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
Pea plant responsiveness under elevated [CO2] is conditioned by the N source (N2 fixation versus NO3 fertilization)
(Elsevier, 2013) Aranjuelo Michelena, Iker; Cabrerizo Geijo, Pablo María; Arrese-Igor Sánchez, César; Aparicio Tejo, Pedro María; IdAB. Instituto de Agrobiotecnología / Agrobioteknologiako Institutua; Ciencias del Medio Natural; Natura Ingurunearen Zientziak
The main goal of this study was to test the effect of [CO2] on C and N management in 2different plant organs (shoots, roots and nodules) and its implication in the 3responsiveness of exclusively N2-fixing and NO3--fed plants. For this purpose, 4exclusively N2-fixingand NO3--fed (10 mM) pea (Pisum sativumL.) plants were 5exposed to elevated [CO2] (1000 mol mol-1versus360 mol mol-1CO2). Gas 6exchange analyses, together with carbohydrate, nitrogen, total soluble proteins and 7amino acids were determined in leaves, roots and nodules. The data obtained revealed 8that although exposure to elevated [CO2] increased total dry mass (DM)in both N 9treatments, photosynthetic activity was down-regulated in NO3--fed plants, whereas N2-10fixing plants were capable of maintaining enhanced photosynthetic rates under elevated 11[CO2]. In the case of N2-fixing plants, the enhanced C sink strength of nodules enabled 12the avoidance of harmful leaf carbohydrate build up. On the other hand, in NO3--fed 13plants, elevated [CO2] caused a large increase in sucrose and starch. The increase in root 14DM did not contribute to stimulation ofC sinks in these plants. Although N2fixation 15matched plant N requirementswith the consequent increase in photosynthetic rates, in 16NO3--fed plants, exposure to elevated [CO2] negatively affected N assimilationwith the 17consequent photosynthetic down-regulation.
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.

Aparicio Tejo, Pedro María

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