Plant development I - plants are composed of repeated structural units Flashcards
1
Q
plants are composed of…
A
repeated structural units
2
Q
… coordinate plant development
A
plant hormones
3
Q
Describe the roots
A
- highly explorative
- explore large areas and volumes of soil
- induce immobility
- allow social acquisition of nutrients
4
Q
What are the constraints of immobility
A
exposed to aggregation and inclemency of weather and elements
5
Q
Describe plant organs
A
can grow above- (shoot system) and under-ground (root system)
6
Q
List some plant organs
A
- reproductive shoot (flower)
- modified leaves (petals)
- stamens and carpels
- bud
- leaf
- taproot
- lateral roots
7
Q
List 3 directions of plant growth
A
- apical
- branching
- radial
8
Q
Give some examples of apical growth
A
- shoots
- taproots
9
Q
Give some examples of branching growths
A
- … branches
- lateral roots
10
Q
Give some examples of radial growth
A
- tubers
11
Q
List three different plant tissue systems
A
- epidermal system
- ground tissue system
- vascular tissue system
12
Q
Describe permanent plant tissues
A
can be simple, complex or secretory
13
Q
Describe the simple permanent plant tissues
A
- parenchyma
- schlerenchyma
- collenchyma
- epidermis
14
Q
Describe plant organs
A
- composed of different tissue systems, each characterised by one or more cell types with characteristics that provide specific functions
15
Q
How can plant tissues be divided?
A
meristems and the permanent tissues
16
Q
Describe the SAM
A
- contained in the terminal bud
- responsible for the production of shoot-organs
17
Q
SAM
A
shoot apical meristem
18
Q
Describe the cambia
A
- vascular cambium and cork cambium
- meristematic tissues that enable increase in thickness of stems and roots
19
Q
Describe the RAM
A
produces new cells at the tip of each root
20
Q
RAM
A
root apical meristem
21
Q
When does production of new organs occur mostly in plants?
A
post-embryonically
22
Q
The root and shoot apical meristems are specified … during embryo development.
A
- early
- by heart-stage embryo
23
Q
Meristems regenerate from…
A
differentiated tissues
24
Q
Describe explants
A
- when supplemented with adequate amounts and ratios of phytohormones, they produce new shoot and root meristems
- can generate new plants
25
phytohormones
growth regulators
26
Describe adventitious roots
produced from de novo formed or inactive pre-existing meristems present along the stem
27
How do plants compensate
for sessility?
high regeneration (pretty much any organ can be regenerated)
28
Describe silent meristems
- can be reactivated by severely damaged plant parts to restore growth
- such as after wildfires
29
Why is regeneration essential?
grazing activity of herbivores.
30
How do we visualise plant meristems?
- signalling reporter proteins mark meristematic cells
- fluorescent markers: GFP, RFP
- chromogenic markers: GUS
- luminescent markers (luciferase)
31
Describe transcriptional reporters
reporter protein produced by reporter gene that follows the cell-specific promotor
32
Describe a post-transcriptional/translational reporter
cell-specific protein reporter fusion produced from reporter gene that follows a gene, which itself follows a cell-specific promotor
33
How a genetic reporters constructed?
fusing together promoters and/or coding ones with reporter genes
34
Describe the Arabidopsis root
- few cell types originate from the meristematic initials
- organised around a QC
- three root tip regions: division zone, elongation zone and differentiation zone
35
QC
- quiescent centre
- controls meristematic activity
36
Describe the division zone
where new cells are produced
37
Describe the differentiation zone
where adult cells acquire their final specific function
38
Describe root hair cell specialisation
- distal part of the RAM
- epidermal cells in contact with two dorsal cortex cells elongate into a root hair with high SA:Vol
- maximise exchange of water and minerals from the soil
39
Describe xylem specialisation
- progressive cell wall thickening and disappearance of cytoplasm
- generates lignified conduits
40
Describe phloem sieve element specialisation
loss of citoplasmic components and perforation of transverse cell walls
41
What is the role of the phloem?
transport of photosynthates
42
Describe lateral root formation
- cells from the pericycle in proximity of xylem pole cells divide to generate a new LRP
- self-organises to produce a lateral root
43
pericycle
external part of the stele
44
LRP
lateral root primordium
45
Describe the function of the cambial meristem
- new (secondary) xyla and phloems are produced here
- organising core directs the activity of neighbouring meristematic cells
- organiser cell differentiates into a xylem cell
- stem cell divides asymmetrically to generate a new organiser cell.
