Electron Microscope Observations on Intranuclear Paracrystals in Some Pteridophyta

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Abstract
77 species of Pteridophyta were investigated at the electron microscope. In mesophyll cells of 59 species an impressive occurrence of intranuclear paracrystals was observed. Their sizes are approximately 1–3 μm varying according to the age of the plant. The paracrystals are usually polygonal-shaped but different forms are frequently encountered. At higher magnification a crystal lattice pattern can be resolved. Its substructure consists of a series of electron-opaque parallel subunits alternated with others whose electron opacity is less evident. The centre to centre spacing between two electron-opaque subunits is about 120 Å. A nonspecific proteolytic enzyme (pronase) has been successfully tested, showing the essential proteic nature of the nuclear paracrystals. In general terms a correlation of paracrystals with the aging of the plant is indicated. No inverse size relationship, as reported by other authors, between nucleolus and these paracrystal-line formations was observed. Taxonomic perspectives have also been taken in account. The fact that paracrystals have not been detected in those Pteridophyta which seem to be archaic (Psilotopsida, Lycopsida, Filicopsida Eurosporangiatae and Protoleptosporangiatae) deserves special mention.