Artificial Selection on Microbiomes To Breed Microbiomes That Confer Salt Tolerance to Plants

Climate change is causing soil salinization, resulting in crop losses throughout the world. The ability of plants to tolerate salt stress is determined by multiple biochemical and molecular pathways. Here we discuss physiological, biochemical, and cellular modulations in plants in response to salt stress. Knowledge of these modulations can assist in assessing salt tolerance potential and the mechanisms underlying salinity tolerance in plants. Salinity-induced cellular damage is highly correlated with generation of reactive oxygen species, ionic imbalance, osmotic damage, and reduced relative water content. Accelerated antioxidant activities and osmotic adjustment by the formation of organic and inorganic osmolytes are significant and effective salinity tolerance mechanisms for crop plants. In addition, polyamines improve salt tolerance by regulating various physiological mechanisms, including rhizogenesis, somatic embryogenesis, maintenance of cell pH, and ionic homeostasis. This research project focuses on three strategies to augment salinity tolerance capacity in agricultural crops: salinity-induced alterations in signaling pathways; signaling of phytohormones, ion channels, and biosensors; and expression of ion transporter genes in crop plants (especially in comparison to halophytes).

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The Role of Betacyanins in Plant Salt Tolerance

10.26686/wgtn.17147906 ◽

2021 ◽

Author(s):

