Question

What is endosperm? Explain the types.

Answer 1

1. Endosperm: The primary endosperm nucleus (PEN) divides immediately after fertilization but before the zygote starts to divide, into an endosperm. The primary endosperm nucleus is the result of triple fusion (two polar nuclei and one sperm nucleus) and thus has a 3n number of chromosomes. It is a nutritive tissue and regulatory structure that nourishes the developing embryo. Depending upon the mode of development three types of endosperm are recognized in angiosperms. They are nuclear endosperm, cellular endosperm, and helobial endosperm.
   

2. Nuclear endosperm:

   1. The Primary Endosperm Nucleus undergoes several mitotic divisions without cell wall formation thus a free nuclear condition exists in the endosperm.

   2. Examples: Coccinia, Capsella, and Arachis.

3. Cellular endosperm:

   1. The primary endosperm nucleus divides into 2 nuclei and it is immediately followed by wall formation.

   2. Subsequent divisions also follow cell wall formation.

   3. Examples: Adoxa, Helianthus, and Scoparia.

4. Helobial endosperm:

   1. The primary Endosperm Nucleus moves towards the base of the embryo sac and divides into two nuclei.

   2. Cell wall formation takes place leading to the formation of a large micropylar and small chalazal chamber. The nucleus of the micropylar chamber undergoes several free nuclear divisions whereas that of the chalazal chamber may or may not divide.

   3. Examples: Hydrilla and Vallisneria.

5. Ruminate endosperm:

   1. The endosperm with irregularity and unevenness in its surface forms ruminate endosperm.

   2. Examples: Areca catechu, Passiflora, and Myristica