Catabolism of Endogenous and Exogenous Compounds by Plant Cell Cultures

Abstract

A. IntroductionMany reports in the literature over the past decade have established that higher plants possess a much greater capacity than previously expected for the degradation of a wide variety of organic compounds (3,19,23,55). These observations are of special interest in the field of secondary plant constituents because such compounds were generally regarded as storage products without any further metabolism during the life time of a plant (49, 54). The present concept, however, holds that. the majority of plant products is in a state of permanent metabolism with concomitant synthesis and degradation of both primary and secondary constituents. Therefore, stationary concentrations of plant products are the result of the ratio of the rate of synthesis and turnover (steady-state-concentrations) (for details see 3,5,70).Turnover of plant products in plants primarily consists of two types of reactions (1) complete degradative pathways leading to primary constituents and finally CO 2 and (2) polymerisation reactions where organic material is tightly bound into cell wall and membrane structures. The ratio of these two reactions depends upon both the availability of enzymes and the chemical structure of the compounds involved. Cell cultures offer many advantages for the elucidation of catabolic pathways. The reliable absence of microorganisms and the ease of physiological manipulation of cells with phytohormones and various other molecular effectors require special emphasis (4, 5).In the context of biotechnological application of cell cultures the phenomenon of degradation of cellular constituents is of twofold importance:1. Extensive production of secondary constituents should best occur without any loss of intermediates or endproducts by degradative reactions, 2. Applicable biotransformations with cell cultures require high rate of substrate conversion with subsequent protection of product from catabolic reactions.Turnover of endogenous and catabolism of exogenous compounds will separately be discussed because of possible differences in the metabolism of endogenously formed and exogenously applied compounds. Compartmentalization of cells may hinder exogenous compounds to reach t~e natural. site of cellular metabolism but rather lead to unphysiolog~cal react~ons, altered pathways or the preferential formation of storage products (34,63

In vitro propagation of Senecio candicans DC and comparative antioxidant properties of aqueous extracts of the in vivo plant and in vitro-derived callus

“…As the callus growing in a nutrient-rich culture medium is undoubtedly exposed to more carbon influx than the field-grown plant parts, it may influence the metabolic flux for the biosynthesis of elevated levels of phenolics (Lukmanul et al, 2007). The accumulation of phenolics in the callus is based on the abundance of carbon source in the medium (Paula et al, 2002), and also depends on the growth rates of the cultured tissue (Barz, 1977), and on auxin/cytokinin levels into the medium (Sargent and Skoog, 1960;Skoog and Montaldi, 1961). Environmental factors such as the incubation period, light and dark conditions, and temperature have an impact on callogenesis.…”

Shoot Multiplication and Callus Induction of Labisia pumila var. alata as Influenced by Different Plant Growth Regulators Treatments and Its Polyphenolic Activities Compared with the Wild Plant

“…Since callus growth in a nutrient-rich culture medium is inevitably subjected to greater carbon influx than field-grown plant specimens, it may affect the metabolic flux for the biosynthesis of elevated levels of phenolics [ 66 ]. The production of phenolics in the callus is determined by the abundance of the carbon source in the medium [ 67 ], as well as the growth rates of the cultured tissue [ 68 ] and the levels of auxin/cytokinin in the medium [ 69 , 70 ].…”

Plant Growth Regulators I: Introduction; Auxins, their Analogues and Inhibitors

“…The natural rate of formation of some phenolic compounds has been observed to depend on the rate of growth of cultured tissues (Barz, 1977) and on auxin/cytokinin levels in the medium (Sargent and Skoog, 1960;Skoog and Montaldi, 1961). Their presence has frequently been correlated with the morphogenetic capacity of tissues (Tryon, 1956;Hackett, 1970;Kefeli and Kadyrov, 1971).…”