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18-pmnu322

Fig. 18: experimentally induced changes in macronucleus

In one experiment in which electric shock was applied to Paramecium cells to trigger trichocyst discharge the macronucleus in one cell was observed to undergo morphological changes of two types. First, a large area of the nucleus, normally found to contain electron-opaque foci, had changed into whorls of more electron-transparent filamentous material. Secondly, a section of the nuclear envelope had folded into a stack like the annulate lamellae seen in oocytes of many vertebrate and invertebrate cells (see Kessel, Int. Rev. Cytol. 82:181-303, 1983). The nuclear pores were present in part of this stack of the nuclear envelope while in other parts the pores were reduced or absent and a layer of dots or lines occupied the nucleoplasmic space between the two envelope segments. Presumably these annulate lamellae represent a temporary storage mechanism for excess nuclear envelope. EM taken on 2/28/84 by R. Allen with Zeiss 10A TEM. Neg. 12,000X. Bar = 0.5µm.
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