Update publication information. Root proteomic changes in the seedlings of two alfalfa varieties with different drought-tolerance exposed to -1.2 MPa PEG 6000 for 9 days were analyzed using iTRAQ-LC/MS-MS. A total of 225,188 spectra were generated through the iTRAQ analysis. Among these spectra, we detected a total of 52,774 spectra corresponding to known spectra, 38,474 spectra corresponding to unique spectra, 16,755 peptides, 13,916 unique peptides, and 4272 proteins.