Plant growth activity, laboratory

In a search for safer biodegradable plant growth substances that may have potential uses in agriculture, particularly for crop production, our laboratory has developed some new bioassay systems to screen various plants for growth-regulating activity. Our screening efforts resulted in the discovery of both growth promoters and inhibitors. 

In an attempt to overcome the limitation that only surface feeding chewing insects can be controlled by the known antifeedant compounds, Jermy and coworkers (Jermy and Matolcsy, 1967 Matolcsy et al. 1968) investigated the antifeedant activity of some substituted phenoxyethanols and phenoxyacetic acids which do not affect plant growth and which are known to possess systemic properties. 2,4,6-Trichlorophenoxyethanol (6) and 2,4,6-trichlorophenoxyacetic acid (7) have shown the highest antifeeding activity both under laboratory and field conditions. 

The plant physiological actions of aromatic nitriles were first studied at the end of the 1930s by Wegler and Binder (1938) in the research laboratories of the former I.G. Farbenindustrie. The plant growth modifying action of several aromatic nitriles and the importance of 2,6-dichloro-substitution from the aspect of biological activity were recognised in the same laboratories. 

The accumulation of substances such as silica, iron, aluminum, carbonate, and other salts can result in cemented layers, which change the physical, chemical, and biological behavior of the soil. For example, a cemented layer retards percolation and restricts root activity. Furthermore, the availability of nutrients for plant growth is reduced, i.e., the cation exchange capacity is reduced. There are accumulations in the soil which show the enrichment of one substance and/or the depletion of another substance. This can be expressed by diagnostic subsurface horizons, which are listed in alphabetically order in Table 14.5. It should be stressed that some characteristics can be measured only in the laboratory and not in the field. 

Cobalt is one of twenty-seven known elements essential to humans (28) (see Mineral NUTRIENTS). It is an integral part of the cyanocobalamin [68-19-9] molecule, ie, vitamin B 2> only documented biochemically active cobalt component in humans (29,30) (see Vitamins, VITAMIN Vitamin B 2 is not synthesized by animals or higher plants, rather the primary source is bacterial flora in the digestive system of sheep and cattle (8). Except for humans, nonmminants do not appear to requite cobalt. Humans have between 2 and 5 mg of vitamin B22, and deficiency results in the development of pernicious anemia. The wasting disease in sheep and cattle is known as bush sickness in New Zealand, salt sickness in Florida, pine sickness in Scotland, and coast disease in AustraUa. These are essentially the same symptomatically, and are caused by cobalt deficiency. Symptoms include initial lack of appetite followed by scaliness of skin, lack of coordination, loss of flesh, pale mucous membranes, and retarded growth. The total laboratory synthesis of vitamin B 2 was completed in 65—70 steps over a period of eleven years (31). The complex stmcture was reported by Dorothy Crowfoot-Hodgkin in 1961 (32) for which she was awarded a Nobel prize in 1964. 

Possible Mechanism of Allelopathlc Action of Water-Insoluble Plant Lipids. Many non-polar natural products with germination and growth regulation activities In laboratory tests are In pure form not sufficiently water soluble to account for their allelopathlc activities observed In the field. For this reason the notion exists that sterols and other non-polar plant constituents are not likely to play a role In allelopathlc actions, and It Is generally concluded that the bioactivity data observed In the laboratory are therefore coincidental. 

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. 

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