Plant antibiotics, phytoalexins

VanEtten HD, Mansfield JW, Bailey JA, Farmer EE (1994) Two classes of plant antibiotics phytoalexins versus phytoanticipins . Plant Cell 6 1191-1192... 

VANETTEN, H.D., MANSFIELD, J.W., BAILEY, J.A., FARMER, E.E., 2 Classes of plant antibiotics - phytoalexins versus phytoanticipins, Plant Cell, 1994,6, 1191-1192. 

Van Bambeke F, Glupczynski Y, Plesiat P, Pechere 1C, Tulkens PM (2003) Antibiotic efflux pumps in prokaryotic cells occurrence, impact on resistance and strategies for the future of antimicrobial therapy. J Antimicrob Chemother 51 1055-1065 VanEtten HD, Mansfield JW, Bailey lA, Farmer EE (1994) Two classes of plant antibiotics phytoalexins versus phytoanticipins. Plant Cell 6 1191-1192 Vattem DA, MihaUk K, Ciixell SH, McLean RIC (2007) Dietary phytochemicals as quorum sensing inhibitors. Fitoterapia 78 302-310... 

Over 20,000 terpenoids have been identihed (1), and more are being discovered continuously. Plant terpenoids are important in both primary and secondary (speciahzed) metabolism. Their importance in primary metabolism includes physiological, metabolic, and stmctural roles such as plant hormones, chloro-plast pigments, roles in electron transport systems, and roles in the posttranslational modihcation of proteins. In secondary metabolism, the roles of plant terpenoids are incredibly diverse but are associated most often with defense and communication of sessile plants interacting with other organisms. Examples include terpenoid chemicals that form physical and chemical barriers, antibiotics, phytoalexins, repellents and antifeedants against insects and other herbivores, toxins, attractants for pollinators or fruit-dispersing animals, host/nonhost selection cues for herbivores, and mediators of plant-plant and mycorrhiza interactions (2, 3). 

Hormonal action of oligosaccharides (10 examples). Some free oligosaccharides occur in some plants as a response to contamination, and elicit the production of phytoalexines, plant antibiotics against fungi. 

Plant phytoalexins [natural plant antibiotics] [1] have the potential of becoming a new class of useful compounds in the control of insect pests. Some phytoalexins have been demonstrated as deterrents to insect feeding. Considerable progress has been made to characterize them chemically and to extend the study of their function in plant disease resistance, but exploration of their role in the control of insect pests is just beginning. 

Another compound bordering between preformed and induced defenses is gossypol. This compound accumulates within epidermal glands on the surface of cotton plants and is very toxic to some insects [ .]. Gossypol, and a series of structurally related compounds on the same biosynthetic pathway, accumulate to substantially increased levels in plants that have been challenged by potential pathogens. For this reason they have been considered phytoalexins by some plant pathologists. Phytoalexins are inducible antibiotics and will be discussed later. 

Soybean plants can produce the antibiotic phytoalexin when exposed to a fungal /1-glucan. A phytoalexin elicitor hexasaccharide was synthesized by automation using glycosyl phosphate building blocks (Scheme 7). The functionalized resin was submitted to building blocks in a five-fold excess with stoichiometric amounts of trimethylsilyl trifluoromethanesulfonate for 15 minutes at - 15 °C. The resin was washed and treated with hydrazine to affect the deprotection of the C6 hydroxyl. The sequence was repeated three times,... 

Plant terpenes may deter herbivores and attract pollinators. They may participate in competition among plants and may act as antibiotics, called phytoalexins, to protect plants from bacteria and fungi.84 In invertebrate animals terpenes serve as hormones, pheromones, and defensive repellants (Figs. 22-3,22-4). The terpene squalene is the precursor to sterols. Some terpenes are toxic. For example, thujone (Fig. 22-3), which is present in the liqueur absinthe, causes serious chronic poison-... 

