Per Anderhag³, Peter K. Hepler², and Mark D. Lazzaro^{1, 3*} (2000) Microtubules and microfilaments are both responsible for pollen tube elongation in the conifer Picea abies (Norway spruce). Protoplasma (2000) 214: 141-157

¹Department of Biology, College of Charleston, Charleston, SC 29424, USA. ²Department of Biology, University of Massachusetts, Amherst, MA 01003, USA. ³Department of Botany, Stockholm University, S 10691 Stockholm, Sweden. * Corresponding author: Email: lazzarom@cofc.edu

SUMMARY

In Picea abies (Norway spruce) microtubules and actin microfilaments both form a dense matrix throughout the tube mainly parallel to the direction of elongation. The organization of this matrix is different in conifer pollen tubes compared to angiosperms. This study tests our hypothesis that differences in cytoskeletal organization are responsible for differences in tube growth and physiology. Pollen grains were germinated in media containing cytoskeletal disruptors and analyzed for germination, tube length, tube branching, and tip swelling. Disruption of microtubules significantly inhibits tube elongation and induces tube branching and tip swelling. Tip swelling is probably caused by disruption of the microtubules in the tip that are perpendicular to the direction of elongation. Confocal microscopy indicates that colchicine and propyzamide cause fragmentation of microtubules throughout the tube. Oryzalin and amiprophosmethyl cause a complete loss of microtubules from the tip back towards the tube midpoint, but leave microtubules intact from the midpoint back to the grain. Disruption of microfilaments by cytochalsins B and D and inhibition of myosin by N-ethylmaleimide or 2,3-butanedione monoxime stops tube growth and inhibits germination. Microfilament disruption induces short branches in tubes, probably originating from defective microfilament organization behind the tip. In addition, confocal microscopy coupled with microinjection of fluorescein-labeled phalloidin into actively growing pollen tubes indicates that microfilament bundles extend into the plastid free zone at the tip but are specifically excluded from the growing tip. We conclude that microtubules and microfilaments coordinate to drive tip extension in conifer pollen tubes in a model that differs from angiosperms.