Dynamics of female flower and seed growth and development in Quercus dentata

Objective This paper aims to elucidate the reproductive cycle and developmental timing characteristics of female flowers in Quercus dentata.

Method This study used artificially pollinated female flowers at different developmental stages as experimental materials. The external morphology, seed development process, and abortion dynamics of female flowers and ovaries at different developmental stages before and after pollination were observed through morphological and histological examination methods, such as paraffin section, as well as physiological indicators.

Result (1) Throughout the entirety of female flower’s growth and development, the spiny bracts underwent a gradual process of hardening, while simultaneously transitioning from a green to yellow hue. Additionally, exhibited a continuous reduction in size, while the style underwent a shortening process. The ovary’s volume, on the other hand, experienced a continuous expansion, with the outer shell gradually thickening, ultimately culminating in the formation of brown seeds at approximately 140 d post-pollination. (2) Observation of paraffin sections showed that at 17 d after pollination, ovule was completed; at 30 d after pollination, the embryo sac matured; at 38 d after pollination, the primary endosperm nucleus appeared, and the pro-embryo formed; after about 13 d of dormancy, it underwent differentiation of globular embryo, heart-shaped embryos, torpedo-shaped embryos, and cotyledon embryos in sequence. As a nourishing tissue, the endosperm had always been in a highly divided state, and was fully absorbed and utilized by the cotyledons during the seed maturation stage, ultimately harvesting mature seeds without endosperm. (3) It was preliminarily confirmed that there were two peak periods of abortion in the entire growth cycle of Q. dentata, which were respectively at 69 d and 99 d after pollination. (4) The appearance of seed abortion was mainly manifested as browning of ovary wall of aborted embryo, shrinking of ovule, and microstructure was mainly manifested as abnormal development of integument, embryo malformation or empty embryo sac.

Conclusion This study establishes the relationship between external morphological changes and internal anatomical characteristics during the differentiation of female flowers and seed formation in Q. dentata. It provides the theoretical basis for future research on the embryology, the mechanism of flowering and fruiting, and embryo abortion mechanism of Quercus.