Rearrangement of the actin filament and microtubule cytoskeleton during induction of microspore embryogenesis in Brassica napus L. cv. Topas

Changes in the actin filament and microtubule cytoskeleton were examined du ring heat- and cytochalasin D-induced embryogenesis in microspores of Brass ica napus cv. Topas by rhodamine phalloidin and immunofluorescence labellin g respectively. The nucleus was displaced from its peripheral to a more cen tral position in the cell, and perinuclear actin microfilaments and microtu bules extended onto the cytoplasm. Heat treatment induced the formation of a preprophase band of microtubules in microspores; preprophase bands are no t associated with the first pollen mitosis. Actin filament association with the preprophase band was not observed. The orientation and position of the mitotic spindle were altered, and it was surrounded with randomly oriented microfilaments. The phragmoplast contained microfilaments and microtubules , as in pollen mitosis I, but it assumed a more central position. Cytoskele tal reorganisation also occurred in microspores subjected to a short cytoch alasin D treatment, in the absence of a heat treatment. Cytochalasin D trea tment of microspores resulted in dislocated mitotic spindles, disrupted phr agmoplasts, and symmetric divisions and led to embryogenesis, confirming th at a normal actin cytoskeleton has a role in preventing the induction of em bryogenesis.