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The Sequence of Inhibition of Tobacco Mosaic Virus Synthesis by Actinomycin D, 2-Thiouracil, and Cycloheximide in a Synchronous Infection. W. O. Dawson, Department of Plant Pathology and Cell Interaction Group, University of California, Riverside, 92502; D. E. Schlegel, Department of Plant Pathology, University of California, Berkeley, 94720. Phytopathology 66:177-181. Accepted for publication 29 July 1975. DOI: 10.1094/Phyto-66-177.

The time-courses of inhibition of tobacco mosaic virus (TMV) synthesis in synchronous infections by actinomycin D (AMD), 2-thiouracil (2TU), and cycloheximide (CX) were determined. Young tobacco leaves were systemically infected at 3 C (DTI-3C leaves) or 12 C (DTI-12C leaves) using the differential temperature inoculation procedure. Three degrees and 12 C inhibited different steps of TMV replication. After transfer of the DTI leaves to 25 C, TMV replication became resistant to different inhibitors sequentially. In DTI-3C leaves, the AMD-sensitive step occurred prior to the transfer to 25 C. When 2TU treatment began during the first 3 hours at 25 C, TMV synthesis was reduced about 95%, but when treatment began at later times the amount of inhibition rapidly declined to no inhibition by 12 hours. Cycloheximide inhibited TMV replication (> 95%) when treatment began at 12 hours or before, after which the inhibition declined until little inhibition occurred by 48 hours at 25 C. In DTI-12C leaves, neither AMD nor 2TU inhibited TMV replication when treatment began at any time after the transfer from 12 C to 25 C. Immediately after the transfer to 25 C, CX inhibited TMV synthesis maximally, but the amount of inhibition began immediately declining when treatments began at later times. This establishes the sequence of inhibition of TMV replication as: Infection → AMD → 3 C → 2TU → 12 C → CX → TMV-RNA → Virus.