Effects of tentoxin on enzymic activities in cucumber and cabbage cotyledons.

Tentoxin, produced by Alternaria alternata (Fr.) Keissl. causes severe variegated chlorosis in germinating seedlings of certain dicotyledonous species. However, it does not impair radicle and hypocotyl elongation or cotyledon expansion. Effects of the toxin on the activity of selected enzymes from both chloroplasts and cytoplasm were determined. Cucumber (Cucumis sativus L.), which is highly sensitive to tentoxin and cabbage (Brassica oleracea L.), which is resistant, were used as test plants. The activities of chloroplastic, but not cytoplasmic, enzymes were decreased by treatment of cucumber cotyledons with tentoxin. Neither group of enzymes was affected by the toxin in cabbage cotyledons. The decreased enzymic activities are probably related to reported inhibition of photophosphorylation by tentoxin.