Assessment of seabed litter at Concepción Seamount (Canary island) using a remotely operated towed vehicle.

The seafloor is recognised as a major sink for marine litter. However, studies conducted in this compartment addressing marine litter densities and its interactions with fauna are scarce, mainly due to sampling constraints. In this paper, we assess marine litter density, composition and interactions with marine communities and evaluate its relationship with fishing activities at the "Banco de la Concepción" seamount (Canary Islands, Spain). We took advantage of underwater video records taken with a Remotely Operated Towed Vehicle in the framework of the LIFE IP INTEMARES project. A total of 56 video transects were analysed covering about 9 km with 19 h of video recording. Transects were categorised as high, low, and null fishing effort based on the Vessel Monitoring System (VMS) positional data registered between 2009 and 2017. Litter items were recorded in 70% of the transects with a mean density of 2122 (±2464) items km-2. There were significant differences in litter densities over the three levels of fishing pressure, with a density decrease from stations of high to stations of null fishing pressure. Regarding categories, plastic was by far the most abundant category found (83.1%), mainly consisting of fishing lines, both monofilaments and entangled longlines. The study of the interactions of marine litter with fauna showed that less than 20% of the items presented an interaction with benthic organisms either by causing or not a visible impact. The sponge Asconema setubalense accounted for more than half (57.4%) of all interactions, but only 5% of all A. setubalense specimens showed physical damage.

Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars.

During their thermally pulsing phase, asymptotic giant branch (AGB) stars eject material that forms extended dusty envelopes1. Visible polarimetric imaging found clumpy dust clouds within two stellar radii of several oxygen-rich stars2-6. Inhomogeneous molecular gas has also been observed in multiple emission lines within several stellar radii of different oxygen-rich stars, including W Hya and Mira7-10. At the stellar surface level, infrared images have shown intricate structures around the carbon semiregular variable R Scl and in the S-type star π1 Gru11,12. Infrared images have also shown clumpy dust structures within a few stellar radii of the prototypical carbon AGB star IRC+10°216 (refs. 13,14), and studies of molecular gas distribution beyond the dust formation zone have also shown complex circumstellar structures15. Because of the lack of sufficient spatial resolution, however, the distribution of molecular gas in the stellar atmosphere and the dust formation zone of AGB carbon stars is not known, nor is how it is subsequently expelled. Here we report observations with a resolution of one stellar radius of the recently formed dust and molecular gas in the atmosphere of IRC+10°216. Lines of HCN, SiS and SiC2 appear at different radii and in different clumps, which we interpret as large convective cells in the photosphere, as seen in Betelgeuse16. The convective cells coalesce with pulsation, causing anisotropies that, together with companions17,18, shape its circumstellar envelope.

Twitter data analysis to assess the interest of citizens on the impact of marine plastic pollution.

Few studies have mined social media platforms to assess environmental concerns. In this study, Twitter was scraped to obtain a ~140,000 tweet dataset related specifically to marine plastic pollution. The goal is to understand what kind of users profiles are tweeting and how and when they do it. In addition, topic modelling and graph theory techniques have allowed us to identify main concerns on this topic: i) impact on wildlife, ii) microplastics/water pollution, iii) estimates/reports, iv) legislation/protection, and v) recycling/cleaning initiatives. Results reveal a scarce influence of organizations involved in research and marine environmental awareness, so some guidelines are depicted that could help to adjust their communication plans. This is relevant to engage society through reliable information, change habits and reinforce sustainable behaviour. A visualization tool has been created to analyze the results over time.

Ectopic expression of the atypical HLH FaPRE1 gene determines changes in cell size and morphology.

