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March 28, 2005
Plant Tissues
Chapter 26
Jin Hoe Huh
Angiosperms – flowering plants
• The angiosperms are seed-bearing
vascular plants
• In terms of distribution and diversity,
they are the most successful plants on
Earth
• The structure and function of this plant
group help explain its success
Flowering
Plant Life
Cycle
Diploid
Double fertilization
Haploid
pollination
Two
sperms
enter
ovule
Meiosis
microspores
Female gametophyte
Meiosis
Mitosis
without
cytoplasmic
division
Plant Life Histories
• Annuals complete life cycle in one
growing season
• Biennials live for two seasons; flowers
form in second season
• Perennials grow and produce seeds
year after year
Shoot and Root
Systems
Shoot system
- produces sugars by
photosynthesis
Shoot
System
- carries out reproduction
Root system
- anchors the plant
- penetrates the soil and
absorbs water and minerals
- stores food
Root
System
Shoot and root
systems are
interdependent
water &
minerals
sugar
SHOOT SYSTEM
ROOT SYSTEM
Plant Tissue
Systems
• Ground tissue
system
• Vascular tissue
system
• Dermal tissue
system
EPIDERMIS
VASCULAR TISSUES
GROUND TISSUES
SHOOT SYSTEM
ROOT SYSTEM
Meristems – Where Tissues Originate
• Regions where cell divisions produce
plant growth
• Apical meristems
– Lengthen stems and roots
– Responsible for primary growth
• Lateral meristems
– Increase width of stems
– Responsible for secondary growth
Apical Meristems
Lengthen shoots and roots:
SAM and RAM
activity at
meristems
Cells that form at apical
meristems:
protoderm  epidermis
new cells
elongate
and start to
differentiate
into primary
tissues
ground meristem  ground
tissues
procambium  primary
vascular tissues
Lateral Meristems
Increases girth of older roots and stems
Cylindrical arrays of cells
vascular cambium  secondary vascular tissues
periderm  cork cambium
thickening
Simple Tissues
Made up of only one
type of cell
Parenchyma
Collenchyma
Sclerenchyma
Morphology of three simple tissue types
parenchyma
collenchyma
sclerenchyma
Parenchyma: A Simple Tissue
• Comprises most of a plant’s soft primary growth
• Cells are pliable, thin walled, many sided
• Cells remain alive at maturity and retain
capacity to divide
• Mesophyll is a type of parenchyma that
contains chloroplasts
Collenchyma: A Simple Tissue
• Specialized for support for primary tissues
• Cells are elongated, with walls (especially
corners) thickened with pectin
• Makes stems strong but pliable
• Cells are alive at maturity
Sclerenchyma: A Simple Tissue
• Supports mature plant parts
• Protects many seeds
• Cells have thick, lignified walls and are dead
at maturity
• Two types:
– Fibers: Long, tapered cells
– Sclereids: Stubbier cells
Complex Tissues
Composed of a mix of cell types
Xylem
Phloem
Epidermis
Xylem
• Conducts water
and dissolved
minerals
• Conducting cells
are dead and
hollow at maturity
tracheids
vessel
member
Phloem:
A Complex Vascular Tissue
sieve plate
• Transports sugars
• Main conducting
cells are sievetube members
• Companion cells
assist in the
loading of sugars
sieve-tube
member
companion
cell
Epidermis:
A Complex Plant Tissue
- Covers and protects plant
surfaces
- Secretes a waxy,
waterproof cuticle
- In plants with secondary
growth, periderm replaces
epidermis
Monocots and Dicots – same
tissues, different features
1 cotyledon
4 or 5 floral
parts
3 floral
parts
Parallel veins
1 pore
Vascular
bundles
in ring
2 cotyledons
Netlike veins
3 pores
Vascular
bundles
dispersed
shoot apical
meristem
Shoot
Development
cortex
procambrium
protoderm procambrium
pith
ground meristem
primary xylem
primary phloem
Bud = undeveloped shoot of
meristematic tissue
Leaves
Internode
Axillary bud at node
Longitudinal section of terminal bud
Roots also have meristems
Internal Structure of a
Dicot Stem
- Outermost layer is epidermis
- Cortex lies beneath epidermis
- Ring of vascular bundles
separates the cortex from the pith
- The pith lies in the center of the
stem
Internal
Structure
of a
Monocot
Stem
• The vascular bundles
are distributed
throughout the ground
tissue
• No division of ground
tissue into cortex and
pith
Dicots
Monocots
Ground tissue
system
Dermal tissue
system
Vascular tissue
system
Dicots and Monocots have different stem and root anatomies
Leaf Gross Structure
DICOT
MONOCOT
petiole
axillary
bud
blade
node
sheath
blade
node
Adapted for Photosynthesis
• Leaves are usually thin
– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in,
oxygen out
• Leaves are arranged to capture sunlight
– Are held perpendicular to rays of sun
– Arrange so they don’t shade one another
Leaf Structure
UPPER
EPIDERMIS
cuticle
PALISADE
MESOPHYLL
xylem
SPONGY
MESOPHYLL
phloem
LOWER
EPIDERMIS
O2
CO2
one stoma
Mesophyll:
Photosynthetic Tissue
• A type of parenchyma tissue
• Cells have chloroplasts
• Two layers in dicots
– Palisade mesophyll
– Spongy mesophyll
Collenchyma
Parenchyma
Leaf Veins: Vascular Bundles
• Xylem and phloem –
often strengthened with fibers
• In dicots, veins are netlike
• In monocots, they are parallel
Root Systems
Root Structure
• Root cap covers tip
• Apical meristem produces
the cap
• Cell divisions at the apical
meristem cause the root to
lengthen
• Farther up, cells
differentiate and mature
root apical
meristem
root cap
Internal Structure of a Root
• Outermost layer is epidermis
• Root cortex is beneath the epidermis
• Endodermis, then pericycle surround
the vascular cylinder
• In some plants, there is a central pith
epidermis
endodermis
cortex
pericycle
root hair
phloem
xylem
Root Hairs and Lateral Roots
• Both increase the surface
area of a root system
• Root hairs are tiny extensions
of epidermal cells
• Lateral roots arise from the
pericycle and must push
through the cortex and
epidermis to reach the soil
new
lateral
root
Secondary Growth
• Occurs in perennials
• A ring of vascular cambium produces
secondary xylem and phloem
• Wood is the accumulation of these
secondary tissues, especially xylem
Secondary Growth
Woody Stem
periderm (consists of
cork, cork cambium,
and secondary cortex)
BARK
vascular cambium
secondary
phloem
HEARTWOOD
SAPWOOD
Annual Rings
• Concentric rings of secondary xylem
• Alternating bands of early and late wood
• Early wood
– Xylem cells with large diameter, thin walls
• Late wood
– Xylem cells with smaller diameter, thicker
walls
Types of Wood
• Hardwood (oak, hickory)
– Dicot wood
– Xylem composed of vessels, tracheids,
and fibers
• Softwood (pine, redwood)
– Gymnosperm wood
– Xylem composed mostly of tracheids
– Grows more quickly