Proteome analysis of soybean leaves, hypocotyls and roots under salt stress

Soybean plants were exposed to 0, 20, 40, or 80 mM NaCl for one week. The effect of treatment at 20 mM NaCl on plant growth was not severe, at 80 mM NaCl was lethal, and at 40 mM NaCl was significant but not lethal. Based on these results, proteins were extracted from the leaves, hypocotyls and roots of soybean treated with 40 mM NaCl. Nineteen, 22 and 14 proteins out of 340, 330 and 235 proteins in the leaves, hypocotyls and roots, respectively, were up- and down-regulated by NaCl treatment. In leaves, hypocotyls and roots, metabolism related proteins were mainly down-regulated with NaCl treatment. Glyceraldehyde-3-phosphate dehydrogenase was down-regulated in the leaf/hypocotyls, and fructokinase 2 was down-regulated in the hypocotyls/root with NaCl treatment. Stem 31 kDa glycoprotein precursor was up-regulated in all three organs with NaCl treatment. Glyceraldehyde-3-phosphate dehydrogenase was specifically down-regulated at the RNA and protein levels by salt stress.These results suggest that metabolism related proteins play a role in each organ in the adaptation to saline conditions.Soybean is an important dicot crop due to the high content of oil and protein in its seeds [1]. However, soybean is subject to abiotic stresses that reduce its yield like many crops. Salinity is one of the most widespread agricultural problems in arid and semi-arid regions that makes fields unproductive, and soil salinization is a serious problem in the entire world [2]. Salt stress severely inhibits plant growth for two reasons: first by an osmotic or water-deficit effect of salinity and second by a salt-specific or ion-excess effect of NaCl. However, plants suffer from composite stresses caused by salinity, including water deficit and ion imbalance [3]. Adaptation to salt stress requires alterations in gene expression and subsequently the protein profile of the plant and is very complicated at the whole plant and cellular levels [4,5].Some salt-inducible genes have been investigate