46
Describe the SAM - the specifics
- embedded in layers of leaf primordia that protect it
- domed shape can be separated into 3 layers of meristematic cells
- OC and overlying layers visualized using fluorescent reporters (based on marker genes)
47
OC
organising centre
48
Describe the activity of the vegetative SAM
protrusion produced by the proliferation of the SAM form a phytomer
49
Describe a phytomer
consists of a leaf, an axillary meristem and an internode.
50
Describe the production of new leaves
- phyllotaxis
- plastochron
51
Describe phyllotaxis
position of a new leaf along the stem as compared to the previous one
52
Describe plastochron
the time interval between the production of two consecutive phyotomers
53
Describe the phyllotaxis of an alternate leaf
180 degrees
54
Describe the phyllotaxis of opposite and decussate leaves
90 degrees
55
Describe the phyllotaxis of whorls
45 degrees
56
Describe the phyllotaxis of spiralled leaves
137 degrees
57
Describe the establishment of a new leaf
- all three layers of cells in the SAM contribute to the the tissues
- L1 generates the epidermis
- L2 produces the mesophyll parenchyma
- L3 gives rise to the vasculature
58
vasculature
leaf veins
59
Describe the determination of leaf shape
- gradients of growth
- direction of growth
60
Describe gradients of growth
- generated by cell division (initially) and expansion (subsequently)
- in most dicots, a mature leaf is composed of a petiole
61
Describe a petiole
contains the midvein and a blade (distal and proximal areas).
62
Describe the direction of growth
controlled by how cells divide and in which direction they expand
63
Describe the steps of new leaf formation
- founder cell recruitment (lateral and medial growth)
- distal growth (of primordium)
- blade initiation
- intercalary growth (of developing leaf)
64
Describe a mature leaf
- midrib petiole
- B/P junction
- proximal to distal
65
Describe a simple leaf
single undivided blade
66
Describe a compound leaf
subunits are separated by a bladeless region
67
Leaf shape is ultimately defined by ...
serrations, lobes and leaflets.
68
Within the same species simple genetic alteration can
- severely affect leaf structure
- e.g. tomato
69
Lobes and leaflets are created by ...
initiation during
primordium morphogenesis and differentiation
70
initiation
persistence of meristematic regions
71
Describe a transverse section of a leaf
- shows asymmetric cell organization
- adaxial side
- abaxial side
72
Describe the adaxial side
- upper
- optimised for light capture and to retain water
73
Describe the abaxial side
- lower
- suited for gas exchanges
74
Describe the polarity of the leaf blade
- established very early in the primordium
- defined by the proximity to the SAM (adaxial closer)
75
Mutations in the genes that regulate polarity generate
abaxialized or adaxialized leaves
76
In its reproductive phase, the SAM turns into an
IM
77
IM
- inflorescence meristem
- produces FMs
78
FMs
- floral meristems
- determinate meristems that produce whorls of new organs
79
Describe the floral organs
- concentric series
- sepals (form the calyx)
- petals (form the corolla)
- stamens
- carpels
80
sepals and petals together form the
perianth
81
What connects the sepal to the bract?
pedicel
82
Describe the shoot architecture
- based on meristem termination
- vegetative meristems at terminal and lateral positions can turn into RMs
- RMs develop into alternative inflorescences depending on whether they terminate with a flower meristem or continue producing new meristems
- terminal flower meristems give rise to alternative flower architecture depending on the way they branch and produce alternative floral organs
83
RMs
reproductive meristems
84
vegetative shoot systems
no flowers
85
Raceme
C2D1
86
Panicle
C2D2
87
Mutations of homeotic genes alter
- organ identity
- not their number (except for agamous)
88
What are the main classes of homeotic gene mutations
A, B, C and E
89
Ectopic expression of one D class gene is sufficient to
confer hybrid identity to petals
90
‘D’ class mutants produce
fruits with ovules reminiscent of carpels
91
Plant organs are produced...
post-germination from the meristematic tissues
92
The meristems consist of...
- undifferentiated dividing cells
- non-diving core that coordinates
their activity
93
Root architecture depends on...
the activity of the RAM and the LRPs
94
Shoot architecture is determined by
phyllotaxis and branching
95
* At the reproductive stage of a plant’s lifecycle, the SAM produces flower meristems that terminate into flowers
