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Nitrogen (N) is an important nutrient for plant growth and yield production, and rice grown in paddy soil mainly uses ammonium (NH4+) as its N source. Previous studies have shown that N status is tightly connected to plant defense; however, the roles of NH4+ uptake and assimilation in rice sheath blight disease response have not been studied previously. Here, we analyzed the effects of different N sources on plant defense against Rhizoctonia solani. The results indicated that rice plants grown in N-free conditions had higher resistance to sheath blight than those grown under N conditions. In greater detail, rice plants cultured with glutamine as the sole N source were more susceptible to sheath blight disease compared to the groups using NH4+ and nitrate (NO3-) as sole N sources. N deficiency severely inhibited plant growth; therefore, ammonium transporter 1;2 overexpressors (AMT1;2 OXs) were generated to test their growth and defense ability under low N conditions. AMT1;2 OXs increased N use efficiency and exhibited less susceptible symptoms to R. solani and highly induced the expression of PBZ1 compared to the wild-type controls upon infection of R. solani. Furthermore, the glutamine synthetase 1;1 (GS1;1) mutant (gs1;1) was more susceptible to R. solani infection than the wild-type control, and the genetic combination of AMT1;2 OX and gs1;1 revealed that AMT1;2 OX was less susceptible to R. solani and required GS1;1 activity. In addition, cellular NH4+ content was higher in AMT1;2 OX and gs1;1 plants, indicating that NH4+ was not directly controlling plant defense. In conclusion, the present study showed that the activation of NH4+ uptake and assimilation were required for rice resistance against sheath blight disease. [ABSTRACT FROM AUTHOR]

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It is unclear how plants optimize their preference for different forms of inorganic nitrogen to enhance their survival and fitness in challenging environments. Using a hydroponics culture system, we monitored morphological, physiological, and molecular changes in Malus hupehensis seedlings when drought conditions (induced by 5% polyethylene glycol, or PEG) were combined with a low or normal supply of N (0.05 mM or 1 mM NH 4 NO 3 , respectively). We found here that PEG-induced drought stress negatively inhibited the growth of Malus hupehensis seedlings and resulted in higher NH 4 + /NO 3 − ratios in their roots and leaves. The net ammonium influx at the surface of fine roots rose dramatically under drought treatment, while that of nitrate was less changed. This was confirmed by higher absorption of stable 15 NH 4 + isotope than of 15 NO 3 − under drought conditions. Consistently, two ammonium transporter genes closely related to ammonium uptake ( AMT4;2 and AMT4;3 ) were notably up-regulated in response to drought stress, while transcript levels of most genes related to nitrate uptake/reduction and nitrogen assimilation decreased. Therefore, in acclimating to drought, Malus hupehensis plants exhibited relatively increased uptake of NH 4 + compared to NO 3 − . In addition, reducing N supply may alleviate the adverse affect of drought stress on the growth of Malus hupehensis . [ABSTRACT FROM AUTHOR]

Abstract: The tomato (Solanum lycopersicum L.) cultivar Micro‐Tom (MT) is widely used in physiological studies, but the effects of nitrate ( NO 3 - ) and ammonium ( NH 4 + ) ratios ( NO 3 - : NH 4 + ratios) and, in particular, the effects of the accompanying ions in NH 4 + sources are unknown. To determine whether the accompanying ions in NH 4 + sources influence NH 4 + toxicity, the effects of NO 3 - : NH 4 + ratios on the physiology, electrolyte leakage index, nutrition, and dry weight were studied using hydroponics. The NH 4 + sources were ammonium chloride (NH4Cl) or ammonium sulfate [(NH4)2SO4], and five NO 3 - : NH 4 + ratios were used: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. The NO 3 - source was calcium nitrate [Ca(NO3)2], and the nitrogen (N) concentration was 15 mmol L−1. The results indicate that NH4Cl or (NH4)2SO4 can be used in studies on NH 4 + toxicity because the accompanying ions did not influence the tomato plants. In addition, NO 3 - : NH 4 + ratios of 100 : 0 and 75 : 25 resulted in the highest dry weight of tomato plants, whereas ratios of 25 : 75 or 0 : 100 were toxic. [ABSTRACT FROM AUTHOR]

An experiment was conducted to investigate the effects of calcium and nitrogen on quality and quantity of Rosa hybrida in hydroponic culture, using factorial complete randomized design with different levels of ammonium-N (0, 2.5, and 5 mM) and calcium (1.6 and 4.8 mM). The results indicated that ammonium-N concentration of 2 mM increased the number of flowers, length of pedicles, and fresh weight of flower stem per plant. 5 mM of ammonium-N caused a significant decrease in most of the measured characteristics. Increase in calcium concentration enhanced nitrogen, calcium, manganese, and boron; while, potassium, zinc, and copper decreased in the leaf. Flower diameter and fresh weight of flower stems per plant increased significantly. With application of ammonium in the nutrient solution, calcium and potassium concentration in the leaf decreased, whereas phosphorus, zinc, manganese, iron, and boron significantly increased. Therefore, application of 2.5 mM ammonium-N and 4.8 mM calcium are recommended. [ABSTRACT FROM AUTHOR]

Guzmania monostachia (Bromeliaceae) is a tropical epiphyte capable of up-regulating crassulacean acid metabolism (CAM) in its photosynthetic tissues in response to changing nutrient and water availability. Previous studies have shown that under drought there is a gradient of increasing CAM expression from the basal (youngest) to the apical (oldest) portion of the leaves, and additionally that nitrogen deficiency can further increase CAM intensity in the leaf apex of this bromeliad. The present study investigated the inter-relationships between nitrogen source (nitrate and/or ammonium) and water deficit in regulating CAM expression in G. monostachia leaves. The highest CAM activity was observed under ammonium nutrition in combination with water deficit. This was associated with enhanced activity of the key enzyme phosphoenolpyruvate carboxylase, elevated rates of ATP- and PPi-dependent proton transport at the vacuolar membrane in the presence of malate, and increased transcript levels of the vacuolar malate channel- encoding gene, ALMT. Water deficit was consistently associated with higher levels of total soluble sugars, which were maximal under ammonium nutrition, as were the activities of several antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase). Thus, ammonium nutrition, whilst associated with the highest degree of CAM induction in G. monostachia, also mitigates the effects of water deficit by osmotic adjustment and can limit oxidative damage in the leaves of this bromeliad under conditions that may be typical of its epiphytic habitat. [ABSTRACT FROM AUTHOR]

