Download Chapter 6: Neotropical Pharmacy

Secondary
Metabolites for Plant
Defense
Katie Williams
Q&A
• What are the three main groups of Secondary
Metabolites?
•
What are the four determinates of toxicity
for plant defense?
• What are the main characteristics of each
regarding plant defense?
• What is the term specific to the decrease in
latitude resulting in an increase of plants bearing
alkaloids?
• What are the two main types of drainage rivers
(regarding nutrient retention) and in which do you
find ‘SM-rich’ or ‘SM-poor’ Plants?
Why do plants need extra defense?
• Plants are “sitting ducks”
for herbivores.
• They constitute over 99%
of all living mass in
tropical rainforests (~900
metric tons per hectare).
• Leaf damage severely
affects plant ecology.
• Competition living space.
Secondary Metabolites?
Primary Metabolites (PMs)
The universal compounds
found in all plants: the known
sugars, protein amino acids,
purines, purimidiness of
nucleic acids, chlorophylls,
etc.
Secondary Metabolites (SMs)
All other plant chemicals that
vary in plant species and also
do not appear to have an
essential role in metabolism:
Alkaloids, terpenoids,
phenolics, etc.
Origin
Secondary Metabolites are
said to have first been a
photosynthetic byproduct or
chemical waste, proving ‘fit’
those plants creating them.
Then evolution did its stuff....
Classification Choices
1) According to carbon skeletal type. This was found to be
“far too cumbersome for practical use.”
2) According to biogenesis or biosynthetic origin. This is the
most widely used system of SM classification.
Using a biosynthetic classification system, largest groups of
Secondary Metabolites:
Terpenoids
Alkaloids and other nitrogen compounds
Phenolics
Terpenoids
Terpenoids (isoprenoids)
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Common biosynthic origin
from isopentenule and
dimethyulallyl
purophosphates
generally lipophilic, plant
oils
•
leaf glandular trichomes,
bud exudates, bark resins
•
Flavonoids, aromatics,
carotenoids, chlorophylls
May mimic insect growth
hormones
Include Cardiac Glycosides
which affect the heart.
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Toxic to most fungi and
insects
Alkaloids
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Best known nitrogencontaining Metabolites
Low content offset by
biological potency
Found in 20%
angiosperms
Most familiar and
addictive. Cocaine,
morphine, THC, caffeine,
nicotine
insecticide
Bitter tasting, affect cell
membrane function,
cause difficulties in
digestion. Generally
affect Nervous system.
Phenolics
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Common biosythetic origin
from phenylalanine
Aromatic
Ionize in presence of a
base
Used in spices
Tannins are used in tanning
leather
SMs and Herbivory
Scenarios:
•
Herbivore does not taste chemicals, eats them, and dies, for example,
if it ate an alkaloid-rich plant.
• Herbivore eats small portion of plant and suffers from ‘unpleasant
symptoms’ afterwards. Most vertebrates can associate the two
events and learn to avoid that plant.
 Herbivore does not feed on a single plant but feeds on many different
species. Using this approach, the herbivore avoids ingestion of
high levels of one kind of chemical.
 Herbivore is adapted to on a particular plant species (food specialist)
and is immune to affects of chemical. Also, many species of
insect use plant chemicals to their advantage.
Defense
SMs and Herbivory
How Herbivores Survive Such a Toxic HELL
Common in insects, known
poisonous butterflies
Alkaloid Content and Specialist- Aphids
• Aphids and
phloem
•Sweet lupins
vs. Toxic
lupins
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*
•Specialized
aphid,
Macrosiphum
Albifrons,
sequestration
M.Wink et al (1992)
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What determines high levels of toxicity?
Latitude
(Tropical vs. Temperate)
Availability of Nutrients
Rates of succession
Age of Plant Tissue
Latitudinal Trends
Latitudinal Cline
Decrease in latitude
results in an increase of
plants bearing alkaloids.
Why?
Potency
Tropical vs. Temperate
Alkaloid Content
Kricher:
27%
45%
Nutrients
• Expensive Leaf
Production
Areas:
– Blackwater River
draining areas
– Whitewater River
draining areas
Black water forest stream,
called an Igarape
Succession
Rates
• Trade off:
– Fast Growing vs.
