Unequal distribution of DNA-containing organelles in generative and sperm cells of Erythrina crista-galli (Fabaceae)

Abstract 

The generative cell at anthesis in the mature pollen grain of Erythrina crista-galli (Fabaceae) was examined by 4,6-diamidino-2-phenylindole(DAPI)-fluorescence microscopy using the squash method. An unequal, polarized distribution of DNA-containing organelles (plastids and/or mitochondria) within the generative cell was observed in every mature pollen grain examined. Polarization of DNA-containing organelles is obvious when generative cells are freed and assume a spherical shape soon after microspore mitosis, as revealed by fluorescence-microscopic observations of specimens embedded in Technovit 7100 resin and thin-sectioned at different developmental stages. Early establishment of polarized localization of organelles in young generative cells of E. crista-galli and maintenance of this unequal distribution until pollen maturation strongly suggests that the organelles may still be clustered at pollen mitosis. Production of a dimorphic pair of sperm cells, as has been reported in Plumbago zeylanica, was observed in some pollen tubes germinated in vitro. The differentiation of the two sperm cells is discussed in relation to possible preferential double fertilization in angiosperms.