Lipids and Lipid Polymers in Higher Plants

Abstract

The prenyllipids found in higher plants are either completely terpenoid in origin (simple), e.g., the carotenoids, or consist of a terpenoid and a non-terpenoid part (mixed), as is the case with ubiquinone. Terpenoids are biosynthesized from a basic branched five carbon unit, If we formally designate this unit ip, then two units join head to tail to give a monoterpene, ipip; further sequential head-to-tail additions lead to sesquiterpenes (ipipip), diterpenes (ipipipip), and polyprenols (8 or more ip units). If, however two sesquiterpene units join tail-to-tail, the result is a triterpene (ipipippipipi) and if two diterpenes join in this way a tetraterpene is formed. Typical examples of simple prenyllipids are given in Table 1. The mixed terpenoids with which we are mainly concerned are listed in Table 2. A diterpene phytol, or a closely related compound, is a constituent of all these compounds except the ubiquinones and plastoquinones, which contain a polyprenol side chain. The ubiquinone (Q) isoprenologue usually present is Q-9 or Q-10; i.e., the quinone residue with a side chain of nine (45C) or ten (50C) isoprene residues [38].