Surface Expansion Rate Research Articles

Abandoned cropland compensates the decrease in net ecosystem productivity of impervious surface expansion in China

Abandoned cropland and impervious surface expansion are generally considered to have positive and negative impacts on net ecosystem productivity (NEP), respectively. However, the comprehensive comparison of the impacts of these two land use changes on NEP remains lacking. We use multi-year land cover data, NEP data, and statistical data to track the interannual variability of abandoned cropland and impervious surface expansion in China, and subsequently estimate their impacts on NEP. From 2000 to 2019, 30.8 × 106 ha of cropland in China was abandoned, while the impervious surface area expanded by 8.97 × 106 ha over the period. The average annual abandonment rate and impervious surface expansion rate were 0.83% and 2.96%, respectively. The average annual NEP of abandoned cropland and impervious surface expansion were 39.9 g C/m2 and 16.2 g C/m2, respectively. Using the space-for-time method to estimate NEP changes, results showed that the carbon sink of 0.013 Tg C accumulated by abandoned cropland not only offset the carbon source of 0.01 Tg C from impervious surface expansion but sequestered additional 0.003 Tg C during the study period. Further analysis of the relationships between NEP and natural and anthropogenic factors revealed that temperature had the most significant positive impact on NEP (0.35, p < 0.01), while the urbanization rate had the most significant negative impact on NEP (−0.33, p < 0.01). This study provides a new insight for regulating the effects of land use changes on natural carbon sink/source, and highlights the importance of abandoned cropland to enhancing natural carbon sink.

Beta diversity of urban spontaneous plants and its drivers in 9 major cities of Yunnan province, China

Urbanization has significantly reshaped regional biodiversity structure globally. Previous studies suggested that urban communities of spontaneous plants are well adapted to the urban environment. However, a perspective of urbanization that accounts for the joint impacts of the current state (as expressed by urbanization intensity) and the historical progress of urbanization (as expressed by urbanization rate) to reveal the mechanisms underlying the biodiversity patterns of spontaneous plants in cities is still lacking. Here we present data and analysis of spontaneous plants sampled in 709 patches within 82 sites of built-up areas from nine cities distributed across climatic and floristic zones in Yunnan province, a biodiversity hotspot in China. We used the exponent (z) of a species accumulation curve (SAC) model to characterize beta diversity among patches in a site, and found a higher beta diversity of native species compared with non-natives, indicating that the species composition of native plants is more heterogeneous. The beta diversity of all species groups was best explained by the constant c of the SAC (a proxy of alpha diversity), followed by the urbanization intensity (as expressed by the proportion of sealed surface and patches’ Shannon diversity index), and urbanization rate (as expressed by the sealed surface expansion rate). Moreover, beta diversity of non-native species was additionally negatively correlated with altitude. Our results suggest that the interplay of natural environmental factors and human-induced urbanization shape diversity of urban spontaneous plants in Yunnan province. Our findings emphasize that urban spontaneous plants diversity is not only a reflection of the current state of urbanization, but also a consequence of historical processes of urbanization.

A prospective study on the expansion rule of the directional skin and soft tissue expander in abdominal scar reconstruction

A prospective study on the expansion rule of the directional skin and soft tissue expander in abdominal scar reconstruction

Hypergolic ignition induced by head-on collision of bi-propellant droplets: Monoethanolamine-based fuel and hydrogen peroxide

Hypergolic ignition by the binary collision of H2O2 and Monoethanolamine (MEA)-NaBH4 droplets has been experimentally studied with an emphasis on droplet inter-mixing, heat transfer, droplet swelling, and flame propagation. The entire ignition is phenomenally categorized into five stages. The H2O2 droplet penetrates the MEA- NaBH4 droplet after the collision and coalesces with it. The H2O2 fluid rapidly restores its sphericity inside the coalesced droplet, which is theoretically proved to be driven by interfacial tension. The average measured restoration time is 14.0 ms. Large-scaled bubbles are generated at the interfacial structure, leading to swelling of the coalesced droplet. The existence of apparent interface tension tends to limit the rate of droplet inflation at the beginning. As more bubbles are produced, the interface tension wanes, and the droplet swells rapidly. The droplet surface expansion rate is identified via the gray-level information in recorded images. A theoretical model quantifying the swelling rate was established based on the underlying mechanism for the swelling of the reacting droplet, which can be attributed to the flash boiling of the superheated H2O2 fluid. As bubbles accumulate inside the coalesced droplet, a dual-bell-shaped droplet configuration is formed. A flame ring structure is observed when the ignition occurs. Luminant flame sustains more than 10 ms until the fuel vapor is depleted.