◽

Tanja Karl

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

High Light ◽

Crop Plants ◽

Ion Flux ◽

Mesophyll Cells ◽

Leaf Discs ◽

Green Leaves ◽

Flux Response ◽

Salt Secretion

<p>Soil salinity is a major threat to future food stability. Almost 20% of irrigated land is currently too saline to grow traditional crops. Moreover, rising sea levels, scarcity of fresh water, and more intense and prolonged periods of drought are exacerbating the problem. Saline soils severely reduce yields of most crop plants. By contrast, halophytes, which naturally thrive on saline substrates, have a variety of mechanisms to tolerate both the osmotic and cytotoxic components of salt stress. There has been concerted scientific effort worldwide to understand these mechanisms, and to introduce genes that may increase salinity tolerance in crop plants. Many halophytes in the Caryophyllales are pigmented red owing to a tyrosine-derived alkaloid called betacyanin. Recent studies using Disphyma australe, a succulent halophyte common on coastal dunes and rocky outcrops throughout New Zealand, have indicated a role for betacyanins in salinity tolerance. This thesis focuses on how the mechanism through which betacyanins might affect salt tolerance mechanisms in D. australe and whether the putative benefits of betacyanins on salt tolerance might be transferred to naturally non-betacyanic plants. Effects of betacyanin on Na+ distribution in salt-stressed leaves of red and green morphs of D. australe were studied using fluorescence microscopy, cryo-scanning electron microscopy with energy dispersive X-ray analysis, and atomic absorption spectrometry (AAS). In betacyanic leaves Na+ accumulated in the epidermis, while in green leaves Na+ was distributed more evenly across the epidermis and mesophyll. Both leaf types had similar numbers of salt glands, but salt secretion rates were higher in red than in green leaves. Betacyanic leaves under salt stress were able to maintain relatively high K+/ Na+ ratios, essential for many metabolic processes, while the leaves of green plants were not. Leaf sections stained with fluorescein diacetate and propidium iodide showed that mesophyll viability decreased significantly in green leaves under salt stress, while there was almost no decrease in mesophyll viability in the presence of betacyanins. Thus, betacyanic leaves might protect the photosynthetically active mesophyll from cytotoxic effects of Na+ by accumulating Na+ in the epidermis instead of the mesophyll. This in turn leads to more efficient salt secretion and higher K+/ Na+ ratios in the mesophyll, resulting in increased mesophyll viability under salt stress. Effects of high apoplastic sodium concentrations on ion flux kinetics in mesophyll tissue was studied using the non-invasive microelectrode ion flux estimation technique. Mesophyll cells of both betacyanic and green leaves showed a highly unusual K+ flux response; most crop plants leak K+ out of cells upon salt stress, but D. australe and the native Australian Disphyma crassifolium both showed K+ influx upon salt stress. Actively taking up K+ from the apoplast to maintain a high cytosolic K+/ Na+ ratio during salt stress might be an entirely new mechanism to combat the cytotoxic stress component of salinity stress in these halophytes. The salt induced K+ uptake was dependent on the presence of Cl- and Cl- was also taken up into mesophyll cells upon salt stress. Taking up both cations and anions at the same time could avoid membrane depolarisation. Voltage-gated channels, which are involved in the salt induced K+ efflux in glycophytes, would not be activated and this could be a new mechanism to avoid a K+ leak during salt stress. To test whether the beneficial effect of betacyanin production on salt tolerance could be transferred to naturally non-betacyanic plants, transgenic betacyanin-over-expression (BtOE) mutants of Nicotiana tabacum were generated by our colleagues at Plant & Food Research Ltd. Betacyanins in leaf discs of N. tabacum were associated with decreased chlorophyll degradation upon high light and high salt stress. Additionally, the decline in maximum quantum efficiency of PSII after high light and salt treatment was significantly greater in green than in betacyanic leaves. Placing a polycarbonate filter with a similar absorption spectrum to betacyanin over green N. tabacum leaf discs had a similar effect to the presence of betacyanin. Thus, betacyanins probably have a photoprotective effect in N. tabacum, which is essential as both high light and salinity can impair photosynthesis. To assess if the salt tolerance enhancing effect of betacyanin production observed in the leaf discs also occurs in whole N. tabacum plants, the ability to recover from exposure to saturating light was assessed. Betacyanic plants were able to fully recover quicker after exposure to saturation light than green leaves. This research shows that the presence of betacyanins during salt stress correlates with an altered Na+ distribution in leaf tissues and a higher salt secretion rate, which contributed to higher mesophyll viability. Moreover, a completely new ion flux response to salt stress was observed in D. australe and D. crassifolium. The observed salt induced K+ uptake into the mesophyll cells during salt stress might be an entirely new mechanism, to maintain a high K+/ Na+ ratio in the cytosol and avoid the cytotoxic effects of Na+ in photosynthetically active tissue. The beneficial effects of betacyanins could also be transferred to non-betacyanic species, by introducing betacyanin production. These results strongly suggest that betacyanins play a role in salt tolerance in halophytes and might be a valuable resource in increasing the salt tolerance of naturally non-betacyanic crop plants.</p>

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The Role of Betacyanins in Plant Salt Tolerance

10.26686/wgtn.17147906.v1 ◽

2021 ◽

Author(s):

