Department of Molecular Genetics, The Ohio State University, Columbus, OH 43210, USA.
J Exp Bot. 2011 Mar;62(5):1621-31. doi: 10.1093/jxb/err032.
The male germ cells of angiosperm plants are neither free-living nor flagellated and therefore are dependent on the unique structure of the pollen grain for fertilization. During angiosperm male gametogenesis, an asymmetric mitotic division produces the generative cell, which is completely enclosed within the cytoplasm of the larger pollen grain vegetative cell. Mitotic division of the generative cell generates two sperm cells that remain connected by a common extracellular matrix with potential intercellular connections. In addition, one sperm cell has a cytoplasmic projection in contact with the vegetative cell nucleus. The shared extracellular matrix of the two sperm cells and the physical association of one sperm cell to the vegetative cell nucleus forms a linkage of all the genetic material in the pollen grain, termed the male germ unit. Found in species representing both the monocot and eudicot lineages, the cytoplasmic projection is formed by vesicle formation and microtubule elongation shortly after the formation of the generative cell and tethers the male germ unit until just prior to fertilization. The cytoplasmic projection plays a structural role in linking the male germ unit, but potentially plays other important roles. Recently, it has been speculated that the cytoplasmic projection and the male germ unit may facilitate communication between the somatic vegetative cell nucleus and the germinal sperm cells, via RNA and/or protein transport. This review focuses on the nature of the sperm cell cytoplasmic projection and the potential communicative function of the male germ unit.
被子植物的雄性生殖细胞既不是自由生活的，也没有鞭毛，因此它们依赖花粉粒的独特结构来进行受精。在被子植物雄性配子体发生过程中，不对称有丝分裂产生生殖细胞，该细胞完全被较大花粉粒营养细胞的细胞质所包围。生殖细胞的有丝分裂产生两个精子，它们通过共同的细胞外基质保持连接，具有潜在的细胞间连接。此外，一个精子细胞有一个与营养细胞核接触的细胞质突起。两个精子细胞的共享细胞外基质和一个精子细胞与营养细胞核的物理联系形成了花粉粒中所有遗传物质的连接，称为雄性生殖单位。在代表单子叶植物和真双子叶植物两个谱系的物种中都发现了这种细胞质突起，它是在生殖细胞形成后不久通过小泡形成和微管伸长形成的，并将雄性生殖单位固定在一起，直到受精前。细胞质突起在连接雄性生殖单位方面起着结构作用，但可能具有其他重要作用。最近，有人推测细胞质突起和雄性生殖单位可能通过 RNA 和/或蛋白质运输促进体细胞营养细胞核和生殖精子细胞之间的通讯。这篇综述重点介绍了精子细胞质突起的性质以及雄性生殖单位的潜在通讯功能。
