline stress, 5-AzaC could increase the stem diameter, biomass, root length, fresh weight of root, and root/shoot ratio and minimize damages to the anatomical structure. Moreover, absorption of Na+ was reduced; ionic balance was maintained; POD and CAT activities were significantly improved; proline and soluble sugar contents increased, and H2O2 and MDA contents decreased. Transcriptome analysis revealed that 5-AzaC functioned via regulating KEGG pathways such as plant hormone signal transduction, phenylpropanoid biosynthesis, photosynthesis, amino sugar and nucleotide sugar metabolism, and glutathione metabolism under saline-alkaline stress. Particularly, enhanced expression of genes from the auxin pathway in plant hormone signal transduction; the lignin synthetic pathway in phenylpropanoid biosynthesis; and photosystem II, photosystem I, photosynthetic electron transport, and F-type ATP pathway in photosynthesis may be related to 5-AzaC-induced saline-alkaline resistance. The results provided theoretical references for A. trifoliata cultivation in saline-alkaline soil and application of 5-AzaC to improve saline-alkaline tolerance in plants.

Under saline-alkali stress conditions, inoculation with Rhizophagus irregularis or the application of biochar can both promote plant growth and improve soil physicochemical properties. However, the effects of their combined use on switchgrass growth and soil mechanical properties remain unclear. This study established four treatments: no Ri inoculation and no biochar addition (control, CK), biochar addition alone (BC), Rhizophagus irregularis inoculation alone (Ri), and their combination (RB). The aim was to investigate the effects of these treatments on the biomass, root morphology, and soil mechanical properties of switchgrass under saline-alkali stress. The results showed that compared to the CK treatment, the RB treatment significantly increased the root, stem, leaf, and total biomass of switchgrass by 67.55%, 74.76%, 117.31%, and 82.93%, respectively. Among all treatment groups, RB treatment significantly reduced soil bulk density, soil water-soluble sodium ions (Na+), soil exchangeable sodium percentage (ESP), and sodium adsorption ratio (SAR), while increasing soil porosity. Furthermore, RB treatment significantly improved infiltration rate and shear strength. Compared to the CK treatment, the stable infiltration rate and shear strength under 400 kPa vertical load increased by 70.69% and 22.5 kPa, respectively. In conclusion, the combination of Ri and biochar has the potential to improve soil mechanical properties and increase the biomass of switchgrass under saline-alkali stress.

Cucumbers, cultivated globally on 3.7 million hectares, face yield losses due to salinity, highlighting the need for effective mitigation strategies for degraded soils. Melatonin (MT) has gained significant interest for its ability to relieve plant stress. To explore the regulatory role of exogenous MT in maintaining redox homeostasis in cucumber seedlings under saline-alkali stress (SA), this study employed the cucumber cultivar 'Xinchun No. 4 '. Simulated saline-alkali conditions were applied, and the effects of exogenous MT on seedling growth, reactive oxygen species (ROS) production, the ascorbate-glutathione (AsA-GSH) cycle, and changes in leaf anatomy were systematically assessed. The findings reveal that exposure to 40 mmol center dot L-1 saline-alkali stress significantly impaired cucumber seedling growth, reduced biomass, and led to excessive accumulation of hydrogen peroxide (H2O2) and superoxide anions (O2 center dot ) in the leaves. This, resulted in increased lipid peroxidation (indicated by elevated malondialdehyde (MDA) levels), whichi further compromised the cell membrane. Application of 10 mu mol center dot L-1 MT effectively reduced ROS levels, lowered MDA content, and mitigated electrolyte leakage. MT also enhanced AsA and GSH levels, improved AsA/DHA and GSH/GSSG ratios, and upregulated key AsA-GSH cycle genes (CsAPX, CsAAO, CsMDAR, CsDHAR, CsGR), leading to a significant increase in enzymatic activity. In addition, MT alleviated stress-induced stomatal closure, thereby restoring normal stomatal function. These findings suggest that MT enhances saline-alkali tolerance by mitigating oxidative damage, promoting antioxidant defenses, and effectively preserving stomatal function. Thus, our study points to a sustainable strategy to improve crop resilience in salinized environments via MT application.

Key messageA plant growth regulator, 5-aminolevulinic acid, enhanced the saline-alkali tolerance via photosynthetic, oxidative-reduction, and glutathione metabolism pathways in pepper seedlings.AbstractSaline-alkali stress is a prominent environmental problem, hindering growth and development of pepper. 5-Aminolevulinic acid (ALA) application effectively improves plant growth status under various abiotic stresses. Here, we evaluated morphological, physiological, and transcriptomic differences in saline-alkali-stressed pepper seedlings after ALA application to explore the impact of ALA on saline-alkali stress. The results indicated that saline-alkali stress inhibited plant growth, decreased biomass and photosynthesis, altered the osmolyte content and antioxidant system, and increased reactive oxygen species (ROS) accumulation and proline content in pepper seedlings. Conversely, the application of exogenous ALA alleviated this damage by increasing the photosynthetic rate, osmolyte content, antioxidant enzyme activity, and antioxidants, including superoxide dismutase, catalase, glutathione reductase, and glutathione peroxidase, and reducing glutathione to reduce ROS accumulation and malonaldehyde content. Moreover, the transcriptomic analysis revealed the differentially expressed genes were mainly associated with photosynthesis, oxidation-reduction process, and glutathione metabolism in saline-alkali stress + ALA treatment compared to saline-alkali treatment. Among them, the change in expression level in CaGST, CaGR, and CaGPX was close to the variation of corresponding enzyme activity. Collectively, our findings revealed the alleviating effect of ALA on saline-alkali stress in pepper seedlings, broadening the application of ALA and providing a feasible strategy for utilize saline-alkali soil.

