CA2-AL (ALUMINUM TRIS[ETHYL PHOSPHONATE]) OF PEROXIDASE-ACTIVITY FROMSUSPENSION-CULTURED GRAPEVINE CELLS( AND MG2+ IONS COUNTERACT THE REDUCTION BY FOSETYL)

Grapevine (Vitis vinifera cv. Monastrell) cell suspension cultures wer e treated with 1.5 mM fosetyl-Al, a frequently used systemic fungicide for grapevine diseases caused by oomycetes. These cells showed a redu ction in the level of peroxidase activity secreted into the culture me dia when compared to non-treated cells, the effect being mainly relate d to a decrease in the level of the basic Br peroxidase isozyme. The e ffect of fosetyl-Al on peroxidase was analogous to that observed with the Ca2+-channel blockers Co2+, Cd2+ and La3+, and was counteracted by Ca2+ ions, but was not reversed when the Ca2+-ionophore A23187 was ad ded to the culture media. Moreover, the effect of fosetyl-Al on peroxi dase activity and peroxidase isozymes was also partially reversed by M g2+ ions but not by Sr2+, and was accentuated by Ba2+ ions. These resu lts suggested that Ca2+ and Mg2+ ions specifically overcome the inhibi tory effect of fosetyl-Al on peroxidase. In this context, an apoplasti c Ca2+/Mg2+-displacement hypothesis is proposed for the mechanism of a ction of fosetyl-Al on peroxidase from grapevine cells.