Anatomy & Growth of Angiosperms
Two plant groups: monocots & eudicots
I. Introduction
A. Uniqueness of Plants
http://www.fugu-sg.org/~elia/cambodia/templesfacesweb/pages/A3_Embracing_Roots.htm
B. Forces for Change
1. Genetics
2. Environment – two time scales:
a. Long-term: accumulation of adaptations that
enhanced survival & reproduction (evolution by
natural selection)
b. Short-term: plasticity = wide range of
phenotypes for each genotype. Allows plants to
adjust to changing environment (ex. Shorter plant in
dry year so that it can still reproduce)
Cells
Muscle cell
Tissues
Muscle tissue
Organs
Heart
Systems
Circulatory
system
Parenchyma cell
Dermal tissue
Leaves
Shoot system
II. Plant Organs: Roots, Stems, Leaves
A. Roots
1. Functions
a. Collect water & minerals from soil
b. Anchor plant
c. Store food (carb’s from photosynthesis) to
be used for flowering & fruiting
d. Covered with root hairs – increases surface
area for absorption
Fig. 35.2
2. Types
a. Prop root
d. Buttress root
Fig. 35.4
b. Storage root
c. Aerial strangler root
e. Pneumatophore
B. Stems/shoots
1. Functions
a. Support, transport
b. Some photosynthesis
2. Two types of shoots
a. Vegetative – leaves only
b. Reproductive – produces flowers
3. Parts of the stem:
a. Node – point of leaf attachment
b. Inter-node – stem segments between nodes
4. Buds
Apical dominance = the presence of an apical bud
inhibits the growth of axillary buds.
- remove or depress apical bud, axillary buds
begin to grow.
a. Terminal bud – contains a shoot apical
meristem; shoot growth is concentrated here
b. Axillary buds – in angle (axil) between leaf &
branch, contain meristem with potential to become a
vegetative shoot. Mostly dormant.
Fig. 35.2
5. Modified Shoots (stems):
a. Stolons – above-ground
runners
b. Rhizomes – below-ground
runners
c. Bulbs – swollen underground
shoots
d. Tubers – swollen rhizomes
Asexual, vegetative
propagation
Stores food for
later growth
Fig. 35.5
C. Leaves – main photosynthetic organs
1. Parts
a. Petiole
b. Blade
http://www.knotweed.co.uk/japknot_Info.htm
2. Types
Compound, doubly
compound – why??
a. Tendrils
Fig. 35.7
3. Modified leaves
b. Spines
c. Succulents
III. Plant Tissue
Fig. 35.8
A. Dermal or Epidermis
1. Characteristics
a. single layer of tightly packed cells covering
the young parts of the plant.
b. Functions in protection
c. Root hairs are specialized epidermal
extensions
d. Secretes waxy cuticle of the leaf
B. Ground
1. Characteristics
a. Fills the space between dermal and
vascular tissue systems.
b . Diverse functions:
Photosynthesis, storage, &
support
pith
In eudicots stems:
cortex
C. Vascular
1. Characteristics
a. function in transport between roots & shoots,
and structural support of plant
2. Types
a. Xylem: H2O & minerals transported up to
shoot system
b. Phloem: Food transported to roots & nonphotosynthetic parts such as the flowers
IV. The Plant Cell
Fig. 7.8
A. Generalized
Same as animals, except:
1. No lysozomes (digestive organelle)
2. Cell walls: maintains shape, structural support,
protects from damage. Made of cellulose, protein, &
sometimes lignin
3. Chloroplasts
4. Vacuole – storage, waste breakdown, growth!
5. Plasmodesmata – holes in cell wall, creates
channels to connect cytoplasm of adjacent cells
B. Plant Cell Categories
1. Parenchyma
4. Water-conducting cells of the xylem
3. Sclerenchyma
5. Sugar-conducting cells of the phloem
2. Collenchyma
1. Parenchyma
a. Characteristics
i. Least specialized cell. Can differentiate into
other cell types
ii. Primary cell walls only - thin and flexible
iii. Lack secondary plant cell walls
iv. Most metabolically active – lots of chloroplasts
for PSN (PhotoSyNthesis)
v. Starch, carbohydrate production & storage in
stems
2. Collenchyma
a. Characteristics
i. Primary walls are unevenly thickened
ii. Usually lack secondary walls.
iii. Usually grouped in strands to support young
parts of plants without restraining growth
iv. Flexible, elongate with growing shoots
3. Sclerenchyma
a. Characteristics
i. Function in mechanical support
ii. Have rigid and thick secondary walls
strengthened with lignin.
iii. May be dead at functional maturity
iv. Cell walls left behind as skeleton
Lignin:
b. Two types, both function in support:
i. Fibers - long, slender, tapered cells occurring in
bundles.
ii. Sclereids - short, irregularly-shaped. Ex. hard seed
coats
Fig.35.10
Fig.35.10
4. Water/Mineral conducting cells of the xylem:
a. 2 types: tracheids & vessel elements
i. Tracheids
Cells that are long, thin tapered cells having lignin-hardened
secondary cell walls with pits.
