toxic plants

• Explain why plant toxins are often from the same classes of secondary compounds as plant medicines

  • Both toxins and medicines are usually secondary compounds — chemicals not essential for plant survival, but used for defense or communication.

  • These compounds evolved to deter herbivores or pathogens by disrupting their physiology — and those same effects can be harnessed in small doses as medicine, or be harmful in larger amounts.

  • As Paracelsus said: “The dose makes the poison.”

• Recall some plant families that are well-known for producing toxins

  • Fabaceae (legume family)

    • Includes locoweeds (Astragalus), wild peas, and beans

  • Solanaceae (nightshade family)

    • Includes deadly nightshade, tobacco, and tomatoes

  • Apiaceae (carrot family)

    • Includes poison hemlock

  • Ranunculaceae (buttercup family)

    • Includes monkshood (Aconitum)

  • Rosaceae (rose family)

    • Includes wild cherries and almonds

  • Euphorbiaceae (poinsettia family)

    • Includes castor bean, manchineel

• Provide examples of toxins, and their effects, from major categories of compounds (i.e. alkaloids, etc.)

Alkaloids

• Swainsonine (Fabaceae): Causes appetite loss; suspected in Chris McCandless' case

• Coniine (Poison hemlock): Respiratory paralysis; blocked acetylcholine receptors

• Aconitine (Monkshood): Disrupts sodium channels; paralysis, death

• Nicotine, atropine, scopolamine (Solanaceae): Neuroactive compounds, vary from stimulant to hallucinogen

Glycosides

• Digitoxin (Foxglove): Affects heart function

• Amygdalin (wild cherry, bitter almonds): Cyanogenic glycoside that releases cyanide

• Coumarin glycosides (legumes): Can be anticoagulants

Phytotoxins

• Ricin (castor bean): Inactivates ribosomes → stops protein synthesis

• Abrin (precatory bean): Similar action to ricin, highly lethal

• Identify other harmful chemicals besides alkaloids and glycosides, and mechanical mechanisms, that can cause injury, poisoning, or discomfort.

  • Raphides (Calcium oxalate crystals):

    • Found in dumbcane, agave

    • Cause mechanical injury: burning, swelling when eaten

  • Allergens:

    • Urushiols in poison ivy, poison oak, cashews, mangos

    • Cause contact dermatitis; often from skin exposure

  • Thiaminase (Bracken fern): Breaks down vitamin B1 → neurological symptoms

  • ODAP (Grass pea): A neurotoxic amino acid that causes lathyrism (leg paralysis)

• Give examples of unusual mechanisms of poisoning from plants

  • Ricin/Abrin: Ribosome inactivation → shuts down protein synthesis

  • Urushiols: Cause delayed allergic reactions via immune hypersensitivity

  • Raphides: Cause mechanical damage rather than chemical toxicity

  • ODAP: Mimics glutamate, causing neurological dysfunction (e.g., lathyrism)

• Identify the toxic principle that led to the death of Chris McCandless.