DIFFERENTIAL EXPRESSION OF A CELL WALL-LOCALIZED PEROXIDASE ISOENZYMECAPABLE OF OXIDIZING 4-HYDROXYSTILBENES DURING THE CELL-CULTURE OF GRAPEVINE (VITIS-VINIFERA CV AIREN AND MONASTRELL)

Differential expression and localization of peroxidase isoenzymes capa ble of oxidizing 4-hydroxystilbenes was studied during establishment o f callus cultures from Vitis vinifera 'Airen' (anthocyanin-non accumul ating) and 'Monastrell' (anthocyanin-accumulating) berries. Callus for mation from mesocarp tissues was accompanied by differential expressio n of several peroxidase isoenzyemes located in cell walls, among which only peroxidase isoenzyme A(1) was capable of oxidizing 4-hydroxystil bene to any great extent. Likewise, grape cell cultures were capable o f accumulating the grape stilbene phytoalexin, resveratrol. However, e psilon-viniferin, the most powerful phytoalexin in grapevines and prev iously considered as the product of peroxidase-mediated oxidative coup ling of two resveratrol moieties, was only detectable in trace amounts . Since grapevine suspension cell cultures were unable to produce H2O2 as revealed by the luminol test, H2O2 production by the cultured cell s appears to be one of the main factors which limits resveratrol oxida tion in the cell walls of grapevine cells cultured in suspension.