Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

DB3 > Plant Development > Flashcards

Plant Development Flashcards

1
Q

Multicellularity evo in plants?

A

No common multicellular ancestor w animals
Independent
Development may be different from animals then

In plants - cells joined by cell walls so don’t change neighbours
-no cell migration
-so development potentially simpler?
-done by directional growth instead

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why no central control unit?

A

land Plants stationary
Also get bigger to compete
Need to harvest nutrients from ground w roots so can’t move

Can’t run away
Perpetually getting eaten partially
So if had central unit and it was eaten whole plant done for
So instead have many stem cell pockets - and the stem cells are more flexible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Higher flexibility plant stem cells?

A

Animal adults usually have just multipotent progrnitor types that can just make specific tissue

Plant stem cells are much more totipotent
Makes cloning easier too

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Plant organ origin?

A

Apical meristems

Shoots and roots grow from tips
Right in middle of meristem are stem cells
Make organs - eg leaves and flowers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

SAM makes?

A

Basically everything above ground
Germ cells
Leaves
Flowers
Often times parts of roots?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Modularity of plant development

A

Iterated developmental unit
Primary shoot meristem makes PHYTOMERS - functional units of the plant -can give rise to other shoots??

If bit is taken off and eaten - another dormant meristem is activated and get another healthy plant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Plant germ cell origin differences

A

In animals - cells are put away v early to become germ cells - strict differentiation

Plant germ cells develop much later

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Multicellular diploid embryo evolution

A

Evolved in land plants
Land plants all evolved from freshwater aquatic algae

Multicellular gen in FW algae is haploid
Fertilisation to make diploid zygote but that immediately undergoes mitosis to make 4 haploid spores

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Bryophyte embryo

A

In land plants - bryophytes
Diploid zygote divides to make multicellular embryo
Benefiti as swimming sperm cannot easily swim on land (too dependent on water)
Then that can produce many haploid spores (many more than 4)

Benefitial as increases odds of successful spore on land

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Vascular land plant embryo

A

Have specialised cells for carrying water and nutrients
So vascular plants can grow bigger

Embryos in vascular plants covered in seed
Seed can store nutrients for development as seed is likely underground when germinating

Helps with dispersal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Plant embryo development within seed
-double fertilisation

A

2 gametes within female ovule
-haploid egg cell - 1 speed fertulises this to make zygote -> goes on to become embryo
-2 sperm fuse with homoploid central cell - makes endosperm which fills seed and is consumed as embryo grows - is ephemeral and consumed by embryo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Maternal tissue in seed

A

Integuments
Surround seed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Suspensor

A

Holds embryo in seed
Nutrients can go up
Undergoes apoptosis during embryo development

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Somatic embryogenesis

A

Possible due to totipotent stem cells being present dispersed around body
Can be activated by hormones or muse pressing certain embryo genes
Can be used for cloning
Occurs naturally in a few species

Kalanchoe (“mother of thousands”) forms embryos around its leaves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Apomixis

A

eg Dandelion - is triploid
Are sterile due to triploidy - usually cannot make seed

Except they do it with unfertilised flowers - embryo ends up with no paternal info

Often meiosis breaks down giving diploid egg cell - parthenogenesis
Gives clinal propagation by seed - APOMIXIS

The PAR gene confers parthenogenesis
Is expressed in sperm cells - so sworn cell delivers product to mother which kicks off parthenogenesis

Mutant in dandelion which expresses PAR in ovule ends up w no seed in embryo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Embryo Germination

A

Stem cells at what will be SAM and RAM
Cotyledons - embryonic leaf
Hypocotyl - embryonic stem

So apical basal axis set up in embryo
But many adult structures (seed, fruit, flowers) are not
So development is continuous throughout life(flowers develop in adult plant)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Plant developmental patterning timing

A

Most occurs post embryonically
Embryogenesis establishes the:
-apical/basal pattern (shoot/root)
-Inside/outside pattern (epidermis/ground tissue/vasculature)
-and stem cells (shoot and root meristems)

Most of plant body plan produced after embryogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Post embryonic patterning

