Bioactive metabolites of plants and microbes and their role in agricultural sustainability and mitigation of plant stress

Abstract

Primary metabolites are ubiquitous in nature and actively involved in growth while secondary metabolites (SMs) are involved in interaction with the environment. In plants terpenes are the largest group of secondary metabolites that play an important role in defense mechanisms against the herbivores and pathogens. Plant secondary metabolites such as alkaloids, phenolics and diterpenes have a great potential against many carcinogens. Carotenoids provide photoprotection and act as a pigment to absorb light during photosynthesis. Carotenoids are also efficient in the interaction with other organisms as they are phagostimulant and allelopathic agent. Flavonoids from the higher plants play a significant role in ultra-violet (UV) filtration, nitrogen fixation, floral pigmentation, and defense mechanisms against many diseases. These secondary metabolites provide protection to plants in a different type of biotic and abiotic stresses. Microorganisms also contain a high number of bioactive metabolites but not all of them. Marine microorganisms are a rich source of secondary metabolites such as alkaloids, terpenoids, polyketides, isoprenoids and non-isoprenoid and quinones amongst others. These metabolites are anti-inflammatory, anti-bacterial and anti-tumor in action. Secondary metabolites from fungi have a great therapeutic value as they have antifungal and antibacterial activity against many pathogens. Plant growth promoting rhizobacteria (PGPR) and Plant growth regulators (PGR) are the key biological entities to enhance the production of bioactive secondary metabolites in plants and can change the plant metabolome in response to various environmental stresses. This review paper will provide a new insight about the role of secondary metabolites in plant defense and the role of microorganisms in modulating the plant metabolome under various environmental stresses and their interactions with other microorganisms and plant growth regulators.