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BLGY1115 > Plant Development and Organs > Flashcards

Plant Development and Organs Flashcards

1
Q

Distinctive Features of Plant Growth and Development

A
  • majority of development is post embryonic
  • plant cells do not migrate
  • plant cells are totipotent and have developmental plasticty
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2
Q

Post Embryonic Development

A
  • the plant has embryo has a simplified body plan
  • most of the plant is produced post embryonically by meristem activity
  • morphogenesis occurs continuously throughout the plants life cycle allowing it to respond to changes i nthe environment
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3
Q

What are the two most important regions of the late stage plant embryo?

A
  • the future shoot apical meristem (SAM)
  • the future root apical meristem (RAM)
  • -groups of stem cells
  • -produce primary plant growth
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4
Q

Migration of Plant Cells

A
  • plant cells cannot migrate
  • so relative positions of plants within the plant body are very important as they cant be changed
  • cellular processes must be highly coordinated in space an time
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5
Q

What are the three processes that underpin development of all plant organs?

A
  • cell division (timing & orientation)
  • cell expansion (extent & direction)
  • cell differentiation
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6
Q

Dicots and Monocots: Number of Cotyledons

A

Dicots - 2

Monocots - 1

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7
Q

Dicots and Monocots: Leaf Structure

A

Dicots - sheath

Monocots - petiole

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8
Q

Dicots and Monocots: Leaf Venation

A

Dicots - network

Monocots - parallel

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9
Q

Dicots an Monocots: Stem Vascular Bundles

A

Dicots - circular pattern

Monocots - scattered

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10
Q

Dicots and Monocots: Root System

A

Dicots - taproot

Monocots - fibrous

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11
Q

Dicots and Monocots: Root Protoxylem Poles

A

Dicots - small number

Monocots - large number

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12
Q

Dicots and Monocots: Secondary Growth

A

Dicots - present

Monocots - absent

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13
Q

Dicots and Monocots: Adventitious Roots

A

Dicots - absent

Monocots - present

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14
Q

Dicots and Monocots: Flower Parts

A

Dicots - multiples of 2 or 5

Monocots - multiples of 3

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15
Q

Which plant is used as the genetic model for angiosperms?

A

Arabidopsis thaliana

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16
Q

Properties of Arabidopsis

A
  • small enough to be grown in sterile lab conditions
  • first plant to have genome sequnced
  • prolific see producer
  • short 6-8 week life cycle
  • easy transformation / introduction of new DNA
  • small genome (115Mb 5 chromosomes)
  • large number of mutant lines
  • c. 25000 genes
  • considerable genetic resources/stock to support research
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17
Q

Embryogenesis in Dicots

A
  • development of three tissue systems (protoderm, procambium and ground tissue) and the future shoot & root apical meristems
  • highly defined cell processes leading to specific structure
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18
Q

Embryo Genesis in Dicots

First Division

A
  • zygote divides across horizontal midline forming two cells
  • top cell is the proembryo
  • bottom cell is the suspensor
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19
Q

Embryo Genesis in Dicots

Further Divisions

A

proembro divides along vertical midline

  • suspensor divides along horizontal midline
  • further precisely determined divisions leading to globular stage embryo
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20
Q

Embryo Genesis in Dicots

Globular Stage Embryo

A
  • spherical ball of cells
  • linked suspensor (line of cells) to parent plant
  • outer layer of cells is called the protoderm which goes on to form the dermal tissues
  • these outer cells are defined by anticlinal divisions (new cell walls form perpendicular to the outer surface of the embryo
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21
Q

Embryo Genesis in Dicots

Heart Shaped Embryo

A
  • procambium forms in the centre of the embryo

- cotyledons begin to form creating the heart shape

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22
Q

Embryo Genesis in Dicots

Mature Embryo

A
  • future root apical meristem at point where suspensor joins to embryo
  • future shoot apical meristem in the dip between the two forming cotyledons
  • the ground tissue is made up of all the cells that aren’t RAM, SAM, precambium or protoderm
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23
Q

Monocot Embryo Development

A
  • similar to dicot
  • asymmetry in development
  • one cotyledon - notch forms at globular stage and embryonic axis forms at one side
  • meristems are more developed
  • SAM enclosed in sheath - coleoptile
  • multiple root meristems may form directly in embryo
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24
Q

Cellular Mechanisms That Lead to Embryogenesis

A
  • molecular mechanisms are unclear
  • embryo initiates with the establishment of the apical-basal axis
  • recent research has also suggested that a cytesine rich peptide is required for formation of zygotic basal cell lineage and pre-embryonic patterning
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25
Q

Hypogeal Seed Germination

A
  • cotyledons remain under the soil
  • no photosynthesis in the cotyledons
  • energy for growth primarily derived from the endosperm
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26
Q

Epigeal Seed Germination

A
  • cotyledons emerge above the soil
  • the cotyledons turn green and act as the first leaves of the plant
  • energy for growth primarily derived from photosynthesis in the cotyledon
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27
Q

What are the three tissue systems in plants?