A

Most of plant body plan produced after embryogenesis
Flowers
Germline
Lateral roots
Branches
Most leaves
Tubers

Continued patterning from groups of stem cells termed meristems
Different to animals where body plan largely formed in embryo

Gives flexibility
Predation problem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Difference to plants - Drosophila embryo patterning

A

Counter to plants. - patterning of adult stuff set up in embryo
AP and DV axes prefigured in egg
So maternal info in egg determine zygote axes

Localised determinants are localised at piles of egg/zygote (eg bicoid)

Kinase signalling pathways determine terminal elements AP pattern

AP fates determined early on

Localise TF expression (homeodomain proteins) specify regional fate on AP axis

Cell-cell interactions and signals important for segment polarity (wingless etc)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Apical basal pattern appearing in arabidopsis

A

Egg cell long and thin
The asymmetric cell division giving small apical cell and large basal cell

Apical cell:
Divides longitudinally to give 4 then 8 cells
Then makes layer around to make future epidermis
Apical cell goes on to form embryo

Basal:
Basal cell forms the suspensor and parts of root meristem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Apical basal fate determination

A

If after zygote 1st division kill apical cell
Basal cell becomes apical in nature
So fate of the cells are due to signaling
If signalling changes then fate of cell changes

Basal cell is capable of producing embryo but is blocked by inhibitory signal from apical cell that inhibits embryo identity/promoted basal fate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Auxin in apical and basal cells

A

Auxin normally accumulates in apical cell
Important for establishing the vertical/longitudinal division planes and setting off 3D growth
Auxin accumulation promotes vertical rather than horizontal division patterns?

Polar PIN7 efflux protein localisation in basal cell causes this accumulation

Isolating basal cell from both apical and maternal tissue means it does not respectfully like if just apical is ablated
So some +ve signal must be coming from maternal tissues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Basics - how is apical and basal axis and shoot root suspensor fates specified?

A

Kinase mediate signalling pathways

Localised determinants

Localised TFs

Polar transport of auxin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Zygote polarisation properties

A

Is long and thin
Nucleus toward one end
Vacuole towards other
Zygote is transiently symmetrical after fertilisation but elongates and becomes polar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Promoter of basal fate in embryo

A

YODA Activity promoted basal fate
Loss of yoda causes suspensor cells to divide longitudinally like in embryos

YDA gene encodes a MAP3K
Component of signalling pathways
Phosphorylase’s downstream MAP kinases such as MPK3 and MPK6

Constitutive activation of YDA gives opposite effect of loss of function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Hyperactive YODA phenotype

A

Have defective more suspensor like embryos

Lose YDA - base become embryo like
Hyperactive YDA - apical becomes suspensor like

YDA kinase signalling promotes basal fates and inhibits apical fates in early embryo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Stomata formation

A

Stomata with 2 guard cells forming mouth like structure
Involves asymmetric divisions in epidermis - smaller daughter remains in stomata lineage - divides again to form 2 daughters becoming guard cells

Bigger daughter becomes elidermis pavement cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

YDA and stomata

A

YDA inhibits stomata fate
YDA- = more stomata
Hyperactive YDA = all pavement cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Breaking of asymmetry in stomat lineage BASL

A

BASL determines asymmetric division in stomatal lineage
Mutant gives lots of nearby stomata instead of spread out
because BASL needed for asymmetric division

No good BASL = symmetric stomatal lineage division -> both go on to guard cell lineage causing close by stomata

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

BASL localisation

A

Is in polar localisation on cell periphery
Predicts the asymmetric division plane

Localised to the nucleus and the edge of the cell
Cell will then divide so that the cell was forms distal to the cortical BASL crescent
The larger daughter cell inherits cortical BASL and the smaller daughter enters the stomatal lineage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

YDA and BASL

A

YDA required for BASL polar localisation
YDA mediates BASL phosphorylation and is required for its polar localisation

A similar pathway may control asymmetrical division in zygote

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

YDA and zygote asymmetrical division

A

(BASL not present here)

