Inductive Effect of Inosine on Formation of Secondary Appressoria from Conidia of Botrytis cinerea

Abstract

Purine-related compounds, cyclic AMP, 5'-AMP, 5'-IMP, adenosine and inosine, induced formation of secondary appressoria of Botrytis cinerea on slide glass in the presence of glucose. Among these purine-related compounds, formation of the secondary appressoria was remarkable in inosine. Formycin B, which is an analogue to inosine, reduced inductive effects of the secondary appressoria with inosine, and competed with inosine in forming the secondary appressoria. The administration of inosine to mycelia of B. cinerea resulted in an increase of syntheses of both DNA and RNA, followed by an increase of protein synthesis. When the mycelia incorporated ¹⁴C-inosine were fractionated, radioactivity was detected in RNA fraction at early time after incubation, and afterward in DNA fraction. Formycin B did not inhibit biosynthesis of cellular macromolecules in the mycelia, but inhibited DNA synthesis stimulated with inosine. It was shown that formycin B competed with inosine for DNA synthesis. These results indicated that inosine stimulated DNA synthesis, followed by an increase in RNA and protein syntheses in the mycelia, resulting in induction of the secondary appressoria.