Metabolomic approach to understand plant adaptations to water and salt stress

Abstract

The metabolic networks in plants are highly complex and comprise numerous biochemical steps. Therefore the employment of appropriate analytical methods capable of identifying and quantifying changes in metabolite composition is crucial. At present, a set of integrated technologies and methodologies are used, such as nondestructive nuclear magnetic resonance spectroscopy (NMR) (Schripsema, 2010) and mass spectrometry (MS)-based methods, including GC-MS (gas chromatography-MS), LC-MS (liquid chromatography-MS) and CE-MS (capillary electrophoresis-MS) (Baran et al., 2009; Kaspar et al., 2011; Lee et al., 2012), and FI-ICR-MS (Fourier transform ion cyclotron resonance-MS) (Junot et al., 2010) (Fig. 6.1). Particularly, the liquid phase separations, high performance liquid chromatography (HPLC) and ultrahigh per- formance liquid chromatography (UPLC), provide a useful tool for the analysis of metabolites in several applications, and are a powerful analytical technique that allows the detection of a wide range of plant metabolites when they are coupled with MS (Theodoridis et al., 2012). GC-MS is excellent for the detection of biological samples with very complex matrices, offering highly efficient separation and resolution because this technology uses an electronic impact (EI) ionization source. On the other hand, LC-MS is useful in handling thermolabile, polar metabolites and high-molecular-weight compounds without derivatization, using soft ionization source, such as electrospray ionization (ESI) or atmospheric pressure chemical ionization. Indeed, MS with LC is the most frequently applied analytical technique in plant metabolomics studies because of its high sensitivity and extensive coverage of biological information relevant to the metabolism of organisms (Jorge et al., 2016). Metabolomic analysis of plant samples is now regarded as a viable counterpart for protein and transcript pro- filing technologies. The comprehensive identification and quantification of metabolites through the integration of methods based on MS allows metabolomics to be a robust technology comparable with or even better than conventional genomic or proteomic technologies. Indeed, metabolomic analyses have shown their potential in plant metabolomics studies in several food crops, among others. Nevertheless, assessing their robustness on plant metabolomic studies for more crops other than rice (Hu et al., 2014), maize (Rao et al., 2014), soybean (Kusano et al., 2015), and wheat (Francki et al., 2016) is needed.In this chapter, we summarize the metabolomics technology to dissect the responses of plant species to water and salt stresses. To establish the similarity and specificity of the metabolic responses to both types of abiotic stresses, data available in the literature as well as our own data were used. The understanding of these stress responses through changes occurring at the metabolite level is a fundamental contribution to plant stress improvement programs.