2027 Journal of Cell and Tissue Research Vol. 9(3) 2027-2036 (2009) ISSN: 0904- 0910 (Available online at www.tcrjournals.com) Review Article SECONDARY METABOLITES AND METABOLIC ENGINEERING KATARE, D. P., 1 AERI, V. 2 AND BORA, M. 3 1 Amity Institute of Pharmacy, Amity University Uttar Padesh, Noida, 2 Department of Pharmacognosy and Phytochemistry, Faculty of Pharmacy, Hamdard University, New Delhi, 3 N. V. Patel College of Pure and Applied Sciences, Vallabh Vidyanagar-388120. E. mail: madhumatib@yahoo.co.in Received: September 22, 2009; Accepted: October 14, 2009 Abstract: Unraveling plant secondary metabolism is the way to successful applications in molecular farming, health food, functional food, and plant resistance. Various pathways have been altered using genes encoding biosynthetic enzymes or regulatory proteins and show enormous potential for the genetic engineering of plant secondary metabolism. Recent achievements have been made in the metabolic engineering of plant secondary metabolism. Various pathways have been altered using genes encoding biosynthetic enzymes or genes encoding regulatory proteins. Key words: Secondary metabolism, Metabolic engineering ? INTRODUCTION Plant secondary metabolism has multiple functions throughout the plant’s life cycle. These functions can be classified as mediators in the interaction of the plant with its environment, such as plant–insect, plant–microorganism and plant–plant interacti- ons[1,2]. The production of secondary metabolites forms part of the plant’s defence system, for example, the constitutive production of antifeedants and phytoanticipins, and the inducible production of phytoalexins [2]. Secondary metabolism also plays a role in plant reproduction, for example, in attracting pollinators and in male fertility. Secondary metabolites determine important aspects of human food quality (taste, colour and smell), and plant pigments are important for the diversity of ornamental plants and flowers. Moreover, several plant secondary metabolites are used for the production of medicines, dyes, insecticides, flavours and fragrances. SECONDARY PRODUCTS The sum of all of the chemical reactions that take place in an organism constitutes metabolism. Metabolism is a dynamic process where molecules are constantly turning over the composition of a cell at any given time represent the balance between synthesis and degradation. Much of that carbon and energy ends up in protein, nucleic acids, lipids and other molecules that are common to all organisms, but in plants a significant proportion of assimilated carbon and energy is diverted to the synthesis of molecules that may have no obvious role in growth and development. The molecules are known as secon- dary product. The latter generally occurs in low quality and their production may be widespread or restricted to particular families, genera, or even spec- ies. The secondary products with an emphasis on the biosynthesis physiology and ecological roles are of four major classes viz., (i) terpenes, phenolic compounds, (ii) saponins, (iii) cardiacglycosis, cyano- genic glycosides, glucosinolates and (iv) alkaloids. (i) Terpenoids: The terpenoids are a functionally and chemically diverse group of molecules. They are generally lipophilic substances derived from a single five carbon unit. The terpenoids family includes hormones (gibberellins and abscisic acid); the carotenoid pigments sterols e.g. ergosterol, sitosteral, cholesterol and sterol derivatives (Fig. 1) and many of the essential oils that give plants their distinctive odours and flavours. All terpenes and terpene derivative share a common biosynthetic pathways called mevalonic acid pathway after a key intermediate.