Plants: Poisonous and Allergens

1
Plants Poisonous and Allergens Poisonous plants
have been known and used for centuries. Socrates
was forced to drink hemlock, and the De Medicis
and Borgias knew how to use plant poisons to
achieve their desired results. There are many
poisonous plants the active ingredients in most
are alkaloids or glycosides. They act on the CNS,
on neuromuscular junctions, on the heart, on the
liver, and on basic metabolic processes (electron
transport and ATP synthesis). Some of the
poisonous plants presented in the text chapter
have come up earlier, for example as medicinal
plants when in small doses. Well skip those
here.
2
Hemlocks The two poison hemlocks are water
hemlock (Cicuta maculata and poison hemlock
(Conium maculatum). Both grow to a height range
around 2m. Both are members of the Umbelliferae,
like the carrot.
3
The toxin in poison hemlock is an alkaloid,
coniine (there are other toxic alkaloids present,
including atropine). It is a neurotoxin, causing
convulsions, a paralysis advancing upwards from
the lower limbs, and eventually paralysis of the
breathing apparatus and the diaphragm. Death
follows from suffocation. Socrates death from
hemlock poisoning was described by Plato, and
followed the pattern described. The poison in
water hemlock is different it is an alcohol
called cicutoxin (from the genus name). Its
effect is very similar violent convulsions
followed by death.
4
Strychnos spp. There are a number of species
within the genus Strychnos that are sources of
strychnine, an extremely bitter alkaloid that
affects the basic function of nerve cells. It
blocks a protein involved in the chloride channel
of neurons.
Strychnos nox-vomica
5
Death occurs as a result of continuous muscle
spasms, convulsions that become continuously more
severe, and death either from exhaustion or
uncontrollable convulsions in the muscles of
breathing. The LD50 is 1mg/Kg, or in the range
of 20 40 mg, but you can taste its bitterness
in concentrations as low as 1 ppm (or that
1mg/Kg). Strychnine has frequently appeared in
the movies as a method to kill, for example it
was strychnine that Norman Bates used in
Hitchcocks Psycho to kill both his mother (the
mummified figure sitting in a chair at the end)
and her lover.
6
Curare Strychnos toxifera, below, with a stick
insect on it, is a main source for another potent
alkaloid poison. It is a main source for curare.
7
Curare, from Strychnos toxifera and
Chondrodendron tomentosum, is a paralytic that
used in blowguns to kill game (or members of
opponent tribes). It is a group of poisons, of
which the most important is D-tubocurarine. It is
a muscle relaxant that blocks one of the two
types of acetylcholine receptors on post-synaptic
nerve cells. It kills prey (or humans) by
blocking neuromuscular junctions critical to
breathing. Curare is used as a relaxant for
surgery. The source was discovered by Richard
Schultes in 1941, and a synthetic form
(intracostin) was developed in 1942 by Dr. Harold
Griffith. Now anesthesiologists use a variety of
similar drugs.
8
Richard Schultes
Dr. Harold Griffith
9
Milkweed cardiac glycosides Various Asclepias
species (the milkweeds) contain both galitoxin
and cardiac glycosides. The cardiac glycosides
have an effect similar to digitalis.
While the glycosides are poisonous to livestock
and humans, they are not poisonous to milkweed
butterflies, Danaus plexippus. The larvae
(caterpillars) take up and store the glycoside,
and it is passed on through metamorphosis to the
adult butterfly.
10
Youve already seen a picture of the result of
this a jay throwing up only a few moments after
eating a monarch butterfly. Your text has another
excellent example the rattlebox moth caterpillar
(male) that feeds on the rattlebox plant,
Crotalaria mucronata, but is unaffected and
passes the toxin on to protect the adult moth.
11
The female moth, when frightened, exudes a foam
with the toxin, monocrotaline, that potential
predators avoid. Protection for the female is a
nuptial gift with sperm from the male. It is
spread throughout the females body within
minutes.
The female moth can even sense during courtship
which male will pass along the best level of
protection. Spiders are apparently the main
predators from whom protection is needed.
12
Crotolaria toxins are dangerous-to-fatal in
humans and other animals. The monocrotaline toxin
induces hypertension in the pulmonary arteries
and cardiac hypertrophy, both of which can be the
cause of fatality. Even so, it was introduced
into the southern U.S. because it improves soil
conditions by adding fixed nitrogen to soil.
