Open Access
Leaves play a central role in the adaptation of nitrogen and sulfur metabolism to ammonium nutrition in oilseed rape (Brassica napus)
(BioMed Central, 2017) Coleto, Inmaculada; Peña, Marlon de la; Rodríguez Escalante, Jon; Bejarano, Iraide; Glauser, Gaëtan; Aparicio Tejo, Pedro María; González Moro, María Begoña; Marino Bilbao, Daniel; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Background: The coordination between nitrogen (N) and sulfur (S) assimilation is required to suitably provide plants with organic compounds essential for their development and growth. The N source induces the adaptation of many metabolic processes in plants; however, there is scarce information about the influence that it may exert on the functioning of S metabolism. The aim of this work was to provide an overview of N and S metabolism in oilseed rape (Brassica napus) when exposed to different N sources. To do so, plants were grown in hydroponic conditions with nitrate or ammonium as N source at two concentrations (0.5 and 1 mM). Results: Metabolic changes mainly occurred in leaves, where ammonium caused the up-regulation of enzymes involved in the primary assimilation of N and a general increase in the concentration of N-compounds (NH4 +, amino acids and proteins). Similarly, the activity of key enzymes of primary S assimilation and the content of S-compounds (glutathione and glucosinolates) were also higher in leaves of ammonium-fed plants. Interestingly, sulfate level was lower in leaves of ammonium-fed plants, which was accompanied by the down-regulation of SULTR1 transporters gene expression. Conclusions: The results highlight the impact of the N source on different steps of N and S metabolism in oilseed rape, notably inducing N and S assimilation in leaves, and put forward the potential of N source management to modulate the synthesis of compounds with biotechnological interest, such as glucosinolates.
Open Access
Elevated CO2 improved the growth of a double nitrate reductase defective mutant of Arabidopsis thaliana: the importance of maintaining a high energy status
(Elsevier, 2017) Jáuregui Mosquera, Iván; Aparicio Tejo, Pedro María; Baroja Fernández, Edurne; Ávila, Concepción; Aranjuelo Michelena, Iker; Natura Ingurunearen Zientziak; Ciencias del Medio Natural; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua
Impairments in leaf nitrogen (N) assimilation in C3 plants have been identified as processes conditioning photosynthesis under elevated [CO2], especially when N is supplied as nitrate. Leaf N status is usually improved under ammonium nutrition and elevated [CO2]. However, ammonium fertilization is usually accompanied by the appearance of oxidative stress symptoms, which constrains plant development. To understand how the limitations of direct fertilization with ammonium (growth reduction attributed to ammonium toxicity) can be overcome, the effects of elevated [CO2] (800 ppm) exposure were studied in the Arabidopsis thaliana double nitrate reductase defective mutant, nia1-1/chl3-5 (which preferentially assimilates ammonium as its nitrogen source). Analysis of the physiology, metabolites and gene expression was carried out in roots and shoot organs. Our study clearly showed that elevated [CO2] improved the inhibited phenotype of the nitrate reductase double mutant. Both the photosynthetic rates and the leaf N content of the NR mutant under elevated CO2 were similar to wild type plants. The growth of the nitrate reductase mutant was linked to its ability to overcome ammonium-associated photoinhibition processes at 800 ppm [CO2]. More specifically: (i) the capacity of NR mutants to equilibrate energy availability, as reflected by the electron transport equilibrium reached (photosynthesis, photorespiration and respiration), (ii) as well as by the upregulation of genes involved in stress tolerance were identified as the processes involved in the improved performance of NR mutants.
Open Access
Quantitative proteomics reveals the importance of nitrogen source to control glucosinolate metabolism in Arabidopsis thaliana and Brassica oleracea
(Oxford University Press, 2016) Marino Bilbao, Daniel; Ariz Arnedo, Idoia; Lasa Larrea, Berta; Santamaría Martínez, Enrique; Aparicio Tejo, Pedro María; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
Accessing different nitrogen (N) sources involves a profound adaptation of plant metabolism. In this study, a quantitative proteomic approach was used to further understand how the model plant Arabidopsis thaliana adjusts to different N sources when grown exclusively under nitrate or ammonium nutrition. Proteome data evidenced that glucosinolate metabolism was differentially regulated by the N source and that both TGG1 and TGG2 myrosinases were more abundant under ammonium nutrition, which is generally considered to be a stressful situation. Moreover, Arabidopsis plants displayed glucosinolate accumulation and induced myrosinase activity under ammonium nutrition. Interestingly, these results were also confirmed in the economically important crop broccoli (Brassica oleracea var. italica). Moreover, these metabolic changes were correlated in Arabidopsis with the differential expression of genes from the aliphatic glucosinolate metabolic pathway. This study underlines the importance of nitrogen nutrition and the potential of using ammonium as the N source in order to stimulate glucosinolate metabolism, which may have important applications not only in terms of reducing pesticide use, but also for increasing plants’ nutritional value.
