CEPD1-4 regulates cotton root nitrate uptake under nonuniform nitrate conditions

Ammonium reduces oxalate accumulation in different spinach (Spinacia oleracea L.) genotypes by inhibiting root uptake of nitrate

Nitrate and NO2- transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of NO3- and NO2- was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km, possibly a constitutive uptake system, and a linear system for both NO3- and NO2-. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both NO3- and NO2- uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of NO3- and NO2- uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar, the apparent high Km values of NO3- uptake ranged from 34 to 36 micromolar and of NO2- uptake ranged from 41 to 49 micromolar. A linear system was also found in induced seedlings at concentrations above 500 micromolar. Double reciprocal plots indicated that NO3- and NO2- inhibited the uptake of each other competitively in both uninduced and induced seedlings; however, Ki values showed that NO3- was a more effective inhibitor than NO2-. Nitrate and NO2- transport by both the low and high Km systems were greatly inhibited by p-hydroxymercuribenzoate, whereas the linear system was only slightly inhibited.

Plant growth and nitrate uptake were measured for two Great Basin perennial grasses, Agropyron desertorum and Pseudoroegneria spicata, in sand-filled pots in either monoculture or mixed culture (2 plants/pot). All plants were supplied with the same initial amount of nitrate but delivered in five different pulse durations ranging from 0.5 to 72 h. The pulse duration was controlled by flushing the pots with water at different times after applying the nitrate pulse. The same concentration of nitrate was used in all pulse treatments. Increasing the pulse duration led to significantly increased plant biomass production for both species in both mono- and mixed cultures, and to reduced root/shoot biomass ratio. Biomass and root/shoot ratio were greater for Agropyron in mixed culture than in monoculture. To assess root nitrate uptake capacity, a 30-min tracer pulse was applied to all plants. Plants that had been exposed to longer pulses acquired significantly more nitrate than those that had been exposed to shorter pulses for both total plant acquisition and acquisition per unit root length. With greater root/shoot ratio than Pseudoroegneria, total nitrate acquisition by Agropyron was significantly greater at most pulse durations. Root nitrate uptake per unit mass was also greater for Agropyron than for Pseudoroegneria, indicating that Agropyron is more responsive to nitrate pulsing.

The study aims to investigate at a physiological and molecular level the root absorption of nitrogen (N) during the annual cycle of grapevine. The study was performed on potted Pinot Gris plants grafted on Kober 5BB and grown for two consecutive years in a semi-controlled environment (Northeast, Italy). The study compared the response of plants N-fertilized in spring (T1), or in spring and in post-harvest (T2) or no-N fertilized (C). Results showed that under our climate conditions nitrate was taken up by the grapevines when applied both in spring or in spring and post-harvest. The nitrate acquisition in T1 roots is mediated at molecular and physiological level by a higher activation of high-affinity nitrate-transport system to take up nitrate in comparison to no-fertilized plants. Comparing the two N fertilization managements, the dynamic of nitrate uptake rates showed different patterns with an overall late response of High-Affinity Transport System when the application of part of N-fertilization was delayed to post-harvest (T2) in comparison to T1. Nevertheless, during the 2 years of the trial the fractionation of N fertilization applied in spring and post-harvest did not negatively affect the yield and quality parameters of vines. An increase of N concentration in T2 roots after two consecutive growing seasons may suggest that the fractionation can lead to beneficial effects on long period. Results of this work contribute to improve the comprehension of N acquisition in grapevine in order to optimize the use of N inputs in vineyard.

The nitrate transporter NRT1.1 is a versatile plasma-membrane protein that mediates not only nitrate uptake in roots, but also nitrate sensing and signalling. A study of the structural features of NRT1.1 reveals how this protein can coordinate a range of physiological and morphological responses to nitrate.

