Alkaloids in plant protection

Many investigations have been carried out with the purpose of investigating the possibility of using alkaloids in plant protection Organic farming requires new possibilities to protect plants without strong synthetic pesticides. Natural botanicals and natural compounds extracted from plants are considered as possibilities. Alkaloids are considered useful for this purpose. 

Quinolizidine alkaloids, pure or in mixtures of plant extract, can be used to protect plants against noxious insects. Scientific data has shown that quinolizidine alkaloids play a role in the resistance of some lupine varieties to the pea 

An extract taken from the composted straw of the alkaloid-rich lupin plants has produced very promising results in the development of biological control agents. The fungistatic activity of straw compost extracts increased markedly when the lupin straw used for composting was enriched with alkaloid extract. 

Alkaloids are botanicals. Their use in plant control is a very promising technological challenge in today s world, wrought with ecological problems connected to production and farming. The alkaloids are one group of compounds that seem 

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Folkman, W., Szrechan, J. and Gulewicz, K. 2002. Preparations of alkaloid-rich lupin in plant protection an effect of the preparations on feeding and development of Pieris brassicae L. and Pieris rapae L. Journal of Plant Protection Research, 42(2) 143-155. 

As was the case with terpenes, the function of alkaloids in plants is not known. It has been proposed that they are merely nitrogen-containing waste products of plants, like urea in animals. However, most plants reutilize nitrogen, rather than wasting it. Furthermore, it is difficult to imagine why such complex structures would be needed to store waste nitrogen. Like terpenes, alkaloids have been proposed to serve as protection from herbivores and insects. However, only a few examples of such protection can be demonstrated. Whatever the role of alkaloids is, some 70% to 80% of plants manage to do quite nicely without them. 

This global trend is in line with the Darwinian rationale for xenobiotic metabolism, which is believed to have evolved in an animal-plant "warfare," with herbivores, adaptating to the emergence of protective chemicals (e.g., alkaloids) in plants (180). 

The occurrence of specialized predators indicates the role of alkaloids as plant-protecting agents when the alkaloid becomes in the last resort useless agaist the plant predators, it even in some cases provides immunity for the alkaloid-rich insects from predation by birds and mammals. 

It should also be remembered that the defensive role of alkaloids in host protection is probably not as simple as the presence or absence of a single functional group on an alkaloid or even whether the alkaloid is in the host plant at all. In many cases, there may be additive effects of feeding deterrent compounds based on the entire chemical composition of the host plant. For example, when the alkaloids nicotine and tomatine, each of which have been shown to exhibit feeding deterrences of 25%, were fed in artificial diets to Locusta migratoria the overall feeding deterrence was approximately 50% (19). In this case the alkaloids acted in an additive fashion to produce a more effective chemical defensive mechanism. Adams and Bernays (19) went on to show that this additive characteristic of feeding deterrence was not restricted to alkaloids but was equally effective with alkaloids and various combinations of phenolics, terpenoids, and other miscellaneous secondary plant compounds. 

The alkaloid reserpine [50-55-5], which is isolated from the roots of Raum/fta serpentina T., contains a gallate trimethyl ether moiety. Reserpine is used as an antihypertensive and a tranquilizer. A vinylogue of reserpine, rescinnamine [24815-24-5], is also an antihypersensitive (75). Methoxsalen [298-81-7] (8-methoxypsoralen 7H-9-methoxy-furo[3,2-[Pg.379]

Plants are known to produce toxicants and antinutrilional factors, such as protease inhibitors, hemolytic agents, and alkaloids, which often protect the plant against pests and disease. Many of these toxicants are present in today s crops ai levels that do not cause acute toxicity or do not affect humans or animals when the food is properly prepared. New plant varieties should not contain levels of such toxicants that are above the range that exists in today s crops. 

Dussourd D., Ubik K., Resch J. F., Meinwald J. and Eisner T. (1984) Egg protection by parental investment of plant alkaloids in Lepidoptera. Abstract. 17thlnt l Cong. Entomol., Hamburg, 840. 

Insects that recruit plant defense for their own protection are promising candidates for understanding the specific mechanisms that insects have evolved to cope with alkaloid-mediated plant defense. Several fascinating examples of alkaloid-recruitment have been described for the pyrrolizidine alkaloid system, some of which are given below. Most likely this is due to the unique feature of these alkaloids to exist in two interchangeable forms, as Y-oxide or as free base (tertiary alkaloid form). 

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