| Abstract: | The processes of differentiation of the presumptive cells (prespore and prestalk cens) into mature spores, stalk and basal-disc cells in Dictyotelium discoideum was investigated. The number of stalk and disc cells in pre-labeled culminating cell masses was estimated by determining the radioactivity of the undissociable fraction separated by filtration from the dissociable fraction containing presumptive cells and spores. Changes in the proportion of amoeboid cells stainable with fluorescein-conjugated antispore serum and encapsulated spores were also followed in the dissociable fraction. Formation of stalk and disc cells began at 17 hr of development and was completed at 26 hr, while formation of morphologically identifiable spores began at 18 hr and was completed at 20 hr, long before completion of stalk formation. At the onset of culmination, unstained cells abruptly increased with an accompanying decrease of stained cells, when unstained rear-guard cells appeared in the hind region. Although some of the rear-guard cells soon differentiated into basal-disc cells, the rest remained amoeboid in the upper part of the spore mass (sorus) after complete formation of a fruiting body. Despite the presence of the amoeboid cells in mature sori, the proportion of the sorus to the stalk and disc of a fruiting body was approximately equal to that of stained (prespore) to unstained (prestalk) cells in a migrating slug. |
