Plants stilbenes

Morita H, Noguchi H, Schroder J, Abe I (2001) Novel polyketides synthesized with a higher plant stilbene synthase. Eur J Biochem 268 3759-3766... 

Stilbenolignans are a third interesting group of non-conventional lignans produced by plants. Stilbenes, like flavonoids, are believed to be metabolites of mixed biosynthetic origin and derived from a cinnamoyl CoA and three malonate units... 

I would like to discuss here also a very hypothetical concept of the enzyme s regulation. With rhubarb plants stilbenes are only synthesized in the rhizome. I wonder whether signals released in chloroplasts of leaf cells by light-mediated production of reduced thiol compounds can be passed on the cytoplasm or even to other cells, e. g. cells of the rhizome where a compound like thioredoxine could exert control of the activity of distinct enzyme, e. g. stilbene synthase. 

Stilbenes are a small group of phenylpropanoids characterized by a 1,2-diphenylethylene backbone. Most plant stilbenes have phytoalexin activity and are mainly derivatives of the monomeric unit frans-resveratrol (trans-R, 3,4, 5-trihydroxystilbene) although other stilbene structures are found in plants. 

Verpoorte R, Contin A, Memelink J (2002) Biotechnology for production of plant secondary metabolites. PhytochemRev 1 13-25. doi 10.1023/A 1015871916833 Morales M, Ros Barcelo A, Pedreno MA (2000) Plant Stilbenes recent advances in their chemistry and biology. In Hemantaranjan A (ed) Advances in plant physiology, 1st edn. Scientific Publishers, Jodhpur... 

Metabolism of Lunularic Acid to a New Plant Stilbene by Lunularia cruciata. Phytochem. 11, 1355 (1972). 

Biosynthesis of Plant Stilbenes Part II. Formation of Ring A of Hydrangenol. Monatsh. Chem. 93, 814 (1962). 

Phytoalexins are low molecular weight compounds produced in plants as a defense mechanism against microorganisms. They do, however, exhibit toxicity to humans and other animals in addition to microbes (30). Coumarins, glycoalkaloids, isocoumarins, isoflavonoids, linear furanocoumarins, stilbenes, and terpenes aU. fall into the category of phytoalexins (31). Because phytoalexins are natural components of plants, and because their concentration may increase as a response to production and management stimuli, it is useful to recogni2e the possible effects of phytoalexins in the human diet. 

Glycosides, particularly of phenoHc compounds, are widely distributed in plant tissues (2,10). Glycosides of anthocyanidins, flavones, flavanols, flavanones, flavanonols, stilbenes and saponins, gaUic acid derivatives, and condensed tannins are all common. 

Watts, K. T., R C. Lee et al. (2006). Biosynthesis of plant-specific stilbene polyketides in metabolically engineered Escherichia coli. BMC Biotechnol. 6 22. 

Stilbenes have a 1,2-diphenylethylene as their basic structure (C6-C2-C6). Resve-ratrol, the most widely known compound, contains three hydroxyl groups in the basic structure and is called 3,4, 5-trihydroxystilbene. In plants, piceid, the glucoside of resveratrol, is the major derivative of resveratrol. Stilbenes are present in plants as cis or trans isomers. Trans forms can be isomerized to cis forms by UV radiation (Lamuela-Raventos and others 1995). 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

Condensation of coumaric acid with malonic acid yields the basic chalcone and stilbane skeletons (see Fig. 3.6). Stilbenes are found in most vascular plants, where they exhibit fungicidal and to a lesser extent antibiotic properties. They function as both constitutive and inducible defense substances. Some stilbenes inhibit fungal spore germination and hyphal growth, whereas others are toxic to insects and parasitic nematodes (round-worms). They also possess antifeeding and nematicide properties in mammals. For example, resveratrol (a stilbene in red wine) suppresses tumor formation in mammals. 

Chalcone Synthase / Stilbene Synthase Family of Plant Polyketide Synthases. 199... 

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... 

In this chapter, we describe the atomic resolution structural elucidation of several plant type III polyketide synthases, including chalcone synthase, 2-pyrone synthase, and stilbene synthase. Manipulation of the catalytic activity and specificity of these biosynthetic enzymes by using a structurally guided approach offers a novel... 

CHALCONE SYNTHASE / STILBENE SYNTHASE FAMILY OF PLANT POLYKETIDE SYNTHASES... 

PKSs are characterized by their ability to catalyze the formation of polyketide chains from the sequential condensation of acetate units from malonate thioesters. In plants they produce a range of natural products with varied in vivo and pharmacological properties. PKSs of particular note include acridone synthase, bibenzyl synthase, 2-pyrone synthase, and stilbene synthase (STS). STS forms resveratrol, a plant defense compound of much interest with regard to human health. STS shares high sequence identity with CHS, and is considered to have evolved from CHS more than once. ° Knowledge of the molecular structure of the CHS-like enzymes has allowed direct engineering of CHS and STS to alter their catalytic activities, including the number of condensations carried out (reviewed in Refs. 46, 51, 52). These reviews also present extensive, and superbly illustrated, discussions of CHS enzyme structure and reaction mechanism. 

Tropf, S. et al., Reaction mechanisms of homodimeric plant polyketide synthases (stilbenes and chalcone synthase) a single active site for the condensing reaction is sufficient for synthesis of stilbenes, chalcones, and 6 -deoxychalcones. J. Biol. Chem., 270, 7922, 1995. 

Fischer, R., Budde, L, and Hain, R., Stilbene synthase gene expression causes changes in flower colour and male sterility in tobacco. Plant J., 11, 489, 1997. 

No. Flavanone Formula Flavanone-stilbenes (Figure 15.7) Mr Plant Source Family Organ Ref. 

Stilbenes are naturally occurring phytoalexins found in medicinal plants of Polygonum species and Rheum species (Polygonaceae) [10,11]. Among... 

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