Biosynthetic Relationships of Sesquiterpenoidal Stress Compounds from the Solanaceae

Rishitin (I) was reported as a phytoalexin of potatoes ( 1 ) and tomatoes ( 2 ) in 1968 and was the first sesquiterpenoidal stress compound to be isolated and characterized from the Solanaceae. In the 9 years since, some 20 other, structurally more or less closely related sesquiterpenes have been described from potato, aubergine, thornapple, sweet pepper, and tobacco species (Tables I - V) ( 3 - 19 ). All of these compounds are produced essentially only under stress conditions, that is, after infection of the plant with fungi, bacteria, or viruses, or through wounding, exposure to UV, or treatment with deleterious substances. Not all, however, are necessarily phytoalexins because some lack the antifungal activity which is requisite for that function. In addition, several other compounds (Table VI) ( 20 - 22 ) which are structurally and biogenetically closely related to the stress metabolites, have been obtained in very low amounts from cured tobacco leaves. Because of