Osmotically Induced Cell Swelling versus Cell Shrinking Elicits Specific Changes in Phospholipid Signals in Tobacco Pollen Tubes

Pollen tube cell volume changes rapidly in response to perturbation of the extracellular osmotic potential. This report shows that specific phospholipid signals are differentially stimulated or attenuated during osmotic perturbations. Hypo-osmotic stress induces rapid increases in phosphatidic acid (PA). This response occurs starting at the addition of 25% (v/v) water to the pollen tube cultures and peaks at 100% (v/v) water. Increased levels of PA were detected within 30 s and reached maximum by 15 to 30 min after treatment. The pollen tube apical region undergoes a 46% increase in cell volume after addition of 100% water (v/v), and there is an average 7-fold increase in PA. This PA increase appears to be generated by phospholipase D because concurrent transphosphatidylation of n-butanol results in an average 8-fold increase in phosphatidylbutanol. Hypo-osmotic stress also induces an average 2-fold decrease in phosphatidylinositol phosphate; however, there are no detectable changes in the levels of phosphatidylinositol bisphosphates. In contrast, salt-induced hyperosmotic stress from 50 to 400 mm NaCl inhibits phospholipase D activity, reduces the levels of PA, and induces increases in the levels of phosphatidylinositol bisphosphate isomers. The pollen tube apical region undergoes a 41% decrease in cell volume at 400 mm NaCl, and there is an average 2-fold increase in phosphatidylinositol 3,5-bisphosphate and 1.4-fold increase in phosphatidylinositol 4,5-bisphosphate. The phosphatidylinositol 3,5-bisphosphate increase is detected within 30 s and reaches maximum by 15 to 30 min after treatment. In summary, these results demonstrate that hypo-osmotic versus hyperosmotic perturbation and the resultant cell swelling or shrinking differentially activate specific phospholipid signaling pathways in tobacco (Nicotiana tabacum) pollen tubes

Vesicle trafficking dynamics and visualization of zones of exocytosis and endocytosis in tobacco pollen tubes

Pollen tubes are one of the fastest growing eukaryotic cells. Rapid anisotropic growth is supported by highly active exocytosis and endocytosis at the plasma membrane, but the subcellular localization of these sites is unknown. To understand molecular processes involved in pollen tube growth, it is crucial to identify the sites of vesicle localization and trafficking. This report presents novel strategies to identify exocytic and endocytic vesicles and to visualize vesicle trafficking dynamics, using pulse-chase labelling with styryl FM dyes and refraction-free high-resolution time-lapse differential interference contrast microscopy. These experiments reveal that the apex is the site of endocytosis and membrane retrieval, while exocytosis occurs in the zone adjacent to the apical dome. Larger vesicles are internalized along the distal pollen tube. Discretely sized vesicles that differentially incorporate FM dyes accumulate in the apical, subapical, and distal regions. Previous work established that pollen tube growth is strongly correlated with hydrodynamic flux and cell volume status. In this report, it is shown that hydrodynamic flux can selectively increase exocytosis or endocytosis. Hypotonic treatment and cell swelling stimulated exocytosis and attenuated endocytosis, while hypertonic treatment and cell shrinking stimulated endocytosis and inhibited exocytosis. Manipulation of pollen tube apical volume and membrane remodelling enabled fine-mapping of plasma membrane dynamics and defined the boundary of the growth zone, which results from the orchestrated action of endocytosis at the apex and along the distal tube and exocytosis in the subapical region. This report provides crucial spatial and temporal details of vesicle trafficking and anisotropic growth

Still life: Pollen tube growth observed in millisecond resolution

Our recent work used novel methods to localize and track discrete vesicle populations in pollen tubes undergoing oscillatory growth. The results show that clathrin-dependent endocytosis occurs along the shank of the pollen tube, smooth vesicle endocytosis occurs at the tip, and exocytosis occurs in the subapical region. Here, growth of tobacco and lily pollen tubes is examined in greater temporal resolution using refraction-free high-resolution time-lapse differential interference contrast microscopy. Images were collected at 0.21 s intervals for 10 min, sequentially examined for millisecond details, compressed into video format and then examined for details of growth dynamics. The subapical growth zone is structurally fluid, with vesicle insertion into the plasma membrane, construction of new cell surface and cellular expansion. Incorporation of new membrane and wall materials causes localized disruption at the cell surface that precedes the start of the growth cycle by 3.44 ± 0.39 s in tobacco, and 1.02 ± 0.01 s in lily pollen tubes. Vesicle deposition increases after the start of the growth cycle and supports expansion of the growth zone. Growth reorientation involves a shift in the position and angle of the growth zone. In summary, these results support a new model of pollen tube growth

State and Spectral Properties of Chloride Oscillations in Pollen

Pollen tube growth is a dynamic system expressing a number of oscillating circuits. Our recent work identified a new circuit, oscillatory efflux of Cl(−) anion from the pollen tube apex. Cl(−) efflux is the first ion signal found to be coupled in phase with growth oscillations. Functional analyses indicate an active role for Cl(−) flux in pollen tube growth. In this report the dynamical properties of Cl(−) efflux are examined. Phase space analysis demonstrates that the system trajectory converges on a limit cycle. Fourier analysis reveals that two harmonic frequencies characterize normal growth. Cl(−) efflux is inhibited by the channel blocker DIDS, is stimulated by hypoosmotic treatment, and is antagonized by the signal encoded in inositol 3,4,5,6-tetrakisphosphate. These perturbations induce transitions of the limit cycle to new metastable states or cause system collapse to a static attractor centered near the origin. These perturbations also transform the spectral profile, inducing subharmonic frequencies, transitions to period doubling and tripling, superharmonic resonance, and chaos. These results indicate that Cl(−) signals in pollen tubes display features that are characteristic of active oscillators that carry frequency-encoded information. A reaction network of the Cl(−) oscillator coupled to two nonlinear feedback circuits that may drive pollen tube growth oscillations is considered

Análisis de las alianzas público-privadas en el sector educativo y recomendaciones para el fortalecimiento del Sistema de Alianzas y Cooperación Escolar de la Dirección de Relaciones con el Sector Educativo Privado de la Secretaría de Educación del Distrito

Las asociaciones público-privadas son un reto en Colombia que benefician a todos los involucrados. Al ampliar este campo en el Capstone, se pude observar diferentes obstáculos junto a la normatividad, experiencias de éxito tanto nacionales como internacionales, además de explorar posturas con expertos que permitirá a la Secretaria de Educación Distrital (SED) junto con la Dirección de Relaciones con el Sector Educativo Privado (DRSE) para fortalecer el Sistema de Alianzas y Cooperación Escolar (SACE) y consolidar estrategias para reforzar la creación de dichas asociaciones.In Colombia Public- private partnerships are a challenge which benefit all those involved. By developing this field in the Capstone, it can be recognized different barriers along with normativity, national and international successful experiences, as well as looking into experts’ views allowing to the Secretary of Education of Bogotá (SED), alongside Dirección de Relaciones con el Sector Educativo Privado (DRSE) to improve Sistema de Alianzas y Cooperación Escolar (SACE) and consolidate new strategies to enhance the founding of such partnerships.MaestríaMagíster en Economía y Política de la Educació