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Camellia oleifera is an important woody tree species in China that produces edible oil. Although sterile male C. oleifera plants play an important role in hybrid breeding, the possible cytological characteristics of pollen abortion remain unknown. To characterize the pollen abortion process, a genic petaloid-type sterile male C. oleifera ‘X1’ plant was investigated using a cytological method. The results showed that in male-fertile plants, the anthers were full and butterfly shaped, the pollen viability was as high as 97.5%, and the development of the tapetum and anther vascular bundles was normal. However, in male-sterile C. oleifera ‘X1’, petaloidy in the anther was observed, and the pollen vitality was as low as 4.5%. Pollen abortion in sterile C. oleifera ‘X1’ anthers occurred from the microspore stage to the mature pollen period. Further cytological analyses revealed an abnormally enlarged tapetum and retarded tapetum degeneration, suggesting that insufficient nutrients were provided for microspore development. Moreover, the anther vascular bundles displayed hyperplasia, and the pollen sac area became increasingly smaller, causing most anthers to be sterile and to have few pollen grains. Taken together, the results indicate that petaloid-type male sterility in C. oleifera may be attributed to abnormal development of the tapetum and anther vascular bundles. The findings clarify the pollen abortion period and the cytological characteristics of petaloid-type cytoplasmic male sterility in C. oleifera, and lay a solid foundation for the male sterile line in C. oleifera hybrid breeding.
The normal development of anthers and the formation of functional pollen are the prerequisites for successful pollination and fertilization. In this study, we observed dynamic changes in inflorescence and anther development in the chinquapin (Castanea henryi) using stereomicroscopy, light microscopy, and transmission electron microscopy. We found that cytokinesis during meiosis in microsporocytes was of the simultaneous type, and that the tetrads were mainly tetrahedral. Mature pollen grains contained two cells with three germ pores. The anther wall was of the basic type and composed of epidermis, endothecium, middle layers, and tapetum. Mature anthers had no middle layer and tapetum. The tapetum was of the glandular type. At the early microspore stage, a large number of starch granules appeared in the endothecium, which was deformed at the late microspore stage. Lipid droplets appeared in tapetum during the early microspore stage, and a few lipid droplets were still found during tapetum degeneration. The mature pollen accumulated a large amount of starch and lipids. These findings demonstrated that the anther wall provides nutrients and protection for pollen development. There is relatively stable correspondence between the external morphological characteristics of male flowers and internal structure of anther development.