Spatial and Temporal Induction of Cell Death, Defense Genes, and Accumulation of Salicylic Acid in Tobacco Leaves Reacting Hypersensitively to a Fungal Glycoprotein Elicitor

We have analyzed the spatial and temporal expression of defense responses induced in attached tobacco leaves treated with a Phytophthora megasperma glycoprotein that was previously shown to be an efficient elicitor of the hypersensitive reaction. The infiltrated tissue (zone 1), the surrounding tissue (zone 2), which is 5 mm in width, and tissue at a distance >2 cm from zone 2 (zone 3) were analyzed separately. Cell death occurred only in zone 1 and was completed by 14 h. Defense gene expression was induced in zones 1 and 2 with striking differential patterns, but not in zone 3. There was a rapid (1 to 4 h) induction of genes of the phenylpropanoid, salicylic acid, and ses-quiterpenoid pathways in zones 1 and 2. However, it was strong and transient in the former and of lesser extent but sustained in the latter. High amounts of scopoletin, a phenylpropanoid metabolite, were found synthesized in zone 2. Pathogenesis-related (PR) transcripts and the corresponding PR proteins accumulated in high amounts in zo...