BSCI124, Straney
POISONOUS and MEDICINAL PLANTS
I. Presence of physiologically-active compounds in plants
A. How a plant compound can affect humans and animals
1. compounds that look like hormones, neurotransmitters
2. compounds which look like a substrate and inhibit specific enzymes
3. compounds which damage cells or cell components
B. Reason plants contain these
1. there is an evolutionary advantage to a plant that discourages herbivores from eating it by making compounds which kill, sicken or discourage a herbivore
2. timing and place of chemical production well choreographed to manipulate animal behavior
3. compare to animals which have motility and more active defenses-they generally have few toxic chemicals for defense
C. Types of compounds and plants- poisonous
1. Poisonous (toxic )plants
a. alkaloids (bitter compounds, contain Nitrogen atoms):
1) American Yew, taxine (sudden death)
2) Buttercups (diarrhea, vomiting)
3) Boxwood, buxene (convulsions and death)
4) Poison Hemlock, coniine (paralysis)
5) Strychnine tree (seeds)- strychnine (convulsions, death)
b. cardiac glycosides
1) Oleander (common ornamental shrub in south),
nerioside and oleandroside
2) Lily of the Valley, convallarin (irregular heartbeat)
c. cyanide
1) Seeds of rose family (apples, apricot)
2) Cassava
3) Lima beans (American varieties- reduced by breeding to a safe level)
d. Other compounds
1) Castor bean, ricin (toxic protein one seed can kill child)
2) Wisteria (2 seeds can kill child)
3) Mistletoe
4) Pokeweed
2. Milder discouragement- poisonous but generally not toxic
a. oxalic acid (crystals)
1) Rhubarb, Dumbcane, Caladium (crystals cause damage, paralyze vocal cords, swelling of mouth and throat)
b. saponins (e.g. tomatine in tomato, solanine in potato)
- cause nausea, vomiting, diarrhea
c. tannins in leaves, stems, roots-(e.g. tea)
- make unpalatable- bitter or astringent
d. allergenic components- e.g. poison ivy
-urushiol- oil which triggers your bodies defenses-
gives an reaction to an infection- reddening,
warming, bubbling of skin
3. Human uses
a. natural, pre-existing crop protection
b. selective poisons of pests- strychnine, rotenone and pyrethrum are from daisy family- safe insecticides
c. medicines in smaller doses
d. poison arrows- common in many societies
II. Medicinal uses of plants
A. plants used for long time as medicines
1. Like poisonous plants, contain chemicals that alter human physiology,
but can alter to restore balance
a. many poisonous plants serve as medicine in small doses
2. Origins
a. herbals- books that indicated plants used for treatment of certain symptoms
i. Assyrian herbal of 7th century B.C.
ii. Chinese emperor Shen Nung (2800 B.C.)
iii. Ebers medical papyrus from Egypt : 1550 B.C.
iv. The ancient Greeks studied medicinal plants for centuries
v. Islamic and Indian physicians wrote numerous prior to 1100 A.D.
vi. European Age of Herbals (1488-1682)
-based upon superstition, treatment of symptoms rather than
disease
-Doctorine of Signatures
d. today: 40 % of drugs are plant-based
i. also used as start in making synthetics-
e.g. yam provides starting material for making steroids
3. successes in developing drugs:
Foxglove- digitalis
Willow bark- aspirin
Fever bark tree- quinine
Madagascar periwinkle and Pacific Yew (taxol)- slows
growth of cancerous cells
4. Modern herbal medicine
-companies can sell anything as long as they do not claim a
health benefit
-problems:
-raw plants have variable dose of active chemical
-long term dosage has unknown results
-many plants not acutely toxic, but damage over long
term
-e.g. herbal teas, diet teas, aborfactants
sassafras