Shirt suspensor (ssp) mutant resembles YDA mutants

Ssp encodes a PM localised pelle-like receptor kinase
Misexoresson of ssp in leaves inhibits stomata development - so confirms intersction wit YDA?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Ssp genetics

A

Self heterozygote for mutation and WT plants
50% if resusltung embryos give mutant phenotype not expected 25% that would be mutant homo

Cross male WT to homozygous mutant females
All progeny is WT

Cross ssp mutant males with WT females
All embryos are mutants

Suggests that ssp is active in male side (sperm)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Male activity of ssp

A

Ssp active in male side (sperm)
Pollen expresses ssp RNA
Deposits that RNA in the ovule where it is translated to protein

Explains the odd genetics as maternal is never active

Paternally supplied SSP protein
Localised to one side?
promotes YDA activity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

WUS gene (WUSCHEL)

A

Encodes homeodomain TF
Required for stem cell niche in shoot meristem

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Wox homeodomain genes

A

Patterned on apical basal axis
Due to auxin localisation
Important for apical basal fate specification

WOX2 WOX8
WOX2
WOX8
WOX8 WOX9
WOX9

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Homeosis

A

Assumption by one member of a meristic series of the form or characters proper to other members of the series

Meristic series. -series of repeated homologous units

Homeotic mutations - one member of a repeating series is replaces by another member

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Homeotic genes control

A

Differences between these repeated units

Eve difference between segments in drosophila

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Whorl organs

A

Most flowers have organs in them
Organised in whorls

Whorl number in flowers
1- sepals - form bud
2- petals
3- stamens - male
4- carpel - female

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Homeotic mutations in floral organ identity

A

Class a - affect identity of organs in whorls 1 and 2

Class b- 2 and 3

Class c - 3 and 4

ALWAYS 2 adjacent whorls

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Class a mutant example

A

Arabidopsis
1- sepal - transformed to carpel
2- petals - transformed to stamen

Apetal1
Sepals more leaf like
Petals absent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Class B mutants example

A

Sepals sepals carpels carpels

Arabidopsis- apetala3 ap3, pistillata pi

Antirhinnum- deficiens def and globosa glo

2 and 3 affected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Class C mutants

A

Agamous
No sex organs
Whorls 1 and 2 fine
Stamen replaced by extra whorl of petals
Carpel also converted - and unlike WT where stem cells stop and only get 4 whorls - in agamous keep getting more and more whorls of sepals and petals - double flower

Eg plena in antirrhinum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

abc model of floral organ identity

A

3 Homeotic functions
a b and c
-a function in whorl 1 and 2
-b in 2 and 3
-c in 3 and 4

Combinations on Homeotic functions in a whorl specifies the identity of the organs that form there

a =sepal
a+b=petal
b+c=stamen
c=carpel and STOP

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Mutual inhubition in a and c

A

Class c mutations give sepals and petals everywhere even though A function is needed there and is not normally everywhere

Same with C expression in whorls 1 and 2 in A mutants

Lead to idea that A and C are mutually inhibitory
So mutating one expands range of other into the two other whorls
A and C functions are antagonistic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

Triple mutant for a b and c

A

ap2 pi ag triple mutant
Organs are leaf like
Flowers are modified shoots
Floral organs are modified leaves

Like shoots flowers also the compressed internodes, organs in concentric rings

Flowers are determinate
Shoots usually indeterminate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Genes in the abc model

A

TFs
MADS box mediating DNA binding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

C function genes

A

Agamous RNA expressed where whorls 3 and 4 will be

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

B function genes

A

Apetella3 RNA active where whorls 2 and 3 will be not others

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

A function genes

A

On where whorl 1 and 2 will be

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Are the floral Homeotic genes sufficient for floral identity?