PACLOBUTRAZOL RESISTANCE (PRE) genes code atypical HLH transcriptional regulators characterized by the absence of a DNA-binding domain but present an HLH dimerization domain. In vegetative tissues, the function of these HLH proteins has been related with cell elongation processes. In strawberry, three FaPRE genes are expressed, two of them (FaPRE2 and FaPRE3) in vegetative tissues while FaPRE1 is fruit receptacle-specific. Ubiquitous FaPRE1 accumulation produced elongated flower receptacles and plants due to the elongation of the main aerial vegetative organs, with the exception of leaves. Histological analysis clearly demonstrated that the observed phenotype was due to significant changes in the parenchymal cell's morphology. In addition, transcriptomic studies of the transgenic elongated flower receptacles allowed to identify a small group of differentially expressed genes that encode cell wall-modifying enzymes. Together, the data seem to indicate that, in the strawberry plant vegetative organs, FaPRE proteins could modulate the expression of genes related with the determination of the size and shape of the parenchymal cells.

Oxygen intercalation in PVD graphene grown on copper substrates: A decoupling approach.

We investigate the intercalation process of oxygen in-between a PVD-grown graphene layer and different copper substrates as a methodology for reducing the substrate-layer interaction. This growth method leads to an extended defect-free graphene layer that strongly couples with the substrate. We have found, by means of X-ray photoelectron spectroscopy, that after oxygen exposure at different temperatures, ranging from 280 °C to 550 °C, oxygen intercalates at the interface of graphene grown on Cu foil at an optimal temperature of 500 °C. The low energy electron diffraction technique confirms the adsorption of an atomic oxygen adlayer on top of the Cu surface and below graphene after oxygen exposure at elevated temperature, but no oxidation of the substrate is induced. The emergence of the 2D Raman peak, quenched by the large interaction with the substrate, reveals that the intercalation process induces a structural undoing. As suggested by atomic force microscopy, the oxygen intercalation does not change significantly the surface morphology. Moreover, theoretical simulations provide further insights into the electronic and structural undoing process. This protocol opens the door to an efficient methodology to weaken the graphene-substrate interaction for a more efficient transfer to arbitrary surfaces.

Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates.

Chemical equilibrium has proven extremely useful for predicting the chemical composition of AGB atmospheres. Here we use a recently developed code and an updated thermochemical database that includes gaseous and condensed species involving 34 elements to compute the chemical equilibrium composition of AGB atmospheres of M-, S-, and C-type stars. We include for the first time Ti x C y clusters, with x = 1-4 and y = 1-4, and selected larger clusters ranging up to Ti13C22, for which thermochemical data are obtained from quantum-chemical calculations. Our main aims are to systematically survey the main reservoirs of each element in AGB atmospheres, review the successes and failures of chemical equilibrium by comparing it with the latest observational data, identify potentially detectable molecules that have not yet been observed, and diagnose the most likely gas-phase precursors of dust and determine which clusters might act as building blocks of dust grains. We find that in general, chemical equilibrium reproduces the observed abundances of parent molecules in circumstellar envelopes of AGB stars well. There are, however, severe discrepancies of several orders of magnitude for some parent molecules that are observed to be anomalously overabundant with respect to the predictions of chemical equilibrium. These are HCN, CS, NH3, and SO2 in M-type stars, H2O and NH3 in S-type stars, and the hydrides H2O, NH3, SiH4, and PH3 in C-type stars. Several molecules have not yet been observed in AGB atmospheres but are predicted with non-negligible abundances and are good candidates for detection with observatories such as ALMA. The most interesting ones are SiC5, SiNH, SiCl, PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO, ZrO, VO, FeS, CoH, and NiS. In agreement with previous studies, the first condensates predicted to appear in C-rich atmospheres are found to be carbon, TiC, and SiC, while Al2O3 is the first major condensate expected in O-rich outflows. According to our chemical equilibrium calculations, the gas-phase precursors of carbon dust are probably acetylene, atomic carbon, and/or C3, while for silicon carbide dust, the most likely precursors are the molecules SiC2 and Si2C. In the case of titanium carbide dust, atomic Ti is the major reservoir of this element in the inner regions of AGB atmospheres, and therefore it is probably the main supplier of titanium during the formation of TiC dust. However, chemical equilibrium predicts that large titanium-carbon clusters such as Ti8C12 and Ti13C22 become the major reservoirs of titanium at the expense of atomic Ti in the region where condensation of TiC is expected to occur. This suggests that the assembly of large Ti x C y clusters might be related to the formation of the first condensation nuclei of TiC. In the case of Al2O3 dust, chemical equilibrium indicates that atomic Al and the carriers of Al-O bonds AlOH, AlO, and Al2O are the most likely gas-phase precursors.

