**1. Introduction**

Plant kingdom, comprising about 250,000 species, is a repository of probably hundreds of thousands of low-molecular-weight structurally complex chemical compounds known as secondary metabolites [1]. These high-value metabolites are biosynthesized through

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

phenylpropanoid, mevalonate, 2-C-methyl-d-erythritol-4-phosphate, amino acid, glucose, acetate-malonate pathway, or combined pathways. Secondary metabolites have an important role in the interaction between plants and their environment (e.g., defense against herbivores and pathogens, protection against ultraviolet light, etc.) and, thus, are vital for their existence and subsistence. They are accumulated in specific tissues and structures (e.g., vacuoles, specialized glands, trichomes, etc.), and their production is affected by several factors, like genotype, plant physiology, climate, environmental conditions, and pathogens; in some cases, they are only produced during certain developmental stages [2, 3].

and traditional methods are unfeasible. The mass propagation of plants in aseptic and environmental controlled conditions, and the large-scale production of secondary metabolites in a year-round system without seasonal constraints, are some of the advantages of plant tissue culture techniques [3]. Moreover, cultures can be established in any part of the world independently of the plant growth requisites and are free of microbes and insects avoiding the use of pesticides and herbicides [14, 15]. Plant tissue culture techniques provide a reliable and predictable method for isolating the secondary metabolites at a high efficiency within a short time when compared to the extraction from wild plant populations [16]. Also, the simplicity in the extraction of the metabolites from *in vitro*-produced tissues makes the method appella-

Production of Plant Secondary Metabolites by Using Biotechnological Tools

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Apart from the abovementioned advantages, there are metabolites that are generally not found in the intact plant but can be produced by *in vitro* cultures [18]. Biotechnology opens the opportunity to apply traditional or metabolic engineering strategies to promote the accumulation of desired compounds by *in vitro* cultures. Products from *in vitro* cultures can still be used as models of whole plants, and cell cultures can be radiolabeled so that secondary

The massive and indiscriminate collection of plant material from plants producing important bioactive compounds has threatened the survival of some species. *In vitro* propagation through plant tissue culture techniques allows the large-scale multiplication of true-to-type plants within a short span of time and without a negative impact on the natural resources [16]. This method is particularly valuable for plants difficult to propagate by conventional techniques or with slow propagation rates. In this context, in the last years, there has been an increased interest on the use of these methodologies for the propagation and conservation of

The production of secondary metabolites by *in vitro* cultures usually occurs in a two-step process, biomass accumulation and secondary metabolites synthesis, in which both steps need to be optimized independently [3, 14]. Production could be accomplished by using undifferentiated calli, cell suspension cultures, or organized structures like shoots, roots, or somatic embryos. In some cases, a certain degree of differentiation may be needed for the biosynthesis to occur [20]. The use of differentiated organ cultures is required, for instance, when the target metabolite is only produced in specialized plant tissues or glands as is the case of essential

Among differentiated tissues, hairy roots culture offers new opportunities for the *in vitro* production of plant-valuable compounds [22]. Hairy roots are induced by the infection of plants with *Agrobacterium rhizogenes*, a Gram-negative soil bacterium. During the infection, a DNA segment (T-DNA) from the large root-inducing (Ri) plasmid of the bacterium is transferred into the genome of the infected plant. The higher level of cellular differentiation, rapid growth, genetic and biochemical stability, and maintenance facility are some of the

tive for commercial application [17].

products can be traced metabolically [19].

medicinal plants.

oils [20, 21].

**3. Culture systems**

Over the past decades, efforts have been directed at the extraction, structure elucidation, and evaluation of biological activity of many plant secondary metabolites. Plants continue to be the main source for many important bioactive molecules/pharmacophores [4, 5]. About 25–28% of modern medicines are derived from higher plants [6], and over 60% of anticancer drugs are directly or indirectly derived from plants [7]. According to a recent report of the British Broadcasting Corporation (BBC), plant-derived drugs will grow from \$29.3 billion in 2017 to around \$39.2 billion by 2022 with an annual growth rate of 5.9% [8].

In the last decades, considerable progress has been made concerning the production of secondary metabolites by using plant tissue culture techniques owing to the advantages of this platform over other production systems as discussed in the next section of this chapter. The most studied classes of plant secondary metabolites using plant cell and tissue culture production systems are alkaloids and the landmark example is the anticancer-registered drug Taxol® [3]. Plant tissue culture techniques were even endorsed by Food and Agriculture Organization as safe for the production of compounds for food application [9]. This chapter aims to discuss the main advantages of using plant cell and tissue culture techniques for the production of plant secondary metabolites as well as the different biotechnological approaches available to improve their production. Important and representative examples produced through these methods, as is the case of plant anticancer compounds and metabolites from *Lamiaceae* spp., are addressed.
