Question

Explain the development of the different types of endosperms in angiosperms

Answer 1

Formation of the endosperm is initiated by mitotic division of primary endosperm nucleus, which is triploid and is formed by the triple fusion of polar nuclei to secondary nucleus 2n and with the male gamete (n). Endosperm is formed before the division of zygote. In angiosperms, endosperm development are of three types:
(i) Nuclear type: It is the most common type of endosperm formation. In this type the primary endosperm nucleus gives rise to a number of free nuclei which remain as a peripheral layer and a large central vacuole appears in the embryo sac. Cell wall formation takes later leading to the formation of cellular endosperm e.g., Coconut, Areca.
(ii) Cellular type: In it, first and subsequent divisions of primary endosperm nucleus are accompanied by wall formation, hence endosperm is cellular from the very beginning e.g., Petunia, Datura.
(iii) Helobial Type: It is an intermediate type between the nuclear and cellular types. The first division of endosperm nucleus is followed by wall formation, but the subsequent divisions are free nuclear. The chamber towards the micropylar end of embryo sac is much larger. A large number of nuclei are formed in it by free nuclear divisions while the nucleus of chalazal chamber divides to form a fewer, free nuclei or may divide at all e.g., Drimya.