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Physiology of Organisms > Plant Changes > Flashcards

Plant Changes Flashcards

1
Q

How might plant movements be catagorised?

A

Reversible/Ireversible
Active/passive
Trophic/Nastic

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2
Q

What is a tropism?

A

Directional growth response relative to a stimulus

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3
Q

3 examples of tropisms

A

Gravotropism
Phototropism
Thigmotropism (touch)

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4
Q

What is a nastic movement?

A

Non-directional movement not involving growth

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5
Q

3 Nastic movement examples

A

Photonasty
Nyctinasty (regulated by circdium rhythmn)
Thigmonasty (touch induced)

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6
Q

Whatcell is involved in gravotropism

A

Columella cell

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7
Q

What is the columella?

A

The root cap, central cells used to sense graviy
Contain large, dense amyloplasts

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8
Q

What are amyloplasts

A

Starch containing plasmids found in columella cells
Sediment according to gravity

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9
Q

What columella cells sense gravity?

A

Statocytes, which contain amyloplasts called statoliths

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10
Q

What happens to statocytes when there is a change in gravity and how does this cause gravotropism.

A

Change cellular position, inducing PIN3 to move to the new ‘bottom side’
Auxin fluxes are therefore moved to the lower side of the root tip where they are transported to root elongation zone by PIN2 and AUX1, where they inhibit cell elongation

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11
Q

What is the PIN family

A

Proteins that are auxin transporters

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12
Q

Main steps to gravotropic response

A
  • Statocytes change cellular position
  • PIN3 induced to move to botom side
  • Auxin directed to bottom side and transported to cell elongation site by PIN2 and AUX1
  • Auxins inhbit cell eleongation in the root and stimulates in the stem
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13
Q

How is light detected for the phototropic response

A

Blue light receptors: phototropins

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14
Q

How is phototropism achived?

A

Blue light causes tempeory pause of auxin delivery to elongation zone
PIN3 resumes auxin transport but to the shaded side, which causes auxin to accumulate

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15
Q

What do chloroplasts to in response to light?

A

Low light: accumulate at top of cell
High light (can be damaging): accumulate on the bottom of cells

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16
Q

Example of thigmonasty

A

upon touch/fire, the leaves and branches of mimosa pudica fold down

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17
Q

What is a pulvinius

A

Specialised structure that allows reversible movement in a thigmonastic response

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18
Q

How is a pulvinar AP initiated?

A

At touch site, AP initiated (Cl spike)
Signal moves out from stimulus site
When AP reaches a pulvinus, it is transmitted by plasmodesmata and a pulvinar AP is initiated

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19
Q

How does a pulvinar AP lead to leaves folding?

A

K+ and Cl- move into dorsal(from ventral) motor cells, drawing water into
As water enters dorsal motor cells, they become tugid and elongate, pushing it closed
Also ventral motor cells become flaccid
Hydrolically driven

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20
Q

How does the venus fly trap work?

A
  • 2 convex lobes with 3 mechno-sensitive hairs
  • Hairs convert mechanical stimulus to electrical signal (AP initation) which propagates across cells
  • A 2nd AP is required for the trap to shut (to ensure that something is there)
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21
Q

What is cavitation and how does it cause spore ejection?

A

Formation of air bubbles in a liquid
Causes the sporangium to rapidly spring back at a certain point of dehydration (and spores to be released)

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22
Q

What morphological changes might a plant do in times of stress?

A

Alter root/shoot biomass
- in times of drought root:shoot ratio increases
Change number lateral roots
Change leaf type and orientation

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23
Q

How does temperature affect plants?

A
  • Fluidity of membrane (effects ion transport)
  • Structure and stability of proteins
  • Ice crystal formation
24
Q

What proteins are produced to protect a plant in high temperatures? (heat shock proteins)

A

Dehydrins
Chaperone proteins
Desaturase proteins

25
Q

What proteins are produced in response to cold temperatures

A
  • Antifreeze proteins
  • Desaturases
26
Q

What changes in a plant in anticipation of high temperature?

A
  • Increase in heat shoock signalling
  • Leads to an increase in Heat-Shock proteins mRNA
  • Increase in heat shock proteins
27
Q

What are dehydrins and how do they help plants in high temps?

A
  • Have no tertiary structure
  • Wrap around proteins to protect them
28
Q

What are chaperone proteins and how do they help

A

Promote refolding of damaged proteins

29
Q

What are desaturase proteins and their role?

A

Modulate membrane fluidity in changing temperatures

30
Q

How can changin leaf shape/structure be a response to high light conditions?

A

May choose to reduce cell division and expansion or abscission (loss of leaves), as large leaves risk more light damage
May modifiy leaf surface: thickened waxy cuticle allows more light to be reflected

31
Q

What is heliotropism?

