Effects of fertilization of male gametes with heavy-ion beam irradiation on embryo and endosperm development in Cyrtanthus mackenii

Heavy-ion beams are widely used for mutagenesis. The type and size of the induced mutations vary depending on the ion species and velocity. DNA damage response of male gametes during pollen tube growth has been investigated using heavy-ion beam irradiation to the pollen of Cyrtanths mackerii (Amaryllidaceae), indicating that DNA damage induced by argon-ion beam is more difficult to repair than that by carbon-ion beam. In this study, we investigated the effects of DNA damage or mutations in the male gametes with argon-ion irradiation on double fertilization and subsequent embryo and endosperm development and compared the results with carbon-ion irradiation. In immature seeds after pollination with argon-ion-irradiated pollen grains at 10 Gy, there were two types of embryo sacs with embryo and endosperm and with egg cell/zygote and endosperm. The proportion of embryo sacs in the latter type was higher when using argon-ion-irradiated pollen than carbon-ion-irradiated pollen at 40 Gy, suggesting that qualitative differences between the two kinds of irradiation influenced embryo development. In many endosperms after pollination with the irradiated pollen, abnormal chromosome separation and enlarged endosperm nuclei were observed. This indicated that the chromosomal abnormalities in the irradiated male gametes were transmitted to the endosperm nuclei. The enlarged nucleus formation was higher in pollen irradiated with an argon-ion beam than in that with a carbon-ion beam. In conclusion, argon-ion beams, even at low doses, induce distinctive development of embryo and endosperm, making them valuable for investigating double fertilization.