Microtubules and microfilaments are both responsible for pollen tube elongation in the conifer Picea abies (Norway spruce)

In Picea abies (Norway spruce), microtubules and actin microfilaments both form a dense matrix throughout the tube mainly parallel to the direction of elongation. In these conifer pollen tubes the organization of this matrix is different from that in angiosperms. This study tests our hypothesis that differences in cytoskeletal organization are responsible for differences i n tube growth and physiology. Pollen grains were germinated in media contai ning cytoskeletal disrupters and analyzed for germination, tube length, tub e branching, and tip swelling. Disruption of microtubules significantly inh ibits tube elongation and induces tube branching and tip swelling. Tip swel ling is probably caused by disruption of the microtubules in the tip that a re perpendicular to the direction of elongation. Confocal microscopy indica tes that colchicine and propyzamide cause fragmentation of microtubules thr oughout the tube. Oryzalin and amiprophosmethyl cause a complete loss of mi crotubules from the tip back toward the tube midpoint but leave microtubule s intact from the midpoint back to the grain. Disruption of microfilaments by cytochalasins B and D and inhibition of myosin by N-ethylmaleimide or 2, 3-butanedione monoxime slops tube growth and inhibits germination. Microfil ament 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 i nto actively growing pollen tubes indicates that microfilament bundles exte nd into the plastid-free zone at the tip but are specifically excluded from the growing tip. We conclude that microtubules and microfilaments coordina te to drive tip extension in conifer pollen tubes in a model that differs f rom angiosperms.