Analytical density-gradient centrifugation of southern bean mosaic virus from seedcoats of Phaseolus vulgaris

Analytical density gradient centrifugation of clarified extracts of seedcoats from southern bean mosaic virus (SBMV)-infected Phaseolus vulgaris indicated three sedimenting components not present in comparable extracts from healthy plants. Two components, the SBMV monomer, C 1, and a slightly faster sedimenting species, C 2, were observed in extracts from immature seedcoats; in extracts from mature seedcoats, only C 2 was observed. In the transition from immature to mature seedcoats, there was a decline in the amount of C 1, an increase in the level of C 2, a transitory appearance of the fastest sedimenting component C 3, and finally the disappearance of C 1 and C 3. When immature seedcoats were dehydrated and then rehydrated, similar qualitative changes occurred. C 2 and C 3 do not appear to be simple polymers of C 1; the possibility that they represent associations between SBMV and a host compound is discussed.