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Biological Systems > Chapter 26 Plant Growth and Development > Flashcards

Chapter 26 Plant Growth and Development Flashcards

1
Q

What characteristics differentiate plants from animals?

A

meristems - permanent collections of stemc ells that allow growth through their lifetime
Postembryonic organ formation
Differential growth

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2
Q

What is differentail growth?

A

When resources are allocated for beneficial growth patterns - e.g. more leaves

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3
Q

What factors are involves in plant growth regulation?

A

environmental cues
Receptors to sense environmental cues
Hormones
Plant’s genome

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4
Q

How do seeds maintain dormancy?

A
  • Exclusion of water or O2 by impermeable seed coat
  • Mechanical restraint of embryo with tough seed coat
  • Chemical inhibition of germination
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5
Q

What is photodormancy

A

When seeds require a period of light or dark to germinate

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6
Q

What is thermodormacy

A

When plants require a period of high or low temperature to germinate

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7
Q

What are the advantages of dormancy?

A
  • Survival through poor conditions
  • results in germination in good conditions
  • Helps seed survive long distance dispersal - allowing plants to colonize new territory
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8
Q

What are some means for breaking seed dormancy?

A
  • Passage through an animal’s digestive tract can damage seed coat
  • Burial in soil
  • Germination inhibitors may be washed away in rain
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9
Q

Define germination

A

Seed begins to grow or sprout

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10
Q

What is imbibition?

A

seeds take up water if seed coat is permeable

  • FIRST step in germination
  • Leads to enzyme activation, RNA and protein synthesis, increase in cellular respiration and metabolic pathways start
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11
Q

Where does the embryo get its food from?

A

From cotyledons or endosperm

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12
Q

When is germination complete?

A

when radicle (embryo root) emerges

At that point becomes a seedling

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13
Q

How are monocots and eudicots different regarding early shoot development?

A

Monocots - growing shoot protected by sheath of cells (Coleoptile)
Eudicots - growing shoot protected by cotyledons

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14
Q

What are photoreceptors?

A

proteins associated with pigments that absorb light

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15
Q

Why is Arabidopsis important?

A

model organism for understanding signal transduction

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16
Q

What is a genetic screen?

A

A large group of mutated plants that are created by mutagens or insertion of transposons

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17
Q

What were the first plant hormones identified?

A

Gibberellins

Auxin

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18
Q

What does the absence of gibberellins and auxin cause?

A

dwarfism

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19
Q

What are the actions of gibberellins?

A

Role in:

  • stem elongation
  • Fruit growth
  • Seed germination (trigger hydrolysis of stored food molecules)
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20
Q

How are gibberellins used for agriculture?

A

sprayed on seedless grapes to get larger fruit

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21
Q

What was auxin discovered in the context of?

A

phototropism - response to light - where stems bend towards light source

22
Q

What are the 4 processes that cause polar transport?

A
  • Diffusion of auxin across cell membrane
  • Membrane protein asymetry - carrier proteins for auxin are located only in basal end of cell
  • Proton pump moves H out of cell = chemiosmotic gradient to drive transport of auxin
  • Ionization of a weak acid (Auxin)
23
Q

What determines the direction of growth from auxin?

A

pH and location of auxin efflux carriers

Stem elongates on side opposite to auxin

24
Q

Which hormone has a role in gravitropism?

A

Auxin

25
Q

What is negative gravitropism?

A

Upward gravitropic response of shoots

26
Q

What other roles does auxin have in plant growth and development?

A
  • root initiation
  • Inhibition of leaf abscission
  • Helps maintain apical ominance
  • Fruit development
  • Cell expansion
27
Q

Define leaf abscission

A

detachment of old leaves from the stem

28
Q

How does auxin contribute to cell expansion

A

H+ pumped into cell wall -> low pH activated expansins which catalyze chagnes that loosen cell wall

*auxin increases synthesis of proton pumps

29
Q

How do gibberellins and auxin work similarly?

A

Remove a repressor from transcription factor that stimulates expression of growth promoting genes

  • Bind to a receptor that binds to repressor protein - targets repressor fro breakdown in proteasome
30
Q

Where are the mutations of excessively tall plants and excessively short plants?

A

In gene that encodes repressor protein

  • Tall plants- growth promoting gene is always on, mutation in repressor region tha tbinds to transcription factor
  • Dwarf plants- repressor is always bound to transcription factor
31
Q

What is the F-box?

A

region of receptors that facilitate protein-protein interactions necessary for protein breakdown

32
Q

What is the action of ethylene gas?

A

promote leaf abscision and senescence (seeds ripening of fruit)

  • also increases its own production
  • accelerate ripening of fruit
33
Q

How is the apical hood of eudicots maintained/

A

by asymetrical production of ethylene - inhibits elongation of cells on inner surface
- ethylene production stops when seedling breaks through soil

34
Q

How does ethylene affect plant growth?

A

inhibits stem elongation
Promotes lateral swelling of stems
Decreases sensitivity of stems to gravitropic stimulation

35
Q

What are the effects of cytokinins?

A
  • induce proliferation of cultured plant seeds
  • promote formation of shoots in high cytokinin:auxin ratio (low ratio promotes roots)
  • cause some light requring seeds to germinate in darkness
  • inhibit stem elongation, lateral swelling
  • stimulate auxillary buds to grow
  • Delay senescence of leaves
36
Q

What determines the extent of branching?

A

cytokinin to auxin ratio

37
Q

What are the 2 parts of cytokinin signalling

A

receptor - protein kinase, phosphorylating itself and a target protein
Target protein - transcription factor to regulate response

38
Q

Define phosphorylating

A

Introducing a phosphate group

39
Q

What are the effects of brassinosteroids?

A
  • enhance cell elongation and cell division in shoots
  • Xylem differentiation
  • Growth of pollen tube
  • seed germination
  • apical dominance and leaf senescence
40
Q

What are the effects of abscisic acid?

A

Involve inhibition of other hormones

  • Prevent seed germination while seed on parent plant
  • promote seed dormancy (inhibit gibberellins)
  • Mediate response to environmental stresses and pathogens
41
Q

What is photomorphogenesis?

A

developmental events controlled by light

e.g. germination, phototropism, shoot elongation, flowering etc.

42
Q

What do plants respond to regarding light?

A

Quality (wavelengths)

Quanitity (duration and intensity of exposure)

43
Q

What is a phototropin?

A

Blue light receptor

44
Q

How do phototropins work?

A

start signal transductio that release auxin

45
Q

What is Zeaxanthin?

A

another blue light receptor involved in opening of stomata

46
Q

What is Cryphochomes?

A

Blue light receptor in nucleus - affects seedling development and flowering

47
Q

What are Phytochomres

A

Red light receptors
- Have 2 interconvertible isoforms
Daylight - Pfr predominates
Shade/night Pf predominates

48
Q

How do Phytochomes alternate?

A

They are a protein with 2 subunites that each have a pigment (chromophore)
- When Pr absorbs red light, chromophore changes shape -> Pf
Exposes two regions of phytochome - prompts growth towards light

49
Q

How much of the genome to phytochomes affect?

A

10%, 2500 genes

50
Q

How does Pft affect gibberellins

A

When formed at seed germination - genes for gibberellins synthesis are activated and gibberellins breakdown is repressed

51
Q

Which form of Phytochrome is present during day/night

A

Day - Pr quickly becomes Pfr

Night - Pfr slowly converted to Pr

Biological Systems (20 decks)

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