Broad band high resolution rotational spectroscopy for Laboratory Astrophysics.

We present a new experimental setup devoted to the study of gas phase molecules and processes using broad band high spectral resolution rotational spectroscopy. A reactor chamber has been equipped with radio receivers similar to those used by radio astronomers to search for molecular emission in space. The whole Q (31.5-50 GHz) and W bands (72-116.5 GHz) are available for rotational spectroscopy observations. The receivers are equipped with 16×2.5 GHz Fast Fourier Transform spectrometers with a spectral resolution of 38.14 kHz allowing the simultaneous observation of the complete Q band and one third of the W band. The whole W band can be observed in three settings in which the Q band is always observed. Species such as CH3CN, OCS, and SO2 are detected, together with many of their isotopologues and vibrationally excited states, in very short observing times. The system permits automatic overnight observations and integration times as long as 2.4×105 seconds have been reached. The chamber is equipped with a radiofrequency source to produce cold plasmas and with four ultraviolet lamps to study photochemical processes. Plasmas of CH4, N2, CH3CN, NH3, O2, and H2, among other species, have been generated and the molecular products easily identified by their rotational spectrum, and mass spectrometry and optical spectroscopy. Finally, the rotational spectrum of the lowest energy conformer of CH3CH2NHCHO (N-Ethylformamide), a molecule previously characterized in microwave rotational spectroscopy, has been measured up to 116.5 GHz allowing the accurate determination of its rotational and distortion constants and its search in space.

Reversible Graphene decoupling by NaCl photo-dissociation.

We describe the reversible intercalation of Na under graphene on Ir(111) by photo-dissociation of a previously adsorbed NaCl overlayer. After room temperature evaporation, NaCl adsorbs on top of graphene forming a bilayer. With a combination of electron diffraction and photoemission techniques we demonstrate that the NaCl overlayer dissociates upon a short exposure to an X-ray beam. As a result, chlorine desorbs while sodium intercalates under the graphene, inducing an electronic decoupling from the underlying metal. Low energy electron diffraction shows the disappearance of the moiré pattern when Na intercalates between graphene and iridium. Analysis of the Na 2p core-level by X-ray photoelectron spectroscopy shows a chemical change from NaCl to metallic buried Na at the graphene/Ir interface. The intercalation-decoupling process leads to a n-doped graphene due to the charge transfer from the Na, as revealed by constant energy angle resolved X-ray photoemission maps. Moreover, the process is reversible by a mild annealing of the samples without damaging the graphene.

Direct visualization of the native structure of viroid RNAs at single-molecule resolution by atomic force microscopy.

Viroids are small infectious, non-protein-coding circular RNAs that replicate independently and, in some cases, incite diseases in plants. They are classified into two families: Pospiviroidae, composed of species that have a central conserved region (CCR) and replicate in the cell nucleus, and Avsunviroidae, containing species that lack a CCR and whose multimeric replicative intermediates of either polarity generated in plastids self-cleave through hammerhead ribozymes. The compact, rod-like or branched, secondary structures of viroid RNAs have been predicted by RNA folding algorithms and further examined using different in vitro and in vivo experimental techniques. However, direct data about their native tertiary structure remain scarce. Here we have applied atomic force microscopy (AFM) to image at single-molecule resolution different variant RNAs of three representative viroids: potato spindle tuber viroid (PSTVd, family Pospiviroidae), peach latent mosaic viroid and eggplant latent viroid (PLMVd and ELVd, family Avsunviroidae). Our results provide a direct visualization of their native, three-dimensional conformations at 0 and 4 mM Mg2+ and highlight the role that some elements of tertiary structure play in their stabilization. The AFM images show that addition of 4 mM Mg2+ to the folding buffer results in a size contraction in PSTVd and ELVd, as well as in PLMVd when the kissing-loop interaction that stabilizes its 3D structure is preserved.

