Abstract: Actin filament (AF) distribution in Zea mays pollen and Gladiolus gandavensis pollen protoplasts was localized by FITC conjugated phalloidin fluorescence microprobe. The pollen was incubated in Brewbaker and Kwack (BK) medium, and the pollen protoplasts were isolated enzymatically and cultured in K3 medium containing various supplements by a previously reported method. Samples were fixed for 30 min with 1.5% paraformaldehyde dissolved in 0.1 mol/1 phosphate buffer (pH 7), half strength of BK elements, 1 mol/1 EGTA and sucrose, stained for 30–60 min with 1 μg/ml FITC-phalloidin in the buffer solution, and observed by a fluorescence microscopy. In hydrated corn pollen grains, the AFs constituted an irregular network. Prior to germination a part of the pollen grains showed polarized pattern of Afs. At the opposite pole to the germ pore, there was a center from which AF bundles radiated and converged toward the pore, often making a spindle-shaped configuration. In just isolated gladiolus pollen protoplasts, the AFs appeared as irregular fine network. After 4–7h of culture, the AF distribution coincided in some cases with the unevenly regenerated new wall area as exhibited by FITC-phalloidin and Calcofluor White ST double staining, indicating a possible involvement of AF in wall synthesis. After 17–18 h of culture, a part of the pollen protoplasts went on germination. The AFs became polarized in such protoplasts and converged into the tubes produced, and ran longitudinally along the tubes just like in the tubes germinated from pollen grains. However, in ungerminated pollen protoplasts, the AFs behaved abnormalty, showing various irregular arrangements. When protoplasts bursted, the actin aggregates often located at the protrusion site from which the protoplasts would burst, and were discharged into the medium. In neither corn pollen nor gladiolus pollen protoplasts AFs were observed within the generative or sperm cells.

Key words: Pollen, Pollen protoplast, Actin filament, Zea mays, Gladiolus gandavensis