Behavior of organelle nuclei (nucleoids) in generative and vegetative cells during maturation of pollen in Lilium longiflorum and Pelargonium zonale

The behavior of organelle nuclei during maturation of the male gametes of Lilium longiflorum and Pelargonium zonale was examined by fluorescence microscopy after staining with 4′,6-diamidino-2-phenylindole (DAPI) and Southern hybridization. The organelle nuclei in both generative and vegetative cells in L. longiflorum were preferentially degraded during the maturation of the male gametes. In the mature pollen grains of L. longiflorum, there were absolutely no organelle nuclei visible in the cytoplasm of the generative cells. In the vegetative cells, almost all the organelle nuclei were degraded. However, in contrast to the situation in generative cells, the last vestiges of organelle nuclei in vegetative cells did not disappear completely. They remained in evidence in the vegetative cells during germination of the pollen tubes. In P. zonale, however, no evidence of degradation of organelle nuclei was ever observed. As a result, a very large number of organelle nuclei remained in the sperm cells during maturation of the pollen grains. When the total DNA isolated from the pollen or pollen tubes was analyzed by Southern hybridization with a probe that contained the rbc L gene, for detection of the plastid DNA and a probe that contained the cox I gene, for detection of the mitochondrial DNA, the same results were obtained. Therefore, the maternal inheritance of the organelle genes in L. longiflorum is caused by the degradation of the organelle DNA in the generative cells while the biparental inheritance of the organelle genes in P. zonale is the result of the preservation of the organelle DNA in the generative and sperm cells. To characterize the degradation of the organelle nuclei, nucleolytic activities in mature pollen were analyzed by an in situ assay on an SDS-DNA-gel after electrophoresis. The results revealed that a 40kDa Ca-dependent nuclease and a 23 kDa Zn -dependent nuclease were present specifically among the pollen proteins of L. longiflorum. By contrast, no nucleolytic activity was detected in a similar analysis of pollen proteins of P. zonale. © 1992 Springer-Verlag.