Secondary metabolites plant

Among the worldwide total of 30 000 known natural products, about 80% stems from plant resources. The number of known chemical structures of plant secondary metabolites is four times the number of known microbial secondary metabolites. Plant secondary metabolites are widely used as valuable medicines (such as paclitaxel, vinblastine, camptothecin, ginsenosides, and artemisinin), food additives, flavors, spices (such as rose oil, vanillin), pigments (such as Sin red and anthocyanins), cosmetics (such as aloe polysaccharides), and bio-pesticides (such as pyrethrins). Currently, a quarter of all prescribed pharmaceuticals compounds in industrialized countries are directly or indirectly derived from plants, or via semi-synthesis. Furthermore, 11% of the 252 drugs considered as basic and essential by the WHO are exclusively derived from plants. According to their biosynthetic pathways, secondary metabolites are usually classified into three large molecule families phenolics, terpenes, and steroids. Some known plant-derived pharmaceuticals are shown in Table 6.1. 

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JulsingMK et al. (2006) Combinatorial biosynthesis of medicinal plant secondary metabolites. Biomol Eng 23(6) 265-279... 

The quantity, quality and purity of the template DNA are important factors in successful PGR amplification. The PGR is an extremely sensitive method capable of detecting trace amounts of DNA in a crop or food sample, so PGR amplification is possible even if a very small quantity of DNA is isolated from the sample. DNA quality can be compromised in highly processed foods such as pastries, breakfast cereals, ready-to-eat meals or food additives owing to the DNA-degrading action of some manufacturing processes. DNA purity is a concern when substances that inhibit the PGR are present in the sample. For example, cocoa-containing foodstuffs contain high levels of plant secondary metabolites, which can lead to irreversible inhibition of the PGR. It is important that these substances are removed prior to PGR amplification. Extraction and purification protocols must be optimized for each type of sample. 

Bourgaud,F., Gravot, A., Milesi, S. and Gontier, E. (2001) Production of plant secondary metabolites ahistorical perspective. Plant Science (Shannon, Ireland), 161 (5), 839-851. 

Another field of research is the possibility offered by phytochemicals in protecting plants against diseases and pathogens (fungus, bacteria and nematodes). Numerous studies have suggested that plant-pathogen interactions are partially mediated via plant secondary metabolite production, despite the inconsistency revealed by some works on the ability of particular compounds to provide resistance to a specific pathogen. 

Theis N and Lerdau, M (2003), The evolution of function in plant secondary metabolites , Int. J. Plant Sci., 164 (3 Suppl.), S93-S102. 

Wink M (1999), Introduction biochemistry, role, and biotechnology of secondary metabolites , in Michael Wink, Functions of Plant Secondary Metabolites and their Exploitation in Biotechnology, Annual Plant Reviews, Academic Press, UK, 3, 1-16. 

Heldt HW and Heldt F. 2005. Phenylpropanoids comprise a multitude of plant secondary metabolites and cell wall components. In Plant Biochemistry, 3rd ed. San Diego, CA Elsevier Academic Press, pp. 435 154. 

WINK, M., Functions of Plant Secondary Metabolites and their Exploitation in Biotechnology, Sheffield Academic Press, 1999, 362 p. 

Recently, a new polyketide biosynthetic pathway in bacteria that parallels the well studied plant PKSs has been discovered that can assemble small aromatic metabolites.8,9 These type III PKSs10 are members of the chalcone synthase (CHS) and stilbene synthase (STS) family of PKSs previously thought to be restricted to plants.11 The best studied type III PKS is CHS. Physiologically, CHS catalyzes the biosynthesis of 4,2, 4, 6 -tetrahydroxychalcone (chalcone). Moreover, in some organisms CHS works in concert with chalcone reductase (CHR) to produce 4,2 ,4 -trihydroxychalcone (deoxychalcone) (Fig. 12.1). Both natural products constitute plant secondary metabolites that are used as precursors for the biosynthesis of anthocyanin pigments, anti-microbial phytoalexins, and chemical inducers of Rhizobium nodulation genes.12... 

Humphrey AJ, Beale MH (2006) Terpenes. In Crozier A (ed) Plant secondary metabolites in diet and health. Blackwell, Oxford, pp 47-101... 

McKey D (1974) Adaptive patterns in alkaloid physiology. Am Nat 108 305-320 McKey D (1979) The distribution of secondary compounds within plants. In Rosenthal GA, Janzen DH (eds) Herbivores their interactions with plant secondary metabolites. Academic, New York, pp 55-133... 

In order for allelochemicals to enter the body of a herbivore, absorption must occur across the gut lining. Curtailing the initial absorption of dietary allelochemicals may be a herbivore s first line of defense against plant toxins. Studies have citied the lack of absorption or metabolism of lipophilic plant secondary metabolites (i.e., terpenes), conducive to phase I or II detoxification, in the gut of terrestrial herbivores rather these compounds are excreted unchanged in the feces (Marsh et al. 2006b). While physical barriers or surfactants have been used to explain this limited adsorption in both marine and terrestrial herbivores (Lehane 1997 Barbehenn and Martin 1998 Barbehenn 2001 for review of marine herbivores, see Targett and Arnold 2001), active efflux of plant allelochemicals out of enterocytes into the gut lumen has received limited attention until now. 

Foley WJ, Moore BD (2005) Plant secondary metabolites and vertebrate herbivores - from physiological regulation to ecosystem function. Curr Opin Plant Biol 8 430 135 Freeland WJ (1991) Plant secondary metabolites biochemical coevolution with herbivores. In Palo RT, Robbins CT (eds) Plant defenses against mammalian herbivory. CRC, Boca Raton, FL, pp 61-81... 

Wadleigh RW, Yu SJ (1988) Detoxification of iso thiocyanate allelochemicals by glutathione transferase in three lepidopterous species. J Chem Ecol 14 1279-1288 Werck-Reichhart D, Feyereisen R (2000) Cytochromes P450 a success story. Genome Biol 1 1-9 Williams AB, Jacobs RS (1993) A marine natural product, patellamide D, reverses multidrug resistance in a human leukemic cell line. Cancer Lett 71 97-102 Yazaki K (2006) ABC transporters involved in the transport of plant secondary metabolites. FEBS Lett 580 1183-1191... 

Terpenoids and Steroids. The Information given in Tables IV-VII and the blogenetlc relationships shown in Figures 2 and 3 speak for themselves. This class of compounds accounts for more than one-third of the known cotton plant secondary metabolites. The monoterpenoids listed in Table V, many of which have the para-menthane skeleton, are generally common compounds widely spread in the essential oils of plants. 

At the cellular level, plant secondary metabolites have five major effects on herbivores (a) alteration of DNA replication, RNA transcription, and protein synthesis (b) alteration of membrane transport processes (c) enzyme inhibition and activation (d) blocking of receptor sites for endogenous chemical transmitters and (e) affecting the conformation of other macromolecules (Robinson, 1979). 

Plant secondary metabolites and nutrients in fruits and seeds... 

How much a mammal eats of a given plant often depends on the levels of different classes of chemical constituent, notably nutrients and plant secondary metabolites. As in birds, it is not the plant defense compounds alone, but rather complex balances between nitrogen and carbohydrate contents, levels of defense compounds, and fiber that determine palatability. 

Table 11.5 Plant secondary metabolites inhibiting feeding by birds...

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