Abstract
Double fertilization is unique reproductive system to flowering plants. One of two sperm cells delivered by the pollen tube fertilizes the egg cell to produce the embryo and the other fertilizes the central cell to produce a nutritional tissue, the endosperm. Genes involved in gamete fusion have been identified. However, dynamics of two sperm cells deep in the female tissue, including the long lasting issue of preferentiality fertilization, remains unknown. In this study, we observed 132 examples of double fertilization. Migration of sperm cells during pollen tube discharge is finished within 20 sec and the maximum velocity was 10 μm/sec. Fertilization in egg and central cells occurred in 8.4 ± 4.1 min, 8.5 ± 3.1 min respectively without preference of order. Furthermore, when we marked two sperm cells the position in pollen tube by photo-conversion of mKikGR, front sperm cell fertilized egg and central cell equal frequency. This result suggests that the target of isomorphic Arabidopsis sperm cells is not determined in pollen tube. Actual behavior of gametophytic cells provide us insights in to the mechanism of double fertilization.
