Human leukocyte interferon and the antiviral factor (AVF) from virus-infected plants stimulate plant tissues to produce nucleotides with antiviral activity.

Leaves of Nicotiana glutinosa and tobacco, as well as tobacco callus cultures, were treated with the plant antiviral factor AVF or with a purified subspecies of human leukocyte interferon. After incubation, a fraction containing short oligonucleotides was extracted directly from the plant tissue. In addition, a synthetase preparation was fractionated from treated tissues, which polymerized ATP in the presence of polyinosinic, polycytidylic acid (poly(I:C)). The various plant nucleotides were applied to tobacco mosaic virus (TMV)-infected leaf disks, the TMV content of which were determined by an enzyme-linked immunosorbent assay. The nucleotide fraction extracted directly from TMV-infected leaves exhibited a considerable antiviral activity, whereas similar fractions from AVF- or interferon-treated leaves did not, even though an antiviral state was induced in the tissue by these agents. However, when the synthetase fraction from TMV-infected, AVF-treated, or interferon-treated tissues was incubated with ATP and poly(I:C), the resultant, heat-stable, acid-soluble, polymerized ATP markedly inhibited TMV multiplication. It is concluded that the presence of double-stranded RNA is obligatory for the formation of the antiviral nucleotides. The analogy to interferon-induced resistance in animal tissues is discussed.