Ammonium is a major nitrogen source for plants; it is assimilated into glutamine via a reaction catalyzed by glutamine synthetase (GLN). Arabidopsis expresses four cytosolic GLN genes, GLN1; 1, GLN1; 2, GLN1; 3 and GLN1; 4, in roots. However, the function and organization of these GLN1 isozymes in ammonium assimilation in roots remain unclear. In this study, we aimed to characterize the four GLN1 isozymes. The levels of growth of the wild type and gln1 single and multiple knockout lines were compared in a hydroponic culture at ammonium concentrations of 0.1 and 3 mM. Under the low-ammonium concentration, in single mutants for each GLN1 gene, there was little effect on growth, whereas the triple mutant for GLN1; 1, GLN1; 2 and GLN1; 3 grew slowly and accumulated ammonium. Under the highammonium concentration, the single mutant for GLN1; 2 showed 50% decreases in fresh weight and glutamine, whereas the other gln1 single mutants did not show notable changes in the phenotype. The double mutant for GLN1; 1 and GLN1; 2 showed less growth and a lower glutamine concentration than the single mutant for GLN1; 2. Promoter analysis indicated an overlapping expression of GLN1; 1 with GLN1; 2 in the surface layers of the roots. We thus concluded that: (i) at a low concentration, ammonium was assimilated by GLN1; 1, GLN1; 2 and GLN1; 3, and they were redundant; (ii) low-affinity GLN1; 2 could contribute to ammonium assimilation at concentrations ranging from 0.1 to 3 mM; and (iii) GLN1; 1 supported GLN1; 2 within the outer cell layers of the root. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of wetland plants in the treatment of coking wastewater, Oenanthe javanica (Blume) DC (OC), Artemisia selengensis Turcz. ex Bess. (AB), Echinochloa crusgalli (L.) Beauv. (EB), Brasenia schreberi J.F.Gmel. (BG), and Lythrum salicaria L. (LL) were used to remove ammonia–nitrogen and chemical oxygen demand (COD) from coking wastewater. Results showed high concentrations (> 30%, diluted by deionized water) of coking wastewater caused decreased photosynthetic rate, transpiration rate, and relative growth rate in all studied plants. OC, BG, and LL showed higher adaptability than AB and EB. Wastewater concentrations < 30% resulted in less affected growth of OC, BG, and LL; However, AB and EB were suppressed when coking wastewater concentrations were > 15%. High concentrations of coking wastewater generated oxidative stress which resulted in increased malondialdehyde and proline contents and inhibition of superoxide dismutase. OC, BG, and LL were considered tolerable species in purifying coking wastewater (concentrations < 30%). [ABSTRACT FROM AUTHOR]

An adequate carbon supply is fundamental for plants to thrive under ammonium stress. In this work, we studied the mechanisms involved in tomato (Solanum lycopersicum L.) response to ammonium toxicity when grown under ambient or elevated CO2 conditions (400 or 800 p.p.m. CO2). Tomato roots were observed to be the primary organ dealing with ammonium nutrition. We therefore analyzed nitrogen (N) and carbon (C) metabolism in the roots, integrating the physiological response with transcriptomic regulation. Elevated levels of CO2 preferentially stimulated root growth despite the high ammonium content. The induction of anaplerotic enzymes from the tricarboxylic acid (TCA) cycle led to enhanced amino acid synthesis under ammonium nutrition. Furthermore, the root transcriptional response to ammonium toxicity was improved by CO2- enriched conditions, leading to higher expression of stressrelated genes, as well as enhanced modulation of genes related to signaling, transcription, transport and hormone metabolism. Tomato roots exposed to ammonium stress also showed a defense-like transcriptional response according to the modulation of genes related to detoxification and secondary metabolism, involving principally terpenoid and phenolic compounds. These results indicate that increasing C supply allowed the co-ordinated regulation of root defense mechanisms when dealing with ammonium toxicity. [ABSTRACT FROM AUTHOR]

Microcystis aeruginosa causes harmful algal blooms in the Nakdong River of Korea. We studied the effect of different concentrations and ratios of ammonium (NH4+), nitrate (NO3-), and phosphate (PO4 3-) on growth of this species in BG-11 medium: each nutrient alone, NO3- : NH4 + ratio, the N : P ratio with fixed total N (TN), and the N : P ratio with fixed total P (TP). The single nutrient experiments indicated that M. aeruginosa had the highest growth rate at NH4 + and NO3- concentrations of 500 μM, and at a PO4 3- concentration of 5 μM. The NO3- : NH4+ ratio experiments showed that M. aeruginosa had the highest growth rate at a ratio of 1 : 1 when TN was 100 μM and 250 μM, and the lowest growth rate at a ratio of 1 : 1 when the TN was 500 μM. The N : P ratio with fixed TN experiments indicated that M. aeruginosa had the highest growth rates at 50 : 1, 20 : 1, and 100 : 1 ratios when the TN was 100, 250, and 500 μM, respectively. In contrast, the N : P ratio with fixed TP experiments showed that M. aeruginosa had the highest growth rates at 200 : 1 ratio at all tested TP concentrations. In conclusion, our results imply that the NO3- : NH4+ ratio and the PO4 3- concentration affect the early stage of growth of M. aeruginosa. In particular, our results suggest that the maximum growth of M. aeruginosa is not simply affected by the NO3- : NH4+ ratio and the N : P ratio, but is determined by the TN concentration if a certain minimum PO4 3- concentration is present. [ABSTRACT FROM AUTHOR]

Although biological functions of ammonium (NH 4 + ) transporters (AMTs) have been intensively studied in many plant species, little is known about molecular bases responsible for NH 4 + movement in tobacco. Here, we reported the identification and functional characterization of a putative NH 4 + transporter NtAMT1.3 from tobacco ( Nicotiana tabacum ). Analysis in silico showed that NtAMT1.3 encoded an integral membrane protein containing 464 amino acid residues and exhibiting 10 predicted transmembrane α-helices. Heterologous functionality study demonstrated that NtAMT1.3 expression facilitated NH 4 + entry across plasma membrane of NH 4 + -uptake defective yeast and Arabidopsis qko mutant, allowing a restored growth of both yeast and Arabidopsis mutant on low NH 4 + . qPCR assay revealed that NtAMT1.3 was expressed in both roots and leaves and significantly up-regulated by nitrogen starvation and resupply of its putative substrate NH 4 + and even nitrate, suggesting that NtAMT1.3 should represent a nitrogen-responsive gene. Critically, constitutive overexpression of NtAMT1.3 in tobacco per se improved obviously the growth of transgenic plants on NH 4 + and enhanced leaf nitrogen (15% more) accumulation, consistent with observation of 35% more NH 4 + uptake by the roots of transgenic lines in 20 min root-influx test. Together with data showing its plasma membrane localization and saturated transport nature with K m of about 50 μM for NH 4 + , we suggest that NtAMT1.3 acts an active NH 4 + transporter that plays a significant role in NH 4 + acquisition and utilization in tobacco. [ABSTRACT FROM AUTHOR]

