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

SUMMARY

Inclusions with tubular substructure occurring in the nuclei of mesophyll chlorenchyma cells are peculiar to the genus Linaria. The inclusion consists of layers of parallel tubules with outer diameter of about 20–25 nm and central lumen about 7.0–8.0 nm. The direction of the tubules in each layer is offset 60° with respect to the tubular direction in the adjacent layers. The distance between tubules belonging to the same layer or to adjacent ones is 14–15 nm. The research were carried out on 54 samples corresponding to 36 taxa of Linaria; in 29 of them we found intranuclear inclusions. Observing the biogenesis of such structures, the tubules in young, incompletely differentiated mesophyll cells start to organize from a minutely fibrillar material which deposits just close to the granular pars of nucleolus. We provide a ultrastructural model in which a tubule consists of two filaments, about 8.0–9.0 nm in diam., wound around a central lumen. Besides we suggest that each of these filaments is itself made up of thinner fibrils, about 2.5–3.5 nm thick, on the ground of everything founded in the first stages of inclusion deposition. The structural interrelationship between tubular inclusions in Linaria and amorphous ones in the other genera of Antirrhineae is discussed.