Toxic substances plant toxins

Substances toxic to all individuals are called toxic substances or toxins. Once a toxic substance has contacted the body it may have either acute (immediate) or chronic (long term) effects. Most of food-born toxins are substances with low acute toxicity (such as the pungent alkaloid piperine in black pepper), although some may present chronic effects, such as hepatotoxic pyrrohzidine alkaloids in plants (such as comfrey and coltsfoot species) or cause pathological changes to the respiratory system (e.g., tobacco smoke). 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Davis (19) in 1940 extracted and purified the toxic substance frcm the hulls and roots of walnut (JugIans) and found it to be identical to juglone (5-hydroxy-l,4-naphthoquinone). This compound proved to be a powerful toxin when injected into the stems of tomato, potato and alfalfa plants. The allelopathic action in the case of juglone (walnut tree and its vicinity) is well established. 

The creatures of the world, both animals and plants, produce a wide range of biologically active substances. Biologically active substances produced by animals or plants that cause an adverse effect are called toxins. Toxins refers only to toxic agents produced by animals and plants, not toxic substances such a lead or pesticides. The classification of a substance as a toxin tends to be in the eye of the beholder. Is caffeine, a naturally occurring agent in many plants, a toxin or just a pharmacologically active compound or both ... 

There are many different kinds of toxicants. Chemicals that are used for industrial and household purposes can be poison when misused or when there is an accident. Agricultural pesticides in the field can also cause poisoning. Chemicals might come in the form of conventional drugs which we use in a legitimate way, or in the form of designer drugs used illicitly for recreational substance abuse. Natural toxins found in the environment, such as mushrooms, plant toxins, snake/insect toxins and marine toxins, can also inadvertently harm a patient. 

This volume of the series Medicinal Plants of the World Chemical Constituents, Modern and Traditional Medicinal Uses contains information on 16 plant species and follows the same format as volumes 1 and 2. Some of the plants discussed in volume 3 may be considered controversial in their classification as medicinal. However, the Paracelsian dictum that sola dosis fecit venenum has been appreciated since ancient times, and throughout the ages many highly toxic materials used for lethal purposes have also found applications in modern medicine. It has been recognized that plants contain substances that are either harmful or toxic. However, it is wrong to think that there are plant toxins that are known or that are likely to have adverse effects on any and every form of life. A common feature of most toxic plants is that they are also known for their curative properties, and although they may provide the cure for an individual s disease at one dose, they may cause the death of the same individual at another. 

Organisms that have a very restricted diet can be expected to have evolved more specific mechanisms to target chemicals in the diet that are especially toxic substances. Thus, an insect living on one plant might protect itself against one toxin by specific biochemical traits—see Chapter 9. 

Toxic substances acquired from the host plaint may provide resistance to parasitoids (24), pathogens (25), and predators (45). By avoiding some toxins in plant material and selecting superior food tissues, insects feeding on variable hosts may become more susceptible to some enemies. Of course, other substances in preferred tissues may still be toxic to certain of these enemies, but this is less likely than it would be were plant compounds uniformly encountered by the host insect. 

The nutritional requirements of insect species exhibiting different feeding habits like scavengers, parasites, predators and phytophagous insects, are similar in a qualitative sense (O. Each insect species needs, however, a particular quantitative composition of nutrients in its diet to complete development ( ). The presence of toxic substances in plants, secondary plant substances as they were formerly called by phytochemists, forms a barrier which phytophagous insects have overcome by specialization. Thus, an insect can tolerate or detoxify the secondary plant substances present in its host plants, while the majority of these substances being present in other plants still acts as toxins (J ). In this way phytophagous insects are adapted to the metabolic qualities of their host plants, i.e. a particular chemical composition of nutrients and secondary plant substances. 

A very large number of plant toxins are classified in a diverse group of natural products. What is this group What are some of the toxic effects of substances belonging to it ... 

Harmful chemical compounds called poisons have accompanied humanity since ancient times. The first poisons were substances of natural origin, that is, toxins (produced by plants), venoms (produced by animals) and mineral substances (As, Sb, Sn and Cu). Dynamic advances in the synthesis of chemical compounds, initiated at the turn of the nineteenth and twentieth century, as well as the rapid progress of civilisation, led to introduction into the human enviromnent of a huge number of synthetic chemical substances. Currently, therefore, we are faced with an increasing number of toxic substances of natural and synthetic origin. 

Edible and nonedible plants contain numerous naturally occurring chemical substances that can be toxic if exposures are excessive. Many of these chemicals act as natural pesticides that help protect the plant from insects and other predators. As far as the edible plants are concerned, eating a varied diet containing fresh fruits and vegetables with beneficial properties usually avoids significant risks of poisoning by naturally occurring plant toxins. 

Toxins Toxic substances that are produced as metabolic by-products of microorganisms, plants, and animals, or are synthetically produced, and can be used to poison other living organisms. 

Animals encounter poison in the plants they eat, from other animals that use poisons in attack and for protection, and from toxin-producing bacteria and fungi. Animals are exposed to toxic metals released from minerals, and even the oxygen that all animals depend on is a very poisonous gas. Leakage of mineral oil, with many toxic and lipohilic substances, is also an old challenge that organisms had to adapt to. Substances produced inside the animal (e.g., ammonia, epoxides, phenolic substances) may also be toxic. Animals must therefore have many protection mechanisms against toxic substances in order to survive and reproduce. 

According to some reports, Egyptian Armed Forces Commander-in-Chief Field Marshall Mohammed Abd el Hakim Amer, who headed the defeated Egyptian Army in the 1967 Six Days War, was later poisoned, institutionally, by this substance. Allegedly, he committed suicide by means of aconitine that had been introduced to him while arrested [69]. An unidentified toxicant, possibly the same plant toxin, was used to replace the antidote with which Egyptian autoinjectors were filled, for personal assassinations [70]. 

Another interesting case of phytotoxicity, mentioned by Bonner (1950), is that of Encelia farinosa, a desert shrub. This plant, unlike most desert shrubs, does not harbor a growth of annuals under its branches. Investigations gave no indication of excretion of toxins from the roots but when leaves were added to soil, pepper, tomato and com plants were severly injured or killed barley, oats and sunflower were little affected. The toxic substance was shown to have the structure 3-acetyl-6-methoxybenzaldehyde. When leaves of the plant fall on the ground they retain their toxicity for a year or more even though much of the phytotoxin is leached into the soil. 

When young peach trees are planted in an old peach orchard they often grow poorly. As McCalla and Haskins (1964) state, the factors involved probably include soil toxins, nematodes, fungi, bacteria and soil fertility. Amygdalin, which is not itself toxic, is present in peach roots and on decomposition can yield toxic substances that in part account for stunting of the young peach trees. 

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