Salinity Stress in Roots of Contrasting Barley Genotypes Reveals Time-Distinct and Genotype-Specific Patterns for Defined Proteins

ABSTRACT Soil salinity is one of the most severe abiotic stress factors threatening agriculture worldwide. Hence, particular interest exists in unraveling mechanisms leading to salt tolerance and improved crop plant performance on saline soils. Barley is considered to be one of the most salinity-tolerant crops, but varying levels of tolerance are well characterized. A proteomic analysis of the roots of two contrasting cultivars (cv. Steptoe and cv. Morex) is presented. Young plants were exposed to a period of 1, 4, 7, or 10 d at 0, 100, or 150mM NaCl. The root proteome was analyzed based on two-dimensional gel electrophoresis. A number of cultivar-specific and salinity stress-responsive proteins were identified. Mass spectrometry-based identification was successful for 74 proteins, and a hierarchical clustering analysis grouped these into five clusters based on similarity of expression profile. The rank product method was applied to statistically access the early and late responses, and this delivered a number of new candidate proteins underlying salinity tolerance in barley. Among these were some germin-like proteins, some pathogenesis-related proteins, and numerous as-yet uncharacterized proteins. Notably, proteins involved in detoxification pathways and terpenoid biosynthesis were detected as early responsive to salinity and may function as a means of modulating growth-regulating mechanisms and membrane stability via fine tuning of phytohormone and secondary metabolism in the root. SUMMARY The root proteome of two barley cultivars contrasting in salt tolerance was compared at four different time points after stress exposure. The changes in the proteome including the kinetic patterns showed remarkable differences between the two cultivars. Identification of proteins enabled the tracing of metabolic networks associated with stress tolerance mechanisms.