Development is a process in which an individual goes through certain changes in its form and function during its life in response to certain levels of control. In plants, this course starts with embryogenesis.
Embryogenesis is the formation of a multicellular embryo from a single-celled zygote.Involves processes such as pattern formation and morphogenesis that are critical in the growth of the plant.
The next “milestone” in the development of polarity
The next “milestone” in the development of polarityAsymmetry is complemented by the subtle variations in the distribution of organelles and in the concentration of macromolecules
Upper tier of cells – stem tip and cotyledonsLower tier of cells – derivatives to part of the cotyledon, hypocotyl and most of the RAMHypophysis – remainder of the RAM (qc) and the columellaThe suspensor has sired at least four or five cells (Mansfiel and Briarty, 1991; Jurgens and Mayer, 1994)
Basal cell remains active after the collapse of the suspensor (Schulz & Jensen, 1969)
Core of 8-cells and a periphery made up of 8-cells.First evidence of histodifferentiation.The protoderm is cut off and becomes mre similar to the epidermis by the formation of a cuticle.The tangential divisions initiate the formation of a radial patterning seen as concentric layers at the basal part of the embryo.
The difference of cells in the apex region.The upper cell of the hypophysis is lens shaped and just abuts the lower end of the globular embryo.The lower cells contacts laterally with the embryo epidermis and, at its basal end, with the uppermost suspensor cell.
Change from radial to bilateral symmetry by entering a transient triangular stage or early heart-shaped stage.
Accompanied by periclinal divisions of the adjacent cells for additional derivative for the shoot apex
To analyze and distinguish the different stages of development in an angiosperm embryo. To observe the stages of embryo development in flowering plants.
weedecology.css.cornell .edu microscope-manufacturers.comCapsella bursa fruit l.s.
Zygote is highly polarized (Raghavan, 1997) ◦ Due to its orientation ◦ Due to its ultrastructural profile
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 embryoPlanes 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
Terminal cell undergoes longitudinal division ◦ Crucifer (or Onagrad) type ◦ Asterad type Terminal cell undergoes transverse division ◦ Solanad type ◦ Caryophyllad type ◦ Chenopodiad type
apical cell suspensor basal cellCapsella – following 1st division of zygote: 2-celled Capsella terminal cell divided longitudinally to produce 2-proembryo: terminal cell and basal cell celled embryo properTaken from: Botanical Society of America (BSA) Taken from BSA<http://secure.botany.org/plantimages/ImageData.asp?IDN <http://secure.botany.org/plantimages/ImageData.asp?IDN=20-001> =20-003>
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).
quadrant suspensor basal cell 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>
octant suspensor basal cellCapsella octant stage (4 cells in plane of section, 4 additional cells behind) Taken from: BSA<http://secure.botany.org/plantimages/ImageDat a.asp?IDN=20-005>
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
suspensor suspensorSuspensor of a heart stage Capsella embryo Suspensor of a heart stage Capsella embryo
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.
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.
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.
Division and differentiation at the basal tier of the embryo give rise to the hypocotyl.
initiating cotyledons protoderm SAM hypocotyl hypophysis suspensor basal cell Capsella – early cotyledons (heart-shaped or slightly beyond)Capsella heart shaped embryo Taken from : BSA <http://secure.botany.org/plantimages/ImageData.asp?IDN =20-009>
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
protoderm procambium SAM hypocotyl RAMCapsella – torpedo stage of embryo – cotyledons,procambium presentTaken from: BSA<http://secure.botany.org/plantimages/ImageData.asp?IDN=20-011>
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.
SAMprocambium protoderm cotyledons hypocotyl RAM seed coat root cap
protoderm SAM procambium hypocotyl ground meristem seed coat cotyledonsroot cap RAM
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.
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.