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Life of Earth 2 > Biotic & abiotic stresses > Flashcards

Biotic & abiotic stresses Flashcards

Plants lecture 4

1
Q

What is stress?

A

Change in enviro conditions that might reduce a plant’s survival, growth, development or reproduction

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2
Q

What are the 3 types of biotic stress?

A

Pathogens
Herbivores
Competitors

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3
Q

What are the 4 types of abiotic stress?

A

Water
Temp
Light
Chemicals

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4
Q

What are the 2 forms of water stress?

A

Drought

Flooding –> anoxia

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5
Q

What are the 2 forms of light stress?

A

Photo-inhibition

UV damage

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6
Q

What are the 4 types of chemical stress?

A

Salinity
Heavy metals
Mineral deficiency
Acid soils

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7
Q

Describe the issues with plant-human interactions

A

Stress impacts agri –> impacts food

Humans impact enviro —> impacts stress on plants

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8
Q

What are the 4 ways in which humans are exacerbating stresses on plants?

A

> natural resource depletion
pollution - soil, water & atmosphere
irrigation - salinity
climate change - temp, rain, sea level & weather

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9
Q

What are the 3 types of plant responses to stress?

A

> injury/death
avoidance - spatially or temporally
tolerance - alter metabolism to tolerate impact of stress

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10
Q

Give an example of how plants avoid stress

A

Desert plants have v short life cycles & flower v rapidly only after rain

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11
Q

Give an example of how plants tolerate stress

A

Drought tolerance in resurrection plants (can survive desiccation to 7% water w/out injury

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12
Q

What are adaptations to stress?

A

Heritable modifications of structure/function that enable plants to survive & reproduce in otherwise adverse environments

Allows for tolerance or avoidance

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13
Q

What happens to plants during a water deficit?

A

Water loss via transpirations exceeds uptake from roots

–> leads to stress

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14
Q

What mechanisms can plants have to conserve water?

A

> close stomata via loss of turgor pressure in guard cells
ABA hormone acts on guard cell membrane
slow leaf growth
rolled grass leaves
shed leaves

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15
Q

What is the ABA hormone?

A

Abscisic acid

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16
Q

What is the issue w/ shedding leaves?

A

Reduces photosynthesis –> diminishes crop yield

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17
Q

How is Cassava (Manihot esculenta) tolerant to drought?

A

Sheds all leaves in drought

–> regrow rapidly after rain

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18
Q

How do roots respond to water deficit?

A

Shallow roots in dry, surface soil lose turgor = inhibited growth
Deep roots in moist soil = continue to grow

THUS root system proliferates to maximise exposure to water

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19
Q

Give an example of plants adapted to excess water

A

Mangroves have aerial roots exposed to air

–> can aerobically respire

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20
Q

How do plants respond to water logging?

A

O2 deprivation stimulates ethene production
–> causes some cells of root cortex to undergo apoptosis
–> creates air tubes (function as snorkels)
= provide O2 to submerged roots

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21
Q

What can excess salts in soil lead to?

A

Lower water potential of soil –> water deficiency of plant

Sodium & other ions = toxic when concs high enough to overwhelm selective permeability capabilities of root

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22
Q

How can plants respond to excess salts in soil?

A

Produce ‘compatible solutes’ = proline or glycine betaine

–> lower WP of cells w/out admitting toxic quantities of salts

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23
Q

What is the name of plants that can survive salt stress for long periods?

A

Halophytes

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24
Q

How does heat stress affect plants?

A

Kill them by denaturing proteins & disrupting metabolism

25
Q

What do plants do above 40 degrees C?

A

Synthesise heat-shock proteins
(include chaperonin that prevent denaturation)
- protect other proteins from stress

26
Q

How does cold stress affect plants?

A

Membranes lose fluidity
= crystalline
= alters solute transport

27
Q

How do plants respond to cold stress?

A

Alter lipid composition
- increase proportion of unsaturated fatty acids
–> increases membrane fluidity
(takes hours/days)

28
Q

How does freezing affect plants?

A

Ice forms in cell walls & intercellular spaces
–> H20 leaves cytoplasms due to reduced WP in cell wall
= increase in ion conc in cytoplasm
= death

29
Q

Why doesn’t cytoplasm freeze?

A

High solute conc

30
Q

How are cold-tolerant plants adapted?

A

Accumulate higher levels of solutes (e.g. sugars)

& unsaturation of fatty acids

31
Q

What do antifreeze proteins do?

