Glucosinolate Metabolism and its Role in Plant Defense

Abstract

Glucosinolates are sulfur and nitrogen containing plant secondary metabolites found commonly in the Brassicaceae and related plant families. The glucosinolates are found naturally and give pungent smell in many plants such as mustard, cabbage etc. In the plant, they generally coexist with an enzyme called myrosinase, though glucosinolates are stored in the vacuoles cells and myrosinase exist in separate but adjacent cells. As the plant tissue is damaged, glucosinolates are released and getshydrolyzed by myrosinase. The chemical nature of the hydrolysis products depends on the structure of the glucosinolate side chain, plant species and reaction conditions. Till date, more than 130 types of glucosinolates have been identified. Biosynthesis of glucosinolates takes place in three phases: amino acid chain elongation, conversion of the amino acid moiety to the glucosinolate core structure and subsequent side chain modifications. Depending on developmental stage, tissue and photoperiod, glucosinolate pattern differs between species and ecotype as well as betweenand even within individual plants. The change of the glucosinolate profile by several genetic and environmental factors has brought forward different theories regarding their potential roles in the plant activities and defense. However, the most accepted theory is that the glucosinolate-myrosinase system is involved in defense against herbivores and pathogens. Among many, the main signal molecules which are recognized by the plant, are derivatives of jasmonic acid, salicylic acid and ethylene which mediate the plant response resulting in the activation of distinct sets of defense genes. This review summarizes the glucosinolate biosynthesis, degradation, organization of the myrosinase-glucosinolate system and its role in the plant defense.