What are the plant poisons? /Importance of plant poisons

If the whole or part of a plant, when brought into contact with the body in quantities likely to be brought into such contact, is capable of acting d3eleteriously because of chemical substances, singly, cumulatively or due to hypersensitivity, such as a plant may be referred to as a poisonous plant

Many of the poisonous plants have medicinal qualities. Some well known examples are cinchona, Ipecacuanha and opium. Many such plants are used in Aurvedhic medicine after boiling in cow’s milk and other agents which are though to detoxify them.

Classification of plant poisons

Several classifications are available but no one is perfect.

· The following classification is based on the main system that is affected by the plant poison. But there can be an overlap as well.

1. Neurotoxin (opium, cannabis, strychnine)
2. Cardio-toxin (yellow oleander)
3. Gastrointestinal irritants (Gloriosa superba, Adenia palmate)
4. General cellular toxin (manioc, Adenia palmate)

· Classification according to the chemical constituents of the plant poison

1. Alkaloids (strychnine, cocaine)
2. Glycosides (yellow oleander)
3. Glycoprotein (Ricin)
4. Oxalates (Dieffenbachia)

· Classification according to the botanical family to which the plant belongs

1. Euphorbiaceae (manioc)
2. Passifloraceae(Adenia palmate)
3. Apocyanaceae (yellow oleander, nerium oleander)
4. Lilliaceae (Gloriosa superba)
5. Loganiaceae (strychnos nux vomica)

Autopsy features

Autopsy features are often non specific. They will depend on the poison and the pathophysiology it causes.

Smell of poison

Poison/seeds in stomach

Features of dehydration

Features of cyanide poisoning

Manioc/Manihot utilissma/ Cassava

Manioc poisoning occurs due to the presence of a cyanogenic glycoside (CG), linamarine and the enzyme linase in the leaves and root of the plant. The CG occurs in two forms; autolysable and hydrolysable. In the presence of the enzyme linase the autolysable form is autolysed to form HCN (hydrocyanic).When exposed the hydrolysable form is hydrolyzed and release HCN. This HCN is highly toxic.

Gloriosa superba

All parts of the plant are poisonous. Accidental poisoning can occur as the tuber resemble the sweet potato.The main poisonous agent is the alkaloid, colchicine. This chemical is used to treat gout.

Adenia palmata/ Modecca palmate

The plant is common in moist areas. The fruit resembles passion fruits. Therefore accidental poisoning in children occurs. The toxic effects are due to;

Cyanogenic glycoside (and enzyme emulsion that release HCN)

Free HCN

Toxalbumin

Hypersensitivity reaction

Thevetia peruviana (yellow oleander)

Poisoning is due to the ingestion of seeds of the yellow oleander. The toxic substance is a cardiac glycoside (thevetin, cerberine) Consumin 2-8 seeds may cause death of an adult.

Nerium oleander

All parts of the plan are poisonous. It contains a cardiac glycoside (oleandrin, nerin0 as the poison.

Strychnos nux vomica

It contains one of the most deadly known poisons and it is called strychnine (an alkaloid). The quantity of poison in one seed could be lethal.