Expression dynamics of genes encoding nitrate and ammonium assimilation enzymes in rice genotypes exposed to reproductive stage salinity stress

Effects of NH4 +-N: NO3 --N ratio on growth, nutrient uptake and production of blueberry (Vaccinium spp.) under soilless culture

Blueberry (Vaccinium corymbosum) is a small pulp shrub, which prefers to grow on a soilless culture. For soilless culture, nutritional management remains typically vital for blueberry production. However, the effect of different nutritional treatments on blueberry growth and production is largely unknown. This study was designed to investigate to formulate a specific nutritional treatment for blueberry. The results showed that NH4 +-N: NO3 --N ratios significantly affected the growth, nutrient uptake, physiological characteristics, and flowering, as well as the fruiting characteristics of blueberry plants. The number of shoots and top projection area was increased considerably by 25:75 treatment. In contrast, 50:50 treatment promotes plant height, shoot length, and stem thickness, increasing chlorophyll contents, photosynthetic capacity, and P, Ca, and Mg in leaves. In contrast, 50:50 treatment promotes the flowering fruiting rate and prolongs the blueberry flowering period. The maximum soluble sugar contents were noted in 25:75, while maximum starch contents were reported in the 50:50 treatment. The treatments 100:0 and 75:25 promote early flowering and accelerate fruit set. Notably, NH4 +-N: NO3 --N ratios; 50:50 treatment significantly encourages plant growth, nutrient uptake, chlorophyll contents, photosynthetic capacity, and fruit setting rate in blueberry plants. These findings suggested that NH4 +-N: NO3 --N ratios 50:50 is the most appropriate treatment that significantly promotes vegetative growth and enhances production in blueberry plants. This study provides valuable information for improved blueberry production under a controlled environment.

Effect of ammonium stress on phosphorus solubilization of a novel marine mangrove microorganism Bacillus aryabhattai NM1-A2 as revealed by integrated omics analysis

BACKGROUND

Phosphorus is one of the essential nutrients for plant growth. Phosphate-solubilizing microorganisms (PSMs) can alleviate available P deficiency and enhance plant growth in an eco-friendly way. Although ammonium toxicity is widespread, there is little understanding about the effect of ammonium stress on phosphorus solubilization (PS) of PSMs.

RESULTS

In this study, seven PSMs were isolated from mangrove sediments. The soluble phosphate concentration in culture supernatant of Bacillus aryabhattai NM1-A2 reached a maximum of 196.96 mg/L at 250 mM (NH4)2SO4. Whole-genome analysis showed that B. aryabhattai NM1-A2 contained various genes related to ammonium transporter (amt), ammonium assimilation (i.e., gdhA, gltB, and gltD), organic acid synthesis (i.e., ackA, fdhD, and idh), and phosphate transport (i.e., pstB and pstS). Transcriptome data showed that the expression levels of amt, gltB, gltD, ackA and idh were downregulated, while gdhA and fdhD were upregulated. The inhibition of ammonium transporter and glutamine synthetase/glutamate synthase (GS/GOGAT) pathway contributed to reducing energy loss. For ammonium assimilation under ammonium stress, accompanied by protons efflux, the glutamate dehydrogenase pathway was the main approach. More 2-oxoglutarate (2-OG) was induced to provide abundant carbon skeletons. The downregulation of formate dehydrogenase and high glycolytic rate resulted in the accumulation of formic acid and acetic acid, which played key roles in PS under ammonium stress.

CONCLUSIONS

The accumulation of 2-OG and the inhibition of GS/GOGAT pathway played a key role in ammonium detoxification. The secretion of protons, formic acid and acetic acid was related to PS. Our work provides new insights into the PS mechanism, which will provide theoretical guidance for the application of PSMs.

Transcriptional Expression of Nitrogen Metabolism Genes and Primary Metabolic Variations in Rice Affected by Different Water Status

