RESTRICTED GENETIC EXPRESSION OF THE ENZYMATIC POLYMORPHISM OF PEROXIDASE IN GRAPEVINES (VITIS-VINIFERA)

Measurement of the peroxidase activity (EC 1.11.1.7) in ten grapevine cultivars (Airen, Clairette, Riesling, Servant, Carignan, Cinsaut Noir , Gamay Rouge, Grenache, Monastrell and Mourvedre) with four hydrogen donors (4-methoxy-alpha-napthol, o-phenylenediamine, coniferyl alcohol and guaiacol) reveals that peroxidase activity is differentially disp layed during the veraison of grape berries, being found at the detecti on limit of both the 4-methoxy-alpha-naphthol and o-phenylenediamine a ssays in green grapes harvested from the same vineyard. Even so, level s of peroxidase activity in mature grapes remain extremely low when co mpared with grapevine cell cultures or with other fruits and vegetable s. Analysis of the peroxidase isoenzqme patterns in mature grapes sugg ests that the low level of peroxidase activity is probably due to a re pression of peroxidase (genes) in the whole fruit, only those isoenzym es located in both vacuoles and cell walls being present. Peroxidase i soenzymes, exclusively located in cell walls and abundant in cell cult ures, are not present in the whole fruit, this perhaps being the reaso n for the extremely low level of peroxidase activity in grapes.