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Life of Earth 2 > Plant responses to internal + external stimuli > Flashcards

Plant responses to internal + external stimuli Flashcards

1
Q

Briefly describe how plant cells respond to stimuli

A
  1. hormone or enviro stimulus binds to receptor
  2. relay proteins + 2nd messengers in cascade of transduction events
  3. activation of cellular responses
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2
Q

How were plant growth regulators discovered?

A

Coleoptile bent towards the light

Phototropic response only when tip is illuminated

Phototropic response only when tip separated by permeable barrier

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3
Q

Describe the conclusions formed when auxin was discovered

A

Derived from coleoptile tip
Diffusible
Present at higher conc on dark side of shoot

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4
Q

What is required for plants to respond to hormones?

A

Different hormones must interact in the right ratios and balance

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5
Q

What does IAA stand for?

What is it, briefly?

A

Indole acetic acid

A common auxin

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6
Q

How is auxin transported?

A

Tip to base polar transport

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7
Q

What are auxins?

A

Any substance that promotes elongation of coleoptiles

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8
Q

What does auxin do?

A

Stimulates cell elongation in young developing shoots
by binding to auxin receptors + transporters at the plasma membrane
-> permits fluxes in auxin conc in target cells

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9
Q

What can high auxin conc do?

A

Inhibits growth by inducing the production of other hormones
e.g. ethylene which inhibits growth

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10
Q

What is the acid growth hypothesis?

A

Ability of plant cells + cell walls to elongate or expand quickly at low pH.
This form of growth does not involve an increase in cell no.

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11
Q

Describe the acid growth hypothesis

A 
1. auxin increases proton pump activity 
= pumps H+ into cell wall from cytoplasm
2. cell wall becomes more acidic 
3. low pH activates expansins which separate microfibrils from cross-linking polysaccharides 
4. cleaving allows microfibrils to slide
5. cell can elongate
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12
Q

What does the polar transport of auxin play a role in?

A

Pattern formation of developing plant
- reducing auxin flow from shoot of a branch stimulates growth in lower branches (=apical dominance)

Leaf venation pattern

Phyllotaxy

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13
Q

What is IBA?

What does it do?

A

Indolbutyric acid
= an auxin

Stimulates adventitious root formation

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14
Q

What are synthetic auxins used for?

A

> preventing leaf abscission
preventing fruit drop
promoting flowering + fruiting
controlling weeds

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15
Q

What is 2,4-D?

What is it used for?

A

A synthetic auxin

Overdose can kill plants
= herbicide

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16
Q

What do cytokinins do?

A

Stimulate cytokinesis

cell division

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17
Q

What are all cytokinins similar to?

A

Adenine

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18
Q

Where is cytokinin synthesised?

A

Mainly in roots

also embryos + fruit

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19
Q

How is cytokinin transported?

A

Non-polar fashion

through xylem, phloem + parenchyma cells

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20
Q

Which hormone to cytokinins work with?

A

Auxin

  • to regulate cell division _ differentiation
  • ratio is important*
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21
Q

What do high concs of auxin alone promote?

What about high concs of cytokinin alone?

A

Cell expansion

Cell division

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22
Q

What is apical dominance?

A

A terminal bud’s ability to suppress development of axillary buds

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23
Q

How are auxins and cytokinins involved in apical dominance?

A

Auxins - maintaining dominance of apical bud

Cytokinins - stimulate axillary buds

Cytokinin acts antagonistically to auxin in apical dominance

24
Q

What is the direct inhibition hypothesis?

A

Auxin from apical buds travels down shoots to inhibit axiliary bud growth
–> promotes shoot growth, + restricts lateral branching

Cytokinin moves from the roots into the shoots, eventually signaling lateral bud growth

25
Q

How do cytokinins delay leaf senescence?

A

> inhabit protein degradation
stimulate RNA + protein synthesis
mobilise nutrients from surrounding tissues

26
Q

What are the roles of gibberellins (GAs)?

A

Enhance cell elongation + cell division

Can induce dwarfing mutants to grow tall

27
Q

Which hormone is responsible for ‘bolting’ during the switch from vegetative to reproductive growth?

A

Gibberellins

28
Q

Which 2 hormones must be present in most plants for fruit to develop?

A

Auxins + Gibberellins

29
Q

Which hormone is sprayed onto Thompson seedless grapes?

Why?

A

Gibberellins

No seeds to produce the hormone

30
Q

How are gibberellins involved in germination?

A

After taking on water…

  1. GAs send signal to aleurone
  2. Aleurone secretes alpha-amylase + other enzymes
  3. Sugars + other nutrients are consumed
31
Q

What does ABA stand for?

A

Abscisic acid

32
Q

Where is ABA produced + how is it transported?

A

Most cells

Non-polar fashion

33
Q

What is the overall role of ABA?

A

Slows growth - acts as antagonist to other hormones

34
Q

What are the 2 effects of ABA?

A

Seed dormancy
- stops germination at inappropriate times of year etc
Drought tolerance

35
Q

How is seed dormancy broken?

A

When ABA is removed by heavy rain, light or prolonged cold

36
Q

What determines whether a seed remains dormant or germinates?

A

Ratio of GA to ABA

37
Q

How is ABA involved in drought tolerance?

A

ABA accumulation causes stomata to close rapidly

due to massive efflux of K+ ions

38
Q

What are the effects of ethylene?

A

> response to stresses
senescence
leaf abscission
fruit ripening

39
Q

What is ethylene synthesis inhibited by?

A

CO2

40
Q

What can high auxin levels stimulate the synthesis of?

A

Ethylene

41
Q

What is the triple response to mechanical stress?

A

Slowing stem elongation , thickening the stem + horizontal growth in order to avoid obstacles

42
Q

Which hormone induces the triple repose to mechanical stress?

A

Ethylene

43
Q

What is a burst in ethylene production associated with?

A

Apoptosis

44
Q

What does a change in the auxin-ethylene balance lead to?

A

Leaf abscission

45
Q

What is the ripening of fruit?

A

Enzymatic breakdown of cell wall components + conversion of starches + acids to sugars

46
Q

Which hormone leads to fruit ripening?

A

Ethylene

47
Q

What is the effect of light on morphology called?

A

Photomorphogenesis

48
Q

What are the 2 main classes of photoreceptor?

A

Blue-light

Red/far-red (phytochromes)

49
Q

What do blue-light photoreceptor control?

A

Hypocotyl elongation
Stomatal opening
Phototropism

50
Q

What do phytochrome control?

A 
Seed germination
Shade avoidance
Photoperiodism
Seasonal responses
Flowering
51
Q

How does phytochrome work?

A

Red light causes conformational change in protein from Pr to Pfr
-> responses: seed germination, flowering control etc

52
Q

What is phytochrome reversed by?

A

Far-red light

53
Q

What does phytochrome conversion mark?

A

Sunrise + sunset

= thus provides biological clock w/ environmental cues

54
Q

What is photoperiodism?

A

A physiological response to photoperiod

= environmental stimulus that enables plants to sense time of yr

55
Q

What is crucial for the control of flowering?

A

The length of the dark period

56
Q

What are the other internal + external stresses that plants respond to?

A

Gravitropism
Thigmotropism

Abiotic stresses - drought, flooding, salt, heat, cold

Biotic - herbivores, pathogens

Life of Earth 2 (20 decks)

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