Adaptability of Scanning Electron Microscopy to Studies of Pollen Morphology

Abstract

We have explored methods to achieve excellent results in study of the pollen grain wall by using only one electron microscope, the scanning electron microscope (SEM). While the secondary electron imaging mode , the most common in use, has great value in characterizing the exine surface it is possible to obtain a more comprehensive representation of pollen grain walls by expanding the capability of the secondary mode and mak ing use of backscatter and transmission imaging detectors. In this way information is obtained about internal exine features that are likely to be more stable phylogeneticall y than the generally late-to-form surface structure. We illustrate the usefulness ofnatural and induced fractures, cryornicrotorny, thin-section examination, section deplasticization, localized acetolysis and pollen erosion by ionic bombardment in imaging exine structure. Techniques for expand ing the use of SEM in taxonomic stud ies of mature pollen grain walls are outlined in flow chart sketches and illustrated with numerous examples from angiosperm pollen.

Ontogeny of pollen grains inZingiber spectabile(Zingiberaceae)

“…Similar observations has been made for Canna, where the wall channels include electron dense material between spinules at the surface of the channelled zone. This material is presumed t o be sporopollenin that protects channel components against hydrolysis (Skvarla et al 1988). …”

Pollen morphology of the tribe Pterostegieae (Polygonaceae: Eriogonoideae)

“…For studies of the exine and endoapertural structures with SEM, the acetolysed samples were sectioned by the cryomicrotomy method (cf. Skvarla et al 1988) using a MICROM HM-500 cryostat microtome and prepared for SEM study as stated above.…”

Pollen Morphology and Ultrastructure of the Cabombaceae: Correlations With Pollination Biology

“…In order to observe transverse sections (i.e., fractured exines) with the SEM, pollen was pipetted from ethanol into a frozen mortar and then ground under liquid nitrogen with the accompanying pestle (Skvarla, Rowley, and Chissoe, 1988). In order to observe transverse sections (i.e., fractured exines) with the SEM, pollen was pipetted from ethanol into a frozen mortar and then ground under liquid nitrogen with the accompanying pestle (Skvarla, Rowley, and Chissoe, 1988).…”