An ultrastructural study of microsporogenesis in tobacco line SR1

This article provides an ultrastructural atlas of microsporogenesis in the tobacco model line SR1. The stages of cell-wall remodeling and reorganization of the intercellular channels, accompanying this process, are reported for the microspore mother cells. The meiotic changes in the cell nucleus and cytoplasm are traced. The appearance of single-, double-, or multi-membrane nuclear vacuoles in microspore mother cells and their further elimination from the nucleus are for the first time described for the genus Nicotiana as well as deviations from a normal course for this process. Intercellular chromatin migration (cytomixis) was observed in the microsporogenesis of the line SR1 and behavior of the nuclear vacuoles within the cytomictic nucleus was described for the first time. The enzymatic activity of spherosome-like vesicles in the tobacco microsporogenesis is discussed. The features of microsporogenesis in the tobacco line SR1 are compared with those of other plant species and its association with the transition from a diploid to a haploid phase of the life cycle is discussed.