Transcript Plant Reproduction and Development

Chapter 38:
Plant Reproduction and
Development
Flowers



Sexual organs of
Angiosperms.
Develop from
compressed shoots with
four whorls of modified
leaves.
Flower Whorls
1. Sepals
2. Petals
3. Stamens
4. Carpels
Sepals



Whorl of sterile leaf-like structures.
May be brightly colored.
Function


Protect other flower parts.
Attract pollinators.
Petals



Whorl of sterile flower
parts.
Often brightly colored.
Function

Attract pollinators.
Stamens


Male reproductive
flower structure.
Function

Produce pollen (sperm).
Stamen Structure


Anther - pollen
producing sac.
Filament - stalk.
Carpel



Female reproductive flower structure.
Also called pistil.
Function


Carpel Structure




Produce embryo sac (eggs).
Stigma – receives the pollen.
Style – stalk.
Ovary – contains the ovules.
Ovule

A rudimentary seed before fertilization.
Flowers


Are highly variable in form, shape, and
color.
Not all flowers contain the same
combination of whorls.
Flower Variations




Complete Flowers - have all four whorls.
Incomplete Flowers – less than all four
whorls.
Perfect Flowers - have stamens and carpels.
Imperfect Flowers - have stamens or carpels.
Monoecious Plants


Staminate and pistillate
flowers are on the same
plant.
Ex: corn


Tassel – staminate flowers
Ears – carpellate flowers
Dioecious Plants



Have staminate or pistillate flowers, but not
both.
Ex: Holly, Ginkgo
Comment - "Seedless" plants may be a
staminate plant.

Ex: male Ginkgo
Pollen Development


Pollen is the male gametophyte.
Starts with a 2N cell called a microsporocyte.
Microsporocyte


Undergoes meiosis and produces 4
Microspores (1N).
Each Microspore undergoes mitosis and
produces a pollen grain, which is the male
gametophyte.
Mature Pollen Grain



Special cell wall.
Tube Nucleus (cell).
Generative Nucleus (cell)
which will divide and
produce two sperm nuclei.
Embryo Sac Development



The Embryo Sac is the female gametophyte.
Starts with a megasporocyte (2N).
Megasporocyte


Undergoes meiosis and produces 4 Megaspores
(1N).
Three of the megaspores abort, leaving only one
to develop into the embryo sac.
Megaspore



Undergoes three rounds of mitosis to produce a
“sac” with 8 nuclei.
The nuclei may wall off or may remain as part of a
large cell.
Embryo Sac




3 Antipodal cells.
2 Polar nuclei (1 cell)
2 Synergid cells
1 Egg cell
Pollination: The transfer of pollen from a
stamen to the stigma.

Pollen Vectors




Bees
Flies
Butterflies Moths
Birds
Beetles
Bats
Wind
Comment


The flower is usually highly
adapted to the pollen vector.
Ex:




Colors
Rewards
Scents
Shape
Fertilization

The union of egg and
sperm to produce a
zygote (2N).
Angiosperms
Have double fertilization.
1. Egg + sperm  zygote
2. Polar nuclei + sperm 
Endosperm
 Endosperm


Is Triploid (3N) tissue that will be used as a
nutrition source for the embryo.
After Fertilization



Zygote  Embryo
Ovule  Seed
Ovary  Fruit
Embryo Development



Root/shoot polarity set with 1st cell division.
Mature embryo has all three primary tissues,
apical meristems etc.
Endosperm


Monocots - large tissue.
Dicots - transfer the energy over to the embryo's
two cotyledons.
Seed Coat



Formed from the integuments of the ovule.
Hard layer to protect the seed.
Fruit



A mature ovary.
Sometimes includes other plant parts.
Ex: apple
Fruit Functions

Protect the seeds.
Aid in seed dispersal.

Fruit Types



Fleshy: soft ovary
walls.
Dry: hard ovary walls.
Fruit Types

Simple Fruit: from a single ovary.


Aggregate Fruit: from a flower with multiple
carpels.


Ex: Peach, Cherry
Ex: Raspberry
Multiple Fruit: develops from several flowers
into one structure.

Ex: Pineapple
Seeds



Contain a miniature plant.
Main dispersal mechanism for plants.
Embryo is often “dormant” when the seed is
mature.
Seed Dormancy




When a seed is not actively growing.
Used to increase the chances that the plant
will develop when conditions are favorable.
Usually controlled by plant hormones.
May require changes in temperature,
moisture, etc. before growth will continue.
Imbibition




The absorption of water by a seed.
First step in seedling growth.
Causes “swelling” which ruptures the seed
coat.
Starts metabolism to resume growth.
Germination



The continuation of growth of the plant within
a seed.
Root usually emerges first.
Shoot tip must break through the soil surface.
Role of Light


Light is the usual clue that the shoot has broken
above ground.
Light causes many growth changes in the shoot


Ex. Leaves to expand
Stem elongation rate decreases
Asexual Reproduction


Offspring produced by mitosis.
Also called “cloning”.
Normal Method


Fragmentation of the plant
body so that new plants are
formed.
Ex: Cuttings
Grafting
Offshoots
High-Tech Methods



Tissue Culture.
Clumps of cells grow
into embryoids which
can be used to
regenerate whole
plants.
Often used in genetic
engineering of plants.


Protoplast Fusion.
A "naked" plant cell
(no cell wall).
Used to create new
hybrids
Plants

Frequently use both sexual and asexual
reproduction depending on the environment.


Asexual - stable
Sexual - unstable
Plant Development



Growth: increase in size
Development: changes in body form and
structure.
Plant Problems

Determining the direction of cell growth because
of the cell wall.
Control Mechanism


Cytoskeleton: determines the direction of cell
expansion.
Cellulose Microfibrils: are arranged in parallel
strips as guided by microtubules in the cell
membrane.
Cell Expansion


Increase in cell size is usually caused by
turgor pressure.
Direction of cell increase is at right angles to
the cellulose mircofibrils.
Cell Differentiation


Depends on the control of gene expression.
(review previous chapters on this topic)
Pattern Formation


The development of specific
structures in specific
locations.
Important in plants since
cells don’t usually migrate.
Juvenile
Mature
Positional Information

Gradients of chemicals that provide clues of
position of cells to each other.

Ex: why some cells develop into shoots and
others into roots.
Organ-Identity Genes


Genes for normal organ development.
Used in positional information to determine
which organ the cells should develop into.
Example





The combination of three genes that give
rise to the flower parts.
A  sepals
A + B  petals
B + C  stamens
C  carpels
Mutations


Cause other floral parts
to form in the flowers.
(review Chapter 21).
Summary



Know the general structures of flowers.
Know the general life cycle of flowers.
Review the items on plant development.