Bioactive gibberellins (GAs) are tetracyclic diterpenoid plant hormones that promote important processes of plant growth and development, such as seed germination, growth through elongation, and ...floral transition. Thus, mutant plants that are affected in GA biosynthesis or signalling exhibit altered seed germination and, at the adult stage, are dwarf and dark green and also show delayed flowering. The components of the GA metabolism and signalling pathways are reviewed here and recent findings regarding the regulation and possible mode of action of DELLA proteins are discussed.
In Arabidopsis, the flagellin-derived peptide flg22 elevates antibacterial resistance 1 and inhibits growth 2 upon perception via the leucine-rich repeat receptor-like kinase Flagellin-Sensitive 2 ...(FLS2) 3. DELLA proteins are plant growth repressors whose degradation is promoted by the phytohormone gibberellin 4. Here, we show that DELLA stabilization contributes to flg22-induced growth inhibition. In addition, we show that DELLAs promote susceptibility to virulent biotrophs and resistance to necrotrophs, partly by altering the relative strength of salicylic acid and jasmonic acid (JA) signaling. A quadruple-DELLA mutant (which lacks four out of the five Arabidopsis DELLA proteins 5) was partially insensitive to gene induction by Methyl-Jasmonate (MeJA), whereas the constitutively active dominant DELLA mutant gai6 was sensitized for JA-responsive gene induction, implicating DELLAs in JA-signaling and/or perception. Accordingly, the elevated resistance of gai to the necrotrophic fungus Alternaria brassicicola and susceptibility to the hemibiotroph Pseudomonas syringae pv. tomato strain DC3000 (Pto DC3000) was attenuated in the JA-insensitive coi1-16 mutant 7. These findings suggest an explanation for why the necrotrophic fungus Gibberella fujikuroi, causal agent of the foolish-seedling disease of rice, makes gibberellin.
Proton Exchange Membrane Fuel Cells are more and more considered as energy converters for mobile applications, such as road vehicles, boats and airplanes. The feasibility of PEMFC integration to ...aircraft raises several difficulties such as the loss of performance due to altitude and ambient pressure decrease.
An aerobic PEMFC system is experimentally investigated at three different altitudes representative of aircraft cruise (200 m, 1200 m and 2200 m), and at different air stoichiometric factors (from 1.5 to 2.5). The experimental results are employed to perform fitting of PEMFC numerical model parameters and validation of the model. A least square method is implemented in a Matlab® code to determine one set of model parameters for all experimental data sets. The model based on literature is modified in order to better represent the effect of ambient pressure on voltage response. Comparisons of experimental and numerical results are presented and show good agreement. Fuel cell performance is found to decrease drastically as altitude increases, as well as air stoichiometric factor decreases. The air pressure in cathode gas channels is measured and analysed. The decline of PEMFC performances in altitude is due to ambient pressure decrease, to air compressor efficiency drop and to flooding in the gas channels. This PEMFC loss of performances is attenuated by high cathode stoichiometric factors.
► Proton Exchange Membrane Fuel Cell properties for aeronautical applications. ► Proton Exchange Membrane Fuel Cell experimented at three different altitudes and five different air stoichiometric factors.► Proton Exchange Membrane Fuel Cell numerical model adaptation and validation. ► Significant effects of altitude at low stoichiometric factors. ► Altitude effects reduced at high stoichiometric factor.
The ubiquitin proteasome system is a key regulator of many biological processes in all eukaryotes. This mechanism employs several types of enzymes, the most important of which are the ubiquitin E3 ...ligases that catalyse the attachment of polyubiquitin chains to target proteins for their subsequent degradation by the 26S proteasome. Among the E3 families, the SCF is the best understood; it consists of a multi-protein complex in which the F-box protein plays a crucial role by recruiting the target substrate. Strikingly, nearly 700 F-box proteins have been predicted in
Arabidopsis, suggesting that plants have the capacity to assemble a multitude of SCF complexes, possibly controlling the stability of hundreds of substrates involved in a plethora of biological processes. Interestingly, viruses and even pathogenic bacteria have also found ways to hijack the plant SCF and to reprogram it for their own purposes.
New organic aerogels were prepared using cellulose derivatives as precursors. The elaboration process and the structural characterisations of these porous cellulose-based materials are described in ...the present study. Series of monolithic gels were synthesised in acetone by crosslinking cellulose acetate with a non-toxic isocyanate
via sol–gel route, using tin-based catalyst. Gelation times (ranging from 15 to 150
min) were significantly dependent on reagents' nature and concentration. Low-density materials (from 0.25
cm
3/g to 0.85
cm
3/g) were obtained after supercritical carbon dioxide drying. These newly developed nanostructured materials were characterised using mercury porosimetry, nitrogen adsorption and scanning electron microscopy. All the prepared materials have shown both a nanostructured solid network (specific surface areas between 140 and 250
m
2/g) and a nanoporous network (characteristic pore sizes between 13 and 25
nm) together with specific porous volumes as large as 3.30
cm
3/g.
Influence of sol–gel synthesis parameters as crosslinker content and cellulose degree of polymerisation or concentration was investigated. First empirical correlations between synthesis parameters and final material properties were obtained. A special attention was dedicated to the different shrinkages occurring during the elaboration process. In particular, the important shrinkage occurring during the supercritical drying step was studied in terms of affinity between the crosslinked polymeric network and carbon dioxide. In parallel, first thermo-mechanical properties were presented in terms of bulk modulus and effective thermal conductivity.
The increase in complexity of computational neuron models makes the hand tuning of model parameters more difficult than ever. Fortunately, the parallel increase in computer power allows scientists to ...automate this tuning. Optimization algorithms need two essential components. The first one is a function that measures the difference between the output of the model with a given set of parameter and the data. This error function or fitness function makes the ranking of different parameter sets possible. The second component is a search algorithm that explores the parameter space to find the best parameter set in a minimal amount of time. In this review we distinguish three types of error functions: feature-based ones, point-by-point comparison of voltage traces and multi-objective functions. We then detail several popular search algorithms, including brute-force methods, simulated annealing, genetic algorithms, evolution strategies, differential evolution and particle-swarm optimization. Last, we shortly describe Neurofitter, a free software package that combines a phase-plane trajectory density fitness function with several search algorithms.
Gibberellin signaling in plants Davière, Jean-Michel; Achard, Patrick
Development,
03/2013, Letnik:
140, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The plant hormone gibberellin (GA) regulates major aspects of plant growth and development. The role of GA in determining plant stature had major impacts on agriculture in the 1960s, and the ...development of semi-dwarf varieties that show altered GA responses contributed to a huge increase in grain yields during the 'green revolution'. The past decade has brought great progress in understanding the molecular basis of GA action, with the cloning and characterization of GA signaling components. Here, we review the molecular basis of the GA signaling pathway, from the perception of GA to the regulation of downstream genes.
Plant phenotypic plasticity is controlled by diverse hormone pathways, which integrate and convey infor- mation from multiple developmental and environmental signals. Moreover, in plants many ...processes such as growth, development, and defense are regulated in similar ways by multiple hormones. Among them, gibberellins （GAs） are phytohormones with pleiotropic actions, regulating various growth processes throughout the plant life cycle. Previous work has revealed extensive interplay between GAs and other hor- mones, but the molecular mechanism became apparent only recently. Molecular and physiological studies have demonstrated that DELLA proteins, considered as master negative regulators of GA signaling, inte- grate multiple hormone signaling pathways through physical interactions with transcription factors or reg- ulatory proteins from different families. In this review, we summarize the latest progress in GA signaling and its direct crosstalk with the main phytohormone signaling, emphasizing the multifaceted role of DELLA proteins with key components of major hormone signaling pathways.
Previous work has demonstrated the feasibility of synthesizing low-density polyurethane- and polyisocyanurate-based aerogels that exhibit low effective thermal conductivity. On the basis of this ...literature, the present study synthesized and characterized nanostructured polyurethane aerogel-like materials processed via subcritical drying routes. Two families of polyurethane gels were studied. Wet gels were synthesized with two polyols of different functionality. The influence of the composition of the reaction media is discussed. Depending on the solubility of the precursors, macroporous foam-like or mesoporous aerogel-like materials can be obtained as observed by scanning electron microscopy coupled with mercury porosimetry. Prior to drying, specific washing steps were performed. Preliminary results obtained by evaporative and freeze-drying were then compared to reference aerogel materials dried through a direct supercritical route. Only a slight density increase was observed. Effective thermal conductivities were also measured and discussed.
Organic aerogels based on polyurethane were elaborated
via
sol-gel synthesis and dried with supercritical carbon dioxide (CO
2
). The influence of the catalyst concentration was investigated, first ...in order to decrease the reaction kinetics, then to study its impact on the obtained materials properties. It was shown that this parameter also influences the global shrinkage and the bulk density of the resulting materials. Its effect on the dry materials was studied in terms of morphological, textural and thermal properties in order to determine the main correlations thanks to scanning electron microscopy (SEM), nitrogen adsorption, non-intrusive mercury porosimetry and thermal conductivity measurements. Results allowed us to demonstrate a correlation between the bulk density, the texture and the thermal conductivity of this family of polyurethane aerogels and to determine an optimal density range for thermal performance associated with a fine internal mesoporous texture.
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