Transcriptome and anatomical studies reveal alterations in leaf thickness under long-term drought stress in tobacco

Drought is one of the foremost environmental factors that limit the growth of plants. Leaf thickness (LT) is an important quantitative trait in plant physiology. The experiment was carried out in a growth room and the plants were divided into two groups such as well-watered and drought-stressed. This work investigated leaf growth in terms of leaf surface growth and expansion rate, leaf stomata traits, LT, anticlinal growth, and leaf cell layers. The results showed that the leaf area and leaf surface expansion rate were decreased by drought stress (DS). Similarly, LT, anticlinal expansion rate, palisade and spongy tissue thickness, and their related expansion rates were also decreased at different days’ time points (DTP) of DS. However, a steady increase was observed in the aforementioned parameters after 12 DTP of DS. The stomatal density increased while stomata size decreased at 3 DTP and 12 DTP (low leaf water potential and relative leaf water content at these time points) and vice versa at 24 DTP compared with the well-watered plants indicating adaptations in these traits in response to DS, and thus the leaf water status played a role in the regulation of leaf stomata traits. The cell length decreased in the upper epidermis, palisade and spongy tissues by DS up to 12 DTP led to lower LT while an increase was observed after 12 DTP that resulted in higher LT. The increase in the LT was supported by the upregulation of starch and sucrose metabolism, glycerolipid metabolism, protein processing in endoplasmic reticulum pathways at 18 DTP along with the differentially expressed genes induced that were related to cell wall remodeling (cellulose, expansin, xyloglucans) and cell expansion (auxin response factors and aquaporin). The results explain the response of leaf thickness to drought stress and show alterations in LT and leaf stomatal traits. This study might serve as a valuable source of gene information for functional studies and provide a theoretical basis to understand leaf growth in terms of leaf anatomy and leaf stomatal traits under drought stress.

Longitudinal surface measurements of human blastocysts show that the dynamics of blastocoel expansion are associated with fertilization method and ongoing pregnancy

BackgroundDespite all research efforts during this era of novel time-lapse morphokinetic parameters, a morphological grading system is still routinely being used for embryo selection at the blastocyst stage. The blastocyst expansion grade, as evaluated during morphological assessment, is associated with clinical pregnancy. However, this assessment is performed without taking the dynamics of blastocoel expansion into account. Here, we studied the dynamics of blastocoel expansion by comparing longitudinal blastocoel surface measurements using time-lapse embryo culture. Our aim was to first assess if this is impacted by fertilization method and second, to study if an association exists between these measurement and ongoing pregnancy.MethodsThis was a retrospective cohort study including 225 couples undergoing 225 cycles of in vitro fertilization (IVF) treatment with time-lapse embryo culture. The fertilization method was either conventional IVF, intracytoplasmic sperm injection (ICSI) with ejaculated sperm or ICSI with sperm derived from testicular sperm extraction (TESE-ICSI). This resulted in 289 IVF embryos, 218 ICSI embryos and 259 TESE-ICSI embryos that reached at least the full blastocyst stage. Blastocoel surface measurements were performed on time-lapse images every hour, starting from full blastocyst formation (tB). Linear mixed model analysis was performed to study the association between blastocoel expansion, the calculated expansion rate (µm2/hour) and both fertilization method and ongoing pregnancy.ResultsThe blastocoel of both ICSI embryos and TESE-ICSI embryos was significantly smaller than the blastocoel of IVF embryos (beta -1121.6 µm2; 95% CI: -1606.1 to -637.1, beta -646.8 µm2; 95% CI: -1118.7 to 174.8, respectively). Still, the blastocoel of transferred embryos resulting in an ongoing pregnancy was significantly larger (beta 795.4 µm2; 95% CI: 15.4 to 1575.4) and expanded significantly faster (beta 100.9 µm2/hour; 95% CI: 5.7 to 196.2) than the blastocoel of transferred embryos that did not, regardless of the fertilization method.ConclusionLongitudinal blastocyst surface measurements and expansion rates are promising non-invasive quantitative markers that can aid embryo selection for transfer and cryopreservation.Trial registrationOur study is a retrospective observational study, therefore trial registration is not applicable.

