Tissue specific changes in elements and organic compounds of alfalfa (Medicago sativa L.) cultivars differing in salt tolerance under salt stress

Physiological response mechanism of alfalfa seedlings roots to typical explosive cyclotrimethylene trinitramine (RDX)

This study explored the physiological response mechanism of alfalfa seedlings roots to a typical explosive, cyclotrimethylenetrinitramine (RDX), so as to improve the efficiency of phytoremediation. The response of plants to different levels of RDX were analyzed from the perspectives of mineral nutrition and metabolic networks. Exposure to RDX at 10-40 mg L^-1 had no significant effect on root morphology, but the plant roots significantly accumulated RDX in solution (17.6-40.9%). A 40 mg L^-1 RDX exposure induced cell gap expansion and disrupted root mineral metabolism, The key response elements, P, Cu, and Mg, were significantly increased by 1.60-1.66, 1.74-1.90, and 1.85-2.50 times, respectively. The 40 mg L^-1 RDX exposure also significantly disturbed root basal metabolism, resulting in a total of 197 differentially expressed metabolites (DEMs). The main response metabolites were lipids and lipid-like molecules, and the key physiological response pathways were arginine biosynthesis and aminoacyl-tRNA biosynthesis. A total of 19 DEMs in root metabolic pathways, including L-arginine, L-asparagine, and ornithine, were significantly responsive to RDX exposure. The physiological response mechanism of roots to RDX therefore involve mineral nutrition and metabolic networks and are of great significance for improving phytoremediation efficiency.

Graphene oxide affected root growth, anatomy, and nutrient uptake in alfalfa

The increasing application of carbon nanomaterials has resulted in their inevitable release into the environment. Their toxic effects on plant roots require careful investigation. In the present study, alfalfa (Medicago sativa L.) was exposed to graphene oxide (GO) at levels of 0.2 %, 0.4 %, and 0.6 % (w/w) in potting soil. This study aims to better understand the impact of GO on the root growth, structure, and physiology of alfalfa in the soil matrix. The results demonstrated that GO significantly affected the development and structure of alfalfa roots, and the effect varied with GO level. The highest level of GO (0.6 %) reduced the root length, diameter, volume, dry weight, number of lateral roots, and root activity by 36.1 %, 31.3 %, 60.0 %, 89.6 %, 55.8 %, and 72.3 % (p < 0.05), respectively, and the vascular cylinder diameter, periderm thickness, vessel diameter, and phellem thickness decreased by 51.5 %, 50.7 %, 80.9 %, and 49.1 % (p < 0.05), respectively. These observations might be associated with GO-induced oxidative stress, which was indicated by the activity of antioxidant enzymes. Furthermore, high GO levels (0.4 % and 0.6 %) inhibited the uptake of N, P, K, Mg, Zn, Fe, Mo, Si, and B in roots. Our findings indicate that GO at high levels has a negative impact on root growth and development by inducing oxidative stress, structural impairment, and nutritional imbalance. Careful soil GO management should be emphasized.

Exogenous melatonin promotes the growth of alfalfa (Medicago sativa L.) under NaCl stress through multiple pathways

Salinity is one of the most common factors affecting alfalfa (Medicago sativa L.), and NaCl is one of the main factors of salinity stress which can cause heavy losses in agricultural production in the world. The application of exogenous melatonin (MT) plays a major role in numerous plants against various stress environments. The effects of exogenous MT on the NaCl tolerance of alfalfa treated with the control, 100 µmol L^-1 MT, 150 mmol L^-1 NaCl, or 150 mmol L^-1 NaCl+ 100 µmol L^-1 MT were investigated. The results showed that MT increased growth parameters, inhibited chlorophyll degradation and promoted photosynthetic gas exchange parameters (photosynthetic rate, conductance to H₂O, and transpiration rate) and stomatal opening under NaCl stress. Osmotic regulation substances such as soluble sugar, proline and glycine betaine were the highest in the NaCl treatment and the second in the NaCl+MT treatment. Nitrogen, phosphorus, potassium, calcium and magnesium were reduced and sodium was increased by NaCl, whereas these levels were reversed by the NaCl+MT treatment. MT inhibited cell membrane imperfection, lipid peroxidation and reactive oxygen species (ROS) accumulation caused by NaCl stress. MT up-regulated the gene expression and activity of antioxidant enzymes and increased the content of antioxidant non-enzyme substances to scavenge excessive ROS in NaCl-treated plants. In addition, all indicators interacted with each other to a certain extent and could be grouped according to the relative values. All variables were divided into PC 1 (89.2 %) and PC 2 (4 %). They were clustered into two categories with opposite effects, and most of them were significant variables. Hence, these findings reveal that exogenous MT alleviates the inhibitory effects of NaCl stress on photosynthesis, stomata opening, osmotic adjustment, ion balance and redox homeostasis, enhancing tolerance and growth of alfalfa. Furthermore, it suggests that MT could be implemented to improve the NaCl tolerance of alfalfa.

