CHANGES IN ENDOGENOUS CYANIDE AND 1-AMINOCYCLOPROPANE-1-CARBOXYLIC ACID LEVELS DURING THE HYPERSENSITIVE RESPONSE OF TOBACCO MOSAIC-VIRUS-INFECTED TOBACCO-LEAVES

Leaves of Nicotiana tabacum L. cv. Xanthi necroticum plants form, local necrotic lesions at the site of infection by tobacco mosaic virus. During the first seven days post-inoculation, endogenous levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and N-malonyl-ACC increased in the lesion area. The time course of ACC accumulation coincided with an increase in the endogenous cyanide level which began within two days after inoculation Concomitantly, the activity of beta-cyanoalanine synthase, the main HCN detoxifying enzyme, decreased. Likewise, treatment of leaf discs of uninfected plants with ACC led to cyanide accumulation. Exogenously applied KCN caused necrotic spots on tobacco leaves very similar to the whitish centers of virus-induced local lesions. Possible implications of cyanide in cell death during TMV-induced lesion development are discussed.