The era of climate change strongly requires higher efficiency of energies, such as light, water, nutrients, etc., during crop production. Rice is the world's greatest water-consuming plant, and, thus, water-saving practices such as alternative wetting and drying (AWD) are widely recommended worldwide. However the AWD still has concerns such as lower tillering, shallow rooting, and an unexpected water deficit. The AWD is a possibility to not only save water consumption but also utilize various nitrogen forms from the soil. The current study tried to investigate the transcriptional expression of genes in relation to the acquisition-transportation-assimilation process of nitrogen using qRT-PCR at the tillering and heading stages and to profile tissue-specific primary metabolites. We employed two water supply systems, continuous flooding (CF) and alternative wetting and drying (AWD), during rice growth (seeding to heading). The AWD system is effective at acquiring soil nitrate; however, nitrogen assimilation was predominant in the root during the shift from the vegetative to the reproductive stage. In addition, as a result of the greater amino acids in the shoot, the AWD was likely to rearrange amino acid pools to produce proteins in accordance with phase transition. Accordingly, it is suggested that the AWD 1) actively acquired nitrate from soil and 2) resulted in an abundance of amino acid pools, which are considered a rearrangement under limited N availability. Based on the current study, further steps are necessary to evaluate form-dependent N metabolism and root development under the AWD condition and a possible practice in the rice production system.

Sustaining nitrogen dynamics: A critical aspect for improving salt tolerance in plants

In the current changing environment, salt stress has become a major concern for plant growth and food production worldwide. Understanding the mechanisms of how plants function in saline environments is critical for initiating efforts to mitigate the detrimental effects of salt stress. Agricultural productivity is linked to nutrient availability, and it is expected that the judicious metabolism of mineral nutrients has a positive impact on alleviating salt-induced losses in crop plants. Nitrogen (N) is a macronutrient that contributes significantly to sustainable agriculture by maintaining productivity and plant growth in both optimal and stressful environments. Significant progress has been made in comprehending the fundamental physiological and molecular mechanisms associated with N-mediated plant responses to salt stress. This review provided an (a) overview of N-sensing, transportation, and assimilation in plants; (b) assess the salt stress-mediated regulation of N dynamics and nitrogen use- efficiency; (c) critically appraise the role of N in plants exposed to salt stress. Furthermore, the existing but less explored crosstalk between N and phytohormones has been discussed that may be utilized to gain a better understanding of plant adaptive responses to salt stress. In addition, the shade of a small beam of light on the manipulation of N dynamics through genetic engineering with an aim of developing salt-tolerant plants is also highlighted.

Nitrogen assimilation and photorespiration become more efficient under chloride nutrition as a beneficial macronutrient

Chloride (Cl^-) and nitrate ( NO 3 - ) are closely related anions involved in plant growth. Their similar physical and chemical properties make them to interact in cellular processes like electrical balance and osmoregulation. Since both anions share transport mechanisms, Cl^- has been considered to antagonize NO 3 - uptake and accumulation in plants. However, we have recently demonstrated that Cl^- provided at beneficial macronutrient levels improves nitrogen (N) use efficiency (NUE). Biochemical mechanisms by which beneficial Cl^- nutrition improves NUE in plants are poorly understood. First, we determined that Cl^- nutrition at beneficial macronutrient levels did not impair the NO 3 - uptake efficiency, maintaining similar NO 3 - content in the root and in the xylem sap. Second, leaf NO 3 - content was significantly reduced by the treatment of 6 mM Cl^- in parallel with an increase in NO 3 - utilization and NUE. To verify whether Cl^- nutrition reduces leaf NO 3 - accumulation by inducing its assimilation, we analysed the content of N forms and the activity of different enzymes and genes involved in N metabolism. Chloride supply increased transcript accumulation and activity of most enzymes involved in NO 3 - assimilation into amino acids, along with a greater accumulation of organic N (mostly proteins). A reduced glycine/serine ratio and a greater ammonium accumulation pointed to a higher activity of the photorespiration pathway in leaves of Cl^--treated plants. Chloride, in turn, promoted higher transcript levels of genes encoding enzymes of the photorespiration pathway. Accordingly, microscopy observations suggested strong interactions between different cellular organelles involved in photorespiration. Therefore, in this work we demonstrate for the first time that the greater NO 3 - utilization and NUE induced by beneficial Cl^- nutrition is mainly due to the stimulation of NO 3 - assimilation and photorespiration, possibly favouring the production of ammonia, reductants and intermediates that optimize C-N re-utilization and plant growth. This work demonstrates new Cl^- functions and remarks on its relevance as a potential tool to manipulate NUE in plants.