Trehalose alleviates salt tolerance by improving photosynthetic performance and maintaining mineral ion homeostasis in tomato plants

Trehalose (Tre), which was an osmoprotective or stabilizing molecule, played a protective role against different abiotic stresses in plants and showed remarkable perspectives in salt stress. In this study, the potential role of Tre in improving the resistance to salt stress in tomato plants was investigated. Tomato plants (Micro Tom) were treated with Hoagland nutrient solution (CK), 10 mM Tre (T), 150 mM sodium chloride (NaCl, S), and 10 mM Tre+150 mM NaCl (S+T) for 5 days. Our results showed that foliar application of Tre alleviated the inhibition of tomato plant growth under salt stress. In addition, salt stress decreased the values of net photosynthetic rate (Pn, 85.99%), stomata conductance (gs, 57.3%), and transpiration rate (Tr, 47.97%), but increased that of intercellular carbon dioxide concentration (Ci, 26.25%). However, exogenous application of Tre significantly increased photosynthetic efficiency, increased the activity of Calvin cycle enzymes [ribulose diphosphate carboxylase/oxygenase (Rubisco), fructose-1,6-bisphosphate aldolase (FBA), fructose-1, 6-bisphosphatase (FBPase), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and transketolase (TK)], up-regulated the expression of genes encoding enzymes, induced stomatal opening, and alleviated salt-induced damage to the chloroplast membrane and structure. In the saline environment, photosynthetic electron transport was restricted, resulting the J-I-P phase to decrease. At the same time, the absorption, capture, and transport energies per excited cross-section and per active reaction center decreased, and the dissipation energy increased. Conversely, Tre reversed these values and enhanced the photosystem response to salt stress by protecting the photosynthetic electron transport system. In addition, foliage application with Tre significantly increased the potassium to sodium transport selectivity ratio (S _K-Na ) by 16.08%, and increased the levels of other ions to varying degrees. Principal component analysis (PCA) analysis showed that exogenous Tre could change the distribution of elements in different organs and affect the expressions of SlSOS1, SlNHX, SlHKT1.1, SlVHA, and SlHA-A at the transcriptional level under salt stress, thereby maintaining ion homeostasis. This study demonstrated that Tre was involved in the process of mitigating salt stress toxicity in tomato plants and provided specific insights into the effectiveness of Tre in mediating salt tolerance.

Effects of nitrogen and phosphorus addition on growth and leaf nitrogen metabolism of alfalfa in alkaline soil in Yinchuan Plain of Hetao Basin

Alkaline soil is widely distributed in China. Its rational utilization is an effective measure to solve land shortage and improve the environment. Alfalfa is characterized by strong salt and alkali tolerance and high yield and protein content. Nitrogen (N) and phosphorus (P) are the main nutrients for plant growth, and N metabolism is one of the primary forms of plant metabolism, which plays a vital role in quality and yield formation. The exploration of the effect of N and P on N metabolism and alfalfa growth will provide a theoretical basis for scientific fertilization for alfalfa in the alkaline soil of the Yinchuan Plain of the Hetao Basin. Therefore, a 2-year experiment of N and P addition was conducted. Six treatments were set up with a randomized block design, including without N (WN), medium N (MN), high N (HN), without P (WP), medium P (MP), and high P (HP). It was found that the MN and MP treatments increased plant height, stem diameter, stem/leaf, dry/fresh, and dry matter of alfalfa. The HN and HP treatments inhibited alfalfa biomass formation. The MN and MP treatments increased key products and enzymes of leaf N metabolism of alfalfa and promoted activities of leaf nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT), glutamic-oxalacetic transaminase (GOT), and glutamic-pyruvate transaminase (GPT), and inhibited activities of leaf protease of alfalfa. The MN and MP treatments increased contents of leaf N, P, ammonium nitrogen (NH₄ ⁺-N), nitrate nitrogen (NO₃ ^--N), total chlorophyll, and protein and reduced leaf chlorophyll a/b and amino acid, results after HN and HP treatments were opposite. The correlation among leaf P, N, NO₃ ^--N, amino acid, and protein reached significant levels (P < 0.01). It is suggested that MN and MP treatments can improve the yield and quality of alfalfa by increasing key products and enzymes of N metabolism and can be adopted to promote alfalfa production in the alkaline soil of the Yinchuan Plain of the Hetao Basin.

