Phenols bioassays

Oryza sativa decomposing straw phenolics toxic in lettuce rice seed bioassays mungbean root assay 119... 

Studies used in the meta-analyses of induction of resistance (using bioassays) and induction of phenolics are marked with and respectively. 

Phenol has been tested in animals for carcinogenicity by the oral and dermal routes, but results are equivocal. In a chronic NCI cancer bioassay (NCI 1980), a significant incidence of tumors (pheochro-mocytomas of the adrenal gland, leukemia, or lymphomas) occurred only in male rats exposed to the lowest dose level (2,500 ppm, 277 mg/kg/day) of phenol but not in male or female mice or male rats exposed to a higher dose level (5,000 ppm, 624 mg/kg/day). Since tumors occurred only in males in one of the two species tested, and since a positive dose-response relationship was not established, this study does not provide sufficient evidence to conclude that phenol is carcinogenic when administered by the oral route. Dermal application of phenol has been shown to result in tumors in mice phenol is a tumor promoter when it is applied after the application of the tumor initiator DMBA (Boutwell and Bosch 1959 Salaman and Glendenning 1957 Wynder and Hoffmann 1961). However, this effect occurs at dose levels of phenol that produce severe skin... 

NCI. 1980. Bioassay of phenol for possible carcinogenicity. Bethesda, MD U.S. Department of Health and Human Services. National Cancer Institute. Technical Report Series No. NCI-CG-TR-203. 

Thus, a synthetic source of promising allelochemicals is essential if we are to comprehensively study the agent s mode of activity and establish its basic structure-activity profile. The proposed work addresses this need. We will synthesize alleopathic natural products isolated from the sunflower (the heliannuols), and structurally related compounds, in optically pure form based on biomimetic phenol-epoxide cyclizations. The bioactivity of the targets and intermediates will be evaluated through laboratory tests on plant germination and growth. Bioassays will be performed on the synthetic intermediates to allow for the development of a preliminary structure-activity profile for these novel natural herbicides. 

National Cancer Institute Bioassay of Phenol for Possible Carcinogenicity. CAS No 108-95-2, NCI-CG-TR-203, NTP-80-15. DHHS (NIH) Pub No 80-1759, 123pp. Washington, DC, US Government Printing Office, August 1980. 

It is also important to understand that most allelopathic effects apparently result from the combined actions of several allelochemicals, often with each below a threshold concentration for impact. In allelopathic situations which implicate phenolic acids, soil concentrations have ranged from below 10 to above 1000 ppm for each compound. The lower end of the spectrum is below a concentration required for an effect in current bioassays. Additive and synergistic effects have been demonstrated, however, for combinations of cinnamic acids (102), benzoic acids (103), benzoic and cinnamic acids (10 ). and -hydroxybenzaldehyde with coumarin (105). It appears that such combined interactions may be very important under field conditions. 

I often observed that under greenhouse conditions there was considerable variation in the effect a particular concentration of a phenolic inhibitor had on the growth of seedlings. Since procedures used in these bioassays were quite uniform, it was logical that environmental factors were influencing the results. 

Several lines of evidence support the conclusion that allelopathic inhibition of germination and plant growth typically occurs from the joint action of several allelochemicals. Additive or synergistic effects have been shown in bioassays with combinations of monoterpenes, organic acids, and several classes of phenolic compounds. These experiments demonstrate that a specific compound may be present below its threshold for inhibition and still be active in allelopathic interference by its effect in concert with other allelochemicals. 

B-rings of their constituent dihydrochalcone monomers. A concise synthesis of verbenachal-cone (316) by catalytic copper-mediated coupling of phenol and aryl halides has been reported by Xing et al., who also prepared two further derivatives for preliminary structure-activity studies. One of the latter, the corresponding bichalcane (deoxo) derivative of verbenachalcone showed no activity in the neural outgrowth stimulation bioassay mentioned above. 

Since phenolic compounds are ubiquitous in many plants, another, more-specific method for examination of the extract was sought. The ideal method would allow homologs of 1 to 3 to be targeted specifically. (By this point of the work, the PKC inhibition bioassay was no longer available to us as a screening tool. In any event, this bioassay would not readily pick up homologs of 1 to 3 which were inactive, yet which are important for structure-activity relationship studies.) The most practical method proved to be the use of MS and MS-HPLC techniques to identify potential homologs in the extract. 

In relation with phenolics, Indeqit et al. (1997) conducted a study to understand the effects of certain phenolics, terpenoides, and their equimolar mixture through agar gel and soil growth bioassays and their recovery from soils. The eight compounds... 

Low molecular weight phenolic compounds have been identified in fresh leaves and in soils in which leaves of five varieties of Capsicum annuum were decomposing. Six phenolic compounds were tested in laboratory bioassays for their allelopathic... 

The results of file bacterial bioassays indicated that file toxicity of the samples was caused mainly (75%) by phenols (p-cresol, 3,4-dimefiiylphenol, and phenol), and to a lesser degree by sulfates (about 25%)... 

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