Occurrence and involvement of adenylate cyclase activity in the first step of tobacco mosaic virus infection of Nicotiana tabacum cv Xanthi nc leaves

Abstract

Adenylate cyclase activity and its involvement in a physiopathological process (virus infection) were observed in a higher plant, Nicotiana tabacum cv Xanthi nc. The enzyme was characterized in leaves by measuring the conversion of [α- 32P]ATP into cyclic [α- 32P]AMP using a cell membrane preparation. The basal enzyme activity was 1–2 pmol/min per mg protein, was linear with time and protein concentration, and had a temperature optimum between 20 and 25% C. The K m for ATP was 2 mM in the presence or absence of stimulators. GTP (10 −7 M) increased both basal and sodium fluoride-stimulated activities. During the hypersensitive reaction which follows tobacco mosaic virus (TMV) infection, we detected in the first 10 min a 40–80% increase in the basal activity. These results indicate that cAMP could play an important role by mediating the viral and plant host-cell interaction. The rapid pulse-release of cAMP leads us to propose that this nucleotide may, as in animal tissues, represent a secondary messenger in higher plants.