Composition of the essential oils from roots of some apiaceae in relation to the development of their oil duct systems

In the roots of Apiaceae seedlings, the essential oils are accumulated in triangular primary oil ducts between the pericycle cells. In a later stage, when the roots are increasing in diameter, secondary oil ducts continually develop in the cortex near the cambium, thereafter moving outwards. In different stages of development after germination, the composition of the essential oils from the roots of caraway, Carum carvi L., fennel, Foeniculum vulgare ssp. capillaceum Gilib, var. azoricum (Mill.) Thell., parsnip, Pastinaca sativa L. ssp. sativa L. var. hortensis Ehrh., and lovage, Levisticum officinale Koch was analysed parallel to microscopical observation of the roots. Compared with the ‘adult’ oils, the essential oils of the seedlings consist of large amounts of sesquiterpene hydrocarbons, and only small changes occur until the beginning of the secondary thickening. At that time, the changes in the oil composition start, although the secondary oil ducts have not yet developed. Just when the secondary oil ducts appear, the oil content in the roots increases remarkably, accompanied by rapid changes in the oil composition into that of the ‘adult’ oils. Only L. officinale did not fit into this pattern. The phthalides, characteristic compounds of the adult oils of this species, are found in considerable amounts only after many complete secondary oil ducts have been developed.