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Auxin is a crucial growth regulator that governs plant development and responses to environmental perturbations. It functions at the heart of many developmental processes, from embryogenesis to organ senescence, and is key to plant interactions with the environment, including responses to biotic and abiotic stimuli. As remarkable as auxin is, it does not act alone, but rather solicits the help of, or is solicited by, other endogenous signals, including the plant hormones abscisic acid, brassinosteroids, cytokinins, ethylene, gibberellic acid, jasmonates, salicylic acid, and strigolactones. The interactions between auxin and other hormones occur at multiple levels: hormones regulate one another's synthesis, transport, and/or response; hormone-specific transcriptional regulators for different pathways physically interact and/or converge on common target genes; etc. However, our understanding of this crosstalk is still fragmentary, with only a few pieces of the gigantic puzzle firmly established. In this review, we provide a glimpse into the complexity of hormone interactions that involve auxin, underscoring how patchy our current understanding is.

The allene functional group and the indole ring have emerged as recurring building blocks in organic chemistry due to their diverse reactivity and straightforward preparation. In addition, the biological properties and natural occurrence of indole give a remarkable added-value to newly-prepared indole-based structures. In the last decade, the combination of allenes and indoles as co-reactants has revealed a fruitful reactivity allowing the synthesis of complex structures and the investigation of new mechanistic pathways, such as the challenging asymmetric nucleophilic addition using optically pure allenes as chirality transfer agents, the double nucleophilic addition through metal carbene intermediates, or novel hybrid catalysis in a bimetallic system. Herein we report a critical review into the wide and fascinating ways allenes and indoles can interact, and the structural diversity that can be therefore achieved.

The complex nature of multifactorial diseases, such as Morbus Alzheimer, has produced a strong need to design multitarget-directed ligands to address the involved complementary pathways. We performed a purposive structural modification of a tetratarget small-molecule, that is contilisant, and generated a combinatorial library of 28 substituted chromen-4-ones. The compounds comprise a basic moiety which is linker-connected to the 6-position of the heterocyclic chromenone core. The syntheses were accomplished by Mitsunobu- or Williamson-type ether formations. The resulting library members were evaluated at a panel of seven human enzymes, all of which being involved in the pathophysiology of neurodegeneration. A concomitant inhibition of human acetylcholinesterase and human monoamine oxidase B, with IC50 values of 5.58 and 7.20 μM, respectively, was achieved with the dual-target 6-(4-(piperidin-1-yl)butoxy)-4H-chromen-4-one (7).

Nucleophilic additions to allenes catalyzed by transition metals represent a powerful tool to obtain selective access to diverse structures with numerous applications. Reported here is a straightforward methodology to achieve selective addition of azoles to the proximal or distal carbon of activated allenes depending on the catalyst used, unravelling a gold-platinum bimetallic catalysis approach for the 1,3-double addition of azoles to activated allenes to give 1,3-bisazole derivatives, an important scaffold in medicinal and organometallic chemistry.

Ruddlesden–Popper oxides, (AO)(ABO3) n , occupy a prominent place in the landscape of materials research because of their intriguing potential applications. Compositional modifications to the cation sublattices, A or B, have been explored in order to achieve enhanced functionalities. However, changes to the anionic sublattice have been much less explored. In this work, new oxygen-deficient manganese Ruddlesden–Popper-related phases, La0.5Ca2.5Mn2O6.5 and La0.5Ca2.5Mn2O6.25, have been synthesized by controlled reduction of the fully oxidized n = 2 term La0.5Ca2.5Mn2O7. A complete structural and compositional characterization, by means of neutron diffraction, electron diffraction and atomically resolved scanning transmission electron microscopy and electron energy-loss spectroscopy techniques, allows the proposition of a topotactic reduction pathway through preferential oxygen removal in the [MnO2] layers along [031] and [0{\bar 1}3] directions. The gradual decrease of the Mn oxidation state, accommodated by short-range ordering of anionic vacancies, reasonably explains the breaking of ferromagnetic interactions reinforcing the emergence of antiferromagnetic ones. Additional short-range order–disorder phenomena of La and Ca cations have been detected in the reduced La0.5Ca2.5Mn2O7−δ, as previously reported in the parent compound.

On-surface synthesis has recently been regarded as a promising approach for the generation of new molecular structures. It has been particularly successful in the synthesis of graphene nanoribbons, nanographenes and intrinsically reactive and instable, yet attractive species. It is based on the combination of solution chemistry aimed at preparation of appropriate molecular precursors for further ultra-high vacuum surface assisted transformations. This approach also owes its success to an incredible development of characterization techniques, such as scanning tunneling/atomic force microscopy and related methods, which allow detailed, local characterization at atomic scale. While the surface-assisted synthesis can provide molecular nanostructures with outstanding precision, down to single atoms, it suffers from basing on metallic surfaces and often limited yield. Therefore, the extension of the approach away from metals and the struggle to increase productivity seem to be significant challenges toward wider applications. Herein, we demonstrate the on-surface synthesis approach for generation of non-planar nanographenes, which are synthesized through a combination of solution chemistry and sequential surface-assisted processes, together with the detailed characterization by scanning probe microscopy methods.

