9630111 Mogensen The pollen grain of flowering plants produces two sperm cells, each of which is utilized in a fertilization event. One sperm fuses with the egg to produce the embryo, and the other sperm fuses with the polar nuclei to produce the stored food within the seed. In corn, the two sperm cells are not recognizably different from each other based on morphology, however, a molecular probe has recently been developed that allows the identification of one sperm cell from the other within pollen and pollen tubes. The probe is based on the recognition of a Beta chromosome-specific DNA sequence. In corn lines containing two Beta chromosomes, only one of the sperm cells receives the Beta chromosomes, and this sperm cell preferentially fertilizes the egg. The use of this probe will form the basis of the research project. Using fluorescence in situ hybridizaiton analysis, we propose to: 1) Directly study B chromosome behavior during pollen development. 2) Track a given sperm type during pollen tube growth. 3) Separate the two sperm types from each other using flow cytometry and cell sorting. 4) Compare the two sperm types with regard to their fertilization abilities in vitro. This research promises to provide long sought after knowledge about basic aspects of Beta chromosome and sperm cell behavior, and will set the stage for further studies on sperm-specific characterizations at the biochemical and molecular levels. Such information will be of direct importance to sexual reproduction in maize specifically, and flowering plants in general.
