ACTIVE OXYGEN-METABOLISM AND LIGNIFICATION IN THE HYPERSENSITIVE RESPONSE IN BEAN

Primary leaves of 7 to 9-day-old Red Mexican bean plants were inoculat ed with virulent or avirulent isolates of Pseudomonas syringae pv. pha seolicola by syringe-infiltration. In the incompatible interaction, re sistance was associated with a hypersensitive response. The inoculated leaf area (zone 1), the surrounding 5-7 mm (zone 2) and the remainder of the leaf (zone 3) were investigated for changes in catalase enzyme activity during the 48 h following inoculation. Changes in the activi ty of enzymes which either utilize H2O2 or are involved in generating or removing active oxygen species were investigated. An increase in th e activities of an acidic peroxidase, xanthine oxidase and glutathione reductase, and a reduction in catalase activity, were detected in zon e 1 in the incompatible interaction. An in situ peroxidase activity st ain correlated with lignification in inoculated tissues. The results a re discussed in terms of the role played by active oxygen species in t he events associated with hypersensitive resistance. (C) 1996 Academic Press Limited.