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Trinity Term 1 > Plant development II - Plant hormones coordinate plant development > Flashcards

Plant development II - Plant hormones coordinate plant development Flashcards

1
Q

List some plant hormones

A
  • auxin
  • cytokinin
  • gibberellin
  • ethylene
  • abscisic acid
  • brassinosteroids
  • peptides
  • salycilates
  • strigolactones
  • jasmonates
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2
Q

Describe hormones

A
  • molecules devoid of metabolic or catalytic function
  • exclusively act as signals
  • effective at very low concentrations (nM cellular range)
  • endocrine function
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3
Q

Describe endocrine function

A
  • regulate the activity of cells that can be far from those which produce them (signalling cells) through the bloodstream
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4
Q

autocrine

A

a signalling cell targets itself

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5
Q

paracrine

A

a signalling cell targets a nearby cell

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6
Q

Describe some processes that hormones regulate

A
  • growth (cell division, expansion, differentiation)
  • development
  • responses to exogenous stimuli (biotic and abiotic)
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7
Q

Hormones have a …

A

pleiotropic effect throughout a plant’s lifecycle.

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8
Q

List some abiotic stressors

A
  • heat/cold
  • flooding/drought
  • salt/nutrient imbalance
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9
Q

Describe some biotic stressors

A
  • pathogens
  • insects
  • herbivores
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10
Q

Describe hormone synthesis

A
  • precursor
  • intermediate
  • active hormone
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11
Q

Describe hormone tranport

A

cell-to-cell or long distance

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12
Q

Describe the life cycle of a hormone

A
  • synthesis
  • transport
  • perception
  • signalling
  • response
  • inactivation
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13
Q

Describe hormone signalling

A

relies upon an active and stable effector for amplification

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14
Q

Describe a hormone response

A

transcription of a transporter

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15
Q

Describe hormone inactivation

A

conjugation or degradation

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16
Q

Describe plant hormone biosynthesis

A
  • most plant cells are able to produce most hormones
  • often enzymes involved in hormone synthesis are regulated by hormone signalling
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17
Q

Describe hormone competition

A

several hormones have primary and secondary metabolites in common as precursors and therefore compete for their consumption.

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18
Q

Describe auxin synthesis

A

tryptophan converted to indolacetic acid

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19
Q

Describe ethylene production

A

from methionine

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20
Q

What can the isoprenoid pathway produce?

A
  • cytokinin
  • gibberellin
  • strigol
  • abscisic acid
  • brassinosteroids
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21
Q

Describe jasmonic acid synthesis

A

from alpha-linolenic acid

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22
Q

Hormone mutants can be rescued by

A

exogenous provision of the hormone

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23
Q

How is the step inactivated by the mutation deduced?

A

adding precursors and observing restoration of the wild-type phenotype

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24
Q

Describe synthetic hormones

A
  • synthetic substances with limited structural similarity can bind to the same receptors
  • often trigger stronger responses since plants are not equipped for their catabolism and thus are more persistent
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25
Q

Give an example of synthetic plant hormone usage

A
  • Orange Agent sprayed to defoliate forests and fields during the Vietnam war contained 2,4-D
  • potent synthetic auxin.
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26
Q

List some native auxins

A
  • IAA
  • IBA
  • 4-CI-IAA
  • PAA
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27
Q

IAA

A

indole-3-acetic acid

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28
Q

IBA

A

indole-3-butyric acid

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29
Q

4-CI-IAA

A

4-chloroindole-3-acetic acid

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30
Q

List some synthetic auxins

A
  • 2,4-D
  • alpha-NAA
  • dicamba
  • tordon or picloram
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31
Q

2,4-D

A
  • 2,4-Dichlorophenoxyacetic acid
  • potent synthetic auxin
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32
Q

alpha-NAA

A

alpha-Naphthalene acetic acid

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33
Q

dicamba

A

2-Methoxy-3,6-dichlorobenzoic acid

34
Q

tordon or picloram

A

4-Amino-3,5,6-trichloropicolinic acid

35
Q

Describe hormone modification for transport

A
  • can be conjugated to sugars and amino acids as inactive forms to be transported or to be degraded
36
Q

Describe jasmonates and salicylates

A
  • defense and stress hormones
  • methylated to serve as aerial messengers between individuals
37
Q

Describe methyl salicylate

A

repels aphids

38
Q

Describe long distance hormone transport

A
  • via the xylem (root to shoot) and the phloem (source to sink organs)
39
Q

How was long distance hormone transport revealed?

A
  • complementation of biosynthetic mutants by reciprocal grafting with wild type
40
Q

Describe cell-to-cell auxin transport

A

non-mediated transport through the acid trap model.

41
Q

Describe the acid trap model

A
  • IAAH diffuses from the apoplast through the membrane into the cytosol
  • dissociates
  • unable to cross phospholipid bilayers again
42
Q

IAAH

A

Protonated auxin

43
Q

Describe influx carriers

A

facilitate diffusion of IAA-

44
Q

IAA-

A

deprotonated auxin

45
Q

P-glycoprotein ABC transporters couple ATP hydrolysis to

A

pump IAA- out of the cell

46
Q

Describe PIN efflux carriers

A

facilitate efflux from the cell into the apoplast

47
Q

Describe auxin gradients

A

PIN1-2-3-4-7

48
Q

Describe PIN proteins

A
  • polar distribution at specific sides of the PM in a cell-type dependent manner
  • maintained by continuous cycling from the ER/Golgi
49
Q

PIN-mediated polar auxin transport determines the formation of

A

auxin maxima

50
Q

Auxin gradients are required for

A

plant development

51
Q

Describe the disruption of auxin gradients

A
  • by inhibiting PIN-mediated transport
  • abolish QC identity
  • alters root development
  • can be viewed using fluorescence
52
Q

