No abstract

Results from quantitative cytochemical analyses of Feulgen-DNA and azure B-RNA content of different stages of ascus development in the pyrenomycete Sordaria fimicola Ces. and DeNot. may be summarized as follows: (a) DNA replication in nuclei of the prefusion ascus (penultimate cell) precedes karyogamy, hence the prefusion nuclei are 2C (replicated haploid), and the fusion nucleus 4C (replicated diploid) in DNA content. These data show that premeiotic S phase and genetic recombination cannot be coincident since DNA replication is complete prior to nuclear fusion in the crozier penultimate cell. (b) DNA replication in the basal and terminal cell nuclei of the crazier does not occur until DNA replication is complete in the subterminal (penultimate) cell. Therefore, DNA replication occurs first in the cell which forms the primary ascus. (c) During ascus enlargement, which occurs during pachytene and diplotene, the total ascus RNA content increases from 18.9 to 195.4 arbitrary units (a.u.), while at the same time nucleolar RNA increases from 0.5 to 1.7 a.u. The concurrent increase in nucleolar and ascus RNA suggests that a rather substantial proportion of the increase in total ascus RNA may be due to the synthesis of ribosomal RNA. (d) In asci which contain binucleate ascospores the total RNA content has increased to 281.5 units. This increase may represent a storage of RNA to be utilized for protein synthesis during the subsequent germination of the ascospore. (e) Ascospores in mature asci of eight day old cultures were always multinucleate. The multinucleate condition is presumably established in preparation for ascospore germination and the initial growth of the germ tube.

The nuclear DNA content of six non‐heterothallic isolates of the myxomycete Didymium iridis was measured by combining the Feulgen reaction with absorption microspectrophotometry. This allowed us to distinguish between homothallic (sexual) and apogamic (non‐sexual) isolates. Four of the isolates studied, Panamanian 4 and 5, California 1, and Missouri 1 are homothallic. Moreover, the average DNA content of the myxamoebal and plasmodial nuclei (0.32 and 0.61 respectively) does not differ significantly from the calculated haploid and diploid values for heterothallic isolates of D. iridis (0.34 and 0.63). Hence, it is concluded that in each of these isolates the myxamoebae are haploid and the plasmodia diploid. In two of the isolates investigated, Georgia 1 and Hawaii 1, the DNA content of the myxamoebal and plasmodial nuclei did not differ significantly. Therefore, in both of these isolates the plasmodia appear to develop apogamically. In addition the mean DNA values recorded for the Ha‐1 isolate suggest that it is aneuploid.

No abstract