Isoprenoids are very stable and persistent substances
Little is known about the catabolism of isoprenoids in plants.
Biologically active compounds, such as phytohormones, are converted by the
introduction of additional hydroxyl groups and glucosylation into inactive
derivatives, which are often deposited in the vacuole. It is questionable
whether, after degradation, isoprenoids can be recycled in a plant. Some
isoprenoids are remarkably stable. Large amounts of isoprenoids are found as
relics of early life in practically all sedimentary rocks as well as in crude
oil. In archaebacteria, the plasma membranes contain glycerol ethers with
isopre-noid chains instead of fatty acid glycerol esters. Isoprenoids are
probably constituents of very early forms of life.