Peroxidase activity in plant leaves exposed to gaseous HCl or ozone

Previous studies of plants subjected to air pollutant stress indicated that increased total peroxidase (PRO) activity and/or altered PRO isozyme patterns are frequently induced. Phaselus vulgaris var. U1 111 and Lycopersicon esculentum var. Heinz 1350 plants exposed to either gaseous hydrogen chloride (HCl) for 20 min or ozone (O₃) for 1 h were employed to determine if (1) total PRO activity increased following pollutant stress, (2) increased PRO activity was associated with non-necrotic injury, and (3) PRO isozyme patterns were altered after pollutant stress. Non-necroroc foliar macroscopic injury was dependent on pollutant concentration in the bean-O₃, tomato-O₃, and bean-HCl combinations, but not for the combination of tomato-HCl where there was little injury. Total PRO activity increased for all combinations. In only one (bean-O₃), however, was elevated PRO activity statistically related to pollutant concentration. In the others, only the post-exposure time interval was related to PRO activity. No differences of isozyme pattern were discerned between PRO samples obtained from tomato exposed to charcoal-filtered air and either O₃ or HCl. The PRO isozyme pattern of samples obtained from bean varied with imposed stress and sampling time. The results obtained indicate that PRO levels may be elevated by subjection to air pollutant stress and that PRO activity is sensitive to the internal physiological conditions of the plants. Its extreme sensitivity, however, precludes its use as a reliable indicator of pollutant stress.