◽

Tanja Karl

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

High Light ◽

Crop Plants ◽

Ion Flux ◽

Mesophyll Cells ◽

Leaf Discs ◽

Green Leaves ◽

Flux Response ◽

Salt Secretion

<p>Soil salinity is a major threat to future food stability. Almost 20% of irrigated land is currently too saline to grow traditional crops. Moreover, rising sea levels, scarcity of fresh water, and more intense and prolonged periods of drought are exacerbating the problem. Saline soils severely reduce yields of most crop plants. By contrast, halophytes, which naturally thrive on saline substrates, have a variety of mechanisms to tolerate both the osmotic and cytotoxic components of salt stress. There has been concerted scientific effort worldwide to understand these mechanisms, and to introduce genes that may increase salinity tolerance in crop plants. Many halophytes in the Caryophyllales are pigmented red owing to a tyrosine-derived alkaloid called betacyanin. Recent studies using Disphyma australe, a succulent halophyte common on coastal dunes and rocky outcrops throughout New Zealand, have indicated a role for betacyanins in salinity tolerance. This thesis focuses on how the mechanism through which betacyanins might affect salt tolerance mechanisms in D. australe and whether the putative benefits of betacyanins on salt tolerance might be transferred to naturally non-betacyanic plants. Effects of betacyanin on Na+ distribution in salt-stressed leaves of red and green morphs of D. australe were studied using fluorescence microscopy, cryo-scanning electron microscopy with energy dispersive X-ray analysis, and atomic absorption spectrometry (AAS). In betacyanic leaves Na+ accumulated in the epidermis, while in green leaves Na+ was distributed more evenly across the epidermis and mesophyll. Both leaf types had similar numbers of salt glands, but salt secretion rates were higher in red than in green leaves. Betacyanic leaves under salt stress were able to maintain relatively high K+/ Na+ ratios, essential for many metabolic processes, while the leaves of green plants were not. Leaf sections stained with fluorescein diacetate and propidium iodide showed that mesophyll viability decreased significantly in green leaves under salt stress, while there was almost no decrease in mesophyll viability in the presence of betacyanins. Thus, betacyanic leaves might protect the photosynthetically active mesophyll from cytotoxic effects of Na+ by accumulating Na+ in the epidermis instead of the mesophyll. This in turn leads to more efficient salt secretion and higher K+/ Na+ ratios in the mesophyll, resulting in increased mesophyll viability under salt stress. Effects of high apoplastic sodium concentrations on ion flux kinetics in mesophyll tissue was studied using the non-invasive microelectrode ion flux estimation technique. Mesophyll cells of both betacyanic and green leaves showed a highly unusual K+ flux response; most crop plants leak K+ out of cells upon salt stress, but D. australe and the native Australian Disphyma crassifolium both showed K+ influx upon salt stress. Actively taking up K+ from the apoplast to maintain a high cytosolic K+/ Na+ ratio during salt stress might be an entirely new mechanism to combat the cytotoxic stress component of salinity stress in these halophytes. The salt induced K+ uptake was dependent on the presence of Cl- and Cl- was also taken up into mesophyll cells upon salt stress. Taking up both cations and anions at the same time could avoid membrane depolarisation. Voltage-gated channels, which are involved in the salt induced K+ efflux in glycophytes, would not be activated and this could be a new mechanism to avoid a K+ leak during salt stress. To test whether the beneficial effect of betacyanin production on salt tolerance could be transferred to naturally non-betacyanic plants, transgenic betacyanin-over-expression (BtOE) mutants of Nicotiana tabacum were generated by our colleagues at Plant & Food Research Ltd. Betacyanins in leaf discs of N. tabacum were associated with decreased chlorophyll degradation upon high light and high salt stress. Additionally, the decline in maximum quantum efficiency of PSII after high light and salt treatment was significantly greater in green than in betacyanic leaves. Placing a polycarbonate filter with a similar absorption spectrum to betacyanin over green N. tabacum leaf discs had a similar effect to the presence of betacyanin. Thus, betacyanins probably have a photoprotective effect in N. tabacum, which is essential as both high light and salinity can impair photosynthesis. To assess if the salt tolerance enhancing effect of betacyanin production observed in the leaf discs also occurs in whole N. tabacum plants, the ability to recover from exposure to saturating light was assessed. Betacyanic plants were able to fully recover quicker after exposure to saturation light than green leaves. This research shows that the presence of betacyanins during salt stress correlates with an altered Na+ distribution in leaf tissues and a higher salt secretion rate, which contributed to higher mesophyll viability. Moreover, a completely new ion flux response to salt stress was observed in D. australe and D. crassifolium. The observed salt induced K+ uptake into the mesophyll cells during salt stress might be an entirely new mechanism, to maintain a high K+/ Na+ ratio in the cytosol and avoid the cytotoxic effects of Na+ in photosynthetically active tissue. The beneficial effects of betacyanins could also be transferred to non-betacyanic species, by introducing betacyanin production. These results strongly suggest that betacyanins play a role in salt tolerance in halophytes and might be a valuable resource in increasing the salt tolerance of naturally non-betacyanic crop plants.</p>