The effects of tree species on the N cycle in forest systems are still under debate. However, contradicting results of different 15N labeling techniques of trees and N tracers in the individual studies hamper a generalized mechanistic view. Therefore, we compared Ca(15NO3)2 and 15NH4Cl leaf-labeling method to investigate: (1) N allocation patterns from aboveground to belowground, (2) the cycles of N in soil-plant systems, and (3) to allow the production of highly 15N enriched litter for subsequent decomposition studies. 20 beeches ( Fagus sylvatica) and 20 ashes ( Fraxinus excelsior) were 15N pulse labeled from aboveground with Ca(15NO3)2 and 40 beeches and 40 ashes were 15N pulse labeled from aboveground with 15NH4Cl. 15N was quantified in tree compartments (leaves, stem, roots) and in soil after 8 d. Beech and ash incorporated generally more 15N from the applied 15NH4Cl compared to Ca(15NO3)2 in all measured compartments, except for ash leaves. Ash had highest 15N incorporation [45% of the applied with Ca(15NO3)2] in its leaves. Both tree species kept over 90% of all fixed 15N from Ca(15NO3) in their leaves, whereas only 50% of the 15N from the 15NH4Cl tracer remained in the leaves and 50% were allocated to stem, roots, and soil. There was no damage of the leaves by both salts, and thus both 15N tracers enable long-term labeling in situ field studies on N rhizodeposition and allocation in soils. Nonetheless, the 15N incorporation by both salts was species specific: the leaf labeling with 15NH4Cl results in a more homogenous distribution between the tree compartments in both tree species and, therefore, 15NH4Cl is more appropriate for allocation studies. The leaf labeling with Ca(15NO3)2 is a suitable tool to produce highly enriched 15N leaf litter for further long term in situ decomposition and turnover studies. [ABSTRACT FROM AUTHOR]

Ammonium is a major inorganic nitrogen source for plants. At low external supplies, ammonium promotes plant growth, while at high external supplies it causes toxicity. Ammonium triggers rapid changes in cytosolic pH, in gene expression, and in post-translational modifications of proteins, leading to apoplastic acidification, co-ordinated ammonium uptake, enhanced ammonium assimilation, altered oxidative and phytohormonal status, and reshaped root system architecture. Some of these responses are dependent on AMT-type ammonium transporters and are not linked to a nutritional effect, indicating that ammonium is perceived as a signaling molecule by plant cells. This review summarizes current knowledge of ammonium-triggered physiological and morphological responses and highlights existing and putative mechanisms mediating ammonium signaling and sensing events in plants. We put forward the hypothesis that sensing of ammonium takes place at multiple steps along its transport, storage, and assimilation pathways. [ABSTRACT FROM AUTHOR]

For microorganisms and plants, nitrate and ammonium are the main nitrogen sources and they are also important signaling molecules controlling several aspects of metabolism and development. Over the past decade, numerous studies revealed that nitrogen transporters are strongly regulated at the transcriptional level. However, more and more reports are now showing that nitrate and ammonium transporters are also subjected to post-translational regulations in response to nitrogen availability. Phosphorylation is so far the most well studied post-translational modification for these transporters and it affects both the regulation of nitrogen uptake and nitrogen sensing. For example, in Arabidopsis thaliana, phosphorylation was shown to activate the sensing function of the root nitrate transporter NRT1.1 and to switch the transport affinity. Also, for ammonium transporters, a phosphorylation-dependent activation/inactivation mechanism was elucidated in recent years in both plants and microorganisms. However, despite the fact that these regulatory mechanisms are starting to be thoroughly described, the signaling pathways involved and their action on nitrogen transporters remain largely unknown. In this review, we highlight the inorganic nitrogen transporters regulated at the post-translational level and we compare the known mechanisms in plants and microorganisms. We then discuss how these mechanisms could contribute to the regulation of nitrogen uptake and/or nitrogen sensing. [ABSTRACT FROM AUTHOR]

Ammonium (NH 4 + ) is the predominant nitrogen (N) source in many natural and agricultural ecosystems, including flooded rice fields. While rice is known as an NH 4 + -tolerant species, it nevertheless suffers NH 4 + toxicity at elevated soil concentrations. NH 4 + excess rapidly leads to the disturbance of various physiological processes that ultimately inhibit shoot and root growth. However, the global transcriptomic response to NH 4 + stress in rice has not been examined. In this study, we mapped the spatio-temporal specificity of gene expression profiles in rice under excess NH 4 + and the changes in gene expression in root and shoot at various time points by RNA-Seq (Quantification) using Illumina HiSeqTM 2000. By comparative analysis, 307 and 675 genes were found to be up-regulated after 4 h and 12 h of NH 4 + exposure in the root, respectively. In the shoot, 167 genes were up-regulated at 4 h, compared with 320 at 12 h. According to KEGG analysis, up-regulated DEGs mainly participate in phenylpropanoid (such as flavonoid) and amino acid (such as proline, cysteine, and methionine) metabolism, which is believed to improve NH 4 + stress tolerance through adjustment of energy metabolism in the shoot, while defense and signaling pathways, guiding whole-plant acclimation, play the leading role in the root. We furthermore critically assessed the roles of key phytohormones, and found abscisic acid (ABA) and ethylene (ET) to be the major regulatory molecules responding to excess NH 4 + and activating the MAPK (mitogen-activated protein kinase) signal-transduction pathway. Moreover, we found up-regulated hormone-associated genes are involved in regulating flavonoid biosynthesis and are regulated by tissue flavonoid accumulation. [ABSTRACT FROM AUTHOR]

Two kinds of field experiments were conducted in Yongshou, Shaanxi Province, and Louyang, Henan Province, to study wheat responses to nitrate and ammonium N applied at different times with three treatments: control, nitrate and ammonium N at a rate of 100 kg N ha −1 as basal fertilizer. During the plant growing period, pH, ammonium and nitrate N were determined in rhizosphere and bulk soil, and nitrate N, ammonium N and amide N in plants at three wheat growing stages. Results showed that in Yongshou, sown at 23 Sep. wheat seed yield increase by nitrate N was 1661 and 565 kg ha −1 in the two fields while 1022 and 336 kg ha −1 by ammonium N. In contrast, sown at 15 Oct. the respective increase was 378 and 399 kg ha −1 for nitrate N and 157 and 145 kg ha −1 for ammonium N, the increased ratio of nitrate to ammonium N being much higher for the second sowing time than for the first. Similarly, when N fertilizer was applied 15 days before wheat sowing, the yield difference between the two N forms was not large or even not significant at 0.05 level while at late time, the differences was remarkably significant. Such different results were caused by the velocity of the ammonium N nitrification: earlier sowing with N fertilization or earlier N fertilization before wheat sowing, higher soil temperature rapidly promoted ammonium N nitrified into nitrate N while the reverses were the case for N input later. Soil pH in rhizosphere increased with nitrate while decreased with ammonium N. Compared to ammonium N, nitrate N not only increased nitrate N concentrations and uptake amounts in plants, but ammonium N and amide N as well by rapid transformation of nitrate N. As a direct result, fertilization of nitrate N ensured a beneficial N nutrition environment for wheat growth. [ABSTRACT FROM AUTHOR]

