Abstract
The subcellular localization of diamine oxidase (DAO, EC 1.4.3.6) activity in Helianthus tuberosus L. tubers was investigated in different physiological stages (tuber formation and dormancy). DAO activity was found to be associated with protoplasts and mitochondria. In all cases optimum enzyme activity was found at 200µg protein per test tube; the highest specific activity was found in mitochondria. No DAO activity was detectable in residual protoplast digesting medium and in protoplast wash solution, as well as in the cell wall fraction and its fibrous residue. In protoplasts, mitochondria and crude homogenate DAO activity, on a protein basis, slowly decreased during tuber formation and dormancy. Although a role in the apoplast has been proposed in Leguminosae, in Helianthus tuberosus tubers DAO activity appears to be symplastic and compartmented in mitochondria; therefore, an alternative role of this enzyme in the regulation of intracellular polyamine levels is hypothesized.
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