Present-day movement trends of the major tectonic faults in the Sichuan-Yunnan region based on the constraint of GPS velocity fields

Based on the known fault distribution in Sichuan-Yunnan region (SYR), a rigid Euler rotation model is constructed by using GPS velocities (1998 ~ 2016) after excluding the stations near the fault boundaries and simultaneously a translation-rotation-strain model is constructed by using almost all GPS velocities to calculate three periods strain rate fields (2008.6 ~ 2010.4, 2010.5 ~ 2013.4 and 2013.5 ~ 2016.12) after Wenchuan earthquake. The results show that: (1) the strike-slip activity is the most common trends for the regional faults. The Xianshuihe-Xiaojiang fault, the Lancangjiang-Weixi-Weishan-Wuliangshan fault and the Longmenshan fault are the most active in the whole SYR, and the dislocation rate is more than 15 mm/a, and the trend of activity gradually decreases from the northwest to the southeast. (2) The different activity rates of the faults in the study area indicate that some of the eastward extrusion of the Tibet Plateau is absorbed and adjusted by the inside faults, and it is not a few large strike-slip faults. (3) Through the analysis of three periods’ grid velocity fields, we found that the movement rates of the Bitu section of Lanchangjiang fault, the Northwestern section of Weixi-Weishan fault and the Nujiang fault after Wenchuan earthquake are larger than that after Yushu and Ya’an earthquake, and the difference is about 8 mm/a. Besides, the activity rate of Northwestern section of Longmenshan fault after the Wenchuan earthquake is larger than that after the Ya’an earthquake, although the two epicentres distances are relatively close. (4) The strain rate fields and surface expansion rates show that the high value area is mainly distributed at or around the intersection among some fault zones and its surroundings, and the maximum area is mainly located at some long and deep fault zones such as the Longriba fault, the Longmenshan fault zone, the Ganzi-Yushu fault and the Xianshuihe, and the magnitude is about 35 ~ 50 nanstrain/a. The research should provide fundamental material for the study of crustal stress variation and earthquake prediction in Sichuan-Yunnan region.

Experimental study on expansion mechanism and characteristics of expansive grout

Aiming to address the problem of traditional grouting reinforcement of jointed rock mass only providing bonding force to the joint surface, the grouting reinforcement technology of expansive grout was proposed. This technology generates compression force through the volume expansion of the grout itself, leading to a reinforcement idea of “first squeezing and then bonding” to increase the overall strength of the jointed rock mass. To solve the problem of the preparation of expansive grout materials, an expansive grout proportion test using high efficiency soundless crush agent (HSCA) as the expansion source and cement as the cementing material was performed. Considering the single free surface expansion rate (SFSER) and lateral expansion pressure (LEP) of expansive grout specimens as the investigated indices, the expansion evolution law of expansive grout and the effect of cement content and expansion agent content on its expansion characteristics were explored from both macro and micro level. The experimental results show that: (1) The expansion evolution processes of expansive grout after final setting can be divided into four phases viz. rapid expansion period, slow expansion period, residual expansion period and stable period. After 120 h of final setting, the grout expansion basically ended. (2) the expansive grout with different cement contents could produce SFSER between 0.83% and 18.54% and LEP between 0.08 MPa and 1.83 MPa when the content of the expansion agent was 3–12%. (3) The effects of the expansion agent content on the SFSER and LEP of the expansion agent were similar, and they all showed an S-shaped curve with increase in the expansion agent content. The experimental results provide a significant understanding of the expansion mechanism and characteristics of expansive grout.