The allene functionality has participated in one of the most exciting voyages in organic chemistry, from chemical curiosities to a recurring building block in modern organic chemistry. In the last decades, a special kind of allene, namely, allenol, has emerged. Allenols, formed by an allene moiety and a hydroxyl functional group with diverse connectivity, have become common building blocks for the synthesis of a wide range of structures and frequent motif in naturally occurring systems. The synergistic effect of the allene and hydroxyl functional groups enables allenols to be considered as a unique and sole functionality exhibiting a special reactivity. This Review summarizes the most significant contributions to the chemistry of allenols that appeared during the past decade, with emphasis on their synthesis, reactivity, and occurrence in natural products., This work was supported in part by AEI (MICIU) and FEDER (Project PGC2018-095025−B-I00). We thank Prof. Benito Alcaide and Prof. Pilar M. Fresneda for their mentorship in past years.

Cellulose synthesis is essential for plant morphology, water transport and defense, and provides raw material for biomaterials and fuels. Cellulose is produced at the plasma membrane by Cellulose Synthase (CESA) protein complexes (CSCs). CSCs are assembled in the endomembrane system and then trafficked from the Golgi apparatus and trans-Golgi Network (TGN) to the plasma membrane. Since CESA enzymes are only active in the plasma membrane, control of CSC secretion is a critical step in the regulation of cellulose synthesis. However, the regulatory framework for CSC secretion is not clarified. In this study, we identify members of a family of seven transmembrane domain-containing proteins (7TMs) as important for cellulose production during cell wall integrity stress. 7TM proteins are often associated with guanine nucleotide-binding protein (G) protein signalling and mutants in several of the canonical G protein complex components phenocopied the 7tm mutant plants. Unexpectedly, the 7TM proteins localized to the Golgi apparatus/TGN where they interacted with the G protein complex. Here, the 7TMs and G proteins regulated CESA trafficking, but did not affect general protein secretion. Furthermore, during cell wall stress, 7TMs’ localization was biased towards small CESA-containing vesicles, specifically associated with CSC trafficking. Our results thus outline how a G protein-coupled module regulates CESA trafficking and reveal that defects in this process lead to exacerbated responses upon exposure to cell wall integrity stress.

New genetic tools to study RGL1 expression and function through plant development allowed the uncovering of an RGL1-specific role in the control of female gametophyte development., Ovule development is essential for plant survival, as it allows correct embryo and seed development upon fertilization. The female gametophyte is formed in the central area of the nucellus during ovule development, in a complex developmental programme that involves key regulatory genes and the plant hormones auxins and brassinosteroids. Here we provide novel evidence of the role of gibberellins (GAs) in the control of megagametogenesis and embryo sac development, via the GA-dependent degradation of RGA-LIKE1 (RGL1) in the ovule primordia. YPet-rgl1Δ17 plants, which express a dominant version of RGL1, showed reduced fertility, mainly due to altered embryo sac formation that varied from partial to total ablation. YPet-rgl1Δ17 ovules followed normal development of the megaspore mother cell, meiosis, and formation of the functional megaspore, but YPet-rgl1Δ17 plants had impaired mitotic divisions of the functional megaspore. This phenotype is RGL1-specific, as it is not observed in any other dominant mutants of the DELLA proteins. Expression analysis of YPet-rgl1Δ17 coupled to in situ localization of bioactive GAs in ovule primordia led us to propose a mechanism of GA-mediated RGL1 degradation that allows proper embryo sac development. Taken together, our data unravel a novel specific role of GAs in the control of female gametophyte development.

Auxin is a crucial plant growth regulator. Forward genetic screens for auxin-related mutants have led to the identification of key genes involved in auxin biosynthesis, transport, and signaling. Loss-of-function mutations in genes involved in glucosinolate biosynthesis, a metabolically related route that produces defense compounds, result in auxin overproduction. We identified an allelic series of fertile, hypomorphic Arabidopsis (Arabidopsis thaliana) mutants for the essential glucosinolate biosynthetic gene ROOTY (RTY) that exhibit a range of phenotypic defects characteristic of enhanced auxin production. Genetic characterization of these lines uncovered phenotypic suppression by cyp79b2 cyp79b3, wei2, and wei7 mutations and revealed the phenomenon of interallelic complementation in several RTY transheterozygotes. Structural modeling of RTY elucidated the relationships between structure and function in the RTY homo- and heterodimers, and unveiled the likely structural basis of interallelic complementation. This work underscores the importance of employing true null mutants in genetic complementation studies.

RATIONALE Mass spectrometry imaging of young seedlings is an invaluable tool in understanding how mutations affect metabolite accumulation in plant development. However, due to numerous biological considerations, established methods for the relative quantification of analytes using infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) mass spectrometry imaging are not viable options. In this study, we report a method for the quantification of auxin-related compounds using stable-isotope-labelled (SIL) indole-3-acetic acid (IAA) doped into agarose substrate. METHODS Wild-type Arabidopsis thaliana seedlings, sur2 and wei8 tar2 loss-of-function mutants, and YUC1 gain-of-function line were grown for 3 days in the dark in standard growth medium. SIL-IAA was doped into a 1% low-melting-point agarose gel and seedlings were gently laid on top for IR-MALDESI imaging with Orbitrap mass spectrometry analysis. Relative quantification was performed post-acquisition by normalization of auxin-related compounds to SIL-IAA in the agarose. Amounts of auxin-related compounds were compared between genotypes to distinguish the effects of the mutations on the accumulation of indolic metabolites of interest. RESULTS IAA added to agarose was found to remain stable, with repeatability and abundance features of IAA comparable with those of other compounds used in other methods for relative quantification in IR-MALDESI analyses. Indole-3-acetaldoxime was increased in sur2 mutants compared with wild-type and other mutants. Other auxin-related metabolites were either below the limits of quantification or successfully quantified but showing little difference among mutants. CONCLUSIONS Agarose was shown to be an appropriate sampling surface for IR-MALDESI mass spectrometry imaging of Arabidopsis seedlings. SIL-IAA doping of agarose was demonstrated as a viable technique for relative quantification of metabolites in live seedlings or tissues with similar biological considerations.

