Capsaicin biosynthesis in cell cultures of Capsicum frutescens

Webb, C. Book author
Mavituna, F. Book author

Chichester, West Sussex Ellis Horwood United Kingdom

1987

p.45-63

REP.PP-0535

The use of plant-cell cultures as a source of valuable products of secondary metabolism has been under investigation for over twenty years. The initially slow progress which has been made in the utilisation of cell cultures for the production of biochemicals has been largely due to the generally low levels of product formation in cultured cells in comparison with the parent plant. However, there are some recent examples where manipulation of the culture conditions, predominantly by altering media constituents, can increase culture yields to the same level or even higher than the parent plant (Brodelius, 1985). Indeed, one such product, shikonin, a dye with antibacterial and anti-inflammatory properties, is now produced commercially using cultures of Lithospermum erythrorhizon (Curtin, 1983). Other treatments have also been developed which increase culture yield. The addition to cultures of precursors has been shown to result in higher accumulation of the desired product (e.g. Brodelius and Nilsson, 1980; Yeoman et al., 1980; Lindsey and Yeoman, 1984b). Fungal and bacterial elicitors have also increased product synthesis in a number of systems (e.g. Lamb et al., 1983). The physical as well as the chemical environment of the cultured cells can also be manipulated in order to increase product accumulation, and one of the most promising tools for physical manipulation is cell immobilisation. Different methods of immobilisation have been reported to increase product yield over the levels found in freely suspended cultures for a range of species (Lindsey et al., 1983; Brodelius, 1985; Lindsey and Yeoman, 1985). The first techniques developed for plant cell immobilisation employed cell entrapment within a variety of gel-forming polymers. The gel most commonly used has been calcium alginate, although other polymers have been employed with variable success (Brodelius and Nilsson, 1980). Another method of plant-cell immobilisation which also derives from techniques developed for animal and microbial cell entrapment involves the use of hollow fibres. The plant cells are cultured on bundles of membranous hollow fibres through which medium is pumped and the whole structure is maintained inside a sterile sheath (Shuler, 1981; Prenosil and Pedersen, 1983). A third method of immobilisation of plant cells has recently been developed (Lindsey et al., 1983). Blocks of polyurethane foam of defined pore size are used as the entrapment matrix which, when placed in a suspension culture, become invaded with plant cells which divide and thereby become trapped in a purely natural process. The results presented in this chapter were obtained from studies using this method of immobilisation. The accumulation of capsaicin (the hot flavour compound of chilli pepper fruit) in cell cultures of Capsicum frutescens has been used as an experimental system to study the regulation of secondary metabolite production. Capsaicin biosynthesis in cell cultures is of particular interest in studying the relationship between primary and secondary metabolism as the accumulation of this secondary product is under tight control in the whole plant. Synthesis of capsaicin in the plant occurs over a relatively short period during the later stages of fruit development (Iwai et al., 1979), and the pathway is expressed in only one organ of the plant, namely the fruit and not in roots, shoots or leaves. However, suspension cultures derived even from stem tissue will synthesise capsaicin when given the appropriate culture conditions (Lindsey and Yeoman, 1984b). In order to understand the biochemical basis of this metabolic differentiation, a comparison has been made of the regulation of the accumulation of capsaicin in suspension cultures, immobilised cell cultures and in the whole fruit of C. frutescens.

Plant and animal cells: process possibilities

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