白刺胚乳早期发育的超微结构研究

THE ULTRASTRUCTURAL STUDY ON THE EARLY DEVELOPMENT OF ENDOSPERM OF NITRARIA SIBIRICA

白刺(Nitraria sibirica)胚乳发育经历游离核阶段、细胞化阶段和被吸收解体阶段。游离核胚乳沿胚囊壁均匀排列为一层,胞质浓厚,其中有丰富的质体、线粒体、高尔基体、内质网和各种小泡等细胞器。珠孔区域的胚囊壁具发达的分枝状壁内突,而周缘区域的胚囊壁具间隔的钉状内突,内突周围的细胞质中具多数线粒体和小泡。胚乳细胞化时,初始垂周壁源于核有丝分裂产生的细胞板。在细胞板两端开始壁的游离生长,一端与胚囊壁相连接,另一端向心自由延伸。壁的游离生长依赖于小泡的融合。早期胚乳细胞具大液泡,具核或无核,细胞质中有大量的线粒体,质体缺乏,其壁仍由多层膜结构组成。

On the basis of the previous studies with light microscopy, we attempted to use TEM observing the early development of the endosperm in Nitraria sibirica Pall.The endosperm undergoes three developmental phase: free nuclear endosperm, cellularization, and disintegrative and absorbtive phase. At the free nuclear stage, the nuclei are surrounded by mass of dense cytoplasmic matrix. An attenuated layer of cytoplasm extends around the periphery of the central cell. Many organelles, such as plastids, mitochondra, dictyosomes and ER are involved in the cytoplasmic matrix. Well-developed, branching transfer cell wall ingrowths develop from the micropylar region of the embryo sac wall, and pegsha-ped wall ingrowths develop from the periphery region. The cytoplasm near the wall projections contain a lots of vesicles and mitochondria.At the later globular embryo stage, the nuclear endosperm begin to cellularize in themicropylar region, cell plates develop from the typical phragmoplast as a result of normal mitosis. Free growing wall extends from the free margin of the cell plates. The outer free growing margin soon fuse with the wall of the central cell, and the inner free growing margin continues to grow towards the central vacuole, thus the anticlinal walls have formed. The free growing wall is dependent on the fusion of the vesicles.After the beginning of endosperm cellularization, large vaculoes, a lot of vesicles, and mitochondria are full of endosperm matrix. The incipient endosperm cells contain a large vacuole, and many mitochondria and plastids. Their walls are made of some membrane structure, and wall material is possibly deposited late. It's nucleus has a mininucleolus.