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BLGY2163 How plants Work > Hormones > Flashcards

Hormones Flashcards

1
Q

What are the 4 major bioactive gibberellins and which is the major active group in arabidopsis?

A

GA4 - arabodopsis
GA7
GA3
GA1

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2
Q

What does ethylene promote?

A

Senescence of leaves and petals

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3
Q

How can ethylene be removed from the air?

A

Zeolite absorption

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4
Q

How can we limit ethylene synthesis?

A

Introduction of antisense constructs to interfere with expression of biosynthesis enzymes in an effective way to control ethylene production. Such as using antisense ACC synthase enzymes

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5
Q

What do ethylene perception mutants interfere with?

A

Ripening, inducible overexpression of NR2

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6
Q

What is auxin a regulator of?

A

Pattern and growth

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7
Q

Describe 4 classic auxin experiments

A
  1. Cut off the tip and replace with an opaque cap, prevent shoot curvature
  2. Mica sheet inserted on dark side prevents curvature, on light side allows curvature. Insert gelatin between tip and coleoptile results in normal phototrophic curvature
  3. Remove tip and replace on one side of coeloptile, growth curvature develops
  4. Coleoptile tips on gelatin, cut gelatin into blocks and discard tips. Place each gelatin block on one side of coleoptile. Bending in total darkness. IAA
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8
Q

How is IAA synthesised?

A

Tryptophan (trp transaminase)
Indole-3-pyruvic acid (IPA decarboxylase)
Indole-3-acetaldehyde (IAId dehydrogenase)
Indole-3-acetic acid

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9
Q

How is IAA transport controlled?

A

IAA transporters are polarly localised, flow is restricted to downwards. The cytoplasm is an ion trap. Auxin is ionised and transported into the cytoplasm, it cannot get out because the cytoplasmic pH is higher

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10
Q

What are PIN proteins?

A

Important in generating the downwards movement of auxin, asymmetric subcellular localisation.

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11
Q

Where is the division zone?

A

Root apical meristem

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12
Q

What is the Cholodny-Went model of gravitropic response?

A

Auxin moves directly down to the division zone and then back up the sides of the root apical meristem. Involves PIN1, 2, 4, 3 & 7

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13
Q

What are the central columella cells of the root cap?

A

Statocytes

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14
Q

How is auxin concentration asymmetry generated?

A

PIN proteins in the columella cells, regulated by endo- and exocytosis

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15
Q

Where does gravity sensing occur in the root?

A

The central columella cells of the root cap - Statocytes

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16
Q

How do cells know which way is down?

A

Starch statolith hypothesis - gravity is percieved through the displacement of statoliths in the columella cells of the root cap. Mutants with reduced levels of starch biosynthesis show reduced graviresponse

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17
Q

What effect does auxin have in the shoot?

A

Promotes cell elongation

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18
Q

What happens to auxin in the phototrophic response?

A

Auxin is redistrubuted to the shaded side of the shoot, causes bending towards the light. Transcription of the DR5 promoter is elevated on the dark side.

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19
Q

What are ARF genes?

A

Regulate transcription by binding to auxin response elements in the promoters of auxin-inducible genes. Not auxin inducible and encode stable nuclear proteins

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20
Q

What are Aux/IAA genes?

A

Auxin-inducible genes which encode unstable nuclear proteins and regulate transcription indirectly through interaction with ARFs

21
Q

How is the ARF protein activated?

A

A Q-rich middle region. Lots of glutamine residues,

22
Q

Name two key mutants in auxin biology

A

axr3-1 (auxin resistant 3) and tir1-1 (transport inhibitor resistant 1)

23
Q

What does auxin do to Aux/IAA proteins?

A

Destabilises them

24
Q

What is the SCF complex?

A

SKP1 CULLIN F-box protein complex

25
Q

What happens without the presence of auxin?

A

AUX/IAA dimerises with ARFa preventing transcription of auxin regulated genes by inducing a transcriptionally repressed chromatin state

26
Q

What happens with the presence of auxin?

A

AUX/IAA is degraded by the SCF complex and the peroxisome allowing the transcription of auxin regulated genes

27
Q

How are AUX/IAA proteins reintroduced?

A

Their genes are also upregulated by auxin

28
Q

What does TIR1 do?

A

Encodes the F-box protein which is the auxin receptor

29
Q

What are E1 and E2?

A

E1 brings ubiquitin

E2 is the ubiquitin conjugating enzyme

30
Q

Using DII-venus as a reporter protein what could we see auxin doing?

A

When the fluorescent protein levels drop there is more auxin, support for Cholodney-Went model

31
Q

Which direction does the auxin move in the pre-globular stage?

A

Upwards, controlled by PIN1

32
Q

What does monopteros encode?

A

ARF protein, regulates PIN1

33
Q

Which genes encode the auxin receptor F-box proteins?

A

TIR1 and AFBs (closely related)

34
Q

What does bodenlos encode?

A

An AUX/IAA protein, prevents recognition by F-box protein receptors

35
Q

What do PIN genes encode?

A

Auxin efflux carriers

36
Q

What does auxin do at the basal end of the embryo?

A

Triggers degradation of BDL to activate MP-dependent gene expression

37
Q

What is phyllotaxis?

A

The radial arrangement of leaves (and other lateral organs such as flowers) around the main shoot axis

38
Q

What does I stand for?

A

Insipient primordium, there the next primordium is going to develop, can be predicted because it is a very regular process.

39
Q

what can block leaf initiation?

A

Polar auxin transport inhibitors such as NPA

40
Q

How do the cells generate a high concentration of auxin?

A

Localise their pins to a convergence point. Moving auxin towards neighboring cells with higher auxin concentrations

41
Q

What is Wardlaw’s model?

A

There is a zone of inhibition allowing them to grow on opposite sides. Actually a depletion of a promoter.

42
Q

What is a phytochrome?

A

A chromophore + a polypeptide called the apoprotein

43
Q

What is Pr?

A

A red light absorbing form which is biologically inactive

44
Q

What is Pfr?

A

A far-red light-absorbing form which is biologically active and results in changes in gene expression and photomorphogenesis

45
Q

What are the 4 functions of phytochromes?

A
  1. Germination
  2. Seedling deetiolation
  3. Plant architecture
  4. Reproductive development
46
Q

One class of R-insensitive mutants were found to carry mutations in which gene?

A

phyB, resembles the shade avoidance phenotype of wt plants

47
Q

What signals that other plants are near by?

A

The red to far red ratio

48
Q

What is shade tolerance?

A

Producing thinner leaves with a higher chlorophyll content, to increase the photosynthetic efficiency

49
Q

What is shade avoidance?

A

elongate leaves and stems to overtop competitors

BLGY2163 How plants Work (5 decks)

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