Abstract: The progeny of the nucleic male sterile (NMS) line, ms86-1, in sesame (Sesamum indicum) display 3 types of pollen: fertile, sterile, and partially sterile. The differences in the three fertility types are reflected in the morphologic features of their anthers and pollen grains. Alexander’s staining revealed blue-green staining of outer walls of partially sterile pollen grains, and the inner walls were unevenly stained magenta-red, which differed from the staining of fertile or sterile pollen grains. To explore the mechanism of partial sterility, we compared the microsporogenesis of the three fertility types by electron microscopy. The microspores of fertile plants metabolized vigorously at meiosis as massive lipid globules accumulated in the cytoplasm. Tapetal cells began to degrade at tetrad stage, and some Ubisch bodies were secreted from tapetal cells at microspore stage. A large number of Ubisch bodies were inside and around the pollen sac at pollen maturation. The pollen exine surface, with 11–13 pieces of bulged strips, was covered with abundant bacula, which formed a close cover. Sterile plants showed abnormal microsporogenesis at meiosis. Lipid globules did not appear in the microspore cytoplasm, whereas callose began to accumulate around the cell wall at meiosis. Tapetal cells did not degrade at tetrad stage, and no Ubisch bodies were secreted at the microspore stage; A large number of aborted microspores presented in the pollen sac, without any normal Ubisch bodies, in microspore maturation stage. The microspore exine accumulated with callose except for bacula. In partially sterile plants, lipid globules were observed at meiosis. Parts of the tapetal cells began to distort at microspore stage and then degraded at that stage. The degradation of tapetal cells provided nutrition for the microspores with a developmental delay rhythm, and induced them to develop into normal pollen grains. These pollen grains were relatively plump, with a few granules on the surface, while the covering layer was not formed on the pollen exine. A few Ubisch bodies were observed in the pollen sac and around microspores. The fertility types of microspores during microsporogenesis agreed with the normality or abnormality of tapetum degradation.

Key words: Sesamum indicum, nucleic male sterile, partial sterility, microspore development, ultrastructure