Introduction

Abstract

Plants are metabolically diverse because of their sessile mode of life. Two classes of plant metabolites are identified. These are primary metabolites and plant specialized metabolites. Primary metabolites are essential for cellular functions and are either substrates or products of primary metabolism. Plant specialized metabolites, traditionally known as secondary metabolites, are products of metabolism by different plants specialized for specific plant–environment interactions such as to defend against animals and microorganisms, and to respond to different harsh environmental conditions (drought, flood, cold, heat etc.). Plant specialized metabolites belong to different classes such as different types of phenolic compounds, terpenoids, alkaloids and nitrogen-containing compounds, sulfur containing compounds, and fatty acid derivatives. Many plant specialized metabolites are used as drugs for treating different human ailments.