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Soil salinization and alkalization can cause great losses to agricultural production in arid regions. Cotton, a common crop in arid and semi-arid regions in China, often encounters saline stress and alkaline stress. In this study, NaCl (8 g·kg−1), Na2CO3 (8 g·kg−1), and a compound material (an organic polymer compound material) were mixed with field soil before cotton sowing, and the ion content, photosynthetic characteristics, and metabolite levels of the new cotton leaves were analyzed at the flowering and boll-forming stage, aiming to clarify the photosynthetic and metabolic mechanisms by which compound material regulates cotton's tolerance to saline stress and alkaline stress. The results showed that the application of the compound material led to an increase in the K+/Na+ ratio, stomatal conductance (Gs), efficiency of PSII photochemistry (ψPSⅡ), potential activity (Fv/Fo), and chlorophyll content (Chla and Chlb), as well as the abundances of D-xylonic acid and DL-phenylalanine in the NaCl treatments. Additionally, there were increases in the K+ content, K+/Na+ ratio, Chla/b ratio, net photosynthetic rate (Pn), transpiration rate (Tr), ψPSⅡ, and D-saccharic acid abundance in the Na2CO3 treatments. A correlation analysis and a metabolic pathway analysis revealed that the compound material mainly regulated the photosynthetic characteristics of and the ion balance in the new leaves through regulating the abundance of key metabolites when the cotton was under NaCl stress or Na2CO3 stress. Furthermore, the positive impact of the compound material on the cotton's NaCl stress tolerance was stronger than that on the cotton's Na2CO3 stress tolerance. [ABSTRACT FROM AUTHOR]

Saline–alkali environments restrict soybean production in China. Wild soybean genes can be used to improve the alkaline tolerance of cultivated soybean in molecular breeding. The expansin protein family promotes cell wall expansion. In this study, the relative expression levels of expansin family genes in wild soybean treated with 50 mM NaHCO3 were measured at 0, 3, 6, and 12 h, and the relative expression of GsEXPA8 was found to be higher at 12 h. Wild soybean was treated with abscisic acid (ABA), indole-3-acetic acid (IAA), gibberellic acid (GA), and jasmonic acid (JA), and GsEXPA8 was found to respond to ABA and IAA signals. Sequence analysis shows that GsEXPA8 has DPBB_EXPA and expansin domains. Subcellular localization analysis shows that GsEXPA8 was localized in the cytoplasm in protoplasts and the cell membrane or wall in tobacco, indicating that it has nuclear membrane localization signals. GsEXPA8 overexpression reduced the malondialdehyde content in transgenic plants treated with NaHCO3 and increased peroxidase activity before treatment. After the transformation of soybean roots from hair roots, GsEXPA8 was found to be expressed in the outer root cells and promote the development of thicker, shorter roots, thereby improving the plant's alkaline tolerance. Stable GsEXPA8 transformation improved saline alkaline tolerance via the regulation of the alkali stress-related genes GmKIN1, GmRD22, GmDnaJA6, GmNFYC1, and GmMYB14. These findings provide support for further research on alkali-tolerance regulation pathways and molecular breeding for alkali tolerance. [ABSTRACT FROM AUTHOR]

Under NaHCO3 stress, exogenous 24-epibrassinolide (EBR) markedly alleviated Na+ accumulation in cucumber plants, thereby decreasing the Na+/K+, Na+/Mg2+, and Na+/Ca2+ ratios. This mitigation was accompanied by elevated concentrations of K+, Ca2+, and Mg2+, as well as enhanced expression of the NHX and SOS1 genes. In addition, the activities of plasma membrane H+-ATPase, vesicular membrane H+-ATPase, and vesicular membrane H+-PPase were significantly increased, contributing to the maintenance of ionic balance in cucumber plants. NaHCO3 stress disrupted nitrogen metabolism, as evidenced by reductions in the activities of NR, GS, GOGAT, GOT, and GPT, along with altered GDH activity. These disruptions led to an accumulation of NH4+ and substantial decreases in NO3−-N and total nitrogen content. Exogenous EBR alleviated these effects by enhancing the activities of NR, GS, GOGAT, GOT, and GPT, countering the prolonged suppression of GDH activity, and restoring NO3−-N and total nitrogen levels. Consequently, EBR application reduced NH4+ toxicity induced by alkali stress. Additionally, NaHCO3 stress increased ABA accumulation while decreasing IAA and GA3 content in cucumber seedlings. In contrast, exogenous EBR application elevated IAA and GA3 levels and increased the IAA/ABA and GA3/ABA ratios, thus maintaining hormonal equilibrium under alkali stress. Collectively, these findings highlight that exogenous EBR enhances the alkaline tolerance of cucumber plants by regulating nitrogen metabolism, ion homeostasis, and phytohormonal responses. [ABSTRACT FROM AUTHOR]

Brassinosteroids (BRs) are recognized for their ability to enhance plant salt tolerance. While considerable research has focused on their effects under neutral salt conditions, the mechanisms through which BRs regulate photosynthesis under alkaline salt stress are less well understood. This study investigates these mechanisms, examining plant growth, photosynthetic electron transport, gas exchange parameters, Calvin cycle dynamics, and the expression of key antioxidant and Calvin cycle genes under alkaline stress conditions induced by NaHCO3. The findings indicate that NaHCO3 stress substantially impairs cucumber growth and photosynthesis, significantly reducing chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), antenna conversion efficiency (Fv′/Fm′), and photochemical quenching coefficient (qP). This disruption suggests a severe dysregulation of the photosynthetic electron transport system, impairing electron transfer from photosystem II (PSII) to photosystem I (PSI) and subsequently the Calvin cycle. Application of exogenous 24-epibrassinolide (EBR) alleviated these effects, reducing leaf chlorosis and growth inhibition and significantly enhancing the expression of key genes within the antioxidant system (AsA-GSH cycle) and the Calvin cycle. This intervention also led to a reduction in reactive oxygen species (ROS) accumulation and improved photosynthetic performance, as evidenced by enhancements in Pn, Gs, E, Fv/Fm, ΦPSII, Fv′/Fm′, and qP. Moreover, NaHCO3 stress hindered chlorophyll synthesis, primarily by blocking the conversion from porphobilinogen (PBG) to uroporphyrinogen III (UroIII) and by increasing chlorophyllase (Chlase) and decreasing porphobilinogen deaminase (PBGD) activity. Exogenous EBR countered these effects by enhancing PBGD activity and reducing Chlase activity, thereby increasing chlorophyll content under stress conditions. In summary, EBR markedly mitigated the adverse effects of alkaline stress on cucumber leaf photosynthesis by stabilizing the photosynthetic electron transport system, accelerating photosynthetic electron transport, and promoting the Calvin cycle. This study provides valuable insights into the regulatory roles of BRs in enhancing plant resilience to alkaline stress. [ABSTRACT FROM AUTHOR]

Alkaline stress imposes significant constraints on agriculture by reducing nutrient availability and inhibiting plant growth. This study examines the physiological and biochemical responses of chickpea (Cicer arietinum L.) seedlings to alkaline stress, with implications for improving crop resilience. Chickpea seedlings were subjected to combined Na₂CO₃ and NaHCO₃ treatments, and changes in growth, root morphology, and nutrient uptake were evaluated. Alkaline stress led to substantial reductions in growth metrics (shoot and root length, fresh and dry weights), root-to-shoot ratio, and lateral root number, indicating pronounced root damage. This damage was associated with elevated hydrogen peroxide (H₂O₂) levels, increased membrane damage, and reduced cell viability. In response to alkaline stress, chickpea roots accumulated osmolytes (proline, soluble sugars) and upregulated antioxidant enzymes (catalase, ascorbate peroxidase) as an adaptive response to mitigate osmotic and oxidative stress. Ion homeostasis was disrupted, with decreased uptake of essential nutrients like K, P, Mn, Fe, and Zn, while the uptake of Na, Mg, and Ca increased, disturbing nutrient balance. These findings underscore the need for strategies, such as genetic improvement to enhance alkaline stress tolerance in chickpea, contributing to improved crop performance in challenging soil conditions. [ABSTRACT FROM AUTHOR]

Alkaline stress can induce significant injury to plants, resulting in a range of negative effects, including ion toxicity, oxidative stress, and damage from high pH values. These stress factors can substantially affect normal plant growth and development, as well as yield and quality loss. To counteract alkaline stress, plants have developed a range of defense strategies, enabling them to adapt and thrive in challenging environments. These defense mechanisms operate at multiple levels such as morphological, physiological, biochemical, and molecular. The continuous advancement of genetic engineering has enabled significant breakthroughs in enhancing plant alkali resistance through human intervention. This research provides a scientific basis for crop production and ecological environment construction, and also promotes the effective development and utilization of saline-alkali lands, improving the sustainability of agricultural production. [ABSTRACT FROM AUTHOR]