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Salt tolerance of Glycyrrhiza inflata seedlings in Xinjiang and its ion response to salt stress

Chinese Journal of Plant Ecology ◽

10.3724/sp.j.1258.2013.00088 ◽

2014 ◽

Vol 37 (9) ◽

pp. 839-850 ◽

Cited By ~ 3

Author(s):

Jia-Hui LU ◽

Xin LÜ ◽

Yong-Chao LIANG ◽

Hai-Rong LIN

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

Glycyrrhiza Inflata

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Genetic Potential for Salt Tolerance During Germination in Lycopersicon Species

HortScience ◽

10.21273/hortsci.32.2.296 ◽

1997 ◽

Vol 32 (2) ◽

pp. 296-300 ◽

Cited By ~ 46

Author(s):

M.R. Foolad ◽

G.Y. Lin

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

Genotypic Variation ◽

Control Treatment ◽

Molar Ratio ◽

Wild Accession ◽

Salt Tolerant ◽

Plant Introductions ◽

Genetic Potential ◽

Stress Levels

Seed of 42 wild accessions (Plant Introductions) of Lycopersicon pimpinellifolium Jusl., 11 cultigens (cultivated accessions) of L. esculentum Mill., and three control genotypes [LA716 (a salt-tolerant wild accession of L. pennellii Corr.), PI 174263 (a salt-tolerant cultigen), and UCT5 (a salt-sensitive breeding line)] were evaluated for germination in either 0 mm (control) or 100 mm synthetic sea salt (SSS, Na+/Ca2+ molar ratio equal to 5). Germination time increased in response to salt-stress in all genotypes, however, genotypic variation was observed. One accession of L. pimpinellifolium, LA1578, germinated as rapidly as LA716, and both germinated more rapidly than any other genotype under salt-stress. Ten accessions of L. pimpinellifolium germinated more rapidly than PI 174263 and 35 accessions germinated more rapidly than UCT5 under salt-stress. The results indicate a strong genetic potential for salt tolerance during germination within L. pimpinellifolium. Across genotypes, germination under salt-stress was positively correlated (r = 0.62, P < 0.01) with germination in the control treatment. The stability of germination response at diverse salt-stress levels was determined by evaluating germination of a subset of wild, cultivated accessions and the three control genotypes at 75, 150, and 200 mm SSS. Seeds that germinated rapidly at 75 mm also germinated rapidly at 150 mm salt. A strong correlation (r = 0.90, P < 0.01) existed between the speed of germination at these two salt-stress levels. At 200 mm salt, most accessions (76%) did not reach 50% germination by 38 days, demonstrating limited genetic potential within Lycopersicon for salt tolerance during germination at this high salinity.

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Characterization of Interactions between the Soybean Salt-Stress Responsive Membrane-Intrinsic Proteins GmPIP1 and GmPIP2

Agronomy ◽

10.3390/agronomy11071312 ◽

2021 ◽

Vol 11 (7) ◽

pp. 1312

Author(s):

Jia Liu ◽

Weicong Qi ◽

Haiying Lu ◽

Hongbo Shao ◽

Dayong Zhang

Keyword(s):

