thiouracil and dioxohexahydrotriazine

Dihydroorotic acid hydrazide (DHOH) did not inhibit the replication of potatovirus X (PVX) in leaf disks of Nicotiana tabacum 'Samsun'. In contrast, 5-fluoroorotic acid (5-FOA) completely inhibited the replication of PVX, as demonstrated by a serological virus assay as well as a local lesion bioassay using Gomphrena globosa as the test plant. The corresponding base analogue 5-fluorouracil (5-FU) had only a weak inhibitory effect. Time-course inhibition experiments in synchronized virus-infected leaf disks led us to conclude that 5-FOA, as well as 5-azadihydrouracil (5-ADHU), an uracil catabolite analogue, inhibit the same early event in virus infection. Neither 5-FOA nor 5-ADHU had a direct inactivating effect on free PVX virions.

Topics: Antiviral Agents; Cycloheximide; Fluorouracil; Orotic Acid; Plant Viruses; Thiouracil; Triazines; Virus Replication

Aspirin injected into Xanthi-nc tobacco leaves induces the production of PR protein and resistance to TMV. The concentration of PR protein and resistance increases with increasing aspirin concentration, up to a plateau. 2-Thiouracil and dioxohexahydrotriazine also induce PR protein when injected into tobacco leaves. Barium and manganese salts induced PR protein, but those of eight other cations did not. Certain salts were phytotoxic but did not induce PR protein, confirming that the production of PR protein is not a non-specific stress response.

Topics: Aspirin; Cations; Disease Susceptibility; Nicotiana; Plant Proteins; Plants, Toxic; Thiouracil; Tobacco Mosaic Virus; Triazines

The time course of inhibition of potato virus X ( PVX ) synthesis by the newly developed antiphytoviral compound 2,4- dioxohexahydro -1,3,5-triazine (DHT) was determined in mechanically inoculated leaves of Nicotiana tabacum L. cv. ' Samsun '. At the permissive temperature (22 +/- 3 degrees) DHT inhibited the synthesis of PVX almost 100% within 8 h postinoculation, after which the inhibition declined. In leaves maintained at a temperature of 5 +/- 2 degrees for 5 days, DHT inhibited PVX synthesis about 65% immediately after the shift to permissive temperature. This time course of inhibition was almost identical to that of 2-thiouracil. Uracil completely overcame the inhibition of PVX replication caused by DHT when added within 2 h after incubation of leaf disks with DHT. These results indicate that DHT acts as an analogue of the pyrimidine base uracil.

Topics: Antiviral Agents; Cycloheximide; Drug Interactions; Nicotiana; Plant Diseases; Plant Viruses; Plants, Toxic; Temperature; Thiouracil; Triazines; Uracil; Virus Replication