CAPTURE OF MALE GAMETE DYNAMICS IN POLLEN TUBES pp. 127-134
Authors: (Tomonari Hirano and Yoichiro Hoshino, Field Science Center for Northern Biosphere, Hokkaido University, Kita 11, Nishi 10, Kita-Ku, Sapporo 060-0811, Japan, and others)
Abstract: Different types of pollen are characterized by the number of cells in the microspore at the mature stage. As a consequence of mitosis of the microspore nucleus, a large vegetative cell and a smaller generative cell are produced. In approximately 30% of plant families, further mitosis of the generative cell results in the formation of 2 sperm cells in the pollen. This type of pollen is called a tricellular pollen. In most other plant families, a generative cell and a vegetative cell are maintained in mature pollen and additional mitosis of the generative cell takes place in the elongating pollen tube. Based on the number of cells in mature pollen, the latter type of pollen is called bicellular pollen. Two significant plant families, Gramineaceae, which includes rice, maize, and wheat, and Brassicaceae, which includes Arabidopsis, are categorized into the tricellular pollen group. Therefore, considerable research has conducted on tricellular pollen at the molecular level, including the transcriptome analysis of isolated sperm cells in Arabidopsis (Borges et al. 2008), characterization of polypyrimidine tract-binding protein for pollen germination in Arabidopsis (Wang and Okamoto 2009), establishment of expressed sequence tag libraries from sperm cells in maize (Engel et al. 2003), proteomic analyses of mature pollen in rice (Dai et al. 2006), and transcript profiling compared between distinctive sperm cells of Plumbago zeylanica (Gou et al. 2009). In contrast, studies concerning bicellular pollen are rare; however, several significant works have been performed, including cDNA libraries constructed from generative cells (Xu et al. 1999; Okada et al. 2006) and characterization of the GCS1 protein involved in fertilization in generative cells of the lily (Mori et al. 2006), and isolation of Alstroemeria glsA expressed in generative cell development (Igawa et al. 2009).