Identification of oleoresin in epoxy-embedded slash pine tissue

Sudan black B stains oleoresin blue-black in epoxy-embedded material as well as in living tissue. The Sudan black B staining properties of oleoresin are similar to those of lipid, but it can be distinguished from tannin, which stains brown. Pratically all oleoresin present in resin ducts and intercellular spaces, and much of that contained in epithelial and ray cells, is extracted in preparatory procedure for electron microscopy. A fixation procedure is proposed which preserves significantly more oleoresin in situ. The use of Sudan black B enables one to localize oleoresin by light microscopy, and permits direct comparison of adjacent sections of epoxy-embedded material at the ultrastructure level. Ultrastructurally oleoresin and lipid possess similar electron densities and can be distinguished from the highly electron-opaque tannin deposits.