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In recent years, alkaline soda soil has stimulated numerous biological research on plants under carbonate stress. Here, we explored the difference in physiological regulation of rice seedlings between saline (NaCl) and alkaline carbonate (NaHCO3 and Na2CO3) stress. The rice seedlings were treated with 40 mM NaCl, 40 mM NaHCO3 and 20 mM Na2CO3 for 2 h, 12 h, 24 h and 36 h, their physiological characteristics were determined, and organic acid biosynthesis and metabolism and hormone signalling were identified by transcriptome analysis. The results showed that alkaline stress caused greater damage to their photosynthetic and antioxidant systems and led to greater accumulation of organic acid, membrane damage, proline and soluble sugar but a decreased jasmonic acid content compared with NaCl stress. Jasmonate ZIM-Domain (JAZ), the probable indole-3-acetic acid-amido synthetase GH3s, and the protein phosphatase type 2Cs that related to the hormone signalling pathway especially changed under Na2CO3 stress. Further, the organic acid biosynthesis and metabolism process in rice seedlings were modified by both Na2CO3 and NaHCO3 stresses through the glycolate/glyoxylate and pyruvate metabolism pathways. Collectively, this study provides valuable evidence on carbonate-responsive genes and insights into the different molecular mechanisms of saline and alkaline stresses. Understanding how seedlings respond to stress from salt and alkalis can help inform strategies to boost plant performance in adverse environments. We examined how these stressors affect rice seedling physiology and gene expression. Genes that respond to salt and alkali stress are mainly involved in hormone signalling, and in the synthesis and metabolism of organic acids. These findings will contribute to engineering stress-tolerant crops. [ABSTRACT FROM AUTHOR]

Breeding abiotic stress-tolerant varieties of Rosa chinensis is a paramount goal in horticulture. WRKY transcription factors, pivotal in plant responses to diverse stressors, offer potential targets for enhancing stress resilience in R. chinensis. Using bioinformatics and genomic data, we identified RcWRKY transcription factor genes, characterised their chromosomal distribution, phylogenetic relationships, structural attributes, collinearity, and expression patterns in response to saline stress. Leveraging bidirectional database searches, we pinpointed 66 RcWRKY genes, categorised into three groups. All except RcWRKY60 encoded DNA Binding Domain and Zinc Finger Motif regions of the WRKY domain. Expansion of the RcWRKY gene family was propelled by 19 segmental, and 2 tandem, duplications. We unveiled 41 and 15 RcWRKY genes corresponding to 50 AtWRKY and 17 OsWRKY orthologs respectively, indicating postdivergence expansion. Expression analyses under alkaline stress pinpointed significant alterations in 54 RcWRKY genes. Integration of functional roles from their Arabidopsis orthologs and cis -acting elements within their promoters, along with quantitative reverse transcription PCR validation, underscored the importance of RcWRKY27 and 29 in R. chinensis ' alkaline stress response. These findings offer insights into the biological roles of RcWRKY transcription factors, as well as the regulatory dynamics governing R. chinensis ' growth, development, and stress resilience. The China rose (Rosa chinensis) is known as the 'queen of flowers', and is commercially cultivated globally. To enable breeders to develop varieties tolerant to alkaline soils, we investigated the genes involved in their stress response. This research will also contribute to the broader understanding of plant stress responses and offer potential avenues for enhancing stress tolerance in crop species. [ABSTRACT FROM AUTHOR]

Fluctuating environments that consist of regular cycles of co-occurring stress are a common challenge faced by cellular populations. For a population to thrive in constantly changing conditions, an ability to coordinate a rapid cellular response is essential. Here, we identify a mutation conferring an arginine-to-histidine (Arg to His) substitution in the transcription terminator Rho. The rho R109H mutation frequently arose in Escherichia coli populations experimentally evolved under repeated long-term starvation conditions, during which the accumulation of metabolic waste followed by transfer into fresh media results in drastic environmental pH fluctuations associated with feast and famine. Metagenomic sequencing revealed that populations containing the rho mutation also possess putative loss-of-function mutations in ydcI, which encodes a recently characterized transcription factor associated with pH homeostasis. Genetic reconstructions of these mutations show that the rho allele confers plasticity via an alkaline-induced reduction of Rho function that, when found in tandem with a ΔydcI allele, leads to intracellular alkalization and genetic assimilation of Rho mutant function. We further identify Arg to His substitutions at analogous sites in rho alleles from species that regularly experience neutral to alkaline pH fluctuations in their environments. Our results suggest that Arg to His substitutions in Rho may serve to rapidly coordinate complex physiological responses through pH sensing and shed light on how cellular populations use environmental cues to coordinate rapid responses to complex, fluctuating environments. [ABSTRACT FROM AUTHOR]

Soil alkalization is an adverse factor limiting plant growth and yield. As a signaling molecule and secondary metabolite, γ‐aminobutyric acid (GABA) responds rapidly to alkaline stress and enhances the alkaline resistance of plants. However, the molecular mechanisms by which the GABA pathway adapts to alkaline stress remain unclear. In this study, a transcription factor, MdNAC104 is identified, from the transcriptome of the alkaline‐stressed roots of apple, which effectively reduces GABA levels and negatively regulates alkaline resistance. Nevertheless, applying exogenous GABA compensates the negative regulatory mechanism of overexpressed MdNAC104 on alkaline resistance. Further research confirms that MdNAC104 repressed the GABA biosynthetic gene MdGAD1/3 and the GABA transporter gene MdALMT13 by binding to their promoters. Here, MdGAD1/3 actively regulates alkaline resistance by increasing GABA synthesis, while MdALMT13 promotes GABA accumulation and efflux in roots, resulting in an improved resistance to alkaline stress. This subsequent assays reveal that MdSINA2 interacts with MdNAC104 and positively regulates root GABA content and alkaline resistance by ubiquitinating and degrading MdNAC104 via the 26S proteasome pathway. Thus, the study reveals the regulation of alkaline resistance and GABA homeostasis via the MdSINA2‐MdNAC104‐MdGAD1/3/MdALMT13 module in apple. These findings provide novel insight into the molecular mechanisms of alkaline resistance in plants. [ABSTRACT FROM AUTHOR]

Alkaline stress imposes significant constraints on agriculture by reducing nutrient availability and inhibiting plant growth. This study examines the physiological and biochemical responses of chickpea (Cicer arietinum L.) seedlings to alkaline stress, with implications for improving crop resilience. Chickpea seedlings were subjected to combined Na₂CO₃ and NaHCO₃ treatments, and changes in growth, root morphology, and nutrient uptake were evaluated. Alkaline stress led to substantial reductions in growth metrics (shoot and root length, fresh and dry weights), root-to-shoot ratio, and lateral root number, indicating pronounced root damage. This damage was associated with elevated hydrogen peroxide (H₂O₂) levels, increased membrane damage, and reduced cell viability. In response to alkaline stress, chickpea roots accumulated osmolytes (proline, soluble sugars) and upregulated antioxidant enzymes (catalase, ascorbate peroxidase) as an adaptive response to mitigate osmotic and oxidative stress. Ion homeostasis was disrupted, with decreased uptake of essential nutrients like K, P, Mn, Fe, and Zn, while the uptake of Na, Mg, and Ca increased, disturbing nutrient balance. These findings underscore the need for strategies, such as genetic improvement to enhance alkaline stress tolerance in chickpea, contributing to improved crop performance in challenging soil conditions.

Soil alkalization is a major challenge for global crop production. This study reveals a novel defense mechanism in rice seedlings against alkaline stress, involving methyl jasmonate (MeJA) and auxin pathways. Under alkaline stress (15 mM Na2CO3), rice seedlings exhibited elevated levels of endogenous MeJA and upregulation of JA-responsive genes. Pre-treatment with MeJA (50 µM) significantly improved seedling survival, growth, and mitigated root damage under alkaline stress. This treatment also upregulated genes associated with cell death suppression (OsBI1) and stress tolerance (OsJRL, OsNAC). Notably, MeJA pre-treatment increased auxin (indole-3-acetic acid, IAA) levels in roots, and upregulated genes involved in IAA synthesis (OASA1, OASA2) and auxin signaling (Aux/IAA, ARFs). Blocking auxin transport with N-1-naphthylphthalamic acid intensified root damage under alkaline stress and diminished the protective effect of MeJA. These results highlight the crucial role of MeJA-induced activation of auxin pathway in enhancing rice tolerance to alkaline stress, and provide valuable insights for developing strategies to improve crop resilience in alkaline soils.

