多头绒泡菌染色体构建过程的形态学研究

以同步核内有丝分裂的多头绒泡菌(Physarum polycephalum)原质团为材料,在有丝分裂周期中连续取材,按常规方法制备超薄切片,在电镜下研究了染色体形态构建的整个过程。有丝分裂前期,首先是G_2期凝集的染色质块逐渐解集缩成为松散状,染色质在松散的同时逐渐改组成直径为80～150nm的松散染色线结构。接着是在松散的染色线上形成一些电子密度高的集缩区,随着集缩区的增多和扩展,染色线缩短变粗,最后形成直径300～350nm的染色体。上述两个过程各需30min左右。与上述过程同时发生的是,核仁由中央位置逐渐移向边缘,前期50min左右时在近核膜处呈团块状解体。染色体形态构建的整个过程约需1h,可分为染色质的松散改组和集缩两个连续的步骤,25～30nm染色质纤维是这一过程中能分辨的最细的形态单位。

MORPHOLOGICAL STUDIES ON THE PROCESS OF CHROMOSOME CONSTRUCTION IN PHYSARUM POLYCEPHALUM

The process of morphological construction of chromosomes in Physarum polycephalum was studied with transmission electron microscopy. The synchronous plasmodium materials were sampled in 5 to 10 min time intervals during the mitotic cycle. In mitotic prophase, the compact lumped chromatin of G2-phase gradually decondensed into loose structure. Meanwhile, the loose chromatin gradually reorganized into the chromatin thread structure that was about 80 to 150 nm in diameter. This process was completed in about 30 min. In the loose chromatin threads many condensed regions appeared which increased and expanded, as the prophase proceeded, and the chromatin thread became shorter and thicker. Finally, the metaphase chromosomes of 300 to 350 nm in diameter were formed. This process also took about 30 min. At the same time, nucleoli gradually moved from the center to the edge of the nucleus and disintegrated in about 50 min in the prophase. The results revealed that the whole process of morphological construction of chromosomes in this species was completed in about one hour. The process could be divided into two consecutive steps, that is, the reorganization and condensation of chromatin. The 25 to 30 nm chromatin fibers were the finest morphological unit that could be identified.