Upon initial nitrate exposure, net nitrate uptake rates in roots of a wide variety of plants accelerate within 6 to 8 hours to substantially greater rates. Effects of solution nitrate concentrations and short pulses of nitrate (≤1 hour) upon `nitrate-induced' acceleration of nitrate uptake in maize (Zea mays L.) were determined. Root cultures of dark-grown seedlings, grown without nitrate, were exposed to 250 micromolar nitrate for 0.25 to 1 hour or to various solution nitrate concentrations (10-250 micromolar) for 1 hour before returning them to a nitrate-free solution. Net nitrate uptake rates were assayed at various periods following nitrate exposure and compared to rates of roots grown either in the absence of nitrate (CaSO4-grown) or with continuous nitrate for at least 20 hours. Three hours after initial nitrate exposure, nitrate pulse treatments increased nitrate uptake rates three- to four-fold compared to the rates of CaSO4-grown roots. When cycloheximide (5 micrograms per milliliter) was included during a 1-hour pulse with 250 micromolar nitrate, development of the accelerated nitrate uptake state was delayed. Otherwise, nitrate uptake rates reached maximum values within 6 hours before declining. Maximum rates, however, were significantly less than those of roots exposed continuously for 20, 32, or 44 hours. Pulsing for only 0.25 hour with 250 micromolar nitrate and for 1 hour with 10 micromolar caused acceleration of nitrate uptake, but the rates attained were either less than or not sustained for a duration comparable to those of roots pulsed for 1 hour with 250 micromolar nitrate. These results indicate that substantial development of the nitrate-induced accelerated nitrate uptake state can be achieved by small endogenous accumulations of nitrate, which appear to moderate the activity or level of root nitrate uptake.

The decrease in inorganic phosphate concentration in bean (Phaseolus vulgaris L. cv. Zlota Saxa) roots induced decrease in respiration rate. The decrease observed in ATP pool in phosphate deficient (-P) roots was greater than it would result from the decline in respiration and possible involvement of alternative pathway, suggesting an increased energy utilization for growth and ion uptake. Indeed, relative growth rate was higher in -P plants until 12 d of culture and later dropped to the rate similar to the control. Net nitrate uptake rate was higher in -P plants than in +P plants at the beginning of phosphate starvation, then during the prolonged culture it decreased rapidly in -P plants and after 19 d it was 8 times lower than that in the control. The decline in ATP production during prolonged phosphate starvation influenced NO3 - uptake more than root growth.

Abstract. The efflux of carbon dioxide (CO2) from soils influences atmospheric CO2 concentrations and thereby climate change. The partitioning of inorganic carbon (C) fluxes in the vadose zone between emission to the atmosphere and to the groundwater was investigated to reveal controlling underlying mechanisms. Carbon dioxide partial pressure in the soil gas (pCO2), alkalinity, soil moisture and temperature were measured over depth and time in unplanted and planted (barley) mesocosms. The dissolved inorganic carbon (DIC) percolation flux was calculated from the pCO2, alkalinity and the water flux at the mesocosm bottom. Carbon dioxide exchange between the soil surface and the atmosphere was measured at regular intervals. The soil diffusivity was determined from soil radon-222 (222Rn) emanation rates and soil air Rn concentration profiles and was used in conjunction with measured pCO2 gradients to calculate the soil CO2 production. Carbon dioxide fluxes were modeled using the HP1 module of the Hydrus 1-D software. The average CO2 effluxes to the atmosphere from unplanted and planted mesocosm ecosystems during 78 days of experiment were 0.1 ± 0.07 and 4.9 ± 0.07 μmol C m−2 s−1, respectively, and grossly exceeded the corresponding DIC percolation fluxes of 0.01 ± 0.004 and 0.06 ± 0.03 μmol C m−2 s−1. Plant biomass was high in the mesocosms as compared to a standard field situation. Post-harvest soil respiration (Rs) was only 10% of the Rs during plant growth, while the post-harvest DIC percolation flux was more than one-third of the flux during growth. The Rs was controlled by production and diffusivity of CO2 in the soil. The DIC percolation flux was largely controlled by the pCO2 and the drainage flux due to low solution pH. Modeling suggested that increasing soil alkalinity during plant growth was due to nutrient buffering during root nitrate uptake.

