Adventitious Root Culture—An Alternative Strategy for Secondary Metabolite Production: A Review

Medicinal plants are valuable sources of botanical drugs, extracts and pure compounds. Although several species can be propagated or collected, the access to herbal material is limited in certain cases. The protection of natural habitats and biodiversity demands new sources to provide plant secondary metabolites of medical importance. Adventitious root culture is used to harvest the secondary metabolites from the medicinally important plants, thereby offering an alternative to collection and propagation of medicinal plants. In this review, we comprehensively summarize the previously published data on the use of adventitious root cultures for numerous therapeutic plants. Adventitious roots showed elevated growth rates and production of pharmaceutically important metabolites under sterilized condition with optimized plant-growth regulators in culture media. In the present study, major influencing factors, such as the stages involved in the process of adventitious root formation, medium composition and type of growth regulators, specifically the effect of different auxins on the initiation and formation of roots, are discussed. Elicitation strategies using biotic (yeast extracts, chitosan and pectin) and abiotic factors (MJ, SA, CuSO4, AgNO3, NaCl) that affect the in vitro growth of adventitious roots and the role of bioreactors, which are new advancements in the scale-up process, are also highlighted. The development of adventitious root cultures for the production of secondary metabolites of medicinal importance is a perspective that is advantageous from ecological and economical aspects as well.