Role of the rate of surface dilatation in determining microscopic dynamic contact angle

The factors determining the degree of dynamic wetting, which is characterized by the microscopic dynamic contact angle, have been the subject of much discussion. In this manuscript, it is analytically determined that the microscopic dynamic contact angle is dependent on the rate of surface dilatation in addition to the thermodynamic surface tension. It is argued that, in the vicinity of a moving contact line, this rate of surface dilatation results in a disparity between the thermodynamic and mechanical surface tensions, which are almost always assumed to be equal. It is also found that, in the case of forced wetting, the difference between the receding and advancing contact angles is primarily due to the rate of surface compression at the receding contact line and the rate of surface expansion at the advancing contact line. These findings, which are validated using molecular dynamics simulations, demonstrate that surface dilatation is an important factor responsible for the deviation of the microscopic dynamic contact angle from its static equilibrium value.

Significant change in threshold for plasma formation and evolution with small variation in copper alloys driven by a mega-ampere current pulse

We report the first observation of a significant change in plasma formation and evolution caused by a small change in the material composition (metal alloy). Thick copper rod alloys were varied in the initial diameter from 0.5 mm to 1.59 mm and pulsed to 1 mega-ampere (MA) peak current in 100 ns with a surface magnetic field rising nearly linearly at 45–80 MG/μs. The copper rods were diagnosed with surface radiometry, two-frame laser shadowgraphy, two-frame surface emission imaging, and time resolved load current measurements. Diagnostics determined time resolved surface temperature, surface expansion rates, time of surface plasma formation, and the growth rates of surface instabilities. Data indicate that copper alloy Cu-145 (99.5% Cu, 0%–0.7% Te, 0%–0.012% P) undergoes surface plasma formation when the surface magnetic field reaches 3.0 ± 0.1 MG whereas Cu-101 (&amp;gt;99.99% Cu) forms surface plasma at 3.5 ± 0.2 MG. The Cu-145 alloys also reach higher peak temperatures and form surface instabilities earlier in the current pulse.

RhoA regulates actin network dynamics during apical surface emergence in multiciliated epithelial cells

ABSTRACT Homeostatic replacement of epithelial cells from basal precursors is a multistep process involving progenitor cell specification, radial intercalation and, finally, apical surface emergence. Recent data demonstrate that actin-based pushing under the control of the formin protein Fmn1 drives apical emergence in nascent multiciliated epithelial cells (MCCs), but little else is known about this actin network or the control of Fmn1. Here, we explore the role of the small GTPase RhoA in MCC apical emergence. Disruption of RhoA function reduced the rate of apical surface expansion and decreased the final size of the apical domain. Analysis of cell shapes suggests that RhoA alters the balance of forces exerted on the MCC apical surface. Finally, quantitative time-lapse imaging and fluorescence recovery after photobleaching studies argue that RhoA works in concert with Fmn1 to control assembly of the specialized apical actin network in MCCs. These data provide new molecular insights into epithelial apical surface assembly and could also shed light on mechanisms of apical lumen formation.

RhoA regulates actin network dynamics during apical surface emergence in multiciliated epithelial cells.

Homeostatic replacement of epithelial cells from basal precursors is a multistep process involving progenitor cell specification, radial intercalation and, finally, apical surface emergence. Recent data demonstrate that actin-based pushing under the control of the formin protein Fmn1 drives apical emergence in nascent multiciliated epithelial cells (MCCs), but little else is known about this actin network or the control of Fmn1. Here, we explore the role of the small GTPase RhoA in MCC apical emergence. Disruption of RhoA function reduced the rate of apical surface expansion and decreased the final size of the apical domain. Analysis of cell shapes suggests that RhoA alters the balance of forces exerted on the MCC apical surface. Finally, quantitative time-lapse imaging and fluorescence recovery after photobleaching studies argue that RhoA works in concert with Fmn1 to control assembly of the specialized apical actin network in MCCs. These data provide new molecular insights into epithelial apical surface assembly and could also shed light on mechanisms of apical lumen formation.

