University of Connecticut, Department of Ecology and Evolutionary Biology, 75 North Eagleville Road, Storrs, CT 06269, USA.
Ann Bot. 2011 Jun;107(8):1279-86. doi: 10.1093/aob/mcr079. Epub 2011 Apr 12.
The maternal gametophytic calyptra is critical for moss sporophyte development and ultimately sporogenesis. The calyptra has been predicted to protect the sporophyte apex, including the undifferentiated sporogenous region and seta meristem, from desiccation. We investigate the hypothesis that this waterproofing ability is due to a waxy cuticle. The idea that moss calyptrae are covered by a cuticle has been present in the literature for over a century, but, until now, neither the presence nor the absence of a cuticle has been documented for any calyptra.
The epidermis of the calyptra, leafy gametophyte and sporophyte sporangia of the moss Funaria hygrometrica were examined using scanning and transmission electron microscopy. Thicknesses of individual cuticle layers were quantified and compared statistically. The immunochemistry antibody (LM19) specific for pectins was used to locate cell wall material within the cuticle.
A multi-layered cuticle is present on the calyptra of F. hygrometrica, including layers analogous to the cuticular layer, cell wall projections, electron-lucent and electron-dense cuticle proper observed in vascular plants. The calyptra rostrum has a cuticle that is significantly thicker than the other tissues examined and differs by specialized thickenings of the cuticular layer (cuticular pegs) at the regions of the anticlinal cell walls. This is the first documentation of cuticular pegs in a moss.
The calyptra and its associated cuticle represent a unique form of maternal care in embryophytes. This organ has the potential to play a critical role in preventing desiccation of immature sporophytes and thereby may have been essential for the evolution of the moss sporophyte.
母体配子体帽对于藓类植物孢子体的发育和最终的孢子发生至关重要。帽被预测具有防水功能，可保护孢子体的顶端，包括未分化的孢子发生区和刚毛分生组织，免受干燥的影响。我们假设这种防水能力归因于蜡质的角质层。在文献中，关于藓类植物帽被角质层覆盖的观点已经存在了一个多世纪，但直到现在，还没有文献记录任何帽的角质层的存在或不存在。
使用扫描和透射电子显微镜检查藓类植物 Hygrometrica 的帽、有叶配子体和孢子体的囊的表皮。量化并比较了单个角质层层的厚度。使用针对果胶的免疫化学抗体（LM19）来定位角质层内的细胞壁物质。
在 Hygrometrica 的帽上存在多层角质层，包括类似于角质层、细胞壁突起、在维管植物中观察到的电子透明和电子致密角质层的层。帽的喙部具有比其他检查组织明显更厚的角质层，并且在细胞的细胞壁突起处角质层层的特殊增厚（角质层钉）有所不同。这是首次在藓类植物中记录到角质层钉。
帽及其相关的角质层代表了胚胎植物中一种独特的母体保护形式。该器官有可能在防止未成熟孢子体干燥方面发挥关键作用，因此对于藓类植物孢子体的进化可能是必不可少的。
