IN PLANTA BEHAVIOR OF BEAN POD MOTTLE AND COWPEA MOSAIC COMOVIRUSES -INFECTIVITY AND STRUCTURAL ALTERATIONS

The specific infectivity of bean pod mottle comovirus (BPMV) virions i n the inoculated leaves of Canavalia ensiformis (jackbean), Phaseolus vulgaris cv. Pinto and Chenopodium auinoa declined progressively over time. This loss of infectivity was accompanied by a progressive degrad ation of encapsidated genomic RNA-1, while genomic RNA-2 breakdown was only marginal. Little or no loss of BPMV infectivity occurred over ti me in Pinto bean primary leaves that were sprayed regularly with kinet in or indole-3-acetic acid and virions purified from these leaves yiel ded structurally intact RNA-1. The decline in BPMV infectivity was acc ompanied hy a limited proteolysis of small coat protein subunits and a n alteration in the virion electrophoretic mobility pattern. Cowpea mo saic comovirus (CpMV; type member of comovirus group) virions isolated from Vigna unguiculata or Chenopodium quinoa leaves at different peri ods after infection exhibited capsid alterations that were analogous t o those observed for BPMV. However, CpMV virions underwent no decline in specific infectivity in planta with time and both the genomic RNAs fully retained their structural integrities. Apparently, structural ch anges in BPMV or CpMV capsids neither contribute to nor are responsibl e for any infectivity loss or destabilization of virion RNAs. Furtherm ore, a progressive degradation of RNA-1 as virions age in planta is a consistent and unique BPMV characteristic. (C) 1996 Academic Press Lim ited.