Toward multifaceted roles of sucrose in the regulation of stomatal movement.

Plant atmospheric CO2 fixation depends on the aperture of stomatal pores at the leaf epidermis. Stomatal aperture or closure is regulated by changes in the metabolism of the two surrounding guard cells, which respond directly to environmental and internal cues such as mesophyll-derived metabolites. Sucrose has been shown to play a dual role during stomatal movements. The sucrose produced in the mesophyll cells can be transported to the vicinity of the guard cells via the transpiration stream, inducing closure in periods of high photosynthetic rate. By contrast, sucrose breakdown within guard cells sustains glycolysis and glutamine biosynthesis during light-induced stomatal opening. Here, we provide an update regarding the role of sucrose in the regulation of stomatal movement highlighting recent findings from metabolic and systems biology studies. We further explore how sucrose-mediated mechanisms of stomatal movement regulation could be useful to understand evolution of stomatal physiology among different plant groups.

Precisely controlled fabrication, manipulation and in-situ analysis of Cu based nanoparticles.

The increasing demand for nanostructured materials is mainly motivated by their key role in a wide variety of technologically relevant fields such as biomedicine, green sustainable energy or catalysis. We have succeeded to scale-up a type of gas aggregation source, called a multiple ion cluster source, for the generation of complex, ultra-pure nanoparticles made of different materials. The high production rates achieved (tens of g/day) for this kind of gas aggregation sources, and the inherent ability to control the structure of the nanoparticles in a controlled environment, make this equipment appealing for industrial purposes, a highly coveted aspect since the introduction of this type of sources. Furthermore, our innovative UHV experimental station also includes in-flight manipulation and processing capabilities by annealing, acceleration, or interaction with background gases along with in-situ characterization of the clusters and nanoparticles fabricated. As an example to demonstrate some of the capabilities of this new equipment, herein we present the fabrication of copper nanoparticles and their processing, including the controlled oxidation (from Cu0 to CuO through Cu2O, and their mixtures) at different stages in the machine.

Synthetic microfibers in the marine environment: A review on their occurrence in seawater and sediments.

The objective of this review is to summarize information on microfibers in seawater and sediments from available scientific information. Microfibers were found in all reviewed documents. An heterogeneous approach is observed, with regard to sampling methodologies and units. Microfibers in sediments range from 1.4 to 40 items per 50mL or 13.15 to 39.48 items per 250g dry weight. In the case of water, microfibers values ranges from 0 to 450items·m-3 or from 503 to 459,681items·km-2. Blue is the most common color in seawater and sediments, followed by transparent and black in the case of seawater, and black and colorful in sediments. Related with polymer type, polypropylene is the most common in water and sediments, followed by polyethylene in water and polyester in water and sediments. Some polymers were described only in water samples: high-density polyethylene, low-density polyethylene and cellophane, whilst only rayon was reported in sediments.

Circumstellar chemistry of Si-C bearing molecules in the C-rich AGB star IRC+10216.

Silicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths.

Using radio astronomical receivers for molecular spectroscopic characterization in astrochemical laboratory simulations: A proof of concept.

We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41-49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using different materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH3OH, CH3CH2OH, HCOOH, OCS, CS, SO2 (<10-3 mbar) were detected in a few seconds. Fast data acquisition was achieved allowing for kinetic measurements in fragmentation experiments using electron impact or UV irradiation. Time evolution of chemical reactions involving OCS, O2 and CS2 was also observed demonstrating that reactive species, such as CS, can be maintained with high abundance in the gas phase during these experiments.

Spectroscopic characterization of the on-surface induced (cyclo)dehydrogenation of a N-heteroaromatic compound on noble metal surfaces.

