Hairy root cultures as an alternative source for the production of high-value secondary metabolites

Hairy roots are rapidly growing, highly differentiated transformed root cultures induced by Agrobacterium rhizogenes infection usually at the infected site of the representative medicinal plant. Hairy roots have the ability to rapidly multiply in the culture medium devoid of any hormones. Unlike other plant cell cultures, hairy root cultures are genetically and biochemically stable and produce a variety of secondary metabolites. In the past three decades, researchers across the world have successfully initiated and cultured hairy roots in vitro for a large number of medicinal plants. Hairy root technology is becoming a promising source for the production of pharmaceutically and industrially important secondary metabolites. This is due to the characteristics of hairy roots, such as rapid growth, the lack of geotropism, extensive lateral branching, and, more importantly, genetic stability. This chapter explores the applications of secondary metabolites in drug formulation, cosmetic preparation, food processing, and the study of plant metabolic pathways. It also briefs about the recent advancements in the area of hairy root culture involving other biotechnological approaches like metabolic engineering or genetic engineering, elicitation, metabolic trapping, and phytoremediation. This chapter certainly benefits the researchers to further explore on the applications of hairy root culturing technology to produce desired plant secondary metabolites on a large scale.