Dicot Embryo Development

• Following fertilization, the fertilized egg, known as the zygote or oospore, develops into an embryo.
• The oospore undergoes a period of rest, ranging from a few hours to months, before starting development.
• The zygote divides after the first division of the primary endosperm nucleus (PEN).

Dicot Embryo Development

• The zygote divides transversely forming a two-celled proembryo with a basal cell toward the micropyle and a terminal cell.
• The basal cell undergoes transverse divisions, creating a long suspensor.
• The terminal cell divides longitudinally twice, forming a four-celled stage known as the quadrant stage.
• Cells of the quadrant stage divide transversely to create an octant stage, forming eight cells arranged in two tiers.
• The lower tier differentiates into the stem tip and cotyledons, while the upper tier develops into the hypocotyl.
• Periclinal division in the octant cells results in eight outer cells and eight inner cells.
• The eight outer cells form the dermatogen, which then divides anticlinally to form the epidermis.
• The eight inner cells become the periblem and plerome, which develop into the cortex and stele.
• The basal cell divides multiple times, forming a suspensor of six to ten cells.
• The suspensor's lowermost cell, closest to the developing embryo, is the hypophysis; repeated divisions form the root cap, epidermis, and cortex of the root.
• The embryo develops a curved, horseshoe shape due to the enlargement of the hypocotyl and cotyledons.
• In the mature embryo, the stem tip is terminal, with the two cotyledons positioned laterally.
• Key stages of dicot embryo development include the formation of endosperm, division of the zygote into a proembryo and the subsequent creation of globular, heart-shaped, and horseshoe embryo shapes.
• Dicot embryos have two cotyledons and an embryonal axis.
• The epicotyl, a portion of the embryonal axis above the cotyledons, terminates in the plumule.
• The hypocotyl, a portion of the embryonal axis below the cotyledons, develops into the radicle, or root tip.

Monocot Embryo Development

• In early cell divisions of the proembryo, monocot and dicot development show no key differences, it's the mature embryos that have different structures.
• The embryogeny of Sagittaria sagittifolia exemplifies monocot development.
• The zygote divides transversely, resulting in a terminal cell and a basal cell.
• The basal cell, larger and located toward the micropylar end, does not divide again transforming into a large vesicular cell.
• The terminal cell divides transversely into two cells; the lower cell divides vertically into a pair of juxtaposed cells, and the middle cell divides transversely into two cells.
• The two cells divide vertically, forming quadrants.
• The cell next to the quadrants and the cell next to the upper vesicular cell divide transversely.
• The quadrants divide transversely to produce octants, consisting of eight cells in two tiers.
• Dermatogen, then periblem and plerome are formed and differentiated sequentially.
• All tissues from the octants become a single terminal cotyledon.
• The lowermost cell (L) of the three-celled suspensor divides vertically, forming either the plumule or stem tip.
• The cells marked R form the radicle.
• The upper 3-6 cells contribute to the formation of the suspensor.