Endosperm

Endosperm is a nutritive tissue formed after fertilisation in flowering plants. It is usually triploid and provides food to the developing embryo.

A-D. Nuclear endosperm: A-C. successive stages of the development of nuclear endosperm; D. endosperm of Cassia articulata after cellularization; note a portion at chalazal end that continues to be free nuclear.

Process:

• PEN divides mitotically without cytokinesis(no cell wall formation) - producing many free nuclei in shared cytoplasm.
• A large central vacuole forms, pushing all nuclei to the periphery of the embryo sac.
• Cell walls form later, from the periphery inward, creating multicellular endosperm. In some cases wall formation remains incomplete.

Key Facts:

Most common type - found in approximately 161 angiospermic families (~56%). Examples: Wheat, Rice, Sunflower, Maize, Cotton, Coconut.

A-C. Successive stages of the development of cellular endosperm

Process:

• The very first division of PEN is immediately followed by cytokinesis(cell wall formation).
• The endosperm is cellular right from the beginning— there is no free-nuclear stage at any point.
• Each subsequent nuclear division is also accompanied by cell wall formation, producing irregular multicellular tissue.

Key Facts:

Found in approximately 72 dicotyledonous families (~25%). Examples: Petunia, Balsam (Impatiens), Adoxa, Datura.

A-C. Successive stages of the development of helobial endosperm

Process:

• The first division of the PEN is accompanied by a transverse wall, dividing the embryo sac unequally into two chambers.
• Micropylar chamber(larger): undergoes extensive free nuclear divisions → walls form later → cellular endosperm tissue.
• Chalazal chamber(smaller): undergoes fewer nuclear divisions → this region typically degenerates.

Key Facts

Characteristic of the order Helobiales - a group of monocotyledons (~19% families). Intermediate between nuclear and cellular types. Example: Asphodelus, Eremurus.

• The coconut water = liquid syncytium = free-nuclear endosperm (contains thousands of free nuclei).
• The white kernel = cellular endosperm (wall formation occurred at the periphery).
• Thus, coconut shows both nuclear and cellular endosperm in the same fruit.
• Coconut water also contains a growth-promoting substance called 'coconut milk factor', which is used as a nutrient medium in plant tissue culture experiments.

• Endosperm is a nutritive tissue formed from the triploid primary endosperm nucleus (PEN) after fertilisation.
• The PEN undergoes repeated mitotic divisions, and the embryo and endosperm develop simultaneously inside the ovule.
• Other cells of the embryo sac degenerate, while endosperm formation provides nourishment to the developing embryo.
• Nuclear type is the most common; divisions occur without wall formation initially, forming free nuclei, and walls develop later.
• Cellular type shows immediate wall formation after each division, making it cellular from the beginning.
• Helobial type is intermediate; first division forms two unequal cells (micropylar and chalazal), followed by nuclear divisions and later wall formation.