Pathogenic and non-pathogenic stress effects on peroxidases in leaves of tobacco

Abstract

The effects of stress stimuli of different sources, including pathogenic (fungi, bacteria, viruses), non-pathogenic (excess of water and manganese, γ-irradiation), as well as senescence, were examined in tobacco leaves. Some of these stimuli produced damage symptoms that differed in severity, whereas others did not produce visible damage symptoms. The activity, molecular heterogeneity, and localization of peroxidases (PO; E.C.1.11.1.7) in tobacco leaf tissues as influenced by stress stimuli were studied, using both biochemical and cytochemical approaches. Chlorophyll and lipid peroxide contents were also determined as related to tissue and cell membrane damage. All stress stimuli and senescene triggered an increase in PO activity. In tobacco-fungi interactions, this increase was a plant response to infection and not a contribution of the hyphal PO per se. The PO increases under stress conditions that caused visible tissue damage symptoms were concomitant with chlorophyll loss. The severity of damage corresponded to the rate of PO increase and chlorophyll loss. Under all stress conditions, increases in PO were accompanied by increased lipid peroxidation, resulting in damage to cell membranes. Thus, the responses of PO in tobacco leaves to various stress situations were shown not to depend on the origin of stress stimuli, but on the presence and degree of damage, suggesting a possible involvement of endogenous cell wall elicitors.