Antimicrobial properties of tannins

Tannins are phenolic compounds of widespread occurrence in higher plants. They have complicated structures that have only recently been unraveled by natural products chemists. They are not known to have any physiological function. So what do they do? Examination of their structures and consideration of several possible roles, especially as defensive compounds against plants' enemies, allows much speculation. It is proposed that the enormous structural heterogeneity and natural division of tannins into two broad classes, the condensed and hydrolyzable, has important ecological consequences. It is argued that their structures suggest strong specificities for a variety of target molecules including proteins, digestive enzymes, and polysaccharides. These specificities insure mainline defense against plant enemies, but are nevertheless subject to the coevolutionary "arms race" (Feeny 1976). The idea that condensed tannins are reserved primarily for defense against microbes and pathogens, while the hydrolyzable...

Tannins: does structure determine function? An ecological perspective

Over the past four decades ecosystem scientists have stressed that biotic and abiotic system components must be studied in concert. This philosophy maintains that an ecosystem is a harmonious interplay between organisms and their environment and possesses cybernetic properties that " . . . make possible the orderly cycle of life" ( 84). Although some researchers have emphasized that organisms and their behavior are the building blocks of an ecosystem (5 8, 105), most ecosystem research has been process rather than entity oriented (93). Functional groups, the basic units of an ecosystem model, have usually been defined by broad taxonomic relationships even though criteria that describe roles in a system would be more suitable. Once there is a clear understanding of what roles organisms have, studies can be· directed at how organisms interact to generate ecosystem dynamics.

Arthropod regulation of micro- and mesobiota in below-ground detrital food webs

Polymeric proanthocyanidins are common constituents of many foods and beverages. Their fate in the human body remains largely unknown. Their metabolism by human colonic microflora incubated in vitro in anoxic conditions has been investigated using nonlabeled and (14)C-labeled purified proanthocyanidin polymers. Polymers were almost totally degraded after 48 h of incubation. Phenylacetic, phenylpropionic and phenylvaleric acids, monohydroxylated mainly in the meta or para position, were identified as metabolites by gas chromatography coupled to mass spectrometry (GC-MS). Yields were similar to those previously reported for flavonoid monomers. These results provide the first evidence of degradation of dietary phenolic polymers into low-molecular-weight aromatic compounds. To understand the nutritional properties of proanthocyanidins, it is therefore essential to consider the biological properties of these metabolites.

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Polymeric proanthocyanidins are catabolized by human colonic microflora into low-molecular-weight phenolic acids.

The latest previous comprehensive review of allelopathy (Rice, 1974) covered research done primarily prior to 1973. There have been numerous reviews published in recent years on specific phases of allelopathy (see III), but most of them covered research results published primarily through 1972 also. This review has been restricted, therefore, largely to research conducted subsequent to 1972, except for background information and significant papers overlooked in previous reviews. There has been almost an exponential increase in the rate of publication of papers concerned with allelopathy. Research has been particularly active in relation to the roles of allelopathy in agriculture, forestry, phytopathology, patterning of vegetation, algal succession, and old-field succession. Our increasing knowledge of the conditions under which certain crop residues cause allelopathic effects to subsequent crops should enable us soon to guard against such effects. We are on the threshold of breeding crop plants that will inhibit the chief weeds in a given area through allelopathic action, and thus decrease the need for synthetic weed killers. Our understanding of allelopathic interactions of various plant species has already been used advantageously in reforestation, and future developments are very encouraging. Our increasing knowledge of allelopathy is aiding greatly in our understanding of many ecological phenomena, such as succession and patterning of vegetation. Evidence is mounting that inhibition of nitrification increases as succession progresses toward the climax vegetation, at least in many vegetation types. This leads to a decrease in the loss of nitrogen. Addition of inhibitors to arable lands to prevent nitrification has proved to be valuable in preventing loss of nitrogen and in increasing crop yields. There has been a rapid advance in our knowledge of mechanisms of action of known allelopathic compounds, at increasingly more fundamental levels. We have known for several years, for example, that some of these compounds inhibit uptake of various minerals, but have not known the mechanism of the action. Recent research indicates this may be due, at least in part, to inhibition of a plasma membrane ATPase that is involved with ion absorption. A thorough knowledge of mechanisms of action of allelochemics is essential to our overall understanding and appreciation of the field of allelopathy.

Allelopathy—An update

A strain of Penicillium adametzi Zaleski was isolated from enrichment cultures with condensed tannins as the carbon source. Low-molecular-weight condensed tannins, extracted and purified from Pinus radiata bark, were used as substrates for quantitative growth measurements on this fungus in defined culture conditions.

http://science.sciencemag.org/content/sci/193/4258/1137.full.pdf

WD Grant

Papers

Microbial degradation of condensed tannins