A

Ectopic expression of them in leaves does not transform them
So not sufficient

SEP genes also needed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

SEP genes

A

SEP1 2 and 3 isolated
Sequence similarity to AGAMOUS

Expressed in whorls 1-4
Single mutants have no phenotype (redundancy)
Triple mutant all floral organs are like sepals

SEP1-3 genes are needed for activity of b and c class Homeotic genes

SEP1-4 quadruple mutant - all organs are leaf mike and have branched trichomes
SEP genes also needed for class a activity too

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

SEP protein function

A

Interact with the Homeotic gene products
Need SEP to be expressed in leaves along with abc genes to transform to flower
Have MADS domains like the abc genes
Form tetramer with abc genes at c termini
with aa, ab, bc, cc
MADS domains at either end of tetramer interact with DNA

54
Q

Model of MADS tetramer binding DNA

A

Binding of tetramer of MADS TF complexes results in DNA looping

Change in 3D chromatin structure may be necessary for triggering expression of specific genes and therefore different floral organogenesis depending on tetramer structure (abc contained within it?)

55
Q

Floral quartet model

A

Quartet - depends on the abc and Sep genes present
Abc genes and Sep genes come together into tetramer to confer that identity in that whorl

56
Q

Male reproductive organs

A

Located in stamens inside anther is where meiosis occurs and gametes form

Male gametophytes form in anthers
Microsporocyte
-meiosis
4 haploid microspores
-divide (pollen mitosis I)
Vegetative cell (makes pollen capsule) and generative cell
Generative cell divides (pollen mitosis II)
Generative cell divides to give 2 sperm cells

57
Q

Plant sperm motility

A

Cannot swim
Has no flagella

58
Q

Pollen and pollen tube structure

A

Vegetative nucleus and generative cells that will divide to make 2 sperms

At one point pollen capsule will swell up and grow a tube quickly
Grows fast to reach and fertilise female
Grows with tip growth

59
Q

Female reproductive organs

A

In middle of flower
-Carpel goes on to make fruit
Sopecific to flowering plants (as opposed to naked ovules)
-at top of carpel is stigma where pollen lands and germinates dependent on communication
-pollen tube goes down style and arrive at ovary where gametes are formed

60
Q

Plant Ovary

A

Contains the ovules

-funiculus - pollen tube grows up this
-micropyle - where pollen tube enters ovary
-then sperm delivered
-so no need for water or sleek swimming

61
Q

Female gametophyte formation

A

Maegasporocyte
-meiosis
4 haploid megaspores
3 abort
Survivor forms gametophyte, divides 3 times
-mitosis - 2 nuclei
-mitosis - 4 nuclei
-mitosis - 8 nuclei in 7 cells of embryo sac

62
Q

Central cell

A

Has 2 polar nuclei
Fertilised by sperm cell and forms endosperm

63
Q

Synergids location in gametophyte

A

2 of them right by the micropyle

64
Q

Egg cell location in gametophyte

A

Just behind the synergids

65
Q

Antipodal cells location in gametophyte

A

3 of them
Opposite end from synergids/micropyle

66
Q

Double fertilisation event

A

2 sperm nuclei from pollen

One fertilises egg cell
Gives 2N zygote

The other fertilises the polar nuclei of the central cell
Gives 3N endosperm
Ephemeral tissue - dies and does not contribute to next gen

67
Q

Pollen germination

A

Pollen lands:
Female can determine self and non self
Closely related pollen is refused
Less related/unrelated individuals’ pollen is refused

If communication is successful Pollen germinates - tube grows through style

Tubes go through the funiculus and then through micropyle

68
Q

How do these cells meet?

A

Various signalling pathways

Self incompatibility

Pollen attraction by ovule

Pollen ovule recognition to trigger sperm release

69
Q

Pollen tube guidance basic

A

Pollen tube goes down transmitting tract liens with probably signals that direct pollen
Get into overt and go past ovule they grow to side
Out of transmitting tract
Into ovule
Through funiculus - funicular guidance
Through micropyle - micropyles guidance

Female gametophyte presence is necessary for funicular and micropyles guidance
Something produced by haploid female tissue
Male tissue senses this

70
Q

Transmitting tract role in pollen sensing of ovule

A

Things in T tubes that switch on genes in pollen though receptors
So if no female tissue - no finding ovules

Need to go through T tract to sense ovules

71
Q

Pollen tube attraction by female gametophyte - which cells?

