摘要
本研究对萝卜(Raphanus sativus L.)的成熟胚囊,胚和胚乳的早期发育过程作了亚显微结构观察:(1)萝卜胚囊由7个细胞组成,成熟时反足细胞消失。(2)卵细胞表现明显的极性,其合点端不具完整的细胞壁,它是电子致密物质在卵细胞和中央细胞两者质膜之间沉积所形成的一种非连续结构。(3)助细胞的明显特点是具丝状器,细胞器丰富,内质网发达。(4)中央细胞具大液泡,它的两个极核位于靠近卵器的一侧,细胞壁也有类似助细胞丝状器的结构。(5)授粉后4—5天,萝卜合子开始第一次分裂,胚胎发育遵循柳叶菜型模式。(6)萝卜初生胚乳核比合子早约2天分裂,属核型胚乳。在胚囊的合点端和珠孔端,曾出现胚乳的结节状聚集。授粉后第16天左右,从珠孔区胚乳开始了细胞壁自由生长和形成胚乳细胞的过程。
The ultrastructure of the mature embryo sac,the early stages of the embryo and endos- perm development of common radish,Raphanus sativus was examined.The embryo sac con- sists of 7 cells with antipodal cells disappeared when it matures.The egg cell is highly po- larized.The wall surrounded the chalazal end of the egg cell is incomplete,showing a dis- continuous structure of an electron dense material deposited intermittently in the space be- tween the two plasma membranes of the egg cell and central cell.The synergid has filiform apparatus,rich in organelles and well developed ER.The two polar nuclei of the central cell are located near the egg apparatus because of the big vacuole,and the finger-like pro- trutions from the cell wall,as that in synergid,are found.The first division of the zygote occurs 4—5 days after pollination and the development of the embryo follows the Onagrad type,and the structure of the embryo cell is quite simple for containing small quantity of ER,plastids and other organelles.The primary endosperm nucleus deviates 2 days earlier than zygote.The endosperm is of nuclear-endosperm containing chloroplasts,well developed ER,and plentiful of mitochondria and golgi bodies and the nodule-like aggregation in bod the chalazal and micropylar ends of the embryo sac during the early development appeared, and cell wall starting at the micropylar end by freely-growing forms about 16 days after pol- lination.
