Preferential Disappearance of Chlorophyll Preceding Digestion of Male-derived Chloroplast DNA in Young Zygotes of Monostroma latissimum by a DAPI-epifluorescence Microscopy and Electron Microscopy.

Abstract

The preferential destruction of the chloroplast DNA (cp-DNA) from the male-derived chloroplast 40 min after mating of male and female gametes in Chlamydomonas reinhardtii can explain the inheritance of maternal cp-DNA (Kuroiwa et al. 1982, Kuroiwa 1991). However, there is no information available regarding the structural changes which would be expected to precede the preferential digestion of cp-DNA. Chlorophyll pigments, chloroplast nuclei (cp-nuclei; nucleoids) and fine structures of chloroplasts were examined in young zygotes after mating of male and female gametes in the isogamous alga Monostroma latissimum by epifluorescence microscopy, after staining with 4'-6-diamidino-2-phenylindole DAPI), and by electron microscopy. Each gamete has a large cup-shaped chloroplast which contains several cp-nuclei. At 60 min after mating of male and female gametes, the preferential disappearance of the cp-nuclei in male-derived chloroplasts can be observed in more than 50% of the young zygotes. Epifluorescence microscopy revealed that preferential release of chlorophyll pigments from the male-derived chloroplast precede the disappearance of cp-nuclei. This release of chlorophylls may be due to a change in the membrane systems.Electron microscopy shows that preferntial swelling of membrane systems occurs in just one of the chloroplasts in the young zygotes. Based on these results, we suggest that the release of chlorophyll may be due to changes in the membrane systems, which promote the preferential disappearance of the male-derived cp-nuclei.