Salty-alkaline waters are widely distributed globally, and how to effectively develop saline-alkaline water to improve the utilization rate of water resources has become a global challenge. This study examined the survival performance of juvenile silver crucian carp (Carassius gibelio) under alkaline gradient acclimation conditions and explored the regulatory mechanisms for their adaptation to high alkalinity. Compared to directly immersing in high concentrations, alkaline gradient acclimation significantly improved the survival rate of juvenile silver crucian carp. Long-term high alkaline stress caused significant reduction in the growth performance of juvenile silver crucian carp. After alkaline stress, the enzyme activities of Na+-K+-ATP (NKA) and Ca2+-Mg2+-ATP (CMA) in the gills were significantly decreased. Meanwhile, histopathology of the gills showed structural changes, indicating that the physiological functions of juvenile silver crucian carp were impaired under alkaline conditions. Transcriptomic analysis found that the expression of genes related to metabolism and immune response pathways in the gill and kidney underwent significant changes. Genes related to carbohydrate metabolism were upregulated while those related to protein metabolism were downregulated, indicating that alkaline stress caused the organism to utilize carbohydrates rather than proteins as much as possible to meet enhanced metabolism. The HIF pathway that maintains the body's survival was significantly up-regulated, at the expense of high energy consumption. Dysregulation of genes related to the formation of neutrophil extracellular traps (NETosis) pathway indicated that the immune function of the fish was suppressed. Overall, this study revealed the physiological and molecular responses of juvenile silver crucian carp to alkaline stress, deepening our understanding of their adaptation strategies and the potential impact of alkaline environments on aquatic life.

Abstract Investigating differences in resistance to alkaline stress among three willow species can provide a theoretical basis for planting willow in saline soils. Therefore we tested three willow species (Salix matsudana, Salix gordejevii and Salix linearistipularis), already known for their high stress tolerance, to alkaline stress environment at different pH values under hydroponics. Root and leaf dry weight, root water content, leaf water content, chlorophyll content, photosynthesis and chlorophyll fluorescence of three willow cuttings were monitored six times over 15 days under alkaline stress. With the increase in alkaline stress, the water retention capacity of leaves of the three species of willow cuttings was as follows: S. matsudana > S. gordejevii > S. linearistipularis and the water retention capacity of the root system was as follows: S. gordejevii > S. linearistipularis > S. matsudana. The chlorophyll content was significantly reduced, damage symptoms were apparent. The net photosynthetic rate (Pn), rate of transpiration (E), and stomatal conductance (Gs) of the leaves showed a general trend of decreasing, and the intercellular CO2 concentration (Ci) of S. matsudana and S. gordejevii first declined and then tended to level off, while the intercellular CO2 concentration of S. linearistipularis first declined and then increased. The quantum yield and energy allocation ratio of the leaf photosystem II (PSII) reaction centre changed significantly (φPo, Ψo and φEo were obviously suppressed and φDo was promoted). The photosystem II (PSII) reaction centre quantum performance index and driving force showed a clear downwards trend. Based on the results it can be concluded that alkaline stress tolerance of three willow was as follows: S. matsudana > S. gordejevii > S. linearistipularis. However, since the experiment was done on young seedlings, further study at saplings stage is required to revalidate the results.

Abstract Background Soybean (Glycine max), a vital grain and oilseed crop, serves as a primary source of plant protein and oil. Soil salinization poses a significant threat to soybean planting, highlighting the urgency to improve soybean resilience and adaptability to saline stress. Melatonin, recently identified as a key plant growth regulator, plays crucial roles in plant growth, development, and responses to environmental stress. However, the potential of melatonin to mitigate alkali stress in soybeans and the underlying mechanisms remain unclear. Results This study investigated the effects of exogenous melatonin on the soybean cultivar Zhonghuang 13 under alkaline stress. We employed physiological, biochemical, transcriptomic, and metabolomic analyses throughout both vegetative and pod-filling growth stages. Our findings demonstrate that melatonin significantly counteracts the detrimental effects of alkaline stress on soybean plants, promoting plant growth, photosynthesis, and antioxidant capacity. Transcriptomic analysis during both growth stages under alkaline stress, with and without melatonin treatment, identified 2,834 and 549 differentially expressed genes, respectively. These genes may play a vital role in regulating plant adaptation to abiotic stress. Notably, analysis of phytohormone biosynthesis pathways revealed altered expression of key genes, particularly in the ARF (auxin response factor), AUX/IAA (auxin/indole-3-acetic acid), and GH3 (Gretchen Hagen 3) families, during the early stress response. Metabolomic analysis during the pod-filling stage identified highly expressed metabolites responding to melatonin application, such as uteolin-7-O-(2''-O-rhamnosyl)rutinoside and Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside, which helped alleviate the damage caused by alkali stress. Furthermore, we identified 183 differentially expressed transcription factors, potentially playing a critical role in regulating plant adaptation to abiotic stress. Among these, the gene SoyZH13_04G073701 is particularly noteworthy as it regulates the key differentially expressed metabolite, the terpene metabolite Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. WGCNA analysis identified this gene (SoyZH13_04G073701) as a hub gene, positively regulating the crucial differentially expressed metabolite of terpenoids, Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. Our findings provide novel insights into how exogenous melatonin alleviates alkali stress in soybeans at different reproductive stages. Conclusions Integrating transcriptomic and metabolomic approaches, our study elucidates the mechanisms by which exogenous melatonin ameliorates the inhibitory effects of alkaline stress on soybean growth and development. This occurs through modulation of biosynthesis pathways for key compounds, including terpenes, flavonoids, and phenolics. Our findings provide initial mechanistic insights into how melatonin mitigates alkaline stress in soybeans, offering a foundation for molecular breeding strategies to enhance salt-alkali tolerance in this crop.

Abstract Background and aims The escalating issue of soil saline-alkalization poses a growing global challenge. Leymus chinensis is a perennial grass species commonly used in the establishment and renewal of artificial grasslands that is relatively tolerant of saline, alkaline, and drought conditions. Nonetheless, reduced seed setting rates limit its propagation, especially on alkali-degraded grassland. Inter-annual variations have an important effect on seed yield and germination under abiotic stress, and we therefore examined the effect of planting year on seed yield components of L. chinensis. Methods We grew transplanted L. chinensis seedlings in pots for two (Y2), three (Y3), or four (Y4) years and collected spikes for measurement of seed yield components, including spike length, seed setting rate, grain number per spike, and thousand seed weight. We then collected seeds produced by plants from different planting years and subjected them to alkaline stress (25 mM Na2CO3) for measurement of germination percentage and seedling growth. Results The seed setting rate of L. chinensis decreased with an increasing number of years in pot cultivation, but seed weight increased. Y2 plants had a higher seed setting rate and more grains per spike, whereas Y4 plants had a higher thousand seed weight. The effects of alkaline stress (25 mM Na2CO3) on seed germination were less pronounced for the heavier seeds produced by Y4 plants. Na2CO3 caused a 9.2% reduction in shoot length for seedlings derived from Y4 seeds but a 22.3% increase in shoot length for seedlings derived from Y3 seeds. Conclusions Our findings demonstrate significant differences in seed yield components among three planting years of L. chinensis under pot cultivation in a finite space. Inter-annual variation in seed set may provide advantages to plants. Increased alkalinity tolerance of seed germination was observed for seeds produced in successive planting years.

Soil salinization and alkalization can cause great losses to agricultural production in arid regions. Cotton, a common crop in arid and semi-arid regions in China, often encounters saline stress and alkaline stress. In this study, NaCl (8 g·kg−1), Na2CO3 (8 g·kg−1), and a compound material (an organic polymer compound material) were mixed with field soil before cotton sowing, and the ion content, photosynthetic characteristics, and metabolite levels of the new cotton leaves were analyzed at the flowering and boll-forming stage, aiming to clarify the photosynthetic and metabolic mechanisms by which compound material regulates cotton’s tolerance to saline stress and alkaline stress. The results showed that the application of the compound material led to an increase in the K+/Na+ ratio, stomatal conductance (Gs), efficiency of PSII photochemistry (ψPSⅡ), potential activity (Fv/Fo), and chlorophyll content (Chla and Chlb), as well as the abundances of D-xylonic acid and DL-phenylalanine in the NaCl treatments. Additionally, there were increases in the K+ content, K+/Na+ ratio, Chla/b ratio, net photosynthetic rate (Pn), transpiration rate (Tr), ψPSⅡ, and D-saccharic acid abundance in the Na2CO3 treatments. A correlation analysis and a metabolic pathway analysis revealed that the compound material mainly regulated the photosynthetic characteristics of and the ion balance in the new leaves through regulating the abundance of key metabolites when the cotton was under NaCl stress or Na2CO3 stress. Furthermore, the positive impact of the compound material on the cotton’s NaCl stress tolerance was stronger than that on the cotton’s Na2CO3 stress tolerance.

