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The Green Planet > Growth & Manipulation > Flashcards

Growth & Manipulation Flashcards

1
Q

What is phototropism?

A

Growth in response to light
(Usually towards it)

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2
Q

What part of seedling responds to light?

A

The growing tip
Most sensitive to blue light

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3
Q

What things are needed for a tropism?

A

Something to perceive signal (eg statocytes)

Mechanism to convert signal to response (auxin transduction)

Mechanical response (bending, differential cell expansion)

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4
Q

What is a roots vs a shoots reaction to gravity?

A

Root grows towards it
Shoot grows away

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5
Q

What causes shoot bending in trees?

A

Not due to growth as they are woody (lignified and dead so cannot grow)
As xylem on one side is laid down the lignin content is different, manages to bend trunk and right the tree
Tension wood is formed on upper surface

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6
Q

What causes weeping trees?

A

Impaired gravitropism
Shoots not growing away from gravity, more droopy

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7
Q

Where is gravity perceived?

A

In the root tip by Statocytes (aka amylopasts sometimes)

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8
Q

How do Statocytes work?

A

Contain statolith organelles full of starch which sediment at bottom of the cell
Takes around 5-10 mins to relocate to bottom of cell

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9
Q

What happens to mutants with defective starch synthesis?

A

End up with defective statocysts, gravitropism is impaired

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10
Q

How does signal transduction work in root and shoot tropisms?

A

Redistribution if a growth factor

In roots, a signal comes from the root tip which inhibits growth. (inhibits growth where an why? - C)

In shoots, a signal accumulated at bottom of shoot tip that promotes growth.

Different amounts of this signal in different areas causes bending.

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11
Q

How is auxin transported?

A

Long distance (shoot-root) in phloem sap

Cell-cell via active transport

This is highly polar, in shoots it goes down (basipetal) not up (acropetal)

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12
Q

Describe polarity in plants

A

Shoots and component cells have top-bottom polarity
Auxin accumulates at bottom of cells (mechanism independent of gravity)

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13
Q

What mediates auxin transport?

A

PIN proteins are auxin efflux carriers
They sit in the membrane and pump auxin out of the cell

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14
Q

Why does auxin require an efflux transporter?

A

It’s a weak acid and so charged carboxyl group prevents it from leaving hydrophobic membrane

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15
Q

How does auxin enter the top end of a cell?

A

Outside cell environment is more acidic and auxin is protonates there
Neutrally charged so can pass through the membrane into other cells
(Tho there are influx carriers too)

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16
Q

Where are PIN proteins found?

A

On the bottom of the cells (in root)

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17
Q

Why many different PIN proteins?

A

Mediate different aspects of auxin action
PIN3 is active in Statocytes

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18
Q

What happens to PIN3 localisation when root is reoriented?

A

Relocalises to basal plasma membrane to reestablish polarity

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19
Q

What do you call a plant that is not photoperiodic in flowering?

A

Day-Neutral

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20
Q

Difference between short and long day plants?

A

Short days flower when day length is shorter than a defined period

Long days flower when day length is longer than a critical length

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21
Q

what is Bud dormancy?

A

When Buds cease growing and become dormant in winter, usually triggered by short days

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22
Q

What category is Henbane?

A

Long day plant with critical length of 14 hours

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23
Q

Is it just flowering controlled by photoperiodism?

A

No
Tuberisation occurs in potatoes according to day length

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24
Q

Why is photoperiodism more reliable than using temperature as a measure?

A

Temperature is unreliable as it fluctuates a lot
Day length is a lot more consistent

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25
Q

What matters to short day plants?

A

Night length
Interrupting dark period with flash of red light will interrupt flowering

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26
Q

What is phytochrome

A

A molecule in plants which flips forms in response to red or far-red light.
Absorbs red light - red active form
Absorbs far red light - far red inactive form

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27
Q

Proof that circadian rhythm exists in plants?

A

Putting the plants in artificial light-dark conditions and interrupting the dark period when it would normally be day time has no effect
Interrupting it during the night does though
Plant is sensitive to light at certain times of day due to the rythm

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28
Q

Properties of circadian rhythm?

A

Period of around 24hrs
Runs in constant light or dark
Reset by light
Allows anticipation of daily events (eg plants switching on photosynthetic genes before the light appears)

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29
Q

What is the external coincidence model?

A

1)Internal rhythm of approx 24hr period in the amount of a substance which controls flowering
2)this substance is light sensitive at a particular phase in the rhythm

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30
Q

Effects of a clock mutant (eg Lhy)

A

Disrupts plants ability to measure day length
May cause abnormal photoperiod response

Eg Long hypocotyl (Lhy) mutant, dominant late flowering (over expressor mutant)

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31
Q

Role of Lhy gene in circadian rhythm?

A

Lhy and CCA1 (v similar genes) mRNA levels show circadian rhythm
Misexpression perturbs the rhythm
Double mutants for these genes show early flowering

Thought to be part of central oscillator driving the clock
Genes are turned in early in the morning and activate other responses

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32
Q

What is CONSTANS

A

Part of photoperiod pathway when light interacts with clock at correct time
Promotes flowering in Long days
Encodes a Transcription factor
CO mutants don’t affect rhythms

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33
Q

Where is CONSTANS localised?

