|Plants & Human Affairs (BIOL106) - Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; email@example.com; http://www.employees.csbsju.edu/ssaupe|
Poisonous & Harmful Plants
I. Why are plants poisonous or otherwise harmful?
II. Why don't poisonous plants kill themselves?
Did you ever wonder why toxic secondary metabolites don't kill the plant that makes them? Primarily because after the chemical is produced, it is "locked away". In other words, the poisonous chemicals are stored in the vacuole in the cells. The vacuole is a large water-filled sac teeming with a variety of materials including poisonous chemicals and other waste products. As long as the chemicals are tucked away in the vacuole the remainder of the cell is safe.
III. Allelopathy plant vs. plant
Plants are also "poisonous" to one another. Allelopathy is essentially chemical warfare between plants. Good gardeners know that you shouldn't plant a walnut tree near your garden because a chemical called juglone leaches from the roots and leaves. Juglone will inhibit the growth of many common garden plants especially tomatoes.
IV. Accidental Ingestion of Poisonous Plants
(not on exam)
Some plants that have caused accidental human poisonings include:
A. Henbane/Mandrake (Mandragora officinale)
- used in witches brews
- contain alkaloids, rather toxic.
B. Jimson Weed (Datura stramonium; Solanaceae Tomato Family)
- named after Jamestown where some British sailors died from ingesting it.
- deadly toxic, but hallucinogenic in extremely low doses a good example of the fine line that exists between medicinal/poisonous and toxic plants.
C. Strychnine (Strychnos nuv-vomica)
- nerve toxin
- used in past medicinally, but rather toxic and not used much anymore
- rodent poison
D. Milkweed (Asclepias)
- can be eaten by monarch larvae, poison stored, and makes them toxic to birds. Viceroy looks similar but doesn't eat them to take advantage of protective coloration. Toxic to humans.
- active ingredient is cardiac glycosides (steroids)
E. Rosary Pea (Abrus precatorius; Fabaceae Bean Family)
- made necklaces but children ate; now illegal to do so
F. Lily of the Valley (Convallaria majalis; Liliaceae Lily Family)
- extremely poisonous, all parts
G. Spurge (Euphorbia; Euphorbiaceae Spurge Family)
- plants with a milky sap (and other distinctive features)
- milky sap can cause skin burns
- many are also toxic
- Poinsettiais a relative that has bad reputation but probably has minimal toxicity.
H. Dumbcane (Dieffenbachia sp.; Araceae Arum Family)
- contains calcium oxalate crystals
- contained in sac-like vase, crystals needle-like and shot out of opening
- irritate the lining of the mouth and esophagus
I. Jack-in-the-pulpit (Arisaema triphyllum; Araceae Arum Family)
- another calcium oxalate producer
J. White snakeroot (Eupatorium rugosum; Asteraceae Sunflower Family)
- milk sickness
K. Oleander (Nerium oleander; Apocynaceae Dogbane Family)
- very toxic, cardiac glycosides
- widely planted ornamental shrub
V. Turning the Tables on Poisonous Plants
Humans have taken advantage of poisonous plants in several ways: (a) Medicines - sub-lethal doses of some plants that would otherwise be poisonous can be used medicinally; (b) Hunting - to prepare poisons to put on the tip of arrows; and (c) Murder and other nefarious purposes. We will discuss plants used in hunting and murder briefly:
A. Plants and Hunting.
The main use of plants in hunting is for producing a poison for the tips of arrow. Curare is a arrow poison, mixture of many plants. Cause a rapid paralysis.
- Main active ingredients include Strychnos toxifera (Loganiaceae) and Chondrodendicus tomentosa (Menispermaceae).
- Blocks nerve impulse at muscle/nerve junction
- muscle relaxant used in surgery
B. Plants and Murder
Some poisonous plants have been put to rather sinister uses.
1. Hemlock (Conium maculatum; Apiacee Carrot Family)
- used to kill Socrates
- kills by paralysis beginning with lower limbs and eventually paralyzes diaphragm leading to respiratory failure.
- note this is not the hemlock tree, which is a conifer
2. Castor Bean (Ricinus communis; Euphorbiaceae - Spurge Family)
- the seeds produce ricin a very toxic protein
VI. Plants causing mechanical injury
VIII. Allergy Causing Plants
Antibody/antigens - antibodies are proteins in the blood that bind to and destroy antigens. There is a unique antibody for every antigen. Proteins on the surfaces of cells are common antigens. An antibody is "Y"-shaped, made up of two heavy chains and two light ones. There is a conserved region - found in all antibodies - and a variable region that is different for each antibody and leads to the specificity of antibodies.
Stem cells (bone marrow) � blood cells � B-lymphocytes � antibodies (Ig series) � five different kinds (including IgE which is involved in allergenic responses) � attached to mast cells (line respiratory system, intensine, skin) and basophil cells (blood) after first exposure � when bind antigen on subsequent exposures cause release of histamine � symptoms
Hay-fever - wind pollinated species such as ragweed, pines, oaks, grasses
Contact dermatitis - urushiol produced by poison ivy, and relatives.
Last updated: 01/07/2005 / � Copyright by SG Saupe / URL:http://www.employees.csbsju.edu/ssaupe/index.html