Interactions with other plant allelochemicals

Chemical manipulation of phenolic allelochemical production in plants has two potential values 1) for study of the role of phenolic allelochemicals in plant interactions with other organisms and 2) to alter such interactions for agricultural purposes. The first of these uses has already been accomplished on a limited scale (21, 22, 50, 51, 84, 86), however, there is no published evidence of the latter. This does not mean that herbicide and growth regulator-influences on plant secondary metabolism do not affect agricultural ecosystems by changing allelochemic compositions of plants. It is likely that this is the case, but it... 

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... 

Higher plants interact with other organisms such as animals including insects, other plants, and microorganisms by means of allelochemicals. Some of them are advantageous for higher plants as the producers. Then, these allelochemicals are called allomones. In other cases, allelochemicals are beneficial to receivers such as other plants, animals and micro-organisms. They are called kairomones. In this section two types of compounds will be discussed that work as kairomones. 

Interactions between antifecdant sesquiterpenes and other plant allelochemicals. Binary combinations of one of the more potent WCR feeding deterrents with another at a dose that gives weak feeding deterrence were explored with eight combinations of chemicals in the squash disk bioassay. No synergistic or antagonistic interactions for combinations of deterrents within or between the sesquiterpene (V-VII, IX), diterpene (XI, XII) and flavonoid (XVII) classes were noted. This indicates that the suite of antifeedants present in sunflower inflorescences act jointly in an additive fashion. 

The bulk of the allelopathy literature has dealt with direct toxic effects on other plants. However, as developed in this review, it is obvious that allelochemicals may have a major impact on plant root-microbial interactions. Such interactions could lead to growth inhibition in the microorganisms (or in roots) and affect other factors of the root-microbe association resulting in effects... 

The role of allelochemic-nutrient interactions in insect dietetics has been investigated only rarely. Examples of such interactions abound in vertebrate literature (14, 15) and may supply useful leads for researchers working with Insects. Many of the deleterious physiological effects of plant allelochemics may be due primarily to various interactions between these allelochemics and essential nutrients. In other words, it is Important to not only consider the presence of nutrients, but also the "bio-availability" of these nutrients to the phytophagous Insect. 

Thus, the potential Impact of an allelochemical on plant growth should be evaluated with regard to both the presence of associated allelopathic compounds and the influence of other chemical and physical conditions in the environment. Certainly allelochemical action is not an isolated event, and from the standpoint of plant functions, the controversy between competitive and allelochemical Interference loses some of its significance. Allelochemical action needs to be regarded with a holistic view where one stress may reinforce, or magnify, another. From this perspective, inhibition of plant growth is not so much a matter of which factor is most detrimental instead it is determined by the interaction of multiple stresses. 

As in vitro methods for studying cytochrome P-450 in insects became available (11-131, it soon became clear that insects with high cytochrome P-450 activities were resistant to carbamates and most other insecticides. This phenomenon is termed metabolic cross resistance and derives from the characteristic of cytochrome P-450 of accepting a very wide range of molecular structures as substrates the cytochrome binds the substrate very loosely by a lipophilic interaction and rapidly oxidizes it by an oxygen free radical-mediated reaction, a very powerful combination. Moreover, the cytochrome occurs in several or many different isoenzymic forms with broadly overlapping substrate preferences. A normally infrequent form may be selectively induced by allelochemicals in the crop plants (14), and if the induced form has survival value in the presence of an insecticide, it could be selected to dominate in the exposed population (15). 

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