A

The nucleus (is a TF)

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34
Q

When is CONSTANS gene active?
When is it’s protein product stable?

A

Early in the morning in long days and then more later at night

Needs blue and far red to stabilise the protein
Protein doesn’t accumulate in the dark even if gene is present
Need longer days to have light in early morning or late night to stabilise CO protein (day length overlapping with CONSTANS gene activity)

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35
Q

What is florigen? (actually called FT, florigen early name)

A

A mobile signal moving from leaves to shoot apical meristem after induction by day length.
Regulated by CO

Universal to short and long day plants
Triggers flowering and tuber formation in potatoes

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36
Q

What is the seed/plant life cycle?

A

Double fertilisation

Embryo (2n) and endosperm (3n)

Seed dormancy

Germination to seedling

Vegetative growth and floral induction to flower

Meiosis and gamete production

Again

37
Q

Where are the female reproductive organs?

A

The carpel

38
Q

What is the micropyle

A

Opening on the ovule where the pollen bursts to deliver sperm through pollen tube to ovule

39
Q

Formation of a female gametophyte?

A

Diploid mother cell Megasporocyte does meiosis to give 4 haploid megaspores
3 of them abort
Surviving one becomes gametophyte
Undergoes mitosis 3 times to give 8 nuclei in 7 cells of embryo sac

40
Q

What are the embryo sac’s cells?

A

Egg cell

Synergids, next to egg cell, release attractants to guide pollen tube to ovule and aid bursting

Central cell is diploid, gives rise to endosperm (triploid) after fertilisation

Antipodal cells (3 at opposite end of egg and synergids)

41
Q

How is the endosperm formed?

A

Double fertilisation
2 haploid spent nuclei in pollen tube
One fuses with egg cell
Other fuses with polar nuclei of central cell
Gives Zygote (2N) and endosperm (3N)

42
Q

Point of endosperm?

A

Broken down and absorbed by embryo during development for nutrients

43
Q

What does fruit develop from?

A

The carpel
Triggered by fertilisation

44
Q

What remains of the endosperm at maturity? What is it called?

A

Consumed by embryo so that only a single cell layer of endosperm remains.
It is called the Aleurone

45
Q

What are the stages of embryo development?

A

Morphogenesis- formation of basic pattern

Maturation- Fuel storage + proteins that enable seed to survive desiccation

Degreening- chlorophyll broken down, embryo turns yellow

Desiccation- dries to 5-10% water content

Dormancy 🥱😴

46
Q

What causes dormancy?

A

Failing to germinate under correct conditions

47
Q

Role of Abscisic acid (ABA) in maturation?

A

Increase in late seed development
ABA treatment promotes maturation, desiccation tolerance (closing stomata) and inhibits germination.

48
Q

What is gibberellin?

A

an endogenous growth regulator promoting stem elongation

49
Q

Consequences of ABA loss?

A

Desiccation intolerance
Embryo stays green
Sometimes germination on mother plant (vivipary)
Cannot be viably stored

50
Q

What promotes germination?

A

Gibberellins
Probably antagonise ABA activity as loss of function of Gibberellins and ABA causes OK germination

51
Q

Note aspects of the gibberellin biosynthetic pathway.

A

complex
many different enzymes make inactive precursors, only one form is active
many dwarf mutations as a result of many enzymes that can be affected by mutation

52
Q

Role of Gibberellic acid in cereal grain germination?

A

When grain germinates, produces Gibberellic acid
Causes living aleurone in endosperm to produce amylase to break down the endosperm (also protease and cellulases)
(so aleurone signals to break itself down? - C)(the Aleurone is a thin layer of living cells around the outside region of the endosperm, forgot to add that to the card)(still part of the ednosperm)

53
Q

What breaks seed dormancy?

A

Time
External signals
Internal cellular controls

54
Q

What are some advantages to semi dwarf varieties of wheat and rice?

A

greater proportion of energy goes into grain
less likely to lodge (fall over)
yield much more w/out fertiliser compared to unfertilised normal varieties
yield much more w fertilisers compare to normal varieties
easier for mechanical harvests

55
Q

Effect of light on germination?

A

Red promotes
Far red inhibits
Inhibition is quickly reversible
Phytochrome activity causing an effect on gibberellin

56
Q

Which allele confers dwarfing in wheat?

A

Rht
dominant allele

57
Q

What are the different Rht alleles and why are there multiple?

A

Rht-A, Rht-B and Rht-D
this is because wheat is hexaploid, has 3 genomes which originate from 3 different grasses

58
Q

What is gibberellin used as in wheat?

A

signalling hormone
dwarf wheat varieties are GA insensitive

59
Q

What happens to gibberellin levels in dwarf wheat varieties?

A

levels are increases
when perception is blocked the plant makes more of the hormone

60
Q

Rht is a semidominant allele, what does this mean?

