Infection with avirulent pathogens, tobacco mosaic virus (TMV) or Pseudomonas syringae pv. tabaci induced accumulation of
polyisoprenoid alcohols,
solanesol and a family of
polyprenols [from polyprenol composed of 14
isoprene units (Pren-14) to -18, with Pren-16 dominating] in the leaves of resistant tobacco plants Nicotiana tabacum cv. Samsun NN. Upon TMV
infection,
solanesol content was increased seven- and eight-fold in the inoculated and upper leaves, respectively, while polyprenol content was increased 2.5- and 2-fold in the inoculated and upper leaves, respectively, on the seventh day post-
infection. Accumulation of
polyisoprenoid alcohols was also stimulated by exogenously applied
hydrogen peroxide but not by exogenous
salicylic acid (SA). On the contrary, neither inoculation of the leaves of susceptible tobacco plants nor wounding of tobacco leaves caused an increase in polyisoprenoid content. Taken together, these results indicate that
polyisoprenoid alcohols might be involved in plant resistance against pathogens. A putative role of accumulated polyisoprenoids in plant response to pathogen attack is discussed. Similarly, the content of
plastoquinone (PQ) was increased two-fold in TMV-inoculated and upper leaves of resistant plants. Accumulation of PQ was also stimulated by
hydrogen peroxide, bacteria (P. syringae) and SA. The role of PQ in
antioxidant defense in cellular membranous compartments is discussed in the context of the enzymatic
antioxidant machinery activated in tobacco leaves subjected to
viral infection. Elevated activity of several
antioxidant enzymes (
ascorbate peroxidase,
guaiacol peroxidase,
glutathione reductase and
superoxide dismutase, especially the CuZn
superoxide dismutase isoform) and high, but transient elevation of
catalase was found in inoculated leaves of resistant tobacco plants but not in susceptible plants.