Defense
– Gap specialists
Toxicity and Young
Leaves
• Young leaves are a target
for herbivory;
understandably high levels
of defense compounds
– Toxicity depends on
species
– Alternative defense:
delayed greening, low
nutrient composition, rapid
leaf expansion
Rates of Herbivory
Comparison of rates of herbivory in temperate and tropical forests.
Annual
%
n
Temperate
Tropical wet forest
Shade-tolerant sp.
Gap specialists
Tropical dry forest
7.1
11.1
48.0
14.2
Mature Lves
%/d
n
Young Lves
%/d
n
13
21
4
4
Young/total
%
n
27.0
.03
.18
.07
105
37
78
.71
.65
.15
150
37
61
68.3
47.3
28.7
31
30
62
Annual is the average percentage damage per year, with N being the number of studies
(each study included many species). Daily rates of herbivory are presented for young and
mature leaves (%/d), young/total indicates the percentage of the total lifetime damage
that occurs while leaves are expanding, n indicates the number of species. Data on
young/total from the temperate zone are the average for an entire forest. Data taken from
Coley et al. 1996. (http://ecolsys.annualreviews.org/cgi/content/full/27/1/305/T1)
SMs and People
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According to The National Cancer
Society, Tropical Forests could ccontain
20 ‘superstar’ drugs Anticancer drugs.
Of the 150 most commonly prescribed
drugs in the United States, 57% contain
at least one major active compound
derived from compounds in nature.
While 25% of all Western
Pharmaceuticals are derived from
rainforest ingredients, less than 1% of
these tropical tress and plants have been
tested by scientists
The U.S. National Cancer Institute has
identified 3000 plants that are active
against cancer cells.
•
Taxol/Paclitaxel
– A chemical discovered in the pacific
Yew Tree is now the first drug of
choice in several tumorous cancers
including Breast Candcer.
•
Vinblastine
A chemical discovered in the
Madagascar Periwinkle . First
drug of choice in many forms
of Leukemia and has increased
survival rate of childhood
leukemia by 80%
Q&A
•
•
What are the three main groups of Secondary Metabolites?
– Terpenoids
– Alkaloids
– Phenolics
What are the main characteristics of each regarding plant defense?
– Terpenoids are generally plant oils including flavinoids and aromatics
– Alkaloids are known for their tendency to affect the nervous system, tasting bitter
– Phenolics, including tannins, are generally toxic to insects due to their tendency to
be acidic
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•
What are the four determinates of toxicity for plant defense?
– Latitude
– Availability of nutrients
– Age of Plant tissue
– Rates of succession
What is the term specific to the decrease in latitude resulting in an increase of plants
bearing alkaloids?
Latitudinal Cline
•
What are the two main types of drainage rivers (regarding nutrient retention) and in
which do you find ‘SM-rich’ or ‘SM-poor’ Plants?
•Blackwater rivers, known for nutrient leaching resulting in Highly defended
plants but low rates of growth.
•Whitewater rivers, low levels of nutrient leaching but high sediment erosion,
resulting in poorly defended plants but high rates of growth
Sources
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Coley, P. D., Barone, J. A.. 1996. Herbivory and Plant Defenses in Tropical Forests.
Annu. Rev. Ecol. Syst.. 27:305-335
Harborne, J.B. 1999. Classes and Functions of Secondary Products FromPlants.
Chemicals From Plants. Ed. NJ Walton, De Brown. ICP: London. 1-26
Kricher, J., 1997. A Neotropical Companion. Princeton University Press
Levin, Donald. 1976. Alkaloid-Bearing Plants: An Ecogeographic Perspective.
Am. Nat. 110: 261-284
Novacek, M.J., 2001. The Biodiversity Crisis. NP: N.Y, 1-20
Verpoorte, R. 2000. Plant Secondary Metabolism. Metabolic Engineering of Plant
Secondary Metabolism. Ed. Verpoorte, R., Alferman, A.W.. Kluwer Academic
Publishers. 1-29
Wink, M.. 1998. Functions of Plant Secondary Metabolites and Their
Exploitation in Biotechnology. Sheffield Academic Press: England. 1-19,
110
Smolenski et al. 1972, 1973, 1974a, 1974b. unpublished data taken from:
Levin, D., 1976. Alkaloid-Bearing Plants: An Ecogeographic Perspective. Am. Nat.
110: 261-284
Medicinal Facts found on www.rain-tree.com/plantdrugs.htm
Photo of blackwater stream found at:http://www.amazonianfish.co.uk/indexc40.html