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SUMMARYUnravelling the factors determining the allocation of carbon to various plant organs is one of the great challenges of modern plant biology. Studying allocation under close to natural conditions requires noninvasive methods, which are now becoming available for measuring plants on a par with those developed for humans. By combining magnetic resonance imaging (MRI) and positron emission tomography (PET), we investigated three contrasting root/shoot systems growing in sand or soil, with respect to their structures, transport routes and the translocation dynamics of recently fixed photoassimilates labelled with the shortlived radioactive carbon isotope 11 C. Storage organs of sugar beet (Beta vulgaris) and radish plants (Raphanus sativus) were assessed using MRI, providing images of the internal structures of the organs with high spatial resolution, and while species-specific transport sectoralities, properties of assimilate allocation and unloading characteristics were measured using PET. Growth and carbon allocation within complex root systems were monitored in maize plants (Zea mays), and the results may be used to identify factors affecting root growth in natural substrates or in competition with roots of other plants. MRI-PET co-registration opens the door for non-invasive analysis of plant structures and transport processes that may change in response to genomic, developmental or environmental challenges. It is our aim to make the methods applicable for quantitative analyses of plant traits in phenotyping as well as in understanding the dynamics of key processes that are essential to plant performance.

A facile strategy to obtain magnetically actuated arrays of micropillars able to undergo reversible, homogeneous, drastic, and tunable geometrical changes upon application of a magnetic field with variable strength is demonstrated. A magnetically tunable gecko-inspired adhesive that works under dry and wet conditions is realized using elastomeric micropatterns containing magnetic microparticles.

ABSTRACT:Magnets of the Halbach layout are interesting for the use in mobile NMR/ MRI devices. Therefore, the ideal Halbach magnet was iterated using identical bar magnets, which are positioned and oriented based on analytical equations. These configurations were simulated with two-dimensional finite-element methods. Performance factors were defined to relate field strength with homogeneity and mass. A geometry of 16 magnets provided a good compromise between performance and special requirements for the desired use to store hyperpolarized xenon. The construction of such a magnet required the design of dedicated support frames and procedures to mount them. The field strength and homogeneity in the finished magnet were measured by a Hall probe and agreed well with the simulations. The calculation and construction are described in detail and together with the tabled field values for n magnets with n Յ 80 may prove helpful for building similar devices, which were named NMR Mandhalas (Magnet Arrangements for Novel Discrete Halbach Layout).

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Hyperpolarized fumarate is a promising biosensor for carbon-13 magnetic resonance metabolic imaging. Such molecular imaging applications require nuclear hyperpolarization to attain sufficient signal strength. Dissolution dynamic nuclear polarization is the current state-of-the-art methodology for hyperpolarizing fumarate, but this is expensive and relatively slow. Alternatively, this important biomolecule can be hyperpolarized in a cheap and convenient manner using parahydrogen-induced polarization. However, this process requires a chemical reaction, and the resulting solutions are contaminated with the catalyst, unreacted reagents, and reaction side-product molecules, and are hence unsuitable for use in vivo. In this work we show that the hyperpolarized fumarate can be purified from these contaminants by acid precipitation as a pure solid, and later redissolved to a desired concentration in a clean aqueous solvent. Significant advances in the reaction conditions and reactor equipment allow for formation of hyperpolarized fumarate at 13C polarization levels of 30–45%.

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Arrays of actuated magnetic micropillars that can be tilted, twisted, and rotated in the presence of a magnetic field gradient were obtained. The type and extent of the movements are dependent on the distribution (isotropic, anisotropic) of the magnetizable particles inside the pillars and the strength and the direction of the magnetic field gradient. Independent motion of groups of pillars in the same or opposite directions or homogeneous motion of the whole pattern has been realized. Changing the pattern geometry causes changes in the roll-off angle (ROA) of water droplets on the surface. We show magnetically induced changes in the ROA and direction-dependent ROAs as a consequence of the anisotropy of tilted patterns. We also demonstrate transfer of microparticles between magnetically actuated neighboring pillars.