Nitrate (NO $ _3^ - $) and ammonium (NH $ _4^+ $) are the predominant forms of nitrogen (N) available to plants in agricultural soils. Nitrate concentrations are generally ten times higher than those of NH $ _4^+ $ and this ratio is consistent across a wide range of soil types. The possible contribution of these small concentrations of NH $ _4^+ $ to the overall N budget of crop plants is often overlooked. In this study the importance of this for the growth and nitrogen budget of maize ( Zea mays L.) was investigated, using agriculturally relevant concentrations of NH $ _4^+ $. Maize inbred line B73 was grown hydroponically for 30 d at low (0.5 mM) and sufficient (2.5 mM) levels of NO $ _3^ - $. Ammonium was added at 0.05 mM and 0.25 mM to both levels of NO $ _3^ - $. At low NO $ _3^ - $ levels, addition of NH $ _4^+ $ was found to improve the growth of maize plants. This increased plant growth was accompanied by an increase in total N uptake, as well as total phosphorus, sulphur and other micronutrients in the shoot. Ammonium influx was higher than NO $ _3^ - $ influx for all the plants and decreased as the total N in the nutrient medium increased. This study shows that agriculturally relevant proportions of NH $ _4^+ $ supplied in addition to NO $ _3^ - $ can increase growth of maize. [ABSTRACT FROM AUTHOR]

We conducted a study that shows that light and dark conditions do not affect the uptake rates of ammonium and nitrate by the seagrass Zostera noltei. This is an important advantage over some seaweed species in which these rates are severely reduced at night. In the light, the ammonium uptake rates were initially higher (15 and 20 μmol·g−1·h−1) and stabilized at a rate of 5 μmol·g−1·h−1 after 1 h, whereas in the dark the rates remained constant at a rate of 10 μmol·g−1·h−1 over the first 180 min of incubation. The rates of nitrate uptake in the light were high within the first 120 min of incubation (7.2-11.1 μmol·g−1·h−1) and decreased afterwards to lower values (0.8-3.9 μmol·g−1·h−1), whereas in the dark the rates fluctuated around 0.0-11.1 μmol·g−1·h−1 throughout the whole incubation time (7 h). The soluble sugar content of Z. noltei leaves increased significantly with both ammonium and nitrate incubations in the light, indicating the metabolic outcome of photosynthesis. In the dark, there was no significant variation in either the soluble sugar or in the starch content of leaves, rhizomes or roots in either the ammonium or nitrate incubations. However, the total starch content of plants decreased at night whereas the total soluble sugars increased, suggesting a process of starch catabolism to generate energy with the consequent production of smaller monosaccharide products. The starch content of rhizomes decreased significantly during the light incubations with nitrate but not with ammonium. These results suggest that carbohydrate mobilization is necessary for Z. noltei to account for extra energetic costs needed for the uptake and assimilation of nitrate. Furthermore, our results suggest that nitrate uptake, at least during the day, requires the mobilization of starch whereas the uptake of ammonium does not. [ABSTRACT FROM AUTHOR]

Ammonium toxicity in hydroponically grown crops can affect tomato development. However, it has been shown that the silicon (Si) attenuates ammonium toxicity in plants depending on the plant species, the stage of development and the ammonium concentration in the nutrient solution. Thus, in order to investigate how Si attenuates stress caused by ammonium in tomato, a study was carried out involving plants cultivated up to 40 days after seed germination using nutrient solutions containing ammonium concentrations (1, 2, 4, 6 and 8 mmol L−1), in the absence or presence of Si (1 mmol L−1). The accumulation and efficiency of nitrogen and Si use, as well as the concentrations of chlorophyll, carotenoids, malondialdehyde, hydrogen peroxide and growth parameters was assessed. At a concentration of 1 mmol L−1ammonium, Si increases the accumulation of nitrogen and Si, the nitrogen use efficiency, the root area and dry biomass of the shoot. At concentrations of 1 and 2 mmol L−1ammonium, Si increases the leaf area and root dry biomass, and in higher concentrations, there was no effect of Si after the supply of ammonium. It was observed that the addition of Si mitigates ammonium toxicity by 1 mmol L−1ammonium, and we can recommend its use in the nutrient solution (Si = 1 mmol L−1) to grow tomato cropsthat employs ammonium concentration of 1 mmol L−1. [ABSTRACT FROM PUBLISHER]

Most of the studies about NH4+ stress mechanism simply address the effects of free NH4+, failing to recognize the changed nitrogen assimilation products. The objective of this study was to elucidate the effects of glutamate on root growth under high ammonium (NH4+) conditions in winter wheat (Triticum aestivum L.). Hydroponic experiments were conducted using two wheat cultivars, AK58 (NH4+-sensitive) and Xumai25 (NH4+-tolerant) with either 5 mM NH4+ nitrogen (AN) as stress treatment or 5 mM nitrate (NO3-) nitrogen as control. To evaluate the effects of NH4+-assimilation products on plant growth, 1 μM L-methionine sulfoximine (MSO) (an inhibitor of glutamine synthetase (GS)) and 1 mM glutamates (a primary N assimilation product) were added to the solutions, respectively. The AN significantly reduced plant biomass, total root length, surface area and root volume in both cultivars, but less effect was observed in Xumai25. The inhibition effects were alleviated by the application of MSO but strengthened by the application of glutamate. The AN increased the activities of GS, glutamate dehydrogenase (GDH) in both cultivars, resulting in higher glutamate contents. However, its contents were decreased by the application of MSO. Compared to AK58, Xumai25 showed lower glutamate contents due to its higher activities of glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT). With the indole-3-acetic acid (IAA) contents decreasing in roots, the ratio of shoot to root in IAA was increased, and further increased by the application of glutamate, and reduced by the application of MSO, but the ratio was lower in Xumai25. Meanwhile, the total soluble sugar contents and its root to shoot ratio also showed similar trends. These results indicate that the NH4+-tolerant cultivar has a greater transamination ability to prevent glutamate over-accumulation to maintain higher IAA transport ability, and consequently promoted soluble sugar transport to roots, further maintaining root growth. [ABSTRACT FROM AUTHOR]

Ammonium is the primarily nitrogen source for plant growth, but the molecular basis of ammonium acquisition in fruit species remains poorly understood. In this study, we report on the characterization of two new ammonium transporters (AMT) in the perennial tree Pyrus betulaefolia. In silico analyses and yeast complementation assays revealed that both PbAMT1;3 and PbAMT1;5 can be classified in the AMT1 sub-family. The specific expression of PbAMT1;3 in roots and of PbAMT1;5 in leaves indicates that they have diverse functions in ammonium uptake or transport in P. betulaefolia. Their expression was strongly influenced by ammonium availability. In addition, the transcript level of PbAMT1;5 was significantly affected by the diurnal cycle and senescence hormones. They conferred the ability to uptake nitrogen to the yeast strain 31019b; however, the NH uptake kinetics of PbAMT1;3 were different from those of PbAMT1;5. Indeed, PbAMT1;3 had a higher affinity for NH, and pH changes were associated with this substrates' transport in yeast. The present study provides basic gene features and transcriptional information for the two new members of the AMT1 sub-family in P. betulaefolia and will aid in decoding the precise roles of AMTs in P. betulaefolia physiology. [ABSTRACT FROM AUTHOR]

