FIB-SEM: A new technique for investigating pollen walls

The typically distinctive and elaborate external structures and sculpturing of pollen grains have been widely used in the taxonomy and systematics of the flowering plants. The family Acanthaceae is a striking example, where the widely diverse external pollen grain morphology has proved useful in determining relationships between taxa. Detailed information for external pollen wall morphology has traditionally been accumulated using light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) techniques. Internal pollen wall features from which the external sculpturing is derived, also exhibit complex and diverse characteristics, but lack investigation due to the difficult and cumbersome methods required to examine the underlying exine. Advancing technology in the field of microscopy has made it possible to view the internal structure of pollen grain walls in far greater detail and in 3D. A new technique involving precise cross sectioning or slicing of pollen grains at a selected position for examining pollen wall ultrastructure, using a focused ion beam-scanning electron microscope (FIB-SEM), has been explored and is yielding data which will prove to be of taxonomic importance. The FIB-SEM affords high resolution, 3D views for investigating internal pollen wall structure.