New nanoarchitectures can be built from polycyclic aromatic hydrocarbons (PAHs) by exploiting the capability of some metal surfaces for inducing cyclodehydrogenation reactions. This bottom-up approach allows the formation of nanostructures with a different dimensionality from the same precursor as a consequence of the diffusion and coupling of the PAHs adsorbed on the surface. In this work we present a thorough study, by means of a combination of X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure and scanning tunneling microscopy with first principle calculations of the structural and chemical transformations undergone by pyridyl-substituted dibenzo[5]helicene on three coinage surfaces, namely Cu(110), Cu(111) and Au(111). Upon annealing, on-surface chemical reactions are promoted affecting the adsorbate/substrate and the molecule/molecule interactions. This thermally induced process favours the transformation from diffusing isolated molecules to polymeric nanographene chains and finally to N-doped graphene.

[Effectiveness of education based on neuroscience in the treatment of musculoskeletal chronic pain]. / Efectividad de la educacion basada en neurociencia en el abordaje del dolor cronico musculoesqueletico.

INTRODUCTION: Chronic pain is one of the most frequent health, economic and social problems. Given this, numerous approaches have been described, one of which is pain neuroscience education. AIM: To examine the effectiveness of pain neuroscience education in the treatment of musculoskeletal disorders with chronic pain and to explore the impact of specific aspects of the technique on its effectiveness. MATERIAL AND METHODS: Relevant studies published between 2000 and 2015 were identified by searching PubMed, Scopus and Web of Science. Studies identified by electronic searches were screened against a set of pre-defined inclusion criteria. PEDro and SIGN scales were used to evaluate the methodological quality of the included studies. RESULTS: Ten studies were included in this systematic review. The main outcomes that were measured were pain, disability, neurophysiology pain test, attitudes and beliefs, fear-avoidance beliefs, self-care, kinesiophobia, quality of life and algometry. The results suggest that pain neuroscience education is effective in the short term and medium/long term for pain relief, either alone or combined with multimodal treatment. It was also effective in normalizing cognitions about pain, fear-avoidance beliefs, and self-care. CONCLUSION: Despite some evidence for a positive effect in the short and medium/long term, the heterogeneity in the technical aspects used does not allow the obtaining of conclusive results.

TITLE: Efectividad de la educacion basada en neurociencia en el abordaje del dolor cronico musculoesqueletico.Introduccion. El dolor cronico constituye uno de los problemas sanitarios, economicos y sociales mas frecuentes. Ante esto, se han descrito numerosos enfoques en el abordaje, y destaca en la actualidad la educacion basada en la neurociencia del dolor. Objetivo. Determinar la efectividad de este abordaje y conocer el impacto de aspectos especificos referentes a su aplicacion. Materiales y metodos. Se incluyeron estudios relevantes que cumplieran los criterios seleccionados, identificados en las bases de datos PubMed, Scopus y Web of Science, y publicados desde el año 2000 hasta 2015. La calidad metodologica y el grado de recomendacion se evaluaron mediante las escalas PEDro y SIGN. Resultados. Se incluyeron 10 estudios en la revision sistematica. Las variables medidas fueron dolor, discapacidad, conocimiento sobre la neurofisiologia del dolor, creencias y cogniciones, miedo-evitacion, cinesiofobia, calidad de vida y algometria. Los resultados sugieren que la educacion basada en neurociencia del dolor resulta eficaz a corto plazo y medio/largo plazo para aliviar el dolor, ya sea aplicada sola o combinada con tratamiento multimodal. Tambien resulto eficaz en la normalizacion de cogniciones sobre el dolor, las creencias de miedo-evitacion y el autocuidado. Conclusion. A pesar de la eficacia a corto y medio/largo plazo, la heterogeneidad en los aspectos tecnicos empleados no permite la obtencion de resultados concluyentes.

High-quality PVD graphene growth by fullerene decomposition on Cu foils.

We present a new protocol to grow large-area, high-quality single-layer graphene on Cu foils at relatively low temperatures. We use C60 molecules evaporated in ultra high vacuum conditions as carbon source. This clean environment results in a strong reduction of oxygen-containing groups as depicted by X-ray photoelectron spectroscopy (XPS). Unzipping of C60 is thermally promoted by annealing the substrate at 800ºC during evaporation. The graphene layer extends over areas larger than the Cu crystallite size, although it is changing its orientation with respect to the surface in the wrinkles and grain boundaries, producing a modulated ring in the low energy electron diffraction (LEED) pattern. This protocol is a self-limiting process leading exclusively to one single graphene layer. Raman spectroscopy confirms the high quality of the grown graphene. This layer exhibits an unperturbed Dirac-cone with a clear n-doping of 0.77 eV, which is caused by the interaction between graphene and substrate. Density functional theory (DFT) calculations show that this interaction can be induced by a coupling between graphene and substrate at specific points of the structure leading to a local sp3 configuration, which also contribute to the D-band in the Raman spectra.

