Bioassay herbicide

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. 

We also plan to perform bioassays on synthetic intermediates and target compounds to allow for development of a preliminary structure-activity profile for these novel herbicides. 

In 1989 Cutler et al.1 reported the isolation of 3,7-dimethyl-8-hydroxy-6-methoxyisochro-man (1) from Penicillium corylophilum and demonstrated that it inhibited etiolated wheat coleoptiles at 10-3 and 1(T4M, as did the acetoxy (2) and methoxy (3) derivatives (Figure 5.1).2 The Parent compound had originally been isolated from moldy millet hay implicated in the death of cattle,3 but the metabolite had not been tested in plants. Because of the encouraging results obtained in the wheat coleoptile bioassay, isochromans 1,2, and 3 were assayed on greenhouse-grown bean, com, and tobacco plants. The methyl ether exhibited the greatest herbicidal activity in all the plants treated, while the parent and its acetoxy derivative were active only on corn. 

Reddy and Locke isolated [420] the herbicide imazaquin from soil by carbon dioxide supercritical fluid chromatography [421] corn root bioassay and electrospray mass spectrometry have also been used to determine this herbicide. 

Bogdanffy, M.S., J.C. O Connor, J.F. Hansen, V. Gaddamidi, C.S. Van Pelt, and J.C. Cook (2000). Chronic toxicity and oncogenicity bioassay in rats with the chloro-.v-triazinc herbicide cyanazine. J. Toxicol. Environ. Health, 60 567-586. 

Distributions of the MOE have been presented for individual exposure pathways (drinking water ingestion, dietary consumption, and herbicide handling), for the combined exposure pathways, and for atrazine and simazine both separately and combined. The MOEs have been calculated using a lower bound on the ED10 for the most sensitive effect in the most sensitive sex, strain, and species studied in chronic animal bioassays (i.e., mammary tumors in female SD rats). This mammary tumor response in the SD rat is not relevant to humans (IARC, 1999 United Kingdom, 2000 USEPA, 2003 Australia, 2004). 

Assessments of environmental impacts from herbicides are usually done at the single-species level. These assessments use toxicological data from laboratory bioassay tests and estimates of exposure from laboratory or field studies of environmental chemistry. Few tests have assessed the impacts of herbicides on organisms in the field and few, if any, at the ecosystem level. There are two main reasons why there have been so few field or ecosystem tests They are exceedingly difficult and costly, and the current philosophies of risk assessment have evolved from classical toxicology and the federal regulatory framework that covers pharmaceuticals, food additives, and pesticides. 

Bioassays, with respect to detecting a specific phenotype which confers herbicide resistance... 

Gentile, J.M., E.D. Wagner, and M.J. Plewa. The detection of weak recombinogenic activities in the herbicides alachlor and propachlor using a plant-activation bioassay. Mutat. Res. 48 113-116, 1977. 

Since the use of techniques to measure IAA, bioassays have been important to discover PGR activity of many other compounds. Several bioassays for the PGR gibberellic acid (GA3) have been developed. One bioassay was based on reduction of amaranthin levels in Amaranthus caudatus (tassel flower) seedlings.63 This method was sensitive to GA3 from 0.01 to 1 mg L"1. GA3 was also bioassayed, based on anthocyanin reduction in tomato (Lycopersicon esculentum L.).62 Reduction of anthocyanin in tomato seedlings was linear from 10"5 to 10 mg L 1, and thus, this latter plant bioassay method was more sensitive. A multitude of bioassays for nonvolatile and volatile plant growth regulator compounds have been developed and their uses and limitations have been discussed.129 Since many allelochemicals have been shown to have relatively weak phytotoxicity (especially compared to herbicides), some of these bioassays that have been developed for detecting and quantitatively measuring PGR activity may be useful in allelopathy. 

Specific molecular bioassays can be indispensable in screening compounds that act on certain biosynthetic pathways or enzymes. For example, recent patents report a screening bioassay for detection of herbicides that specifically inhibit the plant purine biosynthetic pathway. Many enzymes are involved in this... 

Leaf discs have commonly been used for bioassays to determine if herbicides inhibit photosynthesis (Table 16.2). The simplest leaf-disc bioassay uses small discs cut from fully expanded cucumber or pumpkin cotyledons, floated in the light on a phosphate buffered medium containing suspected photosynthesis inhibitors.115 Qualitatively, if photosynthesis is inhibited, the leaf disc sinks. There are several variations of this method that can provide quantitative data. Evolution of O2 in the test solution can be measured with an oxygen electrode, CO2 induced pH changes colorimetrically determined with bromothymol-blue, or electrolyte leakage monitored with a conductivity meter. Leaf strips, algae, isolated chloroplasts, and duckweed (Lemna minor) have been used as test subjects. Although the bioassays presented in Table 16.2 are fairly easy to perform, few allelochemicals have been tested as possible inhibitors of photosynthesis. Many... 

Appleby, A. P. 1985. Factors in examining fate of herbicides in soil with bioassays. Weed Sci. 33, (Suppl. 2), 2-6... 

Bains, P. S. 1990. Purification, chemical characterization, host-specificity, bioassay, mode of action, and herbicidal use of the toxin produced by Alternaria brassicae. Dissertation Abst. Internat. 50, 2708-B... 

Horowitz, M. 1976. Application of bioassay techniques to herbicide investigations. Weed Res. 16,209-215... 

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