Physiological response and comparative proteomic analysis of tobacco seedling roots to NH4+

Abstract

Plants absorb nitrogen, an essential element for their growth and development, mainly in the form of nitrate or ammonium. These nitrogen species have different effects on crops, little is known about their precise influence at both physiological and proteomic levels. This study investigated these mechanisms, hydroponically grown tobacco seedlings treated with three different ratios of NO3- to NH4+ (10:0, 5:5 or 0:10) for 15 days. The results showed that exposure to high NH4+ concentration affected root morphology and inhibited root development. Moreover, malondialdehyde content and the activity of glutamine synthetase, superoxide dismutase, peroxidase and glutathione S-transferase increased with the concentration of NH4+ in solution. Two-dimensional protein gel analysis showed that 40 protein were differentially expressed between the three treatments. 36 of these proteins were identified using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Gene ontology analysis indicated that these proteins were involved in metabolism, energy production, cell defense or signal transduction or structural constituents related pathways. Our results suggest that tobacco seedling roots are subjected to NH4+ toxicity that triggers oxidative stress. Our results help understanding the responses to different nitrogen species and to NH4+ toxicity in roots.