Poisonous Plant: Definition and Principles | Toxicology

After reading this article you will learn about:- 1. Definition of a Poisonous Plant 2. Toxic Principles of Plants 3. Diagnostic Spot Tests for Plant Poisons.

Definition of a Poisonous Plant:

“A poisonous plant is one which as a whole or part thereof under all or certain conditions and in manner and in amount likely to be taken or brought into contact with an organism will exert harmful effect or death either immediately or by reason of cumulative action of toxic property due to presence of known or unknown chemical substances in it and not by mechanical action.”

Toxic Principles of Plants:

During metabolic activity, plants not only produce the food material so essential for life but also certain substances which are harmful to man and animals. Such toxic principles of plants vary from simple salts to complex molecules. The deleterious effects of plant toxins may range from simple irritation of skin or mucus membrane to disruption of an enzymic process at the subcellular level.

The present day advancement in the field of analytical chemistry have allowed even low level detection and purification of plant toxins. In many cases plant toxins have been isolated, purified and identified as definite chemical entities. Some of the major plant toxins (active principles) along-with suitable examples are given below (Table 42.1).

The contents of toxic principles vary greatly depending upon prevailing natural conditions. A plant, therefore, can be toxic under drought conditions but safe during other times.

Diagnostic Spot Tests for Plant Poisons:

Most of the cases of plant poisonings go undiagnosed for the want of requisite diagnostic facilities at veterinary hospitals. In fact diagnosis of plant poisoning is not an easy task and can not be based on any single observation.

The diagnosis, therefore, must be synthesis of history, clinical signs, pathological findings, test results, response to therapy and professional judgement. A few spot tests given below can help arriving diagnosis of some of the plant poisons.

1. Nitrite:

(a) Diphenylamine blue test serum/urine or Aqueous extract of plant material. A blue ring at the contact point of diphenylamine (1% in H₂SO₄) and water extract/serum/urine indicates the presence of nitrite, nitrate.

(b) Starch Iodine test: A filter paper soaked in potassium iodide and starch solution (freshly prepared) turns blue when a drop of acidic solution of sample is placed on it.

2. Cyanides/cyanogentic glycosides:

(a) Picrate test:

Small amount of finely chopped plant material is taken in a test-tube and a piece of moistened sodium picrate paper is inserted in it and held at the top with a stopper taking care that it does not touch the sample. A few drops of chloroform and water are added.

The sodium picrate paper gradually turns orange and then brick red. Dry materials particularly, seeds of various plants may be moistened with water and allowed to hydrolyse in stoppered test tube containing sodium picrate paper and placed in a incubator at 37-39°C overnight.

*Strip of filter paper dipped in saturated solution of picric acid in 10% sodium carbonate.

3. Oxalates:

In a test tube take 1ml clear stomach/rumen contents or urine and add 0.2 ml concentrated ammonium hydroxide and heat it on flame of a burner or spirit lamp to evaporate the solution.

Add 40 mg thiobarbituric acid crystals and gently reheat on burner or spirit lamp.

Formation of an orange red colour which is soluble in ethanol is indicative of oxalates in the sample.

4. Detection of Glycosides of Kaner (Certerine/Thevetin):

(a) Alcoholic extract of sample is taken and to it 2 ml of conc. HCl is added. On boiling a blue or bluish green colour is obtained.

(b) Two drops of alcoholic extract are taken into a procelain basin and evaporated to dryness on water. To the dry residue one drop of vanilline- sulfuric acid reagent (Vanilline and sulfuric acid). The basin is lightly tilted so that reagent drop forms a wet-line in the basin. The basin is kept over water bath for a few minutes. A pink to purple colour indicates the presence of Kaner glycosides.

5. Detection of Ratti (Abrus precatorius) needles:

(a) In cases of poisoning, the ratti sui are found embedded in subcutaneous tissues. The sui (needles) obtained are inserted in inner side of a pigeon. Setting up of inflammation within few hours followed by necrosis is indicative of Abrus poisoning.

(b) A portion of suspect tissue is taken and made into thin paste. With 10ml of 0.5 N saline and then clear filtrate is obtained. Two drops of saline solution are added to 2 ml of defibrinated blood in test tube. Agglutination of red cells is an indication of poisoning due to Ratti seeds.

(c) Clumping of red cells can also be observed under the microscope.

6. Alkaloids:

Acidified alcoholic extract (acidified with HCl) is precipitated with ammonia and alkaloid is extracted with chloroform. Extract is taken on the watch glass, add HCl to it and add one or two drops of Dragendorff’s reagent. White precipitate indicates the presence of alkaloid.

(a) 2g bismuth sub-nitrate dissolved in 25 ml glacial acetic acid and to it 100 ml of water is added.

(b) 40g of Potassium iodide in 100 ml water.

Take 10 ml of solution (a) and (b) each, mix them, add 25 ml glacial acetic acid and then dilute with 100 ml of water.

7. Tannins:

Diluted aqueous extract of the sample turns green or bluish or black with addition of ferric chloride solution in presence of tannins. Dilute it until it is transparent. Add a few drops of sodium hydroxide. Now garnet colour is seen. With addition of sulfuric acid, greenish colour is seen which may turn greenish yellow with excess of sulfuric acid.

8. Saponins:

Take a few drops of saponin tincture with water. Foam formation will indicate the presence of saponin in the sample.

9. Detection of Dhatura poisoning:

Take a drop of urine from the animal being suspected for Dhatura poisoning and instill it in the eye of a rabbit. Pupillary dilation (mydriasis) will indicate poisoning due to Dhatura.

10. Strychnine/Nux Vomica poisoning:

Take about 1-2 ml of suspected material in a petri dish. Add equal quantity of concentrated sulfuric acid. Mix well and a few crystals of potassium dichromate. A change in colour from yellow orange to greenish blue is indicative of the presence of strychnine.

The tests described above will give only a rough indication of presence of absence of particular poison. For confirmatory diagnosis, one should attempt only quantitative tests or send the sample for a diagnostic laboratory for analysis.

The poisonous plants are numerous and ubiquitous. Because of biodiversity, it is very difficult to give precise information about variety of toxic principles contained in plant species. Concerted efforts of phyto-chemists, biochemists, veterinarians are needed more urgently so that mechanism of action of poisonous plants, their treatment and prevention can be more intelligently found.