Intra-specific variation in pea responses to ammonium nutrition leads to different degrees of tolerance

▶ We studied adaptative responses to NH 4 + nutrition at the intra-specific level (4 pea varieties). ▶ Snap-pea variety is a reference for NH 4 + tolerance as its growth rate was not affected by N source. ▶ Snap-pea avoids the effects of NH 4 + through low growth potential, and high respiratory and AOX rates. ▶ A multivariate analysis shows high flexibility by the pea varieties in response to NH 4 + nutrition. ▶ Activation of GDH regardless of the degree of tolerance is attributed to a response to C deficit. 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.