Acquisition of mineral nitrogen by roots from the surrounding environment is often not completely efficient, in which a variable amount of leakage (efflux) relative to gross uptake (influx) occurs. The efflux/influx ratio ( E/ I) is, therefore, inversely related to the efficiency of nutrient uptake at the root level. Time-integrated estimates of E/ I and other nitrogen-use traits may be obtainable from variation in stable isotope ratios or through compartmental analysis of tracer efflux (CATE) using radioactive or stable isotopes. To compare these two methods, Populus balsamifera L. genotypes were selected, a priori, for high or low nitrogen isotope discrimination. Vegetative cuttings were grown hydroponically, and E/ I was calculated using an isotope mass balance model (IMB) and compared to E/ I calculated using 15N CATE. Both methods indicated that plants grown with ammonium had greater E/ I than nitrate-grown plants. Genotypes with high or low E/I using CATE also had similarly high or low estimates of E/I using IMB, respectively. Genotype-specific means were linearly correlated (r = 0.77; P = 0.0065). Discrepancies in E/ I between methods may reflect uncertainties in discrimination factors for the assimilatory enzymes, or temporal differences in uptake patterns. By utilizing genotypes with known variation in nitrogen isotope discrimination, a relationship between nitrogen isotope discrimination and bidirectional nitrogen fluxes at the root level was observed. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the relationship between Cd 2 + /NH 4 + sorption and physicochemical properties of biochars produced from different wetland plants. Biochars from six species of wetland plants (i.e., Canna indica , Pennisetum purpureum Schum, Thalia dealbata , Zizania caduciflora , Phragmites australis and Vetiveria zizanioides ) were obtained at 500 °C and characterized, and their sorption for ammonium and cadmium was determined. There were significant differences in elemental composition, functional groups and specific surface area among the biochars derived from different wetland plant species. Sorption of ammonium and cadmium on the biochars could be described by a pseudo second order kinetic model, and the simple Langmuir model fits the isotherm data better than the Freundlich or Temkin model. The C. indica derived biochar had the largest sorption capacity for NH 4 + and Cd 2 + , with a maximum sorption of 13.35 and 125.8 mg g − 1 , respectively. P. purpureum Schum derived biochar had a similar maximum sorption (119.3 mg g − 1 ) for Cd 2 + . Ammonium sorption was mainly controlled by cation exchange, surface complexation with oxygen-containing functional groups and the formation of magnesium ammonium phosphate compounds, whereas for Cd 2 + sorption, the formation of cadmium phosphate precipitates, cation exchange and binding to oxygen-containing groups were the major possible mechanisms. In addition, the sorption of ammonium and cadmium was not affected by surface area and microporosity of the biochars. [ABSTRACT FROM AUTHOR]

In order to investigate the impacts of ammonia nitrogen concentration and the necessity of dredging, five levels of ammonia nitrogen including 0, 2, 4, 8, and 16mgL-1 and two levels of sediments nutriments (high and low) were treated. The total biomass, leaf, root, and flower biomasses were selected as the growth indicators, while total chlorophyll (i.e., chl-a and -b), malondialdehyde (MDA), and free proline as subsidiary physiological index. When ammonia-N contents of the water column were 8-16mgL-1, the total biomass of Vallisneria natans in the first harvest is higher than those in the second harvest, and the total chlorophyll concentration, MDA and free proline of the plants became significantly low. It indicates that high ammonia nitrogen (>8mg L-1) of the water column inhibit the growth of V. natans. The total biomass, the total chlorophyll concentration of plants in the high nutrient sediment is higher than those in the low nutrient sediment, suggesting that high sediments nutrient promote the growth of V. natans. Therefore, using V. natans for water ecological restoration, the water should meet the ammonia nitrogen content of <8mgL-1. Moreover, dredging eutrophication sediment is probably not necessary. [ABSTRACT FROM AUTHOR]

NH4+ nutrition provokes mild toxicity by enhancing H2O2 accumulation, which acts as a signal activating systemic acquired acclimation (SAA). Until now, induced resistance mechanisms in response to an abiotic stimulus and related to SAA were only reported for exposure to a subsequent abiotic stress. Herein, the first evidence is provided that this acclimation to an abiotic stimulus induces resistance to later pathogen infection, since NH4+ nutrition (N- NH4+)-induced resistance (NH4+-IR) against Pseudomonas syringae pv tomato DC3000 (Pst) in tomato plants was demonstrated. N-NH4+ plants displayed basal H2O2, abscisic acid (ABA), and putrescine (Put) accumulation. H2O2 accumulation acted as a signal to induce ABA-dependent signalling pathways required to prevent NH4+ toxicity. This acclimatory event provoked an increase in resistance against later pathogen infection. N-NH4+ plants displayed basal stomatal closure produced by H2O2 derived from enhanced CuAO and rboh1 activity that may reduce the entry of bacteria into the mesophyll, diminishing the disease symptoms as well as strongly inducing the oxidative burst upon Pst infection, favouring NH4+-IR. Experiments with inhibitors of Put accumulation and the ABA-deficient mutant lacca demonstrated that Put and ABA downstream signalling pathways are required to complete NH4+-IR. The metabolic profile revealed that infected N-NH4+ plants showed greater ferulic acid accumulation compared with control plants. Although classical salicylic acid (SA)-dependent responses against biotrophic pathogens were not found, the important role of Put in the resistance of tomato against Pst was demonstrated. Moreover, this work revealed the cross-talk between abiotic stress acclimation (NH4+ nutrition) and resistance to subsequent Pst infection. [ABSTRACT FROM AUTHOR]

Background: Previous studies showed that the two main Mediterranean plant functional groups, summer semi-deciduous and evergreen sclerophylls, differ in soil characteristics and nitrate (NO) use strategies: even though summer semi-deciduous plants have higher NO availability than evergreen sclerophylls, NO reduction (i.e., nitrate reductase activity-NRA) is lower, and is not stimulated by substrate (NO) availability. Aims: Test if in Cistus albidus plants, a summer semi-deciduous species, ammonium (NH) can inhibit NRA, despite the availability of NO, and whether Olea europaea plants, evergreen sclerophyll, are more tolerant of NH than the former. Methods: One-year-old C. albidus and wild O. europaea potted plants were supplied with both NH and NO at increasing levels (0.1; 0.2; 0.4; 0.8 and 1.6 % N). Tolerance of NH was evaluated using integrative (mortality and biomass accumulation) and plant nitrogen metabolism parameters (in vitro NRA and concentrations of NO and NH) determined in roots and leaves. Results: C. albidus plants were consistently less NH tolerant than O. europaea, displaying: higher mortality; growth and NRA inhibition and NH accumulation above 0.2 % NHNO-N in the soil. In contrast, O. europaea plants seemed to buffer the full range of tested NHNO levels. Conclusions: C. albidus plants were less NH tolerant than O. europaea. The ecological implications of this contrasting NH tolerance are discussed. [ABSTRACT FROM AUTHOR]

