Polyamine Metabolism Is Upregulated in Response to Tobacco Mosaic Virus in Hypersensitive, but Not in Susceptible, Tobacco

Change is reported in the biosynthetic and oxidative activity of hypersensitive (NN) and susceptible (nn) tobacco (Nicotiana tabacum) plants in response to tobacco mosaic virus (TMV). Mature leaves of nn and NN tobacco were collected over 0-72 h as uninoculated controls or after inoculation with TMV or phosphate buffer (mock-inoculation). The polyamine response to inoculation was analysed by measuring activity and gene expression of S-adenosylmethionine decarboxylase (SAMDC), arginine-(ADC) and ornithine decarboxylases (ODC); incorporation of labelled putrescine; and activity of diamine oxidase (DAO). In NN leaves SAMDC activity and transcript levels, and DAO activity increased in the TMV-inoculated plants but not in the other treatments; a two-fold increase in DAO activity was seen after 72 h. Both ADC and ODC activity increased in NN leaves at 72 h in TMV-inoculated plants; ADC mRNA increased with activity. The increase in SAMDC mRNA (24 h) preceded the rise in activity (72 h). [3H]putrescine added to NN leaves led to enhanced label recovery and incorporation into spermidine and spermine in TMV-inoculated plants. No significant changes in biosynthetic or oxidative activity occurred in nn plants. After TMV inoculation, NN, unlike nn, tobacco plants upgrade polyamine synthesis and oxidation; this leads to changes in cellular components which might induce programmed cell death.