[EN] Ovule primordia formation is a complex developmental process with a strong impact on the production of seeds. In Arabidopsis this process is controlled by a gene network, including components of the signalling pathways of auxin, brassinosteroids (BRs) and cytokinins. Recently, we have shown that gibberellins (GAs) also play an important role in ovule primordia initiation, inhibiting ovule formation in both Arabidopsis and tomato. Here we reveal that BRs also participate in the control of ovule initiation in tomato, by promoting an increase on ovule primordia formation. Moreover, molecular and genetic analyses of the co-regulation by GAs and BRs of the control of ovule initiation indicate that two different mechanisms occur in tomato and Arabidopsis. In tomato, GAs act downstream of BRs. BRs regulate ovule number through the downregulation of GA biosynthesis, which provokes stabilization of DELLA proteins that will finally promote ovule primordia initiation. In contrast, in Arabidopsis both GAs and BRs regulate ovule number independently of the activity levels of the other hormone. Taken together, our data strongly suggest that different molecular mechanisms could operate in different plant species to regulate identical developmental processes even, as for ovule primordia initiation, if the same set of hormones trigger similar responses, adding a new level of complexity., We wish to thank B. Janssen (Horticulture and Food Research Institute, New Zealand) for the pBJ60 shuttle vector, C. Ferrandiz and M. Colombo (IBMCP, CSIC-UPV, Valencia, Spain) for their help in the generation of 35S:ANT lines and L.E.P. Peres (Universidade de Sao Paulo, Brazil) for the tomato mutant lines. Our thanks also go to C. Fuster for technical assistance. This work was supported by grants from the Spanish Ministry of Economy and Competitiveness-FEDER (BIO2017-83138R) to MAPA and from NSF (DBI-0820755, MCB-1158181, and IOS-1444561) to JMA.

Half-doped praseodymium manganites, Pr0.5Ca0.5MnO3, synthesized by the sol–gel method produce highly crystalline nanoparticles with no structural disorder at the surface. As for most half-doped (Mn3+:Mn4+ = 1) antiferromagnetic (AFM) charge-ordered manganites, ferromagnetism (FM) appears as particle size decreases. A possible origin of FM phase development is the lacking oxygen ligands at the surface that increases Mn3+ at the expense of Mn4+ in order to maintain electronic neutrality. In this work, we show that Mn3+:Mn4+ = 1 ratio is preserved in the whole crystalline particle with the exception of the surface, where this ratio changes to Mn3+:Mn4+ > 1. This Mn3+ excess makes a double exchange Mn3+ → O2– → Mn4+ prevail over the superexchange, giving rise to the FM interactions. We show that a shell thickness of only one unit cell, with acell = 0.38 nm, is enough to explain the onset of FM at the surface, whereas the volume remains AFM. Furthermore, the FM to AFM ratio fits to the increase of surface-to-v...

On-surface synthesis provides a powerful method for the generation of long acene molecules, making possible the detailed investigation of the electronic properties of single higher acenes on a surface. By means of scanning tunneling microscopy and spectroscopy combined with theoretical considerations, we discuss the polyradical character of the ground state of higher acenes as a function of the number of linearly fused benzene rings. We present energy and spatial mapping of the tunneling resonances of hexacene, heptacene, and decacene, and discuss the role of molecular orbitals in the observed tunneling conductance maps. We show that the energy gap between the first electronic tunneling resonances below and above the Fermi energy stabilizes to a finite value, determined by a first diradical electronic perturbative contribution to the polyacene electronic ground state. Up to decacene, the main contributor to the ground state of acenes remains the lowest-energy closed-shell electronic configuration.

We report here our efforts towards understanding the catalytic species involved in a novel Pt/Au heterobimetallic system capable of efficiently catalyse the tandem cyclisation/C-X coupling reaction of heteroarylallenes with C- and N-based nucleophiles. Our evidence confirm that homogeneous Au-catalysis is involved at the beginning of the reaction to generate an intermediate that enters the second catalytic cycle where hybrid homogeneous-heterogeneous catalysis by [Pt-Au] clusters could be responsible for the high efficiency. In this part of the cycle [Pt-AuPPh3] homogeneous clusters (identified by 31P NMR) seem to be aided by Pt-Au particles in the heterogeneous phase (supported by Hg poisoning and filtration experiments, and characterization of the possible catalytic species by several techniques, e.g. 31P NMR, ICP-MS, SEM, DLS), with full Pt- to-Au transmetallation not being observed in contrast with other reported bimetallic systems. There are a few examples of hybrid homogeneous-heterogeneous catalysis in monometallic systems, but to the best of our knowledge this is the first example of hybrid homo- heterogeneous catalysis in systems involving two different metals.

