Effects of Singlet Oxygen Quenchers and pH on the Bacterially Induced Hypersensitive Reaction in Tobacco Suspension Cell Cultures.

Suspension cell cultures of Nicotiana tabacum L. inoculated with the incompatible pathogen Pseudomonas syringae pv pisi undergo a hypersensitive reaction. Addition of the singlet oxygen quencher bixin to cell suspensions had no effect on hypersensitive cell death. Addition of the singlet oxygen quencher 1,4-diazabicyclo octane (DABCO) increased the medium pH and delayed the onset of cell death. This delay was eliminated when cell suspensions were buffered, and could also be induced by increasing medium pH with KOH. Bixin and DABCO also did not suppress the hypersensitive reaction in tobacco leaves. These data do not support a role for singlet oxygen in the hypersensitive reaction. Medium pH, however, appears to be a critical factor in cell suspension cultures.