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The Nucellus, Embryo Sac, Endosperm, and Embryo of Aesculus and their Interdependence during Growth

1965; Oxford University Press; Volume: 29; Issue: 1 Linguagem: Inglês

10.1093/oxfordjournals.aob.a083928

1095-8290

Albert List, F. C. Steward,

Plant tissue culture and regeneration

Immature fruits of Aesculus yield powerful stimuli to growth and cell division. Therefore, the developing fruit of Aesculus woerlitzensis Koehne has been investigated from pollination to maturity. The fluid, or liquid endosperm, which contains the growth-promoting substances is produced in a large vesicle which forms at the chalazal tip of the embryo sac. As the vesicle grows, it encroaches upon the nucellus and, when the embryo develops, one of its cotyledons penetrates into the vesicle of the embryo sac where it grows and absorbs the contents. The embryo, which has only a vestigial suspensor, reaches the vesicle by growing along the neck of the long curved embryo sac. The cotyledon which first penetrates the vesicle grows into a massive structure; the other remains small. The tip of the cotyledon seems to function as an absorbing surface, for the endosperm with which it comes into contact disorganizes. Fertilization and the presence of a viable embryo at the micropylar end of the embryo sac therefore sets in train a number of other events. These are the extensive development of the nucellus at the chalazal end of the embryo sac, the swelling of the vesicle and the formation of a free nuclear and some cellular endosperm, and the disorganization of the nucellus as it is encroached upon by the vesiculate embryo sac. Attention is directed to the organization of the nucellus in the vicinity of the embryo sac. Files or richly protoplasmic nucellar cells(hypostase) which converge upon the chalazal tip of the embryo sac suggest a principal route by which the vesicle may be nourished. Special attention is drawn to the very different sizes of cells, their nuclei and nucleoli, in the different parts of the nucellus. The growth and development of the embryo has also been traced from the zygote to the mature seed. The nutritive role of the veaiculate embryo sac, and the supply of growthstimulating substances, through the function of a cotyledon as an absorbing organ, are now seen as important features of the development of the Aesulus embryo in the ovule. Many outstanding problems still remain. The sequential events that follow fertilization in the different interdependent regions (nucellus, embryo sac, cotyledon, &c.) are here described, but not casually explained.