Polyamine metabolism is upregulated in response to tobacco mosaic virus inhypersensitive, but not in susceptible, tobacco

Change is reported in the biosynthetic and oxidative activity of hypersensi tive (NN) and susceptible (nn) tobacco (Nicotiana tabacum) plants in respon se to tobacco mosaic virus (TMV). Mature leaves of nn and NN tobacco were collected over 0-72 h as uninoculat ed controls or after inoculation with TMV or phosphate buffer (mock-inocula tion). The polyamine response to inoculation was analysed by measuring acti vity and gene expression of S-adenosylmethionine decarboxylase (SAMDC), arg inine(ADC) and ornithine decarboxylases (ODC); incorporation of labelled pu trescine; and activity of diamine oxidase (DAO). In NN leaves SAMDC activity and transcript levels, and DAO activity increas ed 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 in creased in NN leaves at 72 h in TMV-inoculated plants; ADC mRNA increased w ith activity. The increase in SAMDC mRNA (24 h) preceded the rise in activi ty (72 h). [H-3]putrescine added to NN leaves led to enhanced label recover y 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 synt hesis and oxidation; this leads to changes in cellular components which mig ht induce programmed cell death.