水稻中央细胞发育期间超微结构变化的观察

AN ULTRASTRUCTURAL STUDY ON THE DEVELOPMENT OF CENTRAL CELLS IN RICE EMBRYO SAC

摘要:

本文通过透射电镜对水稻受精前胚囊中央细胞发育过程中超微结构的变化进行观察。结果表明，八核胚囊形成后很快就进行细胞化形成7个细胞，其中刚形成的中央细胞由1个大液泡、2个极核（珠孔端和合点端各1个）和一些含有丰富细胞器的胞质组成。中央细胞以后的发育主要是极核的发育和极核周围胞质的变化。极核发育经历以下过程：a．2个核都膨大呈“椭圆”形。核周围胞质呈不对称分布。b．2个核分别向胚囊中央移动并相互靠近。之后2个极核调整排列方式，由纵排（即与胚囊纵轴平行）变成横排。此时期有细胞质“桥”联结珠孔端卵器、2个极核和合点端反足细胞器。c．横排的极核移向卵器，并排列于卵细胞之上。此时胚囊未明显膨大，但极核相靠近的两边核膜有许多处已形成“融合桥”，核周围的胞质也起较大的变化，如质体内淀粉消失和光面内质网增加等。极核进一步发育直至胚囊成熟期间，极核排列方式及其周围胞质组成未观察到明显的变化，但胚囊体积明显增大。

Abstract:

An ultrastructural study on the development of the central cell was carried out on rice (Oryza sativa L.). The results showed that following the formation of the eight nuclei in the embryo sac, cellularization took place resulting in the formation of seven cells. One of the cells situated in the centre of the embryo sac was the central cell. The central cell contained a large vacuole, two polar nuclei (located in micropylar part and chalzal end, respectively) and a large number of cytoplasmic organella. Further development of the central cell mainly involved changes in the orientation of the polar nuclei and the distribution of the cytoplasm. Changes in the orientation of the polar nuclei involved the following stages of developments a. The two polar nuclei increased in size and became elliptical in shape. On both sides of the polar nuclei the cytoplasm showed an asymmetrical pattern of distribution. b. The two polar nuclei moved to the central region of embryo sac. At this stage the two polar nuclei were close to each other and they were lying ("one on top of the other") in parallel to the long axis of the embryo sac. When the polar nuclei moved to the central region of the embryo sac, a thick strand of cytoplasm (forming a cytoplasmic "bridge" ) became associated with the polar nuclei. The cytoplasm "bridge" ran from one end of the embryo sac to the other. c. The two polar nuclei began to move towards the egg cell and finally "sat" themselves on the top of the egg cell. The two polar nuclei had by now changed from a parallel (one on top of the other) to perpendicular (side by side) orientation (with respect to the long axis of the embryo sac). The side of the nuclear envelope of the two polar nuclei facing each other produced a lot of protrusions and fusion bridges throughout the different stages of development and reorientation of the polar nuclei. The cytoplasm surrounding the polar nuclei also went through some changes e. g. starch grains disappeared and smooth ER increased. UP till stage c the size of the embryo sac did not change much. But immediately after the completion of stage c the embryo sac greatly increased in size. The embryo sac then reached full maturity and apparently did not undergo any further changes.