Abstract
Agrobacterium rhizogenes induces hairy root disease in plants. The neoplastic (cancerous) roots produced by A. rhizogenes infection, when cultured in hormone free medium, show high growth rate and genetic stability. These genetically transformed root cultures can produce levels of secondary metabolites comparable to that of intact plants. Several elicitation methods can be used to further enhance the production and accumulation of secondary metabolites. Thus, hairy root culture offer promise for high production and productivity of valuable secondary metabolites in many plants. Hairy roots can also produce recombinant proteins from transgenic roots, and thereby hold immense potential for pharmaceutical industry. Hairy root cultures can be used to elucidate the intermediates and key enzymes involved in the biosynthesis of secondary metabolites, and for phytoremediation due to their abundant neoplastic root proliferation property. Various applications of hairy root cultures and potential problems associated with them are discussed in this chapter.