Carafa A, Duckett J G, Ligrone R
Dipartimento di Scienze ambientali, Seconda Università di Napoli, via A. Vivaldi 43, 81100 Caserta, Italy.
Ann Bot. 2003 Aug;92(2):299-307. doi: 10.1093/aob/mcg140.
Placental morphology is remarkably diverse between major bryophyte groups, especially with regard to the presence and distribution of transfer cells in the sporophyte and gametophyte. In contrast, with the exception of metzgerialean liverworts, placental morphology is highly conserved within major bryophyte groups. Here we examine the ultrastructure of the placenta in Monoclea forsteri and Treubia lacunosa, basal members of the marchantialean and metzgerialean liverwort lineages, respectively. In both species several layers of transfer cells are found on both sides of the placenta, with sporophytic transfer cells exhibiting prominent wall labyrinths. Consistent with previous reports of a similar placenta in other putatively basal and isolated liverwort genera such as Fossombronia, Haplomitrium, Blasia and Sphaerocarpos, this finding suggests that this type of placenta represents the plesiomorphic (primitive) condition in liverworts. Distinctive ultrastructural features of placental cells in Monoclea include branched plasmodesmata in the sporophyte and prominent arrays of smooth endoplasmic reticulum, seemingly active in secretion in the gametophyte. These arrays contain a core of narrow tubules interconnected by electron-opaque rods, structures with no precedent in plants. Analysis of the distribution of different types of placenta in major bryophyte groups provides valuable insights into their inter-relationships and possible phylogeny.
主要苔藓植物类群之间的胎盘形态差异显著，尤其是在孢子体和配子体中传递细胞的存在和分布方面。相比之下，除了美苔目地钱外，主要苔藓植物类群内部的胎盘形态高度保守。在这里，我们分别研究了地钱目和美苔目地钱谱系基部成员福氏单角苔和多孔三列苔的胎盘超微结构。在这两个物种中，胎盘两侧都发现了几层传递细胞，孢子体传递细胞具有明显的壁迷路。与之前关于其他假定的基部和孤立地钱属（如短角苔属、单倍苔属、管叶苔属和球蒴苔属）中类似胎盘的报道一致，这一发现表明这种类型的胎盘代表了地钱中的原始状态。单角苔胎盘细胞独特的超微结构特征包括孢子体中的分支胞间连丝和配子体中明显的光滑内质网阵列，这些内质网似乎在分泌过程中活跃。这些阵列包含由电子不透明杆相互连接的狭窄小管核心，这种结构在植物中尚无先例。对主要苔藓植物类群中不同类型胎盘分布的分析为它们之间的相互关系和可能的系统发育提供了有价值的见解。
