A single degree of freedom ‘lollipop’ model for carbon nanotube bundle formation

Current carbon nanotube (CNT) synthesis methods include the production of ordered, free-standing vertically aligned arrays, the properties of which are partially governed by interactions between adjacent tubes. Using material parameters determined by atomistic methods, here we represent individual CNTs by a simple single degree of freedom ‘lollipop’ model to investigate the formation, mechanics, and self-organization of CNT bundles driven by weak van der Waals interactions. The computationally efficient simple single degree of freedom model enables us to study arrays consisting of hundreds of thousands of nanotubes. The effects of nanotube parameters such as aspect ratio, bending stiffness, and surface energy, on formation and bundle size, as well as the intentional manipulation of bundle pattern formation, are investigated. We report studies with both single wall carbon nanotubes (SWCNTs) and double wall carbon nanotubes (DWCNTs) with varying aspect ratios (that is, varying height). We calculate the local density distributions of the nanotube bundles and show that there exists a maximum attainable bundle density regardless of an increase in surface energy for nanotubes with given spacing and stiffness. In addition to applications to CNTs, our model can also be applied to other types of nanotube arrays (e.g. protein nanotubes, polymer nanofilaments).National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762

Splice variants of DOMINO control Drosophila circadian behavior and pacemaker neuron maintenance.

Circadian clocks control daily rhythms in behavior and physiology. In Drosophila, the small ventral lateral neurons (sLNvs) expressing PIGMENT DISPERSING FACTOR (PDF) are the master pacemaker neurons generating locomotor rhythms. Despite the importance of sLNvs and PDF in circadian behavior, little is known about factors that control sLNvs maintenance and PDF accumulation. Here, we identify the Drosophila SWI2/SNF2 protein DOMINO (DOM) as a key regulator of circadian behavior. Depletion of DOM in circadian neurons eliminates morning anticipatory activity under light dark cycle and impairs behavioral rhythmicity in constant darkness. Interestingly, the two major splice variants of DOM, DOM-A and DOM-B have distinct circadian functions. DOM-A depletion mainly leads to arrhythmic behavior, while DOM-B knockdown lengthens circadian period without affecting the circadian rhythmicity. Both DOM-A and DOM-B bind to the promoter regions of key pacemaker genes period and timeless, and regulate their protein expression. However, we identify that only DOM-A is required for the maintenance of sLNvs and transcription of pdf. Lastly, constitutive activation of PDF-receptor signaling rescued the arrhythmia and period lengthening of DOM downregulation. Taken together, our findings reveal that two splice variants of DOM play distinct roles in circadian rhythms through regulating abundance of pacemaker proteins and sLNvs maintenance

Negative feedback control of jasmonate signaling by an alternative splice variant of JAZ10

The plant hormone jasmonate (JA) activates gene expression by promoting ubiquitin-dependent degradation of JAZ transcriptional repressor proteins. A key feature of all JAZ proteins is the highly conserved Jas motif, which mediates both JAZ degradation and JAZ binding to the transcription factor MYC2. Rapid expression of JAZ genes in response to JA is thought to attenuate JA responses, but little is known about the mechanisms by which newly synthesized JAZ proteins exert repression in the presence of the hormone. Here, we show that desensitization to JA is mediated by an alternative splice variant (JAZ10.4) of JAZ10 that lacks the Jas motif. Unbiased protein-protein interaction screens identified three related bHLH transcription factors (MYC2, MYC3, and MYC4) and the co-repressor NINJA as JAZ10.4-binding partners. We show that the N-terminal region of JAZ10.4 contains a cryptic MYC2-binding site that resembles the Jas motif, and that the ZIM motif of JAZ10.4 functions as a transferable repressor domain whose activity is associated with recruitment of NINJA. Functional studies showed that expression of JAZ10.4 from the native JAZ10 promoter complemented the JA-hypersensitive phenotype of a jaz10 mutant. Moreover, treatment of these complemented lines with JA resulted in rapid accumulation of JAZ10.4 protein. Our results provide an explanation for how the unique domain architecture of JAZ10.4 links transcription factors to a co-repressor complex, and suggest how JA-induced transcription and alternative splicing of JAZ10 pre-mRNA creates a regulatory circuit to attenuate JA responses.Fil: Moreno, Javier Edgardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; Argentina. Michigan State University; Estados UnidosFil: Shyu, Christine. Michigan State University; Estados UnidosFil: Campos, Marcelo L.. Michigan State University; Estados UnidosFil: Patel, Lalita C.. Michigan State University; Estados UnidosFil: Chung, Hoo Sun. Michigan State University; Estados UnidosFil: Yao, Jian. Michigan State University; Estados UnidosFil: He, Sheng Hang. Michigan State University; Estados UnidosFil: Howe, Gregg A.. Michigan State University; Estados Unido

