Involvement of lipoxygenase, lipoxygenase pathway volatiles, and lipid peroxidation during the hypersensitive reaction of pepper leaves to Xanthomonas campestris pv. vesicatoria

Lipoxygenase activity and protein, production of lipid-derived volatiles, a nd lipid peroxidation levels were determined in pepper (Capsicum annuum L., cv. Early Calwonder-10R) leaves during the hypersensitive reaction induced by avirulent race 2 of Xanthomonas campestris pv. vesicatoria. Lipoxygenas e activity increased during the collapse phase of the hypersensitive reacti on (8 to 12 h after inoculation), and an increase in electrolyte leakage oc curred. However, Western blot analysis revealed thai lipoxygenase proteins decreased during the same period. When only one longitudinal half of a pepp er leaf was inoculated with the avirulent bacterium race, a significant inc rease in lipoxygenase activity was observed in both inoculated and noninocu lated leaf halves, 10 h after inoculation. In addition, lipoxygenase protei n decreased in inoculated leaf halves, but remained unchanged in noninocula ted ones. The evolution of some volatile compounds derived from the lipoxyg enase pathway [(E, E)-2,4-hexadienal, 1-hexanol, 3-hexen-1-ol, 2,4-hexadien al and 2,4-eptadienal] and carotenoid degradation (alpha- and beta-ionone) increased in the incompatible interaction during the collapse phase of the hypersensitive reaction. The level of the oxidative index (A(235)/A(205)) o f leaf lipid extracts, determined to estimate lipid peroxidation, significa ntly increased in the advanced stage of the hypersensitive reaction. Furthe rmore, determination of the oxidative index in neutral lipid, glycolipid an d phospholipid fractions showed that the oxidative index was significantly increased only in the glycolipid fraction. Lipoxygenase activity and protei n, electrolyte leakage, volatiles and lipid peroxidation were nor changed i n pepper leaves inoculated with the virulent race 1 of X. campestris pv. ve sicatoria during the time interval considered (2-12 h after inoculations). The hypothesis that a lipoxygenase with chloroplastic location is induced i n the incompatible interaction, and which is responsible for the increase i n lipid peroxidation is advanced. (C) 1999 Academic Press.