A

Solar tracking - flowers follow the sun throughout the day (or avoids the sun if high light levels)
Based on the circadian clock

32
Q

How can heliotropism be benefical in cold environments?

A

Warm up the flower to attract pollinators - improving pollen germination

33
Q

How does nitrate soil compesition affect lateral root formation?

A

Low nitrate:
- NRT1.1 reconises this and removes auxin from the root = no outgrowth

High nitrate
- Recognised by NRT1.1 causes auxin to accumlate and stimulate lateral root formation towards the nitrate

34
Q

How is auxin involved in root hairs?

A

Promotes root hair development, which can increase nutrient uptake
Response to low phosophate (as triggered by microRNA)

35
Q

How might a plant react to toxic compounds in soil?

A

Break down/ remove them once absorbed
Reduce absorption all together
Use them as a defence instead

36
Q

How can a plant increase removal of toxic ions?

A
  • Upregulate ion pumps for export
  • Chelation of the ion to make it less chemically active
  • Hyperaccumulation in the vacoule
37
Q

What is the result of too much water to a plant

A

Hypoxia (water has a lower O2 concentration than air)
which can lead to…
- reduced respiration, switch to fermentation, energy depletion and cell death

38
Q

How do plants repsond to hypoxia?

A
  • Ethylene
  • Creation of aerenchyma: spongy tissue with air spaces. They are created by selective cell death triggered by ethylene
39
Q

How do aerenchyma help with hypoxia?

A

Gas filled spaces facilitate the low resistance movement of O2 into submerged regions of the plant

40
Q

How is ABA used to detect water?

A

Is a negative hydrosignal, accumulating when there is a deficet in water
- blocks plasmodesmata, preventing auxin movement and decreasing auxin levels so there is less root formation

41
Q

What is a plants response to drought and heat?

A

Close stomata
- BUT this causes leaves to heat up a lot which can be very detrimental
- very deadly combination

42
Q

What is found in a seed?

A
  • SAM and RAM
  • Cotyledons
  • Establishes polarity
  • Seed coat
  • Endosperm
43
Q

What is maturation

A

Pausing of developmemt. The seed dries out and develops dessication tolerance

44
Q

How is a seed able to cope with dessication?

A

Seed coat
- accumlates osmoprotectors (sugars)
- Synthesises LEA proteins (late embryogeneis-abundant) which are like dhydrins and bond with sucros to convert cell to a viscous, glassy state

45
Q

What is dormancy and why do seeds do it?

A

Prolonged resting state/maturation
- Germination is prevented even in favourable conditions

Gives the seed extra time for dispersal and allows for seasonal dormancy (so seeds only germinate a particular time of year)

46
Q

How is dormancy imposed?

A
  • Seed coat physically preventing growth
  • Levels of ABA and gibberellins (ratio)
47
Q

How does a seed wake up?

A

Rehydration (reduced ADA and increased gibberllins)
Tissue sensitivity to ABA reduces over time

48
Q

What are some environmental influences on breaking dormancy?

A

Light
Number of days at a cold/warm temperature
Chemical signals (eg. smoke from a fire)

49
Q

How is a seedling established?

A

Auxin is the main PGR in regulating growth for seediling establishment through cell expansion in the stem and photomorphogenesis

50
Q

How do cells expand with a cell wall?

A

Stress relaxation mechanism (extention of cell wall followed by expansion)
- Increased turgour pressure dirves cell expansion
- Turgor pressure stretches cell walls and generates tension
- Expansin proteins allow the cell wall to stretch a bit in response to this
- Reduced water potencial drives water into the cell causing cell expansion and restores turgor so it can continue

51
Q

What are the three molecular groups of a plant cell wall and their propertie

A

Celluloses: forms fibres and resist being stretched
pectins and hemicelluloses: matrix polysaccharides and form a hydrated gel that allows cell wall to stretch

52
Q

How can auxin promote cell expansion?

A

Expansin proteins only operate at acidic pHs. Auxin can encorage proton extrusion which lowers pH
Auxin can also promote expression of expansin proteins

53
Q

Photomorphogenesis (page 61)

A
54
Q

How may photoperiod sensitive plants be catagorised?

A

Long and short day plants
long day plants flower in summer (in response to shorter nights)
and short day in winter (in response to longer nights)

55
Q

What is vernalisation

A

A requirement that a plant must experience cold temperatures before it flowers

56
Q

How can vernalisation requirements be usful to crop growth

A

Winter wheat has a vernalisation requirement and so only flowers when cold - VRN1 gene only expressed when cold
Spring wheat does not have this requiement (due to mutations in VRN1 gene). VRN1 gene is expressed without cold temperatures

57
Q
A

Physiology of Organisms (10 decks)

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