Abstract
In order to clarify the process of seed abortion of prarthenocarpic Hiratanenashi persimmon, a comparative histology of the developing ovules of Hiratanenashi and Fuyu, the latter having strong seed-producing abilities, was studied.
1. The developing process of normal ovule of Hiratanenashi was very similar to that of Fuyu until bloom. Embryo-sac mother cell in Hiratanenashi was formed in nucellus portion 15-18 days before bloom. Normal embryo-sac with an egg cell, synergid cells, antipodal cells and polar nuclei was completed 2-3 days before bloom in both the cultivars.
2. Fifty% of ovules in Hiratanenashi fruits and 20% of those in Fuyu fruits were abnormal ones with undifferentiated egg cell and polar nuclei.
3. In the fertilized ovules of both the cultivars, 10 or more free nuclei appeared 6-8 days after bloom, and soon the endosperm became completely cellular. In the case of Hiratanenashi, some ovules contained in complete cellular endosperm even at the beginning of its formation, and most of them were found a little later to contain the collapsed endosperm due to the abnormal division of cells. Therefore, it seems likely that the embryo may cease the growth as a result of the degeneration of endosperm.
4. From an immature embryo of Hiratanenashi 6-10 weeks after fertilization, a single young plant-not the one redifferentiated from callus was reproduced by using tissue culture technique.
5. These findings that 1) incomplete ovules are abundantly present in this cultivar, 2) the degradation of endosperm occurs partly due to the insufficient formation of cellular endosperm and mainly due to the abnormal division of endosperm cells, would give the reasons for the seed abortion of Hiratanenashi persimmon.