Cerebrovascular diseases such as ischemic stroke are known to exacerbate dementia caused by neurodegenerative pathologies such as Alzheimer’s disease (AD). Besides, the increasing number of patients surviving stroke makes it necessary to treat the co-occurrence of these two diseases with a single and combined therapy. For the development of new dual therapeutic agents, eight hybrid quinolylnitrones have been designed and synthesized by the juxtaposition of selected pharmacophores from our most advanced lead-compounds for ischemic stroke and AD treatment. Biological analyses looking for efficient neuroprotective effects in suitable phenotypic assays led us to identify MC903 as a new small quinolylnitrone for the potential dual therapy of stroke and AD, showing strong neuroprotection on (i) primary cortical neurons under oxygen–glucose deprivation/normoglycemic reoxygenation as an experimental ischemia model; (ii), neuronal line cells treated with rotenone/oligomycin A, okadaic acid or β-amyloid peptide Aβ25–35, modeling toxic insults found among the effects of AD., This work was supported by the Instituto de Salud Carlos III and cofinanced by the Euro- pean Development Regional Fund (FEDER), grant number PI18/00255 and RETICS RD16/0019/0006, to A.A, Programa Miguel Servet CPII19/00005, PI19/00082 to JE, and by MINECO (Government of Spain) grant number SAF-2015-65586-R to J.M.-C. D.D.-I. thanks the Spanish Ministry of Science, Innovation and Universities for predoctoral FPU grant. A.E.-P. thanks Instituto de Salud Carlos III for the predoctoral contract IFI18/00011.

Epoxyacenes adsorbed on metal surfaces form acenes during thermally induced reduction in ultrahigh vacuum conditions. The incorporation of oxygen bridges into a hydrocarbon backbone leads to an enhanced stability of these molecular precursors under ambient condition; however, it has also a distinct influence on their adsorption and self-assembly on metal surfaces. Here, a low-temperature scanning tunneling microscopy (LT-STM) study of two different epoxyacenes on the Au(111) surface at submonolayer coverage is presented. Both molecules show self-assembly based on hydrogen bonding. While for the molecules with a single epoxy moiety nanostructures of three molecules are formed, extended molecular networks are achieved with two epoxy moieties and a slightly higher surface coverage. Upon annealing at 390 K, the molecules are reduced to the respective acene; however, both systems keep a similar assembled structure. The experimental STM images supported by theoretical calculations show that the self-assembly of...

Acenes are intriguing molecules with unique electronic properties. The difficulties in their preparation owing to low stability under ambient conditions are apparent because successful syntheses of long unsubstituted acenes are still scarce, in spite of the great attention they have attracted. Only unsubstituted acenes up to heptacene have been isolated in bulk, with nonacene being the largest acene detected to date. Herein we use on-surface assisted reduction of tetraepoxy decacene precursors on Au(111) as the key step to generate unprecedented decacene which is visualized and its electronic resonances studied by scanning tunneling microscopy (STM) and spectroscopy (STS).

Synthesis of a triporous nanographene with 102 sp2 carbon atoms by combining solution and surface chemistry., The synthesis of porous nanographenes is a challenging task for solution chemistry, and thus, on-surface synthesis provides an alternative approach. Here, we report the synthesis of a triporous nanographene with 102 sp2 carbon atoms by combining solution and surface chemistry. The carbon skeleton was obtained by Pd-catalyzed cyclotrimerization of arynes in solution, while planarization of the molecule was achieved through two hierarchically organized on-surface cyclodehydrogenation reactions, intra- and inter-blade. Remarkably, the three non-planar [14]annulene pores of this nanographene further evolved at higher temperatures showing interesting intra-porous on-surface reactivity.

The field of plant hormone biology, like many other research areas in plant sciences, has benefited tremendously from the adoption of Arabidopsis ( Arabidopsis thaliana ) as a model system. The development of a great genetic toolbox in this species led to the identification of many of the core

Magnetic properties of spinel zinc ferrites are strongly linked to the synthesis method and the processing route since they control the microstructure of the resulting material. In this work, ZnFeO nanoparticles were synthesized by the mechanochemical reaction of stoichiometric ZnO and α-FeO, and single-phase ZnFeO was obtained after 150 h of milling. The as-milled samples, with a high inversion degree, were subjected to different thermal annealings up to 600 °C to control the inversion degree and, consequently, the magnetic properties. The as-milled samples, with a crystallite size of 11 nm and inversion degree δ= 0.57, showed ferrimagnetic behavior even above room temperature, as shown by Rietveld refinements of the X-ray diffraction pattern and superconducting quantum interference device magnetometry. The successive thermal treatments at 300, 400, 500, and 600 °C decrease δfrom 0.57 to 0.18, affecting the magnetic properties. A magnetic phase diagram as a function of δcan be inferred from the results: For δ< 0.25, antiferromagnetism, ferrimagnetism, and spin frustration were observed to coexist; for 0.25 < δ< 0.5, the ferrimagnetic clusters coalesced and spin glass behavior vanished, with only a pure ferrimagnetic phase with a maximum magnetization of M = 3.5μ remaining. Finally, for δ> 0.5, a new antiferromagnetic order appeared due to the overpopulation of nonmagnetic Zn on octahedral sites that leads to equally distributed magnetic cations in octahedral and tetrahedral sites., This work was supported by grants from the Spanish Ministry of Science and Innovation MAT2015- 67557-C2-1-P.

