Metabolic responses of tobacco to induction of systemic acquired resistance

Tobacco (Nicotiana tabacum L. cv. Xanthi-nc) plants carry the N resistance gene against Tobacco mosaic virus (TMV) and localize the infection to cells adjacent to the site of viral entry, developing a hypersensitive response in the form of local necrotic lesions. Previous studies have shown changes in metabolic activity, lipid peroxidation and lipid composition in TMV-inoculated Xanthi-nc plants. Here we report the comparative analysis of these changes in wild-type (WT) Xanthi-nc and salicylic acid-deficient phenotype NahG tobacco plants during TMV-induced cell death. TMV-inoculated WT plants develop systemic acquired resistance (SAR), while NahG tobacco plants are not able to establish SAR against a second inoculation by TMV. Heat efflux and ethane emission from uninoculated leaves of NahG plants were found to be significantly lower than from WT tobacco. However, the rates of heat efflux and lipid peroxidation increased up to similar levels in TMV-inoculated WT plants either expressing or not expressing SAR, and in NahG plants. TMV-inoculated leaves of NahG tobacco had a higher ratio of stigmasterol to sitosterol than those of WT plants. Furthermore, ratio of linoleic acid to linolenic acid was also higher in NahG tobacco. Possible reasons why induction of SAR had little or no effect on TMV-induced lipid peroxidation and metabolic activity are discussed.