Post embryonic development

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Embryo Development
Begins once the egg cell is fertilized
-The growing pollen tube enters angiosperm
embryo sac and releases two sperm cells
-One sperm fertilizes central cell and
initiates endosperm development
-Other sperm fertilizes the egg to
produce a zygote
-Cell division soon follows, creating
the embryo

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Embryo Development

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Embryo Development (Cont.)

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Embryo Development

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Development of Body Plan
-Apical meristems establish the root-shoot
axis in the globular stage
The 3 basic tissue systems arise at this stage
-Dermal, ground and vascular

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Formation of Tissue Systems
Primary meristems differentiate while the
plant embryo is still at the globular stage
-No cell movements are involved
The outer protoderm develops into dermal
tissue that protects the plant
The ground meristem develops into ground
tissue that stores food and water
The inner procambium develops into vascular
tissue that transports water & nutrients

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The heart-shaped globular stage gives rise to
bulges called cotyledons
-2 in dicots and 1 in monocots
These bulges are produced by embryonic
cells, and not by the shoot apical meristem
-This process is called morphogenesis

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During embryogenesis, angiosperms undergo
three other critical events:
-Storage of food in the cotyledons or
endosperm
-Differentiation of ovule tissue to form a
seed coat
-Development of carpel wall into a fruit

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Seeds
In many angiosperms, development of the
embryo is arrested soon after meristems
and cotyledons differentiate
-The integuments and ovule wall develop
into a relatively impermeable seed coat
-Encloses the seed with its dormant
embryo and stored food

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Seeds
Seeds are an important adaptation because:
1. They maintain dormancy under
unfavorable conditions
2. They protect the young plant when it is
most vulnerable
3. They provide food for the embryo until it
can produce its own food
4. They facilitate dispersal of the embryo

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Seeds
Once a seed coat forms, most of the embryo’s
metabolic activities cease
Germination cannot take place until the seed
absorbs enough water and oxygen for metabolism.
-Seeds of some plants have been known to
remain viable for thousands of years
-Germination requires an additional environmental
signal such as specific wavelength of light, or
appropriate temperature

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Seeds
Germination may also require:
- That the seeds pass through the intestines of birds
or mammals
- The seeds lie within tough cones that do not open
until exposed to fire

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Fruits
Fruits are most
simply defined
as mature
ovaries
(carpels)
-During seed
formation, the
flower ovary
begins to
develop into
fruit

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Dispersal and Pollination
Occurs through a wide array of methods
-Ingestion and transportation by birds or
other vertebrates
-Hitching a ride with hooked spines on
birds and mammals
-Burial in caches by herbivores
-Blowing in the wind
-Floating and drifting on water

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Germination
Germination is defined as the emergence of
the radicle (first root) from the seed coat
- It begins with imbibition, the absorption of
water
- Various enzymes are activated which in turn
activate biochemical process like respiration
and growth.
- Gibberellic acid, hormones, are activated

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Germination
Parts of the embryo
- Epicotyl: top of embryo which becomes
shoot tip
- Plumule: first true leaves attached to
epicotyl
- Hypocotyl: below epicotyl, it becomes the
shoot
- Radicle: below hypocotyl, it becomes root
- Coleoptile: surrounds and protects epicotyl

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