Nuclear behaviour during the life cycle of Derbesia (Chlorophyceae)

Abstract

Changes of DNA content of nuclei during the life cycle of Derbesia tenuissima, D. marina and D. cf. novae-zelandiae have been studied under culture conditions. In D. tenuissima ranges of DNA contents in the nuclei of the sporophytic filaments, gametophytes and macrogametes are identical, and the nuclei are hence considered as haploid. Karyogamy is indicated by higher DNA contents of nuclei in young sporangia of heterokaryotic sporophytes. There are no indications of karyogamy in homokaryotic sporophytes raised from macrogametes by parthenogenesis. In D. marina and D. cf. novae-zelandiae both the sporophytic filaments and gametophytes have identical ranges of DNA contents of their nuclei. Furthermore, in young sporangia of D. marina DNA contents indicating diploid nuclei were found. It is presumed that meiotic divisions of diploid nuclei take place soon after karyogamy without prior mitotic divisions and the life cycle of all three species is considered to be haplo-heterokaryotic. In D. cf. novae-zelandiae a heteromorphic life history with a Halicystis phase has been observed.