Disruption of cellulose synthesis by isoxaben causes tip swelling and disorganizes cortical microtubules in elongating conifer pollen tubes.

In elongating pollen tubes of the conifer Picea abies (Norway spruce), microtubules form a radial array beneath the plasma membrane only at the elongating tip and an array parallel with elongation throughout the tube. Tips specifically swell following microtubule disruption. Here we test whether these radial microtubules coordinate cell wall deposition and maintain tip integrity as tubes elongate. Control pollen tubes contain cellulose throughout the walls, including the tip. Pollen tubes grown in the presence of isoxaben, which disrupts cellulose synthesis, are significantly shorter with a decrease in cellulose throughout the walls. Isoxaben also significantly increases the frequency of tip swelling, with no effect on tube width outside of the swollen tip. The decrease in cellulose is more pronounced in pollen tubes with swollen tips. The effects of isoxaben are reversible. Following isoxaben treatment, the radial array of microtubules persists beneath the plasma membrane of nonswollen tips, while this array is specifically disrupted in swollen tips. Microtubules instead form a random network throughout the tip. Growth in these pollen tubes is turgor driven, but the morphological changes due to isoxaben are not just the result of weakened cell walls since pollen tubes grown in hypoosmotic media are not significantly shorter but do have swollen tips and tubes are wider along their entire length. We conclude that the radial microtubules in the tip do maintain tip integrity and that the specific inhibition of cellulose microfibril deposition leads to the disorganization of these microtubules. This supports the emerging model that there is bidirectional communication across the plasma membrane between cortical microtubules and cellulose microfibrils.

Microtubule organization in germinated pollen of the conifer Picea abies (Norway spruce, Pinaceae).

The organization of microtubules in germinated pollen of the conifer Picea abies (Norway spruce, Pinaceae) was examined using primarily confocal microscopy. Pollination in conifers differs from angiosperms in the number of mitotic divisions between the microspore and the sperm and in the growth rate of the pollen tube. These differences may be orchestrated by the cytoskeleton, and this study finds that there are important functional differences in microtubule organization within conifer pollen compared to the angiosperm model systems. Pollen from P. abies contains two degenerated prothallial cells, a body cell, a stalk cell, and a vegetative cell. The body cell produces the sperm. In the vegetative cell, microtubules form a continuous network from within the pollen grain, out through the aperture, and down the length of the tube to the elongating tip. Within the grain, this network extends from the pollen grain wall to the body and stalk cell complex. Microtubules within the body and stalk cells form a densely packed array that enmeshes amyloplasts and the nucleus. Microtubule bundles can be traced between the body and stalk cells from the cytoplasm of the body cell to the adjoining cell wall and into the cytoplasm of the stalk cell. Body and stalk cells are connected by plasmodesmata. The organization of microtubules and the presence of plasmodesmata suggest that microtubules form a path for intercellular communication by projecting from the cytoplasm to interconnecting plasmodesmata. Microtubules in the elongating tube form a net axial array that ensheathes the vegetative nucleus. Microtubules are enriched at the elongating tip, where they form an array beneath the plasma membrane that is perpendicular to the direction of tube growth. This enriched region extends back 20 µm from the tip. There is an abrupt transition from a net perpendicular to a net axial organization at the edge of the enriched region. In medial sections, microtubules are present in the core of the elongating tip. The organization of microtubules in the tip differs from that seen in angiosperm pollen tubes.

[Diagnosis and therapy of vascular injuries in posterior knee dislocation]. / Diagnostik und Therapie von Gefässverletzungen bei posterioren Knieluxationen.

AIM: We demonstrate the management and treatment of dislocation of the knee associated with vascular injury. The goal of the treatment is to avoid complications due to ischemia. The injured vessel can be repaired either by direct suture or by interposition of a saphenous vein graft. Capsule and ligaments should be reconstructed secondarily. PATIENTS AND METHODS: The charts of ten patients treated in the Division of Traumatology of the University of Zurich between 1979 and 1996 have been retrospectively checked. RESULTS: In eight of ten patients the injured vessel has been reconstructed with a saphenous vein graft, in one patient the artery has been repaired by direct suture. In one patient a flap of the intima has been refixed by endarterectomy. In five patients the knee has been stabilised with a transfixation (external fixation). In two patients the ligaments and the capsule were reconstructed at the time of vascular repair, in seven patients the reconstruction has been performed secondary. CONCLUSIONS: In case of a dislocation of the knee the examination of the vessels is mandatory. In case of a critical perfusion the "on table"--angiography is the procedure of choice. As an alternative method duplex sonography has been established. The vascular reconstruction is performed by saphenous vein graft interposition. We recommend to reconstruct ligamentous and capsular structures secondary.