Localization of the cytotoxic hydroperoxyeudesmanolides in Artemisia umbelliformis

The localization of the cytotoxic hydroperoxyeudesmanolides in Artemisia umbelliformis Lam. (Compositae) was investigated utilizing the histochemical techniques of the colour reactions with acids and with ferrous (II) thiocyanate on samples pre-treated or not with chloroform. All the organs known by chemical analysis to contain sesquiterpene lactones were studied (leaves, twigs, flowers, achenes). A deep red staining with conc. sulphuric acid and a brownish staining with ferrous (II) thiocyanate were observed in the subcuticular space and in the head cells of the biseriate glandular trichomes, and it was shown that for the plant specimens studied these colour reactions are to be considered specific for the sesquiterpenoid hydroperoxides. Based on the results of their localization in the plant as well as on the available experimental evidence on related compounds, a possible ecological significance of the compounds as feeding deterrents and/or allelopathic substances, is suggested.