They are dead at maturity in which water flows from cell to cell
(laterally) through the pits in the cell walls 1o wall only. Their role
is in a support function
ii. Vessel Elements
These cells are wider, shorter and arranged end-to-end to form
tubes.
Their end walls are perforated to allow for the free flow of water
and are more efficient as water conductors than tracheids.
Fig. 35.10
5. Sugar-conducting cells of the phloem
a. 2 types
i. Sieve-tube members (or elements):
Chains of cells arranged end-to-end, Alive at functional
maturity, Lack a nucleus, ribosomes, & vacuole, and
Cells separated by perforated sieve plates – allow sugar
movement.
ii. Companion cells:
Load sugars into the sieve tube member, Nucleus and
ribosomes also serve the sieve-tube member.
Fig. 35.10
V. Growth & Development
http://www.cneccc.edu.hk/subjects/bio/album/Chapter20/PLANT_GROWTH.html
A. Definitions
1. Development is the sum of all the changes
2. Cell Division
3. Morphogenesis
B. Processes of plant cellular development:
1. Cell Growth
a. Cell division (Mitosis) in itself does not mean an
increase in growth.
b. Cell division yields no expansion of size.
c. Cell elongation increases growth.
Fig. 35.27
2. Cell elongation
a. due to water uptake
b. Direction of expansion = perpendicular to
alignment of cellulose microfibrils in cell wall
c. Enzymes weaken cross-link between microfibrils,
allowing cell to expand.
Fig. 35.29
Fig. 39.8
3. Morphogenesis
a. The coordinated arrangement of cells into tissues & organs
b. Pattern formation – development of specific structures in
specific places (e.g. Flowers born on the terminus of branches as
opposed to leaf axils.
c. Depends on:
i. Positional information – chemical signals from surrounding
cells indicate the cell’s position on plant
ii. Polarity of the plant, asymmetrical cell divisions
iii. Both affect the transcription of homeotic genes
4. Cellular Differentiation
a. Transformation of genetically identical cells into cells with
diverse biochemical and structural features. How?
i. Selective transcription of appropriate genes
ii. How? Chapters 18 & 39
iii. Flow of Info
The Flow of Information
DNA
Replication
Transcription
RNA
Translation
Energy
Amino Acids
Polypeptide
Additional Materials
Energy
Modification
Functional Protein
b. Regulation
i. at transcriptional level
ii. Regulation at translational level
iii. Regulation at post translational level
iv. Hormonal controls
v. Regulation at substrate level
vi. Regulation by environmental signals: light,
gravity,…..
c. Processes
i. Meristem identity genes – cause a vegetative shoot to become a
floral shoot
ii. Positional information (derived from chemical messengers)
selectively turn on or off organ–identity genes.
iii. Organ – identity genes - code for transcriptions factors that
regulate expression of genes controlling the development of specific
organs.
Fig. 35.34
By “turning off” organ identity
genes, we can give a rose
more petals
C. Plant growth vs. Animal growth
1. Comparison:
a. Embryonic, developing, and mature organs exist together
at the same time on one plant.
b. Grow until they die, called indeterminate growth. Some
determinate parts: leaves, flowers.
D. Plant life cycles:
1. Annual – complete life cycle (germination through
fruiting) in one year or less. Examples: grasses, crops,
wildflowers
2. Biennial – complete life cycle in two years (first year
= vegetative, second year = reproductive). Some need a
cold winter period to initiate flowering from vegetative
state. Ex. carrots
3. Perennial – live year after year, do not die after
reproduction. Examples: trees, shrubs, some grasses.
Causes of death = fire, disease
E. Plant Growth Sites  Meristems
Meristems are regions of the plant with continuous cell
division (i.e. perpetually embryonic tissue)
1. Types of meristems:
a. Apical meristem – located at the root and shoot tips,
responsible for growth in length (called primary growth)
b. Lateral meristems – extend lengthwise along the axis of
the stem & roots. Responsible for growth in girth in older parts
of the plant (called secondary growth). Exist only in
perennials
How is indeterminate growth possible?????
