Nucleocytoplasmic Interaction in the Eggs of Pteridium Aquilinum Maturing in the Presence of Thiouracil

Abstract

In the eggs of Pteridium aquilinum maturing in the presence of a small quantity of thiouracil (0.6 x 10-3 M in the medium), known to reduce the rate of maturation by a half or more, the nuclear evaginations are particularly conspicuous. On the grounds of their structural features, their regularly narrow connexion with the nucleus, and the absence of nuclear pores from their envelopes, the evaginations are regarded as specialized formations, and not merely extensions of an amoeboid nucleus. An aggregate of electron-opaque material, probably of nucleolar origin, and believed on the basis of enzyme extractions to be largely protein, but with some ribonucleic acid, is a characteristic feature of the evaginations. The fate of the evaginations, which disappear shortly after fertilization, remains obscure. Refined methods of fixation and staining have, however, revealed striking resemblances between the evaginations, bodies which may be detached evaginations, and mitochondria. The hypothesis that the evaginations become detached, and that some at least differentiate into mitochondria, the simplest interpretation of the events observed, has not been invalidated by this investigation.