关键词: 大孢子发生, 配子体发育, 胚发生, 水松

Abstract: [Objective] This study aims to get insight of the systematic position of Glyptostrobus pensilis and to explore developmental abnormalities of seeds of this species based on its reproductive developmental anatomy. Further to enrich and complement the current understanding of G. pensilis in reproductive biology and to provide a theoretical basis for designing conservation strategies for this species.[Method] During the period of three years from September, 2011 to September, 2013, we observed morphological changes from cone buds emergence to seed cones formation and internal changes during megasporogenesis, gametophyte development, and embryogenesis using paraffin-embedded-sectioning and hematoxylin-staining. [Result] From September to November, the bud scales differentiated into young ovulate cones, and ovulate cones developed from December to May of following year. Fertilization took place in June. The proembryony development was from late June to July; early embryo development was during August; mature embryo development was during September. The meiotic division of the megasporocyte produced four megaspores in a linear tetrad formation. The three megaspores near the micropyle disintegrated, while the megaspore near the chalaza developed into a functional megaspore. The archegonia complex consisting of 6 to 17 archegonia covered by a layer of jacket cells with two nucleuses, were positioned terminally or few laterally. The layer of jacket cells had obvious polarity distribution. The central cell did not divide to form the egg nucleus and ventral canal nucleus. Instead, the central cell directly developed into a mature egg cell. The sperm cell enters archegonium without damage to the neck cells. The fertilization mainly occurred in the center, and occasionally upper or lower part of the archegonium. During the sperm-egg fusion process, the nucleolus of sperm nucleus broken down and gradually disappeared, then become apparent after fused with the egg nucleus. The zygote gradually moved to the bottom of the archegonia, and undergoing mitosis to form proembryony free nuclei. The fertilization is the type of pre-mitotic syngamy. The proembryony belongs to the standard type of coniferales, and has simple polyembyrony pattern. The proembryony only developed into the prosuspensor but not formed the primary suspensor. It has been observed that severe insufficient pollination during fertilization.[Conclusion] The gametophyte development and embryogenesis in G. pensilis, such as number of free nuclei of megagametophyte, archegonia and neck cells, the type and position of archegonia, development process of central cell and proembryony, were quite similar to genera Taiwania, Metasequoia, Cryptomeria, Taxodium, reflecting a closer taxonomic relationship to these genera than to genus Cunninghamia. Insufficient pollination might be an important cause for ‘empty seeds' in G. pensilis.

Key words: megasporogenesis, gametophyte development, embryogenesis, Glyptostrobus pensilis