Correction: RhoA regulates actin network dynamics during apical surface emergence in multiciliated epithelial cells.

ABSTRACT Homeostatic replacement of epithelial cells from basal precursors is a multistep process involving progenitor cell specification, radial intercalation and, finally, apical surface emergence. Recent data demonstrate that actin-based pushing under the control of the formin protein Fmn1 drives apical emergence in nascent multiciliated epithelial cells (MCCs), but little else is known about this actin network or the control of Fmn1. Here, we explore the role of the small GTPase RhoA in MCC apical emergence. Disruption of RhoA function reduced the rate of apical surface expansion and decreased the final size of the apical domain. Analysis of cell shapes suggests that RhoA alters the balance of forces exerted on the MCC apical surface. Finally, quantitative time-lapse imaging and fluorescence recovery after photobleaching studies argue that RhoA works in concert with Fmn1 to control assembly of the specialized apical actin network in MCCs. These data provide new molecular insights into epithelial apical surface assembly and could also shed light on mechanisms of apical lumen formation.

Light is an active contributor to the vital effects of coral skeleton proxies

Symbiotic colonies of the coral Acropora sp. were cultured in a factorial design of three temperatures (21, 25 and 28°C) and two light intensities (200 and 400μmolphotonm−2s−1), under constant conditions. A temperature of 25°C and a light intensity of 200μmolphotonm−2s−1 was the starting culture condition. Metabolic (photosynthesis, respiration, calcification and surface expansion rate) and geochemical measurements (δ18O, δ13C, Sr/Ca and Mg/Ca) were conducted on 6 colonies for each experimental condition.Metabolic measurements confirmed that respiration, photosynthesis, calcification and surface expansion rate responded to the combined effect of temperature and light. Under each light intensity, mean calcification rate was linearly correlated with mean photosynthetic activity. Geochemical measurements were also influenced by temperature and, to a lesser degree, by light. All geochemical proxies measured on 6 nubbins showed a wide scattering of values, regardless of the environmental condition. Compared to the other proxies, δ18O exhibited a different behavior. It was the only proxy exhibiting temperature tracer behavior. However, while mean values of Sr/Ca, Mg/Ca and δ13C were well correlated, the correlation between the later and mean δ18O differed with light level. This suggests that both skeleton deposition and temperature oxygen fractionation differs according to light intensity. Overall, the effect of light on geochemical values seems to compromise the use of proxy calibrations solely based on temperature influence.Under high light conditions, the great amplitude shown by individual net photosynthesis is directly proportional to the highly variable zooxanthellae density. As light is affecting all of the proxies, we thus assume that the strong geochemical variability observed could be explained by various algae densities, each nubbin responding according to its zooxanthellae amount. Accordingly, we suggest that each symbiosome (the assemblage of few corallites with their symbionts) presents its own vital effect influence over time. Therefore, at a bulk sample scale, light could be considered as one of the major causes of what is commonly referred to as the ‘vital effect’. The meaning of δ18O calibration versus temperature established from distinct colonies differs from calibration calculated from samples collected following the growth axis of a single coral head.Finally, in order to quantitatively reconstruct climatic condition, we suggest a new paradigm based on the statistical treatment of the combination of time-series information from several proxies, all measured on the same sample from a continuous symbiosome.

Cell Wall-Related Bionumbers and Bioestimates of Saccharomyces cerevisiae and Candida albicans

Bionumbers and bioestimates are valuable tools in biological research. Here we focus on cell wall-related bionumbers and bioestimates of the budding yeast Saccharomyces cerevisiae and the polymorphic, pathogenic fungus Candida albicans. We discuss the linear relationship between cell size and cell ploidy, the correlation between cell size and specific growth rate, the effect of turgor pressure on cell size, and the reason why using fixed cells for measuring cellular dimensions can result in serious underestimation of in vivo values. We further consider the evidence that individual buds and hyphae grow linearly and that exponential growth of the population results from regular formation of new daughter cells and regular hyphal branching. Our calculations show that hyphal growth allows C. albicans to cover much larger distances per unit of time than the yeast mode of growth and that this is accompanied by strongly increased surface expansion rates. We therefore predict that the transcript levels of genes involved in wall formation increase during hyphal growth. Interestingly, wall proteins and polysaccharides seem barely, if at all, subject to turnover and replacement. A general lesson is how strongly most bionumbers and bioestimates depend on environmental conditions and genetic background, thus reemphasizing the importance of well-defined and carefully chosen culture conditions and experimental approaches. Finally, we propose that the numbers and estimates described here offer a solid starting point for similar studies of other cell compartments and other yeast species.

