Poisons effect chemical reactions in living organisms.

Exercise: List all the poisonous plants you can think of. What function do these poisons serve in plants?

2ary metabolites: serve as anti-insect and anti-herbivore

Biologically, poisons are often very similar to medicine with alkaloids and glycosides prominent

1. Poisonous plants in the wild

2. Poisonous plants in the backyard

15,000 kids under 5 become ill each year and many die by eating poisonous plants

(Klein,  p. 417)

List all local poisonous plants

Outdoor

Nerium oleander: Contains 50 toxic compounds

Lantana (fruits and flowers)

Plumbago

Milkweed

Texas mountain laurel seeds

Jimsonweed (Datura)

a. Milkweedà glycosides

Eaten by Monarch butterfly caterpillars and passes into Monarch butterfly so birds eating them become ill

b. Nerium oleander

1) 50 toxic compounds

2)How can there by so many?

Co-evolution of oleander and insects

Oleander ancestor attacked by insects. Survivor contains toxic compound A, survives & reproduces

Offspring attacked and decimated except for oleander ancestor containing compound B

Over millions of years, the current oleander has arisen

3. Plants causing mechanical injury

Mechanical injury is physical injury such as punctures and scrapes.

Examples:

Cactus spines

Lots of desert plants like Ocotillo and Agave

Philodendron raphides are needle-shaped crystals

4. Allergy plants

a. Respiratory allergies

Cause: Allergens are harmless substances triggering immune responses

(runny nose, coughing, sneezing, itchy eyes)

This immune response would be beneficial if the invader were a parasite (protozoans and other simple organisms that can be harmful). Parasites often enter through openings such as the nose, mouth and anus. Symptoms of an allergy would help to dislodge parasites.

Pollen is a common allergen. Wind pollinated plants such as grasses and most non-desert trees produce lots of pollen. Why would a wind-pollinated plant produce so much pollen? If plants self-pollinate, pollen would only need to travel a short distance. However, many plants are self-incompatible, they cannot pollinate themselves. Genetic diversity results from reproducing only with other plants of the same species.

The surface of pollen has special recognition molecules that are glycoproteins only recognized by the stigma of the correct species.

Humans with allergies incorrectly recognize this glycoprotein as an invader.

Cells called mast cells line throat and nasal passages. These cells are filled with compounds called histamines. Histamines can be beneficial when an injury occurs because they dilate blood vessels to bring food and oxygen to help repair the injury.

Histamines are released when the allergen binds to an antibody, a protein that recognizes foreign substances. The histamine causes the runny nose and watery eyes of an allergy.

Prevention: Don’t plant allergy causing grass and wind-pollinated trees

Drugs: Anti-histamines

Desensitization: Allergen injections cause an increase in IgG antibodies. Allergic reactions are caused by IgE antibodies. Therefore, the allergens will tend to bind to the IgG antibodies and no allergic reaction will occur. As you might expect, people with allergies have higher levels of IgE antibodies and this trait is hereditary.

b. Skin irritants

Some plants cause an allergic reaction of the skin. Poison ivy, poison sumac have an allergen called urushiol. About 50% of the population is sensitive. It takes about 24 hours for rash to appear.

c. Food allergies

Sensitivity to various foods. Symptons vary.

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