A CYTOPHOTOMETRIC INVESTIGATION OF THE RELATIONSHIP OF DNA AND RNA SYNTHESIS TO ASCUS DEVELOPMENT INSORDARIA FIMICOLA

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 TEMPORAL RESPONSE OF RECOMBINATION EVENTS TO GAMMA RADIATION OF MEIOTIC CELLS INSORDARIA BREVICOLLIS

“…For Neurospora, Sordaria and Podospora, the principle genera used in genetic studies, the formation of asci from the binucleate penultimate cell of the crozier is followed by the fusion of the uninucleate stalk and terminal cells to generate a second and subsequent croziers. In both Neottiella (Rossen and Westergaard, 1966) and Sordaria (Bell and Therrien, 1977) premeiotic DNA synthesis occurs in the prefusion nuclei before it occurs in the nuclei which contribute to the next crozier. Thus, in meiosis in these organisms, crozier formation continues over a period of time, yielding developing asci at various times.…”

“…The period of lethal sensitivity of prefusion croziers to 20 krad irradiation in the 25 to 40 h interval most likely corresponds to the period of premeiotic DNA synthesis. Premeiotic-S is associated with prefusion croziers in Sordaria (Bell and Therrien, 1977). In yeast, sensitivity to radiation during the period of premeiotic DNA synthesis has been explained as due to the arrest of synthesis followed by excessive degradation of the damaged DNA (Simchen et al, 1973;Salts et al, 1976).…”

Meiosis in Mycelial Fungi

“…Despite the general realization of the importance of premeiotic S-phase, timing of S-phase remains questionable in mycelial ascomycetes (e.g., Farman 2002). Based on microspectrophotometric quantitation of DNA (a technique potentially subject to artifacts), replication was found to precede karyogamy in Neottiella rutilans, N. crassa and S. fimicola (Rossen and Westergaard 1966;Iyengar et al 1976;Bell and Therrien 1977). By contrast, timing of S-phase is clearly defined in C. cinereus, in which replication also occurs before karyogamy (Kanda et al 1990;Pukkila 1994).…”