Soil salinization is one of the major environmental factors that restrict plant growth and development. Zeaxanthin epoxidase (ZEP) functions in ABA biosynthesis and the xanthophyll cycle and has a vital role in plant responses to various environmental stresses. It was found by quantitative real-time PCR (qRT-PCR) that MhZEP responded to saline-alkali stress and showed the highest expression at 48 h of saline-alkali stress, which was 14.53-fold of 0 h. The MhZEP gene was cloned from the apple rootstock begonia (Malus halliana Koehne) and its protein physicochemical properties were analyzed. Subsequently, the functional characterization of MhZEP (ID: 103403091) was further investigated in Arabidopsis thaliana. The MhZEP contained a complete open reading frame with a length of 1998 bp, and encoded 665 amino acids with an isoelectric point of 7.18. Phylogenetic tree analysis showed that MhZEP was the most homologous and closely related to Glycine max. Compared with wild-type, transgenic plants grew better under saline-alkali stress and the MhZEP-OE line showed higher chlorophyll content, carotenoid content, enzyme activities (POD, SOD, CAT and APX) and K+ content, whereas they had lower chlorosis and Na(+ )content than the wild type (WT), which indicated that they had strong resistance to stress. The expression levels of saline-alkali stress-related genes in A. thaliana MhZEP-OE were examined by qRT-PCR, and it was found that the MhZEP improved the tolerance of A. thaliana to saline-alkali stress tolerance by regulating the expression of carotenoid synthesis genes (MhPSY, MhZDS, MhLYCB and MhVDE) and ABA biosynthesis genes (MhNCED5, MhABI1 and MhCYP707A2). And the potassium-sodium ratio in the cytoplasm was increased to maintain ionic homeostasis by modulating the expression of Na+ transporter genes (MhCHX15 and MhSOS1) and K+ transporter genes (MhHKT1;1, MhNHX1 and MhSKOR1). Moreover, the expression of H+-ATPase genes (MhAHA2 and MhAHA8) was increased to reduce the oxidative damage caused by saline-alkali stress. In summary, MhZEP acted as an essential role in plant resistance to saline-alkali stress, which lays the foundation for further studies on its function in apple.

Key messageSaline-alkali stress induces oxidative damage and photosynthesis inhibition in H. citrina, with a significant downregulation of the expression of photosynthesis- and antioxidant-related genes at high concentration. Soil salinization is a severe abiotic stress that impacts the growth and development of plants. In this study, Hemerocallis citrina Baroni was used to investigate its responsive mechanism to complex saline-alkali stress (NaCl:Na2SO4:NaHCO3:Na2CO3 = 1:9:9:1) for the first time. The growth phenotype, photoprotective mechanism, and antioxidant system of H. citrina were studied combining physiological and transcriptomic techniques. KEGG enrichment and GO analyses revealed significant enrichments of genes related to photosynthesis, chlorophyll degradation and antioxidant enzyme activities, respectively. Moreover, weighted gene co-expression network analysis (WGCNA) found that saline-alkali stress remarkably affected the photosynthetic characteristics and antioxidant system. A total of 29 key genes related to photosynthesis and 29 key genes related to antioxidant enzymes were discovered. High-concentration (250 mmol L-1) stress notably inhibited the expression levels of genes related to light-harvesting complex proteins, photosystem reaction center activity, electron transfer, chlorophyll synthesis, and Calvin cycle in H. citrina leaves. However, most of them were insignificantly changed under low-concentration (100 mmol L-1) stress. In addition, H. citrina leaves under saline-alkali stress exhibited yellow-brown necrotic spots, increased cell membrane permeability and accumulation of reactive oxygen species (ROS) as well as osmolytes. Under 100 mmol L-1 stress, ROS was eliminate by enhancing the activities of antioxidant enzymes. Nevertheless, 250 mmol L-1 stress down-regulated the expression levels of genes encoding antioxidant enzymes, and key enzymes in ascorbate-glutathione (AsA-GSH) cycle as well as thioredoxin-peroxiredoxin (Trx-Prx) pathway, thus inhibiting the activities of these enzymes. In conclusion, 250 mmol L-1 saline-alkali stress caused severe damage to H. citrina mainly by inhibiting photosynthesis and ROS scavenging capacity.

