Transcript Ch. 31 – Plant Structure, Growth and Differentiation

Ch. 31 – Plant Structure, Growth
and Differentiation
Plant Body
• Root system
– Underground
– Anchor and absorb
• Shoot system
– Vertical stem, leaves (flowers, fruits w/seeds)
– photosynthesis
Fig. 35-2
Reproductive shoot (flower)
Apical bud
Node
Internode
Apical
bud
Vegetative
shoot
Leaf
Shoot
system
Blade
Petiole
Axillary
bud
Stem
Taproot
Lateral
branch
roots
Root
system
Plant Cells and Tissues
• Ground tissue system – majority
– Photosynthesis, storage, support
• Vascular tissue system
– Conduction, strength, support
• Dermal tissue system
– Covering, protection
All 3 are Interconnected throughout the plant
Fig. 35-8
Dermal
tissue
Ground
tissue Vascular
tissue
Ground Tissue System
• Parenchyma, collenchyma, sclerenchyma
tissue
• Primary cell wall – secreted by growing cell;
stretches and expands as cell grows
• Secondary cell wall – secreted when cell stops
growing; thick and strong (inside primary)
Parenchyma
•
•
•
•
Living, metabolizing
Most common
Soft parts
Function
– Photosynthesis – green chloroplasts
– Storage – starch, oil, water, salt
– Secretion – resins, tannins, hormones, enzymes, nectar
• Can differentiate if plant injured (i.e. xylem cells)
Fig. 35-10a
Parenchyma cells in Elodea leaf,
with chloroplasts (LM)
60 µm
Parenchyma
Collenchyma
•
•
•
•
Flexible, structural support (nonwoody parts)
Elongated cells
Alive at maturity
Primary CW – unevenly thick, thicker in
corners
• Near stem surface, leaf veins
Fig. 35-10b
5 µm
Collenchyma cells (in Helianthus stem) (LM)
Collenchyma
Sclerenchyma
• Structural support
• Primary and secondary CW (strong and hard,
extreme thickening, so can’t stretch, elongate)
• Cells dead at maturity
• 2 types:
– Sclereids – variable shape, nut shells, pits of stone fruits,
pears gritty (clusters of sclereids)
– Fibers – long, tapered – patches, clumps; wood, inner
bark, leaf veins
Sclerenchyma
Fig. 35-10c
5 µm
Sclereid cells in pear (LM)
25 µm
Cell wall
Fiber cells (cross section from ash tree) (LM)
Vascular tissue
• Embedded in ground tissue
• Transport
• Xylem and phloem
Xylem
• Conducts water, dissolved nutrient minerals
roots  stems, leaves
• Support
• Angiosperms –
– tracheids, vessel elements - conduct
– parenchyma cells - storage
– fibers - support
Tracheids and vessel elements
• Dead at maturity  hollow, CW remain
• Tracheids – long, tapering, patches/clumps;
water passes from 1 tracheid to another by
pits (thin areas where sec. wall did not form)
• Vessel elements – larger in diameter than
tracheid; end walls have perforations; stacked
 water goes between; stack = vessel; pits in
side walls for lateral water transport
Fig. 35-10d
Vessel
Tracheids
100 µm
Pits
Tracheids and vessels
(colorized SEM)
Perforation
plate
Vessel
element
Vessel elements, with
perforated end walls
Tracheids
Phloem
• Conducts food
• Support
• Angiosperms
– Sieve tube members, companion cells – conduct
– Fibers – support
– Parenchyma cells
Sieve tube members
• Conduct food in solution
• Joined end-to-end  long tubes
• CW ends = sieve plates; cytoplasm extends
between cells
• Living at maturity – many organelles
shrink/disintegrate
• Can function w/o nuclei
Companion cells
• Adjacent to each sieve tube member (stm)
• Assists stm
• Living w/ nucleus – directs activities of both
cells
• Plasmodesmata between stm and companion
• Helps move sugar into stm
Fig. 35-10e
Sieve-tube elements:
longitudinal view (LM)
3 µm
Sieve plate
Sieve-tube element (left)
and companion cell:
cross section (TEM)
Companion
cells
Sieve-tube
elements
Plasmodesma
Sieve
plate
30 µm
10 µm
Nucleus of
companion
cells
Sieve-tube elements:
longitudinal view
Sieve plate with pores (SEM)
Food conducting
Dermal tissue system
•
•
•
•
Epidermis and periderm
Protective covering
Herbaceous – single layer = epidermis
Woody – epidermis splits w/ growth
– Periderm – layers thick, under epidermis; replaces
epidermis in stems, roots, composing outer bark
Epidermis
•
•
•
•
Unspecialized dermal cells
Special guard cells + trichomes
Single layer, flat cells
Usually no chloroplasts  transparent
– Allow light through
Fig. 35-18a
Key
to labels
Dermal
Ground
Vascular
Cuticle
Sclerenchyma
fibers
Stoma
Upper
epidermis
Palisade
mesophyll
Spongy
mesophyll
Bundlesheath
cell
Lower
epidermis
Cuticle
Xylem
Vein
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Fig. 35-18b
Guard
cells
50 µm
Stomata
pore
Epidermal
cell
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Fig. 35-18c
Key
to labels
Dermal
Ground
Upper
epidermis
Palisade
mesophyll
Vascular
100 µm
Spongy
mesophyll
Lower
epidermis
Vein Air spaces Guard cells
(c) Cross section of a lilac
(Syringa) leaf (LM)
Cuticle
•
•
•
•
•
Aerial parts
Secreted by epidermal cells
Waxy – water loss
