Secondary Metabolism

Abstract

The phenomenon of secondary metabolism was already recognized in the early phases of modern experimental botany. In his textbook published in 1873, Julius Sachs, one of the great pioneers of plant physiology, gave the following definition: “Als Nebenprodukte des Stoffwechsels kann man solche Stoffe bezeichnen, welche während des Stoffwechsels entstehen, aber keine weitere Verwendung für den Aufbau neuer Zellen finden. Irgend eine Bedeutung dieser Stoffe für die innere Ökonomie der Pflanze ist bis jetzt nicht bekannt” (Sachs 1873, p. 641). Translation: “We can designate as by-products of metabolism such compounds that are formed by metabolism, but that are no longer used for the formation of new cells. Any importance of these compounds for the inner economy of the plant is as yet unknown”. This clear statement is still valid. Sachs did not refer to any functions of the by-products, today known as secondary products (see review by Hartmann 1996). Plants form an important part of our everyday diet, and their constituents have been intensively studied for decades. In addition to essential primary metabolites (e.g., carbohydrates, lipids, and amino acids), higher plants are able to synthesize a wide variety of low molecular weight compounds—the secondary metabolites (Fig. 10.1). The production of these compounds is often low (less than 1% of dry weight), and depends strongly on the physiological and developmental stage of the plant.