Pollen tubes of flavonol-deficient Petunia show striking alterations in wall structure leading to tube disruption (original) (raw)
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Journal of cell science, 1981
Pollen tubes formed following compatible and incompatible intraspecific matings in Petunia have been examined with light and electron microscopes. Compatible and incompatible tubes develop in an identical fashion on the stigma but, on entry into the top 1 mm of the stylar transmitting tissue changes occur both to the cytology of the tubes and their rates of growth. The early cytological changes are common to tubes of both compatibilities but, although both types of tube accelerate on entry into the style, incompatible tubes grow more slowly than compatible. Cytological differences became apparent between compatible and incompatible tubes following a short period of growth in the style, the latter possessing thicker cell walls and a cytoplasm packed with both organelles and reserves. Incompatible tubes subsequently burst or simply cease growth and die. The characteristic image afforded by this cytoplasm resembles that or burst or dead compatible tubes, except in that proportions of t...
The architecture and properties of the pollen tube cell wall
Pollen Tube: Cellular and Molecular Perspective, 2006
The pollen tube wall differs in both structure and function from walls of vegetative plant cells. Cellulose represents only a small portion of the cell wall polymers, so an organized microfibrillar system has not been identified yet. The initial wall, formed by secretion at the growing tip, is mostly composed of methyl esterified pectins. During cell wall maturation, concomitant with its translocation from apex to shank, these are demethylated by pectin methylesterase to yield carboxyl groups which have the potential to bind calcium ions, adding mechanical strength to the gel. Callose synthase activity is established close to the growing tip, and builds a callose layer beneath the fibrous pectic layer. The mature wall also contains proteins, arabinogalactan proteins and pollen extensin-like proteins. The mature wall is a cylinder that resists turgor expansion, but is stronger at the base than the tip due to the presence of the callose layer and the gelation of pectin polymers in the shank. Permeability of the wall is essential, to allow passage of both ions and sporophytic proteins that determine compatibility in many species. Influx of calcium ions affects the tip cytoplasm, especially the cytoskeleton, and oscillatory changes in these fluxes are involved in the "pulsatile" mode of growth. This process deposits extra wall material during the "slow" growth phase, which generates rings of increased density in the walls that can be readily seen with appropriate antibodies.
Ultrastructural Changes During Pollen Wall Development and Germination in Arabidopsis Thalaiana
2016
The Arabidopsis thaliana meiotic mutant 6491 has been identified as displaying temperature sensitive male reduced-fertility. It has been determined that callose wall formation is defective, both in temporal and structural areas. There is irregular rippling in the plasma membrane and aberrant formation of the exine portion of the pollen wall. A developmental study using brightfield, epifluorescence, and transmission electron microscopy of the early stages of wall formation in 6491 has been completed, along with a similar study of Arabidopsis thaliana (L.) heynh, ecotype Wassilewskija (WS). Due to the temperature-sensitive nature of the mutant line, a further study of both lines was completed at three different growth temperatures, all within the acceptable growth range of A. thaliana. Techniques for visualization included Hoffman modulation contrast microscopy to examine structure and aniline blue staining observed by epifluorescence microscopy to examine callose wall formation. Several potentially damaging structural differences were noted in both lines, dependent upon the temperature at which the plants had been grown. Further examination of pollen walls was undertaken, focusing on breakout of the pollen tube through the stiff patterned portion of the pollen wall layer known as exine. It has generally been accepted that pollen tubes exited through the interaperture space, where less biomechanical force iii would be required to breach the wall. However, it is now known that certain species of Arabidopsis thaliana are omniaperturate, breaking through the wall at a point closest in contact with the stigma. Pollen from a known omniaperturate line, Arabidopsis thaliana ecotype Landsberg erecta (Ler), was dusted onto male sterile-1 (MS-1) mutant plants in the same background. Brightfield and transmission electron microscopy were used to determine structural changes occurring within the grain and wall that would allow a pollen tube to breach such a resilient structure as exine.
Review of Palaeobotany and Palynology, 2003
Degradation of mature pollen walls by treatment with potassium permanganate was undertaken in Lavatera arborea (Malvaceae), Oenothera speciosa (Onagraceae) and Stangeria eriopus (Stangeriaceae) in order to investigate the substructural organisation of their exines. In Lavatera arborea the cores of the columellae are eroded so that they appear as hollow tubes and radially oriented rod-like elements (tufts) are revealed in the ectexine and endexine. An oxidative treatment with glacial acetic acid revealed clusters of darkly contrasted Sporopollenin Acceptor Particles (SAPs) along the surface of the columellae. This indicates that the cores of the columellae are formed independently of SAPs, whereas the sporopollenin in the outer parts of the columellae is receptor-dependent and is much more resistant to oxidation. After oxidative treatment of Oenothera pollen only the outlines of the three layers^of tectum, columellae and endexine, represented by the boundary layer, are visible, together with a complex system of tufttubules. The binder elements of tufts and the boundary layer of all exine strata are resistant to degradation and are interpreted as containing sporopollenin laid down on SAPs rather than the receptor-independent material of the remainding exine. Oxidative treatment of the alveolate exine of Stangeria eriopus results in progressive erosion with the duration of treatment. The binder zones of tufts and the tectal part of the exine, which are the walls of the alveolae and also their boundary layer, are the most resistant to oxidation and correspond to SAPs. The core subunits of tufts, that is the central parts of the alveolae, do not resist oxidation and are interpreted as sites of receptorindependent sporopollenin. Thus, in spite of the very different exine structure in Lavatera arborea, Stangeria eriopus and Oenothera speciosa, the exines of these species, on the substructural level, react to oxidative treatment in a similar way. We conclude that the alternative models of exine substructure proposed by various authors differ mainly in terminology rather than in substance. ß
The pollen tube: a soft shell with a hard core
The Plant Journal, 2013
Plant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20-90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.
Protoplasma, 2012
Isolated microspores and pollen suspension of Brassica napus "Topas" cultured in NLN-13 medium at 18°C follow gametophytic pathway and develop into pollen grains closely resembling pollen formed in planta. This culture system complemented with whole-mount immunocytochemical technology and novel confocal laser scanning optical technique enables detailed studies of male gametophyte including asymmetric division, cytoskeleton, and nuclear movements. Microtubular cytoskeleton configurationally changed in successive stages of pollen development. The most prominent role of microtubules (MTs) was observed just before and during nuclear migration at the early and mid-bi-cellular stage. At the early bi-cellular stage, parallel arrangement of cortical and endoplasmic MTs to the long axis of the generative cell (GC) as well as MTs within GC under the plasmalemma bordering vegetative cell (VC) were responsible for GC lens shape. At the beginning of the GC migration, endoplasmic microtubules (EMTs) of the VC radiated from the nuclear envelope. Most cortical and EMTs of the VC were found near the sporoderm. At the same time, pattern of MTs observed in GC was considerably different. Multiple EMTs of the GC, previously parallel aligned, reorganized, and start to surround GC, forming a basket-like structure. These results suggest that EMTs of GC provoke changes in GC shape, its detachment from the sporoderm, and play an important role in GC migration to the vegetative nucleus (VN). During the process of migration of the GC to the VC, multiple and thick bundles of MTs, radiating from the cytoplasm near GC plasma membrane, arranged perpendicular to the narrow end of the GC and organized into a "comet-tail" form. These GC "tail" MTs became shortened and the generative nucleus (GN) took a ball shape. The dynamic changes of MTs accompanied polarized distribution pattern of mitochondria and endoplasmic reticulum. In order to confirm the role of MTs in pollen development, a "wholemount" immunodetection technique and confocal laserscanning microscopy was essential.