Nitrite reductase (NiR, EC1.7.7.1) is a key enzyme that catalyzes the second step of nitrite reduction to ammonium in the process of nitrate assimilation in plants. To study the molecular mechanism underlying nitrate accumulation during plant development, the molecular characterization of the NiR gene ( RsNiR ) and its expression patterns under different nitrate concentrations and induction periods of nitrate treatments in leaf, root, petiole, stem and lateral root of radish ( Raphanus sativus L.) were investigated in this study. Based on our radish transcriptome database, the genomic DNA sequence of RsNiR was isolated with four exons and three introns. The cDNA length was 1756 bp containing an open reading frame (ORF) of 1524 bp. The deduced protein consists of 506 amino acids, and showed highest identity with NiRs from Arabidopsis . Moreover, using the genomic DNA walking approach, the 843-bp 5’-flanking region upstream of RsNiR was isolated, which contained several basic cis -regulatory elements including TATA-box, CAAT-box and nitrate-responsive cis -element (NRE). With the increasing nitrate concentration, the NR activity (NRA), nitrate contents and RsNiR expression levels exhibited increasing trends in leaf and root, reached a maximum at 30 mM nitrate treatment and then decreased. In contrast, there was no obvious relationship among RsNiR expression level, NRA and nitrate content under different induction periods at 30 mM nitrate. These results could provide fundamental insight into clarification of the molecular regulation mechanism underlying nitrate assimilation in radish. [ABSTRACT FROM AUTHOR]

Ammonium (NH4+) is an important nitrogen nutrition for plant growth; however, it is toxic to many plants at high concentration. Eutrophication induces NH4+enrichment in shallow lakes and increases risk of NH4+toxicity to submersed macrophytes. Potassium (K+) was known as an alleviant to the toxic syndromes of plant under NH4+stress. In the present study, we examined the single effects and co-effects of NH4+and K+enrichments (∼0.65 mg L−1NH4–N, ∼45 mg L−1K+) in water column on submersed macrophyteVallisneria natansL. with focus on carbon (C) and nitrogen (N) metabolism, life history and asexual reproduction of the plant in outdoor aquariums lasting for about five months. We found that the NH4+enrichment alone increased growth and decreased death rate of the plant, leading to higher biomass, longer survivorship and more tuber production and ramets of the plants, indicating that the NH4+enrichment was not stressful to the plant. The combination of NH4+and K+enrichments enhanced the plant growth to less extent as did the NH4+enrichment alone, and reduced the plant death rate. The NH4+enrichment increased the concentrations of free amino acids and nitrogen, and decreased the concentrations of soluble carbohydrate in leaves and tubers of the plant irrespective of the K+enrichments. The K+enrichments alone did not affect growth, death rates and C–N metabolism of the plant. The K+alone or together with NH4+enrichments had negligible effect on tuber production and tuber C–N metabolism of the plant. The present results indicated that the K+enrichment had negligible effects on the plant; the NH4+enrichment (0.65 mg L−1NH4–N) benefited the plant growth, while it might negatively affect the asexual reproduction due to low carbohydrate contents of the tubers particularly under low light stress in eutrophic lake. [ABSTRACT FROM AUTHOR]

In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L−1and urea 0 and 2 g L−1concentrations. Results indicated that nickel (Ni; 300 mg L−1) plus urea (2 g L−1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L−1and urea (2 g L−1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L−1without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L−1without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L−1along with urea at 2 g L−1were the best treatments. [ABSTRACT FROM PUBLISHER]

Previously, we demonstrated that drought resistance in rice seedlings was increased by ammonium (NH 4 + ) treatment, but not by nitrate (NO 3 − ) treatment, and that the change was associated with root development. To study the effects of different forms of nitrogen on water uptake and root growth under drought conditions, we subjected two rice cultivars (cv. ‘Shanyou 63’ hybrid indica and cv. ‘Yangdao 6’ indica , China) to polyethylene glycol-induced drought stress in a glasshouse using hydroponic culture. Under drought conditions, NH 4 + significantly stimulated root growth compared to NO 3 − , as indicated by the root length, surface area, volume, and numbers of lateral roots and root tips. Drought stress decreased the root elongation rate in both cultivars when they were supplied with NO 3 − , while the rate was unaffected in the presence of NH 4 + . Drought stress significantly increased root protoplast water permeability, root hydraulic conductivity, and the expression of root aquaporin (AQP) plasma intrinsic protein (PIP) genes in rice plants supplied with NH 4 + ; these changes were not observed in plants supplied with NO 3 − . Additionally, ethylene, which is involved in the regulation of root growth, accumulated in rice roots supplied with NO 3 − under conditions of drought stress. We conclude that the increase in AQP expression and/or activity enhanced the root water uptake ability and the drought tolerance of rice plants supplied with NH 4 + . [ABSTRACT FROM AUTHOR]

AMT1-3 encodes the high affinity NH4+ transporter in rice roots and is predominantly expressed under nitrogen starvation. In order to evaluate the effect of AMT1-3 gene on rice growth, nitrogen absorption and metabolism, we generated AMT1-3-overexpressing plants and analyzed the growth phenotype, yield, carbon and nitrogen metabolic status, and gene expression profiles. Although AMT1-3 mRNA accumulated in transgenic plants, these plants displayed significant decreases in growth when compared to the wild-type plants. The nitrogen uptake assay using a 15N tracer revealed poor nitrogen uptake ability in AMT1-3-overexpressing plants. We found significant decreases in AMT1-3-overexpressing plant leaf carbon and nitrogen content accompanied with a higher leaf C/N ratio. Significant changes in soluble proteins and carbohydrates were also observed in AMT1-3-overexpressing plants. In addition, metabolite profile analysis demonstrated significant changes in individual sugars, organic acids and free amino acids. Gene expression analysis revealed distinct expression patterns of genes that participate in carbon and nitrogen metabolism. Additionally, the correlation between the metabolites and gene expression patterns was consistent in AMT1-3-overexpressing plants under both low and high nitrogen growth conditions. Therefore, we hypothesized that the carbon and nitrogen metabolic imbalance caused by AMT1-3 overexpressing attributed to the poor growth and yield of transgenic plants. [ABSTRACT FROM AUTHOR]

