EFFECT OF FOSETYL-AL ON PEROXIDASE FROM GRAPEVINE (VITIS-VINIFERA) CELLS

Grapevine (Vitis vinifera cv. Monastrell) suspension cell cultures wer e treated with fosetyl-Al, a widely used systemic fungicide for grapev ine diseases caused by oomycetes, and examined at the electron microsc ope level for peroxidase cytochemistry. The results showed that treatm ent with fosetyl-Al provokes an activation of both vacuolar sap and to noplast-located peroxidase, already described as due to the basic pero xidase isoenzyme, B-5, which was previously characterized as a constit utive marker of disease resistance against Plasmopara viticola in axil lary bud cultures of Vitis spp. This activation of peroxidase isoenzym e B-5, as seen at the electron microscope level, was confirmed by cyto photometric methods, but is in contrast with the unchanged enzyme leve l determined by biochemical methods. These results suggest a metabolic activation of peroxidase isoenzyme B-5 as a consequence of fosetyl-Al treatment, probably due to an acidification of the vacuole. This resp onse was accompanied by the appearance of myelin-like structures insid e the cytoplasm and osmiophylic-bodies inside the mitochondria. Howeve r, the latter structural changes cannot easily be related to the above described specific peroxidase response.