Microtubule organization changes severely after mannitol and n-butanol treatments inducing microspore embryogenesis in bread wheat

Background A mannitol stress treatment and a subsequent application of n-butanol, known as a microtubule-disrupting agent, enhance microspore embryogenesis (ME) induction and plant regeneration in bread wheat. To characterize changes in cortical (CMT) and endoplasmic (EMT) microtubules organization and dynamics, associated with ME induction treatments, immunocytochemistry studies complemented by confocal laser scanning microscopy (CLSM) were accomplished. This technique has allowed us to perform advanced 3- and 4D studies of MT architecture. The degree of MT fragmentation was examined by the relative fluorescence intensity quantification. Results In uni-nucleated mannitol-treated microspores, severe CMT and EMT fragmentation occurs, although a complex network of short EMT bundles protected the nucleus. Additional treatment with n-butanol resulted in further depolymerization of both CMT and EMT, simultaneously with the formation of MT aggregates in the perinuclear region. Some aggregates resembled a preprophase band. In addition, a portion of the microspores progressed to the first mitotic division during the treatments. Bi-nucleate pollen-like structures showed a high MT depolymerization after mannitol treatment and numerous EMT bundles around the vegetative and generative nuclei after n-butanol. Interestingly, bi-nucleate symmetric structures showed prominent stabilization of EMT. Conclusions Fragmentation and stabilization of microtubules induced by mannitol- and n-butanol lead to new configurations essential for the induction of microspore embryogenesis in bread wheat. These results provide robust insight into MT dynamics during EM induction and open avenues to address newly targeted treatments to induce ME in recalcitrant species.

Complex resistivity inversion using controlled source electromagnetic data

<p>In some Earth materials, induced polarization (IP) phenomena are occurring when an electric perturbation is applied. These mechanisms are described by a frequency dependent complex resistivity. The study of relaxation model parameters describing these phenomena allows to access indirectly to several properties of interest of the underground, as properties linked to the pore space geometry, fluid content or presence and discrimination of disseminated metallic particles. Nevertheless, complex resistivity is usually studied using electrical method with a direct current hypothesis, neglecting by the way electromagnetic induction that can occurs in the data. Thus, strong limitations appear to recover a complex resistivity image as EM induction increase with frequencies and larger offset.</p><p> </p><p>We implemented a frequency dependent complex resistivity in POLYEM3D, a 3D finite-difference modelling and inversion code for controlled-source electromagnetic data (CSEM) in order to fully recover IP information contained in EM data. CSEM method is a resistivity imaging technique using multi-frequency electromagnetic signals fully taking into account EM induction with larger investigation depth. Following a preliminary sensitivity study, a multi-stages inversion strategy was defined to undertake the multi-parameters problem. Furthermore, to manage the increasing number of parameters, a second order polynomial parametrization is used to describe frequency variation of complex resistivity.</p><p> </p><p>We show through 1D synthetic data inversions and preliminary 3D results that we are able to recover a complex resistivity and its frequency variation from CSEM data in the IP/EM coupling domain, when IP signals are sufficiently large compared to EM induction. Our inversion strategy allows then to access to IP parameters of the medium in an extended frequency domain as well as for greater depth of investigation. A 3D CSEM survey was undertaken in December 2020 on the former mining site of La Porte-Aux-Moines (Côtes-d'Armor, France) presenting strong IP responses, to validate our inversion method for a 3D in-situ dataset.</p>

Three-dimensional electrical conductivity of the world ocean and seabed sediments: effect on EM induction responses

<p>This work presents global 3-D electrical conductivity atlas of the world ocean and seabed sediments. Ocean salinity and temperature data were converted to electrical conductivity by solving a thermodynamic equation of state of seawater. A sediment compaction model was used to estimate the depth-dependent electrical conductivity of the seabed sediments. Electromagnetic responses in a wide period band, including typical ranges used in CSEM, MT and Global studies, are significantly affected by varying ocean and sediments conductivity. Incorporating this information in a model prior to inversion helps avoid artifacts and improve data fit. The atlas is openly available along with a concise and easy to use Python toolbox.</p>