Ammonia (ammonium ion under physiological conditions) is one of the key nitrogen sources in cellular amino acid biosynthesis. It is continuously produced in living organisms by a number of biochemical processes, but its accumulation in cells leads to tissue damage. Current knowledge suggests that a few enzymes and transporters are responsible for maintaining the delicate balance of ammonium fluxes in plant tissues. In this study we analyze the data in the scientific literature and the publicly available information on the dozens of biochemical reactions in which endogenous ammonium is produced or consumed, the enzymes that catalyze them, and the enzyme and transporter mutants listed in plant metabolic and genetic databases (Plant Metabolic Network, TAIR, and Genevestigator). Our compiled data show a surprisingly high number of little-studied reactions that might influence cellular ammonium concentrations. The role of ammonium in apoptosis, its relation to oxidative stress, and alterations in ammonium metabolism induced by environmental stress need to be explored in order to develop methods to manage ammonium toxicity. [ABSTRACT FROM AUTHOR]

Ammonium nutrition is toxic to many plants. Arabidopsis displays high intraspecific variability in ammonium tolerance (shoot biomass), and ammonium accumulation seems to be an important player in this variability.Plants are dependent on exogenous nitrogen (N) supply. Ammonium (NH4+), together with nitrate (NO3–), is one of the main nitrogenous compounds available in the soil. Paradoxically, although NH4+ assimilation requires less energy than that of NO3–, many plants display toxicity symptoms when grown with NH4+ as the sole N source. However, in addition to species-specific ammonium toxicity, intraspecific variability has also been shown. Thus, the aim of this work was to study the intraspecific ammonium tolerance in a large panel of Arabidopsis thaliana natural accessions. Plants were grown with either 1mM NO3– or NH4+ as the N source, and several parameters related to ammonium tolerance and assimilation were determined. Overall, high variability was observed in A. thaliana shoot growth under both forms of N nutrition. From the parameters determined, tissue ammonium content was the one with the highest impact on shoot biomass, and interestingly this was also the case when N was supplied as NO3–. Enzymes of nitrogen assimilation did not have an impact on A. thaliana biomass variation, but the N source affected their activity. Glutamate dehydrogenase (GDH) aminating activity was, in general, higher in NH4+-fed plants. In contrast, GDH deaminating activity was higher in NO3–-fed plants, suggesting a differential role for this enzyme as a function of the N form supplied. Overall, NH4+ accumulation seems to be an important player in Arabidopsis natural variability in ammonium tolerance rather than the cell NH4+ assimilation capacity. [ABSTRACT FROM AUTHOR]

Nitrate-ammonium (N-A) and ammonium-nitrate (A-N) transition experiments were performed with tobacco (Nicotiana tabacum, cv Gatersleben) plants to study whether the increased expression of ammonium assimilation-related genes found under short-term boron (B) deficiency is maintained when the nitrogen source changes. Asparagine synthetase (AS), glutamate dehydrogenase (GDH) and glutamine synthetase (GS) gene overexpressions in roots under B deprivation were detected in both nitrogen transitions, althoughGSand, especially,ASup-regulations were observed earlier in the ammonium-nitrate transition. Transcript levels were inversely correlated with hexose contents after 24 h of B deprivation. Our results suggest that tobacco roots respond to short-term B deficiency by increasing the expression ofAS,GDHandGSgenes irrespectively of the nitrogen source. A hypothetical model to explain these results is proposed and discussed. Thus, the combined action of these enzymes would avoid the accumulation of ammonia and help maintain the activity of the tricarboxylic acid cycle when tobacco roots are affected by B deficiency, the plant organ that first senses this stress. Therefore, under B deficiency, they would act as an ammonium detoxifying mechanism, being a complement to the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. We propose that the protective role of these enzymes could be extended to changing nitrogen-supply conditions. [ABSTRACT FROM PUBLISHER]

Decline of submersed macrophytes has occurred in eutrophic lakes worldwide. Little is known about effects of nutrient enrichment on biomechanical properties of submersed macrophytes. In a 30-day experiment, Myriophyllum spicatum was cultured in aquaria containing two types of sediment (mesotrophic clay vs. fertile loam) with contrasting water NH concentrations (0 vs. 3.0 mg L NH-N). The plant growth, shoot and root morphology, stem biomechanical properties, and stem total nonstructure carbohydrates content (TNC) were examined. The NH-enriched water, particularly combined with the fertile sediment, caused adverse effects on M. spicatum as indicated by reductions in the growth, stem biomechanical properties (tensile force, bending force and structural stiffness), and TNC content. These results indicate that increased sediment fertility and water NH-enrichment made the plant more fragile and vulnerable to hydraulic damage, particularly for the upper stem, implying that M. spicatum was prone to uprooting and fracture by hydraulic force, and the broken fragment from parent shoot of M. spicatum might have low-survival potential due to its low-TNC content. This may be a mechanical aspect for the decline of submersed macrophytes and makes it more difficult to restore submersed vegetation in the eutrophic lakes. [ABSTRACT FROM AUTHOR]

Highlights: [•] We review genetic loci, signaling pathways, and physiological targets of NH4 + stress in the model system Arabidopsis thaliana. [•] Differing NH4 + stress responses between belowground and aboveground sources are dissected. [•] New experimental approaches to the study of NH4 + toxicity are outlined. [•] An integrated view of behavior and signaling in response to NH4 + stress is proposed. [Copyright &y& Elsevier]

AtNUDT7 was reported to be a negative regulator of EDS1-mediated immunity in Arabidopsis. However, the underlying molecular and genetic mechanism of the AtNUDT7-regulated defense pathway remains elusive. Here we report that AtNUDT7 and its closest paralog AtNUDT6 function as novel negative regulators of SNC1, a TIR-NB-LRR-type R gene. SNC1 is upregulated at transcriptional and possibly post-transcriptional levels in nudt6-2 nudt7. The nudt6-2 nudt7 double mutant exhibits autoimmune phenotypes that are modulated by temperature and fully dependent on EDS1. The nudt6-2 nudt7 mutation causes EDS1 nuclear accumulation shortly after the establishment of autoimmunity caused by the temperature shift. We found that a low ammonium/nitrate ratio in growth media leads to a higher level of nitrite-dependent nitric oxide (NO) production in nudt6-2 nudt7, and NO acts in a positive feedback loop with EDS1 to promote the autoimmunity. The low ammonium/nitrate ratio also enhances autoimmunity in snc1-1 and cpr1, two other autoimmune mutants in Arabidopsis. Our study indicates that Arabidopsis senses the ammonium/nitrate ratio as an input signal to determine the amplitude of the EDS1-mediated defense response, probably through the modulation of NO production. [ABSTRACT FROM AUTHOR]

