Huang B. Q., Sheridan W. F.
Department of Biology, University of North Dakota, Grand Forks, North Dakota 58202-9019.
Plant Cell. 1994 Jun;6(6):845-861. doi: 10.1105/tpc.6.6.845.
The developmental stages of the maize embryo sac were correlated with the corresponding silk lengths of ear florets in the female inflorescence. The development of embryo sacs in the ovules of spikes occurs in a gradient pattern with the initiation of the embryo sac beginning at the base of the ear and progressing to the top. At the beginning of meiosis, the presence of conspicuous cortical microtubules coincides with the extensive elongation of the megasporocyte. The spindles at metaphase I and II align along the long axis of the megasporocyte leading to the linear alignment of the dyad and tetrad of megaspores. During megagametogenesis, micropylar and chalazal nuclei of the embryo sac undergo synchronized divisions and migration at the second and third mitosis. Radiate perinuclear microtubules are present during the interphase of the second and third mitosis, and inter-sister nuclear microtubules occur at the late four-nucleate embryo sac. The configuration and orientation of the spindles, phragmoplasts, and pairs of nuclei result in precise positioning of the nuclei. The fusion of the polar nuclei and the formation of a microtubule organizing center-like structure in the filiform apparatus occur right after the first division of the antipodal cells. The different patterns of organization of microtubules in the cells of the mature embryo sac reflect their structural adaptations for their future function.
玉米胚囊的发育阶段与雌花序中穗小花的相应花丝长度相关。穗状花序胚珠中胚囊的发育呈梯度模式，胚囊的起始于穗基部并向上发展。在减数分裂开始时，明显的皮层微管的存在与大孢子母细胞的广泛伸长同时出现。第一次减数分裂中期和第二次减数分裂中期的纺锤体沿大孢子母细胞的长轴排列，导致二分体和四分体大孢子呈线性排列。在雌配子体发生过程中，胚囊的珠孔核和合点核在第二次和第三次有丝分裂时进行同步分裂和迁移。在第二次和第三次有丝分裂的间期存在辐射状的核周微管，在四核胚囊后期出现姐妹核间微管。纺锤体、成膜体和核对的构型和取向导致核的精确定位。极核融合以及在反足细胞第一次分裂后在丝状器中形成类似微管组织中心的结构。成熟胚囊细胞中微管的不同组织模式反映了它们为未来功能所做的结构适应。
