稻胚发育的三维形态研究兼论胚各部分的形态本质

The Tridimensional Morphology of Rice Embryo Development with Special Reference to the Scutellum and the Coleoptile 

运用扫描电镜及塑料半薄切片技术，从水稻（ＯｒｙｚａｓａｔｉｖａＬ．）授粉后２ｄ开始至种子成熟，追踪观察了稻胚的三维形态发育，根据结果，对胚各部分的形态本质提出一些新的见解。（１）授粉后２ｄ的胚由胚柄、胚基和胚体组成。胚基为胚柄和胚体之间的过渡区，呈喇叭状，胚基与胚柄不能等同。２ｄ的胚未出现器官分化，属原胚；但胚背腹分化明显，即存在背腹极性。（２）授粉后第３至第５天幼胚的形态变化及器官分化至关重要。盾片和胚芽鞘在授粉后３ｄ的幼胚上同时出现，两者均直接由原胚分化，并非胚芽鞘从盾片发生。胚芽鞘原基经历这３ｄ的特殊形态演变，形成空心倒锥状的胚芽鞘，展现了禾本科特有的胚芽鞘的形态形成机理。３ｄ幼胚胚根的原形成层、基本分生组织及根冠分化；４ｄ幼胚小丘状生长锥形成，胚根的原表皮分化，茎根轴形成；５ｄ幼胚胚芽、胚轴与胚根初步形成。（３）稻胚具有二型子叶，胚套是胚的外围子叶，盾片是此子叶的一个主要部分（侧生子叶），胚芽鞘是顶生子叶。

Using scanning electron microscopy and semi thin plastic sections, the pattern of development of the rice (Oryza sativa L.) embryo from 2 days after pollination (DAP) to maturity was followed. (1) At 2 DAP,the young embryo was observed to consist of an embryo proper, a hypoblast and a suspensor. The trumpet_shaped hypoblast was a transitional region situated between the suspensor and the embryo proper. To label the hypoblast as suspensor is incorrect. During this time, dorsiventrality was established, but a radicle was not yet differentiated. Therefore it is still referred to as a proembryo. (2) 3～5 DAP, the embryo underwent definite morphological and anatomical changes. In the young embryo at 3 DAP the scutellum and coleoptile appeared simultaneously directly from the proembryo. The coleoptile did not originate from the scutellum. During these foremost 3 days, the coleoptile primordium underwent a special kind of morphological change and formed a young coleoptile having the shape of an inverted hollow cone. This process revealed the true mechanism of coleoptile formation. Anatomical observation indicated that the embryo at 3 DAP began to differentiate procambium, ground meristem and root cap. At 4 DAP a dome like growth cone and protoderm of radicle appeared. Then the shoot root axis became established. At 5 DAP the plumule, hypocotyl and radicle were formed. (3) It was shown that the embryo of rice actually has two cotyledons: the scutellum (a part of the embryonic envelope) and the coleoptile (The scutellum being the lateral cotyledon, a part of outside cotyledon, and the coleoptile the apical cotyledon the coleoptile may be considered to be a modified form of a cotyledon). This kind of structural arrangement can be referred to as dimorphic cotyledon.