Confocal microscopy for pollen and spore studies

What is it about?

Pollen grains and spores of terrestrial plants are microscopical objects (www.paldat.org), studied within the scope of palynology – a discipline akin to both biology and geology. Pollen grains and spores are very diverse and those of different plants differ from each other, allowing palynologists to be aware which plant produced a given pollen grain or spore. On this basis, palynological data are used for the systematics and phylogeny of different groups of extinct and living plants, dating and stratigraphy of geological deposits (http://paleobotany.ru/palynodata), studies of honeys, allergies, as well as for some other purposes. Light microscope, a workhorse of palynology, is conventionally used to observe the general morphology of pollen grains and spores, whereas scanning and transmission electron microscopes provide detailed information about their surface pattern and inner structure. Light microscope gives a lower resolution; electron-microscopical methods are laborious, expensive and destructive. We have tested pros and cons of confocal microscope for studies of fossil and modern pollen and spores. The resolution of confocal laser scanning microscope is higher than that of traditional light microscope and much lower than that of electron microscopes, as are its abilities to reconstruct the surface patterns and inner structure. On the other hand, it can provide information that is unreachable by other microscopical methods. It also allows one to study palynological objects without destroying them, that is particularly pertinent for fossil objects. For this study, we used as test objects pollen grains and spores of different morphologies, botanical affinities, and preservation. We have studied pollen grains of a living angiosperm plants and those of extinct angiosperms, which are more than 66 million years (Ma) in age, pollen grains of extinct gymnosperms (more than 170 Ma), and spores of fossil lycopsids (about 252 Ma). The structure of endoapertures in modern angiosperm pollen grains was directly observed as well as appendages and complicated wall structure in fossil angiosperm pollen grains. The ability of confocal microscope to rotate 3-D reconstructions of studied objects was very helpful. Virtual sections under arbitrary angles through 3-D reconstructions of pollen grains of gymnosperms helped us to understand their morphology in spite of the unusual preservation of these fossils. Fossil megaspores turned to be too large and too thick-walled objects for a confocal study, but some useful information also was amassed.

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