Plasma Membrane ◽

Salt Stress ◽

Salt Tolerance ◽

Expression Profiles ◽

Expression Patterns ◽

Gene Expression Profiles ◽

Early Gene ◽

Plant Responses ◽

Constitutive Overexpression ◽

Important Trait

Salt tolerance is an important trait in soybean cultivation and breeding. Plant responses to salt stress include physiological and biochemical changes that affect the movement of water across the plasma membrane. Plasma membrane intrinsic proteins (PIPs) localize to the plasma membrane and regulate the water and solutes flow. In this study, quantitative real-time PCR and yeast two-hybridization were engaged to analyze the early gene expression profiles and interactions of a set of soybean PIPs (GmPIPs) in response to salt stress. A total of 20 GmPIPs-encoding genes had varied expression profiles after salt stress. Among them, 13 genes exhibited a downregulated expression pattern, including GmPIP1;6, the constitutive overexpression of which could improve soybean salt tolerance, and its close homologs GmPIP1;7 and 1;5. Three genes showed upregulated patterns, including the GmPIP1;6 close homolog GmPIP1;4, when four genes with earlier increased and then decreased expression patterns. GmPIP1;5 and GmPIP1;6 could both physically interact strongly with GmPIP2;2, GmPIP2;4, GmPIP2;6, GmPIP2;8, GmPIP2;9, GmPIP2;11, and GmPIP2;13. Definite interactions between GmPIP1;6 and GmPIP1;7 were detected and GmPIP2;9 performed homo-interaction. The interactions of GmPIP1;5 with GmPIP2;11 and 2;13, GmPIP1;6 with GmPIP2;9, 2;11 and GmPIP2;13, and GmPIP2;9 with itself were strengthened upon salt stress rather than osmotic stress. Taken together, we inferred that GmPIP1 type and GmPIP2 type could associate with each other to synergistically function in the plant cell; a salt-stress environment could promote part of their interactions. This result provided new clues to further understand the soybean PIP–isoform interactions, which lead to potentially functional homo- and heterotetramers for salt tolerance.

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Comprehensive transcriptome and metabolome profiling reveal metabolic mechanisms of Nitraria sibirica Pall. to salt stress

Scientific Reports ◽

10.1038/s41598-021-92317-6 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Huanyong Li ◽

Xiaoqian Tang ◽

Xiuyan Yang ◽

Huaxin Zhang

Keyword(s):

Salt Stress ◽

Amino Acid ◽

Salt Tolerance ◽

Metabolic Pathways ◽

Amino Acid Metabolism ◽

Acid Metabolism ◽

Sulfur Metabolism ◽

Enrichment Analysis ◽

Extracellular Region ◽

Nitraria Sibirica

AbstractNitraria sibirica Pall., a typical halophyte that can survive under extreme drought conditions and in saline-alkali environments, exhibits strong salt tolerance and environmental adaptability. Understanding the mechanism of molecular and physiological metabolic response to salt stress of plant will better promote the cultivation and use of halophytes. To explore the mechanism of molecular and physiological metabolic of N. sibirica response to salt stress, two-month-old seedlings were treated with 0, 100, and 400 mM NaCl. The results showed that the differentially expressed genes between 100 and 400 mmol L−1 NaCl and unsalted treatment showed significant enrichment in GO terms such as binding, cell wall, extemal encapsulating structure, extracellular region and nucleotide binding. KEGG enrichment analysis found that NaCl treatment had a significant effect on the metabolic pathways in N. sibirica leaves, which mainly including plant-pathogen interaction, amino acid metabolism of the beta alanine, arginine, proline and glycine metabolism, carbon metabolism of glycolysis, gluconeogenesis, galactose, starch and sucrose metabolism, plant hormone signal transduction and spliceosome. Metabolomics analysis found that the differential metabolites between the unsalted treatment and the NaCl treatment are mainly amino acids (proline, aspartic acid, methionine, etc.), organic acids (oxaloacetic acid, fumaric acid, nicotinic acid, etc.) and polyhydric alcohols (inositol, ribitol, etc.), etc. KEGG annotation and enrichment analysis showed that 100 mmol L−1 NaCl treatment had a greater effect on the sulfur metabolism, cysteine and methionine metabolism in N. sibirica leaves, while various amino acid metabolism, TCA cycle, photosynthetic carbon fixation and sulfur metabolism and other metabolic pathways have been significantly affected by 400 mmol L−1 NaCl treatment. Correlation analysis of differential genes in transcriptome and differential metabolites in metabolome have found that the genes of AMY2, BAM1, GPAT3, ASP1, CML38 and RPL4 and the metabolites of L-cysteine, proline, 4-aminobutyric acid and oxaloacetate played an important role in N. sibirica salt tolerance control. This is a further improvement of the salt tolerance mechanism of N. sibirica, and it will provide a theoretical basis and technical support for treatment of saline-alkali soil and the cultivation of halophytes.

