Karyogamy follows plasmogamy in the life cycle of Derbesia tenuissima (Chlorophyta)

Fertilization in a multinucleate siphonous green alga, Derbesia tenuissima (Moris et De Notaris) Crouan, was studied using light, fluorescence, and electron microscopy. The male nucleus was smaller and had more condensed chromatin than the female nucleus. Karyogamy was observed within 5 min after plasmogamy. The finding of zygotic karyogamy suggests that the sporophyte of this species develops from a diploid homokaryotic zygote, and this disputes interpretations of the life history of Derbesia based on microspectrophotometric studies.