A

Both synergids ablated - no pollen tube growth towards it

Synergids produce pollen tube attractant
Die after fertilisation so no more pollen attracted (not needed)

LURE

72
Q

Pollen tube growth mechanism

A

Plant cell pressure is important for fast growth of pollen tubes

The tip growing cells loosen wall at top to allow it to grow

Too stiff - cannot grow
Too soft - explodes

73
Q

Attractant in synergids

A

LURE proteins
Cysteine rich peptides - similar structure to many plant ligands
Signal peptides

This LURE:
Specifically expressed in ovary
Specifically in synergids
present Right at tip of synergids
Involuted cell walls here to increase signaling surface

Shown that this peptide is sufficient for pollen tube attraction

74
Q

Express arabidopsis LURE on Torennia synergids

A

Attracts arabidopsis pollen
But no bursting
So something else signals bursting

75
Q

Pollen specific receptor for LURE 1 in arabidopsis

A

PRK6
KO reduces male side fertility only
So pollen specific

Receptor kinase active at tip of pollen tube
Affects growth

Expressing this on other species pollen makes it attracted to arabidopsis LURE

76
Q

Signalling event once it reaches ovule

A

LURE attracts pollen tube to ovule

THEN
Is recognised
Signals to synergids
If successful
One of the synergids does
Pollen tube bursts
Sperm released into ovule

This is why the other species didn’t burst in the experiments earlier - unsuccessful signalling at this point

77
Q

Sirene/Feronia mutant

A

Ovules are not fertile
No pollen tube bursting
Overgrowth of pollen and synergids continue to attract other pollen tubes

Female active
Receptor kinase
Unique receptor domain - carbohydrate molecule receptor - may have role in cell wall perception

Is also in leaf and plays a role in growth and regulating immunity

78
Q

Feronia function

A

Female receptor kinase
Senses signal from male
Has malectin binding domains

Promotes ROS production at tip of ovule in Filiform apparatus
Mutants have no ROS burst

ROS production is important for pollen tube burst

If ROS scavenger used to remove them then no pollen tube burst

79
Q

ANXUR1 and 2

A

Expressed in pollen tube

Closely related to Feronia but instead male specific
Expressed at pollen tube tip

Double mutant pollen burst prematurely
Affects male fertility only

So Involved in maintaining pollen tube integrity during growth through female tissues
Receptors are active to prevent this burst (as their absence causes premature burst)

80
Q

RALF function

A

Rapid alkalinisation factor
Small secreted cysteine rich secreted peptide family
Encode ligands for FER type receptors

Feronia mutants don’t respond to RALF so suggests Feronia is receptor

RALF binds FER
FER autophosohorylates
Inhibits activity of membrane H+ ATPase, promotes Ca2+ ingress, activates ROS signalling (& cell wall properties, actin cytoskeleton…)

81
Q

RALF4 and 19

A

Expressed in pollen tubes
Single mutants are infertile male
Double mutants cause premature burst like anxur mutants

Prevent pollen burst via ANXURE1/2 signalling
Bind anxur 1 and 2
Autocrine signalling stiffening tube and preventing bursting

82
Q

RALF6/7/16/36/37 function

A

Mediate pollen reception
Required in male
In absence pollen not recognised by synergid cell, no burst & overgrowth

Paracrine signalling from pollen to ovule?

83
Q

RALF34 function

A

Promoted pollen tube burst
Expressed in ovule

Out competed RALF4/19 (male autocrine ones)

Signalling from ovule to pollen

84
Q

Summary of RALF model

A

Autocrine signalling by pollen tube
4/19 to stiffen and prevent burst

Pollen signals with RALF 6/7/16/36/37 to synergid (paracrine)

If successful Synergid releases RALF34 - outcompetes RALF4/19 for ANXUR1/2 - triggers pollen bursting and sperm release

85
Q

Phyllotaxy types

A

Spacing of leaves/other leaf like organs around the stem

Spiral
Alternate (aka distichous)
Decussate

86
Q

Spiral phyllotaxy

A

One leaf at each node
Processive leaves arranged 137.5 degrees from last
From oldest leaf and go up - forms spiral around stem

