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

Abstract

• 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). [3 H]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.