Oops! The toxicity to farm animals has led to it
now being considered in invasive, noxious weed.
13
Plants also use chemical poisons against each
other. The chemical interaction is called
allelopathy. In this case, the chemicals are
generally volatile, and include terpenes or
phenols. Allelopathy has been suggested in many
plant interactions, but a few are well
documented. One that occurs locally is the
interaction between black walnut trees (Juglans
nigra) and surrounding plants. A chemical called
juglone is washed off leaves by rainfall (its
also in the bark, walnut husks and roots), and
poisons the ground around the tree against
germination or growth of possible competitors.
Some plants (tomatoes) are far more susceptible
than others.
14
On the right is another example of allelopathy
that occurs in California chaparral. Sagebrush
(Artemesia tridentata) releases monoterpenes into
the surrounding soil that inhibits the growth of
seedlings and lowers the respiration rates of
both seedlings and mature plants. That creates
the bare zone around sagebrush plants evident in
the figure. In some cases the bare and suppressed
zone can extend almost 10m.
15
Common garden plants include a number of species
that are toxic. Rhododendrons range from short
plants to 50m tall trees. You may know them as
azalea.
The picture is of R. ponticum, which was known as
a hallucinogen and toxin as long ago as the
golden age of Greece. The toxin is a
grayanotoxin. It is in the leaves, pollen,
nectar, and therefore honey derived from it.
16
Grayanotoxin (it has other names) is a diterpene
that binds to sodium channels in cell membranes.
It leaves exciteable cell membranes depolarized.
The symptons are salivation, persperation,
vomiting, dizzyness, muscle weakness, and cardiac
rhythm disruption. This toxin is apparently not
usually fatal. Tulips and hyacinths (in flower
soon or now) contain a number of toxic
glycosides. Poinsetta (Euphorbia pulcherrima) is
a member of the Euphorbiaceae. It is named for
the first American ambassador to Mexico, Joel
Poinsett, who brought the plant from its native
range in Mexico into the U.S. Its sap, according
to general wisdom, is toxic. In fact it is an
allergen that may irritate skin and mucous
membranes.
17
However, a relative in the same family, Ricinis
communis, or castor bean, is very toxic. The
beans contain ricin. Ingestion of one bean can
kill a child, and only a few will kill an adult.
A lethal dose is 0.2mg. It is considered to be
the most potent plant toxin.
The beans are also the source for castor oil.
18
Ricin is a two-subunit protein. The A chain
removes an Adenine from ribosomal RNA, which then
blocks protein synthesis (and is eventually
fatal). The B chain is a lectin that binds to
cell surface proteins, and is critical to get the
A chain inside the cell, where is does its damage.
A chain is blue B chain is orange
19
A number of plants, e.g. barley, have the A
chain, but no B chain so that the A chain cant
get inside cells. Clearly, you dont get sick
from eating barley (or drinking beer made with
malted barley). Ricin has been investigated as a
chemical weapon, and was used at least once. The
Russian KGB apparently supplied ricin to the
Bulgarian secret police, who used it in a pellet
fired by compressed gas into the leg of a
dissident, Georgi Markov, who died as a
result. Symptoms only appear slowly. They
include initially nausea, vomiting, diarrhea,
burning in the mouth and throat later retinal
and intestinal hemorrhaging, liver and kidney
damage. Death is usually from kidney failure.
There is no known antidote.
20
Castor beans are not all bad. They, like
soybeans, are the source of an oil that is
valuable in many industrial processes and
products. When you drive home tonight, you will
probably be sitting on automotive seats that are
made in part from hydrogenated oils of soy and
castor beans.
21
Although not usually fatal, some houseplants are
no fun and, to some degree, poisonous. Dumbcane
(Dieffenbachia spp.) and others in its family
(e.g. jack-in-the-pulpit) contain calcium oxalate
crystals that cause swelling of the mouth, lips,
tongue and throat. Difficulty in speaking when
suffering these symptoms is the source of its
name.
22
White snakeroot White snakeroot (Eupatorium
rugosum) is not consumed by humans, but is
sometimes consumed by cattle. Its toxin is
tremetol, an alcohol. Cattle suffer from the
trembles as a result acetone breath (like
diabetics have with very high blood sugar),
sluggishness, and muscular weakness.