Lateral variations of electrical conductivity in the lower mantle constrained by Swarm and CryoSat-2 missions

The electrical conductivity is an important geophysical parameter connected to the thermal, chemical, and mineralogical state of the Earth’s mantle. In this paper, we apply the previously developed methodology of forward and inverse EM induction modeling to the latest version of satellite-derived spherical harmonic coefficients of external and internal magnetic field, and obtain the first 3-D mantle conductivity models with contributions from Swarm and CryoSat-2 satellite data. We recover degree 3 conductivity structures which partially overlap with the shape of the large low-shear velocity provinces in the lower mantle.

Lateral Variations of Electrical Conductivity in the Lower Mantle Constrained by Swarm and CryoSat-2 Missions

The electrical conductivity is an important geophysical parameter connected to the thermal, chemical, and mineralogical state of the Earth's mantle. In this paper we apply the previously developed methodology of forward and inverse EM induction modelling to the latest version of satellite-derived spherical harmonic coefficients of external and internal magnetic field, and obtain the first 3-D mantle conductivity models with contributions from Swarm and CryoSat-2 satellite data. We recover degree 3 conductivity structures which partially overlap with the shape of the large low-shear velocity provinces in the lower mantle.

The first Women's Networking Events at the IUGG General Assembly (2019) and the IAGA EM Induction Workshop (2018)

<p>This presentation reflects on the first Women’s Networking Events at the International Union of Geodesy and Geophysics’s General Assembly (2019) and the International Association of Geomagnetism and Aeronomy’s Electromagnetic Induction Workshop (2018). These meetings are historically extremely male-dominated events and the Women’s Networking Events provided a first-of-its-kind space for women to network with one another, creating solidarity and community for participants to rely on through the meeting and beyond. Both events were well attended, especially by early career women, with ~40 participants in each case. Women’s Networking Events have been present at the American Geophysical Union’s Fall Meeting for many years now, and these inaugural IUGG/IAGA Women’s Networking Events will hopefully lead to many more (indeed, the local organizing committee for the 2020 Electromagnetic Induction Workshop has already included the Women’s Networking Event in the workshop schedule and budget). This presentation will discuss the motivation behind the events, lessons learned, and ideas for the future.</p>

Comparing three approaches to the ground geoelectric field modelling due to space weather events

<p>In order to estimate the potential hazard to technological systems from space weather, it is necessary to understand the spatiotemporal evolution of the geoelectric field during geomagnetic disturbances. Once the geoelectric field is quantitively estimated, geomagnetically induced currents can be calculated from the geometry of transmission lines and system design parameters. To address the complex problem of the ground electromagnetic (EM) field modelling due to space weather events, it is necessary to consider the spatiotemporal structure of the source of the EM induction in a realistic way and take into account a realistic three‐dimensional (3‐D) distribution of the Earth's electrical conductivity.</p><p>In this work we compare three approaches to the geoelectric field modelling. All approaches are based on the numerical solution of Maxwell's equations in Earth's models with 3-D conductivity distribution. The difference between them lies in different setting of the EM induction source. In the first two methods the source is represented by a laterally varying sheet current flowing above the Earth. The current in the first approach is computed on the base of 3-D magnetohydrodynamic simulation of near-Earth space. In the second one the source is constructed using ground-based magnetometers' data. In the third approach the geoelectric field is calculated using plane wave excitation. We carry out geoelectric field modellings for Kola Peninsula and Karelia using these three approaches. In our simulations we utilise the 3-D conductivity model of Fennoscandia (SMAP). The geoelectric field is computed using 3-D EM forward modelling code extrEMe based on a contracting integral equation method. We compare modelling results to EM field observations and discuss advantages and disadvantages of the considered approaches.</p>