Brassinosteroids (BRs) are recognized for their ability to enhance plant salt tolerance. While considerable research has focused on their effects under neutral salt conditions, the mechanisms through which BRs regulate photosynthesis under alkaline salt stress are less well understood. This study investigates these mechanisms, examining plant growth, photosynthetic electron transport, gas exchange parameters, Calvin cycle dynamics, and the expression of key antioxidant and Calvin cycle genes under alkaline stress conditions induced by NaHCO3. The findings indicate that NaHCO3 stress substantially impairs cucumber growth and photosynthesis, significantly reducing chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), antenna conversion efficiency (Fv′/Fm′), and photochemical quenching coefficient (qP). This disruption suggests a severe dysregulation of the photosynthetic electron transport system, impairing electron transfer from photosystem II (PSII) to photosystem I (PSI) and subsequently the Calvin cycle. Application of exogenous 24-epibrassinolide (EBR) alleviated these effects, reducing leaf chlorosis and growth inhibition and significantly enhancing the expression of key genes within the antioxidant system (AsA-GSH cycle) and the Calvin cycle. This intervention also led to a reduction in reactive oxygen species (ROS) accumulation and improved photosynthetic performance, as evidenced by enhancements in Pn, Gs, E, Fv/Fm, ΦPSII, Fv′/Fm′, and qP. Moreover, NaHCO3 stress hindered chlorophyll synthesis, primarily by blocking the conversion from porphobilinogen (PBG) to uroporphyrinogen III (UroIII) and by increasing chlorophyllase (Chlase) and decreasing porphobilinogen deaminase (PBGD) activity. Exogenous EBR countered these effects by enhancing PBGD activity and reducing Chlase activity, thereby increasing chlorophyll content under stress conditions. In summary, EBR markedly mitigated the adverse effects of alkaline stress on cucumber leaf photosynthesis by stabilizing the photosynthetic electron transport system, accelerating photosynthetic electron transport, and promoting the Calvin cycle. This study provides valuable insights into the regulatory roles of BRs in enhancing plant resilience to alkaline stress.

Under NaHCO3 stress, exogenous 24-epibrassinolide (EBR) markedly alleviated Na+ accumulation in cucumber plants, thereby decreasing the Na+/K+, Na+/Mg2+, and Na+/Ca2+ ratios. This mitigation was accompanied by elevated concentrations of K+, Ca2+, and Mg2+, as well as enhanced expression of the NHX and SOS1 genes. In addition, the activities of plasma membrane H+-ATPase, vesicular membrane H+-ATPase, and vesicular membrane H+-PPase were significantly increased, contributing to the maintenance of ionic balance in cucumber plants. NaHCO3 stress disrupted nitrogen metabolism, as evidenced by reductions in the activities of NR, GS, GOGAT, GOT, and GPT, along with altered GDH activity. These disruptions led to an accumulation of NH4+ and substantial decreases in NO3−-N and total nitrogen content. Exogenous EBR alleviated these effects by enhancing the activities of NR, GS, GOGAT, GOT, and GPT, countering the prolonged suppression of GDH activity, and restoring NO3−-N and total nitrogen levels. Consequently, EBR application reduced NH4+ toxicity induced by alkali stress. Additionally, NaHCO3 stress increased ABA accumulation while decreasing IAA and GA3 content in cucumber seedlings. In contrast, exogenous EBR application elevated IAA and GA3 levels and increased the IAA/ABA and GA3/ABA ratios, thus maintaining hormonal equilibrium under alkali stress. Collectively, these findings highlight that exogenous EBR enhances the alkaline tolerance of cucumber plants by regulating nitrogen metabolism, ion homeostasis, and phytohormonal responses.

Background and aims: The escalating issue of soil saline-alkalization poses a growing global challenge. Leymus chinensis is a perennial grass species commonly used in the establishment and renewal of artificial grasslands that is relatively tolerant of saline, alkaline, and drought conditions. Nonetheless, reduced seed setting rates limit its propagation, especially on alkali-degraded grassland. Inter-annual variations have an important effect on seed yield and germination under abiotic stress, and we therefore examined the effect of planting year on seed yield components of L. chinensis. Methods: We grew transplanted L. chinensis seedlings in pots for two (Y2), three (Y3), or four (Y4) years and collected spikes for measurement of seed yield components, including spike length, seed setting rate, grain number per spike, and thousand seed weight. We then collected seeds produced by plants from different planting years and subjected them to alkaline stress (25 mM Na2CO3) for measurement of germination percentage and seedling growth. Results: The seed setting rate of L. chinensis decreased with an increasing number of years in pot cultivation, but seed weight increased. Y2 plants had a higher seed setting rate and more grains per spike, whereas Y4 plants had a higher thousand seed weight. The effects of alkaline stress (25 mM Na2CO3) on seed germination were less pronounced for the heavier seeds produced by Y4 plants. Na2CO3 caused a 9.2% reduction in shoot length for seedlings derived from Y4 seeds but a 22.3% increase in shoot length for seedlings derived from Y3 seeds. Conclusions: Our findings demonstrate significant differences in seed yield components among three planting years of L. chinensis under pot cultivation in a finite space. Inter-annual variation in seed set may provide advantages to plants. Increased alkalinity tolerance of seed germination was observed for seeds produced in successive planting years. [ABSTRACT FROM AUTHOR]

Background: Soybean (Glycine max), a vital grain and oilseed crop, serves as a primary source of plant protein and oil. Soil salinization poses a significant threat to soybean planting, highlighting the urgency to improve soybean resilience and adaptability to saline stress. Melatonin, recently identified as a key plant growth regulator, plays crucial roles in plant growth, development, and responses to environmental stress. However, the potential of melatonin to mitigate alkali stress in soybeans and the underlying mechanisms remain unclear. Results: This study investigated the effects of exogenous melatonin on the soybean cultivar Zhonghuang 13 under alkaline stress. We employed physiological, biochemical, transcriptomic, and metabolomic analyses throughout both vegetative and pod-filling growth stages. Our findings demonstrate that melatonin significantly counteracts the detrimental effects of alkaline stress on soybean plants, promoting plant growth, photosynthesis, and antioxidant capacity. Transcriptomic analysis during both growth stages under alkaline stress, with and without melatonin treatment, identified 2,834 and 549 differentially expressed genes, respectively. These genes may play a vital role in regulating plant adaptation to abiotic stress. Notably, analysis of phytohormone biosynthesis pathways revealed altered expression of key genes, particularly in the ARF (auxin response factor), AUX/IAA (auxin/indole-3-acetic acid), and GH3 (Gretchen Hagen 3) families, during the early stress response. Metabolomic analysis during the pod-filling stage identified highly expressed metabolites responding to melatonin application, such as uteolin-7-O-(2''-O-rhamnosyl)rutinoside and Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside, which helped alleviate the damage caused by alkali stress. Furthermore, we identified 183 differentially expressed transcription factors, potentially playing a critical role in regulating plant adaptation to abiotic stress. Among these, the gene SoyZH13_04G073701 is particularly noteworthy as it regulates the key differentially expressed metabolite, the terpene metabolite Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. WGCNA analysis identified this gene (SoyZH13_04G073701) as a hub gene, positively regulating the crucial differentially expressed metabolite of terpenoids, Hederagenin-3-O-glucuronide-28-O-glucosyl(1,2)glucoside. Our findings provide novel insights into how exogenous melatonin alleviates alkali stress in soybeans at different reproductive stages. Conclusions: Integrating transcriptomic and metabolomic approaches, our study elucidates the mechanisms by which exogenous melatonin ameliorates the inhibitory effects of alkaline stress on soybean growth and development. This occurs through modulation of biosynthesis pathways for key compounds, including terpenes, flavonoids, and phenolics. Our findings provide initial mechanistic insights into how melatonin mitigates alkaline stress in soybeans, offering a foundation for molecular breeding strategies to enhance salt-alkali tolerance in this crop. [ABSTRACT FROM AUTHOR]

BACKGROUND: Enterococcus faecalis biofilm was frequently found on the failed treated root canal wall, which survived by resisting disinfectant during endodontic treatment.Many researches have been conducted to explore the mechanisms of persistence of this pathogen in unfavorable conditions. However, no comprehensive proteomics studies have been conducted to investigate stress response in Enterococcus faecalis caused by alkali and NaOCl. OBJECTIVE: Enterococcus faecalis (E.f) has been recognized as a main pathogen of refractory apical periodontitis, its ability to withstand environmental pressure is the key to grow in the environment of high alkaline and anti-bacterial drug that causes chronic infection in the root canal. This study aims to focus on the protein expression patterns of E.f biofilm under extreme pressure environment". METHODS: Enterococcus faecalis biofilm model was established in vitro. Liquid Chromatograph-Mass Spectrometer (LC-MS/MS)-based label free quantitative proteomics approach was applied to compare differential protein expression under different environmental pressures (pH 10 and 5% sodium hypochlorite (NaOCl)). And then qPCR and Parallel Reaction Monitoring Verification (PRM) were utilized to verify the consequence of proteomics. RESULTS: The number of taxa in this study was higher than those in previous studies, demonstrating the presence of a remarkable number of proteins in the groups of high alkaline and NaOCl. Proteins involved in ATP-binding cassette (ABC) transporter were significantly enriched in experimental samples. We identified a total of 15 highly expressed ABC transporters in the high alkaline environment pressure group, with 7 proteins greater than 1.5 times. CONCLUSIONS: This study revealed considerable changes in expression of proteins in E.f biofilm during resistance to environmental pressures. The findings enriched our understanding of association between the differential expression proteins and environmental pressures. [ABSTRACT FROM AUTHOR]

