ABSTRACT
Secondary metabolites, which do not get involved in the primary metabolism of plants, are a group of compounds whose role has always been underestimated. The great misconceptions on the function of these compounds lead to naming them by erroneous terms like “waste products”, “end products”, “excretory products”, etc. But now there is a genuine realization of the varied roles of these compounds, most of which are as adaptational and survival mechanisms. Thus, alkaloids are defensive agents, deterring the herbivores due to their bitter taste; volatile oils act as pheromones (for attracting insects for pollination) and protect the plant from microbes (and sometimes suppresses neighbouring plants, as in case of Eucalyptus) and diterpenes or triterpenes, when present in resin, perform wound healing and antimicrobial functions. Limonoids and quassinoids are insect repellants and thus protect the plant (especially wood) from insect attack. Phenolics are the best antioxidants, protecting cellular membranes and tissues containing lipids from oxidation. Among them, anthocyanins and flavonoids are flower pigments, which make the flowers visible to the “color blind” insects, and thus act as pollinator guides. All sulphur-containing compounds are antimicrobial in nature.
