Ultrastructure de l'oosphère et du zygote du Marsilea vestita après un faible abaissement de température

Abstract

Young archegonia of Marsilea vestita were subjected to a weak cooling from 24 °C (optimum temperature) to 16 or 12 °C. The female gamete rapidly reacts to this treatment by ultrastructural modifications of various organelles. The enlarged plastids lose their starch and a great number of plastoglobuli are always observed in the stroma; they contain a poorly defined lamellar system with very few grana structures. Some mitochondria break down and assume a vacuolar appearance; the endo-membranous system is very abundant: numerous endoplasmic reticulum profils as well as a great number of dictyosomes appear. Ribosomes become indistinct and it is impossible to distinguish polysomes in the hyaloplasm. The fertilization cone, which is used by the spermatozoid during its moving towards the female nucleus, is normally funnel shaped. After the treatment it is changed into a basal area spreading along the cell sides and separated from the remaining part of the gamete by a more or less continuous envelope of neoformed endoplasmic reticulum. Finally, it is possible by this treatment to remove the usual barrier to polyspermy and to observe several spermatozoids in the female cytoplasm.