Development of Endosperm and Embryo 

The development of endosperm and embryo is a crucial post-fertilisation event in flowering plants. Together, these processes ensure the formation of a viable seed capable of germination and continuation of the species. The endosperm provides nutrients for the growing embryo as it develops into a new plant. Both processes occur inside the ovule after fertilisation.

1.0Endosperm Development

The endosperm is a nutritive tissue formed from the primary endosperm nucleus (PEN), which results from the fusion of a male gamete with two polar nuclei during triple fusion. It plays a vital role in nourishing the developing embryo until seed germination.

Process of Endosperm Development

1. Primary Endosperm Nucleus Formation:

• After double fertilisation, one male gamete fuses with two polar nuclei to form the triploid primary endosperm nucleus (3n).
• This nucleus divides mitotically to produce the endosperm.

2. Types of Endosperm Development:
   Based on the pattern of nuclear division and wall formation, endosperm can be of three main types:

• Nuclear Endosperm:
• Free nuclear divisions occur without cell wall formation.
• Cytoplasm becomes multinucleate.
• Example: Coconut water represents free-nuclear endosperm.

• Cellular Endosperm:
• Each nuclear division is immediately followed by wall formation, leading to a multicellular structure.
• Example: Petunia and Datura.

• Helobial Endosperm:
• An intermediate type between nuclear and cellular.
• The first division creates two chambers: a large micropylar chamber and a small chalazal chamber.
• Example: Asphodelus.

3. Functions of Endosperm:

• Provides nutrition (starch, proteins, fats) to the embryo.
• Supports early seedling growth.
• Sometimes persists in mature seeds as endospermic (albuminous) seeds—e.g., maize, castor.
• In other cases, it is entirely absorbed by the developing embryo (non-endospermic or exalbuminous seeds)—e.g., pea, groundnut.

2.0Embryo Development (Embryogenesis)

Embryo development begins from the zygote formed after the fusion of male and female gametes. The zygote undergoes a series of mitotic divisions and differentiations to create a mature embryo.

Process of Embryo Development

1. Zygote Formation and First Division:

• The zygote divides asymmetrically into a small apical cell (toward the chalazal end) and a large basal cell(toward the micropylar end).
• The basal cell forms the suspensor, which anchors the embryo to the endosperm.

2. Formation of Suspensor and Embryo Proper:

• The suspensor pushes the developing embryo into the nutritive endosperm region.
• The embryo proper develops from the apical cell.

3. Stages of Embryo Development in Dicots:

• Zygote Stage: Single-celled zygote.
• Two-celled Stage: Formation of apical and basal cells.
• Globular Stage: Spherical embryo with visible protoderm.
• Heart-shaped Stage: Formation of two cotyledons.
• Torpedo Stage: Embryo elongates with distinct radicle and plumule.
• Mature Embryo Stage: Fully developed with cotyledons, embryonal axis, radicle, and plumule.

4. Embryo Structure in Dicots:

• Embryonal Axis: Central line containing radicle (root end) and plumule (shoot end).
• Cotyledons: Two seed leaves store food.
• Radicle: Develops into the root.
• Plumule: Develops into the shoot.

5. Embryo Structure in Monocots:

• Contains a single cotyledon, the scutellum.
• Coleoptile covers the plumule, and coleorhiza covers the radicle.
• Example: Maize embryo.

3.0Relationship Between Endosperm and Embryo

• The developing embryo depends on the endosperm for nutrition.
• In some species, the endosperm persists in the mature seed (e.g., cereals), whereas in others it is completely absorbed (e.g., legumes).
• The synchronised development of both ensures successful seed formation.

4.0Significance of Endosperm and Embryo Development

• Endosperm: Supplies nutrients during embryo development and germination.
• Embryo: Forms the new generation of the plant.
• Together, they ensure the continuation of the species through viable seed production.