EFFECT OF UV-C ON PEROXIDASE ISOENZYMES IN AXILLARY BUD CULTURES OF VITIS SPECIES DIFFERING IN FUNGAL RESISTANCE TO PLASMOPARA-VITICOLA

The effect of shortwave (250 nm) UV radiation (UV-C) on the level of p eroxidase activity and peroxidase isoenzyme patterns in leaves of resi stant ([Vitis vinifera x Viris riparia] x Vitis rupestris and Vitis ru pestris) and susceptible (Vitis vinifera) grapevine species to Plasmop ara viticola (downy mildew) was studied. The results show that althoug h UV-C did not produce significant changes in peroxidase activity in s usceptible species, and only minor changes in resistant species, treat ment with UV-light induces an acidic isoperoxidase (isoperoxidase A1), capable of oxidising 4-hydroxystilbenes in resistant species. It was named HSPrx 2. Since peroxidase is apparently the enzyme responsible f or epsilon-viniferin synthesis from resveratrol in grapevines, a close relationship between this peroxidase isoenzyme and epsilon-viniferin synthesis which occurs in grapevine leaves after UV-C treatment must b e expected.