REGULAR ARTICLE Inhibition of endogenous urease activity by NBPT application reveals differential N metabolism responses to ammonium or nitrate nutrition in pea plants: a physiological study S. Cruchaga & B. Lasa & I. Jauregui & C. González-Murua & P. M. Aparicio-Tejo & I. Ariz Received: 8 October 2012 / Accepted: 2 July 2013 # Springer Science+Business Media Dordrecht 2013 Abstract Background and aims Urea is the predominant form of N applied as fertilizer to crops, but it is also a significant N metabolite of plants themselves. As such, an understand- ing of urea metabolism in plants may contribute signifi- cantly to subsequent N fertilizer management. It currently appears that arginase is the only plant enzyme that can generate urea in vivo. The aim of this work was, therefore, to gain a more in-depth understanding of the significance of the inhibition of endogenous urease activity and its role in N metabolism depending on the N source supplied. Methods Pea (Pisum sativum cv. Snap-pea) plants were grown with either ammonium or nitrate as the sole N source in the presence or absence of the urease inhibitor NBPT. Results When supplied, NBPT is absorbed by plants and translocated from the roots to the leaves, where it reduces endogenous urease activity. Different N metabolic responses in terms of N-assimilatory enzymes and N-containing compounds indicate a different degree of arginine catabolism activation in ammonium- and nitrate-fed plants. Conclusions The arginine catabolism is more highly ac- tivated in ammonium-fed plants than in nitrate-fed plants, probably due to the higher turnover of substrates by enzymes playing a key role in N recycling and remobilization during catabolism and in early flowering and senescence processes, usually observed under ammonium nutrition. Keywords Ammoniumnutrition . Arginine catabolism . NBPT . Protein turnover . Urea metabolism . Urease . Urease inhibitor Abbreviations BCAA Branched-chain amino acids GDH Glutamate dehydrogenase Plant Soil DOI 10.1007/s11104-013-1830-x Responsible Editor: Ad C. Borstlap. Electronic supplementary material The online version of this article (doi:10.1007/s11104-013-1830-x) contains supplementary material, which is available to authorized users. S. Cruchaga : B. Lasa : I. Jauregui Departamento Ciencias del Medio Natural, Universidad Pública de Navarra, Campus de Arrosadía s/n, 31006 Pamplona, Navarra, Spain C. González-Murua Department of Plant Biology and Ecology, Universidad del Pais Vasco - Euskal Herriko Unibertsitatea, Campus Bizkaia, Apdo. 644, 48080 Bilbao, Spain P. M. Aparicio-Tejo : I. Ariz (*) Instituto de Agrobiotecnología, IdAB—CSIC-Universidad Pública de Navarra—Gobierno de Navarra, Campus de Arrosadía s/n, 31006 Pamplona, Navarra, Spain e-mail: iaarnedo@fc.ul.pt I. Ariz Faculdade de Ciências, Centro de Biologia Ambiental—CBA, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal