Lectin-binding histochemistry of intracellular and extracellular glycoconjugates of the reserve cell zone of growth plate cartilage

The distribution of intracellular and extracellular lectin-binding glycoconjugates of the reserve cell zone of growth plate cartilage was studied in the distal radial growth plate of 4-week-old Yucatan swine using a postembedment method on Epon-embedded sections. Direct comparisons were made to articular, tracheal, and auricular cartilages not involved in endochondral ossification. All patterns of lectin binding that in the growth plate were restricted to the reserve cell zone were also patterns characteristic of tracheal, articular, and auricular cartilages. These included: (a) pericellular binding with peanut agglutinin (PNA) without prior digestion with neuraminidase; (b) pericellular binding with wheat germ agglutinin (WGA) at 24 h; (c) intracellular cytoplasmic binding to concanavalin A (CON-A), Lens culinaris agglutinin (LCA), and Lotus tetragonobolus agglutinin (LTA) after periodic acid oxidation; and (d) a lack of pericellular binding with CON-A and ricin agglutinin 1 (RCA-1) after periodic acid oxidation. We conclude that reserve zone chondrocytes lack specific phenotypic markers as defined by lectin-binding affinity that are found in the cellular zones of the growth plate that undergo calcification and vascularization. The reserve zone has identical lectin-binding affinities to the three structural cartilages used as controls. One interpretation of these results is that the reserve zone may not be involved directly in endochondral ossification, but may have a structural function in growth plate cartilage.