Silicon nanoparticles (Si NPs) have long been acknowledged for their ability to enhance plant defense against various biotic and abiotic stresses. Maize (Zea mays L.), among the plants known to accumulate Si NPs, is enhanced under stress conditions like alkalinity. In Pakistan's soils, sodium (Na+) is a dominant cation, and alkalinity (pH > 7) owing to Na+ salt is a big issue in the soil solution of agricultural soils of Pakistan. This study aimed to investigate the effects of different concentrations of Na2CO3 (0 and 75 mM) on maize seeds, along with varying levels of silicon nanoparticles (Si NPs) seed priming 0, 1.5 mM, and 3 mM over 25 days. The alkaline stress significantly impaired growth parameters, leaf relative water content (LRWC), and the concentrations of photosynthetic pigments, soluble sugars, total phenols, and potassium ions (K+), as well as the potassium/sodium ion (K+/Na+) ratio. However, this stress led to increased levels of soluble proteins, total free amino acids, proline, and sodium ions (Na+), and elevated the activities of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) in the stressed plants. Conversely, applying silicon nanoparticles through seed-priming mitigated the growth impediments in stressed plants. This intervention resulted in improved LRWC, higher levels of photosynthetic pigments, soluble sugars, soluble proteins, total free amino acids, and potassium ions (K+). Moreover, Si NPs enhanced the activities of SOD, CAT, and POD enzymes. Si supplementation also led to decreased levels of proline and sodium ions (Na+), which in turn facilitated a more favorable adjustment of the K+/Na+ ratio in stressed plants. [ABSTRACT FROM AUTHOR]

Species of the genus Atraphaxis are xerophytic shrubs growing in steppe and semidesert habitats on various soil types, including saline ones. Despite much interest in Atraphaxis species as sources of phenolic and polyphenolic compounds, information on approaches to the cultivation of these plants’ tissues is not available in the literature. In this study, an in vitro technology of A. frutescens propagation was developed for the first time. The Murashige and Skoog (MS) medium supplemented with 0.5 µM 6-benzylaminopurine was chosen as optimal. Microshoots were successfully rooted on the ½ MS medium without auxins or supplemented with 1 µM indole-3-butyric acid. All the media regarding the in vitro propagation contained 3% of sucrose and 0.6% of agar. The subcultivation period was 30 days. The A. frutescens in vitro culture showed resistance to osmotic stress (up to 150 mM D-mannitol) and to a wide pH range: 3.8 to 8.3. Under the influence of the culture medium, there was an increase in concentrations of catechins, tannins, phenolic acids, and saponins and in the total phenolic content and a decrease in the levels of flavonols as compared to a natural sample. Cultivation of samples on culture media with D-mannitol reduced the levels of flavonols and phenolic acids as compared to a control medium. The highest concentrations of tannins, catechins, and flavonols were noted at pH 8.3, and the same was true for saponins at pH 3.8. Meanwhile, no significant correlations were found between phenolic compounds and antiradical activity. Thus, in vitro culture of A. frutescens microshoots can serve as an alternative source of valuable classes of secondary metabolites such as catechins, tannins, saponins, and phenolic acids. In future studies, to create large-scale in vitro systems of A. frutescens, the selection of a proper bioreactor type and optimization of process parameters will be crucial for maximizing secondary-metabolite production.Key Message: This is the first report of an efficient in vitro methodology for Atraphaxis frutescens propagation and offers a tool for implementation of its conservation and for obtaining valuable secondary metabolites. [ABSTRACT FROM AUTHOR]

Alkaline soils pose an increasing problem for agriculture worldwide, but using stress-tolerant plants as green manure can improve marginal land. Here, we show that the legume Sesbania cannabina is very tolerant to alkaline conditions and, when used as a green manure, substantially improves alkaline soil. To understand genome evolution and the mechanisms of stress tolerance in this allotetraploid legume, we generated the first telomere-to-telomere genome assembly of S. cannabina spanning ∼2,087 Mb. The assembly included all centromeric regions, which contain centromeric satellite repeats, and complete chromosome ends with telomeric characteristics. Further genome analysis distinguished A and B subgenomes, which diverged approximately 7.9 million years ago. Comparative genomic analysis revealed that the chromosome homoeologs underwent large-scale inversion events (>10 Mb) and a significant, transposon-driven size expansion of the chromosome 5A homoeolog. We further identified four specific alkali-induced phosphate transporter genes in S. cannabina; these may function in alkali tolerance by relieving the deficiency in available phosphorus in alkaline soil. Our work highlights the significance of S. cannabina as a green tool to improve marginal lands and sheds light on subgenome evolution and adaptation to alkaline soils. [ABSTRACT FROM AUTHOR]

• We revealed the impact of Zn biofortification on rice productivity in alkaline soil. • Zn sulfate application improves growth, and photosynthetic pigments. • Zn sulfate triggered an antioxidant defense system and protected from oxidative damage. • Basmati-198 outperformed other cultivars regarding its overall performance in alkaline soils. Zinc (Zn) is a crucial trace mineral with diverse roles in plants; its deficiency in edible plant parts results in micronutrient malnutrition, leading to stunted growth. Zinc deficiency in the soil is a significant factor leading to poor rice quality. This research aimed to reveal the impact of Zn biofortification on rice productivity and to introduce rice cultivars with enriched nutrients. The effects of various zinc sulfate (ZnSO 4) rates viz. 100, 200, 300, 400 and 500 mM (designated as T1, T2, T3, T4 and T5, respectively) on the germination process, chlorophyll pigments, biochemical activities, and the mitigation of oxidative damage in four different rice (Oryza sativa L.) cultivars (KSK-133, Basmati-198, Basmati-515, and PK-386) grown in alkaline Zn-deficient soil were evaluated. A control without Zn application (T0) was kept for comparison. Results demonstrated that Zn treatments significantly affected the germination rates, vegetative growth, photosynthetic attributes, and enzymatic and non-enzymatic activities of all tested cultivars. Zn application significantly ameliorated the oxidative stress by increasing antioxidant enzyme activities such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), 2,2-diphenyl-1-picrylhydrazyl (DPPH), glutathione peroxidase, and non-enzymatic compounds (such as flavonoids, proline, phenolics, reducing sugar and non-reducing sugar, total carbohydrates, and free amino acid) in all tested cultivars. Among the application rates, ZnSO 4 application at 400 mM depicted the highest values of the above-mentioned traits. Furthermore, recorded data also revealed that ZnSO 4 had a significant impact on flavonoids, total carbohydrates, and phenolic contents where its application at 400 mM depicted significantly higher values than other treatments. Among the tested cultivars, Basmati-198 exhibited the highest values of flavonoids, total carbohydrates, and phenolic contents showing an increase of 134.53%, 103.57%, and 265.34%, respectively, over the average of other cultivars. In sum, ZnSO 4 application at 400 mM significantly improved rice performance under alkaline conditions whereas its application at 500 mM onsets toxic effect on all tested cultivars. However, to gain a comprehensive understanding of the underlying mechanisms, further research is needed to conduct long-term field studies at the molecular level. [ABSTRACT FROM AUTHOR]

Abstract Globally, land alkalinization affecting agricultural development. Considering the increasingly serious effects of alkaline stress on agriculture and environment, phytoremediation may be an efficient way to addressed land alkalinization. Broomcorn millet (Panicum miliaceum L.) is a saline‐alkaline‐tolerant crop and bioenergy crop. However, the molecular mechanism of alkaline response on broomcorn millet remains large gap. To explore the alkaline stress on broomcorn millet and the mitigation of 24‐epicastasterone (BR), the effects of CK (nutrient solution only), CB (nutrient solution + 0.5 mg L−1 BR), AS (alkaline stress), and AB (alkaline stress + 0.5 mg L−1 BR) on TA289 (alkaline‐tolerant) and SA223 (alkaline‐sensitive) were investigated. Alkaline stress enhanced reactive oxygen species and membrane lipid peroxidation. BR boosted antioxidant enzyme activities to reduce oxidative stress. Simultaneously, BR attenuated Na+ toxicity and maintained ion homeostasis. Additionally, BR significantly maintained the physiological structure and photosynthetic properties. Transcriptomic and metabolomic analyses were applied to further evaluate the effect of BR on photosynthetic and antioxidant defense. The results showed that BR significantly reduced the transcriptional responses of photosynthesis and antioxidant defense and promoted the accumulation of effective metabolites such as biliverdin, l‐glutamate, and phosphoric acid. Taken together, BR application can significantly alleviate the damage of alkaline stress to broomcorn millet by altering transcriptional expression and metabolite accumulation and is a simple and effective strategy to alleviate alkaline stress. This study reveals the molecular mechanism of BR to enhance photosynthetic capacity and antioxidant defense of broomcorn millet under alkaline stress, which provides theoretical support for the cultivation of bioenergy crops on alkaline lands and the breeding of alkaline‐tolerant bioenergy varieties.

