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J Integr Plant Biol, 1985, 27 (6): -, Research Article
The Development and Structure of the Late Embryo in Torreya grandis
Tang Zhong-xun, Chen Zu-keng and Wang Fu-xiong Wang Fu-hsiung
The materials used in this investigation were collected during 1980–1983 from Zhuji county of Zhejiang province, China. Seed of Torrcya grandis is an important dry “fruit” and used for edible oil. It is endemic to China. The primordia of male strobili are differentiated before October in the first year, while those of female strobili occur later. The microspore mother cells and megaspore mother cells are found in March and April in the second year respectively. The fertilization takes place in August and the dormant embryo overwinters at the proembryo stage. Eventually the proembryo begins to differentiate and its development starts in July of the third year. Thus the interval from fertilization to latembryogeny of Torreya grandis lasts for about 11 months. When the seeds of Torreya grandis are shed 'in August the embryo within the seed is still immature. It requires a period of after-ripening. The experiments show that the embryo resumes to develop and differentiate during 1–3 months in stratification in moist sands. The development and structure of late embryo are characterized as follows: 1. The cotyledon of the mature embryo in Torreya grandis is of 15000 μm in length and 87% of the embryo. The hypocotyl is vary shert and only 13% of the embryo. This kind of structure of the embryo in Torreya is very rare among conifers and in some degree similar to that of Keteleeria. When seed is shed the meristem of cotyledon is just differentiated and only 100–200 μm in length at the end of July to the middle of August. As the seeds are stratified in moist sands for 1–3 months, the cotyledon increases about 100 times than in room temperature in Zhuji county. 2. There is a large secretory canal in either side between the procambium and the cortex of the mature embryo. The secretory canal consists of epithelial cells of 4–5 layers. It is very peculiar in conifers. 3. The shoot apex does not begin to differentiate, until the seed has been fallen from the tree. 4. The column of the root cap is rather short and consists of the cells of about 10 layers in height and 6 layers in width. 5. Proteins are only found in the focal zone of the free apex of the young embryo but without any starch grains. The starch is abundantly distributed in the opposite end from the root initials down to root cap and the entire transitional zone. It is interesting to note that neither proteins nor starch grains are found in the suspensor system. It is assumed that the protein may be the main form of storing material in the actively growing cells and tissues of embryo in Torreya grandis.
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