POLYAMINE SYNTHESIS AND ACCUMULATION IN THE HYPERSENSITIVE RESPONSE TO TMV IN NICOTIANA-TABACUM

The possible involvement of polyamines in the tobacco mosaic virus (TM V)-induced hypersensitive reaction (HR) in Nicotiana tabacum (L.) cv. Samsun NN, which bears the N resistance gene, was investigated. Concen trations of free and conjugated polyamines, as well as the activities of their biosynthetic enzymes ornithine decarboxylase (ODC) and argini ne decarboxylase (ADC), were analysed in the necrotic area (I, interna l zone) and in the two concentric zones surrounding it (M, middle zone ; E, external zone) during the progression of the HR (1, 3 and 5 d fro m TMV inoculation). Results were compared with those obtained in contr ol plants (mock-inoculated) and with the pattern in susceptible TMV-in fected tobacco plants. In the HR, concentration increased towards zone I for free putrescine and spermidine. Highest concentrations in zones NI and I occurred on day 3. Conjugated polyamines similarly showed an increasing concentration gradient towards zone I, with maximum accumu lation on day 5. ODC and ADC activities also showed an increasing grad ient towards zone I that could be related to the increase in free and conjugated polyamines. By contrast, in control plants concentrations o f free and conjugated polyamines decreased from day 1 to day 5, ODC ac tivity increased slightly, whereas ADC activity did not show significa nt changes. In the TMV-infected susceptible tobacco plants, polyamines tended to remain in the free state instead of being conjugated as inf ection progressed. These results suggest that polyamines could play a role in mechanisms of resistance to biotic stress.