New insights on arabidopsis thaliana root adaption to ammonium nutrition by the use of a quantitative proteomic approach

Nitrogen is an essential element for plant nutrition. Nitrate and ammonium are the two major inorganic nitrogen forms available for plant growth. Plant preference for one or the other form depends on the interplay between plant genetic background and environmental variables. Ammonium-based fertilization has been shown less environmentally harmful compared to nitrate fertilization, because of reducing, among others, nitrate leaching and nitrous oxide emissions. However, ammonium nutrition may become a stressful situation for a wide range of plant species when the ion is present at high concentrations. Although studied for long time, there is still an important lack of knowledge to explain plant tolerance or sensitivity towards ammonium nutrition. In this context, we performed a comparative proteomic study in roots of Arabidopsis thaliana plants grown under exclusive ammonium or nitrate supply. We identified and quantified 68 proteins with differential abundance between both conditions. These proteins revealed new potential important players on root response to ammonium nutrition, such as H+ -consuming metabolic pathways to regulate pH homeostasis and specific secondary metabolic pathways like brassinosteroid and glucosinolate biosynthetic pathways

High irradiance induces photoprotective mechanisms and a positive effect on NH 4 + stress in Pisum sativum L.

8 p., 7 figures and bibliographyPhotosynthesis provides plant metabolism with reduced carbon (C) but is also the main source of oxidative stress in plants. Likewise, high doses of NH4+ as sole N source have been reported to be toxic for most plants, resulting in reduced plant growth and restricting C availability. The combination of high photosynthetic photon flux densities (PPFD) and NH4+ nutrition may provide higher C availability but could also have a detrimental effect on the plants, therefore the objective of this study is to evaluate whether NH4+ induces photo-oxidative stress that is exacerbated under high light conditions. Pea plants (Pisum sativum cv. sugar-snap) were grown hydroponically with NH4+ (0.5, 2.5, 5 and 10mM) under high (750μmolphotonsm -2s -1) or low PPFD conditions (350μmolphotonsm -2s -1). High PPFD contributes to a higher tolerance to ammonium by pea plants, as it originated higher biomass content due to higher photosynthetic rates. However, a deficit of N (0.5 and 2.5mM NH4+) under high PPFD conditions caused an antioxidant response, as indicated by increased photoprotective pigment and chloroplastic superoxide dismutase contents. Plants grown with higher doses of N and high PPFD showed less need for photoprotection. An increase in the specific leaf weight (SLW) ratio was observed associated not only with high PPFDs but also with the highest NH4+ dose. Overall, these results demonstrate that, despite the activation of some photoprotective responses at high PPFD, there were no photoinhibitory symptoms and a positive effect on NH4+ toxicity, thus suggesting that the harmful effects of NH 4 + are not directly related to the generation of photo-oxidative stress.This work was supported by the Spanish MICIIN (grant nos. AGL2006-12792-CO2-01 and AGL2003-06571-CO2-01 [to P.A.-T.] and AGL2007-64432/AGR [to J.F.M.]), by the Government of Navarra (Res 57/2007 to J.F.M.), and BFU 2007-62637 of MEC and EHU-GV IT-299-07 of the Basque Government to JMB and JIG-P. IA was supported by a doctoral Fellowship from the Public University of Navarre, Spain.Peer reviewe