Hypersensitive and Apoptotic Responses of Pepper Fruit Against Xnthomonas axonopodis pv. glycines Infection

Generally, plants defend themselves against pathogens by structural and biochemical reactions. Defense structures act as physical barriers and inhibit the pathogen from gaining entrance and spreading through the plant. Xanthomonas axonopodis pv glycines, the causal pathogen of bacterial pustule of soybean, causes hypersensitive response (HR). When pepper fruits were inoculated with X. axonopodis pv. glycines, in situ, time-series defense-related structural changes occurred in the inoculated sites. Early responses were programmed cell death (PCD), characterized by condensation and vacuolization of the cytoplasm, condensation of nuclear materials, and fragmentation of the nuclear DNA, which were observed by transmission electron microscopy. Nuclear fragmentation was proven by TUNEL method under confocal laser scanning microscopy and DNA laddering through eletrophoresis. At later stages, plant responses were cell elongation and cell division, forming a periderm-like boundary layer that demarcated healthy tissues from the inoculation sites. Using several stains such as toluidine blue, sudan IV, annexin V, and phloroglucinol-HCl, defense-related materials and structural changes were also examined.