Production of Soybean (Glycine max), an important oil seed crop is severely influenced by several abiotic factors, such as flooding, and drought. Water stress is one of the ruminating factors of soybean crop. Plants adapt to water and temperature stresses via modulating signal molecules associating the protein changes thus altering several metabolic pathways. To obtain insight into the effects of WS and HS on molecular and cellular functions of soybean, changes in leaf protein composition were studied by 2-DE Gel electrophoresis complemented with Mass spectrometry. Two soybean cultivars, drought tolerant (A) and susceptible (B) were exposed to different heat and water conditions. PD Quest analysis revealed at least 200 proteins in both cultivars, of which, 61 proteins were differentially expressed in response to WS and HS. Differentially expressed leaf proteins were excised from 2-DE gel, and trypsin digested. The peptide sequence tags generated from the spots were queried through MASCOT search. Gene ontology analysis for each protein reveals functional categories including photosynthesis, metabolism, transport, stress and defense, and glycolysis.
The majorities of heat responsive-proteins were up regulated during heat stress and combined stress in cultivar B; these proteins were down regulated to water stress. However in cultivar A, the heat shock proteins were generally down regulated to all levels stress. Proteins involved in folding and biosynthesis were either over expressed or did not change due to heat stress. Our studies showed that differentially expressed proteins involved in antioxidant defense were mostly up-regulated, whereas proteins associated with photosynthesis, secondary metabolism, and amino acid and protein biosynthesis were down-regulated in response to heat stress. In both cultivars, proteins involved in folding and biosynthesis were either highly abundant or remains unchanged to heat stress. Furthermore, a pattern of cross-tolerance phenomenon was detected in both cultivars for two different stresses when subjected independently. Proteins involved in antioxidant defense were most relatively abundant, whereas proteins associated with photosynthesis, secondary metabolism, and amino acid and protein biosynthesis were detected in low abundance to heat stress.