What are the different types of endosperm briefly describe them?
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flowering plants are: (i) Nuclear type (ii) Cellular type and (iii) Helobial type!
The formation of endosperm is initiated by mitotic divisions of the primary endosperm nucleus (3N). The formation of endosperm occurs usually prior to the zygotic division.
Endosperm accumulates food reserves and functions as the nutritive tissue for the developing embryo.
(i) Nuclear type:
In nuclear type of endosperm the first division of primary endosperm nucleus and few subsequent nuclear divisions are not accompanied by wall formation. The nuclei produced are free in the cytoplasm of the embryo sac and they may remain free indefinitely or wall formation takes place later. In the coconut, cell wall formation of endosperm is never found complete. In Areca and Phoenix the endosperm becomes very hard.
(ii) Cellular type:
In this case, there is cytokinesis after each nuclear division of endosperm nucleus. The endosperm, thus, has a cellular form, from the very beginning because first and subsequent divisions are all accompanied by wall formation e.g. Petunia, Datura, Adoxa, etc.
(iii) Helobial type:
It is an intermediate type between the nuclear and cellular types. The first division is accompanied by cytokinesis but the subsequent ones are free nuclear. The chamber towards micropylar end of embryo sac is usually much larger than the chamber towards chalazal end.
A large number of nuclei are formed in the micropylar chamber by free nuclear divisions while the nucleus of the chamber towards chalazal end divides to form a fewer free nuclei or may not divide at all.
The formation of endosperm is initiated by mitotic divisions of the primary endosperm nucleus (3N). The formation of endosperm occurs usually prior to the zygotic division.
Endosperm accumulates food reserves and functions as the nutritive tissue for the developing embryo.
(i) Nuclear type:
In nuclear type of endosperm the first division of primary endosperm nucleus and few subsequent nuclear divisions are not accompanied by wall formation. The nuclei produced are free in the cytoplasm of the embryo sac and they may remain free indefinitely or wall formation takes place later. In the coconut, cell wall formation of endosperm is never found complete. In Areca and Phoenix the endosperm becomes very hard.
(ii) Cellular type:
In this case, there is cytokinesis after each nuclear division of endosperm nucleus. The endosperm, thus, has a cellular form, from the very beginning because first and subsequent divisions are all accompanied by wall formation e.g. Petunia, Datura, Adoxa, etc.
(iii) Helobial type:
It is an intermediate type between the nuclear and cellular types. The first division is accompanied by cytokinesis but the subsequent ones are free nuclear. The chamber towards micropylar end of embryo sac is usually much larger than the chamber towards chalazal end.
A large number of nuclei are formed in the micropylar chamber by free nuclear divisions while the nucleus of the chamber towards chalazal end divides to form a fewer free nuclei or may not divide at all.
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