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1. Plant Physiology Forum Co-ordinators: Phillip Joy
2. Insect-Induced Conifer Defense. Miller, B., Madilao, L.L, Ralph, S., and Bohlman, J. 2005. Plant Physiol. 137: 369-382.
3. Forestry Problems Bark invading insects are major economic and ecological concerns
Beetles and their vectored fungal pathogens are the most destructive agents of conifer forests worldwide.
Pest management practices in agriculture do not apply to forestry.
Conifers have evolved defense strategies towards these invaders
overlapping mechanical and chemical defenses and the capacity to up-regulate additional defenses.
5. Chemical Defense Diverse group of terpenoids
derived from isoprene C5H8 units
different terpenoids have different multiples of units
Mono-, di-, and, sesqui-
Major components of oleresins
Function as repellents or toxins to herbivores or pathogens
6. Resin Secretion formed in special resin canals
Exuded in soft drops from wounds
Resins seal the plant's wounds, kill insects and fungi, and allow the plant to eliminate excess metabolites.
8. The Experiment Purpose:
To determine if stem-boring insects and methyl jasmonate (MeJA) treatments invoke similar defenses in conifers.
Emissions of terpenoid volatiles
Expression of terpenoid synthase (TPS) genes
9. Methyl-Jasmonate (MeJA) Among the most potent plant signaling molecules
Damaged or infested plants produce higher levels of MeJA
Defense mechanisms include:
Interference with herbivore digestive system deterring insect feeding.
Volatile organic molecules
that serve as attractants for predators of the herbivores.
act as a messenger to neighboring undamaged plants, prompting them to produce defensive chemicals
Treatment with MeJA induced
formation of resin ducts
increased accumulation of oleoresin terpenoids
Unclear how well MeJA treatment mimics the effects of insects in inducing defense.
10. Results Trepenoid accumulation in stems
Both Weevil and MeJA induced traumatic resin duct formation
Increase of Terpenoids after treatment with MeJA or Weevil attack
11. Results TPS Transcript Accumulation in Stems
Both MeJA and Weevil induce mono-TPS
Both MeJA and Weevil induce di-TPS
Weevil induces Sesqui-TPS
Spatial Patterns of Weevil defense
Weevils on top: no increase of terpenoids in distal tissue
Weevils on bottom: an increase of TPS in upper tissue
12. Results Emissions
Max at 3d
Max at 6-12hr
Active mechanisms, not passive release from ducts and blisters
Larger variety of emissions where ID
13. Results What’s going on in the needles?
Monotrepeniods, specifically (-)- linaloon (an alcohol) is formed and released from the needles
No Ditrepeniods are found
14. Discussion Both Weevil and MeJA induce similar chemical defense
Weevil defense is stronger and more complex
They activated similar TPS genes, but Weevils induced more and with more strength
So, can MeJA be used to ‘jump-start’ Weevil defense??
15. Discussion Both Weevil and MeJA induce Traumatic resin ducts to be formed
Stronger for Weevils
Due to the wounding factor?
Due to continues feeding?
Is MeJA releasing the passive/stored terpenoids?
More likely activating their production
What is the role of the stored terpenoids?
16. Discussion Weevil feeding causes some signal translocation, will MeJA?
What other Octadecanoid pathway intermediates are involved?
JA synthesis pathway
What about other xylem regulators (forms TDs)?
17. Conclusion MeJA induces some of the same defenses as Weevil attack, therefore it may be able to activate Weevil defense prior to attack
The role of TDs are still not truly understood
Contain terpenoids, are formed as a defense mechanism, fills with resin
Are the emissions inter-plant communication?
18. Questions & Comments