Dendritic molecular assemblies for singlet oxygen generation: meso-tetraphenylporphyrin-based biphotonic sensitizers with remarkable luminescence

International audienceFour new TPP-based chromophores (1-4) peripherally functionalized with dendrons contg. 2-fluorenyl groups were studied for their potential to serve in photodynamic therapy. Their linear and nonlinear optical properties were investigated. With significant TPA cross-sections at 790 nm, good singlet oxygen generation capabilities and relatively large intrinsic fluorescence, sensitizers such as 1 might become particularly appealing for theranostics

Test de Germination des Graines de Ricin (Ricinus communis L.) Sous Différentes Contraintes Abiotiques

Ricinus communis L., est utilisé comme biocarburant et possède de nombreuses vertus. Cependant, les récentes recherches menées en Afrique de l’Ouest fournissent peu d’information sur ses potentialités encore moins sur sa croissance. L’objectif de cette étude est d’évaluer la réponse des graines de ricin à différentes méthodes de prétraitement. Le dispositif utilisé est un bloc complètement randomisé à quatre répétitions et neuf traitements. Les traitements ont été constitués de graines témoins ; de graines scarifiées à la main (SM) ; de graines trempées dans l’eau de robinet à la température ambiante pendant 12 heures (ER12h), pendant 24 heures (ER24h), pendant 48 heures (ER48h) ; de graines trempées dans l’eau préalablement portée à ébullition ( ̴ 100°C) pendant 20 minutes (EC20min), pendant 40 minutes (EC40min) ; de graines trempées dans l’eau à la température ambiante après scarification de celles-ci, pendant 24 heures (SM24h), pendant 48 heures (SM48h). Vingt graines ont été semées par traitement et les observations ont porté d’une part, sur la capacité de germination, le temps moyen de germination, le délai de germination et le coefficient de vélocité de germination ; et d’autre part sur la croissance des jeunes plants. Les résultats ont montré que les graines de ricin ne présentent pas réellement de résistance mécanique, ce qui s’est traduit par une capacité de germination élevée après un trempage à l’eau pendant 12 heures. La scarification appliquée uniquement et le traitement thermique des graines n’ont pas favorisé une bonne germination des graines. Le temps de germination moyen a été plus court au niveau de la graine scarifiée avec un temps d’imbibition plus long. Un pré trempage des graines à l’eau chaude pendant 20 minutes n’a pas permis la germination des graines, contrairement à celui qui a duré 40 minutes. La croissance des plantes et le rythme d’apparition des feuilles ont été plus rapide avec les graines scarifiées et trempées à l’eau. Cette étude a montré que la multiplication par graine de cette espèce pourrait être limitée par un prétraitement à la chaleur.   Ricinus communis L. is used as a biofuel and has many virtues. In recent research conducted in West Africa, little information exists on its potential and even less about its growth. The objective of this study was to evaluate methods of breaking seed dormancy and stimulating the growth of R. communis. The device used is a completely randomized block in four repetitions and nine treatments. The treatments consist of control seeds, hand-scarified seeds (SM), seeds soaked in tap water at ambient temperature for 12 hours (ER12h), for 24 hours (ER24h), for 48 hours (ER48h); seeds soaked in water previously boiled ( ̴ 100°C) for 20 minutes (EC20min), for 40 minutes (EC40min); seeds soaked in water at ambient temperature after scarifying the seeds for 24 hours (SM24h), for 48 hours (SM48h). Twenty seeds of R. communis were sown per treatment and observations were made on the one hand on germination capacity, mean germination time, germination time and velocity coefficient; and on the other hand, on the growth of young plants. The results showed that the castor seeds did not really show any mechanical resistance which resulted in a high germination capacity after soaking in water for 12 hours. Scarification alone and heat treatment of the seeds does not promote good seed germination. The average germination time is shorter when the seed is scarified with a longer soaking time. Soaking in hot water for 20 minutes did not allow the seeds to germinate, unlike 40 minutes. Plant growth was faster with scarified and water-soaked seeds. This study showed that multiplication by seed of this species could be limited by heat pretreatment.   &nbsp