Plant Tissues
Chapter 28 Part 1
Impacts, Issues
Drought Versus Civilization
 Without plants, we would die – prolonged
drought can destroy crops and civilizations
28.1 Components of the Plant Body
 The unique organization of tissues in flowering
plants is part of the reason why they are the
dominant group of the plant kingdom
The Basic Body Plan
 Shoots
• Aboveground plant parts such as stems, leaves,
and flowers
 Roots
• Structures that absorb water and dissolved
minerals, store food, and support the plant
• Usually grow down and outward in the soil
Plant Tissue Systems
 Ground tissue system
• Photosynthesis, storage, and structural support of
other tissues
 Vascular tissue system
• Distributes absorbed water and mineral ions and
products of photosynthesis
 Dermal tissue system
• Covers and protects exposed plant surfaces
Body Plan: Tomato Plant
shoot tip (terminal bud)
lateral (axillary) bud
young leaf
flower
node
internode
node
dermal tissue
vascular tissues
leaf
seeds
in fruit
ground tissues
SHOOTS
ROOTS
primary root
lateral root
withered seed
leaf (cotyledon)
stem
root hairs
root tip
root cap
Fig. 28-2, p. 476
Animation: Tissue systems of a tomato
plant
Eudicots and Monocots
 Flowering plants are divided into two classes
with tissues organized into different patterns
 Eudicots have two cotyledons (seed leaves)
 Monocots have one cotyledon
Eudicots and Monocots
A
In seeds, two
cotyledons (seed
leaves of embryo)
Flower parts in fours or Leaf veins usually
fives (or multiples of
forming a netlike
four or five)
array
Pollen grains with
three pores or
furrows
Vascular
bundles
organized in a
ring in ground
tissue
Pollen grains with
one pore or furrow
Vascular
bundles
throughout
ground tissue
B
In seeds, one
cotyledon (seed
leaf of embryo)
Flower parts in
threes (or multiples
of three)
Leaf veins usually
running parallel with
one another
Fig. 28-3, p. 477
Animation: Eudicots and monocots
Introducing Meristems
 All plants tissues arise at meristems (regions of
rapidly dividing, undifferentiated cells)
 Growth in apical meristems at tips of shoots
and roots (primary growth) increases length
 In some plants, growth in lateral meristems
(secondary growth) thickens roots and shoots
Apical and Lateral Meristems
Fig. 28-4a, p. 477
shoot apical meristem
(new cells forming)
cells dividing,
differentiating
three tissue
systems
developing
three tissue
systems
developing
cells dividing,
differentiating
root apical meristem
(new cells forming)
a Many cellular descendants of apical meristems are the start of lineages of
differentiated cells that grow, divide, and lengthen shoots and roots.
Fig. 28-4a, p. 477
Fig. 28-4b, p. 477
vascular cambium
cork cambium
thickening
b In woody plants, the activity of two lateral meristems—vascular cambium and
cork cambium—result in secondary growth that thickens older stems and roots.
Fig. 28-4b, p. 477
28.2 Components of Plant Tissues
 Different plant tissues form just behind shoot
and root tips, and on older stem and root parts
 Tissue systems are organized as simple tissues
(one cell type) or complex tissues (two or more
cell types)
Simple Tissues
 Parenchyma makes up most primary growth
• Functions in secretion, storage, photosynthesis
(mesophyll), and tissue repair
 Collenchyma supports growing plant parts
• Pectin provides flexibility
 Sclerenchyma contains lignin for support
• Cells (fibers, sclereids) are dead at maturity
Simple Tissues
collenchyma
parenchyma
Fig. 28-7a, p. 479
lignified secondary wall
Fig. 28-7c, p. 479
Complex Tissues: Vascular Tissues
 Xylem carries water and ions through the plant
• Consists of two types of cells that are dead at
maturity: tracheids and vessel members
• Lignin-filled secondary walls
 Phloem conducts sugars, other organic solutes
• Sieve tubes connect end to end at sieve plates
• Companion cells load sugars into sieve tubes
Vascular Tissues
one
cell’s
wall
pit in
wall
a
sieve plate
of sievetube cell
companion
cell
b
parenchyma vessel of
xylem
c
phloem
fibers of
sclerenchyma
Fig. 28-8, p. 479
Complex Tissues: Dermal Tissues
 Epidermis
• Usually a single outer layer of cells that secrete a
waxy, protective cuticle
• May contain specialized cells that form stomata
for gas exchange
 Periderm
• Replaces epidermis in woody stems and roots
Plant Cuticle
leaf surface
cuticle epidermal cell
photosynthetic cell
Fig. 28-9, p. 479
Flowering Plant Tissues
Studying Plant Parts: Tissue Specimens
 Tissue specimens are cut along standard planes
radial:
tangential:
transverse:
Fig. 28-6, p. 478
Tissues in a Buttercup Stem
sclerenchyma (fibers)
xylem
parenchyma
epidermis
phloem
Fig. 28-5, p. 478
28.1-28.2 Key Concepts
Overview of Plant Tissues
 Seed-bearing vascular plants have a shoot
system, which includes stems, leaves, and
reproductive parts; most also have a root system
 Such plants have ground, vascular, and dermal
tissues
 Plants lengthen or thicken only at active
meristems
28.3 Primary Structure of Shoots
 Inside the soft, young stems and leaves of both
eudicots and monocots, the ground, vascular,
and dermal tissue systems are organized in
predictable patterns
Behind the Apical Meristem
 Terminal buds
• Main zones of primary growth in shoots
• Naked or encased in modified leaves (bud scales)
• Form leaves at nodes
 Lateral buds (axillary buds)
• Dormant shoots in leaf axils
• Form side branches, leaves, or flowers
Apical Meristem and Primary Growth
Fig. 28-10 (a-c), p. 480
immature
leaf
shoot apical
meristem
a Sketch of the shoot tip in the
micrograph at right, tangential
cut. The descendant meristematic
cells are color-coded orange .
b Same tissue region later on, after
the shoot tip lengthened above it
primary primary
cortex phloem xylem pith
c Same tissue region later still, with lineages
of cells lengthening and differentiating
Fig. 28-10 (a-c), p. 480
Fig. 28-10d (1), p. 480
immature
leaf
youngest
immature
leaf
apical
meristem
epidermis
forming
lateral bud
forming
vascular
tissues
forming
pith
Fig. 28-10d (1), p. 480
Fig. 28-10d (2), p. 480
Inside the Stem
 Vascular bundles
• Multistranded cords of vascular tissues threaded
lengthwise through ground tissues of all shoots
 Two distinct patterns of vascular bundles
• Eudicot stems: Cylinders run parallel with stem,
divide ground tissue into cortex and pith
• Monocot stems: Bundles distributed throughout
ground tissue
Eudicot and Monocot Stems
Fig. 28-11a, p. 481
vessel in meristem
xylem
cell
epidermis
cortex
vascular
bundle
pith
A Stem fine structure for alfalfa (Medicago), a eudicot
sieve tube companion
cell in
in phloem
phloem
Fig. 28-11a, p. 481
Fig. 28-11b, p. 481
collenchyma air vessel in
sheath cell space xylem
epidermis
vascular
bundle
pith
B Stem fine structure for corn (Zea mays), a monocot
sieve tube in
phloem
companion
cell in phloem
Fig. 28-11b, p. 481
Animation: Stem organization
Animation: Apical meristems
Animation: Cutting tissue specimens
Animation: Ground tissues
Animation: Vascular tissues