Biological and Molecular Comparison Between Localized and Systemic Acquired Resistance Induced in Tobacco by a Phytophthora Megasperma Glycoprotein Elicitin.

We have compared localized (LAR) and systemic (SAR) acquired resistance induced in tobacco by a hypersensitive response (HR) inducing Phytophthora megasperma glycoprotein elicitin. Three different zones were taken into account: LAR, SART and SARS. The LAR zone was 5–10 mm wide and surrounded the HR lesion. SART was the tissue of the elicitor-treated leaf immediately beyond the LAR zone. The systemic leaf was called SARS. Glycoprotein-treated plants showed enhanced resistance to challenge infection by tobacco mosaic virus (TMV). Disease resistance was similar in SART and SARS, and higher in LAR. The expression pattern, in glycoprotein-treated plants, of acidic and basic PR1, PR2, PR3 and PR5 proteins and of O-methyltransferases (OMT), enzymes of the phenylpropanoid pathway, was similar to that in TMV-infected plants. OMT was stimulated in LAR but not in SART and SARS. The four classes of acidic and basic PR proteins accumulated strongly in LAR. Reduced amounts of acidic PR1, PR2, PR3 and only minute amounts of basic PR2 and PR3 accumulated in SART and SARS. In glycoprotein-treated plants, expression of the acidic and basic PR proteins in LAR and SAR of transgenic NahG and ETR tobacco plants and in LAR of plants treated with inhibitors of salicylic acid accumulation and of ethylene biosynthesis indicated a salicylic acid-dependent signalling pathway for acidic isoform activation and an ethylene-dependent signalling pathway for basic isoform activation.