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In the presence of inhibitors of protein synthesis and energy metabolism, tobacco protoplasts were shown to retain 14C-labelled tobacco mosaic virus (14C-TMV) with the same intensity as in control. At 2 degrees C, the protoplasts retained 14C-TMV at approximately the same rate as at 25 degrees C. In protoplasts inocculated at different temperatures, approximately equal amounts of infectious virus were produced, this being possibly indicative of a non-physiological nature of the first stages of virus penetration into the protoplast.

The effect on Tobacco mosaic virus (TMV) accumulation of actinomycin D (AMD) introduced shortly after inoculation into isolated tobacco protoplasts under varying light conditions was examined. The emission spectrum of the light source contained lines in the visible range and in the ultraviolet band (300-400 nm). AMD absorbed light in the visible (400-500 nm) and in the uv (200-400 nm) ranges. AMD substantially inhibited TMV multiplication in the light, and also when the protoplasts were incubated in petri dishes covered with a black filter that allowed only uv light in the range 260-390 nm to pass. In the dark, and also in petri dishes covered with blue or yellow filters that passed in the ranges 400-500 or 500-600 nm, respectively, AMD stimulated TMV reproduction. The suppression of TMV multiplication in isolated tobacco protoplasts was assumed to be associated with a photodynamic effect caused by absorption of uv light by AMD.