Induction of Alkaloid Biosynthesis and Accumulation in Plants and in Vitro Cultures in Response to Elicitation

Abstract

This chapter reviews the area of induced rapid alkaloid accumulation in plants and focuses on the regulatory mechanisms involved. The majority of known alkaloids are constitutively expressed secondary metabolites and are considered to be part of a constitutive defense system. However, alkaloid biosynthesis is affected by environmental factors such as light/irradiation, temperature, and water supply. Changes in one or more of these factors exert direct effects on primary metabolism and thus influence the direction of secondary metabolism as well. The resulting alterations in alkaloid content are generally not expected to occur rapidly, i.e., within a few hours or 1–2 days. Alternatively, alkaloid biosynthesis may be directly regulated by environmental factors, if, for example, light receptors are involved and the pathway is localized partially or fully in plastids/chloro-plasts. Thus, both direct and indirect regulatory effects resulting from photosynthesis would be responsible for changes in alkaloid accumulation. Overall alkaloid induction by environmental factors is difficult to interpret with respect to the physiological role of the products. As for the numerous data on the effect of culture conditions on alkaloid accumulation in vitro, only a description of the phenomena observed can presently be given. This topic is reviewed in related chapters of this book (Chapters 5, 7, and 8) and interesting comparisons of the effects of culture conditions, as well as the inducing factors, on the accumulation of secondary metabolites are made.