Can be R or L handed
R= clockwise

Common one

87
Q

Alternate phyllotaxy

A

Single leaf at each node
Leaves at processive nodes are spaced 180 degrees from each other
So alternate sides

88
Q

Decussate phyllotaxy

A

2 leaves at each node 180 degrees from each other (opposite sides of stem)

Next node’s leaves are at 90 degrees from the last

89
Q

Phyllotaxy and growth pattern

A

Spiral and Decussate make sense for upward growth
Leaves at each node offset so they are in gaps in shading by leaves above

Distichous/alternate usually found in stems that grow horizontally

90
Q

Phyllotaxy switch during development

A

Antirhinnum starts as Decussate

But once sexual development begins and flowering genes activate - it switches to 137.5 degree spiral

Flowers are in whorled arrangement
Look inside flower and see that primordial that give rise to the flower structures are spaced in gaps of last ring

See switch in vegetative growth
Start with Decussate
But then changes and starts releasing 3 leaves at each node instead of 2
Can see that leaves at one node are offset in gaps of leaves at last node still
Means that the pattern is meta stable - can switch and then maintain itself once switched

91
Q

Spiral phyllotaxy and golden ratio

A

Angle between one leaf and next is 137.5 degrees
The golden angle

No of spirals in the phyllotaxy represent consecutive numbers in Fibonacci sequence
Can trace left and right handed sets of spirals of organs
The number of these spirals always represents consecutive nos in sequence
Eg 3L 5R
21L 34R

92
Q

Leaf production at shoot tip

A

Originate from SAM
Dome of cells in SAM that contains the stem cells
Division of stem cells pushes daughters to side and that’s where they differentiate
Can eithe produce internode
Or go out to produce lateral organs

Leaf primordial grows out and assumes leaf shape
Shoot goes through cycles of producing leaf primordia in cycles leaving them behind in the phyllotaxy structure
Leaves behind some stem cells in the axils of leaf primordia

93
Q

Axillary meristems

A

Left behind in leaves from SAM lateral organ production

These allow main stem to branch
Goes through cycle of initiating leaves and repeatedly growing out

Activation of axillary meristems is repressed by auxin from the apex (apical dominance)
Meaning that branching out is repressed toward apex

94
Q

Transitions to flowering development

A

Activation of inflorescence meristem (the SAM In sexual development)
Stem cells can stay and make internode or go out and make lateral organs
Domes of stem cells in middle producing lateral organs on flanks
Lateral organs have diff identities
Floral meristems go out of side and make the lateral organ flowers (different from inflorescence meristem)

Sets:
Sepal primordia
Petal
Stamen
Carpel

Carpel production uses up the floral meristem’s stem cells which differentiate into carpel

95
Q

SAM in embryogenesis

A

Formed in embryogenesis
Stem cells set aside during embryogenesis

In the torpedo stage? Loooks like it in diagram

96
Q

visible Stages of plant embryogenesis

A

Octant
Globular
Heart
Torpedo

Then the inverted U (I think)

97
Q

Central zone of SAM

A

Part of SAM (other is peripheral zones)
Low rate of cell division - once a week
Weakly histologically staining cells (not metabolically active)
Stem cells

98
Q

Peripheral zone(s) of SAM

A

High rate cell division
Densely staining cells (metabolically active
Region of leaf formation
Leaf primordia come from here?

99
Q

Stem cell vs leaf identity in SAM

A

Stem cell:
KNOX homeobox genes
Giberellin down (due to KNOX)
Cytokinin up (due to KNOX)
Represses ARP genes (due to KNOX)

Leaf:
ARP genes
ARP do:
-myb TFs
-represses KNOX genes

100
Q

KNOX KO?