The growth of carbon chains in IRC +10216 mapped with ALMA.

Linear carbon chains are common in various types of astronomical molecular sources. Possible formation mechanisms involve both bottom-up and top-down routes. We have carried out a combined observational and modeling study of the formation of carbon chains in the C-star envelope IRC +10216, where the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons can drive the formation of linear carbon chains of increasing length. We have used ALMA to map the emission of λ 3 mm rotational lines of the hydrocarbon radicals C2H, C4H, and C6H, and the CN-containing species CN, C3N, HC3N, and HC5N with an angular resolution of ~1″. The spatial distribution of all these species is a hollow, 5-10″ wide, spherical shell located at a radius of 10-20″ from the star, with no appreciable emission close to the star. Our observations resolve the broad shell of carbon chains into thinner sub-shells which are 1-2″ wide and not fully concentric, indicating that the mass loss process has been discontinuous and not fully isotropic. The radial distributions of the species mapped reveal subtle differences: while the hydrocarbon radicals have very similar radial distributions, the CN-containing species show more diverse distributions, with HC3N appearing earlier in the expansion and the radical CN extending later than the rest of the species. The observed morphology can be rationalized by a chemical model in which the growth of polyynes is mainly produced by rapid gas-phase chemical reactions of C2H and C4H radicals with unsaturated hydrocarbons, while cyanopolyynes are mainly formed from polyynes in gas-phase reactions with CN and C3N radicals.

Microplastics in coastal sediments from Southern Portuguese shelf waters.

Microplastics are well-documented pollutants in the marine environment that result from fragmentation of larger plastic items. Due to their long chemical chains, they can remain in the environment for long periods of time. It is estimated that the vast majority (80%) of marine litter derives from land sources and that 70% will sink and remain at the bottom of the ocean. Microplastics that result from fragmentation of larger pieces of plastic are common to be found in beaches and in the water surface. The most common microplastics are pellets, fragments and fibres. This work provides original data of the presence of microplastics in coastal sediments from Southern Portuguese shelf waters, reporting on microplastic concentration and polymer types. Microplastic particles were found in nearly 56% of sediment samples, accounting a total of 31 particles in 27 samples. The vast majority were microfibers (25), identified as rayon fibres, and fragments (6) identified as polypropylene, through infrared spectroscopy (µ-FTIR). The concentration and polymer type data is consistent with other relevant studies and reports worldwide.

Mesophyll conductance to CO2 and Rubisco as targets for improving intrinsic water use efficiency in C3 plants.

Water limitation is a major global constraint for plant productivity that is likely to be exacerbated by climate change. Hence, improving plant water use efficiency (WUE) has become a major goal for the near future. At the leaf level, WUE is the ratio between photosynthesis and transpiration. Maintaining high photosynthesis under water stress, while improving WUE requires either increasing mesophyll conductance (gm ) and/or improving the biochemical capacity for CO2 assimilation-in which Rubisco properties play a key role, especially in C3 plants at current atmospheric CO2 . The goals of the present analysis are: (1) to summarize the evidence that improving gm and/or Rubisco can result in increased WUE; (2) to review the degree of success of early attempts to genetically manipulate gm or Rubisco; (3) to analyse how gm , gsw and the Rubisco's maximum velocity (Vcmax ) co-vary across different plant species in well-watered and drought-stressed conditions; (4) to examine how these variations cause differences in WUE and what is the overall extent of variation in individual determinants of WUE; and finally, (5) to use simulation analysis to provide a theoretical framework for the possible control of WUE by gm and Rubisco catalytic constants vis-à-vis gsw under water limitations.