Exercise 4

Plant Embryo Development

1. Exercise 4 Plant Embryo Development Espino , Fermin , Paculan , Pajinag , Quesada

2. Plant Development umanitoba.ca

3. Embryogenesis bio.miami.edu

4. To analyze and distinguish the different stages of development in an angiosperm embryo. To observe the stages of embryo development in flowering plants. Objectives

5. Methodology Capsella bursa fruit l.s . weedecology.css.cornell.edu microscope-manufacturers.com

6. Results and Discussion

7. Zygote is highly polarized ( Raghavan , 1997) Due to its orientation Due to its ultrastructural profile The Zygote

8. 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 terminal cell and subsequent contributions of the basal cell to the formation of the embryo have led to a frame- work of classification of embryos Asymmetric Cell Division

9. 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

10. Capsella  – following 1st division of zygote: 2-celled proembryo : terminal cell and basal cell Taken 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 proper Taken from BSA < http://secure.botany.org/plantimages/ImageData.asp?IDN=20-003 > apical cell basal cell suspensor

11. 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 the terminal cell, once or occasionally twice transversely. The cell closest to the terminal cell, the suspensor cell divides transversely forming a filament of seven to nine cells ( Raghavan , 2006). Globular Stage

12. 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

13. 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

14. 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

15. Suspensor of a heart stage Capsella embryo Suspensor of a heart stage Capsella embryo suspensor suspensor

16. 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

17. 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

18. Capsella  – globular stage Capsella  – globular stage Taken from : BSA < http://secure.botany.org/plantimages/ImageData.asp?IDN=20-007 > proembryo protoderm hypophysis suspensor suspensor basal cell

19. 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

20. Division and differentiation at the basal tier of the embryo give rise to the hypocotyl . Heart Stage

21. 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

22. 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

23. Capsella  – torpedo stage of embryo – cotyledons, procambium present Taken from: BSA < http://secure.botany.org/plantimages/ImageData.asp?IDN=20-011 > protoderm procambium hypocotyl SAM RAM

24. 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.

25. protoderm procambium hypocotyl SAM RAM root cap cotyledons seed coat

26. protoderm procambium hypocotyl SAM RAM cotyledons root cap ground meristem seed coat

27. 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

28. Raghavan , V. (1997). Molecular Embryology of Flowering Plants. Cambridge University Press. 40 West 20 th St., New York, USA. Raghavan , V. (2006). Double Fertilization: Embryo and Endosperm Development in Flowering Plants. Springer- Verlag Berlin Heidelberg. Leipzig, Germany. References