Involvement of hydrogen peroxide in repression of catalase in TMV-infected resistant tobacco

Abstract

Catalases are ubiquitous, and play a role in plant defense against pathogens. We have reported that catalase mRNA and enzyme activity are repressed in the vicinity of hypersensitive tobacco lesions following TMV infection. We wished to identify the signals involved in this repression. Inoculation with TMV reduced catalase levels 26 to 28 h following infection, coincident with the known timing of endogenous salicylic acid (SA) accumulation. Application of SA caused a transient reduction in Ngcatl mRNA level and catalase activity 4 to 6 h after treatment. However, repression was also observed in transgenic plants harboring the salicylate hydroxylase gene (NahG) and in TMV susceptible plants, which do not accumulate SA following TMV infection. In the same blots there was no induction of PR-1 or enhanced expression of H2O2-inducible glutathione-S-transferase and found that exposure to H2O2 also repressed Ngcatl mRNA. Our findings suggest that repression of catalase transcription may be caused by the accumulation of H2O2 rather than of SA.