Soybean is an important oil crop used as a plant protein and oil resource by humans, worldwide. However, abiotic stresses have significantly inhibiting soybean seed germination and yield. Plant hormones can improve stress tolerance by regulating gene expression and physiological processes. In this study, the effect of exogenous SL (strigolactone) was studied on germination and post-germination attributes of soybean grown under alkaline stress. Alkaline stress showed significant delayed response of the germination process and also reduced the radicle length. The qRT-PCR (real-time quantitative PCR) analysis showed that alkali stress increased the expression levels of GmABF4, GmAAO3, GmABI5, GmNCED5, and GmNCED9 genes in ABA (Abcisic acid) pathways. The exogenous application of SL promoted soybean radicle length. The SL-treated plants were much more tolerant to alkali stress exhibiting higher germination rates, longer radicles, increased fresh weight, and higher catalase enzyme activity as compared to control plants. After alkaline stress, the expression of SL biosynthetic and signaling genes, such as GmD27, GmCCD8, GmMAX2 and GmDAD2, was substantially increased under SL exogenous application while expression patterns of ABA biosynthetic and signaling genes, such as GmABI5, GmNCED9, and GmAAO3, were decreased. In conclusion, these results exhibited a positive role of SL on seed germination attributes via alleviation of ABA-mediated germination inhibition, improved antioxidant system as well as efficient biosynthesis, perception, and signaling of SL hormone. [ABSTRACT FROM AUTHOR]

Alkaline stress disrupts transcriptional expression and causes metabolite accumulation, thus affecting plant growth. However, there are gaps in the response mechanism of plants to alkaline stress at the molecular dimension. Broomcorn millet (Panicum miliaceum L.) is a pioneer plant for stress resistance also is a future smart food crop. To explore the physiological‐molecular response and adaptation mechanism of broomcorn millet root to alkaline stress, we conducted physiological, transcriptomic, and metabolomic analyses on roots of two broomcorn millet cultivars (alkaline‐sensitive S223 and alkaline‐tolerant T289) that were exposed to normal conditions (CK) and alkaline stress (AS) treatments (40 mM and a molar ratio of Na2CO3: NaHCO3 = 1:9) for 7 days. Alkaline stress inhibited mineral uptake in broomcorn millet roots and enhanced the antioxidant enzyme activities, malondialdehyde, and soluble substances, resulting in changes in growth, biomass, and root structure. Correspondingly, differentially expressed genes induced by alkaline stress were prominently enriched in the plant hormone signal transduction, mitogen‐activated protein kinase (MAPK) signaling, phenylpropanoid biosynthesis, ATP binding cassette (ABC) transporters, and other biological pathways. Similar results were obtained from the differentially accumulated metabolites analysis. In addition, joint transcriptome and metabolome analysis indicated that genes of phenylpropanoid and flavonoid biosynthesis pathways were upregulated or downregulated in AS groups, however, the related metabolite accumulations were inhibited. This study integrates multiple methods to uncover the mechanisms of broomcorn millet response to alkaline stress. These findings suggest a new direction for phytoremediation of alkaline lands. [ABSTRACT FROM AUTHOR]

Globally, land alkalinization affecting agricultural development. Considering the increasingly serious effects of alkaline stress on agriculture and environment, phytoremediation may be an efficient way to addressed land alkalinization. Broomcorn millet (Panicum miliaceum L.) is a saline‐alkaline‐tolerant crop and bioenergy crop. However, the molecular mechanism of alkaline response on broomcorn millet remains large gap. To explore the alkaline stress on broomcorn millet and the mitigation of 24‐epicastasterone (BR), the effects of CK (nutrient solution only), CB (nutrient solution + 0.5 mg L−1 BR), AS (alkaline stress), and AB (alkaline stress + 0.5 mg L−1 BR) on TA289 (alkaline‐tolerant) and SA223 (alkaline‐sensitive) were investigated. Alkaline stress enhanced reactive oxygen species and membrane lipid peroxidation. BR boosted antioxidant enzyme activities to reduce oxidative stress. Simultaneously, BR attenuated Na+ toxicity and maintained ion homeostasis. Additionally, BR significantly maintained the physiological structure and photosynthetic properties. Transcriptomic and metabolomic analyses were applied to further evaluate the effect of BR on photosynthetic and antioxidant defense. The results showed that BR significantly reduced the transcriptional responses of photosynthesis and antioxidant defense and promoted the accumulation of effective metabolites such as biliverdin, l‐glutamate, and phosphoric acid. Taken together, BR application can significantly alleviate the damage of alkaline stress to broomcorn millet by altering transcriptional expression and metabolite accumulation and is a simple and effective strategy to alleviate alkaline stress. This study reveals the molecular mechanism of BR to enhance photosynthetic capacity and antioxidant defense of broomcorn millet under alkaline stress, which provides theoretical support for the cultivation of bioenergy crops on alkaline lands and the breeding of alkaline‐tolerant bioenergy varieties. [ABSTRACT FROM AUTHOR]

Abstract It is currently unclear whether the mechanism of endophytic fungi improving the alkali tolerance of Hordeum bogdanii affects secondary metabolites. Unveiling this knowledge is crucial for understanding the tolerance mechanism of H. bogdanii to alkaline stress. The aim of this study was to investigate how endophytic fungi affect secondary metabolites of H. bogdanii under alkaline stress at different concentrations. Endophyte-infected (E +) and endophyte-free (E−) individuals of H. bogdanii were used as materials in this study. The method of indoor vermiculite aseptic planting was adopted. After mixed alkali stress treatment, the roots, stems, and leaves of the plants were collected to measure the indicators related to secondary metabolites. The results showed that endophytic fungi improved the alkali resistance of H. bogdanii by improving the related indicators of secondary metabolites. endophytic fungi significantly increased the contents of phosphorus, polyphenols, and alkaloids, and the activities of polyphenol oxidase and acid phosphatase, and significantly reduced flavonoid content. The content of polyphenols and alkaloids in stems, polyphenol oxidase activity in stems and leaves, and acid phosphatase activity in leaves were significantly affected. The findings of this study may aid in amplifying the alkali resistance mechanism of endophytic fungi to H. bogdanii as well as provide insights into improving the alkali resistance of other plants.

Salt stress poses a serious challenge to crop production and a significant threat to global food security and ecosystem sustainability. Soil salinization commonly occurs in conjunction with alkalization, which causes combined saline–alkaline stress. Alkaline soil predominantly comprises NaHCO 3 and Na 2 CO 3 and is characterized by a high pH. The combined saline–alkaline stress is more harmful to crop production than neutral salt stress owing to the effects of both elevated salinity and high pH stress. Through genome association analysis of sorghum, a recent study has identified Alkaline tolerance 1 (AT1) as a contributor to alkaline sensitivity in crops. AT1 , which is the first gene to be identified as being specifically associated with alkaline tolerance, encodes a G protein γ-subunit (Gγ). Editing of AT1 enhances the yields of sorghum, rice, maize, and millet grown in alkaline soils, indicating that AT1 has potential for generating alkaline-resistant crops. In this review, we summarize the role of AT1 in alkaline tolerance in plants and present a phylogenetic analysis along with a motif comparison of Gγ subunits of monocot and dicot plants across various species. [ABSTRACT FROM AUTHOR]

Alkaline stress is important abiotic stress that restricts the growth and physiological activity of sorghum (Sorghum bicolor L. Moench). We aimed to investigate the effects of alkaline stress on alkali-tolerant SX44B and alkali-sensitive 262B sorghum inbred lines. The results showed that alkaline stress decreased the content of chlorophyll, activity of photosystem II, net photosynthetic rate, and destroyed chloroplast morphology. These changes were less pronounced in SX44B, possibly owing to its higher antioxidant enzyme activity and nonphotochemical quenching. Alkaline stress decreased water content, transpiration rate, and stomatal conductance while increasing the leaf temperature, with the effect being more pronounced in 262B. A significant correlation was observed between leaf-air temperature difference (ΔT) and relative water content and gas-exchange parameters, especially in 262B. Therefore, ΔT is an effective indicator for monitoring changes in sorghum leaves under alkaline stress and evaluating the alkali tolerance of different sorghum germplasm.

