Download Plant Defense III

Plant
Defense:
N-containing
compounds
N-containing secondary
compounds
• Synthesized from aliphatic and aromatic
amino acids
• aliphatics via TCA cycle
• aromatics via shikimic acid pathway
Classes of N-containing 2o compounds:
1. Alkaloids, 2. cyanogenic glycosides,
3. glucosinolates, 4. nonprotein amino
acids
ALKALOIDS
• more than 15,000 compounds found in
20% of vascular plants.
• nitrogen is usually part of a heterocyclic
ring with N and C atoms
EPHEDRA
Amino acids lysine, tyrosine, ornithine, and tryptophan are often
precursors of alkaloids
ALKALOIDS
• large pharmacological effects on animals.
• most effective at deterring mammalian
herbivores.
• Livestock deaths due to over-consumption of
alkaloid containing plants such as lupines and
groundsels.
ALKALOIDS
• Often alkaloids are used as medicines
for humans
• Some examples: morphine, codeine, and
scopolamine
• cocaine, nicotine, and caffeine used as
stimulants and sedatives.
Insects can sequester compounds
to use in their own defense
• Larvae of the cinnabar
moth, Tyria jacobea,
accumulate alkaloids and
become distasteful to
predators. All stages of
the moths have warning
coloration.
Some grasses host fungal symbionts
that produce alkaloids
Bioprotective Alkaloids of Grass-Fungal
Endophyte Symbioses
Lowell P. Bush, Heather H. Wilkinson, and Christopher Schardl
Plant Physiol. (1997) 114: 1-7
Well described in Festuca spp., Lolium
perenne because of effects on livestock.
Fungi are Epichloe species and relatives
Neotypkodium spp.
Alkaloids include pyrrolizidines, ergot
alkaloids, indole diterpenes, &
pyrrolopyrazines
Wild tobacco can “sense”
which herbivore is feeding
on it. It normally produces
nicotine (an alkaloid) in
response to herbivore
feeding. But if nicotinetolerant caterpillars are
feeding, the tobacco
produces terpenes instead.
These terpenes can attract
the predators of the
herbivore.
Wild tobacco-Nicotiana sylvestrus
2. CYANOGENIC GLYCOSIDES
• Release the toxic gas hydrogen cyanide.
• plants must have enzymes to break down the
compounds and release a sugar molecule
yielding a compound that can decompose to
form HCN.
• glycosides and enzymes which break them
down are usually spatially separated (in
different cellular compartments or different
tissues)
The degradation process is
stimulated by herbivore feeding.
S. American native peoples eat cassava
(Manihot esculenta), has high levels of
cyanogenic glycosides. Chronic cyanide
poisoning are not uncommon.
3. GLUCOSINOLATES
• These compounds release volatile
defensive substances, “mustard oils”,
(often herbivore repellents)
• Plants like cabbage, broccoli, and
radishes (Brassicaceae family) have
these.
4. NON-PROTEIN AMINO ACIDS
• These amino acids are not incorporated
into proteins but instead act as
protective substances.
• can “mistakenly” be incorporated into
protein and therefore resulting in a
nonfunctional protein.
Herbivore Damage can
Elicit a Signaling Pathway
(Induced Defenses)
Jasmonic Acid
• Levels of jasmonic acid rise in response to
damage .
• This hormone can trigger many types of plant
defenses including terpenes and alkaloids.
• The action of jasmonic acid induces the
transcription of many genes involved in plant
defense.
Systemic Acquired Resistance
• When a plant survives the infection of a
pathogen at one site it can develop increased
resistance to subsequent attacks.
Although plants don’t have “immune systems” they
have signaling mechanisms that can act in this
way.
Talking trees?
Or listening trees?
Finally, plant defenses
against herbivores can
alter ecosystem processes
Induced carbon-based
defensive compounds
Non-infested leaf
Normal litter
C:N = 15
= Carbon- based
defensive compound
Herbivoreattacked leaf
More recalcitrant
litter
C:N = 20
Herbivory consumes up to
20% of plant productivity in
CHRONIC herbivory
situations
(Matson and Addy 1978)
The consumption can be much more
in OUTBREAK herbivory situations
Spruce beetle damage, Alaska
Spruce aphid defoliation, southeast Alaska.
Outbreaks are preceded by mild winters.
In 2004, one low temperature event on January 26,
-18 to -15 °C (0 to 5 °F) caused the aphid population
to crash.
Spruce beetle larvae, Dendroctonus rufipennis,
area infested up 40% in 2004 to 129,000 acres.
Larch sawfly, Pristiphora erichsonii
Peaked @ 450,000 acres in 1999, now
increasing again.
Spruce
sawfly
Spruce aphid Elatobium abietinum
on Sitka spruce needle
Aspen leaf miner, Phyllocnistis populiella
584,000 acres in 2004 and up from 2003.
Adult moths overwinter in duff and
beneath bark.
Aggregate mean annual temperature for forested regions of Alaska
rose 2.5–3.5 °F between1949 and 2003.
“In interior Alaska, the first recorded spruce budworm outbreak, from 1993–1995,
resulted from elevated summer temperatures that produced drought stress in the
host white spruce trees while simultaneously resulting in increased budworm
reproductive rates. A second spruce budworm outbreak that began in 2002–2003
is believed to be the result of the continued trend in warm, dry summers in interior
Alaska. The 2004 wildfire season, the largest on record, was a direct result of
record temperatures and little precipitation……….
Climate-related forest health problems are expected to continue. Drought stress and
reduced growth rates of some trees species are expected, thereby leading to larger
and more frequent insect outbreaks. Larger and more severe fires are expected to
result from a continuation of warmer, drier summers. Loss of forested acres will
continue as a result of thawing of permafrost-laden soils. Also, the total number of new
species in the Arctic,including Alaska, is expected to increase as a result of an influx of
new species under a warmer climate. Some of these species will be invasive plants
and insects that will create new forest health issues.”
Direct and indirect effects of forest pests
•Loss of mechantable value of killed trees.
•Long-term stand conversion.
•Impacts on wildlife habitat.
•Impacts on scenic quality.
•Fire hazard.
•Impact on fisheries due to reduced large woody
debris in spawning streams.
•Impacts on watersheds.