Anatomy and ultrastructure of the haustorium in Comandra (Santalaceae)

Abstract

The endophyte of the haustorium in Comandra and the tissues of the upper haustorium have a complex developmental and structural relationship with each other. Glands may be found near the tip of a young endophyte, providing evidence that the gland and surrounding tissues have been moved into the host as a unit. A distinct interrupted zone is present, traversed by a small number of unbranched vessels. Additionally, some apparently blind vessels in the more central portion of this zone are occluded with fibrous material which seems to be secreted by vesicles in the adjacent parenchyma. Advance into the host seems to involve crushing host cells and subsequent absorption of cell contents. It is suggested that superficial digitate cells are also crushed and that the lytic enzymes thus liberated play a role in the attack on host cells. The dark-staining non-cellular layer delimiting many parts of the endophyte seems to be made up of crushed cell walls from both partners. No cytoplasmic connections between host and parasite have been observed. Mature xylem contacts may be abutments in pit areas of host vessels or actual invasions of the latter, often with cell divisions within such invaded tracheary members. The function of the gland remains obscure.