High soil salinity is a growing problem that adversely affects agriculture by inhibiting plant growth resulting in larger losses in crop yield1. Barley is rated as salt-tolerant among cereal crops (i.e. rice, wheat, corn) and exhibits a great variation in salt tolerance amongst its cultivars2. Physiological responses to salinity are complex and have mostly been studied using bulked plant tissues that do not unveil tissue specific metabolic responses3. Roots are important plant organs that provide anchoring, water and nutrient uptake and sensing of environmental stresses4. Matrix assisted laser desorption/ionization - mass spectrometry imaging (MALDI-MSI) was used to examine the in-situ distribution of several lipid species in longitudinal sections of seminal roots. This project aimed to analyse the spatial changes and profiles of lipids in three distinct root zones (zone of cell division, zone of elongation and zone of maturation) in young developing barley seminal roots to reveal plant lipid response before and after salinity stress.
Barley grains were germinated, grown on agar plates and subjected to a 150 mM NaCl stress for 48 hours. Roots and root lipid extracts were analysed in both positive and negative ionization mode using a Bruker SolariX XR FT-ICR-MS and a Sciex 6600 Triple-TOF-MS, for spatial and targeted lipidomics analysis, respectively.
Targeted lipidomics analysis revealed larger differences between root zones than between treatments in all barley cultivars. Further, a higher number of significantly increased and significantly decreased lipid species after salinity was found in Clipper and Hindmarsh, respectively. Further, MALDI-MSI was capable of discriminating between control and salt treated root sections revealing a non-uniform spatial distribution of major lipid species on longitudinal root sections. Glycerophospholipids (i.e PC, PA, PE, LPC) showed distinct distribution patterns in tissue and were identified to change the most in roots after salinity stress. The combination of LC-MS and MALDI-MSI in this work helped elucidate the lipid changes salinity in roots that has not been described before.