Fig. 35.11
Fig. 35.12
2. Primary Growth of Roots
a. Description
i. Occurs at root tip (Root Apical Meristem)
ii. Root cap – layer of cells that protect the RAM as it pushes
through the soil
b. Zones
i. Zone of cell division – contains the RAM
ii. Zone of cell elongation – cells elongate, thereby pushing
the root tip through the soil
iii. Zone of maturation – cells differentiate and become
functionally mature (i.e. become part of one of the 3 tissue
systems)
Fig. 35.12
3. Shoot Growth
a. Leaves arise on sides of the Shoot Apical
Meristem (SAM)
b. Axillary buds arise from areas of meristematic
cells left behind at the bases of the leaf primordia.
c. Bud = cluster of leaf primordia created by meristem.
No internodes
d. Lateral branches arise from axillary buds
Fig. 35.15
F. Secondary Growth in Shoots
1. Description
a. Shoots of perennials only, not in leaves
b. Occurs in oldest parts of plant
2. Layers (two lateral meristems):
a. Vascular cambium – produces secondary xylem (= wood)
& phloem
i. Vascular cambium – layer of cells between primary xylem &
primary phloem. Puts on successive layers of secondary phloem
to outside & secondary xylem to inside =====> stem widens
ii. Dormant in winter, leaves scar when activity resumes ==>
annual ring
iii. Wood = accumulation of secondary xylem. Dead at maturity,
contains lignin
Fig. 35.20
b. Cork cambium – replaces the epidermis with
cork: tough, thick cover for stems, roots.
i. Located in the cortex
ii. Produces cork cells to replace epidermis
iii. Periderm = cork + cork cambium
iv. Lenticels = cracks in the periderm that allow gas
exchange for living cells in the interior
v. “bark” = all cells external to the vascular
cambium (secondary phloem & periderm)
vi. Cork continually sloughs off
vii. Growing secondary phloem becomes new cork
cambium (thus no build up of secondary phloem)
Fig. 35.19a
Fig. 35.19b
Fig. 35.22
G. Secondary growth in roots
1. Description
a. Vascular cambium forms within stele, produces secondary
xylem & phloem
b. Cortex & epidermis shed
c. Cork cambium arises from pericycle & produces the
periderm
d. Periderm – impermeable to water! Thus only young roots
absorb from soil, old roots function = anchor & transport
VI. Tissue Arrangement in Plant Parts
A. Roots
1. Epidermis – water, minerals absorbed through
root hairs
2. Stele – central cylinder of vascular tissue
(monocots have slightly different arrangement).
3. Pericycle = outermost layer of stele. Lateral
roots arise from this in order to remain continuous
with vascular system.
4. Ground tissue – mostly parenchyma cells of the
cortex – area between the stele & epidermis; stores food
& takes up minerals.
5. Endodermis – single cell layer between cortex &
stele. Selective barrier for uptake of soil solution
contents into vascular system.
Eudicot/Gymnosperm root cross section
Epidermis
Endodermis
Cortex
Stele
xylem
phloem
Fig. 35.14a
pith
endodermis
epidermis
xylem
phloem
cortex
pericycle
Fig. 35.14b Cross section of a monocot root
B. Stems
1. Eudicots:
a. Epidermis
b. Vascular bundles arranged in ring
i. Ground tissue = pith & cortex
ii. xylem faces pith, phloem faces cortex
2. Monocots: vascular bundles scattered throughout
ground tissue
Eudicot/Gymnosperm stem cross section
Pith
Phloem
Cortex
Xylem
Epidermis
Fig. 35.16
Sclerenchyma cells
Vascular bundle
Monocot stem cross-section
Ground Tissue
Vascular
bundle
Epidermis
Fig. 35.16
C. Leaves
Ex. of how structure reflects function – designed for
maximum photosynthetic efficiency
1. Layers:
a. Upper & lower epidermis – tightly interlocked cells,
secrete waxy cuticle. Contains stomata flanked by guard cells
b. Vascular tissue – leaf veins, branch throughout
mesophyll
c. Mesophyll – ground tissue between upper & lower
epidermis
i. 2 kinds of parenchyma cells:
Palisade – columnar, at top of leaf
Spongy – smaller, below palisade, gas-filled spaces
between cells
Fig. 35.18