Phosphate (P) is an essential macronutrient for plant growth. Roots employ adaptive mechanisms to forage for P in soil. Root hair elongation is particularly important since P is immobile. Here we report that auxin plays a critical role promoting root hair growth in Arabidopsis in response to low external P. Mutants disrupting auxin synthesis (taa1) and transport (aux1) attenuate the low P root hair response. Conversely, targeting AUX1 expression in lateral root cap and epidermal cells rescues this low P response in aux1. Hence auxin transport from the root apex to differentiation zone promotes auxin-dependent hair response to low P. Low external P results in induction of root hair expressed auxin-inducible transcription factors ARF19, RSL2, and RSL4. Mutants lacking these genes disrupt the low P root hair response. We conclude auxin synthesis, transport and response pathway components play critical roles regulating this low P root adaptive response.

[EN] Ovule formation is a complex developmental process in plants, with a strong impact on the production of seeds. Ovule primordia initiation is controlled by a gene network, including components of the signaling pathways of auxin, brassinosteroids and cytokinins. By contrast, gibberellins (GAs) and DELLA proteins, the negative regulators of GA signaling, have never been shown to be involved in ovule initiation. Here, we provide molecular and genetic evidence that points to DELLA proteins as novel players in the determination of ovule number in Arabidopsis and in species of agronomic interest, such as tomato and rapeseed, adding a new layer of complexity to this important developmental process. DELLA activity correlates positively with ovule number, acting as a positive factor for ovule initiation. In addition, ectopic expression of a dominant DELLA in the placenta is sufficient to increase ovule number. The role of DELLA proteins in ovule number does not appear to be related to auxin transport or signaling in the ovule primordia. Possible crosstalk between DELLA proteins and the molecular and hormonal network controlling ovule initiation is also discussed., This work was supported by grants from the Ministerio de Economia y Competitividad and the European Regional Development Fund (BIO2014-55946) and Generalitat Valenciana (ACOMP/2014/106) to M.A.P.-A, from the National Science Foundation (MCB-0923727) to J.M.A., and from the National Institutes of Health (R01GM112976-01A1) and the Saltman Endowed Chair in Science and Education to M.F.Y. Deposited in PMC for release after 12 months.

On-surface synthesis represents a successful strategy to obtain designed molecular structures on an ultra-clean metal substrate. While metal surfaces are known to favor adsorption, diffusion, and chemical bonding between molecular groups, on-surface synthesis on non-metallic substrates would allow the electrical decoupling of the resulting molecule from the surface, favoring application to electronics and spintronics. Here, we demonstrate the on-surface generation of hexacene by surface-assisted reduction on a H-passivated Si(001) surface. The reaction, observed by scanning tunneling microscopy and spectroscopy, is probably driven by the formation of Si-O complexes at dangling bond defects. Supported by density functional theory calculations, we investigate the interaction of hexacene with the passivated silicon surface, and with single silicon dangling bonds.

The metal-catalyzed [2+2+2] cocycloaddition of arynes with pyramidalized alkenes is presented. The generation of a highly reactive pyramidalized alkene in the presence of a large excess of in situ-produced arynes led to the corresponding cocyclotrimerization (1 : 2)-adducts in good yields, establishing the first example of a palladium-based reaction of a pyramidalized alkene.

Auxin is a major phytohormone that controls numerous aspects of plant development and coordinates plant responses to the environment. Morphogenic gradients of auxin govern cell fate decisions and underlie plant phenotypic plasticity. Polar auxin transport plays a central role in auxin maxima generation. The discovery of the exquisite spatiotemporal expression patterns of auxin biosynthesis genes of the WEI8/TAR and YUC families suggested that local auxin production may contribute to the formation of auxin maxima. Herein, we systematically addressed the role of local auxin biosynthesis in plant development and responses to the stress phytohormone ethylene by manipulating spatiotemporal patterns of WEI8. Our study revealed that local auxin biosynthesis and transport act synergistically and are individually dispensable for root meristem maintenance. In contrast, flower fertility and root responses to ethylene require local auxin production that cannot be fully compensated for by transport in the generation of morphogenic auxin maxima.

The original version of this Article omitted the following from the Acknowledgements: ‘We also thank DBT-CREST BT/HRD/03/01/2002.’ This has been corrected in both the PDF and HTML versions of the Article.

Heterobimetallic catalysis offers new opportunities for reactivity and selectivity but still presents challenges, and only a few metal combinations have been explored so far. Reported here is a Pt-Au heterobimetallic catalyst system for the synthesis of a family of multi-heteroaromatic structures through tandem cyclization/C-X coupling reaction. Au-catalyzed 6-endo-cyclization takes place as the first fast step. Pt-Au clusters are proposed to be responsible for the increased reactivity in the second step, that is, the intermolecular nucleophilic addition which occurs through an outer-sphere mechanism by hybrid homogeneous-heterogeneous catalysis.

The controlled gold-catalyzed preparation of 3-iodo 2,4,6-trisubstituted 9H-carbazoles has been developed by starting from (3-iodoindol-2-yl)butynols. These results could be explained through an initial 6-endo-dig alkyne carbocyclization by chemo- and regiospecific attack of the C3-indole position at the external alkyne carbon followed by a stepwise 1,3-iodine transfer and dehydration. This reaction outcome for the gold-catalyzed transformation of (3-iodoindol-2-yl)alkynols sharply contrasts with that observed for conventional metal-catalyzed processes of iodoarenes, because iodine transfer is feasible. This selective reaction has been studied experimentally; additionally, its mechanism has been investigated by means of density functional theory calculations.

