DEVELOPMENT OF ENDOSPERM AND EMBRYO IN RECIPROCAL CROSSES BETWEEN 2X AND 4X IN RAPHANUS SATIVUS

抄録

Embryological studies were made to clarify developmental processes, leading to seed collapse in crosses between diploid Raphanus sativus (2n=18) and its autotetraploid (2n=36).
Hybrid embryos of reciprocal crosses appeared to develop normally in the early developmental stage, but in the cross, 2x×4x, they failed in general to develop beyond the globular stage because of degeneration of the endosperm. In the reciprocal cross, 4x×2x, viable hybrid seeds were produced, though their sizes were only one-fourth those of their parents.
In the 2x×4x cross, cell wall formation in the endosperm was inhibited, and abnormal vacuolization of endosperm occurred in all ovules, resulting in various nuclear irregularities and degeneration of ovules.
In the 4x×2x cross, the amount of endosperm was smaller but cell wall formation took place in it earlier than in parental endosperm. Development of the embryo was faster than in the parents.
A possible cause for the failure of viable seed formation was discussed in relation to the various abnormalities observed in various developmental stages.