INHIBITION BY CONDITIONED GROWTH-MEDIUM OF ACCUMULATION OF VIRAL-ANTIGEN IN PLANT-CELL SUSPENSION-CULTURES INOCULATED WITH TMV

Conditioned medium from suspension-cultured cells of tobacco or carrot infected with TMV contains an activity that results in a reduction of the TMV viral antigen content in cultured cells and tobacco leaf disks. The maximum inhibition of antigen accumulation was observed with medium from 6-day-old tobacco cells and 7-day-old carrot cells. This timing corresponds to the period of fastest growth of the cells and so it is suggested that production if the inhibitor(s) may be cell division- or growth-related. No inhibition was seen in the case of medium from uninfected cells. The inhibitory activity showed specificity in that conditioned medium resulted in twice the inhibition when applied to cells of the same species as used to condition the medium compared with the other species used. Conditioned medium from tobacco cells also reduced the accumulation of TMV antigen in persistently-infected tobacco cells, indicating that replication rather than infection events are inhibited.