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Callose and cellulose are fundamental components of the cell wall of pollen tubes and are probably synthesized by distinct enzymes, callose synthase and cellulose synthase, respectively. We examined the distribution of callose synthase and cellulose synthase in tobacco (Nicotiana tabacum) pollen tubes in relation to the dynamics of actin filaments, microtubules, and the endomembrane system using specific antibodies to highly conserved peptide sequences. The role of the cytoskeleton and membrane flow was investigated using specific inhibitors (latrunculin B, 2,3-butanedione monoxime, taxol, oryzalin, and brefeldin A). Both enzymes are associated with the plasma membrane, but cellulose synthase is present along the entire length of pollen tubes (with a higher concentration at the apex) while callose synthase is located in the apex and in distal regions. In longer pollen tubes, callose synthase accumulates consistently around callose plugs, indicating its involvement in plug synthesis. Actin filaments and endomembrane dynamics are critical for the distribution of callose synthase and cellulose synthase, showing that enzymes are transported through Golgi bodies and/or vesicles moving along actin filaments. Conversely, microtubules appear to be critical in the positioning of callose synthase in distal regions and around callose plugs. In contrast, cellulose synthases are only partially coaligned with cortical microtubules and unrelated to callose plugs. Callose synthase also comigrates with tubulin by Blue Native-polyacrylamide gel electrophoresis. Membrane sucrose synthase, which expectedly provides UDP-glucose to callose synthase and cellulose synthase, binds to actin filaments depending on sucrose concentration; its distribution is dependent on the actin cytoskeleton and the endomembrane system but not on microtubules.

Herbicides are chemical compounds widely used in agriculture. As their intensive application is becoming a cause of environmental pollution, detailed and more sophisticated investigations are needed to understand better their consequences at the biological level. After herbicides are dispersed in the fields, they establish chemical interactions with both target and non-target plants. In both cases, herbicides can interact with the plant reproductive apparatus; consequently they could play a role during the fertilisation process in higher plants. Using an antibody to the alpha-tubulin subunit in immunofluorescence and immunoelectron microscopy techniques, we investigated the distribution of microtubules in Nicotiana tabacum pollen tubes grown under in vitro conditions in the presence of five different herbicides selected among those used frequently in central Italy. Herbicides have a specific effect on the microtubular apparatus of both pollen tube and generative cell. In addition to other tests and assays, these results suggest that the microtubule cytoskeleton of pollen tubes can be used as a bioindicator for studying the toxicity effects induced by herbicides.

The pollen tube is a cell with unusual features that plays a fundamental role during reproduction in higher plants, transporting the generative cell and sperm cells from the pollen grain to the ovary. Pollen tubes elongate by apical growth, which is, in turn, elicited by the fusion of secretory vesicles carrying plasma membrane and cell wall components. Organelle trafficking in the pollen tube, which occurs bi-directionally along the longitudinal axis, has been the focus of much research for many years. The movement of organelles along the pollen tube relies on the cytoskeleton, which consists of microtubules, actin filaments and associated proteins. Motor proteins are a special subset of cytoskeleton proteins that induce organelles to move by using the energy of ATP hydrolysis. The pollen tube, like other plant cells, uses actin-myosin interactions as a basis for the intracellular movement of organelles. The role of microtubules during organelle movement is not yet defined, despite the fact that microtubule motor proteins have been identified. The differential distribution of organelles and vesicles, which is observable along the main axis of the pollen tube, is essential for the proper growth of the pollen tube. How this level of organization is preserved is not known. However, other mechanisms of regulation are being identified in the pollen tube which might also be important in modulating the activity and structure of the cytoskeleton elements. [ABSTRACT FROM AUTHOR]