Toxic effects plant phenols

The biochemical mechanisms through which allelochemicals exert deleterious or toxic effects on plants are, for the most part, unknown (1). Some phenolic acids, cinnamic acids, coumarins, and flavonoids have been reported to inhibit photosynthesis and respiration of intact plants and microorganisms. However, the mechanisms, at the molecular level, through which the compounds interfere, remain to be ascertained. Some phenolic acids, coumarins, and flavonoids were reported to Inhibit C02-dependent 0 ... 

For many years, the cytoprotective effects of plant phenolic compounds were attributed to their ability to direct scavenge oxidants and free radicals. However, as discussed in the last section, this concept is oversimplified and misleading. More and more evidence suggess that plant phenolic compounds could interact with cellular components and trigger a series of cellular responses, which are able to modulate the redox status of the cells and protect the cells from potentially toxic electrophiles/oxidants. 

At present, the percentage contribution of vitamins to the cancer-protective activity of vegetables or fruits is unknown. In this paper, we present results suggesting an involvement of naturally occurring phenolics in the prevention of genotoxicity and carcinogenicity. Since the number of phenolics in various plants is staggering and the discussion of their beneficial or toxic effects is beyond the scope of any short review, we have focused on non-flavonoid simple phenolics (C6), phenolic acids (C6-C1), cinnamic acid and related compounds (C6-C3). 

To the consumer, the most evident properties of phenolic compounds are the colors and the astringent taste they impart to foods. With few exceptions such as safrole and coumarin, most low molecular weight plant phenols have been shown to be non-toxic/non-carcinogenic in experimental animals. Further, plant phenols form a very small portion of total food intakes under normal food consumption patterns and would not be likely to have any serious toxic or antiphysiological effects. It is therefore reasonable to ask, why consider food safety of plant polyphenols Some of the reasons include ... 

Insofar as phenolic acids synthesised by plants influence the grov/th of other plants, the effects, whether toxic or stimulatory, are allelopathic (i.e. they represent a biochemical interaction between plants). The subject of allelopathy has been reviewed extensively by Rice and by Putnam and Duke, and in this review only those effects involving phenolic acids will be considered. 

Essential oils are known to have detrimental effects on plants. The inhibitory components have not been identified, but both alde-hydic (benzol-, citrol-, cinnamal-aldehyde) and phenolic (thymol, carvacol, apiol, safrol) constituents are suspected. Muller et al. (104) demonstrated that volatile toxic materials localized in the leaves of Salvia leucophylla, Salvia apiana, and Arthemisia californica inhibited the root growth of cucumber and oat seedlings. They speculated that in the field, toxic substances from the leaves of these plants might be deposited in dew droplets on adjacent annual plants. In a subsequent paper, Muller and Muller (105) reported that the leaves of S. leucophylla contained several volatile terpenes, and growth inhibition was attributed to camphor and cineole. 

Enrichment of processed food with plant material or plant extracts rich in polyphenols has two aspects in relation to human nutrition and human health. Food protected against oxidation has better keeping quality and will stay healthy longer since formation of toxic oxidation products, like cholesterol oxides, is being prevented (Britt et al., 1998). The other aspect is the beneficial effects of the intake of polyphenols on human health. Both of these aspects are, however, related to the availability of the phenolic substances. 

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