In this video we are going to go over the
steps involved in embryogenesis in plants.
Embryogenesis in plants is the process where
an embryo is formed and develops, and where
axial and radial patterning observed in mature
plants are established.
The first step of embryogenesis occurs with
the first cell division of the zygote.
This cell division is asymmetrical creating
a smaller apical cell and a larger basal cell.
It is at this stage that the apical-basal
axial developmental pattern is established.
The apical cell contains more cytoplasm than
the basal and goes on to divide and create
the embryo.
The basal cell has a large vacuole and goes
on to divide horizontally along its axis to
form a 6-9 cell filament called the suspensor
which connects the developing embryo to the
endosperm.
The one cell closest to the basal cell is
the only cell deriving from the basal cell
to contribute to the embryo, and is called
the hypophysis and goes on to develop into
the columella of the root.
After the zygote has split to create the apical
and basal cell, the developing embryo goes
through four main stages.
The first of these stages is the globular
stage which occurs after the apical cell undergoes
several divisions to create an eight celled
or octant emrbyo, and then continues to divide
to form a more globular and then more triangular
shaped embryo.
It is in this stage that radial patterning
is first established, and continues to develop
through the rest of the stages creating the
ring layers of structures found in the stems
and roots.
The outermost cells are one layer thick and
called the protoderm and go on to form the
epidermis.
The next layer of cells in from the protoderm
will become the ground tissue meristem and
eventually form the endodermis and the cortex.
The central layer of cells are elongated and
called the procambium and go on to become
the vascular tissues and the pericycle in
the root.
The next stage is the heart stage and occurs
through rapid cell division on each side of
the embryo.
The centre of these outgrowths will become
the shoot apical meristem.
These outgrowths on each side will eventually
become the cotyledons.
It is at this stage that bilateral symmetry
in the embryo is established.
The apical-basal axial patterning is even
more clear at this stage, with three clear
defined regions.
The apical region gives rise to the cotyledons
and shoot apical meristem.
The middle or central region gives rise to
the hypocotyl, root and the majority of the
root meristem.
The Hypophysis give rise to the root meristem.
The next stage is the torpedo stage and occurs
from cell elongation throughout the embryo
as well as continued growth in the cotyledons
around what will become the shoot apical meristem.
The final stage is the maturation stage.
During this stage, at the end of embryogenesis,
the embryo folds over within the seed.
The embryo and the seed that it is in both
start to lose water and head into dormancy.
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