A comparison of seed storage proteins in subspecies and cultivars of Medicago sativa

Abstract

Seeds of alfalfa contain two storage globulins: alfin, a 7S vicilinlike protein, and medicagin, an 1IS leguminlike globulin. Alfin is easily solubilized and is found predominantly in the initial low salt soluble extract. Repeated extractions with this buffer (0.2 M NaCl, pH 7.0) fail to solubilize the medicagin protein. However, if the concentration of salt in the second extraction buffer is increased (0.4 to 1.0 M NaCl), there is a progressive increase in the amount of medicagin protein solubilized. The requirement for salt for solubilization is partially offset if the buffering pH is raised to 9.0. Buffers containing 2% SDS are no more efficient than 1.0 M NaCl in extracting medicagin, and the addition of 10 mM dithiothreitol is ineffective in increasing protein yields. Seed storage proteins of members of the Medicago sativa L. species complex were analyzed using one- and two-dimensional electrophoretic techniques. In total, 29 varieties were examined, including five subspecies, eight landraces, and a diploid and tetraploid isogenic line. For all of the samples examined, the polypeptide profiles for alfin and medicagin were very similar; the major differences between taxa were quantitative rather than qualitative. When medicagin was examined using two-dimensional techniques, minor variations in the polypeptide profile became apparent, In general, the variability was almost exclusively in the acidic polypeptides (size and number) rather than the basic polypeptides.