Moderate Salinity of Nutrient Solution Improved the Nutritional Quality and Flavor of Hydroponic Chinese Chives (Allium tuberosum Rottler)

Sodium chloride (NaCl), as a eustressor, can trigger relevant pathways to cause plants to produce a series of metabolites, thus improving the quality of crops to a certain extent. However, there are few reports on the improvement of nutrient quality and flavor of hydroponic Chinese chives (Allium tuberosum Rottler) by sodium chloride. In this study, five NaCl concentrations were used to investigate the dose-dependent effects on growth, nutritional quality and flavor in Chinese chives. The results show that 10 mM NaCl had no significant effect on the growth of Chinese chives, but significantly decreased the nitrate content by 40% compared with 0 mM NaCl treatment, and the content of soluble protein and vitamin C was increased by 3.6% and 2.1%, respectively. In addition, a total of 75 volatile compounds were identified among five treatments using headspace solid-phase microextraction gas chromatography/mass spectrometry (HS-SPME/GC-MS). Compared with the 0 mM NaCl treatment, 10 mM NaCl had the greatest effect on the quantity and content of volatile compounds, with the total content increased by 27.8%. Furthermore, according to the odor activity values (OAVs) and odor description, there were 14 major aroma-active compounds (OAVs > 1) in Chinese chives. The “garlic and onion” odor was the strongest among the eight categories of aromas, and its highest value was observed in the 10 mM NaCl treatment (OAVs = 794).Taken together, adding 10 mM NaCl to the nutrient solution could improve the nutritional quality and flavor of Chinese chives without affecting their normal growth.

Insights into carbon and nitrogen metabolism and antioxidant potential during vegetative phase in quinoa (Chenopodium quinoa Willd.)

The present investigation was carried out to understand the impact of carbon and nitrogen metabolism in quinoa genotypes IC411824, IC411825, EC507747 and EC507742 during pre-anthesis stage. It was observed that activities of acid invertase, sucrose synthase (cleavage) and sucrose phosphate synthase (SPS) increased up to 75 days after sowing (DAS) and this might be responsible for providing reducing sugars for the development of vegetative parts. Enhanced activities of nitrate reductase, glutamate synthase, glutamine synthetase during vegetative growth of leaves and stem at 90 DAS assist the fixation of ammonia on glutamate molecule to synthesize amino acids at early stages. However, the glutamate dehydrogenase and nitrite reductase play a central role in the re-assimilation of amides from the amino group of asparaginase. As a result, these photosynthetic products will be responsible for providing both the energy and the C-skeletons for ammonium assimilation during amino acid biosynthesis. Leaves and stem of IC411824 and IC411825 had higher total phenol and total flavonoid content. DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity was found to be higher in leaves of IC411825 and in stem of IC411824 and IC411825 indicating their capability to act as natural antioxidants.

Polyamines Metabolism Interacts with γ-Aminobutyric Acid, Proline and Nitrogen Metabolisms to Affect Drought Tolerance of Creeping Bentgrass

Due to increased global warming and climate change, drought has become a serious threat to horticultural crop cultivation and management. The purpose of this study was to investigate the effect of spermine (Spm) pretreatment on metabolic alterations of polyamine (PAs), γ-aminobutyric acid (GABA), proline (Pro), and nitrogen associated with drought tolerance in creeping bentgrass (Agrostis stolonifera). The results showed that drought tolerance of creeping bentgrass could be significantly improved by the Spm pretreatment, as demonstrated by the maintenance of less chlorophyll loss and higher photosynthesis, gas exchange, water use efficiency, and cell membrane stability. The Spm pretreatment further increased drought-induced accumulation of endogenous PAs, putrescine, spermidine, and Spm, and also enhanced PAs metabolism through improving arginine decarboxylases, ornithine decarboxylase, S-adenosylmethionine decarboxylase, and polyamine oxidase activities during drought stress. In addition, the Spm application not only significantly improved endogenous GABA content, glutamate content, activities of glutamate decarboxylase and α-ketoglutarase, but also alleviated decline in nitrite nitrogen content, nitrate reductase, glutamine synthetase, glutamate synthetase, and GABA aminotransferase activities under drought stress. The Spm-pretreated creeping bentgrass exhibited significantly lower ammonia nitrogen content and nitrite reductase activity as well as higher glutamate dehydrogenase activity than non-pretreated plants in response to drought stress. These results indicated beneficial roles of the Spm on regulating GABA and nitrogen metabolism contributing towards better maintenance of Tricarboxylic acid (TCA) cycle in creeping bentgrass. Interestingly, the Spm-enhanced Pro metabolism rather than more Pro accumulation could be the key regulatory mechanism for drought tolerance in creeping bentgrass. Current findings provide a comprehensive understanding of PAs interaction with other metabolic pathways to regulate drought tolerance in grass species.