The Eudicot plant, morphology, meristems, cell types and tissues
Objectives of the lecture:
1. To illustrate and name some essential parts of plants,
2. show how they are produced,
3. discuss how cell and tissue structure are integrated with morphology,
4. give examples of some variation in morphology between species.
Text book pages:
472-473,
792-808,
800-812
Figure 36-19
Plant cells have cell walls, vacuoles, and
chloroplasts.
Adjacent plant cells are connected
by plasmodesmata.
Cell 2
Smooth ER
Cell wall
Plasma membrane
Cell 1
Vacuole
Chloroplast
Plasmodesma
Plasma membrane
Cell wall
Cell wall
Plasma membrane
Rough ER
Smooth ER
Mitochondria
Golgi apparatus
Communication between cells is
through plasmodesmata
Plant cell walls are flexible but have considerable tensile strength
Figure 8-9
Secondary cell wall
Primary cell
walls
Middle lamella
Cell walls consist of 3 types of layers
Middle lamella is formed during cell division. It makes up the outer wall of the cell and
is shared by adjacent cells. It is composed of pectic compounds and protein.
Primary wall: This is formed after the middle lamella and consists of a skeleton of cellulose
microfibrils embedded in a gel-like matrix of pectic compounds, hemicellulose, and glycoproteins.
Secondary wall: formed after cell enlargement is completed provides compression strength. It is
made of cellulose, hemicellulose and lignin. The secondary wall is often layered.
Figure 8-14
Plasmodesmata create gaps that connect plant cells.
Cell walls
Tubule of
endoplasmic
reticulum
passing through
plasmodesmata
Membrane
of cell 1
Smooth
endoplasmic
reticulum
Cell wall Cell wall
of cell 1 of cell 2
Membrane
of cell 2
Plasmodesmata seen in Transverse Section:
They are not simple openings as they have a
complex internal structure.
Tissues
A
tissue
is a cooperative unit of many similar cells
performing a specific function
within a multicellular organism
Tissues usually have cells that are specialized for
particular functions
The vascular tissue system conducts water and
nutrients from roots to leaves through specialized cells
and conducts the products of photosynthesis, sugars,
from leaves in different but equally specialized cells.
Plants comprises three main tissue types each with different functions.
Dermal tissue – protection and interface with the environment
Ground tissue – frequently the site of storage, sometimes support
Vascular tissue – conduction of water and materials used in synthesis
There is continuity of these individual tissue systems through the plant
Meristematic
tissue
Cross sections:
Leaf
Dermal tissue
system (brown)
Ground tissue
system (gray)
Stem
Root system
Vascular tissue
system (red)
Dermal tissue
system (brown)
Root
Meristematic
tissue
Figure 36-16
Ground tissue
system (gray)
Vascular tissue
system (red)
lateral
(axillary)
bud
shoot tip
(terminal bud)
young leaf
flower
See Fig. 36.3 in
your text book
node
internode
node
EPIDERMIS
Dermal tissue
leaf
VASCULAR TISSUES
seeds
(inside
fruit)
GROUND TISSUES
The angiosperm plant body
withered
cotyledon
SHOOT SYSTEM
ROOT SYSTEM
A tomato plant
primary root
lateral root
root hairs
root tip
root cap
Figure 36-23
activity at
meristems
Shoot apical meristem
Actively dividing cells near the
dome-shaped tip
new cells elongate
and start to
differentiate into
primary tissues
The apical meristem’s
descendant cells divide, grow
and differentiate to form:
Protoderm
Ground meristem
Procambium
new cells elongate and
start to differentiate into
primary tissues
activity at
meristems
Root cap
Root apical meristem
Function of apical meristems
Figure 36-15
Apical meristems and primary
meristems in a root
Apical meristem and primary
meristems in a shoot
Leaf
primordia
Apical
meristem
at tip of
shoot
Apical
meristem
in lateral
bud
Procambium
Protoderm
Ground
meristem
Apical
meristem
Root cap
What does a meristem look like?
Coleus
Longitudinal section through the apical
meristem
Apical meristem
Transverse section through the apical meristem
and newly forming leaves
Coleus
Axilliary bud meristem
The axilliary meristem may develop into a
foliated branch.
L4 S8
Immature leaf
shoot apical meristem
procambium
protoderm procambium
ground meristem
Meristems-> Tissues
Meristems
Tissues
Spiral
thickening
cortex procambium
primary xylem
pith
primary pholem
Figure 23-7
Mutants lacking hypocotyls and roots in Arabidopsis
The MONOTERPOS gene encodes a transcription factor that regulates activity of target
genes and the MONOTERPOS protein is manufactured in response to signals from auxin
which is produced at the apex and occurs in a concentration gradient which provides
positional information.
Regulation of developmental pathways
The expression of genes that encode transcription factors
determines cell, tissue and organ identity
The fate of a cell is determined by its position and not its clonal history
Developmental pathways are controlled by networks of interacting genes
Development is regulated by cell-to-cell signalling
Ligand-induced signalling: cell wall component chemicals that
communicate local positional information
Hormonal signalling: auxin and others
Signalling via regulatory proteins and/or mRNAs through
plasmodesmata
Plants of the day
Celery
Potato
Carrot
Brussels sprout
Cabbage
Simple tissues of parenchyma, collenchyma and sclerenchyma
Important structural tissues of many angiosperms
Transverse section
epidermis
collenchyma
sclerenchyma
xylem
pholem
Pages 804805 of your
text book
parenchyma
Table 36-1
b
x
w
z
Sclerenchyma
Figure 36-25
Fibers
Sclereids
Thick secondary cell walls
Collenchyma
Figure 36-24
Cross section of celery stalk
Close-up of “string,” in cross section
Collenchyma cells, in cross section
Figure 36-22
In leaves, parenchyma cells function in
photosynthesis and gas exchange.
Chloroplasts
Parenchyma
In roots, parenchyma cells function in
carbohydrate storage.
Starch
granules
Figure 36-18
Cross section of a eudicot stem
Cross section of a monocot stem
Epidermis
Cortex
Pith
Ground tissue
Vascular bundles
Lateral
root
Root hair
Root meristem and
structure
Roots must ‘force’ their way through
the soil
Protection of the apical mersitem
Vascular tissue
Ground tissue
Zone of
Cellular Division
Epidermal tissue
Figure 36-17
Apical meristem
Sloughed-off
root cap cells
Root cap
Delayed initiation of lateral meristems
Different requirements for support
and water collection and distribution
Zea mays root apex
Zea mays root apex showing
the junction between root
apex and the root cap
Lateral root development in
Zea mays
A meristem develops from parenchyma and the
lateral root grows out through the cortex
Things you need to know ...
1. The structure of cell walls and how communication between plant cells
may take place.
2. Be able to define a tissue and give examples of cell types and functions
within important tissues of the plant.
3. Define the structure of angiosperm plants.
4. Define the meristems of the angiosperm plant and describe how tissues
develop from them