Plant Structure, Growth, &
Development
Campbell and Reece
Chapter 35
Organization of Plants
• Plants like most multicellular organisms
have organs made of tissues that are made of
different cell types
3 Basic Plant Organs
1. Stems
2. Roots
3. Leaves
Roots
• Organ that
1. anchors a vascular
plant in the soil
2. absorbs water &
minerals
3. stores carbohydrates
Taproot System
• In most eudicots &
gymnosperms
• Taproot develops from
embryonic root
• Forms lateral roots
(branch roots)
• Penetrate deep
• Eudicot: most flowering
plants that have 2 embryonic
seed leaves
• Gymnosperm: vascular plant
that bears naked seeds
Roots in Monocots
• Grasses: no tap root
• Roots called adventitious: grows in unusual
locations
– Example: roots arising from stems or leaves
Adventitious Root Systems
• Each small root forms its own lateral roots 
fibrous root system
Root Hairs
• Emerge near tips of roots
• Increase surface area for absorption of water
and mineral ions (do not help anchor plant)
• are thin, tubular extensions of a root
epidermal cell
Root Adaptations
• Prop Roots: support
tall, top-heavy trees
• Pneumatophores: air
roots, portion above
water line allows them
to get O2
Root Adaptations
• Buttress Roots: tallest
trees in rain forest have
shallow roots; buttress
roots give support to
trunks
• “Strangling” Aerial
Roots: seeds of these
trees (strangler fig)
germinate in branches
of host tree
Stems
• Plant organs that
1. raise or separate leaves  allowing them to
receive more sunlight
2. Raise reproductive structures 
facilitating dispersal of seeds or pollen
Parts of a Stem
• Each stem has alternating system of:
1. Nodes
– Pts @ which leaves are attached
2. Internodes
– Stem segments between nodes
3. Axillary Bud
– Upper angle (axil) formed by each leaf & stem
– Structure that can form a lateral shoot
(branch)
Parts of a Stem
4.Apical Bud
– Part of shoot tip
– The terminal bud (where most of growth occurs)
5. Apical Dominance
– Inhibits growth @ axillary buds
– If eaten by herbivore or if light more intense @
side of a shoot axillary buds break apical
dominance & grow
Why Pruning Makes a Plant
Bushier
Parts of a Stem
Adaptations of Stems
1. Rhizomes: horizontal
shoots that grow just
below surface ;vertical
shoots emerge from
axillary buds
• Ex: Irises, Hops
Stem Adaptations
2.Bulbs: are vertical,
underground shoots
made mostly of
enlarged bases of
modified leaves that
store food
• Ex: onion, tulips
Adaptations of Stems
3. Stolons: horizontal
shoots that grow along
surface; aka “runners”
• Enable plant to
reproduce asexually:
plantlets form @ nodes
• Ex: strawberries, some
grasses
Adaptations of Stems
4. Tubers: enlarged ends
of rhizomes or stolons
specialized for storing
food. “Eye” of potato is
cluster of axillary buds
that mark the nodes
Ex: potato, dahlias
Leaves
• In most plants leaf is main photosynthetic
organ
• General Structure:
– Blade
– Petiole
• not on grasses or most monocots
– Veins
• Patterns differ monocots & eudicots
Structure of a Leaf
Types of Leaves
Leaf Adaptations
• Tendrils: modified leaf
used to support plant
• Ex: pea plants
• Some plants have
tendrils that are
modified stems
(grapevines)
Leaf Adaptations
2. Spines: leaves adapted
for protection
In cacti, stems are main
photosynthetic organ
Leaf Adaptations
3. Storage Leaves: most
succulents have leaves
adapted to store water
Leaf Adaptations
4. Reproductive Leaves:
leaves of some
succulents produce
adventitious plantlets
which fall off & take
root in soil
Ex: some succulents
Hens and Chicks
Leaf Adaptations
5. Bracts: modified leaves
surrounding the real
flower; function:
attract pollinators
The yellow portion of
poinsettia is the flower;
the red leaves are bracts
Tissue Systems
• Are functional units connecting all of the
plants organs
Dermal Tissue System
• Plant’s outer protective
covering:
• Epidermis: nonwoody
plants: tightly packed
cells
• Cuticle: waxy covering
on epidermal surface
prevents water loss
• Periderm: in woody
plants: replaces in older
regions of stems & roots
Vascular Tissue System
Carries out long-distance
transport of materials
between the root & shoot
systems
1. Xylem
–
& dissolved
materials roots 
shoots
H2O
2. Phloem
–
Sugars  roots & sites
of growth
Ground Tissue System
• Tissue that isn’t
dermal or vascular
tissue
• Pith: Internal to
vascular tissue
• Cortex: external to
vascular tissue
Plant Cells
• Cell differentiation involving changes in:
– Cell walls
– Cytoplasm
– Organelles
Parenchymal Cells
• Mature cells have thin, slightly flexible cell
walls (only 1)& large central vacuole
• Functions:
– Perform most of metabolic functions of plant
•
•
•
•
Chloroplasts
Plastids: store starch, found in roots
Make up most of fleshy part of fruits
Most able to divide & differentiate into other cell types
Collenchyma Cells
• Come grouped in strands just below
epidermis
• Support young parts of plant shoot w/out
interfering with growth
• Elongated cells with thicker cell walls
(compared to parenchymal cells) which can
be irregularly thickened
• Remain living cells thru out plant life
Sclerenchymal Cells
• Supportive role but more rigid than
collenchymal cells in regions of plant that
have stopped growing
• 2º cell walls thick, contain lignin (>1/4 dry
mass of wood)Lignin in all vascular plants,
not in bryophytes
• Many dead at plant maturity: rigid cell
walls support plant
Sclerenchymal Cells
• 2 types: (both for support & strength)
1. Sclereids
– Boxy, irregularly shaped cells
– Thick lignified 2º cell walls
