TOBACCO CLASS-I AND CLASS-II CATALASES ARE DIFFERENTIALLY EXPRESSED DURING ELICITOR-INDUCED HYPERSENSITIVE CELL-DEATH AND LOCALIZED ACQUIRED-RESISTANCE

Expression of tobacco class I (CAT1) and class II (CAT2) catalases was analyzed in leaves reacting hypersensitively to tobacco mosaic virus (TMV) or to a fungal glycoprotein elicitor. In TMV-infected plants, Ca t1 transcript levels declined rapidly while Cat2 transcripts accumulat ed strongly, The spatial and temporal changes in catalase transcripts, proteins, and activity during the hypersensitive reaction (HR) were f urther investigated in tobacco leaves infiltrated with a glycoprotein elicitor, Two functionally different zones were discriminated: the inf iltrated tissue in which cells undergo the HR, called the HR-zone 1; a nd the surrounding tissue showing strong induced defense responses, ca lled the LAR (Localized Acquired Resistance)-zone 2, Levels of Cat1 an d Cat2 mRNA and proteins and catalase activity decreased in the HR-zon e 1, In the EAR-zone 2, Cat1 transcripts became rapidly undetectable, but levels of Cat2 mRNA and protein and catalase activity increased. C atalase expression in elicitor-infiltrated leaves reflected that in TM V-infected leaves. A strong rise in hydrogen peroxide occurred in the HR-zone 1 and paralleled the CAT activity decline. No H2O2 increase wa s measured in the LAR-zone 2, There was no correlation between salicyl ic acid levels and catalase activity, Modulation of catalase activity in tobacco leaves undergoing the HR appeared predominantly supported b y changes in catalase transcripts and proteins. We have shown that nei ther H2O2 nor salicylic acid can be the primary mobile signal diffusin g from the HR-zone 1 to the LAR-zone 2 and inducing CAT2 expression. F urthermore, the signaling pathway responsible for decreased CAT2 expre ssion in the HR-zone 1 does not involve reactive oxygen intermediates.