A

SAM differentiates
ARP gene expression extends to central zone of SAM
Stem cells differentiate
So cotyledons present
But no developing shoot cause no stem cells

101
Q

ARP KO

A

Gives meristem characteristics to leaves

102
Q

Inhibitory field model of phyllotaxis

A

3 rules
CZ cannot form primordia
Existing primordia produce inhibitor
Inhibitors effect decreases with distance

Region of least inhibition will correspond with the greatest space available from nearest leaves
So new prinordium isn’t inhibited and so it can develop there
Now produces an inhibitory signal here

Next primordium will form in the new greatest space

Different phyllotaxy depending on jnhibitory field range

103
Q

Inhibitory field surgical experiments

A

Ablate youngest primordium (nearest top)
Position of next primordium establishes nearer to where the ablated
Widens angle to 157 degrees in spiral

104
Q

Inhibitory field and switching metastability

A

Have decissate
Inhibitory field opposite each other from opposite promordia at node

Next 2 at next node 90 degrees from last because of greatest space available

If a field forms that is larger than it should be
Then next node only has space to form 1 primordium in spiral form
Inhibitory fields keep this new pattern metastable

105
Q

Inhibitory fields and Fibonacci who cares

A

Shoot as sheet of paper
Promordia as coins
Once stacked so they occupy greatest available state. - Fibonacci numbers appear in the rows of coins
Geometry
Idk

106
Q

PIN1 auxin efflux transporter localisation role

A

Localisation of PIN1 often asymmetric
Occurs at one end of cell
Suggests auxin moving from one cell to another
Neighbouring cells have coordinated localisation of PIN1 protein
Means that auxin moves with the tissue from one end to another

Can visualise auxin movement with PIN1 localisation

107
Q

Auxin flow in protoderm/SAM

A

Auxin flows in protoderm towards SAM (up the stem to apex)
then to leaf promordia
Comes up to apex in gaps between promordia and is diverted INTO existing promordia

108
Q

Auxin model of phyllotaxy

A

Opposite to inhibitory field kind of
Highest auxin concentration area is where promordia will develop
Next promordia will develop in greatert space
Because existing promordia are sucking away auxin from the tissue
Meaning greatest space has the least sucking and so most auxin transport

109
Q

Auxin localisation in auxin model

A

model Requires relocation of PIN1
From down the gradient (in protoderm?)
To up the gradient towards the promordia
IDK SPECIFICS OF THAT
question of what determines phyllotaxy is now boiled down to. What determines Auxin relocation change

110
Q

What allows relocation of PIN1 towards promordia

A

the Mechanical model for the auxin model

Phyllotaxy is altered when medhanical stresses are changed

Relieving stress locally causes primordium formation
Artificially relaxing cell wall causes formation of ectopic leaf primordium

Auxin loosens cell walls relaxing the cell

111
Q

Mechanical model for auxin model

A

All cells equivalent
One cell by chance ends up w more auxin than neighbours
Loosens it’s cell walls -so turgor pressure blows it up
Pushes more on surrounding cells than they push back

As a result
Reorients stresses I’m surrounding cells
Band of stress around loosened cell

This relorients PIN1 protein - moves towards the middle higher mechanical stress cell

Explains the change from down the gradient to up the gradient

This causes auxin accumulation in this area

112
Q

RAM Basic

A

Roots develop from RAM
At tip of every root
Contains self renewing stem cell pop
Enable continuous root development through life

Similar to SAM
Also has stem cell pop

But it is easier to teach development in root as model
As forms files of cells
Lots of expansion in shoot so messier

113
Q

Roots as models

A

Grow happily in agar (clear)
Can get water and nutrients from it fine

114
Q

Zones of root tip

A

Meristematic zone near tip
Elongation zone - has small boxes (cells) which increase in length as they get older/go up the zone
Then beyond that is the differentiation zone where first get differentiated cell types - this bit has root hair cells

115
Q

Overall cell type organisation in root tip

A

Promeristem
Root cap around root exterior and below promeristem
Vascular tissue (stele) in centre
Ground tissue around that
Epidermis around ground tissue

Can follow individual files of cells from these regions to the promeristem - stem cells somewhere around here

Conserved among species

116
Q

Arabidopsis promeristem

A

Zoom in on promeristem
Cell files converging outside
Small number of central cells in promeristem - the quiescent centre

