Organization of actin filaments in regenerating and outgrowing subprotoplasts from pollen tubes ofNicotiana tabacum L.

The dynamics of actin-filament organization in pollen-tube subprotoplasts ofNicotiana tabacum L. cv. Samsun during regeneration and outgrowth was examined using phalloidin probes and a non-fixation method. A succession of actin arrays was examined during subprotoplast regeneration that strongly resembled the actin dynamics described for developing microspores by Van Lammeren et al. (1989, Planta178, 531-539) and activated pollen by Tiwari and Polito (1988, Protoplasma147, 5-15). At the end of the succession the actin filaments often became extended between two opposite polar foci. The ordering of the cortical actin filaments reflected a polarity in the subprotoplasts which determined the plane of outgrowth. The site of outgrowth was often marked by a ring of actin filaments. As growth proceeded and tube-like structures were formed, the arrangement of cortical actin filaments was found to be transverse to the elongation axis. Since the patterns of actin distribution were identical in both caryoplasts and cytoplasts, it was concluded that the pollen-tube cytoplasm has the intrinsic capacity of reorganizing actin filaments and imposing polarity on the spherical subprotoplasts.