CYTOCHEMICAL-LOCALIZATION OF DIAMINE OXIDASE IN HELIANTHUS-TUBEROSUS DEVELOPING TUBERS

The localization of diamine oxidase (DAO, EC 1.4.3.6) activity was inv estigated in tubers of Helianthus tuberosus by using an electron micro scopy method based on the direct cytochemical detection of DAO-generat ed hydrogen peroxide by reaction with cerous ions (CeCl3). During tube r formation no detectable precipitate was found in samples collected i n September and October while an electron-dense granular precipitate a ppeared in the cell walls, but not in organelles, in samples collected in November 3 reaching the maximum on 19. The trend of DAO activity, measured by the radiometric method based on the recovery of C-14-pyrro line derived from putrescine oxidation, did not parellel the cytochemi cal pattern as it showed high activity in September followed by a decr ease in November. Since total DAO activity does not necessarily reflec t any single particulate one, we infer that the biochemical trend is d etermined by an organellar activity which is not detectable cytochemic ally. The hypothesis that during tuber development apoplastic and symp lastic DAO activities play two different roles and are differently reg ulated in the cell is discussed.