An Oil Droplet Division–Fusion Cycle

Cell division extolls an energetic cost on the system, which makes fission nonspontaneous. In efforts to engineer self-replicating experimental systems, the division step is often affected by purely external forces or through speculated mechanisms. Herein, we demonstrate an oil droplet division event that is intrinsic, coupling interfacial phenomena with internal flow structures that literally pull the original droplet into two or more smaller stable aggregates. Self-division is based on interfacial instabilities driven by a far from equilibrium catanionic surfactant system. Salt-induced droplet fusion initiates feeding and embedded chemical reactions. Together fusion and division demonstrate a rudimentary droplet replication cycle. The droplet as an embodied model of artificial life possesses some relevant characteristics and qualities of living systems, such as a perpetuated body or identity, an embedded metabolism, and the ability to avoid equilibrium through directed movement or chemical chemotaxis. 4] A simple oil-droplet system may also possess a chemical language shared by a population of droplets resulting in group dynamics and higher order behaviors. The oil phase can host chemical reactions, especially those sensitive to water. Enzymatic function is possible as well as very strong hydrogen bonding in the oil phase. The oil droplet can protect water-labile fuel sources encapsulated within the oil phase and can regulate fuel consumption by controlled convective flow and movement. Reverse micelles spontaneously form in oil-in-water systems that contain surfactants and may serve as internal compartments and reservoirs. In addition, monolayers of simple surfactants at an oil–water interface can serve to regulate the exchange of material as well as heat, thus creating gradients. The droplet considered here is distinct from protocell models typically based on lipid membranes with an encapsulated aqueous phase. The droplet replication cycle is based on transient non-equilibrium conditions in catanionic surfactant systems. Catanionic systems at an interface: 1) lower the interfacial tension, 2) locally enhance the surface expansion rate, 3) support internal flows under non-equilibrium conditions, an example of a Marangoni instability, and importantly in this case raise the interfacial tension when the system approaches equilibrium leading to a stable system. We exploit this process for spontaneous fission of droplets. To enforce non-equilibrium initial conditions, we separate the cationic and anionic surfactants into the oil and water phases. From this starting point, the surfactant in the aqueous phase must absorb to the interface from the outside and the surfactant in the oil phase must reach the interface from the inside to approach equilibrium. A droplet of nitrobenzene is first impregnated with 20 mm cationic surfactant (see the Supporting Information). Then the droplet is added to a solution of 5 mm anionic surfactant at pH 12, Figure 1. The droplet becomes unstable and begins to deform (Figure 1, 6–9 sec). The instabilities and slight movements are due to the interface-driven flow structures generated inside the oil droplet. After a few seconds the droplet spreads out further into a torus and dramatically breaks up into two or more smaller droplets (Figure 1, 9–18 sec). The droplets then transform from an aspherical shape to a spherical shape (Figure 1, 18 sec). After the spontaneous fission event the droplets do not fuse back into one droplet even after many minutes, see Movie S1. Spontaneous fission is driven by a transient decrease in droplet interfacial tension. When the droplet is in the fission condition it shows a lower interfacial tension than in its equilibrium condition (5 mm oleate (OA) and 2 mm CTAB at pH 12) or with either surfactant alone, see Figure 2. The maximum volume measurement for the fission condition was repeatedly measured and suggests an interfacial tension of 0.4 mNm ,

Intrinsic curvature: a marker of millimeter-scale tangential cortico-cortical connectivity?

