Pathways of Important Metabolites and Enzymes Involved

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Plants produce diverse chemical compounds that play a crucial role not only in plant growth and development but also hold great economic and ecological importance for mankind. Plants synthesize these compounds to cope with various abiotic and biotic stresses and also in response to the incessantly changing surrounding environment. Broadly, these compounds are categorized as primary and secondary metabolites. While the former play direct roles in plant growth, development, functioning, defense, and stress tolerance, the latter do not hold any direct importance in the growth and development of plants. Primary metabolites include carbohydrates, organic acids, flavonoids, vitamins, amino acids, glucosinolates, hormones, and phenolics. These are also widely used by humans as dietary compounds. Secondary metabolites, on the other hand, can be broadly sub-divided into four major groups, i.e., terpenoids, phenols, alkaloids, and sulphur-containing compounds. These compounds perform various other physiological roles like protecting plants against microbes and herbivory, insect repellents, allelopathic agents, attractants for pollinators and seed dispersal agents, regulating symbiosis, providing structural support to plants, and alleviating biotic stresses. Additionally, they are also extensively used in cosmetics and pharmaceutical industries, as well as the production of fragrances, drugs, dietary supplements, dyes, and flavours. Although, a myriad of these metabolites are synthesized by plants, and are basically derived by modifying the basic chemical structure of compounds already present in plants. This chapter, therefore, elucidates the biosynthetic pathways of some of the major plant metabolites, giving special attention to the key enzymes involved.