Open Access
Soil moisture modulates biological nitrification inhibitors release in sorghum plants
(Springer, 2023) Bozal-Leorri, Adrián; Arregui Odériz, Luis Miguel; Torralbo, Fernando; González Moro, María Begoña; González Murua, Carmen; Aparicio Tejo, Pedro María; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Institute for Multidisciplinary Research in Applied Biology - IMAB
Background and aims: Sorghum (Sorghum bicolor) is able to exude allelochemicals with biological nitrifcation inhibition (BNI) capacity. Therefore, sorghum might be an option as cover crop since its BNI ability may reduce N pollution in the following crop due to a decreased nitrifcation. However, BNI exudation is related to the physiological state and development of the plant, so abiotic stresses such as drought might modify the rate of BNI exudation. Hence, the objective was to determine the efect of drought stress on sorghum plants’ BNI release. Methods: The residual efects of sorghum crops over ammonia-oxidizing bacteria (AOB) were monitored in a 3-year feld experiment. In a controlled-conditions experiment, sorghum plants were grown under Watered (60% WFPS) or Moderate drought (30% WFPS) conditions, and fertilized with ammonium sulphate (A), ammonium sulphate+DMPP (A+D), or potassium nitrate (KNO3 −). Soil mineral N was determined, and AOB populations were quantifed. Additionally, plant biomass, isotopic discrimination of N and C, and photosynthetic parameters were measured in sorghum plants. Results: In the driest year, sorghum was able to reduce the AOB relative abundance by 50% at feld conditions. In the plant-soil microcosm, drought stress reduced leaf photosynthetic parameters, which had an impact on plant biomass. Under these conditions, sorghum plants exposed to Moderate drought reduced the AOB abundance of A treatment by 25% compared to Watered treatment. Conclusion: The release of BNI by sorghum under limited water conditions might ensure high soil NH4 +-N pool for crop uptake due to a reduction of nitrifying microorganisms.
Open Access
Short term physiological implications of NBPT application on the N metabolism of Pisum sativum and Spinacea oleracea
(Elsevier, 2011-03-01) Cruchaga Moso, Saioa; Artola Rezola, Ekhiñe; Lasa Larrea, Berta; Ariz Arnedo, Idoia; Irigoyen Iriarte, Ignacio; Morán Juez, José Fernando; Aparicio Tejo, Pedro María; Ciencias del Medio Natural; Natura Ingurunearen Zientziak; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Producción Agraria; Nekazaritza Ekoizpena
The application of urease inhibitors in conjunction with urea fertilizers as a means of reducing N loss due to ammonia volatilization requires an in-depth study of the physiological effects of these inhibitors on plants. The aim of this study was to determine how the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) affects N metabolism in pea and spinach. Plants were cultivated in pure hydroponic culture with urea as the sole N source. After 2 weeks of growth for pea, and 3 weeks for spinach, half of the plants received NBPT in their nutrient solution. Urease activity, urea and ammonium content, free amino acid composition and soluble protein were determined in leaves and roots at days 0, 1, 2, 4, 7 and 9, and the NBPT content in these tissues was determined 48 h after inhibitor application. The results suggest that the effects of NBPT on spinach and pea urease activity differ, with pea being most affected by this treatment, and that the NBPT absorbed by the plant caused a clear inhibition of the urease activity in pea leaf and roots. The high urea concentration observed in leaves was associated with the development of necrotic leaf margins, and was further evidence of NBPT inhibition in these plants. A decrease in the ammonium content in roots, where N assimilation mainly takes place, was also observed. Consequently, total amino acid contents were drastically reduced upon NBPT treatment, indicating a strong alteration of the N metabolism. Furthermore, the amino acid profile showed that amidic amino acids were major components of the reduced pool of amino acids. In contrast, NBPT was absorbed to a much lesser degree by spinach plants than pea plants (35% less) and did not produce a clear inhibition of urease activity in this species.
Open Access
Nitrogen isotope signature evidences ammonium deprotonation as a common transport mechanism for the AMT-Mep-Rh protein superfamily
(American Association for the Advancement of Science, 2018) Ariz Arnedo, Idoia; Boeckstaens, Mélanie; Gouveia, Catarina; Martins, Ana Paula; Sanz-Luque, Emanuel; Fernández, Emilio; Soveral, Graça; Wiren, Nicolaus von; Marini, Anna M.; Aparicio Tejo, Pedro María; Cruz, Cristina; Ciencias; Zientziak
Ammonium is an important nitrogen (N) source for living organisms, a key metabolite for pH control, and a potent cytotoxic compound. Ammonium is transported by the widespread AMT-Mep-Rh membrane proteins, and despite their significance in physiological processes, the nature of substrate translocation (NH3/NH4+) by the distinct members of this family is still a matter of controversy. Using Saccharomyces cerevisiae cells expressing representative AMT-Mep-Rh ammonium carriers and taking advantage of the natural chemical-physical property of the N isotopic signature linked to NH4+/NH3 conversion, this study shows that only cells expressing AMT-Mep-Rh proteins were depleted in N-15 relative to N-14 when compared to the external ammonium source. We observed N-15 depletion over a wide range of external pH, indicating its independence of NH3 formation in solution. On the basis of inhibitor studies, ammonium transport by nonspecific cation channels did not show isotope fractionation but competition with K+. We propose that kinetic N isotope fractionation is a common feature of AMT-Mep-Rh-type proteins, which favor N-14 over N-15, owing to the dissociation of NH4+ into NH3+ H+ in the protein, leading to N-15 depletion in the cell and allowing NH3 passage or NH3/H+ cotransport. This deprotonation mechanism explains these proteins' essential functions in environments under a low NH4+/K+ ratio, allowing organisms to specifically scavenge NH4+. We show that N-15 isotope fractionation may be used in vivo not only to determine the molecular species being transported by ammonium transport proteins, but also to track ammonium toxicity and associated amino acids excretion.