J Integr Plant Biol 29 (4): 347-353 (Apr 1987)
Development of the embryo and endosperm in roxburgh rose
[Rosa roxburghii Tratt. f. normalis Rehd. et Wils.] [1987]
Li Shujiu and Hu Shiyi (Beijing Univ. (China). Dept. of Biology)

1. The development of the embryo of roxburgh rose (Rosa roxburghii Tratt. f. normalis Rehd. et Wils.) conforms to the Asterad type with significant variation of forming an oblique wall after the division of the apical cell. A wedge-shaped epiphysis initial is cut off and remained in early stages of proembryo. The mature embryo is typical in dicotyledons and accumulates large amount of protein bodies in its two cotyledons. 2. The endosperm formation is nuclear type. Since the free nuclei become completely separated by the cell wall, the cells in the surface layer of the cellular endosperm may divide periclinally to form a stratified cell zone, as we called secondary endosperm, lining along the boundary of the embryo sac. During the formation of secondary endosperm, the rest endosperm cells degenerate gradually. In mature seed only the secondary endosperm persists and contacts directly with the mature embryo, except at the chalazal end, where it degenerates earlier. 3. The results of this study reveal that degeneration of embryo and endosperm at early stages of embryogeny in some ovules, perhaps caused by the insufficiency of nutrients, may be one of the reasons of seed abortion.

Fig. 1 A diagram of the proembryo development in roxburgh rose. (A). Zygote (B) 2-celled embryo (C) The apical cell divides into two cells by an oblique cell wall and the basal cell is separated by a cross wall (D-F) Multicellular embryos, note the wedge-shaped epiphysis initial cell (G-H) Multicellular embryos, note the globular embryo proper is formed.
 
Table 1 Developmental processes of embryo and endosperm
Days after blossom Endosperm development Embryo development
5-6 1st. division of primary endosperm nucleus Zygote
9-10 Free nuclear stage 1st. division zygote
10-24 Free nuclear stage Proembryo stage
25 Wall formation Differentiation of cotyledon primordium
27 Cell formation completed, growth of secondary endosperm Heart-shaped embryo
28 Growth of secondary endosperm Torpedo-shaped embryo
31 Growth of secondary endosperm Differentiation of vascular tissue
34 Growth of secondary endosperm, primary endosperm degenerate Differentiation completed
38-41 Growth of secondary endosperm, primary endosperm disappeared Embryo grown continuously, accumulation of protein bodies in cotyledon cells
48-87 Accumulation of protein bodies in secondary endosperm, degeneration of its cells near the chalazal end Embryo grown continuously, cotyledon increased in length
113 Secondary endosperm persisted Embryo matured, more than 1882 µm in length

Explanation of Plates

C. cotyledon, D. days after blossom, ES. embryo sac, PE. primary endosperm, SE. secondary endosperm.

 

Plate I Development of proembryo
Fig. 1. A longitudinal section (l.s.) ovary, showing a anatropous ovule. Note two narrow ES in a single ovule (fixed in blossoming day). x13
Fig. 2. A zygote ready for division (8D). x850
Fig. 3. 2-celled proembryo (9D). x850
Fig. 4 and 5. Several celled proembryo. Note a wedgeshaped epiphysis initial at the apex of the embryo proper (arrow) (9-10D). x850
Fig. 6. Several celled proembryo. Note the suspensor composed of 3 cells, the basal two cells are much larger than the other one (14D). x850
Fig. 7. An ES with two embryos. Note the zygote embryo with suspensor (22D). x500
Fig. 8. A globular proembryo. Note the differentiation of the dermatogen (20D). x740
Plate II Differentiation of embryo

Fig. 9. A heart-shaped embryo, showing two cotyledon primodia (27D). x220
Figs. 10-12. Some stages in development of embryo. The torpedo-shaped embryo were formed by the rapid elongation of cotyledons. Note the differentiation of vascular tissue in cotyledons and radicle (28D, 31D and 34D). 10x220, 11x110, 12x50
Fig. 13. A l. s. seed, showing the front section view of a cotyledon. Note the distribution of vascular bundles (arrow) in the cotyledon, protein bodies in the cells, the constitute of a radicle (root cap. dermatogen, cortex and stele), degenerated seed coat (arrow) and secondary endosperm (SE) (48D). x50
Fig. 14. A portion of l.s. embryo, showing the structure of a radicle (35D). x100
Fig. 15. A portion of l.s. embryo, showing shoot apex and young leaf primordia (48D). x100
Fig. 16. A portion of l.s. cotyledon and SE, showing the abundant protein bodies in their cells (57D). x310.

Plate III Development of endosperm

Fig. 17. A micropylar part of l.s. embryo sac, showing the endosperm in free nuclear stage. Note the nuclei are especially aggregated at the micropylar end of the ES (18D). x570
Fig. 18. A Part of dissected endosperm sac, showing the distribution of nuclei. The upper part is the endosperm near the embryo (22D). x500
Fig. 19. Upper portion of l.s. ovule, showing the formation of the SE (arrow), beginning from the surface layer of the cellular endosperm. Note the degeneration of primary cellular endosperm cells between two cotyledons (27D). x 130
Fig. 20. A portion of 1.s. ovule, showing the degeneration of the PE near the cotyledons, and the formation of SE (34D). x 370
Fig. 21. A portion of 1.s. ovule, showing the PE disappeared and the SE developed into a 3-4 layered cell zone (38D). x 370
Fig. 22. A portion of 1.s. ovule, showing the feature of SE at the micropylar end (48D). x 350
Fig. 23. A portion of 1.s. seed, showing the SE persisted in seed maturation and directly contacted with cotyledons (C). Note the degenerated seed coat (black) (113D). x520