Plant Cells and Tissues
An Evolutionary Perspective
1
Web Notes
2
Green Algae
All Plants
3
The Vascular Tissue System consists of
two complex tissues.
Xylem
Phloem
4
Vascular Tissue System
Xylem: Always has tracheary elements, but always has other
cell types too.
5
Vascular Tissue System
Xylem: Moves water and minerals up the plant
……and provides support to the plant.
6
Vascular Tissue System
Phloem: Always has sieve elements but always has other cell
types too.
7
Vascular Tissue System
Phloem: Moves photosynthate (usually sucrose)
around the plant
8
Xylem is a complex tissue that
includes tracheary elements
9
10
Tracheary elements are dead at
maturity and have always have a
secondary wall.
Water moves through these cells
by mass flow.
The pressure inside tracheary elements
is less than the ambient pressure and
the secondary walls prevent the cells from
collapsing.
11
All Tracheary elements have pits
Red = secondary wall
Black = primary wall
12
Tracheids only have pits
13
We will consider the structure of tracheids
in our lab on the gymnosperms
14
A vessel element is
a tracheary
element with
perforations.
15
A perforation is an area between
tracheary elements where both the
primary and secondary wall has been
removed.
16
Vessels have independently
evolved in six different plant
groups.
Flowering plants have them
Conifers Don’t
The examples of xylem we will see
in the lab all have vessels
17
Phloem is a complex tissue that includes sieve elements
Sieve Cells
(Conifers)
Sieve-Tube Elements
(Angiosperms)
18
Sieve Elements Serve as a Conduit for
the Movement of Photosynthate
This movement is based on a pressure gradient
generated osmotically. To generate this gradient
sugar must be loaded at the source and unloaded at
the sink. Living membranes are necessary both to
control the movement of sucrose and for the
osmotic movement of the water into and out of the
Sieve tubes.
Read about phloem transport in the text pp. 722 -726.
19
Sieve elements are greatly reduced.They
lose their vacuole, nucleus, and most of the
rest of their cellular structure as they
mature.
Adjacent sieve elements are interconnected
by clusters of pores through which
materials flow from one element
to another.
20
Sieve-tube
members are
one type of
sieve element.
They are
found only in
the flowering
plants.
21
Sieve-Tube Members Have
Sieve Plates
22
When injured a substance called P-protein will break
loose from within the sieve-tube and will plug up
the pores, limiting the loss of sugar into the intercellular
space.
23
24
Sieve-Tube Members are
Associated with Companion Cells
25
Gymnosperms
have a different
type of sieve
element called a
sieve cell
26
Associated with albuminous cells
27
Vascular Tissue System
Xylem
Always includes tracheary elements
Tracheids and/or vessel elements
May have
Parenchyma
Fibers
Other types we will not consider
28
Vascular Tissue System
Phloem Always has sieve elements
If sieve-tube members then also companion cells
If sieve cells then also albuminous cells
Some plants have sieve elements that are neither.
In these cases, the cells are simply called sieve
elements
May also have
Parenchyma cells
Fibers
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Part IV: Growth in plants
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Growth is an irreversible increase in size. In plants,
this is a function of cell division coupled with cell
elongation/enlargement.
31
In mature tissues, cells are arrested in interphase
32
Growth is Restricted to
Meristems
33
There are three types of meristems.
34
Apical meristems extend the length of the plant body
35
36
Lateral meristems extend the girth of a stem or root.
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Intercalary Meristems
……are regions of growth situated between two
regions of mature (non-growing) tissue
intercalary meristem
39
This is why a cut blade of grass grows upward after it is mowed.
Apical Meristems
Generate Primary
Tissues
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Lateral Meristems Generate Secondary Tissues
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Primary growth is a product of
Cell division
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Primary growth proceeds from
apical meristems and is a product of
Cell division
Cell elongation
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Primary growth proceeds from
apical meristems and is a product of
Cell division
Cell elongation
Ending with cell/tissue differentiation-maturation
46
47
In primary growth, cell division isn’t entirely restricted to
the apical meristem proper. Cell division continues in the
derived immature tissues behind the apical meristem.
These tissues are called Primary Meristematic Tissues.
Protoderm matures to form the epidermis
Ground Meristem matures to form the ground tissue
Procambium matures to form the vascular tissue
48
Undifferentiated Cells of Apical Meristem
Protoderm
Ground Meristem
Procambium
Epidermis
Ground Tissue
Vascular Tissue
49
Primary growth in the root
Is simpler than in the shoot as there are no nodes or
internodes
Always includes a root cap. The apical meristem
of the root encompasses some of the area of the
root cap
50
Apical Meristem of the Root
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Primary Meristematic
Tissues in a Root Tip
Protoderm = outer layer of cells
Procambium = inner core of cells
Ground Meristem = everything else
52
Protoderm
Protoderm
53
Procambium
Procambium
54
55
Ground Meristem
Ground Meristem
Primary Growth
in the Shoot
Is more complex because it generates
both stems and leaves
56
Apical Meristem
of the Shoot
Gross Morphology
57
Leaf Primordium
58
Protoderm
Three primary meristmatic
tissues
59
Procambium
60
Ground Meristem
61
Secondary Tissues are Derived
from Lateral Meristems Called
Cambia
62
Except for the pith and some primary xylem
bordering the pith, this is all secondary tissue
63
Secondary growth produces
vascular tissue and dermal
tissue, but not ground tissue.
64
The Vascular Cambium Produces Xylem to the
Inside and Phloem to the Outside
65
The Cork Cambium Produces Dermal Tissue (cork)
to the Outside
66
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Part V:
How Structure Follows Function in Plants
68
Not surprisingly, the differences in the
tissue organization between the root, stem,
and leaf are related to their function.
69
70
The environmental pressures to
which the root is subject is
reflected in its anatomy. These
are
Anchorage
71
72
How is it adaptive to concentrate the into the center of
a root?
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Basic root functions:
Anchorage
Absorption
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The root epidermis must allow for the
passage of water and minerals, hence, does
not have a cuticle, hence, does not have
stomata with guard cells.
75
Root hairs are extensions of individual
epidermal cells that increases the surface
area for absorbing water and nutrients.
Root hairs are simply extensions of basal epidermal cells.
76
In the shoot, axillary
buds form new
branches.
77
In roots, branching occurs from within in
a tissue layer called the pericycle.
78
Shoot System
The shoot system is composed of the
stem and the leaf. These are subject to
different environmental imperatives,
and this is reflected in their anatomy.
79
The epidermis of the shoot is associated with a cuticle ………….
80
with stomata.
81
The Epidermis of the shoot is also associated with cellular
structures attached to the basal epidermal cells called trichomes
82
These trichomes of Coleus are multicellular and help defend
the plant…..
83
84
Unlike in roots, the vascular tissue of the
shoot is not restricted to one mass in the
center.
In dicot (= Eudicot) stems the vascular
tissue is arranged in a ring of vascular
bundles embedded in the ground tissue.
The arrangement of the vascular bundles
divides the ground tissue into two regions.
85
The region inside the ring of vascular
bundles is the Pith.
Pith
86
…and the region between the epidermis and the ring
of vascular bundles called the cortex
87
How does the internal organization of the vascular tissue
between the root and stem reflect the different environmental
stresses to which each is subject?
88
The basic function of the leaf is
Photosynthesis
89
A thin flat structure optimizes the
materials used to construct the leaf
No cell in the leaf is far from the outside
this facilitates diffusion of gasses in and
out of the leaf
You get maximum surface area to
Intercept light for the materials used.
90
Cross section of lilac leaf
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Cross section ofGround
lilac leaf
Tissue
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Dermal Tissue
93
Vascular Tissue
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