ACTIVE OXYGEN PRODUCTION IN MELON CELL-FREE HOMOGENATES ELICITED WITH HYPHAL WALL COMPONENTS OF FUSARIUM OXYSPORUM F.SP. MELONIS II. INVOLVEMENT OF A LIPOXYGENASE/FATTY ACID SYSTEM

Abstract

The release of active oxygen (AO) species as a consequence of lipoxygenase (LOX) activity was observed in callus cell-free homogenates of two melon cvs, ‘Retato degli Ortolani’ and ‘Jerac’, respectively susceptible and resistant to Fusarium oxysporum f.sp. melonis race 0, treated with hyphal wall components (HWCs) of race 0 and race 1,2. LOX activity and AO generation were found in ‘Jerac’ homogenates combined with HWCs of race 0 or with arachidonic and linoleic fatty acids, but not in compatible combinations between ‘Jerac’ with race 1,2 or between ‘Retato’ and each of the races. LOX activity and H2O2 production were promoted on soybean LOX by the elicitor of race 0 only. It is suggested that the relative content of LOX in the plant and unsaturated fatty acids in the fungus could play a role in some melon-F. oxysporum f.sp. melonis incompatible combinations.