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.
Keywords: Nitrogen compounds, Methyl jasmonate, Phenolic compounds, Secondary metabolites, Terpenes.
