Wheat coleoptile assay

Figure 5. Results of wheat coleoptile assay for three tripeptides (1, 3, and 5).

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. 

A coleoptile emergence assay was used to determine the herbicidal potency of compounds 1-5. Seeds of downy brome (B. tectorum) were chosen for the assay because downy brome is a prominent weed pest in organic (wheat) farming. Water (zero... 

There are two types of receptor, termed fast and slow sites [21]. The fast responses (detectable in <5 min) appear to be brought about by membrane-mediated phenomena, while the slow responses, which involve protein synthesis, are not detectable within the first half hour. The receptor types have different molecular requirements, and the fast reaction is not a pre-requisite for the slow. Growth assays employed to assess activity include Avena coleoptile, lettuce hypocotyl, rice seedling, and bean axis. Other types include lettuce seed and wheat embryo germination, transpiration assays, leaf disk senescence, and more recently, a-amylase production. Stomatal closing using epidermal strips is an assay for the fast receptor. 

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