Untitled Quiz

Dicot and Monocot Embryo

• Dicot Embryo Development:

  • After fertilization, the fertilized egg becomes a zygote, which develops into an embryo.
  • The oospore rests for a period before development, ranging from hours to months.
  • The zygote (oospore) divides immediately after the primary endosperm nucleus (PEN) divides.
  • The zygote divides transversely to form a two-celled proembryo.
  • The cell towards the micropyle is the basal cell; the other is the terminal cell.
  • The basal cell forms a suspensor.
  • The terminal cell divides longitudinally twice, forming a four-celled structure, the quadrant stage.
  • The four cells further divide transversely, forming an octant stage (eight cells arranged in two tiers of four).
  • The lower tier gives rise to stem tip and cotyledons, while the upper tier forms the hypocotyl.
  • Periclinal division in the octant cells produces eight outer and eight inner cells.
  • The eight outer cells form the dermatogen, which develops into the epidermis.
  • The eight inner cells form the periblem and plerome, developing into the cortex and stele.
  • The basal cell forms a suspensor made of six to ten cells.
  • The lowest cell of the suspensor is the hypophysis, which produces root cap, epidermis, and cortex.
  • The cotyledons curve, and the embryo is horse-shoe shaped.
  • The stem tip is terminal, and cotyledons are lateral in the mature embryo.
  • Embryo development stages: globular, heart-shaped, and horse-shoe shaped, eventually maturing.

• Monocot Embryo Development:

  • There is no essential difference in the early cell divisions between monocots and dicots.
  • Mature embryos differ significantly between monocots and dicots.
  • Sagittaria sagittifolia embryogeny is used as an example.
  • The zygote divides transversely to form a terminal and basal cell.
  • The basal cell does not divide, but becomes large and vesicular.
  • The terminal cell divides transversely into two cells.
  • The lower cell divides vertically, forming juxtaposed cells, and the middle cell also divides transversely.
  • The two-cell stage subdivides into quadrants.
  • The cell next to the quadrants and the upper vesicular cell divide vertically and transversely, respectively.
  • The quadrants divide transversely to form octants (eight cells).
  • Periclinal division results in the formation of the dermatogen.
  • Periblem and plerome are also differentiated.
  • The octants form a single terminal cotyledon.
  • The lowermost cell of the three-celled suspensor divides vertically, producing the plumule or stem tip.
  • The cells R form the radicle.
  • Three to six upper cells form the suspensor.