ATOMIC-FORCE MICROSCOPY OF POLLEN GRAINS, CELLULOSE MICROFIBRILS, ANDPROTOPLASTS

Atomic force microscopy (AFM) holds unique prospects for biological mi croscopy, such as nanometer resolution and the possibility of measurin g samples in (physiological) solutions. This article reports the resul ts of an examination of various types of plant material with the AFM. AFM images of the surface of pollen grains of Kalanchoe blossfeldiana and Zea mays were compared with field emission scanning electron micro scope (FESEM) images. AFM reached the same resolutions as FESEM but di d not provide an overall view of the pollen grains. Using AFM in torsi on mode, however, it was possible to reveal differences in friction fo rces of the surface of the pollen grains. Cellulose microfibrils in th e cell wall of root hairs of Raphanus sativus and Z. mays were imaged using AFM and transmission electron microscopy (TEM). Imaging was perf ormed on specimens from which the wall matrix had been extracted. The cell wall texture of the root hairs was depicted clearly with AFM and was similar to the texture known from TEM. It was not possible to reso lve substructures in a single microfibril. Because the scanning tip da maged the fragile cells, it was not possible to obtain images of livin g protoplasts of Z. mays, but images of fixed and dried protoplasts ar e shown. We demonstrate that AFM of plant cells reaches resolutions as obtained with FESEM and TEM, but obstacles still have to be overcome before imaging of living protoplasts in physiological conditions can b e realized.