Slows diffusion of CO2 – stomata help
Stomata
– Open – day – photosynthesis, evaporative cooling
– Closed – night
– Closed in day if drought
Trichomes
• Outgrowths or hairs
• Many shape, sizes, functions
• Ex:
– Roots hairs – increase SA
– Salty env. – remove excess salt
– Aerial parts – increase light reflection, cooler
– Protections – stinging nettles
Growth at Meristems
• Cell division
– Increase # cells
• Cell elongation
– Vacuole fills, increase pressure on CW, expands
• Cell differentiation
– Specialize into cell types
• Meristems = where plant cells divide, mitosis
– No differentiation
2 kinds of Growth
• Primary growth
– Increase stem, root length
– All plants, soft tissues
• Secondary growth
– Increase width
– Gymnosperms, woody dicots
– Wood + bark
Fig. 35-11
Primary growth in stems
Epidermis
Cortex
Shoot tip (shoot
apical meristem
and young leaves)
Primary phloem
Primary xylem
Pith
Lateral meristems:
Vascular cambium
Cork cambium
Secondary growth in stems
Periderm
Axillary bud
meristem
Cork
cambium
Cortex
Root apical
meristems
Pith
Primary
xylem
Secondary
xylem
Vascular cambium
Primary
phloem
Secondary
phloem
Primary growth
• Increase in length
• Apical meristem – tips of roots + shoots (buds)
• Buds = dormant embryonic shoot (develop into
branches next spring
• Root tip
– Root cap – protective layer of cells, covers root tip
– Root apical meristem – directly behind root cap
– Cell elongation – behind meristem, push tip ahead,
some differentiation
Fig. 35-13
Cortex
Vascular cylinder
Epidermis
Key
to labels
Dermal
Root hair
Zone of
differentiation
Ground
Vascular
Zone of
elongation
Apical
meristem
Root cap
100 µm
Zone of cell
division
Fig. 35-14a1
Epidermis
Key
to labels
Cortex
Dermal
Endodermis
Ground
Vascular
Vascular
cylinder
Pericycle
Xylem
100 µm
Phloem
(a) Root with xylem and phloem in the center
(typical of eudicots)
Fig. 35-14a2
(a) Root with xylem and phloem in the center
(typical of eudicots)
Endodermis
Key
to labels
Pericycle
Dermal
Ground
Vascular
Xylem
Phloem
50 µm
Fig. 35-14b
Epidermis
Cortex
Endodermis
Key
to labels
Vascular
cylinder
Pericycle
Dermal
Ground
Vascular
Core of
parenchyma
cells
Xylem
Phloem
100 µm
(b) Root with parenchyma in the center (typical of
monocots)
• Shoot apex = terminal bud
– Shoot meristem
– Give rise to leaf primordia and bud primordia
Fig. 35-16
Shoot apical meristem
Leaf primordia
Young
leaf
Developing
vascular
strand
Axillary bud
meristems
0.25 mm
Fig. 35-17a
Phloem
Xylem
Sclerenchyma
(fiber cells)
Ground tissue
connecting
pith to cortex
Pith
Key
to labels
Cortex
Epidermis
Vascular
bundle
Dermal
Ground
1 mm
(a) Cross section of stem with vascular bundles forming
a ring (typical of eudicots)
Vascular
Fig. 35-17b
Ground
tissue
Epidermis
Key
to labels
Dermal
Vascular
bundles
Ground
Vascular
1 mm
(b) Cross section of stem with scattered vascular bundles
(typical of monocots)
Secondary Growth
• Increase in width
• Make secondary tissues: sec. xylem, sec.
phloem, periderm
• Lateral meristem – cells divide, not elongate
• 2 types:
– Vascular cambium
• Between wood and bark
• Make sec. xylem (wood) + sec. phloem (inner bark)
Fig. 35-20
Vascular cambium
Growth
X X C P P
X X C P
Vascular
cambium
Secondary
xylem
Secondary
phloem
X C P
C
X C
C
C
After one year
of growth
After two years
of growth
Fig. 35-22
Growth
ring
Vascular
ray
Heartwood
Secondary
xylem
Sapwood
Vascular cambium
Secondary phloem
Bark
Layers of periderm
– Cork cambium
• In outer bark
• Form cork to outside +parenchyma (storage)
• Periderm = cork, parenchyma, cork cambium
• Bark – outermost covering of woody stems
– Everything outside of vascular cambium
– 2 regions:
• Living inner bark of secondary phloem
• Mostly dead outer bark of periderm
Fig. 35-19a3
(a) Primary and secondary growth
in a two-year-old stem
Epidermis
Cortex
Primary phloem
Pith
Primary xylem
Vascular cambium
Primary phloem
Cortex
Epidermis
Vascular cambium
Primary xylem
Pith
Vascular ray
Secondary xylem
Secondary phloem
First cork cambium
Cork
Periderm (mainly
cork cambia
and cork)
Most recent cork
cambium
Secondary phloem
Bark
Secondary
xylem
Cork
Layers of
periderm
Fig. 35-19b
Secondary xylem
Secondary phloem
Vascular cambium
Late wood
Early wood
Bark
Cork
cambium Periderm
0.5 mm
Cork
Vascular ray
0.5 mm
Growth ring
(b) Cross section of a three-yearold Tilia (linden) stem (LM)
You should now be able to:
1. Compare the following structures or cells:
– Dermal, vascular, and ground tissues
– Parenchyma, collenchyma, sclerenchyma, waterconducting cells of the xylem, and sugarconducting cells of the phloem
– Sieve-tube element and companion cell
2. Describe in detail the primary and secondary growth
of the tissues of roots and shoots
3. Describe the composition of wood and bark