Flower Bud Differentiation, Mega-micro Spore Production, and Male-female Gametophyte Development in Camellia weiningensis

Abstract

Camellia weiningensis is a typical woody edible oil tree species in the northwest alpine area of Guizhou Province, China, but its embryological development is not fully elucidated. Here, we assessed flower bud differentiation, microsporogenesis, and male-female gametophyte development in this species. We performed cytological observations of flower bud development in C. weiningensis through conventional paraffin sectioning, scanning electron microscopy, and stereomicroscopy to establish the corresponding relationships between the external morphology and internal structure. The flowers were hermaphroditic and exhibited a short flower bud differentiation time. Although pistil development occurred later than stamen development, both organs matured synchronously before flowering. The anther contained four sacs that exhibited a butterfly shape in transverse sections. The anther wall comprised the epidermis, anther chamber inner wall, two middle layers, and a glandular tapetum (from outside to inside). Microspore mother cells formed a tetrahedral tetrad through meiosis, mature pollen was two-celled with three germination pores, and the ovary comprised three to five chambers (three chambers predominated). Multiple ovules were invertedly attached to the axial placentation and exhibited double integuments and a thin nucellus. The embryo sac exhibited Allium-type development, and the mature embryo sac was seven-celled and eight-nucleated. In C. weiningensis, embryonic development does not exhibit abnormalities, and stamen development occurs earlier than pistil development. During flower bud development, the inner development process of male and female cells can be judged according to their external morphological characteristics. Our results may provide a theoretical basis for regulating flowering in and the cross-breeding of C. weiningensis.