The development of a dicot embryo in flowering plants is a precise and well-orchestrated process that begins after fertilization. While the provided reference only describes the early stages of cell division, we can understand the initial phases. The development starts with the zygote, which undergoes several divisions to eventually form the embryo.
Early Stages of Dicot Embryo Development
The provided reference focuses on the initial cell divisions of the terminal cell, derived from the zygote. Here’s a breakdown:
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Initial Division: The terminal cell divides longitudinally, twice.
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Quadrant Stage: This division results in four cells, collectively referred to as the quadrant stage.
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Octant Stage: The four cells of the quadrant stage then divide transversely. This produces eight cells, arranged in two layers of four cells each, marking the octant stage.
A More Comprehensive View (Based on General Knowledge)
While the reference only provides a snippet of the early stages, a complete picture of dicot embryo development includes:
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Zygote Formation: Fertilization leads to the formation of a diploid zygote.
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First Division: The zygote divides transversely, forming two unequal cells: the apical (terminal) cell and the basal cell.
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Basal Cell Development: The basal cell divides transversely to form a suspensor, which anchors the embryo to the endosperm and provides nutrients. The suspensor's terminal cell, called the haustorium, is responsible for nutrient absorption.
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Apical Cell Development (as described in the provided text):
- Longitudinal divisions (twice) leading to the quadrant stage.
- Transverse divisions leading to the octant stage.
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Histogen Differentiation: The octant stage cells differentiate into three primary meristems:
- Protoderm: Gives rise to the epidermis.
- Ground meristem: Develops into the ground tissue (cortex and pith).
- Procambium: Forms the vascular tissue (xylem and phloem).
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Heart-Shaped Stage: Differential growth in the cotyledon region results in the formation of two cotyledons, giving the embryo a heart-shaped appearance.
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Torpedo Stage: Continued elongation and differentiation lead to the torpedo stage.
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Mature Embryo: The mature embryo consists of:
- Cotyledons: Two seed leaves that store food.
- Plumule: The embryonic shoot, including the shoot apex and young leaves.
- Radicle: The embryonic root.
- Embryonic axis (hypocotyl): The region between the radicle and the cotyledons.
Summary Table
| Stage | Description |
|---|---|
| Zygote | The initial single cell formed after fertilization. |
| 2-celled stage | Apical and Basal cell formed by the transverse division of the Zygote |
| Quadrant | Four cells formed by longitudinal divisions of the apical cell. |
| Octant | Eight cells in two layers formed by transverse division of quadrant cells. |
| Heart-shaped | Development of two cotyledons, giving the embryo a heart-like shape. |
| Torpedo | Elongation and differentiation of the embryo into a torpedo-like structure. |
| Mature Embryo | Fully developed embryo with cotyledons, plumule, and radicle. |
