Allelochemicals chemical nature

While virtually all plants contain chemical constituents which have allelopathic potential, only those chemical constituents that are released to the surrounding environment can be considered potential allelochemicals. A potential allelochemical can only be designated as an allelopathic agent after it has undergone a rigorous proof of demonstrated phytotoxic activity. The chemical nature of recognized allelochemicals is diverse, and almost every class of secondary plant metabolite has been implicated in allelopathy. 

To produce QSAR models, a data set containing chemicals within a specified well-defined end-point is necessary. Since our knowledge about the properties of the natural compounds that surround us is very poor, especially for allelochemicals and toxicological evaluation of synthetic pesticides is well documented (regulators oblige the chemical industry to produce experimental data for synthetic chemicals, before they can be marketed), when allelochemicals toxicity values are not available, pesticides with similar structure can be used in the analysis. Therefore suitable data sets can be defined with pesticides and their activities, to predict the toxicity (activity) of the allelochemicals. 

How to deal with the pests that attack plants under cultivation is a continuing challenge to the food and agricultural production system. Natural resistance or tolerance to pests has proven to be one of the safest and least costly ways to protect plants. As we identify the specific plant components involved and their actions, it will be easier to incorporate the capacity to produce the desired chemical into the plant of Interest. There is the further possibility to identify additional natural chemicals that may be useful as pest control materials. The latter might be through the use of natural products or it might be products of industrial synthesis patterned after the natural products. It is clear that allelochemicals are involved in these complex processes and they hold promise for even a greater role. 

Rice, E. L. "Pest Control with Nature s Chemicals Allelochemicals and Pheromones in Gardening and Agriculture" University of Oklahoma Press Norman, 1983. 

Opportunity exists in agroecosystems for two sources of chemical interference, natural and synthetic. The origin of allelochemicals... 

While much research on the nature and impact of phytotoxins has been conducted, many questions remain unanswered. Little is known about the rate of phytotoxin production and accumulation, localized concentration, threshold soil concentration for expression of bioactivity, duration of bioactivity, stability in soil, and environmental redistribution. Although the fate of specific chemicals under defined experimental conditions is discussed, it is hoped that the principles involved can be extended to provide a basic understanding of the fate of the wide range of allelochemical substances in the soil. 

Plant chemists show several different approaches to the way they view chemicals in plants. Some are interested in the isolation of the molecule per se, its structure and synthesis (1 ). Others are searching for interesting and hopefully patentable biologically active plant products or molecules as new drugs (2), as antibiotics O), or as pesticides (M. A third group seeks to understand the role such compounds (allelochemicals) play in the environment, that is the way in which they may influence or control many of the complex interactions that occur between living organisms in natural plant communities O, ). As has been shown in this Symposium these three approaches are not necessarily mutually exclusive. 

Barbosa, P. and Saunders, J. A. (1985). Plant allelochemicals linkage between herbivores and their natural enemies. In Chemically Mediated Interactions Between Plants and Other Organisms, eds. G. A. Cooper-Driver and T. Swain, pp. 197-137. New York Plenum Press. 

In this review we point out the value of bioassays in the study of allelopathic interactions but do not attempt to critically evaluate or prioritize bioassay techniques that have been published. Since it is also not possible to propose a general bioassay for researchers, we present selected examples of bioassays that have been used to understand these plant-plant and plant-microbe chemical interactions. Furthermore, we attempt to provide an overview of some bioassays that are useful or that may be adaptable to allelochemicals. The general focus will be on laboratory bioassays since they are paramount to determine quantitative effects of allelochemicals and to ascertain actual mechanisms of allelopathy in nature. 

Another problem or consideration that may interfere with some aspects of allelopathy (especially in field experiments) has arisen over the past fifty years with the introduction and use of a multitude of xenobiotic compounds as insecticides, fungicides, plant growth regulators, harvest aids, and herbicides. A variety of such compounds have been and continue to be used on a world-wide scale. Some of these chemicals and/or their transformation products are persistent in soils and water. Other such chemicals are routinely applied at various times during a year. These xenobiotics may interfere or interact with naturally occurring allelochemics and thus alter or even mask certain natural allelochemical effects. Researchers will have a more difficult time to find natural areas that do not contain xenobiotic... 

Chemical analysis of sweetgum seedlings treated with fescue leachates showed that growth inhibition was associated with an impaired absorption of phosphorus an nitrogen. Obviously, conditions of decomposition, allelochemical enhancement of disease, the nature of the secondary products from microbial activity, and interactions among allelochemicals are all significant variables in intercrop allelopathy. The uniqueness of the chemical environment for each crop sequence and situation will continue to confound precise analyses of effects on yield. 

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