Plant Defense:

N-containingcompounds

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.

• Larvae of the cinnabar moth, Tyria jacobea, accumulate alkaloids and become distasteful to predators. All stages of the moths have warning coloration.

Insects can sequester compounds to use in their own defense

Some grasses host fungal symbionts that produce alkaloids

Bioprotective Alkaloids of Grass-FungalEndophyte Symbioses

Lowell P. Bush, Heather H. Wilkinson, and Christopher SchardlPlant 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-Nicotiana sylvestrus

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.

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

Non-infested leaf

More recalcitrant litter

C:N = 15 C:N = 20

Herbivore-attacked leaf

= Carbon- based defensive compound

Induced carbon-based defensive compounds

Normal litter

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.

Larch sawfly, Pristiphora erichsoniiPeaked @ 450,000 acres in 1999, now increasing again.

Spruce aphid Elatobium abietinum on Sitka spruce needle

Sprucesawfly

Spruce beetle larvae, Dendroctonus rufipennis,area infested up 40% in 2004 to 129,000 acres.

Aspen leaf miner, Phyllocnistis populiella584,000 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.

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.”

“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……….

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.