Trehalose Alleviated Salt Stress in Tomato by Regulating ROS Metabolism, Photosynthesis, Osmolyte Synthesis, and Trehalose Metabolic Pathways

Trehalose plays a critical role in plant response to salinity but the involved regulatory mechanisms remain obscure. Here, this study explored the mechanism of exogenous trehalose-induced salt tolerance in tomato plants by the hydroponic test method. Our results indicated that 10 mM trehalose displayed remarkable plant biomass by improving growth physiology, which were supported by the results of chlorophyll fluorescence and rapid light-response curve. In the salinity environment, trehalose + NaCl treatment could greatly inhibit the decrease of malondialdehyde level, and it increases the contents of other osmotic substances, carbohydrates, K⁺, and K⁺/Na⁺ ratio. Meanwhile, trehalose still had similar effects after recovery from salt stress. Furthermore, trehalose pretreatment promoted trehalose metabolism; significantly increased the enzymatic activity of the trehalose metabolic pathway, including trehalose-6-phosphate synthase (TPS), trehalose-6-phosphate phosphatase (TPP), and trehalase (TRE); and upregulated the expression of SlTPS1, SlTPS5, SlTPS7, SlTPPJ, SlTPPH, and SlTRE under saline conditions. However, the transcriptional levels of SlTPS1, SlTPS5, and SlTPS7 genes and the activity of TPS enzyme were reversed after recovery. In addition, we found that hydrogen peroxide (H₂O₂) and superoxide anion (O₂ ^-) were accumulated in tomato leaves because of salt stress, but these parameters were all recovered by foliar-applied trehalose, and its visualization degree was correspondingly reduced. Antioxidant enzyme activities (SOD, POD, and CAT) and related gene expression (SlCu/Zn-SOD, SlFe-SOD, SlMn-SOD, SlPOD, and SlCAT) in salt-stressed tomato leaves were also elevated by trehalose to counteract salt stress. Collectively, exogenous trehalose appeared to be the effective treatment in counteracting the negative effects of salt stress.

Transcriptome revealed the molecular mechanism of Glycyrrhiza inflata root to maintain growth and development, absorb and distribute ions under salt stress

BACKGROUND

Soil salinization extensively hampers the growth, yield, and quality of crops worldwide. The most effective strategies to counter this problem are a) development of crop cultivars with high salt tolerance and b) the plantation of salt-tolerant crops. Glycyrrhiza inflata, a traditional Chinese medicinal and primitive plant with salt tolerance and economic value, is among the most promising crops for improving saline-alkali wasteland. However, the underlying molecular mechanisms for the adaptive response of G. inflata to salinity stress remain largely unknown.

RESULT

G. inflata retained a high concentration of Na+ in roots and maintained the absorption of K+, Ca2+, and Mg2+ under 150 mM NaCl induced salt stress. Transcriptomic analysis of G. inflata roots at different time points of salt stress (0 min, 30 min, and 24 h) was performed, which resulted in 70.77 Gb of clean data. Compared with the control, we detected 2645 and 574 differentially expressed genes (DEGs) at 30 min and 24 h post-salt-stress induction, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that G. inflata response to salt stress post 30 min and 24 h was remarkably distinct. Genes that were differentially expressed at 30 min post-salt stress induction were enriched in signal transduction, secondary metabolite synthesis, and ion transport. However, genes that were differentially expressed at 24 h post-salt-stress induction were enriched in phenylpropane biosynthesis and metabolism, fatty acid metabolism, glycerol metabolism, hormone signal transduction, wax, cutin, and cork biosynthesis. Besides, a total of 334 transcription factors (TFs) were altered in response to 30 min and 24 h of salt stress. Most of these TFs belonged to the MYB, WRKY, AP2-EREBP, C2H2, bHLH, bZIP, and NAC families.

CONCLUSION

For the first time, this study elucidated the salt tolerance in G. inflata at the molecular level, including the activation of signaling pathways and genes that regulate the absorption and distribution of ions and root growth in G. inflata under salt stress conditions. These findings enhanced our understanding of the G. inflata salt tolerance and provided a theoretical basis for cultivating salt-tolerant crop varieties.