Epithallial and initial cell fine structure in species of Lithothamnion and Phymatolithon (Corallinales, Rhodophyta)
Epithallial and initial cell fine structure in species of Lithothamnion and Phymatolithon (Corallinales, Rhodophyta)
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Lithothamnion 和 Phymatolithon 物种（珊瑚目、红藻门）的上皮细胞和初始细胞精细结构
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发表时间：
2002
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通讯作者：
C. M. Pueschel
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作者：
S. Wegeberg;C. M. Pueschel
摘要应用透射电镜技术研究了石羊膜属三种植物的上皮细胞、近端上皮细胞和原始细胞的超微结构。冰川湖corallioides和L. sonderi和四种Phymatolithon：P. laevigatum，P. purpureum，P. lenormandii，和P. calcareum（Cormichiaceae，Melobesioideae亚科）。用于划分石羊膜属的主要特征之一是其上皮细胞的喇叭形形态。超微结构检查表明，这种喇叭状外观是由完整上皮细胞的最外层细胞壁的梯形轮廓产生的，结合脱落上皮细胞的残余近端壁的存在。不像大多数珊瑚物种的超微结构研究，没有三个物种的Lithothamnium有叶绿体在他们的上皮细胞。没有叶绿体区分上皮细胞从叶绿体丰富的初始细胞，使这些细胞类型的容易歧视。广泛的壁向内生长的原始细胞的远端面上开发的初始细胞分裂后，产生上皮细胞和新的初始细胞，向内生长的继承新形成的上皮细胞。细胞壁的脱钙作用是上皮细胞更新过程的一部分;随后可能发生再钙化。在L.的残余近端壁和远端上皮细胞表面之间的壁层中存在继发性钙化。glaciale和L.珊瑚状。石羊膜corallioides是独特的，在每个上皮细胞的远侧表面上具有电子致密的半球形结构，这一功能可能被证明是一个有用的分类特征。在Phymatolithon中，每根细丝的上皮细胞数量从零到三个不等。终末上皮细胞呈圆顶状，比亚终末上皮细胞和起始细胞大得多。表面上皮细胞的外表面被一层厚的有机材料覆盖，其中含有提取的CaCO 3小晶体的轮廓，但钙化非常轻。看起来健康的上皮细胞的叶绿体类囊体间距类似的盘状叶绿体的亚叶细胞。最初准备分裂的细胞被厚厚的有机壁包围。分裂的衍生物在大小上相等，直到它们扩大，这对共同被旧的原始细胞的持久壁包围。下部细胞，即新的原始细胞，发育了远壁向内生长，而上部细胞，即新的上皮细胞，继承了亲本原始细胞的向内生长。即使在衰老的上皮细胞中，远端壁向内生长仍然存在。叶上细胞形态在泡壳石属和石羊膜属的分类分离中起着重要作用。上皮细胞的精细结构表现出额外的，系统有用的字符，如叶绿体的存在下Phymatolithon的上皮细胞和他们的情况下，从上皮细胞的Lithothamnion，这是一致的Phymatolilhon的识别。超微结构的研究也为正确鉴别假石中的上皮细胞和原始细胞提供了新的标准。
Abstract Transmission electron microscopy was used to study the ultrastructure of epithallial, subepithallial, and initial cells in three species of Lithothamnion: L. glaciale, L. corallioides, and L. sonderi, and four species of Phymatolithon: P. laevigatum, P. purpureum, P. lenormandii, and P. calcareum (Corallinaceae, subfamily Melobesioideae). One of the principal characters used to delimit Lithothamnion is the flared morphology of its epithallial cells. Ultrastructural examination showed that this flared appearance is produced by the trapezoidal outline of the outermost cell wall of the intact epithallial cell, incombination with the presence of the remnant proximal wall of shed epithallial cells. Unlike most coralline species studied ultrastructurally, none of the three species of Lithothamnion had chloroplasts in their epithallial cells. Absence of chloroplasts distinguished epithallial cells from chloroplast-rich initial cells, allowing easy discrimination of these cell types. Extensive wall ingrowths developed on the distal face of initial cells; upon division of an initial cell to produce an epithallial cell and a new initial cell, the ingrowths were inherited by the newly formed epithallial cell. Decalcification of cell walls occurs as part of the process of epithallial cell turnover; subsequent recalcification may then occur. Secondary calcification was present in the wall layer between the remnant proximal wall and the distal epithallial cell surface in L. glaciale and L. corallioides. Lithothamnion corallioides was unique in having an electron-dense hemispherical structure on the distal face of each epithallial cell; this feature may prove to be a useful taxonomic character. In Phymatolithon, the number of epithallial cells per filament varied from none to three. Terminal epithallial cells were domed and much larger than the subterminal epithallial and initial cells. The outer face of the surface epithallial cell was covered by a thick layer of organic material containing the outlines of extracted small crystals of CaCO3, but calcification was very light. Healthy-looking epithallial cells had chloroplasts with thylakoid spacings similar to that of the discoidal chloroplasts of subepithallial cells. Initial cells preparing to divide were surrounded by a thick organic wall. The derivatives of the division were equal in size and until they enlarged, the pair was collectively surrounded by the persistent wall of the old initial cell. The lower cell, the new initial cell, developed distal wall ingrowths, whereas the upper cell, the new epithallial cell, inherited the ingrowths of the parent initial cell. Distal wall ingrowths were still present even in senescent epithallial cells. Epithallial cell morphology has played an important role in the taxonomic separation of Phymatolithon from Lithothamnion. Epithallial fine structure demonstrates additional, systematically useful characters, such as the presence of chloroplasts in the epithallial cells of Phymatolithon and their absence from epithallial cells in Lithothamnion, that are consistent with the recognition of Phymatolilhon. Ultrastructural study also provides new criteria for the proper identification of epithallial and initial cells in Phymatolithon.