Describe morphogen gradients

A

sufficient to produce patterning

53
Q

Describe morphogen feedback

A

cell identity can affect morphogen distribution and perception

54
Q

Describe hormone perception - the details

A
  • membrane associated receptors bind the hormone ligand
  • (in)activated mainly by means of intra- or extra-molecular transfer of phosphate groups
55
Q

Describe the role of the soluble receptors

A
  • exploit the hormone as a molecular glue for transient protein interactions
  • lead to effector activation
56
Q

Describe proteolytic hormone signalling

A
  • in hormone absence, specific transcriptional regulators (corepressors bound to transcriptional activators, bound to the enhancer) are maintained inactive by interaction with a co-repressor
  • when hormone levels increase (binding to corepressor), this is marked for proteasomal degradation by polyubiquination
57
Q

polyubiquination

A

ubiquitin ligases bind to hormone

58
Q

Describe the auxin signalling pathway

A
  • AUX/IAA proteins bind and repress the activity of ARFs via domain III and IV
  • TIR1+auxin connect the AUX/IAA repressors with a ubiquitin E3 ligase complex to be polyubiquitinated
  • polyubiquitinated AUX/IAA are degraded via the proteasome
  • ARFs recruit RNA polymerase II on target genes
59
Q

AUX/IAA

A

auxin

60
Q

ARFs

A

Auxin Response Factors

61
Q

Describe phosphorylating hormone signalling

A
  • can be intra- or inter-molecular phosphorylation
  • upon hormone binding, receptor transfers one or more phosphate groups to a soluble protein (with possible intermediates)
  • protein acts as shuttle to the nucleus where it experiences high turnover
  • gene expression is activated or repressed
62
Q

Describe cytokinin signalling

A
  • phosphorylation-based
  • TCS: phosphotransfer between a membrane bound receptor and a soluble shuttle (His to Asp residues)
63
Q

TCS

A

Two component system

64
Q

Give some examples of when hormonal responses are used in metabolism, physiology or development

A
  • activation of proton pumps
  • protein relocalisation (PIN)
  • cell cycle regulators
  • primary and secondary metabolism
  • synthesis of other hormones
65
Q

Describe feedback looped hormonal responses

A
  • inhibition of hormone biosynthesis
  • stimulation of hormone degradation
  • promotion of hormone sequestration/inactivation
  • negative regulators of signal transduction (competitors/co-repressors)
66
Q

How are enhancers responsible for hormone responsiveness identified

A
  • sequence comparison of hormone-inducible promoter
  • progressive deletions and test of reporter gene activity
67
Q

Describe output reporters

A
  • transcriptional modules able to perceive a specific hormone
  • typically consist of several repeats of the same enhancer fused to a minimal promoter, controlling the expression of a reporter gene
68
Q

Describe soluble receptors

A
  • exploit hormone as a molecular glue for transient protein interactions
  • lead to effector activation
69
Q

Describe ratiometric output

A
  • hormone-sensitive and insensitive modules joined genetically
  • independent of the concentration of the reporter
70
Q

Describe the hormonal control of vegetative development

A
  • SAM maintenance: cytokinin (+)
  • production of primordia: auxin (+)
  • leaf expansion: gibberellin (+), brassinosteroids
  • leaf senescence: cytokinin (-)
  • lateral root production: auxin (+)
  • axyllary bud dormance: auxin (+), strigolactones (+), cytokinin (-)
  • root elongation: gibberellin (+)
  • root differentiation: cytokinin (+)
  • root meristem maintenance and activity: auxin (+), cytokinin (-)
71
Q

… and … are the main hormones involved in the regulation of meristem maintenance, identity and activity in both roots and shoots

A

auxin, cytokinins

72
Q

Describe the hormonal control of reproductive development

A
  • seed dormancy: abscisic acid (+)
  • seed germination: gibberellin (+)
  • flowering: gibberellin (+), ethylene (+)
  • flower development: auxin, ethylene, gibberellin
  • fruit development: gibberellin(+), auxin (+)
  • fruit ripening: ethylene, brassinosteroids
  • abscision: ethylene, auxin
73
Q

Reproductive development involves

A

the coordinated activity of several hormones, which may vary in a species-specific manner.

74
Q

Describe hormonally-mediated interactions with other organisms

A
  • ethylene, salicylates and jasmonates are rapidly synthesized and signal attack by other organisms and induce defence mechanisms
  • strigolactones mediate synbiosis with mycorrhizal fungi
75
Q

Describe plant defence mechanisms

A
  • production of secondary metabolites
  • induction of apoptosis.
76
Q

Describe the applications of hormones to agriculture

A
  • used for plant propagation
  • auxins and cytokinins most used hormones for tissue culture
  • auxin main active principle in rooting powders
77
Q

tissue culture in plants

A

in vitro regeneration from explants

78
Q

Describe hormonal control of tissue culture

A
  • shoot induction: cytokinin
  • root induction: auxin
  • callus induction: auxin + cytokinin
79
Q

rooting powders

A

used for clonal propagation of plants.

80
Q

Describe hormonal applications in ripening fruits

A

Ethylene synthesis inhibition and ethylene supplementation applied to control fruit ripening

81
Q

Describe ripening syndrome

A
  • softening: change in cell wall composition
  • pigmentation (chlorophyll→carotenoid/anthocyanins) - secondary metabolites accumulate (aroma)
  • starch broken down into soluble sugars
82
Q

Describe the domestic control of tomato ripening

A
  1. Low O2 inhibits ethylene production (delays ripening)
  2. Release ethylene to promote uniform ripening

Trinity Term 1 (38 decks)

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