[Effect of low temperature on the ultrastructure of hepatocyte nuclei in 11-day-old chick embryos].

A study was made of the ultrastructure of nuclei of 11-day old chick embryos exposed to low temperature (-15 degrees C) for various periods of time and returned to the normal conditions of incubations (+37 degrees). The exposure to the low temperature induced some drastic ultrastructural alterations in the nuclear pore complex that involved the loss of lateral components of annulus (annular granules) and of the central granule. Some pores displayed a diaphragm or its structures (peripheral granules), whereas in other pores the pore complex material was seen totally disorganized. The degree of chromatin condensation in such nuclei increased. After the normal condition of chick embryo incubation was resumed, the ultrastructural organization of the chromatin and the pore complex appeared to be normalized. The pore complex reorganization occurred one hour after heating. It is suggested that the abnormal pore structure may correspond to an inactive state of the pore.