ABSTRACT
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The term lipid in the following text is restricted to the naturally occurring esters of the long-chain aliphatic monocarboxylic acids, the fatty acids (FAs), and to compounds that are closely related biosynthetically or functionally. Most abundant in the living organisms, including plants, are the FA esters with glycerol (1,2,3-trihydroxy
propanol), denoted as glycerolipids. In their turn, glycerolipids are usually classified according to the number of hydrolytic products per mole. Simple (often denoted as neutral) lipids release two types of products: glycerol and FA, while complex (denoted usually as polar) lipids give three or more products such as FA, glycerol, phosphoric acid, and aminobase, for example. Triacylglycerols (TAG) comprise the most abundant simple lipid group, and phospholipids (PLs) and glycolipids (GLs) are the most abundant complex lipid groups. Closely related to these according to the earlier-mentioned definition are the sterols and the sterol esters usually accompanying the glycerolipids in plants. Plant lipids, therefore, present a complex mixture of several lipid types, denoted later as groups: simple and complex glycerolipids, sterol esters, and sterols. Free FA, mono-, and diacylglycerols are usually considered as artifacts.
