Plant Defense: N-containing compounds

1
Plant Defense N-containingcompounds
2
(No Transcript)
3
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

4
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

5
(No Transcript)
6
EPHEDRA
7
Amino acids lysine, tyrosine, ornithine, and
tryptophan are often precursors of alkaloids
8
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.

9
ALKALOIDS

• Often alkaloids are used as medicines for humans
• Some examples morphine, codeine, and scopolamine
• cocaine, nicotine, and caffeine used as
  stimulants and sedatives.

10
(No Transcript)
11
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.

12
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
13
Wild tobacco can sense which herbivore is
feeding on it. It normally produces nicotine (an
alkaloid) in response to herbivore feeding. But
if nicotine-tolerant caterpillars are feeding,
the tobacco produces terpenes instead. These
terpenes can attract the predators of the
herbivore.
Wild tobacco-Nicotiana sylvestrus
14
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)

15
The degradation process is stimulated by
herbivore feeding.
16
S. American native peoples eat cassava (Manihot
esculenta), has high levels of cyanogenic
glycosides. Chronic cyanide poisoning are not
uncommon.
17
3. GLUCOSINOLATES

• These compounds release volatile defensive
  substances, mustard oils, (often herbivore
  repellents)
• Plants like cabbage, broccoli, and radishes
  (Brassicaceae family) have these.

18
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.

19
(No Transcript)
20
Herbivore Damage can Elicit a Signaling
Pathway(Induced Defenses)
21
(No Transcript)
22
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.

23
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 dont have immune systems they
  have signaling mechanisms that can act in this
  way.

24
(No Transcript)
25
Talking trees?
26
Or listening trees?
27
Finally, plant defenses against herbivores can
alter ecosystem processes
28
Carbon- based defensive compound
Induced carbon-based defensive compounds
Herbivore-attacked leaf
Non-infested leaf
More recalcitrant litter
Normal litter
CN 15
CN 20
29
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
30
Spruce beetle damage, Alaska
31
(No Transcript)
32
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.
33
Spruce beetle larvae, Dendroctonus
rufipennis, area infested up 40 in 2004 to
129,000 acres.
Larch sawfly, Pristiphora erichsonii Peaked _at_
450,000 acres in 1999, now increasing again.
Spruce sawfly
Spruce aphid Elatobium abietinum on Sitka spruce
needle
34
Aspen leaf miner, Phyllocnistis
populiella 584,000 acres in 2004 and up from
2003. Adult moths overwinter in duff and beneath
bark.
35
Aggregate mean annual temperature for forested
regions of Alaska rose 2.53.5 F between1949 and
2003.
36
In interior Alaska, the first recorded spruce
budworm outbreak, from 19931995, 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 20022003 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.
37

• 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.