Hairy root cultures are mainly used for:
Differentiated roots possess endodermis, pericycle, and organized transport tissues that compartmentalize biosynthetic pathways and sequester toxic end products safely in vacuoles. Hairy root cultures preserve this organization while displaying exponential growth in hormone-free liquid, combining advantages of organized tissue and microbial-like scalability. Many pharmaceuticals like atropine, scopolamine, withanolides, and tanshinones are synthesized primarily in root cortex and stored in vacuoles, so root cultures maintain expression of pathway genes including putrescine N-methyltransferase
Ref: Guillon Curr Opin Plant Biol 2006 metabolites; Srivastava Biotechnol Adv 2007; NCBI PMC3644105 hairy root factories; PubMed 17270743.