Ultrastructure of Cells in the Overwintering Dormant Shoot Apex of Rhododendron maximum L.

Abstract

Tissue arrangement and cell structure of terminal leaf buds of Rhododendron maximum were observed while in the dormant overwintering condition. The apical anatomy was typical of angiosperms with a two-cell-layer tunica superior to a corpus which gives rise to a poorly defined rib meristem-pith region below. The tunica-corpus cells had thin cell walls with many plasmodesmata; cells of the rib meristem pith, cortex, and procambium had thick primary cell walls with manifold pit fields. The cells of all these regions contained large ovoid or lobate nuclei, small proplastids with lipid droplets and phytoferritin, abundant dictyosomes, lipid bodies, and small vacuoles which appeared to arise from abundant myeloid figures. Tannins produced in the myeloid vacuolar complexes accumulated in the central vacuoles of cells of the rib meristem, pith, and cortex.