Ruddlesden–Popper’s manganates, An+1MnnO3n+1, built from the ordered intergrowth between one rock-salt and n perovskite blocks, display a wide variety of functionalities related to their physical-chemistry properties which can be in principle tuned by chemical modifications. Nevertheless, the poor thermodynamic stability of the high members constitutes an inherent impediment, limiting the development of new functionalities in this family. Actually, for n ≥ 2, defects involving disordered intergrowths between perovskite and rock-salt blocks are always present avoiding the correct characterization of their properties. For that purpose, the use of sophisticated and expensive physical methods is required. In this article, the stabilization, following a chemical strategy, of micrometric La0.5Ca2.5Mn2O7 crystalline particles exhibiting a well ordered distribution of two perovskite and one rock-salt block, according to an ideal n = 2 unit cell, is reported. This apparently long-range structural ordering is linked to an unconventional short-range order–disorder phenomenon of La and Ca cations, characterized at the atomic level, which allows a rational explanation of the crystallochemical and magnetic properties of this Ruddlesden–Popper compound., A.T-P. acknowledges a postdoctoral fellowship from the Moncloa Campus of International Excellence (UCM).

The role of auxin in ripening strawberry (Fragaria ×ananassa) fruits has been restricted to the early stages of development where the growth of the receptacle is dependent on the delivery of auxin from the achenes. At later stages, during enlargement of the receptacle, other hormones have been demonstrated to participate to different degrees, from the general involvement of gibberellins and abscisic acid to the more specific of ethylene. Here we report the involvement of auxin at the late stages of receptacle ripening. The auxin content of the receptacle remains constant during ripening. Analysis of the transcriptome of ripening strawberry fruit revealed the changing expression pattern of the genes of auxin synthesis, perception, signaling and transport along with achene and receptacle development from the green to red stage. Specific members of the corresponding gene families show active transcription in the ripe receptacle. For the synthesis of auxin, two genes encoding tryptophan aminotransferases, FaTAA1 and FaTAR2, were expressed in the red receptacle, with FaTAR2 expression peaking at this stage. Transient silencing of this gene in ripening receptacle was accompanied by a diminished responsiveness to auxin. The auxin activity in the ripening receptacle is supported by the DR5-directed expression of a GUS reporter gene in the ripening receptacle of DR5-GUS transgenic strawberry plants. Clustering by co-expression of members of the FaAux/IAA and FaARF families identified five members whose transcriptional activity was increased with the onset of receptacle ripening. Among these, FaAux/IAA11 and FaARF6a appeared, by their expression level and fold-change, as the most likely candidates for their involvement in the auxin activity in the ripening receptacle. The association of the corresponding ARF6 gene in Arabidopsis to cell elongation constitutes a suggestive hypothesis for FaARF6a involvement in the same cellular process in the growing and ripening receptacle.

Powders of (LaSr)MnO (LSM85) and (LaSr)MnO (LSM80) perovskites have been synthesized and characterized in detail, and then sintered to evaluate their electrical and magnetic properties at low temperatures and at near room temperature. Microstructural observations/analyses after the dilatometric essays show that the perovskites have compositions that deviate from the nominal ones. Furthermore, magnetic characterization of both samples reveals a ferromagnetic behavior with a Curie temperature above 300 K for LSM80 and of 260 K for LSM85. In addition, LSM85 is insulator from 15 up to 300 K, whereas LSM80 is metallic up to 160 K and insulator up to 300 K. This significant discrepancy of behaviour is attributable to structural and compositional differences between the two perovskites., This work was supported by MINECO (Government of Spain) under Grants no. MAT2012-31090, MAT2013-48009-C4-1 and MAT2016-78700-R and MINECO and Feder Funds under Grant no. MAT2013-41012-P. Financial support from a 2016 BBVA Foundation Grant for researchers and culture creators is also acknowledged.

cited By 7; International audience; Surface-assisted reduction of specially designed air-stable precursors allows us to study single hexacene molecules on Au(111) by scanning tunneling microscopy and spectroscopy, mapping with intramolecular resolution their extended electronic eigenstates.

During the century-long history of plant hormone research, the focus in this area has shifted from the original physiological experiments to molecular, genetic, biochemical, and, more recently, genomic approaches. During this journey, we have learned about the many effects these natural compounds have on plant growth and development at the morphological and molecular levels. We have also uncovered how these molecules are sensed by the plant cell and how they trigger signaling cascades that relay information to the nucleus, ultimately culminating in a transcriptional cascade.

Auxin is an essential plant hormone that controls nearly every aspect of a plant's life, from embryo development to organ senescence. In the last decade the key genes involved in auxin transport, perception, signaling and response have been identified and characterized, but the elucidation of auxin biosynthesis has proven to be especially challenging. In plants, a significant amount of indole-3-acetic acid (IAA), the predominant biologically active form of auxin, is synthesized via a simple two-step route where indole-3-pyruvic acid (IPyA) produced from l-tryptophan by tryptophan aminotransferases (TAA1/TAR) is converted to IAA by the YUC family of flavin monooxygenases. The TAA1/TAR and YUC gene families constitute the first complete auxin biosynthetic pathway described in plants. Detailed characterization of these genes' expression patterns suggested a key role of local auxin biosynthesis in plant development. This has prompted an active search for the molecular mechanisms that regulate the spatiotemporal activity of the IPyA route. In addition to the TAA1/TAR and YUC-mediated auxin biosynthesis, several alternative routes of IAA production have been postulated to function in plants, but their biological significance is yet to be demonstrated. Herein, we take a genetic perspective to describe the current view of auxin biosynthesis and its regulation in plants, focusing primarily on Arabidopsis.

