Basis of single-seed formation in chestnut: cytomorphological observations reveal ovule developmental patterns of Castanea henryi

Background: Many plants, including those commonly found in the Fagaceae family, produce more flowers and ovules than mature fruits and seeds. In Castanea henryi, an ovary contains 16-24 ovules, but only one develops into a seed. The other ovules abort or otherwise fail to fully develop, but the reason for this is unknown. Such a strict reproductive screening mechanism is rare in plants.

Methods: In this study, controlled pollination scheme were adopted, and conventional paraffin embedding and semi-thin sectioning techniques, followed by microscopy, were used for cytological studies of ovule development in C. henryi.

Results: Pollination affected not only the process of ovule development, but also the proportion of ovules that formed mature embryo sacs. Approximately 53.53% of the ovules in the pollinated treatment developed normally, while only 16.55% of the ovules in the unpollinated treatment developed into mature embryo sacs with a seven-cell, eight-nucleated structure. Failure to form mature embryo sacs and the abnormal divisions of the zygote, respectively, were the reasons for the pre- and post-fertilization ovule failures. Our findings not only provide basic information on the reproductive biology and also information on seed production of C. henryi.