VL 4

Question 1

Two principal approaches to measuring plant resistance to herbivores

Answer 1

Antibiosis
(how suitable the plant is for the herbivore)
- herbivore fitness
- intrinsic plant traits underlying herbivore fitness

Antixenosis
(how much damage or how many herbivores a plant attracts)
- herbivore presence
- herbivore damage

Question 2

Two types of direct resistance

Answer 2

Physical resistance
- cuticle wax, lignification
- trichomes, spines, thorns
- secretory defenses
- calcium oxalate crystals

Chemical resistance
- Reduced digestibility
- Toxins

Question 3

Cuticle, wax and lignification

Answer 3

Border of a plant and first line of defense
primarily useful for maintaining osmotic balance with environment
has some defensive capabilities against insects

structurally diverse among species but exhibits the organization of a composite material consisting in cutin and suberin, a polyester that is partly covered and interspersed with waxes

Question 4

How does wax reduce insect adhesion?

Answer 4

Roughness hypothesis
wax-dissolving hypothesis
contamination hypothesis
fluid-absorbtion hypothesis

Question 5

Lingnin

Answer 5

Lignin is the second most abundant polymer, after cellulose, found in nature

Lignin provides terrestrail plants with physical structure

synthesized by the phenylpropanoid pathway (as are tannins, flavonoids and other polyphenols)

can be induced locally to prevent or hinder feeding

Question 6

Trichomes, spines and thornes

Answer 6

Limit herbivory by blocking access to plant cells

Glandular thrichomes can:
- trap insects and/or secrete chemical deterrents
- encapsulate volatile chemical deterrents

spines/thorns:
originally thought to only be a deterrent against larger, vertebrate herbivores
recent study shows that spines restrict movement of caterpillars

Question 7

Secretory defenses - three types

Answer 7

Resin
Gum
Latex

Question 8

Resin

Answer 8

Lipid-soluble mixture of volatile and non-volatile terpenoid and/or phenolic compounds

this mixture of secondary metabolites is not involved in growth metabolism. It is not “phloem sap”
(Epithelial cell lining secretes resin)

Resin evolved 320 million years ago
Amber is fossilized plant resin
Effectivity since its evolution is proven by enclosures in amber

Question 9

Gum

Answer 9

Neither terpenoid, nor phenolic in origin (but can contain both)

True gums are complex chains of hydrophilic polysaccharides

Broken plant cell walls result in cavities in the tissue which are filled with sugars

Question 10

Latex

Answer 10

Composed of a complex mixture of hydrophobic molecules (lipid soluble) including tannins, proteins, alkaloids, oils and gum

secreted by laticiferous tissues

Question 11

Calcium oxalate crystals

Answer 11

Raphides: prismatic monoclinic crystals of Ca oxalate

produced in cells called idioblasts

a large “styloid” spans the entire leaf

Raphids faciliate poisoning of the gut in two steps:
- mechanical prcking
- injection of a harmful protease

Question 12

Chemical resistance - reduced digestibility

Question 13

chemical resistance - toxins

Answer 13

gut disruption / destruction as plant defense
- can kill or slow growth of herbivourous insects
- generally, prevents the insect from reaching maturity

Question 14

4 Types of toxins

Answer 14

Cyclopeptides
Lectins
Alkaloids
Glucosinlates

Question 15

Cyclopeptides

Answer 15

Large class of small plant proteins that are post-translationally processed into a continuous loop structure

result in swollen gut due to epithelial cell damage

Question 16

Lectins

Answer 16

Plant lectins are proteins that bind specifically to carbohydrates on the cell surface

highly selective
several lectins are known to cause antibiotic effects in Coleoptera, Hemiptera or Lepidoptera

Question 17

Alkaloids

Answer 17

“True alkaloids” contain nitrogen in a heterocyclic molecule and originate from amino acids
* E.g. Nicotine, Cocaine and Morphine

“Pseudoalkaloids” – alkaloid-like compounds that do not originate from amino acids.
* E.g Caffeine

Other alkaloid groups exist

Question 18

Example of alkaloid

Answer 18

Nicotin:
unique toxin of the Solanaceae family
binds to acetylcholine receptors and causes paralysis in insects, at high concentrations even death

Neonicotinoids:
Very high specifity to insect acetylcholine receptors
most effective insecticides but kills beneficial insects as effectively

Question 19

Glucosinolates

Answer 19

Mustard oils -> two component system called “mustard oil bomb”

unique to brassicaceae

commonly induced by herbivory
initially evolve to deter herbivory

Have resulted in one of the most studied evolutionary arms races in plant-insect interactions

plants evolve new glucosinolates to deter herbivory

Insects evolve new ways to mitigate glucosinolates and repurpose them for other uses

this arms race has resulted in providing humans with the taste that we enjoy in mustard plants

Question 20

4 contermeasures of insects to direct resistance

Answer 20

specialized behaviour
detoxification
sequestration of toxic compounds
highjack host’s metabolism

Question 21

Example of chemical resistance in insects: Nicotine resistance

Answer 21

Manduca sexta (tobacco hornworm) is specialized for life around Solanaceae
The adult hawkmoth feeds (and pollinates) Solanaceae

Manduca caterpillars move unmodified nicotine through ther gut and excrete via their Malpighian tubules

Cotesia parasitoid larvae exhibit increased mortality when feeding on Nicotiana-fed caterpillars

Question 22

Sequestration and modification of nicotine

Answer 22

Unmodified nicotine repels spiders
Manduca sexta larvae do not metabolize nicotine

Nicotine oxidation reduces Spodoptera exigua’s headspace-nicotine and renders it more susceptible to predation by spiders than M. sexta, which exhales unmetabolized nicotine

Question 23

Glucosinolate sequestration and modification

Answer 23

p. 52 - 54

Question 24

Example of specialized behavior

Answer 24

Cutting the midrib eliminates the distal outflow of latex

Question 25

58 - 72
Effect of Daktulosphaira vitifoliae Phylloxeridae on wine production in Europe

Answer 25

p. 58 - 70