Ultrastructure of honey bee, Apis mellifera, sperm with special emphasis on the acrosomal complex following high‐pressure freezing fixation

Abstract

Abstract. The ultrastructure of ejaculated sperm of the honey bee, Apis mellifera L., was studied after sperm were processed by using a high‐pressure freezing fixation and freezing substitution method. The electron micrographs of samples processed by this method clearly revealed previously unobserved or unresolved fine details, particularly those in the acrosomal complex. The present study demonstrates that the acrosomal complex of honey bee sperm consists of an anterior tubular acicular apex, an enlarged spherical region, and the elongated acrosomal proper. Internally, the structures of acrosomal complex confirm the general description of the tri‐layer model; having an extra‐acrosomal layer, an acrosome vesicle, and a central acrosomal rod located in a subacrosomal cavity. The acrosomal rod terminates anteriorly with an electron dense corpuscle in an ensheathing cap at the spherical region. The electron micrographs also show the presence of a centriolar adjunct and a structure possibly of a centriolar or basal body origin. The chemical and functional aspects of these ultrastructures remain unknown.