The hormone ethylene plays numerous roles in plant development. In the last few years the model of ethylene signaling has evolved from an initially largely linear route to a much more complex pathway with multiple feedback loops. Identification of key transcriptional and post-transcriptional regulatory modules controlling expression and/or stability of the core pathway components revealed that ethylene perception and signaling are tightly regulated at multiple levels. This review describes the most current outlook on ethylene signal transduction and emphasizes the latest discoveries in the ethylene field that shed light on the mechanistic mode of action of the central pathway components CTR1 and EIN2, as well as on the post-transcriptional regulatory steps that modulate the signaling flow through the pathway.

Cytokinins play critical roles in plant growth and development, with the transcriptional response to cytokinin being mediated by the type-B response regulators. In Arabidopsis (Arabidopsis thaliana), type-B response regulators (ARABIDOPSIS RESPONSE REGULATORS [ARRs]) form three subfamilies based on phylogenic analysis, with subfamily 1 having seven members and subfamilies 2 and 3 each having two members. Cytokinin responses are predominantly mediated by subfamily 1 members, with cytokinin-mediated effects on root growth and root meristem size correlating with type-B ARR expression levels. To determine which type-B ARRs can functionally substitute for the subfamily 1 members ARR1 or ARR12, we expressed different type-B ARRs from the ARR1 promoter and assayed their ability to rescue arr1 arr12 double mutant phenotypes. ARR1, as well as a subset of other subfamily 1 type-B ARRs, restore the cytokinin sensitivity to arr1 arr12. Expression of ARR10 from the ARR1 promoter results in cytokinin hypersensitivity and enhances shoot regeneration from callus tissue, correlating with enhanced stability of the ARR10 protein compared with the ARR1 protein. Examination of transfer DNA insertion mutants in subfamilies 2 and 3 revealed little effect on several well-characterized cytokinin responses. However, a member of subfamily 2, ARR21, restores cytokinin sensitivity to arr1 arr12 roots when expressed from the ARR1 promoter, indicating functional conservation of this divergent family member. Our results indicate that the type-B ARRs have diverged in function, such that some, but not all, can complement the arr1 arr12 mutant. In addition, our results indicate that type-B ARR expression profiles in the plant, along with posttranscriptional regulation, play significant roles in modulating their contribution to cytokinin signaling.

Plants rely on the levels and concentration gradients of the hormone auxin as crucial information cues to trigger and modulate almost every aspect of their life cycle, from establishing embryo polarity to promoting phototropic and gravitropic responses (1). Thus, it is critical for plants to finely control the levels of the bioactive form of this hormone, both at spatial and temporal levels. Local production, transport, conjugation, storage, and catabolism are all well-known processes participating in the dynamic regulation of auxin homeostasis (2). It is, however, unknown whether or how these different auxin homeostasis mechanisms talk to each other. In the past 30 y, the identification of the genes coding for the key components of the auxin biosynthetic, transport, and conjugation machineries has proven instrumental in assessing the contribution of each of these processes to concrete developmental pathways, as well as to specific plant responses to environmental changes. Although much less is known about the ways the predominant auxin, indole-3-acetic acid (IAA), is catabolized, classical labeling and metabolite quantification experiments indicate that the oxidation of IAA into 2-oxindole-3-acetic acid (oxIAA) is one of the most prevalent mechanisms to inactivate this hormone (3). Identifying the specific enzymes catalyzing this reaction in vivo has proved to be more challenging than anticipated, as different plant peroxidases and oxygenases, the original suspects for catalyzing this reaction, were found not to play a significant physiological role in the production of oxIAA (3). The recent identification of a rice 2-oxoglutarate-dependent-Fe(II) dioxygenase, DIOXYGENASE FOR AUXIN OXIDATION ( DAO ), originally linked to male fertility in rice and capable of oxidizing IAA into oxIAA (1⇓⇓–4), has opened new avenues for addressing the physiological significance of auxin catabolism in plant growth and development. In PNAS, Zhang et al. (5), Porco et al. (6), and Mellor et al. (7 … [↵][1]1To whom correspondence should be addressed. Email: jmalonso{at}ncsu.edu. [1]: #xref-corresp-1-1

Allene chemistry in the presence of transition metal complexes is nowadays a very important topic that underpins many challenges and advances in organic synthesis. The number of research articles covering new transformations of allenes is vast and the development of enantioselective reactions involving allenes has flourished in the last 10–15 years. In this review we cover three important topics in allene chemistry that we feel are timely and appropriate for this special issue celebrating the work of Prof. Trost: the metal-catalysed reactions involving chirality transfer from chiral allenes to products; the analysis of the possible racemization processes that have been observed in the interaction of some metals with allenes; and chirality transfer using racemic allenes in reactions catalysed by metal complexes bearing chiral ligands to produce enantioenriched products. We have focussed the review on intermolecular addition reactions as they are still much less explored than the intramolecular version.

cited By 12; International audience; We present the on-surface reduction of diepoxytetracenes to form genuine tetracene on Cu(111). The conversion is achieved by scanning tunneling microscopy (STM) tip-induced manipulation as well as thermal activation and is conclusively demonstrated by means of atomic force microscopy (AFM) with atomic resolution. We observe that the metallic surface plays an important role in the deoxygenation and for the planarization after bond cleavage.

