Corn Growth and
Development
Randy Wayne
Shoals Marine Laboratory
Summer, 2009
Caryopsis: Embryo within is Bipolar
The plant will be
growing into two
physical phases:
– The plumule will
be growing into a
bright, dry phase.
– The radical will
be growing into a
dark, moist,
nutrient rich
phase.
Bipolar Corn Plant
Plumule Inside Caryopsis
Radical Inside Caryopsis
Mesocotyl Inside Caryopsis
Germination
Germination
Stem Apical Meristem
• The stem and root apical
meristems give rise to all
the primary tissues in the
stem and root,
respectively.
• The stem apical meristem
gives rise to the leaves.
• The apical meristems
carry embryonic stem
cells with them.
• A stem cell is a cell that
divides to form two
daughter cells, one of
which differentiates and
one of which remains a
stem cell.
Intercalary Meristems
Stem:
The Organ that Supports the Leaves
• Primary growth results in an
increase in height not girth.
• Corn and other monocots
stems have scattered
vascular bundles composed
of xylem and phloem tissue.
Each bundle is surrounded by
a ring of cells called a bundle
sheath.
• Corn and other monocots do
not exhibit secondary growth
of concentric annual rings
produced by a vascular
cambium.
Vascular Bundle: One Structure—
Many Functions
Phloem and Xylem in Vascular
Bundle in Stem
The Location of the Vascular Bundles
Provides Mechanical Strength
Corn
Sunflower
Surface View of Corn Leaf Showing
Chloroplast-Containing Mesophyll Cells
Corn Leaf (xs)
Corn Leaves:
The Photosynthetic Organs
• Flat. The high surface-to-volume ratio
maximizes the amount of light intercepted for
photosynthesis (also maximizes water loss).
• Covered with cuticle to prevent water loss.
• Has stomates that allow in the influx of CO2
while controlling water loss.
Stomate on Epidermis of Corn Leaf
The Opening of the Stoma is
Regulated by Guard Cells
• In the morning, light
activates pumps in
the plasma
membrane of guard
cells so that KCl
accumulates.
• The increased
osmotic pressure in
the guard cells
causes water to move
into the guard cells
and they swell.
• This causes the
stoma to open.
The Closing of the Stoma is
Regulated by Guard Cells
• If the plant loses too
much water, the roots
produce a hormone
called abscisic acid,
which travels to the
leaves and causes ion
channels to open and
the KCl leaves the
guard cells.
• The decreased
osmotic pressure
causes water to move
water to move out of
the guard cells and the
they shrink.
• This causes the stoma
to close.
Water is Necessary for Photosynthesis:
Corn Leaf Showing a Cross Link
between Two Vascular Bundles
Ammophila Leaf with the Large Bulliform
Cells in the Epidermis that Allows the Leaf
to Roll up as a Way to Minimize Water Loss
Corn Leaf with the Large Bulliform Cells in
the Epidermis that Allows the Leaf to Roll up
as a Way to Minimize Water Loss
Rolled Up Corn Leaves
Corn Leaf Vascular Bundle with Kranz
Anatomy Important for C4
Photosynthesis
Corn Root (ls):
The Organ for Absorption and Anchoring
Root cap Meristem
Developing vylem
Corn Root (xs)
The vascular bundles are not necessary for
support and perhaps are closer to the center to
protect them from predators.
Water Movement through the Plant:
Osmosis
• The solute concentration and
thus the osmotic pressure is
greater in the cells of the root
than in the soil.
• Water enters the root by
osmosis (diffusion).
• The root hairs increase the
surface to volume ratio of
the root to increase the rate
in which water and dissolved
minerals can be taken up.
• The water moves through the
root to the endodermis.
Water Movement through the Plant:
Root Pressure
• The walls between the
endodermal cells have a
Casparian strip, which is a
hydrophobic wax-like
substance called suberin that
prevents water movement
between the endodermal cells
and ensures that all water
moves across the plasma
membrane of the endodermal
cells.
• The endodermal cells allow
the whole root to act as an
osmometer.
Water Movement through the Plant:
Root Pressure
• The endodermal cells pump ions
into the vascular region of the root.
• The increased concentration of
ions in the xylem draws water into
the xylem by osmosis.
• Water moves out of the root and
into the shoot through the xylem as
a result of root pressure.
• Root pressure can be inferred by
looking at the elimination of water
by leaves at night, known as
guttation.
• In more mature roots, the inner wall
of the endodermal cells become
suberized, which prevents water
loss from the xylem.
Guttation Only Occurs When the Humidity is
High, Resulting in a Water Surplus
Water Movement through the Plant:
Transpiration
• The water pressure exerted
by the root is not great
enough to push water
against gravitational
pressure to the top of a
large corn plant or a tree.
• Shoots separated from the
roots still have the ability to
transport water against
gravity to the leaves,
indicating that there is
another mechanism
responsible for long distance
water movement in plants.
Water Movement through the Plant: Transpiration
(Cohesion Tension Theory)
Structure of Tracheary Elements
(Protoxylem and Metaxylem)
Structure of Tracheary Elements Allows
Axial and Lateral Water Movement but
Prevents Cell Collapse
Food Movement through the Plant:
Translocation (Pressure Flow Theory)
Leaves are sources of sugar.
– Sugar is produced by photosynthesis.
– It either diffuses into or is pumped into the sieve tube elements of the
phloem.
– The sugar into the phloem pulls in water from the xylem by osmosis,
creating a high hydrostatic pressure in the phloem near the sugar source.
Food Movement through the Plant:
Translocation (Pressure Flow Theory)
In corn, roots and caryopses are sinks for sugar
– Sugar diffuses or is pumped out of the phloem and is
converted in the sink cells to starch, a non osmotic form.
– The water leaves the phloem by osmosis, causing a drop in
the hydrostatic pressure in the phloem near the sugar sink.
Food Movement through the Plant:
Translocation (Pressure Flow Theory)
The sugar solution within the sieve tube moves
through the sieve tube in response to the
hydrostatic pressure gradient, thus carrying the
sugar from source to sink.
Food Movement through the Plant:
Translocation (Pressure Flow Theory)
Sieve tube elements, unlike the vessel elements of the xylem,
are enucleate living cells.
Sieve tube elements get their proteins from the companion cells.
Sieve tube elements are separated from each other by sieve
plates that become occluded in response to a pressure surge.
Flowering: Switch from Vegetative
Growth to Reproductive Growth
Male Flowers
Female Flowers
Each Silk is Attached to its Own Kernel
• Silk is the stigma that
receives the pollen
• Kernel is the carpel in
which the seed grows.
• The longer the silk, the
greater is the
competition (selection
pressure) between
pollen tubes.
Meiosis: Formation of Female
Gametophyte in Lily
Meiosis: Formation of Female
Gametophyte in Lily
Meiosis: Formation of Female
Gametophyte in Lily
Meiosis: Formation of Female
Gametophyte in Lily
Meiosis: Formation of Female
Gametophyte in Lily
4-Celled Stage of Female
Gametophyte
8-Celled Stage of Female
Gametophyte
The Egg
Meiosis: Formation of Pollen in Anthers
of Stamens
Pollination
Pollination: Pollen Caught by Stigma
Double Fertilization
Seed Formation
Germination
Corn Plants are Very Efficient in Converting
Radiant Energy into Chemical Energy because
they have a Special Kind of Photosynthesis
Involving two Types of Chloroplasts