Characterization of changes in root membrane proteomes in maize (Zea mays L.) in responses to nitrogen sources

Plant roots can uptake nitrogen (N) either in inorganic forms, such as nitrate (NO3-) or ammonium (NH4+), and in organic forms, mostly as free amino acids and short peptides. Among N inorganic sources, NO3- is the predominant form in agricultural soils. Plants can develop biochemical and morphological responses (for example, the regulation of the uptake activities and changes in root architecture) to balance the amount of N acquired from the soil with what is needed for growth and development. This N requirement is emphasized regarding cereal crops, for which maize (Zea mays L.) is worldwide accepted as a model species. In root cells, the membrane system plays key roles in sensing and signaling of N availability as well as in ion transport and storage. This work is part of a wider project, whose final purpose is to study how roots perceive and adapt to different kinds of N nutritional sources, both inorganic and organic, provided singly or in combination. In detail, the aim of this study is to optimize the proteomic approaches needed to analyse the changes in root membrane protein patterns of maize plants grown in hydroponic systems, and exposed to different N availabilities, consisting in NO3-, NH4+ and co-provision. Firstly, different nutritional conditions have been tested in order to appreciate the effects on plant growth, root morphology and plant metabolism. Proteomic analyses of subcellular compartments have been also considered in order to clarify localized cellular responses and investigate relations among subcellular compartments. Since the sample preparation represents one of the most crucial steps in plant proteomics, the research was directed to the examination of different experimental approaches, in order to select the most valuable methods that can assure an adequate quality and reliability in the proteome characterization for the subsequent research activity. At this stage, some methods for obtaining the purified fraction of plasma membrane and microsomal proteins were evaluated. Studies on quality, purity and protein recovery by means of large-scale proteomic approaches based on one-dimensional (1D) Gel Liquid Chromatography-Mass Spectrometry (1D GeLC-MS/MS), are ongoing. This research paves the way for the future project steps in which the proteomic profiles will be compared among different nutritional conditions and their changes will be related to the physiological and biochemical evaluations, in order to individuate possible molecular determinants involved in perception and adaptation to N inputs in maize roots.