Effects of heat shock on nuclear organization in Plasmodia of Physarum polycephalum

Abstract

Plasmodial interphase nuclei were subjected to heat shocks and their ultrastructure was studied after 5, 10, and 15 min at 41 °C as well as during recuperation at normal temperature (26 °C). It was observed that the interphase chromatin, nucleoplasm, and nucleolus are already affected after a 5-min exposure of the plasmodia to a supranormal temperature. The nucleolar granular component rapidly transforms into densely packed material and the nucleoplasm takes on a coarser appearance. Spherical bodies approximately 0.15 μm in diameter are also formed. During recovery, after a 15-min heat shock, modifications in nuclear structure are also quite rapid. Most particularly, nucleolar organization is still more affected than during heat shocks and the nucleolus shows numerous irregular lacunae. Part of the intranucleolar chromatin migrates to the nucleolar surface where it forms conspicuous protrusions. By the end of a 3-h recovery period, nuclear morphology has reverted to normal except that the nucleolus still exhibits a slightly loose organization.