In addition to drought and extreme temperatures, soil salinity represents a growing threat to crop productivity. Among the cereal crops, barley is considered as notably salt tolerant, and cultivars show considerable variation for tolerance towards salinity stress. In order to unravel the molecular mechanisms underlying salt stress tolerance and to utilize the natural genetic variation of barley accessions, a series of hydroponics-based salinity stress experiments was conducted using two genetic mapping parents, cvs Steptoe and Morex, which display contrasting levels of salinity tolerance. The proteome of roots from both genotypes was investigated as displayed by two-dimensional gel electrophoresis, and comparisons were made between plants grown under non-saline and saline conditions. Multivariate analysis of the resulting protein patterns revealed cultivar-specific and salt stress-responsive protein expression. Mass spectrometry-based identification was successful for 26 out of 39 selected protein spots. Hierarchical clustering was applied to detect similar protein expression patterns. Among those, two proteins involved in the glutathione-based detoxification of reactive oxygen species (ROS) were more abundant in the tolerant genotype, while proteins involved in iron uptake were expressed at a higher level in the sensitive one. This study emphasizes the role of proteins involved in ROS detoxification during salinity stress, and identified potential candidates for increasing salt tolerance in barley.

Abstract. Saline habitats cover a wide area of our planet and halophytes (plants growing naturally in saline soils) are increasingly used for human benefits. Beside their genetic and physiological adaptations to salt, complex ecological processes affect the salinity tolerance of halophytes. Hence, prokaryotes and fungi inhabiting roots and leaves can contribute significantly to plant performance. Members of the two prokaryotic domains Bacteria and Archaea, as well as of the fungal kingdom are known to be able to adapt to a range of changes in external osmolarity. Shifts in the microbial community composition with increasing soil salinity have been suggested and research in functional interactions between plants and micro-organisms contributing to salt stress tolerance is gaining interest. Among others, microbial biosynthesis of polymers, exopolysaccharides, phytohormones and phytohormones-degrading enzymes could be involved.

In the present paper, we based a search for candidates underlying different levels of salinity tolerance during germination in the Oregon Wolfe Barley mapping population (DOM ¥ REC) by proteomic profiling of the mature grain of lines showing differing levels of salinity tolerance. By contrasting the parents DOM and REC, displaying divergent stress responses, and two tolerant and two sensitive segregants, six protein spots were identified that showed a differential abundance between the tolerant and the sensitive lines. The tolerant lines expressed a higher level of 6-phosphogluconate dehydrogenase and glucose/ribitol dehydrogenase (Glc/RibDH). Both proteins were heterologously over-expressed in an osmo-sensitive yeast strain and over-expression of Glc/RibDH resulted in an enhanced ability of yeast transformants to grow on salt containing media. A quantitative trait locus (QTL) analysis of the population germinating at different salt concentrations led to the identification of two chromosome regions on 5H and one on 7H associated with salt stress response. A dense barley transcript map was employed to map the genomic region of all identified proteins. Two of these, heat-shock protein 70 and Glc/RibDH, co-localized with the identified QTL on chromosome 5H. The putative functional role of the candidates is discussed.

Proteins in the plant apoplast are essential for many physiological processes. We have analysed and compared six different infiltration solutions for proteins contained in the apoplast to recognize the most suitable method for leaves and to establish proteome maps for each extraction. The efficiency of protocols was evaluated by comparing the protein patterns resolved by 1-DE and 2-DE, and revealed distinct characteristics for each infiltration solution. Nano-LC-ESI-Q-TOF MS analysis of all fractions was applied to cover all proteins differentially extracted by infiltration solutions and led to the identification of 328 proteins in total in apoplast preparations. The predicted subcellular protein localisation distinguished the examined infiltration solutions in those with high or low amounts of intracellular protein contaminations, and with high or low quantities of secreted proteins. All tested infiltration solution extracted different subsets of proteins, and those implications on apoplast-specific studies are discussed.