Alterations in the accumulation of the viral proteins and RNAs in tomato under mixed infection with Potato X potexvirus and Tobacco mosaic tobamovirus.

The acute stage (between 5 and 12 days postinoculation)of the synergistic disease, induced in cultivar Fukuju #2 tomato (a tobacco mosaic tobamovirus (TMV)-susceptible, common Japanese cultivar), which had their primary leaves inoculated at the five-true leaf stage by mixed infection with PVX and TMV, is characterized by the significant enhancement of the concentration of PVX in the systemically infected upper leaf positions 5 or 7, as determined by direct antibody sandwich- enzyme linked immunosorbent assay (DAS-ELISA). Further evaluation of the accumulation dynamics of the coat protein of PVX and its 25 -kDa movement protein, encoded by the ORF2 (triple gene block), by SDS-PAGE followed by Western blot analysis revealed their pattern of accumulation as following those of the virion, being relativelyfaster and higher in doubly than in singly infected plants. On the other hand, both the movement into, and accumulation of the TMV coat protein in the same systemically mixed infected leaves were considerably lower compared to that in singly infected plants. Northern hybridization analysis of samples, on a time series basis, using an RNA probe complementary to 350 nucleotides (nts) of the PVX coat protein gene (inserted into T7 plasmid vector and labeled with digoxigenin (DIG)),showed thatthe genomic RNA of PVX was also relatively enhanced in the systemically mixed infected leaves compared to the singly infected ones.