Abstract
IntroductionMass spectrometry imaging (MSI) is a technology that enables the visualization of the spatial distribution of hundreds to thousands of metabolites in the same tissue section simultaneously. Roots are below-ground plant organs that anchor plants to the soil, take up water and nutrients, and sense and respond to external stresses. Physiological responses to salinity are multifaceted and have predominantly been studied using whole plant tissues that cannot resolve plant salinity responses spatially.ObjectivesThis study aimed to use a comprehensive approach to study the spatial distribution and profiles of metabolites, and to quantify the changes in the elemental content in young developing barley seminal roots before and after salinity stress.MethodsHere, we used a combination of liquid chromatography–mass spectrometry (LC–MS), inductively coupled plasma mass spectrometry (ICP–MS), and matrix-assisted laser desorption/ionization (MALDI–MSI) platforms to profile and analyze the spatial distribution of ions, metabolites and lipids across three anatomically different barley root zones before and after a short-term salinity stress (150 mM NaCl).ResultsWe localized, visualized and discriminated compounds in fine detail along longitudinal root sections and compared ion, metabolite, and lipid composition before and after salt stress. Large changes in the phosphatidylcholine (PC) profiles were observed as a response to salt stress with PC 34:n showing an overall reduction in salt treated roots. ICP–MS analysis quantified changes in the elemental content of roots with increases of Na+ and decreases of K+ content.ConclusionOur results established the suitability of combining three mass spectrometry platforms to analyze and map ionic and metabolic responses to salinity stress in plant roots and to elucidate tolerance mechanisms in response to abiotic stress, such as salinity stress.
Highlights
Mass spectrometry imaging (MSI) is a technology that enables the visualization of the spatial distribution of hundreds to thousands of metabolites in the same tissue section simultaneously
Previous studies have shown that the different barley root zones are highly specialized in their biological function as they revealed region specific responses of metabolites and transcripts in spatially resolved root metabolism (Hill et al 2016; Shelden et al 2016), and the findings presented in this study support this notion form a lipidomics perspective
We have provided a reliable and detailed methodology to study water-rich plant tissues, such as roots, using MALDI–MSI to reveal metabolite distributions and interactions across morphologically different root zones. previous attempts to examine root tissues have been limited by the fragility of the plant tissue
Summary
Mass spectrometry imaging (MSI) is a technology that enables the visualization of the spatial distribution of hundreds to thousands of metabolites in the same tissue section simultaneously. Methods Here, we used a combination of liquid chromatography–mass spectrometry (LC–MS), inductively coupled plasma mass spectrometry (ICP–MS), and matrix-assisted laser desorption/ionization (MALDI–MSI) platforms to profile and analyze the spatial distribution of ions, metabolites and lipids across three anatomically different barley root zones before and after a short-term salinity stress (150 mM NaCl). Plant roots are highly plastic organs and are the first to sense and respond to exogenous stresses, such as high salinity (Ouyang et al 2007). They play a major role in water and nutrient uptake, and anchoring plants to the soil. The zone of cell division (Z1) includes the root cap and the apical meristem where cells are dividing and which give rise to different cell layers following a developmental gradient (Hochholdinger et al. Vol.:(0123456789)
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