Callose in Frankia‐Infected Tissue of Datisca glomerata is an Artifact of Specimen Preparation

Callose, or β‐1,3‐glucan, is a plant cell wall polysaccharide that occurs endogenously at distinct sites in a variety of tissues. Callose is also formed in response to stress involving cell membrane perturbation. In sections of chemically‐fixed nodule tissue of the actinorhizal host, Datisca glomerata, callose was cytochemically detected within the Frankia‐infected cortical cells, as an extensive network of wall material surrounding the microsymbiont, but not in uninfected cortical cells. Callose formation was completely inhibited within the infected cells when 2‐deoxy‐D‐glucose, an inhibitor of callose formation, was included in the tissue fixative. The study concludes that callose deposition in the Datisca nodule infected zone is apparently a stress response to tissue preparation and fixation. However, the rapidity and extent of callose deposition primarily at the symbiotic interface in Frankia‐infected cells suggests an unusual predisposition to biosynthesis of β‐1,3‐glucan in the nodule cortical cells that is related to their interaction with the microsymbiont.