A 
dermal tissue (from protoderm)
vascular tissue (from precambium)
ground / fundamental tissue (from rest of embryo)
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28
Q

Examples of Dermal Tissue

A

epidermis

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29
Q

Examples of Vascular Tissue

A

xylem

phloem

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30
Q

Examples of Ground TIssue

A

pith
cortex
parenchyma

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31
Q

Differences Between Embryogenesis and Meristem

A

Embryogenesis - whole group of cells undergoes changes in form
Meristem - a set of cells undergoing repetitive processes (iterative development)

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32
Q

Meristems

Definition

A

regions that remain embryonic with the capacity to produce new cells
meristem cells can become any cell type
majority of plant body is produced by iterative activity at meristems
contain 50-100 initials

33
Q

Initials

Definition

A

cells that are continually dividing and adding to the population of cells

34
Q

Division of Initials

A
  • an initial divides to produce two daughter cells
  • one daughter cells divides again and the other differentiates
  • dividing this way, an initial can produce a file
35
Q

File

Definition

A
  • a line of attached cells

- as a cell becomes relatively further away from the initial it differentiates further

36
Q

Development of a File

A
  • meristem initial divides producing two daughter cells
  • one cell differentiates and the other divides again producing two more cells
  • -there is now a line of three connected cells, two differentiating and a third that will divide again
37
Q

Meristem Activity

A

Determinate - limited development leading to a specific structure e.g. a flower
Indeterminate - continuous production of organs with no development end point e.g. leaves

38
Q

Comparison of RAM and SAM

A

very different structures

different spatial organisations of divisions and expansions

39
Q

What two tissues does the root meristem produce?

A

the root cap and the root body

40
Q

Root Cap

A
  • produced distally (towards the outside of the plant in front of the meristem and away from the bulk of the root body)
  • continually produced
  • cells are scraped off as the root grows and moves through the soil
  • produces mudlage (slime) which lubricates and protects the root tip
41
Q

Root Body

A
  • produced proximally (towards the centre of the root)
  • continually adding to / extending the root
  • a species specific primary root tissue
  • cells at the centre of the root meristem may divide more slowly, a quiescent centre
  • involved in cell to cell signalling
42
Q

Root Development

Lateral Roots

A
  • produced AFTER differentiation from internal tissues

- originating rom the pericycle

43
Q

Root Development

Cell Differentiation

A

-e.g. root hair cells and epidermal cells

44
Q

Root Development

Cell Elongation Zone

A

-region of root behind the root cap

45
Q 
Primary Root Tissues
Transverse Section (outside to centre)
A
  • epidermis
  • cortex
  • endodermis
  • pericycle
  • phloem
  • xylem (joined together at centre)
46
Q

Pattern of Phloem and Xylem

Dicotyledons

A

diarch
triarch
tetrarch

47
Q

Pattern of Xylem and Phloem

Monocotyledons

A

–polyyarch

48
Q

Shoot Development Compared with Root Development

A
  • more complex than roots with a variety of structures and functions
  • shoot apex organisation is not the same as root apex organisation
49
Q

Which tissues does the shoot apical meristem produce and what are their functions?

A
  • stems - support the plant and help it to reach light
  • leaves - photosynthesis
  • flowers - reproduction and aid cross pollination
  • fruits/seeds - dispersal
  • tubers (modified stems) - storage
  • tendrils (modified leaves) - climbing
50
Q

Root Apex Organisation

A
  • meristem enclosed
  • root cap produced distally
  • root body produced proximally
51
Q

Shoot Apex Organisation

A
  • meristem is not enclosed, it is at the surface of the shoot apex
  • leaf primordia fold over the shoot apex to offer it some protection
  • lateral organs (e.g. leaves, branches) develop directly at apex BEFORE differentiation
  • leaf primordia are seen as distinct bump like structures at apex
52
Q

