Abstract
Pear leaves susceptible to Alternaria kikuchiana and to its host-specific toxin were treated with various compounds to test for possible protective effects. Disulfidereducing reagents (dithiothreitol and mercaptoethanol), applied to susceptible leaves before exposure to toxin, gave partial protection against toxin-induced loss of electrolytes. This protection was completely reversed by an oxidizing reagent [5, 5'-dithiobis-(2-nitrobenzoic acid)]. When an alkylating reagent (N-ethylmaleimide) was applied after application of the reducing reagent, the protective effect was not reversed by the oxidizing reagent. The results suggest that disulfide groups in susceptible cells may be involved in the reaction to toxin. Partial protection by thermal treatments (55C for 2sec in water or 35C for 16hr in air) was evident when measured by toxininduced electrolyte losses from susceptible tissues and by a decrease in toxin-induced necrosis. The protective effects of thermal treatments were gradually lost by the tissues. The data suggest the existence of toxin receptor sites or substances that can be saturated.