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OsNAC45 is Involved in ABA Response and Salt Tolerance in Rice

Rice ◽

10.1186/s12284-020-00440-1 ◽

2020 ◽

Vol 13 (1) ◽

Author(s):

Xiang Zhang ◽

Yan Long ◽

Jingjing Huang ◽

Jixing Xia

Keyword(s):

Transcription Factors ◽

Salt Stress ◽

Salt Tolerance ◽

Stress Responses ◽

Crop Yields ◽

Plant Stress ◽

Root Cells ◽

Nac Transcription Factors ◽

Rice Plants ◽

Plant Stress Responses

Abstract Background Salt stress threatens crop yields all over the world. Many NAC transcription factors have been reported to be involved in different abiotic stress responses, but it remains unclear how loss of these transcription factors alters the transcriptomes of plants. Previous reports have demonstrated that overexpression of OsNAC45 enhances salt and drought tolerance in rice, and that OsNAC45 may regulate the expression of two specific genes, OsPM1 and OsLEA3–1. Results Here, we found that ABA repressed, and NaCl promoted, the expression of OsNAC45 in roots. Immunostaining showed that OsNAC45 was localized in all root cells and was mainly expressed in the stele. Loss of OsNAC45 decreased the sensitivity of rice plants to ABA and over-expressing this gene had the opposite effect, which demonstrated that OsNAC45 played an important role during ABA signal responses. Knockout of OsNAC45 also resulted in more ROS accumulation in roots and increased sensitivity of rice to salt stress. Transcriptome sequencing assay found that thousands of genes were differently expressed in OsNAC45-knockout plants. Most of the down-regulated genes participated in plant stress responses. Quantitative real time RT-PCR suggested that seven genes may be regulated by OsNAC45 including OsCYP89G1, OsDREB1F, OsEREBP2, OsERF104, OsPM1, OsSAMDC2, and OsSIK1. Conclusions These results indicate that OsNAC45 plays vital roles in ABA signal responses and salt tolerance in rice. Further characterization of this gene may help us understand ABA signal pathway and breed rice plants that are more tolerant to salt stress.

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Genome-wide association analysis reveals genetic variations and candidate genes associated with salt tolerance related traits in Gossypium hirsutum

BMC Genomics ◽

10.1186/s12864-020-07321-3 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Peng Xu ◽

Qi Guo ◽

Shan Meng ◽

Xianggui Zhang ◽

Zhenzhen Xu ◽

...