A

Prevent ice crystals growing so large

32
Q

What defences have plants evolved against herbivores?

A

> Thorns
Trichomes = hairs that interfere w/ feeding systems of small herbivores
Chemicals - toxic
e.g. Canavanine

33
Q

How does canavanine affect insects?

A
  1. insect eats plant
  2. canavanine incorporated into insect’s proteins instead of arginine
  3. alters structure & function of proteins
  4. insect dies
34
Q

How do plants recruit predatory animals?

A
  1. Caterpillar eats plant
  2. Wounding & chemicals in saliva triggers signal induction pathway in plant
  3. synthesis & release of volatile attractants
  4. attracts parasitoid wasps that lay eggs in caterpillar
35
Q

What do plants use volatile signals for?

A

Signalling between plants

36
Q

Describe how plants use volatile signals to signal to one another

A
  1. Lima beans infested by spider mites release volatiles - including methyl-jasmonic acid
  2. Signals the attack to neighbouring plants
  3. Neighbouring plants prepare for attack
37
Q

How can neighbouring plants prepare for an attack once they receive volatile signals?

A

> biochemical changes that make them less susceptible to attack
release other volatiles that attract predatory mites that feed on spider mites

38
Q

What 3 things must occur for an interaction to turn into a disease?

A
  1. pathogen must be able to overcome plant’s defences
  2. host plant must be susceptible to pathogen
  3. environment must be in favour of pathogen
39
Q

How have Pseudomonas syringae evolved to invade plants?

A

Evolved coronatine which causes stomata to open

40
Q

What’s special about Puccinia monoica?

A

Fungal pathogen mimics flowers = pseudoflowers

41
Q

What is a plant’s 1st line of defence?

A

Epidermis & periderm

- but pathogens can enter via wounds & natural openings

42
Q

What is a plant’s 2nd line of defence?

What is this defence enhanced by?

A

Chemical attack
- destroy pathogen & prevents spread

Ability to recognise pathogen

43
Q

Describe the zig-zag model of plant-pathogen interactions

A
  1. pathogen recognised = pattern triggered immunity
  2. pathogen effectors suppress defence response
    = effector triggered susceptibility
  3. effector recognised
    = effector triggered immunity
44
Q

What is a virulent pathogen?

A

One that plant’s have little specific defence against

45
Q

What is an avirulent pathogen?

A

One that cannot infect & colonise the host plant due to effective plant immunity

46
Q

What do avirulent pathogens produce?

What are these coded for by?

A

Effector molecules
- recognised by plants

Avirulence genes = Avr genes

47
Q

Avirulent effector molecules are recognised by what?

What are these coded for by?

A

Plant resistance proteins

Resistance genes = R genes

48
Q

What happens if plant resistance proteins detect effector molecules?

A

Activate plant defences by triggering signal transduction pathways

49
Q

What are the 2 signal transduction pathways?

A

Hypersensitive response

Systemic acquired resistance

50
Q

How do virulent proteins evade R protein recognition?

A

Produce molecules not recognised by R proteins

51
Q

What type of evolutionary relationship occurs between plants & pathogens?

A

Arm’s race

52
Q

Which gene combination results in host plant resistance?

A

Dominant R1 + Avr1

53
Q

Describe R-Avr recognition

A
  1. Pathogen Avr effector molecules bind to specific plant R proteins
  2. Triggers signal transduction pathway
  3. Hypersensitive response
54
Q

Describe the hypersensitive response

A

Plant cells produce anti-microbial molecules & PR molecules

  • -> seal ff infected areas by modifying cell walls by synthesis of lignin & cross-linking molecules
  • -> then destroy themselves
55
Q

Describe systemic acquired resistance

A

Infected cells secrete signalling molecules methylsalycilic acid

  • -> distributed to rest of plant via phloem
  • -> converted to salicylic acid = initiates signal transduction pathway
  • -> activate systemic acquired resistance
56
Q

What are the antimicrobial compounds compounds in the hypersensitive response?

A

Phytoalexins

57
Q

What are PR proteins?

involved in the hypersensitive response

A

Pathogenesis related proteins

= enzymes that attack pathogen cell walls

58
Q

Briefly describe the process of defence responses against a virulent pathogen

A
  1. Avirulent protein infects plant
  2. Avr effector protein binds to R protein
  3. Signal transduction pathway
  4. Hypersensitive pathway
  5. Methylsalycilic acid secreted
  6. Distribution via phloem
  7. Signal transduction pathway
  8. Acquired resistance

Life of Earth 2 (20 decks)

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