Fig. 1. Mitotic division cycles can be arrested in male gametophytes of M. vestita. (a) Untreated control cells. Gametophytes were fixed 8 hours after the time of imbibition. Nine mitotic division cycles have occurred, producing 32 spermatids and 7 sterile cells. (b) Hydroxyurea (1 mM) was present in the medium at the time of imbibition. No division cycles were observed, and the gametophyte is unicellular. (c) Gametophytes were loaded with cyclin B dsRNA, present in the imbibition medium at a concentration of 200 µg/ml. No cell division cycles were observed in the gametophytes after 8 hours.The prominent structures in this gametophyte are plastids; one plastid is labeled with an asterisk. (d) Microspores were placed into an imbibition medium containing 100 µM olomoucine. After 8 hours, a few, anomalous cell divisions were observed in the vast majority of gametophytes. A presumptive spermatogenous cell is labeled (sp). (e) Microspores were placed into an imbibition medium containing 100 µM iso-olomoucine and, after 8 hours, development of the gametophytes was normal. (f) Gametophytes were loaded with cyclin A dsRNA, present in the imbibition medium at a concentration of 200 µg/ml. After 8 hours, a few incomplete cell divisions were observed in the vast majority of gametophytes. All images were obtained with DIC. Bar, 25 µm.
