Combined cryo- and thin sectioning (TEM) in the elucidation of mimosoid tetrad/polyad ultrastructure

Cryosections (freeze-sections) of tetrads/polyads and their subsequent examination in the SEM complement traditional methods (LM, SEM, and TEM) by providing both a dynamic three-dimensional overview of polyad morphology and clarifying aperture morphology, internal wall characters and tetrad/polyad cohesion mechanisms. Cryosections of Dinizia tetrads reveal that cohesion is maintained through adhesion/fusion of the apices of clavate elements in localized regions of the subproximal and proximal walls — a feature not discernible using traditional SEM preparations. Cryosections of the globose 20-grained polyads of Parkia species reveal small central grains and triradiate-shaped proximal apertures — features unobservable or misinterpreted using traditional LM, SEM and TEM methods. In Anadenathera polyads, cryosections have clarified the nature and distribution of small gaps present in the lateral and proximal walls of individual grains.