Natural products represent a diversity of chemical compounds with varied biological activities. Natural products are an important source of novel pharmaceuticals as well as agricultural pesticides (1,2). Natural products are derived from a number of pathways that create basic scaffolds that are further modified by various tailoring enzymes to create the wide diversity of structures that exist in nature. Polyketide synthases are responsible for the synthesis of an array of natural products including antibiotics such as erythromycin in bacteria (3) and mycotoxins such as aflatoxin in fungi (4). Furthermore, in plants they are part of the biosynthetic machinery of flavonoids, phytoalexins, and phenolic lipi (5,6). 

Other medically important polyketides include the antibiotics doxorubicin (14-hydroxydaunomycin Fig. 5-23), rifamycin (Box 28-and the antifimgal pimaricin, griseofulvin, and amphotericin (Fig. 21-10), the HMG-CoA reductase inhibitor lovastatin, the 2-butanyl-4-methylthreonine of cyclosporin A (Box 9-F), and other immunosuppressants such as rapamycin. Many characteristic plant products, including stilbenes and chalcones (Box 21-E), are polyketides. A variety of different polyketides serve as phytoalexins. Some such as aflatoxin are dangerous toxins. Ants and ladybird beetles make toxic polyamine alkaloids using a polyketide pathway. ... 

A general term for compounds whose biosynthesis is elicited or induced in plants as the result of attack by a pest is "phytoalexin". These higher plant metabolites are antibiotic to certain potential plant pathogens and also on occasion to insects (Chapter 13 of this volume). The phytoalexins typically are biosynthesized in greater concentrations when the plant is subjected to stress. Therefore, the attacking agent (fungi, bacteria, or viruses in most work to date) elicits the initiation or increased synthesis of phytoalexins (antibiotic compounds). 

Hydroxylated derivatives of stilbene (stilbenoids) are secondary products of heartwood formation in trees that can act as phytoalexins (antibiotics produced by plants). 

Several sesquiterpenes play well-defined and essential roles in higher and lower plants, including the hormone abscisic acid, furanoid phytoalexins, lactone antifeedants, and numerous fungal antibiotics (Herout, 1971 Rucker, 1972). No specific function has been demonstrated for most sesquiterpenes however, an allelopathic or allelochemic role is commonly ascribed to these compounds, as for monoterpenes. Like monoterpenes, sesquiterpenes are not metabolically inert, but are rapidly synthesized and catabolized (Croteau and Loomis, 1972 Francis, 1972) and thus may also play a dynamic role in metabolism. Virtually nothing is known about the catabolism of sesquiterpenes. 

Isol. from the sponge Ircinia strobilina and a Sarcotragus sp. Plant phytoalexin with antibiotic props. Oil. [a]u -4° (c, 1 in CHCI3). 255 nm (MeOH). 20E-Isomer [114761-90-9]. 

Plants produce a variety of chemicals to survive attacks by microbial invasion (Grayer and Harbome 1994). These metabolites are either preformed in the plant (prohibitins) or induced after infection (phytoalexins). Since phytoalexins can also be induced by abiotic factors such as UV irradiation, they have been defined as antibiotics formed in plants via a metabolic sequence induced either biotically or in response to chemical or environmental factors. Many of these substances have been identified as flavonoids (Cowan 1999). Extraction of flavonoids and identification of their antimicrobial activity is useful not only for finding new drugs but also for obtaining natural products useful as food additives to improve the shelf life and safety of foods. In fact, an aliment can be deteriorated by spoilage bacteria, that cause and develop unpleasant odours, taste and texture, whereas foodbome pathogenic bacteria may cause diseases with flu-like symptoms such as nausea, vomiting, diarrhoea, and/or fever. Food additives with antimicrobial activity can be used to overcome such problems, but consumers tend to reject the present use of additives obtained by chemical synthesis flavonoids, as additives derived from natural products, can be a valid and preferred alternative (Cowan 1999). 

---