FINE STRUCTURE OF DWARF MALES IN OEDOGONIUM PLUVIALE (CHLOROPHYCEAE)

Abstract

Oedogonium pluviale Nordstedt is nannandrous, described as possessing single-celled dwarf males. In some studies the dwarf males appear to have a reduced, lensshaped pedicular portion whose nature and structure remain unclear. The present study aims to: 1) establish whether dwarf males of O. pluviale are single-or twocelled, 2) describe the different developmental stages of dwarf males, and 3) understand the nature of the pedicular portion. Mitotic division of the dwarf male was observed, but neither upwards phycoplast migration nor synthesis of a gametangial cell wall occurred. Instead, the phycoplast and cell plate migrated downwards, producing a small pedicular portion whose content then degenerated. The antheridium occupied most of the dwarf male wall. Gametogenesis thus took place inside the wall of the young dwarf male (internal gametangium). Because the pedicular cell degenerated, we define this type of dwarf male as pseudo-single-celled to differentiate it from a true single-celled dwarf male. The antheridial nucleus underwent one mitotic division to give rise to two gametes. Instead of a true wall between gametes, mucilage condensed and was observed as a discrete layer that disappeared during gamete release.