Growth retardation and changes in phenolic compounds, with special reference to scopoletin, in mildewed and ethylene-treated tobacco plants

Tobacco plants (oriental type, cv. Michal) systemically infected with Peronospora tabacina Adam exhibited severe stunting and a considerable accumulation of scopoletin (6-methoxy7-hydroxycoumarin) in the upper part of the stem. The scopoletin concentration increased during the first 10 days of pathogenesis and declined thereafter. P. tabacina-infected plants also contained higher amounts of p-coumaric acid (two isomers), o-coumaric acid and a number of unidentified phenolic compounds than uninoculated plants. Ethylene treatment of tobacco plants (single spray of 2-chloroethylphosphonic acid on leaves) induced a response similar to that arising from a systemic infection with P. tabacina, viz. growth retardation and accumulation of scopoletin in the upper stem. Based on preliminary results which showed that P. tabacina induced an increase in ethylene production in tobacco, it was hypothesized that some of the changes in phenolics detected in plants systemically infected with P. tabacina were ethylene-induced.