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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
What matters to short day plants?
Night length Interrupting dark period with flash of red light will interrupt flowering
26
What is phytochrome
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
27
Proof that circadian rhythm exists in plants?
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
28
Properties of circadian rhythm?
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)
29
What is the external coincidence model?
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
30
Effects of a clock mutant (eg Lhy)
Disrupts plants ability to measure day length May cause abnormal photoperiod response Eg Long hypocotyl (Lhy) mutant, dominant late flowering (over expressor mutant)
31
Role of Lhy gene in circadian rhythm?
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
32
What is CONSTANS
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
33
Where is CONSTANS localised?
The nucleus (is a TF)
34
When is CONSTANS gene active? When is it’s protein product stable?
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)
35
What is florigen? (actually called FT, florigen early name)
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
36
What is the seed/plant life cycle?
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
Where are the female reproductive organs?
The carpel
38
What is the micropyle
Opening on the ovule where the pollen bursts to deliver sperm through pollen tube to ovule
39
Formation of a female gametophyte?
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
What are the embryo sac’s cells?
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
How is the endosperm formed?
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
Point of endosperm?
Broken down and absorbed by embryo during development for nutrients
43
What does fruit develop from?
The carpel Triggered by fertilisation
44
What remains of the endosperm at maturity? What is it called?
Consumed by embryo so that only a single cell layer of endosperm remains. It is called the Aleurone
45
What are the stages of embryo development?
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
What causes dormancy?
Failing to germinate under correct conditions
47
Role of Abscisic acid (ABA) in maturation?
Increase in late seed development ABA treatment promotes maturation, desiccation tolerance (closing stomata) and inhibits germination.
48
What is gibberellin?
an endogenous growth regulator promoting stem elongation
49
Consequences of ABA loss?
Desiccation intolerance Embryo stays green Sometimes germination on mother plant (vivipary) Cannot be viably stored
50
What promotes germination?
Gibberellins Probably antagonise ABA activity as loss of function of Gibberellins and ABA causes OK germination
51
Note aspects of the gibberellin biosynthetic pathway.
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
Role of Gibberellic acid in cereal grain germination?
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
What breaks seed dormancy?
Time External signals Internal cellular controls
54
What are some advantages to semi dwarf varieties of wheat and rice?
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
Effect of light on germination?
Red promotes Far red inhibits Inhibition is quickly reversible Phytochrome activity causing an effect on gibberellin
56
Which allele confers dwarfing in wheat?
Rht dominant allele
57
What are the different Rht alleles and why are there multiple?
Rht-A, Rht-B and Rht-D this is because wheat is hexaploid, has 3 genomes which originate from 3 different grasses
58
What is gibberellin used as in wheat?
signalling hormone dwarf wheat varieties are GA insensitive
59
What happens to gibberellin levels in dwarf wheat varieties?
levels are increases when perception is blocked the plant makes more of the hormone
60
Rht is a semidominant allele, what does this mean?
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
How do semi dominant alleles arise?
a mutation can be semi-dominant if 1 copy of WT is not enough to produce right level of protein, called haploinsufficiency
62
Effect of nitrate on germination?
Promotes germination Increasing nitrate levels causes increasing levels of expression of a gene that promotes ABA breakdown
63
How do fires promote germination?
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
What are DELLA proteins?
negative regulators of GA signalling ie repress growth in absence of GA
65
Difference between fire dependent germinators and regular plants
Both can respond to Karrikin In fire dependents, other pathways may have been toned or shut down
66
What happens to DELLA proteins is presence of GA?
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
What does Karrikin reassemble?
The D ring of strigolactone Plants use related machinery to sense both
68
Which genes encode for DELLA proteins?
Rht
69
Why do some fungi produce gibberellin?
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
How does germination in parasitic plants such as striga work?
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
What does ethylene do in plants?
stimulates ripening promotes ageing promotes enzymatic breakdown of abscission layer
72
How does the parasitic plant striga get nutrients from the host?
Doesn’t close stomata Transpires rapidly Pulls water from host into itself
73
What is an example of a plant with a high ethylene tolerance?
aspidistra
74
What is the purpose of strigolactones?
Signal for VA mycorrhiza fungus Helps to form symbiosis where root gives fungus lipids and sugars Fungi forage for other food in return
75
What molecule is ethylene produced from in plants?
methionine (Met)
76
What induces strigolactone production in plants and why?
Phosphorus starvation Attracts mycorrhiza to help plant to find phosphorus Also signals for less shoot production as lack of phosphorus nutrient
77
What is the immediate precursor to ethylene and how is it made into ethylene?
Amino Cyclo Propane Carboxylic Acid (ACC) by action of ACC oxidase (ACO)
78
Ethylene perception can be screened early on by observing the triple response, what is meant by this?
- reduced elongation - hypocotyl swelling - apical hook exaggeration allows straightforward screens for mutants
79
Why do seedlings produce ethylene when germinating in the dark?
this induces the triple response in seedlings thought to allow seedling to push past a blockage in soil
80
What is ETR?
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
What is ETR1?
encodes an ethylene receptor is membrane localised
82
What is the result of the ETR1 mutation etr1-1?
is a missense in N-terminus causes substitution but doesnt prevent production of receptor receptor is non-functional however
83
What is the structure of the ETR1 receptor?
ethylene binding site -- GAF -- histidine kinase --- receiver
84
What does the ETR1 receptor do?
inhibits the ethylene response in absence of ethylene
85
What is the model of the ethylene response and the ETR1 receptor mutant?
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
What happens if the gene encoding the ETR1 receptor is knocked out?
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
What TFs are involved in the ethylene response pathway?
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
How does flooding affect deepwater varieties of rice?
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

The Green Planet (8 decks)

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