Occurrence, Ultrastructure and Developmental Features of Nuclear Inclusions in the Tribe Antirrhineae (Scrophulariaceae). I. Amorphous Inclusion

SUMMARY

Ultrastructural research carried out on the tribe Antirrhineae (Scrophulariaceae—Scrophularioideae) pointed out how amorphous nuclear inclusions (NI) are typical constituents of the differentiated cells of leaf chlorenchyma in 13 genera coming from both Old and New World (Acantorrhinum, Anarrhinum, Antirrhinum, Asarina, Chaenorrhinum, Cymbalaria, Gambetta, Kickxia, Lophospermum, Mabrya, Maurandya, Misopates and Saccularia). They have been observed in 86 out of 87 examined specimens, coming from different sources and belonging to 58 taxa, but with a varying frequency according to single taxon. High magnifications show that amorphous, spheroidal nuclear bodies (A-type) have a not well-defined granular or minutely fibrillar substructure, mainly composed of thinner fibrils, about 2.5–3.0 nm in diameter, and secondary of filaments about 8.0–9.0 nm wide. With regard to their chemical composition, positive reaction to mercuric bromophenol blue on semithin sections proves their essentially proteinaceous nature, even if enzymatic digestion tests on sections embedding in Epon-Araldite gave negative results. In the genus Cymbalaria only the amorphous material show a peculiar modification during leaf development. Its ultrastructure turning to a condensed arrangement consisting of striations or strands about 14–15 nm wide and spaced 27–30 nm each other. We provide a structural model where each strand consists of a single filament of about 9.0 nm diameter, coiled as a tight helix. Such a model proves how the paracrystalline inclusion (C2-type) is the product of secondary crystallization of the amorphous one. Investigations regarding first stages of amorphous inclusion deposition inside the chlorenchyma cell nuclei of the Antirrhineae and the occurrence in some specimens of other NI types together with amorphous one, are reported and discussed.