Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils.
Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils.
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DOI：
10.1073/pnas.0400484101
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发表时间：
2004-07
影响因子：
11.1
通讯作者：
L. Graham;L. Wilcox;M. Cook;P. Gensel
中科院分区：
文献类型：
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作者：
L. Graham;L. Wilcox;M. Cook;P. Gensel
缺乏大量的前维管植物化石记录的britectes（否则预测的分子系统学）提出了一个主要问题，在我们的理解最早的陆地植物结构。相反，存在着神秘的寒武纪-泥盆纪微体化石（细胞管或细胞片的集合体，或两者的组合），有争议地解释为一组灭绝的早期陆地植物，称为植物。我们使用了一种创新的方法来探索这些问题：比较管和细胞片微体化石与实验降解的现代苔类作为古代早期陆地植物的类似物。下表皮表面组织，包括假根，地钱和Conocephalum conicum耐分解后腐烂的延长时间或高温酸处理（乙酰解），表明tetralization潜力。细胞片层和假根残留分别或同时发生，取决于体降解的程度。在下表皮表面脱落的类人猿在细胞类人猿的中心留下了边缘孔;这些孔在结构、直径和分布上与被称为Cosmochlaina的藻类细胞片微体化石的特征孔相似。地钱假根直径的范围与Cosmochlaina孔隙的范围重叠。大约14%的地钱营养体和40%的配子体干生物量对乙酰水解具有抗性。处理前和处理后的细胞壁自发荧光表明酚类化合物的存在，可能保护下表皮组织免受土壤微生物的攻击，并提供尺寸稳定的配子体。我们的研究结果表明，至少有一些微化石被确定为植物可能是早期地钱类苔类的遗骸，在某些方面类似于现代地钱和Conocephalum。
Absence of a substantial pretracheophyte fossil record for bryophytes (otherwise predicted by molecular systematics) poses a major problem in our understanding of earliest land-plant structure. In contrast, there exist enigmatic Cambrian-Devonian microfossils (aggregations of tubes or sheets of cells or possibly a combination of both) controversially interpreted as an extinct group of early land plants known as nematophytes. We used an innovative approach to explore these issues: comparison of tube and cell-sheet microfossils with experimentally degraded modern liverworts as analogues of ancient early land plants. Lower epidermal surface tissues, including rhizoids, of Marchantia polymorpha and Conocephalum conicum were resistant to breakdown after rotting for extended periods or high-temperature acid treatment (acetolysis), suggesting fossilization potential. Cell-sheet and rhizoid remains occurred separately or together depending on the degree of body degradation. Rhizoid break-off at the lower epidermal surface left rimmed pores at the centers of cell rosettes; these were similar in structure, diameter, and distribution to pores characterizing nematophyte cell-sheet microfossils known as Cosmochlaina. The range of Marchantia rhizoid diameters overlapped that of Cosmochlaina pores. Approximately 14% of dry biomass of Marchantia vegetative thalli and 40% of gametangiophores was resistant to acetolysis. Pre- and posttreatment cell-wall autofluorescence suggested the presence of phenolic compounds that likely protect lower epidermal tissues from soil microbe attack and provide dimensional stability to gametangiophores. Our results suggest that at least some microfossils identified as nematophytes may be the remains of early marchantioid liverworts similar in some ways to modern Marchantia and Conocephalum.