– Hardness in nutshells/grittiness in pear
2. Fibers
– Grouped in strands
– Long, slender, tapered
– Hemp fibers for rope/flax fibers for linen
Water-Conducting Cells of Xylem
• 2 types: both elongated, tubular cells/dead at
plant maturity: form tubular conduit for
water flow; have pits thru which water can
move laterally
1. Tracheids
– In nearly all vascular plants
2. Vessel Elements
– In some vascular/most angiosperms/few
gymnosperms
Sugar-Conducting Cells of the
Phloem
• 4 types all alive @ plant maturity
1. Sieve Cells: in seedless vascular plants &
gymnosperms
2. Sieve Tubes: chains of cells/ enucleated, no
ribosomes, vacuole, or cytoskeleton  sugars
can diffuse thru cell more easily
3. Sieve Plates: pores for flow of sap fluid cell-tocell
4. Companion Cells: nonconducting cells
connected to sieve tube cells by
plasmodesmata/their ribosomes & nucleus serve
both cells
Growth in Plants
Stem Growth
Root Growth
Cross-Section of a Leaf
Anatomy of a Tree Trunk
• bark includes all
tissues external to the
vascular cambian (2º
xylem, wood, and
phloem)
• Sapwood = “living
wood” has lighter color
than heart wood
(center) which is made
of dead cells
Development of a Plant
• Definitions:
• Development: specific series of changes by
which cells form tissues, organs, &
organisms
• Growth: irreversible increase in size
More Definitions
• Morphogenesis:cellular & tissue-based
processes by which an organism takes shape,
depends on cells responding to positional
information from neighboring cells
• Differentiation : process by which a cell or
group of cells become specialized in structure
& function
Plant Cell Division
• Preprophase band made of microtubules
develops in late interphase  determines
where cell plate will form
Asymmetrical Cell Division
• not all plant cells divided equally duting M
Phase of cell cycle
• When occurs: usually signals a key event in
development
• Example:
– Epidermal cell divides
• 1 large epidermal cell
• 1 small guard cell
Cell Polarity
• The condition of having structural or
chemical differences at opposite ends of an
organism
• Typical plant has axis with a shoot end & a
root end
– 1st division of fertilized plant ova 
asymmetrical which initiates polarization of
plant body into shoot & root
Cell Elongation
• Cell division enhances possibility of plant
growth but it is cell elongation that is
responsible for plant growth
Cell Elongation
• Controlled by microtubule orientation 
controls the orientation of cellulose
microfibrils in cell wall
Cell Differentiation
• Arises from differential gene activation
• Enables cells w/in plant to assume different
functions
• Way any particular cell differentiates
depends on its position in developing plant
Pattern Formation
• Is the development of specific structures in
specific locations
• 2 hypothesis to explain
1. Lineage-based mechanism
– Daughter cells have instructions from early
cells in plant development
2. Position-based mechanism
– Cell’s position in emerging organ determines
what kind of cell it will become
Pattern Formation
• Position-based hypothesis
– By destroying cells during development have
shown that cell’s fate determined late in
development & depends mostly on signals from
neighboring cells
– Cell fate in animals mostly lineage-dependent
involving transcription factors
Pattern Formation
• Hox genes
– Homeotic genes that code for transcription
factors
– Critical for proper # & placement of embryonic
structures (legs, antennae in Drosophila)
Pattern Formation
• Knotted-1 homologous to Hox gene found in
maize
• Important in development of leaf morphology
Control of Cell Differentiation
• Depends on control of gene expression: which
genes are transcribed  protein
• But fate of a particular cell is determined by
its final position in the developing organ,
not by cell lineage
– If undifferentiated cell is misplaced  it will
differentiate into cell type appropriate to its
position
Activation of Genes
• Depends on signals from neighboring cells
Phase Changes
• Cues from plant itself or from its
environment cause plant to switch from 1
developmental stage to another: called Phase
Changes
• Most obvious changes in leaf shape & size
Genetic Control of Flowering
• Flower formation involves phase change from
vegetative growth  reproductive growth
• transition triggered by:
1.
–
2.
–
Environmental cues
Length of daylight
Internal signals
Plant hormones
Genetic Control of Flowering
• Production of a flower by a shoot apical
meristem stops the primary growth of the
shoot
• Is ass’c with the switching on of floral
meristem identity genes
• Meristem: plant tissue that remains embryonic as long as
plant live, allowing for indeterminate growth
Meristem Identity Genes
• Code for transcription factors that regulate
genes needed for conversion of the
indeterminate vegetative meristems 
determinate floral meristems
Organ Identity Genes
• A plant homeotic gene that uses positional
information to determine which emerging
leaves develop into which type of floral
organs
Organ Identity Genes
• Provide model system for studying pattern
formation:
– The development of a multicellular organism’s
spatial organization: arrangement of organs &
tissues in their characteristic places in 3-D
Organ Identity Genes
• 3 classes identified by studying mutants
with abnormal flowers
• ABC Hypothesis
• A model of flower formation identifying 3
classes of organ identity genes that direct
formation of the 4 types of floral organs
• http://www.slideshare.net/jayswan/chapter35-presentation