Alkaloids. There are many different kinds of plant and mushroom toxins. Alkaloids, the major type of poisonous compound found in the potato and its relatives, are common and widely distributed in the plant kingdom, especially but not exclusively among the flowering plants or angiosperms. Alkaloids are compounds derived from amino acids and are alkaline in nature.
toxin a poisonous substance compound a substance formed from two or more elements domesticate to tame an organism to live with and to be of use to humans propagate to create more of through sexual or asexual reproduction alkaloid bitter secondary plant compound, often used for defense belladonna the source of atropine; means "beautiful woman," and is so named because dilated pupils were thought to enhance a woman's beauty
cyanogenic giving rise to cyanide tannins compounds produced by plants that usually serve protective functions; often colored and used for "tanning" and dyeing cyanogenic giving rise to cyanide tannins compounds produced by plants that usually serve protective functions; often colored and used for "tanning" and dyeing
Their molecular structure is cyclical, and they all contain nitrogen. They are generally bitter tasting, and many are similar in chemical structure to substances produced by humans and other animals to transmit nerve impulses. Consequently, when ingested, they often affect animals' nervous systems. Many alkaloids, while potentially toxic, are also valued as medicines. Some, like the caffeine found in coffee (Coffea arabica), tea (Camellia sinensis), and other beverages, are consumed by humans all over the world as stimulants. One particularly useful alkaloid-containing plant is ipecac (Cephaelis ipecacuanha), a plant in the coffee family. Syrup of Ipecac, made from this plant, causes vomiting when swallowed, and this makes it one of the most useful treatments for poisoning or suspected poisoning by plants or mushrooms. It is a standard item in poison control kits, but should never be used without medical advice.
Glycosides. Glycosides are another type of toxic compound, even more widely distributed in plants than alkaloids. These highly variable compounds consist of one or more sugar molecules combined with a non-sugar, or agly-cone, component. It is the aglycone that usually determines the level of toxicity of the glycoside. For example, one class of glycosides, the cyanogenic glycosides, break down to produce cyanides, which in concentrated doses are violently poisonous. Cyanogenic glycosides are found in many plants, including the seed kernels of cherries, apples, plums, and apricots. They can be detected by the bitter almond smell they produce when the tissues are broken or crushed. In small amounts they are not harmful, but swallowing a cup of blended apricot pits could be fatal.
Like alkaloids, many glycosides have important medicinal properties. Foxglove (Digitalis purpurea), for example, produces digitalis and related compounds. These are cardioactive glycosides affecting the functioning of the heart. Foxglove has been used with great care as an herbal remedy by knowledgeable practitioners for centuries. In Western medicine, digitalis and its chemical relatives digoxin and digitoxin have wide application as drugs to help regulate heart function and treat heart-related illnesses. The same glycosides in foxglove that make it a useful medicine, however, can be deadly in the wrong dosage.
Oxalates. Other types of toxic substances include oxalates, which can interfere with calcium uptake. Calcium oxalate crystals are found in plants of the arum family, like skunk cabbage (Lysichitum spp., Symplocarpus spp.), rhubarb (Rheum raponticum), philodendron, and dieffenbachia. If ingested, these minute crystals cause intense burning and irritation to the tissues of the tongue and throat. The name dumbcane is sometimes used for dieffen-bachia because it can make a person unable to speak by causing swelling of the tongue.
Many other classes of compounds, including tannins, alcohols, resins, volatile oils, and even proteins and their derivatives, can be toxic to humans and animals. Some types of toxins, phototoxins, are activated by ultraviolet light and can cause intense irritation to the skin but only if the affected area is exposed to ultraviolet light, such as in sunlight.
Perhaps the most insidious plant substances are those that are cancer-causing (carcinogenic), because their effects are more long-term and not easily traced. Some fungi, especially certain molds, such as Aspergillus flavus, which grows on improperly stored peanuts, are known to produce tumor-inducing substances; Aspergillus produces carcinogens called aflatoxins that can cause liver cancer.
Some toxins are so concentrated that only the tiniest amount can be fatal. The seeds of castor bean (Ricinus communis), for example, produce a high molecular weight protein called ricin, which is reputed to be one of the most toxic naturally occurring substances known. Ricin inhibits protein synthesis in the intestinal wall. It and other proteins of its type, called lectins, are violently toxic; eating one to three castor bean seeds can be fatal for a child, two to six for an adult. (Ricin injected from an umbrella tip was used to assassinate the Bulgarian dissident Georgi Markov while he waited for a bus in London in 1978.)
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