TRANSMISSION ELECTRON MICROSCOPE (TEM) — A USEFUL TOOL FOR THE STUDY OF EXINE ULTRASTRUCTURE OF THE FOSSIL MEGASPORE
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Abstract:
The transmission electron microscope (TEM) has an excellent performance on revealing the nanoscale structure of the most solid body. It thus has been widely used in various studies of Materials Science, Physics, Biology as well as some associated areas. Here we summarize the detailed laboratory procedures of the sample preparation for TEM, including the pretreatment process, material selection, gradient dehydration, resin preparation, embedding, polymerization, ultrathin section preparation, and staining based on our recent study of the fossil megaspore ultrastructure. By using the TEM techniques described here, the exine ultra-structure of Longhuashanispora reticuloides Lu and Ouyang, 1978, which was recovered from the Middle Devonian Givetian Shangshuanghe Formation of the Longhuashan section in Zhanyi County, Yunnan Province was investigated in detail. Its exine is composed outwardly by the innermost multilamellate zones, the basal lamina, the spongy region, and the solid region. Long-huashanispora reticuloides from the Longhuashan section shows the closest affinity with the fossil plant Leclercqia complexa by the similar spinous-verrucate biform processes and the multilamellate zones at the base of the labrum of in situ microspores of L. complexa. Longhuashanispora reticuloides shares ultrastructural and morphological characteristics of in situ spores yielded by both the heterosporous and homosporous ligulate lycopsids. Its parent plant probably represents a transitional form from the ho-mosporous ligulate lycopsids to the heterosporous ligulate lycopsids. The present study demonstrates that scientists can obtain a clear and intact TEM image of fossil megaspore through experimental procedures described here. Thus, TEM deserves to be ap-plied in the studies of other fossils with an organic wall.
