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Induced Resistance

Plant Defense — Herbivore Offense. Induced Resistance. Advantage: lower allocation costs and ecological costs when herbivores are absent. Disadvantage: Lag-time between first attack and fully induced resistance. Conceptual model. How to reduce the cost of the lag-time?.

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Induced Resistance

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  1. Plant Defense — Herbivore Offense Induced Resistance Advantage: lower allocation costs and ecological costs when herbivores are absent. Disadvantage: Lag-time between first attack and fully induced resistance. Conceptual model How to reduce the cost of the lag-time?

  2. Detection and response of plants to oviposition Bruchus pisorum

  3. assay plants damaged plants control plants "Communication" between plants • Baldwin & Schulz (1983): Populus and Acer trees Glasshouse experiment Results: • phenolics increased in damaged plants • phenolics increased in assay plants !!! "Talking trees"

  4. • Karban et al. (2000) Field experiment: Nicotiana Artemisia Prop. leaves damaged (Nicotiana) PPO activity Artemisia clipped/unclipped • Dolch & Tscharntke (2000) Field experiment: Alnus Alnus leaf damage (%) eggs per leaf distance distance from defoliated tree (m)

  5. What signals are emitted by plants after wounding by herbivores? • Volatile organic compounds (VOCs): terpenes, green leafy volatiles • Methyljasmonate (MeJA) Who can perceive and respond to signals? • Neighboring plants (?) • Parasitoids and predators

  6. Parasitoids & Predators Herbivores ? Plants Tri-trophic interactions

  7. Indirect defense in the field Manduca quinquemaculata on Nicotiana attenuata Survival of Manduca Oviposition by Manduca Oviposition rate % survival Con. MeJA 1 2 4 7 8 Con. MeJA Manduca 4 Volatiles applied to plants Kessler & Baldwin (2001)

  8. Indirect defense — slow growth/high mortality hypothesis Slow growth rate of herbivores may lead to increased parasitism/predation Pieris rapae reared on artificial diet and exposed to Cotesia glomerata parasitoid Fast development (warm temperature) Fast development (casein-rich diet) Slow development (cold temperature) Slow development (casein-deficient) Parasitism rate (%) Parasitism rate (%) Larval age (days) Benrey & Denno (1997)

  9. Herbivore offense How insects adapt to defensive chemicals in plants

  10. • Rapid excretion Experiment: Nicotine dose in artificial diet –> 93% excreted within 2 hours! Experiment: Nicotine injected into hemolymph Manduca sexta

  11. • Enzymatic detoxification Mixed-function oxidases (e.g. cytochrome P450) can metabolise a large array of plant secondary chemicals. Ubiquitous in herbivorous insects, in midgut. Example: Spider mites adapted to bean

  12. Helicoverpa zea (Noctuidae) Recent discovery : Cytochrome P450 induced by jasmonate and salicylate!!! (Li et al. 2002)

  13. Disarming the mustard oil bomb - Plutella xylostella using glucosinolate sulfatase (GSS) Ratzka et al. 2002

  14. Disarming the mustard oil bomb - Pieris rapae using nitrile-specifier protein (NSP) NSP Wittstock et al. 2004

  15. • Target-site insensitivity Na+,K+-ATPase is sensitive to ouabain (a cardiac glycoside). In Monarch butterflies a single-point mutation resulted in insensitive ATPase. Other example: induction of proteases in herbivore gut, which are insensitive of proteinase inhibitors

  16. • Sequestration (use of plant toxins by herbivore for his own defense) Involves complex adaptations: 1) Herbivore must be willing to ingest the hosts secondary chemicals 2) Herbivore must be tolerant of chemicals 3) Herbivore must digest chemical without metabolising it into a non-toxic form. 4) Herbivore must deposit chemicals in particular tissues or store them.

  17. Nuptial gifts in Utetheisa ornaztix (moth)

  18. • Compensatory feeding Pieris rapae Consumption rate (mg dry weight per day) Nitrogen content of plant (% dry weight) Slansky and Feeny 1977

  19. • Behaviour

  20. • Symbionts E.g. Buchnera bacteria in aphids

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