Secondary pit connections in Hildenbrandia (Rhodophyta, Hildenbrandiales)

Abstract

Scanning electron microscopic study demonstrates an abundance of secondary pit connections in three species of Hildenbrandia: H. crouanii, H. occidentalis and H. rubra. Usually each cylindrical cell in a vertical file is surrounded laterally by about six files of nonkindred cells. Secondary pit connections are established between most or all of the laterally adjacent files. Even subapical cells may possess secondary connections. Fluorescence microscopy using a DNA-specific fluorochrome confirms ultrastructural indications that cells of Hildenbrandia are uninucleate. The combination of multiple secondary pit connections and a uninucleate condition supports the view of Cabioch & Giraud that secondary pit connections in this group are produced directly—without the formation of conjunctor cells as is typical of most red algae.

The abundance of secondary pit connections in these anatomically simple crusts is consistent with a mechanical role, that of promoting coherence of the vertical filaments.