Exercise 4 Plant Embryo Development
Espino, Fermin, Paculan, Pajinag, Quesada
Plant Development
umanitoba.ca
Embryogenesis
bio.miami.edu
To analyze and distinguish the different stages of development in an angiosperm embryo.
To observe the stages of embryo development in flowering plants.
Objectives
Methodology
Capsella bursa fruit l.s.
weedecology.css.cornell.edu
microscope-manufacturers.com
Results and Discussion
Zygote is highly polarized (Raghavan, 1997)◦ Due to its orientation◦ Due to its ultrastructural profile
The Zygote
First division event in the zygote occuring transversely to its long axis (Raghavan, 2006) forming the:◦ Basal cell – large, vacuolated, directed towards the
micropylar end; froms the suspensor◦ Terminal cell – small, densely cytoplasmic, directed
towards the chalazal end; becomes the embryo Planes of division of the terminalcell and subsequent contributionsof the basal cell to the formationof the embryo have led to a frame-work of classification of embryos
Asymmetric Cell Division
Terminal cell undergoes longitudinal division◦ Crucifer (or Onagrad) type◦ Asterad type
Terminal cell undergoes transverse division◦ Solanad type◦ Caryophyllad type◦ Chenopodiad type
Classification of Embryo Types
Capsella – following 1st division of zygote: 2-celled proembryo: terminal cell and basal cellTaken from: Botanical Society of America (BSA) <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-001>
Capsella terminal cell divided longitudinally to produce 2-celled embryo properTaken from BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-003>
apical cell
basal cell
suspensor
The terminal cell divides longitudinally forming two cells which again divide longitudinally yielding a quadrant (4-celled).
The quadrant divides transversely leading to the octant (8-celled).
The basal cell divides first, prior to theterminal cell, once or occasionally twicetransversely. The cell closest to the terminal cell, thesuspensor cell divides transversely forminga filament of seven to nine cells (Raghavan, 2006).
Globular Stage
Capsella quadrant stage of embryo proper – 3 nuclei visible (out of 4)
Taken from: BSA < http://secure.botany.org/plantimages/ImageData.asp?IDN=20-004
>
quadrant
suspensor
basal cell
Capsella octant stage (4 cells in plane of section, 4 additional cells behind)
Taken from: BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-005
>
octant
suspensor
basal cell
The suspensor functions in the absorption and short-distance translocation and exchange of metabolites necessary for the growth of the embryo (Raghavan, 1997).
May have haustoria. Three Stages of the Suspensor
◦ (a) Octant Embryo – 6-celled◦ (b) Globular Stage Embryo – maximum nuber of
cells attainede◦ (c) Heart Stage Embryo – maximum length attained
and it grows out its genetically permissible life span
The Suspensor
Suspensor of a heart stage Capsella embryo Suspensor of a heart stage Capsella embryo
suspensorsuspensor
The octant embryo undergoes tangential division forming a 16-celled embryo.
The 8 peripheral cells of the 16-celled proembryo become the protoderm and continue to divide anticlinally.
The ground meristem and procambium are derived from the inner cells (the lower and upper tier respectively).
The cortex is formed from the peripheral layer of cells of the inner core of 8.
Procambium initiation starts at this stage as well and occurs in the cells of the cortex or pith of the globular embryo.
Globular Stage
The suspensor cell nearest the embryo divides transversely providing the hypophysis.
The globular stage ends with an additional three rounds of division mostly by the inner core of cells.
Globular Stage
Capsella – globular stage
Capsella – globular stageTaken from : BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-007>
proembryo
protoderm
hypophysissuspensor
suspensor
basal cell
Lateral expansion of the distal poles of the proembryo provide a bilateral symmetry and forecast the imminent formation of the cotyledons.
Vertical division occurs twice to the hypophyseal cells producing two layers of four cells each (Raghavan, 2006).
The shoot apical meristem is organized in a depression between the growing cotyledons.
Heart Stage
Division and differentiation at the basal tier of the embryo give rise to the hypocotyl.
Heart Stage
Capsella heart shaped embryo
Capsella – early cotyledons (heart-shaped or slightly beyond)Taken from : BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-009>
protoderm
suspensor
hypocotyl
initiating cotyledons
hypophysis
basal cell
SAM
Elongation of the hypocotyl and the cotyledons give the embryo a torpedo shape.
Shoot apical meristem is fully established and appears as a mound or dome between the cotyledons.
Root apical meristem is established with the root apex having a delimitation signifying the progenitor of the embryonic radicle.
Primary meristems already visible
Torpedo Stage
Capsella – torpedo stage of embryo – cotyledons, procambium presentTaken from: BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-011>
protoderm
procambium
hypocotyl
SAM
RAM
Mature Embryo Cotyledons curve
towards the hypocotyl due to space restrictions within the ovule.
The tips of the cotyledon eventually reach the tip of the root pole.
protodermprocambium
hypocotyl
SAM
RAM
root cap
cotyledons
seed coat
protoderm
procambium
hypocotyl
SAM
RAM
cotyledons
root cap
ground meristem
seed coat
Plants, with special respect to angiosperms, undergo different phases in its life cycle. One of which is embryogenesis, the formation of a multicellular embryo to a single-celled zygote. This process involves various stages in its development such as the globular, heart, torpedo, and maturation stages which are very critical to the growth of the plant.
Conclusion
Raghavan, V. (1997). Molecular Embryology of Flowering Plants. Cambridge University Press. 40 West 20th St., New York, USA.
Raghavan, V. (2006). Double Fertilization: Embryo and Endosperm Development in Flowering Plants. Springer-Verlag Berlin Heidelberg. Leipzig, Germany.
References