Guth E, Hashimoto T, Conti S F
J Bacteriol. 1972 Feb;109(2):869-80. doi: 10.1128/jb.109.2.869-880.1972.
Ultrastructural changes associated with ascospore formation in Saccharomyces cerevisiae were investigated by using freeze-etching and thin-sectioning techniques. The first nuclear division (meiosis I) is indicated by the appearance of spindle fibers within the nucleus. The nucleus subsequently elongates and eventually assumes a barbell shape; the second nuclear division (meiosis II) occurs before nuclear separation. The spindle fibers involved in meiosis II appear to be oriented perpendicular to those observed in meiosis I. A discrete bilaminar structure (forespore wall) progressively delineates each ascospore nucleus and encloses cytoplasmic material including mitochondria and endoplasmic reticulum. The forespores then elongate, close off, and become separated from the ascus cytoplasm by membranes. The ascospores assume a spherical shape as spore coat material is laid down; the latter stages of ascospore formation are characterized by thickening of the ascospore wall and disintegration of the ascus cytoplasm. No structures which could be identified as chromosomes were observed.
利用冷冻蚀刻和超薄切片技术研究了酿酒酵母中与子囊孢子形成相关的超微结构变化。细胞核内纺锤体纤维的出现标志着第一次核分裂（减数分裂I）。随后细胞核拉长，最终呈杠铃状；第二次核分裂（减数分裂II）在核分离之前发生。参与减数分裂II的纺锤体纤维似乎与减数分裂I中观察到的纺锤体纤维垂直排列。一种离散的双层结构（前孢子壁）逐渐勾勒出每个子囊孢子核，并包围包括线粒体和内质网在内的细胞质物质。然后前孢子拉长、封闭，并通过膜与子囊细胞质分离。随着孢子壁物质的沉积，子囊孢子呈球形；子囊孢子形成的后期特征是子囊孢子壁增厚和子囊细胞质解体。未观察到可被鉴定为染色体的结构。