Phyllotaxy

Definition

A

arrangement of leaves at nodes

53
Q

Plastochron

Definition

A

time interval between successive primordia

54
Q

Arrangement of Cells at the Shoot Apex

A
  • three layers of cells, L1 to L3 with L1 at surface
  • L1 and L2 cells also known as the tunica, division is anticlinal (perpendicular to surface) and produce the epidermis of all shoot tissues
  • L3 cells division is periclinal (parallel to surface) forming pith and internal tissues
  • expanding from the centre of the root tip there is a central zone where cells divide slowly, a peripheral zone and a rib zone where differentiation of central tissues occurs
55
Q

Genetic Control of the Shoot Apical Meristem

A
  • there are genes that control the size of the meristem:
  • -clavata leads to a larger SAM
  • -shoot meristemless (stm) & wuschel (wus) lea to a smaller SAM by causing cells to differentiate
56
Q

Dicot vs. Monocot Stems

Transverse Section

A
  • in a transverse section of a dicot stem the vascular bundles are arranged in a circular pattern
  • in a monocot the vascular bundles are scattereed
57
Q 
Vascular Bundle
Transverse Section (outside to centre)
A
  • sclerenchyma
  • phloem
  • xylem
58
Q

Shoot Anatomy

Xylem and Phloem Arrangement

A
  • xylem is internal to phloem in stems

- xylem is above phloem in leaves

59
Q

Shoot Anatomy

Supporting Tissues

A
  • collenchyma - bundles at periphery of cortex
  • sclerenchyma - vascular tissue found in vascular bundles
  • xylem vessels - very strong, lignified cell walls
60
Q

What kind of growth to both SAM and RAM contribute to?

A
  • axial growth
  • increase in length and height
  • primary growth
61
Q

Secondary Growth

A
  • increase in girth / width

- woody growth

62
Q

Production of Secondary Tissues

A
  • wood
  • greater mechanical strength
  • new functional vascular tissues
  • most important in shoots but roots have it too
63
Q

Which meristems lead to development of secondary growth?

A
  • vascular cambium

- cork cambium

64
Q

What tissues does vascular cambium produce?

A
  • new xylem and phloem to replace non–functioning cells

- in the process it increases the girth of the plant which leads to a need for lateral transport

65
Q

Where is vascular cambium found?

A
  • in stem and root

- cylindrical zone between the primary xylem and primary phloem in vascular bundles

66
Q

How does the vascular cambium work?

A
  • certain cells regain the capacity to proliferate and act as meristem initials undergoing periclinal division
  • these initial cells are fusiform, they have elongated tapered ends
  • the vascular cambium extends so that it is connected between the vascular bundles, in a transverse section it appears as a ring in the cortex connecting the vascular bundles
  • secondary phloem is produced centrifugally, towards the outside
  • secondary xylem is produced centripetally, towards the inside
67
Q

Phleom

A
  • soft
  • no thickened lignified walls
  • can be crushed and lost
68
Q

Xylem

A
  • tough
  • heavily lignified walls
  • persists to produce tree rings
69
Q

Secondary Xylem

A

wood

70
Q

What are vascular rays?

A
  • produced by ray initials in the vascular cambium
  • occur radially through the secondary xylem and phloem
  • they transport and store nutrients
  • made up of parenchyma cells?
71
Q

When does growth as a result of the vascular cambium occur?

A
  • stops in the winter
  • is reactivate in the spring
  • -in the spring large diameter xylem (early wood) is produced
  • -in the summer small diameter xylem (late wood) is produced
  • -this results in tree rings
72
Q

What is the purpose of the cork cambium?

A
  • vascular cambium leads to an increase in girth of the plant
  • this means that the epidermis and cortex form primary growth are no longer sufficient
  • so they are gradually replaced by cork which is produced by the cork cambium
73
Q

Where does the cork cambium come from?

A

outer cortical cells

74
Q

What cells does the cork cambium produce?

A
  • cork cells (centrifugally)

- 1 or 2 layers of parenchyma cells cetripetally

75
Q

Cork Cells

Characteristics

A
  • dead at maturity
  • regular shape
  • closely packed, no spaces
  • evenly thickened walls containing suberin, a wax that is impervious to gas and water
76
Q

Lenticels

Definition

A

regions in cork that facilitate gaseous exchange through the cork

77
Q

Periderm

Definition

A

everything produced by the cork cambium

78
Q

Bark

Definition

A

everything from the surface inwards to the vascular cambium

BLGY1115 (10 decks)

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