Differential proteomic analysis of salt stress response in Sorghum bicolor leaves

Sorghum, an African grass related to sugar cane and maize, is grown for food, feed, fibre and fuel. A proteome study based on 2-D gel electrophoresis and subsequent mass spectrometric identification was performed in order to analyze the salt-stress response of Sorghum bicolor. Overall changes in the protein complement of leaves after 96 h exposure to 200 mM NaCl in hydroponic culture were studied. Twenty one spots with more than 1.5-fold altered expression on 2-DE gel were excised and identified after tryptic digestion using MALDI-TOF-TOF mass spectrometer. Majority of the differentially expressed proteins belonged to the functional category of signal transduction mechanisms and inorganic ion transport and metabolism. Over-expression of reactive oxygen species-scavenging enzymes e.g. glutathione-S-transferases and l-ascorbate peroxidase was in agreement with previous reports in the context of stress responses in other plants. However, with respect to the physiological functions of other identified proteins such as putative sialin, putative inorganic pyrophosphatase, RNA binding protein, and serine/threonine-protein kinase; there appears to be a distinct mechanism of salt-stress adaptation in sorghum plant. Four differentially expressed proteins could not be assigned any function using Pfam and COGnitor search and warrant detailed investigation to elucidate their exact role in salinity tolerance. This is the first proteomic description of salt stress response in sorghum and a further validation of data reported herewith would likely provide, deeper insight pertaining to the stress physiology of this important crop plant.