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