Salinity in soils is one of the major factors that adversely affects agriculture by inhibiting plant growth, resulting in low crop productivity. Among cereal crops (eg. rice, wheat), barley (Hordeum vulgare L.) is rated as salt-tolerant, and exhibits a considerable variation in salt tolerance amongst its cultivars. Barley is a food and brewing crop, and as a glycophyte it suffers substantial yield loss when grown under saline conditions. Relatively little is currently understood of salt stress perception and responses in plant roots, which involve complex changes at the physiological, metabolic, molecular, transcriptional, and genetic levels.
We aim to develop new tools to unravel how plants respond to the perception of salt stress. Evidence is accumulating that lipid signalling is an integral part of the complex regulatory networks that plants utilize to respond to salinity through modifications of membrane lipids. These occur through changes in activity of such enzymes as phospholipase D and diacylglycerol kinase that produce different classes of lipid and lipid-derived messengers. In addition, abiotic stress provokes enhanced production of reactive oxygen species, resulting in lipid modifications by the oxidation of lipid species.
Lipidomics analysis using liquid chromatography mass spectrometry (LC-MS) revealed that roots from tolerant and sensitive cultivars respond differently to salt stress. To investigate the modifications of lipids leading to root responses to salinity, we are using a combination of multiple approaches, such as targeted and untargeted lipidomics of barley roots. Matrix Assisted Laser Desorption Ionisation Mass Spectrometry Imaging (MALDI-MSI) was also employed to examine the spatial distribution of lipids in barley roots grown under control and saline conditions. The combination of LC-MS and MALDI-MSI identified a large number of metabolites and lipids with a unique spatial distribution. MSI was capable of discriminating salt vs control treated roots, identifying major lipid changes under salt treatment in a spatial manner. Non-uniform spatial distribution of metabolites was observed among different barley cultivars. Major PC lipid species and carbohydrates were identified to change the most in salt treated roots compared to control. Given the lack of fundamental knowledge of the lipids involved in signalling and metabolism under saline stress, our results provide insight into novel mechanisms of how barley roots respond to salt stress.