Background Beneficial microorganisms modify root architecture through different mechanisms mostly related to plant hormones synthesis. Less information is available regarding the emission of microbial volatile organic compounds (VOCs) and their effects on root architecture. Numerous studies describe the release of VOCs by bacteria and filamentous fungi, but little information is available regarding soil yeasts. Methods The VOCs released by the soil yeast Solicoccozyma terrea were evaluated in an experiment with tomato seedlings. Four treatments (tomato seedlings, T; S. terrea inoculum without tomato seedlings, St; tomato seedlings exposed to the volatiles of S. terrea inoculum, TSt; and a control without tomato seedlings or yeast inoculum, C) were assessed in terms of root morphology. VOCs were analyzed by GC–MS, and in a second experiment, the response of tomato seedlings and root nitrate uptake transporters to specific compounds identified in the first experiment was evaluated under low and high N supply. Results A mixture with 57 VOCs was identified which promoted lateral roots formation in tomato plants. Three compounds (isopropyl alcohol, 2-pentylfuran and trans-1,3-pentadiene) were exclusively present in the TSt treatment. All three compounds stimulated lateral roots formation and increased root volume. These compounds showed a stimulatory effect on the expression of NRT1.2 , NRT2.1 and NRT2.3 nitrate transporters under N deficiency conditions. Conclusions This study provides, for the first time, information on a soil yeast capable of promoting lateral roots formation in tomato through VOCs and that isopropyl alcohol, 2-pentylfuran and trans-1,3-pentadiene modulate root nitrate transporters expression under N deficiency conditions.

Nitrogen (N) is a crucial macronutrient for plant growth, with nitrate as a primary inorganic N source for most plants. Beyond its role as a nutrient, nitrate also functions as a signalling molecule, influencing plant morphogenetic development. While nitrate utilization and signalling mechanisms have been extensively studied in model plants, the origin, evolution, and diversification of core components in nitrate uptake, assimilation, and signalling remain largely unexplored. In our investigation, we discovered that deep sea algae living in low nitrate conditions developed a high-affinity transport system (HATS) for nitrate uptake and a pathway of nitrate primary assimilation (NR-NiR-GS-GOGAT). In contrast, low-affinity transport systems (LATS) and the plastid GS originated from the ancestors of land and seed plants, respectively. These adaptations facilitated amino acid acquisition as plants conquered terrestrial environments. Furthermore, the intricate nitrate signalling, relying on NRT1.1 and NLP7, evolved stepwise, potentially establishing systematic regulation in bryophytes for self-regulation under complex terrestrial nitrate environments. As plants underwent terrestrialization, they underwent adaptive changes to thrive in dynamic nitrate environments, continually enhancing their nitrate uptake, assimilation, and signal transduction abilities.

Background and Aims: Although AVG (aminoethoxyvinylglycine) is intensely used to decipher signaling in ethylene/indol-3-acetic acid (IAA) interactions on root morphogenesis, AVG is not a specific inhibitor of aminocyclopropane-1-carboxylate synthase (ACS) and tryptophan aminotransferase (TAA) and tryptophan aminotransferase related (TAR) activities since it is able to inhibit several aminotransferases involved in N metabolism. Indeed, 1 mM glutamate (Glu) supply to the roots in plants treated with 10 μM AVG partially restores the root growth. Here, we highlight the changes induced by AVG and AVG + Glu treatments on the N metabolism impairment and root morphogenetic program. Methods: Root nitrate uptake induced by AVG and AVG + Glu treatments was measured by a differential labeling with 15NO3 - and 15Nglutamate. In parallel a profiling of amino acids (AA) was performed to decipher the impairment of AA metabolism. Key Results: 10 μM AVG treatment increases K15NO3 uptake and 15N translocation during root growth inhibition whereas 10 μM AVG + 1 mM 15Nglutamate treatment inhibits K15NO3 uptake and increases 15Nglutamate uptake during partial root growth restoration. This is explained by a nitrogen (N) limitation condition induced by AVG treatment and a N excess condition induced by AVG + Glu treatment. AA levels were mainly impaired by AVG treatment in roots, where levels of Ser, Thr, α-Ala, β-Ala, Val, Asn and His were significantly increased. His was the only amino acid for which no restoration was observed in roots and shoots after glutamate treatment suggesting important control of His homeostasis on aminotransferase network. Results were discussed in light of recent findings on the interconnection between His homeostasis and the general amino acid control system (GAAC) in eukaryotes. Conclusions: These results demonstrate that AVG concentration above 5 μM is a powerful pharmacological tool for unraveling the involvement of GAAC system or new N sensory system in morphological and metabolic changes of the roots in leguminous and non-leguminous plants.

