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, loca l necrotic lesions at the site of infection by tobacco mosaic virus. D uring the first seven days post-inoculation, endogenous levels of 1-am inocyclopropane-1-carboxylic acid (ACC) and N-malonyl-ACC increased in the lesion area. The time course of ACC accumulation coincided with a n increase in the endogenous cyanide level which began within two days after inoculation Concomitantly, the activity of beta-cyanoalanine sy nthase, the main HCN detoxifying enzyme, decreased. Likewise, treatmen t of leaf discs of uninfected plants with ACC led to cyanide accumulat ion. Exogenously applied KCN caused necrotic spots on tobacco leaves v ery similar to the whitish centers of virus-induced local lesions. Pos sible implications of cyanide in cell death during TMV-induced lesion development are discussed.