A

although it is technically recessive, the mutant allele still makes a protein but has novel properties relative to wild type
eg hyperactivity or change in promoter/enhancer that makes the gene expressed at higher levels

61
Q

How do semi dominant alleles arise?

A

a mutation can be semi-dominant if 1 copy of WT is not enough to produce right level of protein, called haploinsufficiency

62
Q

Effect of nitrate on germination?

A

Promotes germination
Increasing nitrate levels causes increasing levels of expression of a gene that promotes ABA breakdown

63
Q

How do fires promote germination?

A

Lots of nitrates left over afterwards
Compound in smoke called Karrikin promotes germination
Karrikin is universal promoter even in species that don’t encounter fire

64
Q

What are DELLA proteins?

A

negative regulators of GA signalling
ie repress growth in absence of GA

65
Q

Difference between fire dependent germinators and regular plants

A

Both can respond to Karrikin
In fire dependents, other pathways may have been toned or shut down

66
Q

What happens to DELLA proteins is presence of GA?

A

GA binds to its receptor GID1
this GID1-GA complex binds to DELLAs which causes them to be ubiquitinated and marked for destruction by proteosome

67
Q

What does Karrikin reassemble?

A

The D ring of strigolactone
Plants use related machinery to sense both

68
Q

Which genes encode for DELLA proteins?

A

Rht

69
Q

Why do some fungi produce gibberellin?

A

increased GA in plants causes increased inhibition of DELLA proteins allowing rapid growth
plant which grow fast are less tolerant to stresses
this would allow the fungi to invade the plant easier

70
Q

How does germination in parasitic plants such as striga work?

A

Germinate only when host plant is nearby
After germination grows to host root and connects to vasculature via adhesive hairs
Penetrates root via haustorium which secretes cell wall digesting enzymes

Strigolactone signal from host root promotes its germination

71
Q

What does ethylene do in plants?

A

stimulates ripening
promotes ageing
promotes enzymatic breakdown of abscission layer

72
Q

How does the parasitic plant striga get nutrients from the host?

A

Doesn’t close stomata
Transpires rapidly
Pulls water from host into itself

73
Q

What is an example of a plant with a high ethylene tolerance?

A

aspidistra

74
Q

What is the purpose of strigolactones?

A

Signal for VA mycorrhiza fungus
Helps to form symbiosis where root gives fungus lipids and sugars
Fungi forage for other food in return

75
Q

What molecule is ethylene produced from in plants?

A

methionine (Met)

76
Q

What induces strigolactone production in plants and why?

A

Phosphorus starvation
Attracts mycorrhiza to help plant to find phosphorus
Also signals for less shoot production as lack of phosphorus nutrient

77
Q

What is the immediate precursor to ethylene and how is it made into ethylene?

A

Amino Cyclo Propane Carboxylic Acid (ACC)
by action of ACC oxidase (ACO)

78
Q

Ethylene perception can be screened early on by observing the triple response, what is meant by this?

A
  • reduced elongation
  • hypocotyl swelling
  • apical hook exaggeration
    allows straightforward screens for mutants
79
Q

Why do seedlings produce ethylene when germinating in the dark?

A

this induces the triple response in seedlings
thought to allow seedling to push past a blockage in soil

80
Q

What is ETR?

A

the ethylene resistant mutant
makes it so plants dont respond to ethylene
it is in the pathway that controls ethylene perception rather than synthesis as it still produces ethylene and doesn’t respond to external ethylene
is a dominant mutation

81
Q

What is ETR1?

A

encodes an ethylene receptor
is membrane localised

82
Q

What is the result of the ETR1 mutation etr1-1?

A

is a missense in N-terminus
causes substitution but doesnt prevent production of receptor
receptor is non-functional however

83
Q

What is the structure of the ETR1 receptor?

A

ethylene binding site – GAF – histidine kinase — receiver

84
Q

What does the ETR1 receptor do?

A

inhibits the ethylene response in absence of ethylene

85
Q

What is the model of the ethylene response and the ETR1 receptor mutant?

A
  1. ethylene receptors inhibit the ethylene response when active
  2. binding of ethylene inhibits the activity of the recepor, allowing ethylene response
  3. dominant ethylene insensitive mutants have active receptors which don’t bind ethylene and can’t be switched off
86
Q

What happens if the gene encoding the ETR1 receptor is knocked out?

A

nothing as ETR1 is part of a family of receptors that would have to be knocked out too
triple mutant etr1-6, etr2-3, ein4-4 triple mutant shows response even in absence of ethylene

87
Q

What TFs are involved in the ethylene response pathway?

A

EIN3 TF family in nucleus is activated which induces expression ERF1 which activated ethylene response genes
in absence of ethylene these TFs or proteins encoded by TFs are being constantly being degraded by proteosome

88
Q

How does flooding affect deepwater varieties of rice?

A

induces accumulation of high levels of ethylene
activated SNORKEL (SK) genes which confer rapid elongation
aerenchyma (spongy air spaces between cells which allow oxygen transport form) are enhanced in response to waterlogging and anocxia by death of cells

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