Investigations on the Inhibition of Potato Virus X by Some Amino Acid Analogues

Ethionine markedly inhibits the replication of potato virus X (PVX) after infiltration into leaf disks of Nicotiana tabacum L. “Samsun”. P-fluorophenylalanine and 5-methyl-DL-tryptophane inhibit this replication less effectively and only at phytotoxic concentrations. Methionine strongly reduces the inhibitory activity of ethionine in the replication of PVX. In leaf disks with synchronized virus infection, the time-response course of ethionine inhibition indicates that a late event is inhibited. Short time after the beginning of ethionine inhibition decline virus protein was detected by ELISA. Contrary to leaf disks, in intact tobacco plants PVX replication is inhibited by ethionine sprays only in very high and phytotoxic doses. However, low doses of ethionine increase synergistically the inhibitory activity of 5-azadihydrouracil.