Cell sloughing and chloroplast inclusions in Hildenbrandia rubra (Rhodophyta, Hildenbrandiales)

Abstract

Light and electron microscope studies of a specimen of Hildenbrandia rubra revealed two unusual features not found in other collections. A large portion of the crust surface was necrotic. The depth of the affected areas varied, but in some places it was great enough to remove conceptacles. Beneath the zone of dead cells, regeneration was indicated by cytokinesis in the top layer of healthy cells. Severing of pit connections in response to cell mortality is described.

Chloroplasts of both living and dead cells had conspicuous spherical inclusions, which were visible even with the light microscope. These inclusions generally had a homogeneously granular substructure. Rarely, a less dense, non-granular substance and phytoferritin were present within the inclusion. It is not known whether there is a causal connection between the presence of chloroplast inclusions and necrosis.