Growth, morphology, NH4 + uptake and mineral allocation in Salvinia cucullata Roxb. ex Bory grown with different amounts of NH4 + were investigated. Plants of uniform size were grown on full strength Smart and Barko medium with different NH4 + concentrations (0.5, 1, 5, 10 and 15mM) and incubated in a greenhouse for four weeks. Salvinia cucullata grew well in the medium with 0.5–1mM NH4 + with a relative growth rate of 0.11–0.12d−1 without exhibiting NH4 + toxicity symptoms. With an NH4 + concentration above 5mM, plant growth was suppressed and signs of NH4 + toxicity were observed. NH4 + toxicity symptoms were obvious in plants supplied with 10mM and 15mM NH4 +. These plants had low growth rates, short roots, low numbers of roots and showed chlorosis. Rotted roots and stems were also found in plants fed with 15mM NH4 +. This species had a high uptake rate even though the NH4 + concentrations increased, making it an ideal candidate for growth in eutrophic environments. The high NH4 + concentration had a negative effect on K uptake resulting in low K concentration in the plant tissue, but the plants increased N content in plant tissue. Thus, harvested plants can be used as soil fertilizer or for animal feed. Furthermore, maintaining plant biomass can improve the efficiency of water treatment. [Copyright &y& Elsevier]

When ammonium is the sole nitrogen (N) source, plant growth is suppressed compared with the situation where nitrate is the N source. This is commonly referred to as ammonium toxicity. It is widely known that a combination of nitrate and ammonium as N source alleviates this ammonium toxicity (nitrate-dependent alleviation of ammonium toxicity), but the underlying mechanisms are still not completely understood. In plants, ammonium toxicity is often accompanied by a depletion of organic acids and inorganic cations, and by an accumulation of ammonium. All these factors have been considered as possible causes for ammonium toxicity. Thus, we hypothesized that nitrate could alleviate ammonium toxicity by lessening these symptoms. We analyzed growth, inorganic N and cation content and various primary metabolites in shoots of Arabidopsis thaliana seedlings grown on media containing various concentrations of nitrate and/or ammonium. Nitrate-dependent alleviation of ammonium toxicity was not accompanied by less depletion of organic acids and inorganic cations, and showed no reduction in ammonium accumulation. On the other hand, shoot growth was significantly correlated with the nitrate concentration in the shoots. This suggests that nitrate-dependent alleviation of ammonium toxicity is related to physiological processes that are closely linked to nitrate signaling, uptake and reduction. Based on transcript analyses of various genes related to nitrate signaling, uptake and reduction, possible underlying mechanisms for the nitrate-dependent alleviation are discussed. [ABSTRACT FROM AUTHOR]

Anthocyanins are major water-soluble and dynamic colouring plant pigment present in plant tissues with the high antioxidant properties. The role of ammonium and potassium nitrate in the culture medium on anthocyanin augmentation is probed thoroughly, but the mechanism of its biosynthesis continues to be unclear. Hence, the present study was undertaken to optimise nitrate ratio in the culture medium for anthocyanin augmentation and examination of its biosynthesis pathway in callus culture of Daucus carota. MS basal medium fortified with various ratio of NH4NO3:KNO3 was employed to find their impact on biomass, anthocyanin augmentation and the expression profile of anthocyanin biosynthesis genes in the callus culture. The data indicated that the highest anthocyanin content (9.30 ± 0.25 mg/100 g FW) was seen in callus grown on the medium supplemented with 20.0 mM NH4NO3:37.6 mM KNO3 and the least was seen in the medium which contained 40.0 mM NH4NO3:18.8 mM KNO3 (2.74 ± 0.27 mg/100 g FW). This indicates an optimal concentration of NH4NO3:KNO3 ratio is essential to produce a higher amount of anthocyanin in in vitro culture. Meanwhile, anthocyanin biosynthesis genes were differentially expressed as confirmed by qRT-PCR in the time interval of 5, 10, 15, 20 and 25 days. The transcript levels of nine anthocyanin biosynthesis genes were increased in the response of varying NH4NO3:KNO3 ratio in the medium. The transcript level of early genes PAL, 4CL, CHS and CHI increased by 19.5, 21.0, 16.2 and 9.98-fold, respectively, compared with control. In addition, late biosynthesis genes LDOX and UFGT resulted in the transcript level of 11.3 and 13.6-fold, respectively. [ABSTRACT FROM AUTHOR]

A table of contents for the December 2016 issue of the "Journal of Plant Nutrition & Soil Science" is presented.

Nitrogen is one of the most important limiting factors for plant growth. However, as ammonium is readily converted into ammonia (NH3) when soil pH rises above 8.0, this activity depletes the availability of ammonium (NH4+) in alkaline soils, consequently preventing the growth of most plant species. The perennial wild grass Puccinellia tenuiflora is one of a few plants able to grow in soils with extremely high salt and alkaline pH (>9.0) levels. Here, we assessed how this species responds to ammonium under such conditions by isolating and analyzing the functions of a putative ammonium transporter (PutAMT1;1). PutAMT1;1 is the first member of the AMT1 (ammonium transporter) family that has been identified in P. tenuiflora. This gene (1) functionally complemented a yeast mutant deficient in ammonium uptake (2), is preferentially expressed in the anther of P. tenuiflora, and (3) is significantly upregulated by ammonium ions in both the shoot and roots. The PutAMT1;1 protein is localized in the plasma membrane and around the nuclear periphery in yeast cells and P. tenuiflora suspension cells. Immunoelectron microscopy analysis also indicated that PutAMT1;1 is localized in the endomembrane. The overexpression of PutAMT1;1 in A. thaliana enhanced plant growth, and increased plant susceptibility to toxic methylammonium (MeA). Here, we confirmed that PutAMT1;1 is an ammonium-inducible ammonium transporter in P. tenuiflora. On the basis of the results of PutAMT1;1 overexpression in A. thaliana, this gene might be useful for improving the root to shoot mobilization of MeA (or NH4+). [ABSTRACT FROM AUTHOR]

Nitrogen is one of the most important limiting factors for plant growth. However, as ammonium is readily converted into ammonia (NH3) when soil pH rises above 8.0, this activity depletes the availability of ammonium (NH4+) in alkaline soils, consequently preventing the growth of most plant species. The perennial wild grass Puccinellia tenuiflora is one of a few plants able to grow in soils with extremely high salt and alkaline pH (>9.0) levels. Here, we assessed how this species responds to ammonium under such conditions by isolating and analyzing the functions of a putative ammonium transporter (PutAMT1;1). PutAMT1;1 is the first member of the AMT1 (ammonium transporter) family that has been identified in P. tenuiflora. This gene (1) functionally complemented a yeast mutant deficient in ammonium uptake (2), is preferentially expressed in the anther of P. tenuiflora, and (3) is significantly upregulated by ammonium ions in both the shoot and roots. The PutAMT1;1 protein is localized in the plasma membrane and around the nuclear periphery in yeast cells and P. tenuiflora suspension cells. Immunoelectron microscopy analysis also indicated that PutAMT1;1 is localized in the endomembrane. The overexpression of PutAMT1;1 in A. thaliana enhanced plant growth, and increased plant susceptibility to toxic methylammonium (MeA). Here, we confirmed that PutAMT1;1 is an ammonium-inducible ammonium transporter in P. tenuiflora. On the basis of the results of PutAMT1;1 overexpression in A. thaliana, this gene might be useful for improving the root to shoot mobilization of MeA (or NH4+). [ABSTRACT FROM AUTHOR]