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

Seed storage proteins were analysed in 27 varieties of alfalfa (Medicago sa tiva L.); these included five subspecies (glomerata, caerulea, falcata, hem icycla, praefalcafa), seven of the nine sources of Medicago germplasm intro duced 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 p rotein (7S globulin, 11S globulin, 2S albumin). The slight variations that were found provided no information on either parentage or evolutionary rela tionships amongst these particular taxa. Nonetheless, persistent and reprod ucible heterogeneity of some minor polypeptides of 11S globulin (medicagin) may be useful under other circumstances for cultivar identification in alf alfa. Both subfamilies (I and II) of the 11S globulin were strongly express ed in all of the cultivars and subspecies examined. It was concluded that t his structural divergence within the 11S storage protein family predated th e evolution of the M. sativa L. species complex. Most of the variability in storage proteins was quantitative. However, even this variability was redu ced when data were standardized with respect to seed dry weights. The consi stent similarities in qualitative and quantitative expression of seed stora ge proteins amongst all of these taxa suggest a high degree of uniformity i n both seed physiology and genetics within the alfalfa species complex.