J Integr Plant Biol. ›› 1965, Vol. 13 ›› Issue (2): -.

• Research Articles •    

Cytological Studies of the Double Fertilization in Rice

S. H. Wu and C. K. Tsai   

Abstract: Detailed studies on the process of double fertilization in rice were conducted in the present work. The results are summarized as follows: 1. In the embryosac 30 minutes after anthesis, the pollen tube has already reached the micropyle in every specimen. In some cases, it has even entered further into the embryosac and discharged its contents, including the two male gametes. 2. 1½ hours after anthesis, the male gamete enters into the egg cell. As soon as it comes in contact with the egg nucleus, it increases in size. 2 hours after anthesis, the male nucleus is found inside the female one. A male nucleolus is now clearly discernible. 3. The male nucleolus is gradually growing until it reaches the size of the female one, and then the fusion of the two takes place. The fusion is generally completed and the zygote is formed 7 hours after anthesis. 4. The first mitotic division of the zygote occurs 9 hours after anthesis. 5. The fusion of the male gamete and the polar nucleus proceeds in a similar way as that of the male and female gametes, but it takes a much shorter time usually being completed within 3 hours after anthesis. 6. The male gamete enters into one of the polar nuclei and reveals its nucleolus which increases rapidly in size and then unites with that of the polar nucleus. As soon as the union is completed, the nuclear membrane between the closely contacted parts of the two polar nuclei disappears and the primary endosperm nucleus is formed. 7. The first mitotic division of the primary endosperm nucleus begins right after its formation. 8. With the fusion of the male and female gametes and the development of the zygote, the mitochondria in the cytoplasm surrounding the nucleus increase in size and number. However, in the central cytoplasm about the polar nuclei they show no notice- able change during the fertilization process. 9. Based on the facts that in the embryosac a secondary pollen tube is often seen in every stage of the fertilization process and that additional nucleoli are also observed sometimes in the egg nucleus, the authors believe that polyspermy most probably exists in rice plants, and that this may be one of the causes of polyploid plants often found in rice field as reported by several authors.

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