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

Candidate Genes ◽

Genetic Variations ◽

Genome Wide Association ◽

Cotton Production ◽

Fresh Matter ◽

Salt Stress Response ◽

Genome Wide ◽

A Genome

Abstract Background Cotton is more resistant to salt and drought stresses as compared to other field crops, which makes itself as a pioneer industrial crop in saline-alkali lands. However, abiotic stresses still negatively affect its growth and development significantly. It is therefore important to breed salt tolerance varieties which can help accelerate the improvement of cotton production. The development of molecular markers linked to causal genes has provided an effective and efficient approach for improving salt tolerance. Results In this study, a genome-wide association study (GWAS) of salt tolerance related traits at seedling stage was performed based on 2 years of phenotype identification for 217 representative upland cotton cultivars by genotyping-by-sequencing (GBS) platform. A total of 51,060 single nucleotide polymorphisms (SNPs) unevenly distributed among 26 chromosomes were screened across the cotton cultivars, and 25 associations with 27 SNPs scattered over 12 chromosomes were detected significantly (−log10p > 4) associated with three salt tolerance related traits in 2016 and 2017. Among these, the associations on chromosome A13 and D08 for relative plant height (RPH), A07 for relative shoot fresh matter weight (RSFW), A08 and A13 for relative shoot dry matter weight (RSDW) were expressed in both environments, indicating that they were likely to be stable quantitative trait loci (QTLs). A total of 12 salt-induced candidate genes were identified differentially expressed by the combination of GWAS and transcriptome analysis. Three promising genes were selected for preliminary function verification of salt tolerance. The increase of GH_A13G0171-silenced plants in salt related traits under salt stress indicated its negative function in regulating the salt stress response. Conclusions These results provided important genetic variations and candidate genes for accelerating the improvement of salt tolerance in cotton.

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Exogenous melatonin improves the salt tolerance of cotton by removing active oxygen and protecting photosynthetic organs

BMC Plant Biology ◽

10.1186/s12870-021-03082-7 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Dan Jiang ◽

Bin Lu ◽

Liantao Liu ◽

Wenjing Duan ◽

Yanjun Meng ◽

...

Keyword(s):

Salt Stress ◽

Salt Tolerance ◽

Oxidative Damage ◽

Photosynthetic Capacity ◽

Photochemical Efficiency ◽

Photochemical Quenching ◽

Plant Tolerance ◽

Signal Molecule ◽

Ion Balance ◽

Photosynthetic System

Abstract Background As damage to the ecological environment continues to increase amid unreasonable amounts of irrigation, soil salinization has become a major challenge to agricultural development. Melatonin (MT) is a pleiotropic signal molecule and indole hormone, which alleviates the damage of abiotic stress to plants. MT has been confirmed to eliminate reactive oxygen species (ROS) by improving the antioxidant system and reducing oxidative damage under adversity. However, the mechanism by which exogenous MT mediates salt tolerance by regulating the photosynthetic capacity and ion balance of cotton seedlings still remains unknown. In this study, the regulatory effects of MT on the photosynthetic system, osmotic modulators, chloroplast, and anatomical structure of cotton seedlings were determined under 0–500 μM MT treatments with salt stress induced by treatment with 150 mM NaCl. Results Salt stress reduces the chlorophyll content, net photosynthetic rate, stomatal conductance, intercellular CO2 concentration, transpiration rate, PSII photochemical efficiency, PSII actual photochemical quantum yield, the apparent electron transfer efficiency, stomata opening, and biomass. In addition, it increases non-photochemical quenching. All of these responses were effectively alleviated by exogenous treatment with MT. Exogenous MT reduces oxidative damage and lipid peroxidation by reducing salt-induced ROS and protects the plasma membrane from oxidative toxicity. MT also reduces the osmotic pressure by reducing the salt-induced accumulation of Na+ and increasing the contents of K+ and proline. Exogenous MT can facilitate stomatal opening and protect the integrity of cotton chloroplast grana lamella structure and mitochondria under salt stress, protect the photosynthetic system of plants, and improve their biomass. An anatomical analysis of leaves and stems showed that MT can improve xylem and phloem and other properties and aides in the transportation of water, inorganic salts, and organic substances. Therefore, the application of MT attenuates salt-induced stress damage to plants. Treatment with exogenous MT positively increased the salt tolerance of cotton seedlings by improving their photosynthetic capacity, stomatal characteristics, ion balance, osmotic substance biosynthetic pathways, and chloroplast and anatomical structures (xylem vessels and phloem vessels). Conclusions Our study attributes help to protect the structural stability of photosynthetic organs and increase the amount of material accumulation, thereby reducing salt-induced secondary stress. The mechanisms of MT-induced plant tolerance to salt stress provide a theoretical basis for the use of MT to alleviate salt stress caused by unreasonable irrigation, fertilization, and climate change.

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