Anther and ovule development in Camellia japonica (Naidong) in relation to winter dormancy: Climatic evolution considerations

- Bract differentiation spiral centripetally, stamen appeared circular centrifugally.
- No pseudopollen in anther, ovules possessed integumentary tapeum and hypostase.
- The pollen and ovule of Naidong stay in gametophyte stage in winter.
- Winter dormancy may be a characteristic evolved with the climates changes.

The Camellia japonica (Naidong) population in Qingdao, Shandong province is the only one in temperate areas in China. While this population has been present in this area since the tertiary, its has evolved independently after that. To date, there are no reports on its embryology, and no research on the connection between embryology and climate. Here, we studied anther and ovule development of C. japonica (Naidong) using light and scanning electron microscopy, in order to determine the characteristics of early flower development, microsporogenesis, microgametogenesis, megasporogenesis and macrogametogenesis in this plant. We observed basic anther wall formation, glandular tapetum and successive microsporocyte cytokinesis. Moreover, microspores tetrads were mostly tetrahedral and occasionally symmetrical, we did not observe pseudopollen grains as previously reported for Camellia. The ovary was superior and presented axial placentation and anatropous, bitegmic ovule, allium type of embryo-sac, integumentary tapetum and hypostate which may provide winter cold temperature resistance. The early flower development sequence placed C. japonica (Naidong) in a most primitive branch of the phylogenetic tree compared to other species. The embryo characteristics and the development of C. japonica (Naidong) are significant for phylogeny research of Theoideae, as the taxonomy of this family is currently problematic at all levels. Moreover, this information is also useful flowering induction as a possible horticultural application. Flower buds went in dormancy during winter as gametophyte state, a characteristic evolved in C. japonica (Naidong) in response to the climates changes.