Li Fangdi, Zhang Xinyu, Zhang Shuo, Ma Lulu, Yue Zhonghui, Li Wei
Key Laboratory of Botany in Heilongjiang Province, College of Life Sciences and Technology, Harbin Normal University, Harbin, 150025, China.
Co-Innovation Center for Sustainable Forestry in Southern China, College of Forestry and Grassland College of Soil and Water Conservation, Nanjing Forestry University, Nanjing, 210037, China.
Protoplasma. 2025 Mar 12. doi: 10.1007/s00709-025-02051-3.
The genus Senecio, which is a basal angiosperm group, holds significant importance for evolutionary and phylogenetic research. It is notable for possessing male meiotic characteristics that are rarely observed in most angiosperms. However, the current understanding about male meiosis in Senecio remains incomplete. Here, we traced the cell morphological characteristics of microsporogenesis, and male gametophyte development of Senecio cannabifolius was observed by transmission electron microscopy. The results showed that the microspore mother cells were surrounded by callose; the cytokinesis was simultaneous; the tetrad was tetrahedral; and the mature pollen was two-celled pollen with three germination pores. During the meiosis of microspore mother cells, there were abundant organelles in the cytoplasm at leptotene stage. Obvious and clear synaptonemal complex was found in pachytene stage. In the prophase I stage, the number of organelles in the cytoplasm decreased; the cristae of mitochondria decreased; and the electron density of plastids was low. It began to recover at the metaphase I and formed an obvious organelle band in the anaphase I, which separated the two daughter nuclei and contained abundant organelles. During this period, the organelles in the cytoplasm changed regularly, which was the phenomenon of cytoplasmic reorganization. The pollen wall was formed at the late uninucleate stage; the pollen wall was mature at the binucleate microspore stage; and the pollen has abortion phenomenon. These results for the first time revealed the ultrastructure of microspores and male gametophytes during the development of S. cannabifolius and enriched the understanding of the formation of pollen grains by microspores in Compositae plants.
千里光属是一个基部被子植物类群，对进化和系统发育研究具有重要意义。它以具有大多数被子植物中罕见的雄配子减数分裂特征而闻名。然而，目前对千里光属雄配子减数分裂的了解仍然不完整。在此，我们追踪了小孢子发生的细胞形态特征，并通过透射电子显微镜观察了大麻叶千里光雄配子体的发育。结果表明，小孢子母细胞被胼胝质包围；胞质分裂为同时型；四分体为四面体型；成熟花粉为具有三个萌发孔的二细胞花粉。在小孢子母细胞减数分裂过程中，细线期细胞质中有丰富的细胞器。粗线期发现明显且清晰的联会复合体。在前期I阶段，细胞质中的细胞器数量减少；线粒体嵴减少；质体的电子密度较低。在中期I开始恢复，并在后期I形成明显的细胞器带，将两个子核分开，且含有丰富的细胞器。在此期间，细胞质中的细胞器有规律地变化，这是细胞质重组现象。花粉壁在单核晚期形成；花粉壁在二核小孢子期成熟；且花粉存在败育现象。这些结果首次揭示了大麻叶千里光发育过程中小孢子和雄配子体的超微结构，丰富了对菊科植物中小孢子形成花粉粒的认识。
