+1 862 207 3288 In the Capsella type of embryo development the zygote divides transversely into two unequal cells. The larger cell towards the micropyle is called the basal cell. The smaller cell towards the centre of the embryo sac is called Apical cell. The basal cell divides transversely once again into two unequal cells. The apical cell divides longitudinally into two apical cells. These four cells are arranged in inverted T( | ) shape and together form a proembryo.
In the proembryo:-
(i) The largest and lowermost cell is called a basal cell which does not divide anymore
(ii) There is a single middle cell above the basal cell.
(iii) There are two apical cells above the middle cell.
Division of Middle Cell:- The middle cell of the proembryo repeatedly divides transversely and produces a 15 to 20 celled long filamentous structure called suspensor. The lowermost cell of the suspensor, towards the micropyle end is the largest. It is called basal cell. The basal cell anchors the proembryo with the wall of embryo sac at the micropylar end. The terminal cell of the suspensor is called hypophysis cell. The hypophysis cell divides repeatedly and the cells so formed give rise to
(i) Epiblem(dermatogen)
(ii) Periblem
(iii) Calyptrogen and the
(iv) Root cap regions of the radicle. When the embryo development is completed the suspensor degenerates.
Divisions of Apical cell: Due to the formation of suspensor the apical cells are pushed towards the endosperm so that the nutritional need of the developing embryo is satisfied. The apical cells first divide longitudinally and then transversely into eight cells forming an octant(a group of 8). The cells of the octant divide peripherally to form 16 celled embryo. Its upper mass of eight cells is called a terminal octant or chalzal octant. Its lower mass of eight cells is called a micropylar octant. The terminal octant or chalzal octant develops into two colyledons and the plumule. The micropylar octant gives rise to the hypocotyl and the stelar region(Plerome) of the radicle.