The effects of auxins on plant growth and development have been known for more than 100 years, yet our understanding of how plants synthesize this essential plant hormone is still fragmentary at best. Gene loss- and gain-of-function studies have conclusively implicated three gene families, CYTOCHROME P450 79B2/B3 (CYP79B2/B3), YUCCA (YUC), and TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1/TRYPTOPHAN AMINOTRANSFERASE-RELATED (TAA1/TAR), in the production of this hormone in the reference plant Arabidopsis thaliana. Each of these three gene families is believed to represent independent routes of auxin biosynthesis. Using a combination of pharmacological, genetic, and biochemical approaches, we examined the possible relationships between the auxin biosynthetic pathways defined by these three gene families. Our findings clearly indicate that TAA1/TARs and YUCs function in a common linear biosynthetic pathway that is genetically distinct from the CYP79B2/B3 route. In the redefined TAA1-YUC auxin biosynthetic pathway, TAA1/TARs are required for the production of indole-3-pyruvic acid (IPyA) from Trp, whereas YUCs are likely to function downstream. These results, together with the extensive genetic analysis of four pyruvate decarboxylases, the putative downstream components of the TAA1 pathway, strongly suggest that the enzymatic reactions involved in indole-3-acetic acid (IAA) production via IPyA are different than those previously postulated, and a new and testable model for how IAA is produced in plants is needed.

A reversible topotactic oxidizing-reducing process has been clearly evidenced in the annealing treatment followed to stabilize rhombohedral and orthorhombic La 1-t mn 1-t O 3 (0.016 ≤ t ≤ 0.038) samples. The study of the surface evolution followed by characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) gives evidence for a diffusion mechanism of La and Mn cations through the grain boundaries which provides a fast pathway in the perovskite related compound; however, contrary to theoretical predictions, the overall cationic ratio (La:Mn 1:1) is kept.

The effect of a high frequency alternating magnetic field on HeLa tumour cells incubated with ferromagnetic nanoparticles of manganese oxide perovskite La0.56(SrCa)0.22MnO3 have been studied. The particles were subjected to a size selection process and coated with silica to improve their biocompatibility. The control assays made with HeLa tumour cells showed that cell survival and growth rate were not affected by the particle internalization in cells, or by the electromagnetic field on cells without nanoparticles. However, the application of an alternating electromagnetic field to cells incubated with this silica coated manganese oxide induced a significant cellular damage that finally lead to cell death by an apoptotic mechanism. Cell death is triggered even thought the temperature increase in the cell culture during the hyperthermia treatment is lower than 0.5 C., Comment: Journal of Physical Chemistry C

The structural simplicity of the gaseous hormone ethylene stands in contrast with the complexity of the physiological processes ethylene regulates. Initial studies suggested a simple linear arrangement of signaling molecules leading from the ethylene receptors to the EIN3 family of transcription factors. Recent discoveries have substantially changed this view. Current models suggest existence of a complex signaling pathway composed of several phosphorylation cascades, feedback-regulated transcriptional networks, and protein and mRNA turnover regulatory modules. Interactions between ethylene and other signals determine which of the ethylene-mediated responses get activated in a particular cell at a particular time. Tissue-specific regulation of auxin biosynthesis, transport, and response by ethylene is emerging as a key element in this signal integration process.

The coordination of cell polarity within the plane of a single tissue layer (planar polarity) is a crucial task during development of multicellular organisms. Mechanisms underlying establishment of planar polarity, however, differ substantially between plants and animals. In Arabidopsis thaliana, planar polarity of root-hair positioning along epidermal cells is coordinated towards maximum concentration of an auxin gradient in the root tip. This gradient has been hypothesized to be sink-driven and computational modelling suggests that auxin efflux carrier activity may be sufficient to generate the gradient in the absence of auxin biosynthesis in the root. Here, we demonstrate that the Raf-like kinase CONSTITUTIVE TRIPLE RESPONSE1 (CTR1; Refs 8, 9) acts as a concentration-dependent repressor of a biosynthesis-dependent auxin gradient that modulates planar polarity in the root tip. We analysed auxin biosynthesis and concentration gradients in a variety of root-hair-position mutants affected in CTR1 activity, auxin biosynthesis and transport. Our results reveal that planar polarity relies on influx- and efflux-carrier-mediated auxin redistribution from a local biosynthesis maximum. Thus, a local source of auxin biosynthesis contributes to gradient homeostasis during long-range coordination of cellular morphogenesis.

SummaryPlants have evolved a tremendous ability to respond to environmental changes by adapting their growth and development. The interaction between hormonal and developmental signals is a critical mechanism in the generation of this enormous plasticity. A good example is the response to the hormone ethylene that depends on tissue type, developmental stage, and environmental conditions. By characterizing the Arabidopsis wei8 mutant, we have found that a small family of genes mediates tissue-specific responses to ethylene. Biochemical studies revealed that WEI8 encodes a long-anticipated tryptophan aminotransferase, TAA1, in the essential, yet genetically uncharacterized, indole-3-pyruvic acid (IPA) branch of the auxin biosynthetic pathway. Analysis of TAA1 and its paralogues revealed a link between local auxin production, tissue-specific ethylene effects, and organ development. Thus, the IPA route of auxin production is key to generating robust auxin gradients in response to environmental and developmental cues.