FAILURE OF LONG-DISTANCE MOVEMENT OF SOUTHERN BEAN MOSAIC-VIRUS IN A RESISTANT HOST IS CORRELATED WITH LACK OF NORMAL VIRION FORMATION

Sunn-hemp mosaic tobamovirus (SHMV) facilitated the spread of the cowp ea strain of southern bean sobemo-virus (SBMV-C) only in inoculated le aves of common bean (Phaseolus vulgaris L. cv. Bountiful), a resistant host for SBMV-C. Tissue prints of bean primary leaves doubly inoculat ed with SHMV and SBMV-C, developed by Western blotting, showed the pre sence of the SBMV-C capsid antigen in the mesophyll and epidermis, but no antigen was detected in the conducting bundles. Typical SBMV-C vir ions were not seen in electron micrographs of immunogold-labelled meso phyll cells; instead, specifically labelled, amorphous protein clumps were found in the vacuole. Particles of smaller diameter than that of typical SBMV-C virions were specifically trapped by SBMV antibodies fo llowing immunosorbent electron microscopy of extracts from doubly infe cted leaves. SBMV-C coat protein from infected Vigna unguiculata L. (c owpea) and bean plants showed no difference in its mobility following electrophoresis in denaturing SDS-polyacrylamide gels. Lack of efficie nt assembly of SBMV-C virions does not impede cell-to-cell movement of the virus in doubly infected leaves of bean, yet it is probably an im portant factor in determining the inability of SBMV-C to move into and /or through the vascular system of this host.