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

Differential expression and localization of peroxidase isoenzymes capable of oxidizing 4-hydroxystilbenes was studied during establishment of callus cultures from Vitis vinifera 'Airen' (anthocyanin-non accumulating) and 'Monastrell' (anthocyanin-accumulating) berries. Callus formation from mesocarp tissues was accompanied by differential expression of several peroxidase isoenzyemes located in cell walls, among which only peroxidase isoenzyme A(1) was capable of oxidizing 4-hydroxystilbene to any great extent. Likewise, grape cell cultures were capable of accumulating the grape stilbene phytoalexin, resveratrol. However, epsilon-viniferin, the most powerful phytoalexin in grapevines and previously considered as the product of peroxidase-mediated oxidative coupling 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 cells appears to be one of the main factors which limits resveratrol oxidation in the cell walls of grapevine cells cultured in suspension.