23
When a human eats the meat or drinks the milk of
a poisoned cow, the result is called milk
disease. It killed Nancy Hanks, Abraham Lincolns
mother. In the 1800s it was the cause of illness
and many deaths. The name of the disease relates
to what it causes. Tremetol blocks the liver from
breaking down lactic acid. Lactic acid
accumulates in the blood, the pH of the blood
drops (acidosis, a characteristic of diabetes),
which leads to the acetone breath. Accumulating
lactic acid also at least in part blocks the
Krebs cycle, leads to a lowered amount of ATP,
and produces the sluggishness and muscle weakness.
24
Locoweeds Oxytropis and Astragalus spp. The
name comes from the behaviour of poisoned
animals. Poisoning causes erratic behaviour,
aggression, lethargy, loss of balance,
nervousness. These are a mixed and conflicting
bag of symptoms. Thats because the active
compound is a neurotoxin called swainsonine. It
inhibits a key enzyme in the Golgi apparatus a
mannosidase. It is considered a possible
anti-cancer agent.
An Astragalus
25
Plants responsible for allergic
reactions Allergic reactions are responses of the
immune system to foreign substances. They
represent a temporary hypersensitivity to the
agent. The most important hypersensitivity
reactions are hay fever (and allergic rhinitis)
with symptoms of runny nose and nasal congestion,
itchy and teary eyes, and various types of
dermatitis, with symptoms of reddening of the
skin and rashes. As much as ¼ of the human
population suffers from hay fever, which has
nothing to do with hay. Hay fever is caused by
allergic reaction to airborne pollen. That pollen
can come from grasses or, more commonly, from
ragweed (Ambrosia artemisifolia and A. trifida)
26
The problem gets its name from the timing that
has ragweed releasing pollen at the same time as
hay ripens (early-August to September or
October). Each plant may produce one billion
pollen grains over a season.
27
The plant is monoecious each plant has separated
male and female flowers. They are well adapted to
pioneer habitats, e.g. land bared for
construction. You will certainly be able to find
some on or around land cleared for construction,
e.g. expansion of parking lots before
construction of the new engineering building. The
worst time of day for hay fever sufferers is mid
morning to early afternoon. Pollen disperses
after the day warms and relative humidity
decreases. Usually the worst is over by late
afternoon, and rain is welcomed, since it reduces
the amount of pollen in the air.
28

• How do you deal with hay fever allergies?
• There are basically two ways
• Decrease the intensity of the symptoms using
  antihistamines to decrease the histamine reaction
  and/or decongestants to reduce the problems with
  mucus produced as part of the histamine reaction.
• Go through a long series of injections to become
  desensitized to the pollen. The injections
  consist of weakened extracts of pollen and cause
  an internal immune reaction that blocks the IgE
  response of hay fever.

29
Contact dermatitis is the other major allergic
reaction. The most common contact dermatitis is
to poison ivy, poison oak, and poison sumac.
While their names seem different, all are in the
same genus, Toxicodendron.
Poison ivy, T. radicans
30
The contact dermatitis is caused by an oil called
urushiol, from a Japanese word transliterated as
urushi. The oil (actually its a mixture of oils)
is polymerized to form the hard lacquer that
protects Japanese lacquerware. The difference
between poison ivy and poison oak is the length
of the side chains in the dominant catechols in
the urushiol in poison ivy they are 15 carbon
atoms long, in poison oak the length is 17
carbons.
31
As you probably know, the urushiols are passed to
you by only brushing against the plant. The
urushiol rapidly binds to proteins in the skin,
but can be spread by rubbing or scratching the
initial itch. The usual course is a rash that
lasts about 3 weeks, but a more severe exposure
(dont ask, Ive had personal experience)
produces blisters.
32
As a sort of warning, recognize and avoid the
leaf pattern leaflets in threes, leaflet margins
typically lobed, but non-symmetrically. Plant
size, and even, to some degree, leaf shape is
variable. Size you are probably used to is as a
ground dwelling plant. However, it can grow as a
woody vine to a few meters, and can be a
free-standing plant up to more than 1m. Leaf size
can range from a few centimeters in width and
length to around 25cm across. As they used to say
on Hill Street Blues, be careful out there.