Evidence for the presence of DNA in the centrosomal plaques of Ascobolus

[Ultrastructure of the fungal nucleus. III. Genesis of the nucleus-associated organelle (NAO equals "KCE")]

The nucleus-associated organelle (NAO) is a structure, significant for division and motion of the fungal nucleus. In the basidiomycete Polystictus (equals Trametes) versicolor it is composed during somatic interphase of two globular entities (GE) and the connecting middle plate (MP). Its genesis is followed electron optically by analysing serial sections of preselected stages. Genesis is strictly determined by time and space. It starts with synthesis of the new MP a few minutes upon karyokinesis has been completed. Synthesis is localized in the area of contact between old GE and outer membrane of the nuclear envelope. After growing of the MP to its maximal size both new GE's develop from swellings at its ends. Old Ge's are dissolved during this developmental process. The period of genesis takes 30--40 min and fills one third of the cell cycle. A GE-field exhibits characteristic alterations throughout the formation of the NAO. It is composed of GE, periglobular zone, microtubules, and both caps of endoplasmic reticulum and multivesicular bodies.

Ultrastructure of mitosis in the amoeboflagellate Naegleria gruberi

Naegleria gruberi is an amoeboflagellate found in soil; mitosis is restricted to the amoeboid phase of its life-cycle. Ultrastructural examination of mitotic stages has confirmed some aspects of karyokinesis reported in earlier light-microscopic studies and expanded on other features of nuclear division described in electron-microscopic studies of Naegleria. The nuclear envelope remained intact throughout division, the nucleolus persisted, and centrioles were not found. Chromosomes were indistinguishable at the ultrastructural level, nor was any evidence detected of sites of microtubular attachment to possible chromosomes. An interzonal body, formed during separation in two of the nucleolus, was not an invariable feature of mitosis. The same was true of the polar caps, which appeared to be little more than the ends of the mitotic spindle. It is suggested that, in line with comparable situations in other protists, expansion of the nuclear envelope is chiefly responsible for separation of the nucleus into two daughter nuclei.