12 - Plant defense

herbivory

every plant is under constant threat of attack

Most widespread plant-animal interaction for herbivory

Insects: feeding on plants day and night

Plant defense mechanisms

mechanical defense

chemical defense

mechanical defense

tissues and organs

growth organs dedicated defense, takes time

chemical defense

plant secondary compounds (toxins )

more spur of moment

Primary compounds

products of photosynthesis, protein synthesis products you need

essential to normal cellular function and life in general

can not silence these genes

example of Primary compounds

carbohydrates, proteins, starches, cellulose, lignin

Secondary compounds

= products have no known direct function in basic metabolism

can silence genes

examples of Secondary compounds

toxins

Role of secondary compounds

Huge complexity of compounds, strict control of synthesis

→ chemical weapons against herbivores

are the chemical weapons dangeorus to humans

no usually our spices

examples of toxins

cocaine

thc

caffinene

cannabis

morphin

mustard oil

cyanide

systemic

defense always presetnn

indus=ced

induced by herbivore attacks

types of denfense by plants

Systemic physical

Systemic chemical

Induced physical

Induced chemical

Physical defense is mostly whcih type

systematic

chemical defense is mostly what type

often induced

who feeds on plannt indirectly

anyone after primary consumer

are plant defense successful

yes cuz alot of plants still exits

Systemic physical defense

Thorns and spines

more density of trichome

fake insect droppings

fake egg on stem

fake damage (spots)

passive hiding

Active hiding

Thorns and spines - example

cactuses

more density of trichome - example

more density of hair makes it harder for insects to get to

passive hiding - example

camoflouge

Pebble plants, Kalahari Desert Rarely if ever getting eaten

Active hiding - example

Touching leaves → within seconds leaves fold → look like twigs Electric currents, signal travels through phloem

ii. Systemic chemical defense

poisen ivy

built in poison

Systemic physical AND chemical

built stinging needle with poison

Induced physical defense

Grass defense and grazing pressure

rarest category

de-induced mehcnaims

if arent being used they stop

Induced chemical defense

after feeding → enzyme produced by plant

help from other insects

after feeding → enzyme produced by plant example

enzyme impairs caterpillar’s nutrient utilization: inhibition of caterpillar’s growth

Enzyme: highest concentration around the wound

help from other insects

Attacked plant emits gas & increased levels of honey to attract ants Ants limit herbivores

whats animals response to plant defense

Herbivores develop ways to circumvent plant defenses → Co-evolutionary arms-race

animals response to plant defense - example

Toxicity → heart attack in small mammals

Monarch: immune → uses chemicals for own benefit → protection against birds

makes birds sick

Why don’t plants always defend themselves?

defense takes alot of energy

Jasmonic acid:

plant-plant signal of imminent herbivore attack → “better gear up your defense”

1. A typical plant produces a large multitude of defense compounds and its production is under strict genetic control

true

“The dose makes the poison. ... All things are poison, and nothing is without poison, the dosage alone makes it so a thing is not a poison.” This is a statement by Paracelsus from the year 1538. For which lines of plant defense is this statement especially true?

Secondary compounds, Chemical defense

1. To what class of compounds does RuBisCO belong

primary

Without primary compounds, plants would most likely be unable to germinate, photosynthesize, establish as a seedling or reach maturity

true

1. To what class of compounds does cannabinol belong?

Secondary compounds, toxins 

1. Much of the spices and herbs we use to make our food less bland contain toxins plants used to fend their enemies

true

Pregnant women and babies have a dislike for certain, especially pungent plant foods because their content of plant chemicals aimed to fend off plant herbivores might be toxic for mammals with a small body size

true

1. To what class of compounds does ATP belong?

primary

1. In contrast to the fast production of alarm volatiles, the start of the production of sugar rewards takes much longer

False

2. To what class of compounds does C6H12O6 belong?

Primary 

3. Without plant secondary compounds, a plant would be unable to maintain the basic metabolic processes of its life

False 

1. To what class of compounds does nicotine belong?

Secondary and toxins

1. In some cases a plant’s herbivores can serve as the reward for carnivorous plant defenders

True 

2. To what class of compounds does caffeine belong?

Secondary and toxins 

3. What will the unfortunate gentleman in the following picture will suffer from?’

Systemic physical defense

4. Primary plant compounds have no known direct function in plant metabolism

False 

5. To what class of compounds does lignin belong?

Primary compounds

While secondary compounds are not necessary for the very basics of plant life, without them a plant could suffer enough leaf area loss due to herbivory that it might not be able to set aside enough energy to flower or produce seeds

true

1. To what class of compounds does cellulose belong

Primary 

2. To what class of compounds does starch belong?

Primary 

3. Inducible chemical defense should be dependent on the extent of herbivore damage. Plants are modular and hence are able to regrow from multiple shoot and root meristems. As such they have adapted to some level of herbivore damage. As a consequence, the production of secondary chemicals should only kick in if herbivore damage takes on life-threatening levels

True 

4. n some cases a plant does not directly reward an animal defender against its herbivores. It simply needs to use resources to emit a gaseous volatile to announce the presence of an herbivore pest and the defender will show up and do the job.

True  

1. In contrast to the production of plant defense chemicals, the ‘call for help’ to carnivores to feed on herbivores as a reward keeps the costs down of plant defense against herbivory

True

1. Inhibition of digestive enzymes in herbivore guts is a common way how plants decrease herbivore pressure and hence essentially starve animals while their stomachs are full

True 

2. Inhibition of digestive enzymes by secondary plant chemicals has been shown to work only in insect herbivores but not in mammals

True 

3. A common reward for insects defending a plant against herbivores is concentrated sugar pellets

True 

4. The production of volatile alarm chemicals to ask for help can be induced within minutes

True