Seed storage proteins in cultivars and subspecies of alfalfa (Medicago sativa L.)

Seed storage proteins were analysed in 27 varieties of alfalfa (Medicago sativa L.); these included five subspecies (glomerata, caerulea, falcata, hemicycla, praefalcafa), seven of the nine sources of Medicago germplasm introduced into North America and a sample of additional cultivars. The protein patterns were remarkably consistent for all of these taxa. One-dimensional and two-dimensional gel electrophoresis revealed only minor differences in polypeptide composition within each of the three major classes of storage protein (7S globulin, 11S globulin, 2S albumin). The slight variations that were found provided no information on either parentage or evolutionary relationships amongst these particular taxa. Nonetheless, persistent and reproducible heterogeneity of some minor polypeptides of 11S globulin (medicagin) may be useful under other circumstances for cultivar identification in alfalfa. Both subfamilies (I and II) of the 11S globulin were strongly expressed in all of the cultivars and subspecies examined. It was concluded that this structural divergence within the 11S storage protein family predated the evolution of the M. sativa L. species complex. Most of the variability in storage proteins was quantitative. However, even this variability was reduced when data were standardized with respect to seed dry weights. The consistent similarities in qualitative and quantitative expression of seed storage proteins amongst all of these taxa suggest a high degree of uniformity in both seed physiology and genetics within the alfalfa species complex.