Active oxygen metabolism and lignification in the hypersensitive response in bean

Primary leaves of 7 to 9-day-old Red Mexican bean plants were inoculated with virulent or avirulent isolates of Pseudomonas syringae pv. phaseolicola by syringe-infiltration. In the incompatible interaction, resistance 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 activity of enzymes which either utilize H2O2 or are involved in generating or removing active oxygen species were investigated. An increase in the activities of an acidic peroxidase, xanthine oxidase and glutathione reductase, and a reduction in catalase activity, were detected in zone 1 in the incompatible interaction. An in situ peroxidase activity stain correlated with lignification in inoculated tissues. The results are discussed in terms of the role played by active oxygen species in the events associated with hypersensitive resistance. (C) 1996 Academic Press Limited.