PDF(Pubmed)
Abstract：
CONCLUSIONS: Developing bryophytes differentially modify their plasmodesmata structure and function. Secondary plasmodesmata formation via twinning appears to be an ancestral trait. Plasmodesmata networks in hornwort sporophyte meristems resemble those of angiosperms. All land-plant taxa use plasmodesmata (PD) cell connections for symplasmic communication. In angiosperm development, PD networks undergo an extensive remodeling by structural and functional PD modifications, and by postcytokinetic formation of additional secondary PD (secPD). Since comparable information on PD dynamics is scarce for the embryophyte sister groups, we investigated maturating tissues of Anthoceros agrestis (hornwort), Physcomitrium patens (moss), and Marchantia polymorpha (liverwort). As in angiosperms, quantitative electron microscopy revealed secPD formation via twinning in gametophytes of all model bryophytes, which gives rise to laterally adjacent PD pairs or to complex branched PD. This finding suggests that PD twinning is an ancient evolutionary mechanism to adjust PD numbers during wall expansion. Moreover, all bryophyte gametophytes modify their existing PD via taxon-specific strategies resembling those of angiosperms. Development of type II-like PD morphotypes with enlarged diameters or formation of pit pairs might be required to maintain PD transport rates during wall thickening. Similar to angiosperm leaves, fluorescence redistribution after photobleaching revealed a considerable reduction of the PD permeability in maturating P. patens phyllids. In contrast to previous reports on monoplex meristems of bryophyte gametophytes with single initials, we observed targeted secPD formation in the multi-initial basal meristems of A. agrestis sporophytes. Their PD networks share typical features of multi-initial angiosperm meristems, which may hint at a putative homologous origin. We also discuss that monoplex and multi-initial meristems may require distinct types of PD networks, with or without secPD formation, to control maintenance of initial identity and positional signaling.
摘要：
结论：发育中的苔藓植物不同程度地修饰其胞浆结构和功能。通过孪生形成次生胞浆似乎是一种祖先性状。刺耳孢子体分生组织中的Plasmodesmata网络类似于被子植物。所有陆生植物类群都使用纤毛（PD）细胞连接进行共质通讯。在被子植物发育中，PD网络通过结构和功能PD修饰进行广泛的重塑，并通过细胞动力学后形成额外的继发性PD（secPD）。由于胚胎植物姐妹组缺乏关于PD动力学的可比信息，我们调查了Anthocerosagrestis(hornwort)的成熟组织，Physcomitriumpatens(moss),和Marchantiapolymorpha（紫草）。就像被子植物一样，定量电子显微镜显示所有模型苔藓的配子体通过孪生形成secPD，产生横向相邻的PD对或复杂的分支PD。这一发现表明，PD孪生是一种古老的进化机制，可以在墙体扩张过程中调整PD数量。此外，所有苔藓植物配子体都通过类似于被子植物的分类单元特异性策略来修饰其现有的PD。可能需要开发具有扩大直径或形成凹坑对的II型PD形态型，以保持壁增厚期间的PD传输速率。类似于被子植物叶，光漂白后的荧光重新分布表明，成熟的P.patensphyllids中的PD渗透性大大降低。与以前关于苔藓植物配子体的单重分生组织的报道相反，我们观察到在A.agrestis孢子体的多初始基础分生组织中形成有针对性的secPD。他们的PD网络共享多初始被子植物分生组织的典型特征，这可能暗示了推定的同源起源。我们还讨论了单重和多初始分生组织可能需要不同类型的PD网络，有或没有secPD形成，控制初始身份和位置信令的维护。
