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BIO251 > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

Features for chemical signalling (4)

A

Perception of environmental change
Signals work on an interactive signal-transduction cascade
Hormones act as a primary signal
Secondary messengers follow hormones

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2
Q

Categories of plant signalling mechanisms (5)

A 
Environmental perception
Plant hormones
Secondary messengers
Genetic transcription & translation
Physiological regulation
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3
Q

Major hormones (6)

A

Auxin (division/expansion/growth/vascular formation/suppress leaf senescence)

Gibberellin (division/elongation/growth/induce germination/stimulate flowering/overcome dormancy)

Cytokinen (division/shoot formation/greening leaves/suppresses senescence + root growth)

Abscisic acid (ABA) (promote dormancy/close stomata/slows division/suppresses growth)

Ethylene (promote ripening/abscission/senescence)

Brassinosteroids (growth regulation/xylem maturation/branching/germination)

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4
Q

Minor hormones (2)

A

Salicylic acid

Jasmonic acid

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5
Q

Hormone characteristics (5)

A

Act as chemical messengers
Physiological/molecular response occurring in the same or distant tissues
Active in low concentrations
Indice specific responses
Act w other hormones (synergistically or antagonistically)

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6
Q

Regulation of hormone effect

A

Has only one active pool, two inactive pools for regulation (must travel and be transported a lot)

Also relies on tissue sensitivity before signal to develop is sent out

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7
Q

What is auxin, where does it originate from? What is the most common form? How does it flow?

A

Auxin refers to a group of molecules the most common being Indole Acetic Acid (IAA)

It originates from the leaf primordia, SAM and RAM

It flows from the site of synthesis down to the base of the plant (polar movement

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8
Q

Auxin functions (9)

A 
Promote cell division/expansion
Induce vascular tissue formation 
Suppress leaf senescence 
Delays leaf abscission
Increase wall extensibility
An intermediary in phototropism/gravitropism
Inhibit lateral stem formation 
Promote lateral/adventitious root formation 
Determines pattern of leaf emergence
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9
Q

Two types of auxins

A

Native

Synthetic

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10
Q

Transport mechanisms (2)

A 
Polar transport (basipetal or acropetal) (in vascular parenchyma)
Nonpolar transport (in sieve tube elements)
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11
Q

Auxin polar transportation

1) what forms (2) do auxin enter as and where? What are the influx carriers?
2) what form does auxin exit? What are the efflux carriers?

A

1)
IAAH in vascular parenchyma by passive diffusion
IAA- in vascular parenchyma by active co-transport
Influx carriers: AUX1 proteins

2)
IAA- exits
Efflux carriers: PIN proteins

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12
Q

What are PIN proteins?

A

Group of proteins that mediate transport of IAA from shoot to root
PIN3 redirects laterally diffused auxin
Transports auxin to where it can be sequestered/stores
Can be recycled or remade by the Golgi

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13
Q

What is AuxRE?

A

Binding sites for Auxin Response Factor (ARF)

Protein-protein interaction domains

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14
Q

What regulates AuxRE? How is this regulator inhibited?

A

Regulated by AUX/IAA repressors

Repressors are inhibited (essentially pathway is activated again) through auxin-dependent degradation (ubiquitin lipase + auxin)

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15
Q

Auxin promoting lateral root formation process

A

Pericycle cells begin undergoing anticlinal divisions
Form lateral root primordia
Lateral root primordia divides periclinally
Make an inner/outer layer
Emergence of primary root

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16
Q

What is KRP2? What does it do and how is it regulated?

A

KRP2 is a protein that inhibits cell cycle progression by inhibiting cyclin dependent kinases

KRP2 + CDKA-Cyclin D inactivates cyclin

Downregulated by auxin

17
Q

How is the positioning of a lateral root established?

A

Polarized PIN1 proteins direct where auxin gradients form -> auxin gradient location decides where lateral root primordia forms

18
Q

GNOM + Polar Auxin Transport + PIN Proteins

A

GNOM regulates formation of vesicles during membrane trafficking

Actin filaments pull vesicles for transport

PIN proteins use these vesicles pulled by/along actin to move from endosomal compartments to the plasma membrane

19
Q

What is gravitropism? What are the types (2)?

A

Gravitropism is where plants grow in response/respect to gravity

Types:
Positive (roots grow down into the soil)
Negative (shoots grow up from the soil)

20
Q

What is used to sense gravity for gravitropism?

A

The root cap contain many columella that have amyloplasts in statocytes (called statoliths) that sense gravity

(If the root cap is removed the root cannot sense gravity/which direction to grow in)

21
Q

What happens when Root position is changed? (Vertical vs. Horizontal)

A

Vertical root position has symmetrical auxin distribution moving back on both sides

Horizontal Root position has redistribution of PIN3 so auxin moves preferentially along the bottom side (inhibits elongation zones on the bottom so growing only occurs on the side)

22
Q

In phototropism what controls one sided elongation? Why does this arise?

A

GSL8 (a callose synthase) control the deposition of plasmodesmata -> ie. closes PDs on the side that has more sunlight to prevent growth

Arise depending on where the sun is:
Directly overhead (no need for GSL8 because there is even auxin distribution)
At an angle (need GSL8 so auxin concentrates on the side that lacks sun to promote its growth toward the sun)

23
Q

What is Apical dominance? How does it work?

A

Apical dominance is where the terminal bud (top/shoot tip) controls (suppresses) auxiliary bud growth

How it works:
If present = auxiliary growth is inhibited by auxin that flows down stem
If absent = auxiliary bud grows due to lack of inhibition (lateral buds are now inhibited)

24
Q

What is Abscisic Acid? Where does it originate from and where is it found?

A

Is a hormone that slows/stops growth and development (inhibitory molecule)

Originates in plastids
Found in all tissues

25
Q

Abscisic acid Function (7)

A 
Slows growth during stress
Signals stress acclimation 
Closes stomata
Promotes seed maturation/seed storage/protein synthesis/seed desiccation tolerance
Promotes dormancy in seeds/buds
Inhibits advanced germination
Promotes senescence of stressed leaves
26
Q

Ca+2-dependent signal transduction pathway in Stomatal Closure

A 
ABA binds to a Receptor on a guard cell membrane
Initiates Ca influx 
Ca binds to CaR 
Open anion efflux channels
Membrane depolarize 
K efflux channels open 
Loss of osmotica 
Loss of turgor 
GCs deflate 
Stomata close
27
Q

How does ABA maintain dormancy?

A

Is abundant when environmental conditions are unfavourable

Only removed from seed coat after heavy moisture

28
Q

Types of cytokinin (2) Where do they originate and where are they transported to afterwards?

A

Kinetin (synthetic)
Zeatin (naturally occurring)

They originate in root meristems and are transported to the shoot

29
Q

Function of cytokinins

A

Delay lead senescence/promote greening
Increase sink strength for nutrients
Accelerate cell cycle (promote D-type cyclin)
Promote shoot/leaf growth (accelerate cell division/expansion)
Suppresses root growth

30
Q

Cytokinin va ABA release depending on environmental conditions

A

High resources: more cytokinin release = root suppression, shoot growth

Low resources: more ABA release = shoot suppression

31
Q

How to plant pathogens manipulate cytokinins to their benefit?

A

Pathogens insert their genes into the T-DNA of the host plant (form a recombinant plastid)
The T-DNA contains cytokinin synthesis genes and when injected with foreign genes causes the over-expression of cytokinin synthesis

Over-expression tricks plant into believing it has a sink to which it should send resources to (forms tumour like growth that pathogens use to their advantage)

BIO251 (9 decks)

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