In this paper, we draw a link between cortical intrinsic curvature and the distributions of tangential connection lengths. We suggest that differential rates of surface expansion not only lead to intrinsic curvature of the cortical sheet, but also to differential inter-neuronal spacing. We propose that there follows a consequential change in the profile of neuronal connections: specifically an enhancement of the tendency towards proportionately more short connections. Thus, the degree of cortical intrinsic curvature may have implications for short-range connectivity.

Evolution of multinucleated Ashbya gossypii hyphae from a budding yeast-like ancestor

In the filamentous ascomycete Ashbya gossypii polarity establishment at sites of germ tube and lateral branch emergence depends on homologues of Saccharomyces cerevisiae factors controlling bud site selection and bud emergence. Maintenance of polar growth involves homologues of well-known polarity factors of budding yeast. To achieve the much higher rates of sustained polar surface expansion of hyphae compared to mainly non-polarly growing yeast buds five important alterations had to evolve. Permanent presence of the polarity machinery at a confined area in the rapidly expanding hyphal tip, increased cytoplasmic space with a much enlarged ER surface for generating secretory vesicles, efficient directed transport of secretory vesicles to and accumulation at the tip, increased capacity of the exocytosis system to process these vesicles, and an efficient endocytosis system for membrane and polarity factor recycling adjacent to the zone of exocytosis. Morphological, cell biological, and molecular aspects of this evolution are discussed based on experiments performed within the past 10 y.

Not-so-tip-growth

In tip-growing plant cells such as pollen tubes and root hairs, surface expansion is confined to the cell apex. Vesicles containing pectic cell wall material are delivered to this apical region to provide the material necessarily to build the expanding cell wall. Quantification of wall expansion reveals that the surface expansion rates are not highest at the pole but instead in an annular region around the pole. These findings raise the question of the precise localization of exocytosis events in these cells. Recently, we used spatio-temporal image correlation spectroscopy (STICS) in combination with high temporal resolution confocal imaging to characterize the intracellular movement of vesicles in growing pollen tubes. These observations, together with the analysis of FRAP (fluorescence recovery after photobleaching) experiments, indicate that exocytosis is likely to occur predominantly in the same annular region where wall expansion rates are greatest. Therefore, tip growth in plant cells does not seem to happen exactly at the tip.

Adsorption Kinetics in Binary Surfactant Mixtures Studied with External Reflection FTIR Spectroscopy

The adsorption kinetics of mixtures of soluble surfactants at the air-water interface was studied on an overflowing cylinder. Vibrational spectra of the adsorbed monolayers were acquired by external reflection Fourier transform infrared spectroscopy, and target factor analysis was used to determine the compositions of mixed monolayers. Laser Doppler velocimetry was employed to measure the surface expansion rates, and hence the effective surface age, which was in the range 0.1-1 s. Three surfactant mixtures with different interactions were investigated. Blends of the cationic hydrocarbon surfactant hexadecyl trimethylammonium bromide (CTAB) and the nonionic hydrocarbon surfactant octaethylene glycol monodecyl ether (C10E8) were found to mix ideally in the monolayer over a wide range of subsurface compositions. Combinations of C10E8 and the anionic fluorosurfactant ammonium perfluorononanoate (APFN) exhibited nonideal mixing that could be described with regular solution theory. APFN adsorbed to the interface at a rate limited by monomer diffusion but the adsorption of C10E8 appeared to be under kinetic control. The adsorption behavior of the cationic-anionic mixture of CTAB and APFN was dominated by the interaction of the oppositely charged headgroups. Either side of equimolar bulk composition only the species in excess was found to adsorb, which is rationalized by the presence of aggregates in the bulk that act as a sink for free monomer. Prior evidence in the literature suggests these aggregates may be vesicles. At equimolar compositions both species were found to coadsorb; this unexpected result may be explained by adsorption of vesicles to the uncharged interface. A semiquantitative model based on the interaction between the electrical double layers of the oppositely charged monolayer and vesicle explains the absence of adsorption of vesicles away from equimolar compositions. The combination of the overflowing cylinder, to generate a steadily expanding surface with well-defined hydrodynamics, and FTIR spectroscopy, to quantify the composition of the adsorbed monolayer, can be used to study a broad range of mixed monolayers at the air-water interface under nonequilibrium conditions.