SUBCELLULAR-LOCALIZATION OF 1-AMINOCYCLOPROPANE-1-CARBOXYLATE OXIDASEIN TOMATO CELLS

The localization of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidas e was examined in suspension-cultured cells of tomato (Lycopersicon es culentum Mill.), using cell-fractionation techniques, followed by immu noblot analysis with monospecific antibodies raised against a tomato A CC oxidase expressed in Escherichia coli. When assayed in vivo, ACC ox idase had a low activity in untreated tomato cells but was strongly in duced when the cells were supplied with its substrate, ACC. Immunoblot s showed that this induction was accompanied by the accumulation of a single protein corresponding to ACC oxidase, with an apparent molecula r mass (M(r)) of 36 kDa. The level of this protein in induced cells, e stimated by immunoblotting, was compared with that in protoplasts and vacuoles, and with that in various particulate and soluble fractions o btained by differential centrifugation of cell homogenates. It was fou nd that the ACC oxidase antigen was absent from the vacuole, and that most of it was localized in the cytoplasm of the protoplasts without b eing associated with membranes. Measurements of ACC oxidase activity i n preparations of protoplasts and vacuoles supported these results.