| Popis: |
Nuclei of uncleaved sporangia of Echinostelium minutum isolate D-3 1971 have a mean Feulgen-DNA content of 1.84. This value does not differ significantly from that recorded for the nuclei of the amoebal and plasmodial phases. No nuclei were found with a DNA content twice that of the nuclei in the amoebae, plasmodia, or uncleaved sporangia. This observation appears to rule out the possibility of zygotic meiosis. A single endosporic nuclear division occurs during the maturation which follows spore cleavage. The mean DNA content of the metaphases measured was 1.99. No metaphases were observed with a DNA content that would be indicative of a second division of meiosis. Also, no 4:2:1 reduction in DNA content was observed. These data confirm our previous hypothesis that this isolate of E. minutum normally lacks a sexual phase. The single nuclear division in the maturing spore is followed by one of the division products becoming euchromatic and undergoing a single round of DNA replication, while the other division product becomes very pycnotic, eventually degenerating. The mean nuclear DNA values for the euchromatic and pycnotic nuclei are 1.84 and 0.88, respectively. Mature spores normally become uninucleate and have a nuclear DNA content which is equivalent to that of the amoebal and plasmodial phases. |
