Search

The form of nitrogen nutrition affects many biochemical and physiological processes in plants, leading to markedly different growth responses. Many plant species have been characterized as ammonium tolerant or sensitive. The objective of this work was to assess the range of physiological adaptative responses involved in tolerance of ammonium nutrition at the intra-specific level. Pisum sativum L was selected as a model of tolerance for the study, and four varieties of agricultural importance (Snap-pea, Rondo, Tristar and Eclipse) were grown hydroponically with ammonium or nitrate (0.5, 2.5, 5.0 and 10.0 mM)as the sole nitrogen source. Physiological parameters including photosynthesis, respiration and ammonium contents were analyzed. Activities/expression of key enzymes of the nitrogen metabolism was also determined, for which novel antibodies against glutamate dehydrogenase and glutamine synthetase were obtained. Snap-pea was considered a reference plant for ammonium tolerance, since its biomass accumulation was not affected by nitrogen source. It avoided the physiological effects of ammonium through low growth potential, high respiratory rates and activity of the alternative pathway. A multivariate analysis of the results showed that each of the four varieties had distinct adaptative responses to ammonium nutrition, highlighting the flexibility of response to ammonium nutrition at the species level. A general activation of glutamate dehydrogenase (GDH) was observed, regardless of the degree of tolerance to ammonium, which may be due to GDH being part of a common stress response to carbon deficit rather than an ammonium tolerance mechanism. (C) 2010 Elsevier B.V. All rights reserved., This work was supported by the Spanish Ministry of Science and Innovation (grant nos. AGL2006-12792-CO2-01 and AGL2003-06571-CO2-01 [to PA-T] and AGL2007-64432/AGR [to JFM]), by the Government of Navarra (Res 57/2007 to JFM). MDD-V was supported by a doctoral Fellowship from the Basque Government, Spain.

Ammonium nutrition is of interest as an alternative to that of using nitrate. However, the former has been reported as stressful to many plant species especially to some important crops, as most abiotic stresses may trigger oxidative imbalances in plants. In this work, we investigate the response of oxidative metabolism of two plant species, spinach (Spinacia oleracea L. cv. Gigante de invierno) and pea (Pisum sativum L. cv. Rondo), which have distinct tolerance to ammonium. Plants were grown in the presence of 1.5 and 3.0 mM N as ammonium and compared with equivalent nitrate nutrition. The antioxidant enzymes and metabolites as well as oxidative damage to proteins were determined. Protein and amino acid contents in both types of plants were also analysed. Ammonium nutrition in sensitive spinach or in the tolerant pea plants does not alter the redox status of ascorbate and glutathione or the phenolic contents, while no clear effect is seen in the antioxidant enzymes. The results showed that the stress originated from applying ammonium as the only N source is not an oxidative stress, independent of the ammonium tolerance of the plant species studied. Moreover, ammonium stress diminishes oxidative damage to proteins in the spinach plants. The data of the protein oxidation together with those from N metabolism highlight the relation between the stress induced by ammonium and an increased protein turnover.