Root development and plasticity are assessed via diverse endogenous and environmental cues, including phytohormones, nutrition, and stress. In this study, we observed that roots in model plant Arabidopsis thaliana exhibited waving and oscillating phenotypes under normal conditions but lost this pattern when subjected to alkaline stress. We later showed that alkaline treatment disturbed the auxin gradient in roots and increased auxin signal in columella cells. We further demonstrated that the auxin efflux transporter PINFORMED 7 (PIN7) but not PIN3 was translocated to vacuole lumen under alkaline stress. This process is essential for root response to alkaline stress because the pin7 knockout mutants retained the root waving phenotype. Moreover, we provided evidence that the PIN7 vacuolar transport might not depend on the ARF-GEFs but required the proper function of an ESCRT subunit known as FYVE domain protein required for endosomal sorting 1 (FREE1). Induced silencing of FREE1 disrupted the vacuolar transport of PIN7 and reduced sensitivity to alkaline stress, further highlighting the importance of this cellular process. In conclusion, our work reveals a new role of PIN7 in regulating root morphology under alkaline stress. [ABSTRACT FROM AUTHOR]

Auxin regulates plant growth and development, as well as helps plants to survive abiotic stresses, but the effects of auxin on the growth of alkaline-stressed rice and the underlying molecular and physiological mechanisms remain unknown. Through exogenous application of IAA/TIBA, this study explored the physiological and molecular mechanisms of alkaline stress tolerance enhancement using two rice genotypes. Alkaline stress was observed to damage the plant growth, while exogenous application of IAA mitigates the alkaline-stress-induce inhibition of plant growth. After application of exogenous IAA to alkaline-stressed rice, dry shoot biomass, foliar chlorophyll content, photosynthetic rate in the two rice genotypes increased by 12.6–15.6%, 11.7–40.3%, 51.4–106.6%, respectively. The adventitious root number, root surface area, total root length and dry root biomass in the two rice genotypes increased by 29.3–33.3%, 26.4–27.2%, 42.5–35.5% and 12.8–33.1%, respectively. The accumulation of H2O2, MAD were significantly decreased with the application of IAA. The activities of CAT, POD, and SOD in rice plants were significantly increased by exogenous application of IAA. The expression levels of genes controlling IAA biosynthesis and transport were significantly increased, while there were no significant effects on the gene expression that controlled IAA catabolism. These results showed that exogenous application of IAA could mitigate the alkaline-stress-induced inhibition of plant growth by regulating the reactive oxygen species scavenging system, root development and expression of gene involved in IAA biosynthesis, transport and catabolism. These results provide a new direction and empirical basis for improving crop alkaline tolerance with exogenous application of IAA. [ABSTRACT FROM AUTHOR]

Background. NDR1/HIN1-like (NHL) family genes are known to be involved in pathogen induced plant responses to biotic stress. Even though the NHL family genes have been identified and characterized in plant defense responses in some plants, the roles of these genes associated with the plant abiotic stress tolerance in wild soybean is not fully established yet, especially in response to alkaline stress. Methods. We identified the potential NHL family genes by using the Hidden Markov model and wild soybean genome. The maximum-likelihood phylogenetic tree and conserved motifs were generated by using the MEME online server and MEGA 7.0 software, respectively. Furthermore, the syntenic analysis was generated with Circos-0.69. Then we used the PlantCARE online software to predict and analyze the regulatory cis-acting elements in promoter regions. Hierarchical clustering trees was generated using TM4: MeV4.9 software. Additionally, the expression levels of NHL family genes under alkaline stress, ABA and MEJA treatment were identified by qRT-PCR. Results. In this study, we identified 59 potential NHL family genes in wild soybean. We identified that wild soybean NHL family genes could be mainly classified into five groups as well as exist with conserved motifs. Syntenic analysis of NHL family genes revealed genes location on 18 chromosomes and presence of 65 pairs of duplication genes. Moreover, NHL family genes consisted of a variety of putative hormone-related and abiotic stress responsive elements, where numbers of methyl jasmonate (MeJA) and abscisic acid (ABA) responsive elements were significantly larger than other elements. We confirmed the regulatory roles ofNHLfamily genes in response to alkaline stress, ABA and MEJA treatment. In conclusion, we identified and provided valuable information on the wild soybean NHL family genes, and established a foundation to further explore the potential roles of NHL family genes in crosstalk with MeJA or ABA signal transduction mechanisms under alkaline stress. [ABSTRACT FROM AUTHOR]

Abstract Background Zinc finger homeodomain (ZHD) protein is a plant-specific transcription factor and a potential regulator of phosphoenolpyruvate carboxylase (PEPCase)-coding genes, and it also participates in plant growth regulation and abiotic stress responses. To study the function of MsZF-HD genes in the alkaline stress response, this paper assessed biological information and performed transcriptome analysis of the MsZF-HD gene family by using the genomes of two different varieties of alfalfa (XinJiangDa Ye and Zhongmu No. 1). Results In total, 49 and 11 MsZF-HD genes were identified in the two different varieties respectively, including the alleles of XinJiangDa Ye. According to their phylogenetic relationships, the 60 MsZF-HD genes were divided into 5 ZHD subfamilies and 1 MIF subfamily. A total of 88.3% of MsZF-HD genes do not contain introns and are unevenly distributed among the 6 chromosomes of alfalfa. A collinearity analysis indicated that 26 genes of XinJiangDa Ye have no orthologous genes in Zhongmu No. 1, although these genes (such as ZHD-X1–2, ZHD-X3–2 and ZHD-X4–2) have homologous genes in Arabidopsis thaliana, Medicago truncatula and Glycine max. Through RNA-seq and qRT–PCR verification, it was found that MsZF-HD genes are downregulated to participate in the alkaline stress response. Conclusion The results of this study may lay the foundation for the cloning and functional study of MsZF-HD genes and provide a theoretical basis for revealing the difference between XinJiangDa Ye and Zhongmu No. 1 at the genome level.

Abstract Background The internal NAD(P)H dehydrogenase (NDA) gene family was a member of the NAD(P)H dehydrogenase (ND) gene family, mainly involved in the non-phosphorylated respiratory pathways in mitochondria and played crucial roles in response to abiotic stress. Methods The whole genome identification, structure analysis and expression pattern of NDA gene family were conducted to analyze the NDA gene family. Results There were 51, 52, 26, and 24 NDA genes identified in G. hirsutum, G. barbadense, G. arboreum and G. raimondii, respectively. According to the structural characteristics of genes and traits of phylogenetic tree, we divided the NDA gene family into 8 clades. Gene structure analysis showed that the NDA gene family was relatively conservative. The four Gossypium species had good collinearity, and segmental duplication played an important role in the evolution of the NDA gene family. Analysis of cis-elements showed that most GhNDA genes contained cis-elements related to light response and plant hormones (ABA, MeJA and GA). The analysis of the expression patterns of GhNDA genes under different alkaline stress showed that GhNDA genes were actively involved in the response to alkaline stress, possibly through different molecular mechanisms. By analyzing the existing RNA-Seq data after alkaline stress, it was found that an NDA family gene GhNDA32 was expressed, and then theGhNDA32 was silenced by virus-induced gene silencing (VIGS). By observing the phenotype, we found that the wilting degree of silenced plants was much higher than that of the control plant after alkaline treatment, suggesting that GhNDA32 gene was involved in the response to alkaline stress. Conclusions In this study, GhNDAs participated in response to alkaline stress, especially NaHCO3 stress. It was of great significance for the future research on the molecular mechanism of NDA gene family in responding to abiotic stresses.

Malus hupehensis is one of the most widely used apple rootstocks in china but is severely damaged by alkaline soil. Alkaline stress can cause more serious harmful effects on apple plants than salt stress because it also induces high pH stress except for ion toxicity, osmotic stress, and oxidative damage. Brassinolide (BL) plays important roles in plant responses to salt stress. However, its role and function mechanism in apple plants in response to alkaline stress has never been reported. This study showed that applying exogenous 0.2 mg/L BL significantly enhanced the resistance of M. hupehensis seedlings to alkaline stress. The main functional mechanisms were also explored. First, exogenous BL could decrease the rhizosphere pH and promote Ca2+ and Mg2+ absorption by regulating malic acid and citric acid contents and increasing H+ excretion. Second, exogenous BL could alleviate ion toxicity caused by alkaline stress through enhancing Na+ efflux and inhibiting K+ expel and vacuole compartmentalization. Last, exogenous BL could balance osmotic stress by accumulating proline and reduce oxidative damage through increasing the activities of antioxidant enzymes and antioxidants contents. This study provides an important theoretical basis for further analyzing the mechanism of exogenous BL in improving alkaline tolerance of apple plants. [ABSTRACT FROM AUTHOR]

An extreme thermophile, Thermus thermophilus, produces 16 different polyamines including long-chain and branched-chain polyamines. The composition and content of polyamines in the thermophile cells change not only with growth temperature but also with pH changes. In particular, cell growth decreased greatly at alkaline medium together with significant changes in the composition and content of polyamines. The amounts of tetraamines (spermine and its homologs) markedly decreased at alkaline pH. Thus, we knocked out the speE gene, which is involved in the biosynthesis of tetraamines, and changes of composition of polyamines with pH changes in the mutant cells were studied. Cell growth in the ΔspeE strain was decreased compared with that of the wild-type strain for all pHs, suggesting that tetraamines are important for cell proliferation. Interestingly, the amount of spermidine decreased and that of putrescine increased in wild-type cells at elevated pH, although T. thermophilus lacks a putrescine synthesizing pathway. In addition, polyamines possessing a diaminobutane moiety, such as spermine, decreased greatly at high pH. We assessed whether the speB gene encoding aminopropylagmatine ureohydrolase (TtSpeB) is directly involved in the synthesis of putrescine. The catalytic assay of the purified enzyme indicated that TtSpeB accepts agmatine as its substrate and produces putrescine due to the change in substrate specificity at high pH. These results suggest that pH stress was exacerbated upon intracellular depletion of polyamines possessing a diaminobutane moiety induced by unusual changes in polyamine biosynthesis under high pH conditions. [ABSTRACT FROM AUTHOR]

Saline-alkali soil is a major environmental problem affecting crop productivity. One of the most effective approaches to combat it is to breed stress-tolerant plants through genetic engineering. Shanrong No. 4 (SR4) is an alkaline-tolerant cultivar of bread wheat (Triticum aestivum) derived from asymmetric somatic hybridization between the common wheat cultivar Jinan 177 (JN177) and tall wheatgrass. In this study, we aimed to explore the structure and function of alkalinity stress-responsive long non-coding RNAs (lncRNAs) in wheat. Sequencing was employed to identify the lncRNAs associated with stress tolerance and their corresponding targets. Approximately 19 000 novel lncRNA sequences were detected in SR4 and JN177. Upon exposure to alkaline stress, SR4 differentially expressed 5691 lncRNAs, whilst JN177 differentially expressed 5932. We selected five of them (L0760, L6247, L0208, L2098, and L3065) and generated seedlings of transiently knocked down strains using the virus-induced gene-silencing method. Knockdown of L0760 and L2098 caused the plants to exhibit sensitivity to alkaline stress, whereas knockdown of L6247, L0208, and L3065 increased the ability of plants to tolerate alkaline stress. We constructed lncRNA–miRNA–target-mRNA networks and alkali-response-related lncRNA–target-mRNA association networks to analyse the functions of lncRNAs. Collectively, our results demonstrate that lncRNAs may perform different roles under alkaline stress conditions. [ABSTRACT FROM AUTHOR]

• Alkaline stress induced decline in growth and nutrient acquisition. • Taurine functioned as an endogenous antioxidant. • Taurine mediated ROS metabolism and ions homeostasis. • Taurine reduced the peroxidation of lipids. Alkaline stress is among major environmental constraints that impair plant growth and yield production worldwide. Taurine protects cells from oxidative injury in animals. There exists no report in the literature on taurine functions in plants under environmental constraints. Therefore, the current study was aimed to assess the role of taurine in lessening the harmful effects of alkaline stress on growth of Trifolium alexandrinum L. (Berseem clover). Alkaline conditions (0, 25, 50 and 75 mM Na 2 CO 3) resulted in a notable reduction in growth, chlorophyll contents, relative water content, and essential nutrient uptake. The uptake of toxic Na+ was significantly greater in plants under stress, creating specific ion toxicity. Further, oxidative damage due to alkaline stress was noticeable in plants mirrored as higher hydrogen peroxide (H 2 O 2), superoxide radical (O 2 •‒), methylglyoxal (MG), malondialdehyde (MDA), and oxidized glutathione GSSG generation. Taurine supplementation (0, 100, and 200 mg L‒1) protected plants from osmotic stress, ions excess toxicity, and oxidative injury under alkaline conditions. Taurine notably reduced the uptake and accumulation of Na+ in plants. In contrast, the K+, Ca2+, and P contents were several folds higher in plants treated with taurine under alkaline conditions. The schematic representation depicts taurine-mediated increased tolerance to alkaline stress. [Display omitted]. [ABSTRACT FROM AUTHOR]

Ribonucleic acid editing (RE) is a post-transcriptional process that altered the genetics of RNA which provide the extra level of gene expression through insertion, deletions, and substitutions. In animals, it converts nucleotide residues C-U. Similarly in plants, the role of RNA editing sites (RES) in rice under alkaline stress is not fully studied. Rice is a staple food for most of the world population. Alkaline stress cause reduction in yield. Here, we explored the effect of alkaline stress on RES in the whole mRNA from rice chloroplast and mitochondria. Ribonucleic acid editing sites in both genomes (3336 RESs) including chloroplast (345 RESs) and mitochondria (2991 RESs) with average RES efficiency ∼55% were predicted. Our findings showed that majority of editing events found in non-synonymous codon changes and change trend in amino acids was hydrophobic. Four types of RNA editing A-G (A-I), C-T (C-U), G-A, and T-C were identified in treated and untreated samples. Overall, RNA editing efficiency was increased in the treated samples. Analysis of Gene Ontology revealed that mapped genes were engaged in many biological functions and molecular processes. We also checked the expression of pentatricopeptide repeat (PPR), organelle zinc-finger (OZI), and multiple organellar RNA editing factors/RNA editing factor interacting proteins genes in control and treatment, results revealed upregulation of PPR and OZ1 genes in treated samples. This induction showed the role of these genes in RNA editing. The current findings report that RNA editing increased under alkaline stress which may contribute in adaptation for rice by changing amino acids in edited genes (88 genes). These findings will provide basis for identification of RES in other crops and also will be useful in alkaline tolerance development in rice. [ABSTRACT FROM AUTHOR]

It is currently unclear whether the mechanism of endophytic fungi improving the alkali tolerance of Hordeum bogdanii affects secondary metabolites. Unveiling this knowledge is crucial for understanding the tolerance mechanism of H. bogdanii to alkaline stress. The aim of this study was to investigate how endophytic fungi affect secondary metabolites of H. bogdanii under alkaline stress at different concentrations. Endophyte-infected (E +) and endophyte-free (E−) individuals of H. bogdanii were used as materials in this study. The method of indoor vermiculite aseptic planting was adopted. After mixed alkali stress treatment, the roots, stems, and leaves of the plants were collected to measure the indicators related to secondary metabolites. The results showed that endophytic fungi improved the alkali resistance of H. bogdanii by improving the related indicators of secondary metabolites. endophytic fungi significantly increased the contents of phosphorus, polyphenols, and alkaloids, and the activities of polyphenol oxidase and acid phosphatase, and significantly reduced flavonoid content. The content of polyphenols and alkaloids in stems, polyphenol oxidase activity in stems and leaves, and acid phosphatase activity in leaves were significantly affected. The findings of this study may aid in amplifying the alkali resistance mechanism of endophytic fungi to H. bogdanii as well as provide insights into improving the alkali resistance of other plants. [ABSTRACT FROM AUTHOR]

Ribonucleic acid editing (RE) is a post-transcriptional process that altered the genetics of RNA which provide the extra level of gene expression through insertion, deletions, and substitutions. In animals, it converts nucleotide residues C-U. Similarly in plants, the role of RNA editing sites (RES) in rice under alkaline stress is not fully studied. Rice is a staple food for most of the world population. Alkaline stress cause reduction in yield. Here, we explored the effect of alkaline stress on RES in the whole mRNA from rice chloroplast and mitochondria. Ribonucleic acid editing sites in both genomes (3336 RESs) including chloroplast (345 RESs) and mitochondria (2991 RESs) with average RES efficiency ∼55% were predicted. Our findings showed that majority of editing events found in non-synonymous codon changes and change trend in amino acids was hydrophobic. Four types of RNA editing A-G (A-I), C-T (C-U), G-A, and T-C were identified in treated and untreated samples. Overall, RNA editing efficiency was increased in the treated samples. Analysis of Gene Ontology revealed that mapped genes were engaged in many biological functions and molecular processes. We also checked the expression of pentatricopeptide repeat (PPR), organelle zinc-finger (OZI), and multiple organellar RNA editing factors/RNA editing factor interacting proteins genes in control and treatment, results revealed upregulation of PPR and OZ1 genes in treated samples. This induction showed the role of these genes in RNA editing. The current findings report that RNA editing increased under alkaline stress which may contribute in adaptation for rice by changing amino acids in edited genes (88 genes). These findings will provide basis for identification of RES in other crops and also will be useful in alkaline tolerance development in rice.