Maternal Cytoplasmic Inheritance and Pollen Nucleolytic Activities in Some Poaceae species

Abstract

Cytoplasmic DNAs of male reproductive cells were examined during the pollen development of Zea mays and Triticale using fluorescence microscopy after staining with DAPI (4', 6-diamidino-2-phenylindole). Nucleolytic activities in mature pollen of Zea mays, Triticale and Triticum aestivum were analysed on SDS-DNA-gels after electrophoresis. Cytoplasmic DNAs were observed in the generative cells both in Z. mays and Triticale. However, a gradual degradation occurred later. In Z. mays, organelle nuclei (nucleoids) were undetectable in young sperm cells. In Triticale, quite a few organelle nuclei remained in the young sperm cells but completely disappeared during the maturation of sperm cells. Nuclease assay showed that two Mg²⁺-dependent and two Mn²⁺-dependent nucleases were specifically associated with the pollen protein of Z. mays and, one Mn²⁺-dependent nuclease was specifically associated with the pollen protein of Triticale. In T, aestivum, where the disappearance of organelle nuclei during maturation of sperm cells had been reported, two Ca²⁺-dependent nucleases were specifically detected in the pollen protein. These results suggest that a preferential degradation of organelle nuclei would occur in the generative and sperm cells which may result in the absence of cytoplasmic DNAs in the mature sperm cells. This preferential degradation of cytoplasmic DNA may be the root cause of maternal cytoplasmic inheritance and the pollen-specific nucleases could be responsible for the degradation.