The electrical response of nitrate-grown maize (Zea mays L.) roots to 0.1 millimolar nitrate was comprised of two sequential parts: a rapid and transient depolarization of the membrane potential, followed by a slower, net hyperpolarization to a value more negative than the original resting potential. The magnitude of the response was smaller in roots of seedlings grown in the absence of nitrate, but, within 3 hours of initial exposure to 0.1 millimolar nitrate, increased to that of nitrate-grown roots. Chloride elicited a separate electrical response with a pattern similar to that of the nitrate response. However, the results presented in this study strongly indicate that the electrical response to nitrate reflects the activity of a nitrate-inducible membrane transport system for nitrate which is distinct from that for chloride. Inhibitors of the plasmalemma H(+)-ATPase (vanadate, diethylstilbestrol) completely inhibited both parts of the electrical response to nitrate, as did alkaline external pH. The magnitude of the initial nitrate-dependent, membrane potential depolarization was independent of nitrate concentration, but the subsequent nitrate-dependent hyperpolarization showed saturable dependence with an apparent K(m) of 0.05 millimolar. These results support a model for nitrate uptake in maize roots which includes a depolarizing NO(3) (-)/H(+) symport. The model proposes that the nitrate-dependent membrane potential hyperpolarization is due to the plasma membrane proton pump, which is secondarily stimulated by the operation of the NO(3) (-)/H(+) symport.

Key message Molinia caerulea (L.) Moench has been observed to significantly reduce budburst in Quercus petraea (Matt.) Liebl. seedlings through water-based M. caerulea root exudates. This suggests direct allelopathic effects between the two species. In terms of nutrient uptake, oak roots primarily take up nitrogen in the forms of ammonium and glycine. Interestingly, the application of root exudates from M. caerulea doubled the nitrate uptake in oak roots. Moreover, gene sets involved in nitrogen metabolism within oak roots exhibited strong deregulation when treated with M. caerulea root exudate, indicating that the interaction between these two plant species alters the nitrogen metabolism in the oak roots. Context Oak regeneration encounters numerous impediments, including interactions with Molinia caerulea (L.) Moench, an understory grass species widespread in temperate forests. Besides competition for resources, our previous work suggested that the interaction between oak and M. caerulea may involve allelopathic processes. Aim This study tested the hypothesis that M. caerulea affects the budburst dynamics, early growth of oak seedlings, and root N uptake transport and assimilation systems. Methods Potted oak seedlings (Quercus petraea (Matt.) Liebl.) were watered with M. caerulea root exudates or water for 6 weeks during April and May 2021. The capacity of oak seedlings to take up nitrogen in its main molecular forms was characterized by an influx analysis of isotopically labeled (15N) nitrate, ammonium, and glycine on excised roots using the “teabag” technique. Concomitantly, targeted transcriptomics were carried out to monitor changes in gene expression related to nitrogen metabolism. Results The treatment resulted in reduced budburst rates (− 50%), together with an early reduction in height increment. Kinetics of N influx rates revealed that ammonium, and to a lesser degree glycine, were the predominant forms in which N was taken up by roots. Application of M. caerulea root exudate barely increased the ammonium influx rate and had no effect on the glycine influx rate. By contrast, the nitrate influx rate, despite its low values, doubled after application of the exudate. Targeted transcriptomic analysis revealed a regulatory shift in gene sets associated with key mechanisms underlying N uptake, assimilation, and long-distance transport in oak roots. Conclusion Interactions between a perennial grass, M. caerulea, and a woody species, Q. petraea, do not only rely upon direct competition for resources. Allelopathic processes must be taken into consideration when designing regeneration operations.

The Diurnal Pattern of Nitrate Uptake and Reduction by Spinach (Spinacia oleracea L.)

Enhancing nitrogen use efficiency (NUE) of wheat is a major focus for wheat breeding programs. NUE may be improved by identifying genotypes that are competitive for nitrogen (N) uptake in early vegetative stages of growth and are able to invest that N in grain. Breeders tend to select high yielding genotypes under conditions of medium to high N supply, but it is not known whether this influences the selection of root plasticity traits or whether, over time, breeders have selected genotypes with higher N uptake efficiency. To address this, genotypes were selected from CIMMYT (1966-1985) and Australian (1999-2007) breeding programs. Genotypes from both programs responded to low N supply by expanding their root surface area through increased total root number and/or length of lateral roots. Australian genotypes were N responsive (accumulated more N under high N than under low N) whereas CIMMYT genotypes were not very N responsive. This could not be explained by differences in N uptake capacity as shown by 15N flux analysis of two representative genotypes with contrasting N accumulation. Expression analysis of nitrate transporter genes revealed that the high-affinity transport system accounted for the majority of root nitrate uptake in wheat seedlings under both low and high N conditions.