ALDH (Aldehyde dehydrogenase), as an enzyme that encodes the dehydroxidization of aldehydes into corresponding carboxylic acids, played an important role inregulating gene expression in response to many kinds of biotic and abiotic stress, including saline-alkali stress. Saline-alkali stress was a common stress that seriously affected plant growth and productivity. Saline-alkali soil contained the characteristics of high salinity and high pH value, which could cause comprehensive damage such as osmotic stress, ion toxicity, high pH, and HCO3-/CO32- stress. In our study, 18 PaALDH genes were identified in sweet cherry genome, and their gene structures, phylogenetic analysis, chromosome localization, and promoter cis-acting elements were analyzed. Quantitative real-time PCR confirmed that PaALDH17 exhibited the highest expression compared to other members under saline-alkali stress. Subsequently, it was isolated from Prunus avium, and transgenic A. thaliana was successfully obtained. Compared with wild type, transgenic PaALDH17 plants grew better under saline-alkali stress and showed higher chlorophyll content, Superoxide dismutase (SOD), Peroxidase (POD) and Catalase (CAT) enzyme activities, which indicated that they had strong resistance to stress. These results indicated that PaALDH17 improved the resistance of sweet cherries to saline-alkali stress, which in turn improved quality and yields.

Licorice is widespread in arid and semi-arid areas, but high soil salinity has always been a limiting factor for vegetation growth in these areas. Gamma-aminobutyric acid (GABA) is a signaling molecule that can regulate tolerance in plant. However, the mechanism by which exogenous GABA regulates the response of licorice to saline-alkali stress is not yet clear. In this study, we investigated the effects of exogenous GABA on growth parameters, oxidative damage, hormone levels and photosynthetic indices of licorice seedlings under different combinations of saline and alkali stress conditions. The experiment involved eight treatments: CK, distilled water (control); CK + GABA, 0.1 mM GABA; salt stress (SS), 150 mM NaCl; SS + GABA, 150 mM NaCl + 0.1 mM GABA; alkali stress (AS), 10 mM Na2CO3; AS + GABA, 10 mM Na2CO3 + 0.1 mM GABA; mixed saline-alkali stress (MAS), 150 mM NaCl + 10 mM Na2CO3; MAS + GABA, 150 mM NaCl + 10 mM Na2CO3 + 0.1 mM GABA. Our results showed that the inhibitory effects of SS and MAS on the seedling height, root length and root-shoot ratio were significantly alleviated by exogenous GABA. Although soluble sugars, chlorophyll a, total chlorophyll, and superoxide dismutase (SOD) activity were lower in the leaves of the seedlings in the SS treatment compared with the control, these physiological parameters increased significantly after GABA application. Exogenous GABA improved glutathione (GSH) activity in both the leaves and roots of the seedlings during the AS treatment. Additionally, take advantage of GABA led to an increase in ABA, GA and IAA contents in leaves under SS, AS and MAS treatments. Furthermore, the photosynthetic parameters, including Pn, gs, Tr, ETR and qP, significantly increased following the utilization of GABA in both the SS and MAS treatments. Therefore, the application of exogenous GABA can reduce the accumulation of harmful substances, preserve cell morphology, and enhance cell function under saline, alkali, and saline-alkali stress. This enhances the resistance of licorice seedlings to stress conditions and reduces physiological damage.

Saline-alkali stress seriously endangers the normal growth of cotton (Gossypium hirsutum). Arbuscular mycorrhizal fungi (AMF) could enhance salt tolerance by establishing symbiotic relationships with plants. Based on it, a pot experiment was conducted to simulate a salt environment in which cotton was inoculated with Paraglomus occultum to explore its effects on the saline-alkali tolerance of cotton. Our results showed that salt stress noticeably decreased cotton seedling growth parameters (such as plant height, number of leaves, dry weight, root system architecture, etc.), while AMF exhibited a remarkable effect on promoting growth. It was noteworthy that AMF significantly mitigated the inhibitory effect of salt on cotton seedlings. However, AMF colonization in root and soil hyphal length were collectively descended via salt stress. With regard to osmotic regulating substances, Pro and MDA values in roots were significantly increased when seedlings were exposed to salt stress, while AMF only partially mitigated these reactions. Salt stress increased ROS levels in the roots of cotton seedlings and enhanced antioxidant enzyme activity (SOD, POD, and CAT), while AMF mitigated the increases in ROS levels but further strengthened antioxidant enzyme activity. AMF inoculation increased the photosynthesis parameters of cotton seedling leaves to varying degrees, while salt stress decreased them dramatically. When inoculated with AMF under a salt stress environment, only partial mitigation of these photosynthesis values was observed. Under saline-alkali stress, AMF improved the leaf fluorescence parameters (phi PSII, Fv '/Fm ', and qP) of cotton seedlings, leaf chlorophyll levels, and root endogenous hormones (IAA and BR); promoted the absorption of water; and maintained nitrogen balance, thus alleviating the damage from salt stress on the growth of cotton plants to some extent. In summary, mycorrhizal cotton seedlings may exhibit mechanisms involving root system architecture, the antioxidant system, photosynthesis, leaf fluorescence, endogenous hormones, water content, and nitrogen balance that increase their resistance to saline-alkali environments. This study provide a theoretical basis for further exploring the application of AMF to enhance the salt tolerance of cotton.