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J Integr Plant Biol, 1984, 26 (4): -, Research Article
Early Embryogeny and Its Starch Distribution in Amentotaxus
Chen Zu-keng and Wang Fu-xiong Wang Fu-hsiung
doi:
Abstract
The present paper deals with the early embryogeny of Amentotaxus argotacnia (Hance) Pitger and its variation in starch distribution. Amentotaxus is endemie to China. The proembryos of Amentotaxus occurred at the end of July to early August, 1980–1981, When the zygote has sueeessive]y divided for four times, the daughter nuelei are becoming smaller and smaller after each division. At first, the zygote is 80–100 μ in diameter. Then, tbe free nuclei of the proembryo are 50–70 μ in diameter in two-nucleate stage, 36–50 μ in four-nucleate stage, and 29–32 μ in eight- to sixteen-nueleate stage, respectively. The wall formation of proembryos in Amentotaxas as in most other members of Taxaeeae also takes place at 16-nucleate stage. After wall formation the cells u each proembryo are arranged in two groups, upper one constitutes the cells of open tier (O) and the lower one, the primary embryonic eells (PE). The ratio of 0 to PE is 9:7 or 8:8 in some eases. The cells of open tier elongate and divide to form the ceils of upper tier (U) and the prosuspensor eens (S). In such ease, The ratio is U:S:PE= 8:8:8. When the eells of open tier and primary embryonie tier sometimes divide simultaneously, the primary embryo cells result in the embryo cells (E), and the ratio is U:S:E=9:9:14 or U:S:E=8:8:16. The young embryos of Amentotaxus begin to differentiate in the first week of August in Jin-Foshan (Golden Buddha Mountain), 1400 to 1600m. Sichuan Province, China The developmental features of the young embryo in Amentotaxus are as follows: (1) The development of the young embryos lasts for 10 to 12 months. This is very unique in Gymnosperms. The development of tile embryo in Amentotaxus is in some deg ree similar to that of Ginkgo, beeause their young embryos develop in maternal plants, whereas the late embryogeny takes place after shedding of the seed. (2) The young embryos pass through the winter at multieellular stage and the late embryos are still undifferentiated when the arils are getting red and the seeds begin to shed. It is interesting to note that the development of embryos are still staying at embryo seleetion stage of simple polyembryony when seeds were stored for six months in 15-20℃. As far as our information goes, the embryos in seeds should get over another winter until embryo matures. The embryos in Amentotaxus is un;quo in this respect and it is considered to be primitive. Though the seeds of pteridosperms have large female gametophytcs, none of embryos have been found in their fossil seeds. Probably their embryos are not well developed when the seeds mature and shed. Thus the embryos of fossil seeds are not easily preserved (Cronquist, 1968). The condition of embryonic developaleut in Amentotaxus resembles strongly with that in pteridosperms. From above, Amentataxus eould be the most primitive genus in Taxaceae. (3) Simple polyembryony in Amentotaxus is pronfinent. The prosuspensors sometimes divide to give rise to “suspensor embryos”. The general tendency of the starch distribution in male and female gametophytes is that the main regions of stareh are gradually transferred frmn mieropylar to chalazal end wiht the development of the ovule. After pollen germination the stareh proceeds together with the sterile cell, tube nueleus and spermatogenous cell down the arehegonium. In early developmental stage of female gametophyte, the starch region always appears round the upper part of the archegonia; after fertilization they mainly appear in tissue of female gamctophyte near the proembryo or young embryo to form the pyramidal region. It is worthy to note that the starch grains of male gametophyte are larger in size than those of female gametophyte and the former is much less in nmnber than the latter. So far as the embryo proper is concerned the starch grains densely appear armmd the nuclei of the embryos, espeeially those of the prosuspensors. Besides, near the basal part of aril and integument there is a stable region of polysaeeharide which shows the positive reaetion for PAS. This region is always present from the origin of aril to its mature and is an important feature of the ovule and seed in Amentotaxus,
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