Organization of the actin cytoskeleton during megasporogenesis in Gasteria verrucosa visualized with fluorescent-labelled phalloidin

The organization of the actin cytoskeleton was studied duringmegasporogenesis in Gasteria verrucosa. Ovules were gently squashed to set free meiocytes, dyads and tetrads. The unfixed cells were permeabilized with Nonidet P-40 and DMSO, and actin filaments were visualized with fluorescent-labelled phalloidin. During premeiosis, actin filaments elongated and were distributed throughout the cytoplasm. During prometaphase actin filaments encaged the future area of chromosome transport. At metaphase, bundles of fluorescent actin filaments were observed in the spindle zone. In the dyad and tetrad, F-actin was redistributed. A large quantity of actin filaments marked the functional megaspore in particular. Before pachytene, at diakinesis and after the selection of the megaspore, actin filaments elongated, which coincided with an increase in the cell volume. Comparison of these data with the findings on the microtubular arrays during megasporogenesis in Gasteria leads to the conclusion that actin filaments and microtubules may co-distribute at several stages during megasporogenesis, i.e. in phragmoplasts and in spindles, as has recently been reported for the process of microsporogenesis in Gasteria.