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Salinity is one of the major environmental constraints limiting yield of crop plants in many semi-arid and arid regions around the world. To understand responses in soybean seedling to salt stress at proteomic level, the extracted proteins from seedling leaves of salt-sensitive genotype Jackson and salt-tolerant genotype Lee 68 under 150 mM NaCl stress for 1, 12, 72 and 144 h, respectively, were analyzed by 2-DE. Approximately 800 protein spots were detected on 2-DE gels. Among them, 91 were found to be differently expressed, with 78 being successfully identified by MALDI-TOF-TOF. The identified proteins were involved in 14 metabolic pathways and cellular processes. Based on most of the 78 salt-responsive proteins, a salt stress-responsive protein network was proposed. This network consisted of several functional components, including balancing between ROS production and scavenging, accelerated proteolysis and reduced biosynthesis of proteins, impaired photosynthesis, abundant energy supply and enhanced biosynthesis of ethylene. Salt-tolerant genotype Lee 68 possessed the ability of higher ROS scavenging, more abundant energy supply and ethylene production, and stronger photosynthesis than salt-sensitive genotype Jackson under salt stress, which may be the major reasons why it is more salt-tolerant than Jackson. (C) 2011 Elsevier B.V. All rights reserved.