117
Q

Quiescent centre

A

Central promeristem region where root’s cell files converge
Could be:
Maintain the undifferentiated state of surrounding initials (organiser)

No evidence of cell division here - is quiescent

Highly conserved in all land plants

118
Q

Stem cells in root promeristem

A

Surround the quiescent centre
Are stem cells for each of the major tissue lineages mentioned earlier - called initials

Contain initials for:
Root cap
Ground tissue
Vascular tissue

119
Q

Testing QC function

A

Focus on root cap
Root cap is covering tissue
Focus on columellar root cap specifically because it begins differentiation v close to QC just one initial layer away
Know it’s differentiated too due to appearance of starch granules

One of the QC cells was laser ablated
Affected organisations and root patterning:
The columella initial became differentiated. -gained starch granules
Near non destroyed QC cells - initials remain undifferentiated

So even tho QC doesn’t divide it
Maintains undifferentiated initials

120
Q

How are the cell lineages in root tip specified

A

Either by lineage
Or by induction
(Is INDUCTION)

Fully ablate QC
look at vascular marker and root cap marker
Shows where QC should be (between the tissues)

But when QC is ablated entirely
Cells above where it should be (should give rise to vascular) instead give rise to root cap tissue

So cell types are not necessarily pre determined

Can double check as this may be due to damage

Use GUS reporter and transposon that activates in only a few cells randomly
Marker activated in one initial
Should stay in one lineage of lineage dependent
BUT instead ends up in root cap and vascular tissue
So an initial divided into cells that gave rise to both
So is not lineage dependent

121
Q

Levels of patterning in root

A

Proximo distal (distance to tip)
Circumferential
Radial (along radius of root)

122
Q

Radial patterning in roots

A

Root can build girth but indergoing radial divisions

123
Q

Genes involved in radial patterning

A

Scarecrow- Scr1 (mutant has short roots)
Short root 1 - Shr1 - similar mutant phenotype

124
Q

Scarecrow mutant pattern

A

WT - The endodermis layer towards centre
Wit a cortex surrounding it

Scarecrow mutant - no cortex or epidermis but a single mutant layer

125
Q

Shr 1 mutant

A

No endodermis
Just cortex

126
Q

Scarecrow properties

A

Expressed in initials
Then after differentiation ONLY in endodermis

Important in endodermis fate decision

Give ability to undergo special anticlinal division
Scr+ initial does this A division
Giving endoderm cell on inside and cortex cell on outside

This division doesn’t occur in scarecrow mutant giving the single mutant layer

127
Q

Short root properties

A

Expressed in QC then initial then only:
Expressed in vascular tissue

Moves out of vascular tissue and interacts with Scr in future endoderm
Sequesters it to the nucleus of these cells so Shr cannot reach the cortex layer

Nuclear Scr/Shr upregulates Scr transcription - sequestering all the Scr preventing any from reaching cortex and giving endoderm its cell fate

Absence of Shr in cortex allows cell fate in cortex as Scr/Shr can’t go in nucleus

Shr mutant causes only cortex identity cause no Scr complex can make it knot nucleus to give endoderm fate

128
Q

Evolution of root system

A

Non vascular plants have hair like rhizoids

Rhizoid only exist in non vascular plants (bryophytes)
Roots only in vascular
But having roots is a polyphyletic group
So common ancestor of all vascular plants didn’t have roots
Evolved 2 separate times in vascular plants

129
Q

RHD6, RSL1 function

A

RDH6 and RSL1 mutants lack root hairs
Both closely related HLH TFs which control root hair development

Single mutants reduce root hair
Redundancy between them cause need double mutant to eliminate hairs completely

RHD6 expressed in developing root hairs

Oberexpression of these genes gives root hairs on hypocotyl - not normally there

So these genes are important in root hair development

130
Q

Bryophytes and RSL

A

Mosses and liverworts both have RSL class 1 genes in genome

Expressed in cells that form rhizoids

Constitutive expression turns shoots into rhizoids

Moss/liverwort RSL genes complement arabidopsis - can rescue RHD6-3 mutant
Conserved regulator among land plants

DB3 (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions