Cells and tissues of
the plant body
Lecture #2
Levels of Organization in Vascular
Plants
• Cells – the basic unit of the plant body
• Tissues – a group of cells with a similar function
in the plant
– Simple tissue – cells all of one type
– Complex tissue – cells of several cell types
• Organs – made up of tissues, e.g., root, stem,
leaf, sporangium (sprg) each with a specific
function
• Tissue systems – a system of tissues that runs
through the whole plant, e.g., dermal, vascular,
ground tissues
Tissue Systems
1. Vascular
2. Dermal
3. Ground
Shoot apex
Mature cell types in the plant
body
• Parenchyma
• Collenchyma
• Sclerenchyma
• Other specialized cells-most fit into
these 3 categories
Basic cell types
• Parenchyma- polygonal cells with thin walls
(primary wall only) of cellulose, have
intercellular spaces and function in storage
in the plant body
• Collenchyma-rectangular
cells with thickened corners,
function in support (usually
found just beneath the epidermis)
• Sclerenchyma-thick-walled cells with both
primary and secondary wall, function in
support, and in conduction of water
Parenchyma cell
Parenchyma tissue
Simple tissue=
composed of one
cell type (parenchyma)
Parenchyma cells have
Primary wall only –
cellulose
Stains green with
fast green stain
Alive & has nucleus &
cytoplasm
Note: intercellular spaces
& shapes of cells
Collenchyma
Celery petiole showing collenchyma
Medicago stem x.s.
collenchyma
Parenchyma
cell
Primary wall
Plasmodesmata=
Cytoplasmic connections
β1,4 linked
Sclerenchyma cell types
• Sclereid (support)
stone cell
stellate sclereid
• Fiber (support)
• Tracheid (support & conduction of
water)
• Vessel element (support & conduction)
in
Pear fruit
Brachysclereids
=stone cells
Stellate (star-shaped) sclereid
Used for support in the leaf of Nymphaea (water lily)
Sclerenchyma - fibers
Bamboo
vascular bundle
Collenchyma and sclerenchyma fiber bundle
Tilia fibers in secondary phloem
Tracheids
Elongate cells
Oblique end walls
Have primary and secondary wall
Imperforate – have thin areas in wall
Dead when functioning in conduction
Function in support of the plant and in
the conduction of water and dissolved
minerals
• Have various secondary wall thickening
patterns
• Found in all vascular plant groups
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Tracheids
Types of
secondary
wall
thickenings
Primary wall
Secondary wall
(Red stain is safranin)
Circular bordered
pit pair
Vessel element
• Found in flowering plants (mostly)
• Shorter, more barrel-shaped cell than a tracheid
• Larger diameter cell – more efficient water
conduction; less drag
• Horizontal end walls
• End wall perforated – perforation plate, i.e., a
hole - dead cell
• Usually has circular-bordered pits but can have
scalariform or other 2o thickenings
• Has both primary and secondary cell wall
• Functions in water conduction & support
• A chain of vessel elements = a vessel - open
pipeline
Vessel element with simple
perforation
Sclerenchyma cells
(in oak wood)
a. Vessel element
b. Vessel element
c. Vessel element
d. Tracheid
e. Fiber
f. Fiber
Differentiation of a vessel element
Tracheary element = any water conducting cell in the xylem
Xylem & Phloem are complex
tissues
i.e., they are composed of several cell
types
Xylem
Function: Conduction of
water and dissolved
minerals
Function of sclerenchyma
cells in xylem: Support
General direction of flow is
upward, from roots
through stem to leaves to
atmosphere
Phloem
Function: Conduction of
sugar (photosynthates)
General direction of flow is
downward from leaves to
stems to roots and
storage in the roots as
starch
Xylem– a complex tissue with
several cell types
• Parenchyma – xylem parenchyma
(wood parenchyma)
• Fibers
• Tracheids- major water conducting cell,
found in all vascular plant groups
• Vessel elements (flowering plants)
(Note we will talk about the arrangement
of these tissues in the plant on 15 Jan.)
Phloem is a complex tissue
• Parenchyma (phloem parenchyma)
• Fibers (phloem fibers)
• Conducting cells
– Sieve cells
– Sieve tube elements
– Companion cells (parenchyma)
Sieve cells
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Basic sugar conducting cell in vascular plants
Elongate
Oblique end walls
Thin-walled
Have sieve areas on side walls and on end walls
Live cells when functioning
No nuclei, have cytoplasm
Sieve area = pit-like areas (small pores) in the
walls, lined with callose and connect to other
sieve cells by plasmodesmata
Conifer sieve cells with sieve areas
Conifer phloem
Aniline blue stains callose - (1,3 linked glucose molecules)
(Cellulose is 1, 4 linked)
(If you are interested in the structure of these molecules see pp. 20-21 text)
Pteridium x.s. vascular tissue
Arrow indicates sieve cell
Sieve tube elements (sieve tube member)
Companion cells (in flowering plants) –come
from the same precursor cell
STE= shorter more barrel-shaped cell than
sieve cell,
More horizontal end walls
Live when functioning, No nucleus; have
cytoplasm, ER
Thin-walled only
Have sieve areas on side walls
Perforate end walls have a SIEVE PLATE can be simple or compound – wider pores in
the end walls than side walls of these cells
Sieve tube = a chain of sieve tube
elements (STE)
Companion cell = small parenchyma cell
attached to the side of an STE by
plasmodesmata, has a large nucleus,
moves substances into and out of STE
originated from the same cell (precursor
cell) in the procambium
Found in flowering plants only
Cucumis sieve plate
Formation of a sieve tube element
a. Mother cell divides b. STE & companion cell c. Nucleus
degenerates & vacuole breaks up, pores develop in sieve
plate (P-protein = phloem protein) d. Pores open— Pprotein, ER, mitochondria & plastids still in STE.
p. 552 textbook
Cucurbita phloem showing sieve plates
Companion cells at arrows