Anatomy and ultrastructure of the young haustorial gland in Comandra (Santalaceae)

Abstract

The haustorial gland of Comandra (Santalaceae) originates from an internal meristem-like area in the young haustorium and involves the differentiation of a double layer of palisade-like parenchyma cells in the median region. These cells secrete substances (positive with periodic acid – Schiff s reagent (PAS)) which seem to be deposited by vesicles that migrate to the median plane to deposit their products between the cell membrane and cell wall. Cell walls in the median area become extremely thin and finally disappear, leaving a cavity filled with secretory products. The lower portion of the gland shows a distinct duct region lined with a single layer of cells secreting a fibrous, layered substance apparently by means of endoplasmic reticulum (ER) vesicles; this substance appears to be neither cellulose nor starch and cannot be called wall-like. The duct in Comandra has not been observed to reach the haustorial surface, but events at the time of penetration of host tissues remain undescribed. Despite past speculations as to the digestive function of the gland, convincing evidence supporting this or any other function is still lacking.