Imbibition of white spruce seeds and somatic embryos: A study of morphological changes in an environmental scanning electron microscope and potassium leakage

Summary Potassium leakage and morphological changes during imbibition of white spruce [Picea glauca (Moench) Voss] seeds and somatic embryos were investigated. A single desiccated somatic embryo, a single somatic embryo exposed to a high relative humidity environment for 2 d, and a single dry zygotic embryo leaked similar amounts of potassium over a 120-min period of imbibition in liquid germination medium. A seed without a seed coat leaked two and eight times more potassium than a single whole seed and a single zygotic embryo, respectively. Nearly 50% of the potassium leaked for all tissues was leaked within the first 20 min of imbibition. Exposure of somatic embryos to an environment with high relative humidity resulted in a reduction in the percentage of potassium leaked after 80 and min to levels equivalent to those for zygotic embryos. Using an environmental scanning electron microscope, we found that desiccated somatic embryos and dry zygotic embryos had wrinkled surface cells, with cells in the surface of zygotic embryos being more shrunken in appearance. Imbibition of both types of embryos in water resulted in turgid surface cells after 2 h. Imbibition in liquid germination medium did not cause much hydration of surface cells, which still had wrinkled appearances after 2 h. Finally, imbibition on filter paper on semisolidified germination medium resulted in slower hydration of somatic and zygotic embryos. Cells near the medium appeared hydrated while cotyledon surface cells furthest from the medium resembled cells in desiccated embryos.     

Adhesion of intermediate filaments and lipid droplets in adrenal cells studied by field emission scanning electron microscopy

High-resolution field emission scanning electron microscopy was used to study the organisation of intermediate filaments around lipid droplets and their binding to these droplets, in primary culture of bovine adrenal cells. Whole-mount preparations of intermediate filaments and bound lipid droplets were prepared from cells grown on Formvar-coated grids and processed by freeze-drying. Intermediate filaments were seen as an interconnected network enveloping the entire droplet. The bound filaments appear to be directly adherent to the surface of the droplet and hence take on its curved contour. The binding of the filaments to the droplets was determined by means of tilting. This study provides a new approach to investigate the cytoskeleton and its associated structures with high-resolution three-dimensional images.     

Visualization of the cytostome in Trypanosoma cruzi by high resolution field emission scanning electron microscopy using secondary and backscattered electron imaging

High resolution scanning electron microscopy was used to analyze the surface of epimastigote, amastigote and trypomastigote forms of Trypanosoma cruzi. Significant differences were observed between these forms and in different areas of the same cell. The cytostome found in amastigote and epimastigote forms could be easily visualized in images, which resemble those obtained only using the freeze-fracture technique. In contrast to other areas of the cell surface, the region of the cytostome, localized close to the flagellar pocket, showed a rugous surface and an opening with a diameter of 90 nm. Gold-labeled concanavalin A binds to the whole cell surface. However, the extent of binding was much higher in the region of the cytostome. The results obtained show that high resolution scanning electron microscopy is a powerful technique for analyzing the surface of protozoa.     

A scanning electron microscope study of ectodermal differentiations in the caudal mantle epithelium of embryos and juveniles of Loligo vulgaris,Loligo forbesi and Sepia officinalis

Summary

The mantle epithelium of embryos and early juveniles of the squids Loligo vulgaris and Loligo forbesi and the cuttlefish Sepia officinalis was studied using scanning electron microscopy. In embryos of L. vulgaris and L. forbesi, previously undescribed epidermal structures were found. They are missing in S. officinalis embryos. These so-called “extruding structures” are located near Hoyle's organ and first appear at stage XIII of Naef. At the same embryonic stage, Hoyle's organ starts to differentiate and “uniform-type” ciliated cells become visible in the epidermis of both L. vulgaris and L. forbesi. Directly after hatching the epidermis of the species examined starts to slough off and finally the extruding structures, Hoyle's organ and both types of ciliated cells of the mantle epithelium disappear. The function of the extruding structures remains obscure.