Climacteric fruit ripening: Ethylene-dependent and independent regulation of ripening pathways in melon fruit

Cantaloupe melons have a typical climacteric behaviour with ethylene playing a major role in the regulation of the ripening process and affecting the ripening rate. Crossing of Cantaloupe Charentais melon with a non-climacteric melon indicated that the climacteric character is genetically dominant and conferred by two duplicated loci only. However, other experiments made by crossing two non-climacteric melons have generated climacteric fruit, indicating that different and complex genetic regulation exists for the climacteric character. Suppression of ethylene production by antisense ACC oxidase RNA in Charentais melon has shown that, while many ripening pathways were regulated by ethylene (synthesis of aroma volatiles, respiratory climacteric and degreening of the rind), some were ethylene-independent (initiation of climacteric, sugar accumulation, loss of acidity and coloration of the pulp). Softening of the flesh comprised both ethylene-dependent and independent components that were correlated with differential regulation of cell wall degrading genes. These results indicate that climacteric (ethylene-dependent) and non-climacteric (ethylene-independent) regulation coexist during climacteric fruit ripening. In addition, ethylenesuppressed melons allowed demonstrating that the various ethylene-dependent events exhibited differential sensitivity to ethylene and that ethylene was promoting sensitivity to chilling injury. Throughout this review, the data generated with melon are compared with those obtained with tomato and other fruit

Synthesis and single crystal X-ray structure of the tetragonal tungsten bronze Pb0.91K1.72Li1.46Nb5O15

Crystals of Pb0.91K1.72Li1.46Nb5O15, belonging to tetragonal tungsten bronze materials, were grown by the slow cooling technique, and characterized by means of single crystal X-ray diffraction: the structure was solved in the P4bm tetragonal space group, with the following unit cell parameters: a = 12.548(5), c = 4.042(5) Å, V = 636.4(9) Å3. The three-dimensional framework can be described as a layered structure down crystallographic axis c, with arrays of NbO6 octahedra, whose corner sharing makes up the formation of tunnels filled up by Li, Pb and K displaying complex cation-oxygen coordinations

Élaboration et caractérisation de cristaux dérivés de K3_{3}Li2_{2}Nb5_{5}O15_{15}

Good quality crystals of K$_{3}$Li$_{2}$Nb$_{5}$O$_{15}$ type were grown from the melt followed by method slow cooling using a pseudo-flux method (an excess of K$_{2}$CO$_{3}$ and Nb$_{2}$O$_{5}$ is present). The crystals were identified by X-ray diffraction, they crystallized with the tungsten bronze-type structure in the tetragonal system at room temperature. The space group is P4bm. Their composition (K$_{2.82}$(Nb–O)$_{0.08}$Li$_{1.54}$Nb$_{5}$O$_{15}$) was determined by chemical analysis. Dielectric measurements were realized along the [001] and [100] directions in the frequency range from 10$^{3}$ to $3 \times 10^{5}$ Hz. The temperature dependences of dielectric constants $\varepsilon^{\prime}_{\rm r33}$ and $\varepsilon^{\prime}_{\rm r11}$ and of birefringence $\Delta n$ show two maximums at $T_{1}\cong 100$ K and $T_{\rm C}\cong 680$ K, the latter being the ferroelectric Curie temperature.Des cristaux de bonne qualité de type K$_{3}$Li$_{2}$Nb$_{5}$O$_{15}$ et de structure “bronze” ont été élaborés par fusion et refroidissement lent en présence d'un pseudo-flux (K$_{2}$CO$_{3}$ et Nb$_{2}$O$_{5}$ en excès). L'analyse chimique montre que leur composition correspond à la formulation K$_{2,82}$(Nb–O)$_{0,08}$Li$_{1,54}$Nb$_{5}$O$_{15}$. Ces matériaux cristallisent dans le système quadratique à 295 K avec le groupe spatial P4bm. Les mesures diélectriques ont été effectuées selon deux directions [001] et [100], perpendiculaires aux grandes faces des cristaux élaborés. Les variations thermiques de la permittivité et de la biréfringence ont permis de mettre en évidence deux maxima l'un à $T_{1}\cong 100$ K selon [100], l'autre à $T_{\rm C}\cong 680$ K selon [001] ; ce dernier correspond à al température de Curie ferroélectrique

Study of structural short order and surface changes of SiO2 compounds

In this work dependence between structure, surface and reactivity of SiO2 is investigated. Different samples are prepared with and without the presence of calcium cations and are characterized by different techniques. The FTIR frequency shifting of the bridging oxygen stretching vibration Si–O–Si and the binding energy shiftingof the Si2p and O1s photoelectron peaks have been observed and discussed. Results show the effect of presence of calcium on the structural change, surface and reactivity of SiO2 aggregate. After reaction, a structural and SiO2 surface changes occur, as the FTIR spectra illustrate depending on the presence of the calcium cations

Élaboration et caractérisation de cristaux dérivés de K3Li2Nb5O15

Des cristaux de bonne qualité de type K3Li2Nb5O15 et de structure “bronze” ont été élaborés par fusion et refroidissement lent en présence d'un pseudo-flux (K2CO3 et Nb2O5 en excès). L'analyse chimique montre que leur composition correspond à la formulation K2,82(Nb–O)0,08Li1,54Nb5O15. Ces matériaux cristallisent dans le système quadratique à 295 K avec le groupe spatial P4bm. Les mesures diélectriques ont été effectuées selon deux directions [001] et [100], perpendiculaires aux grandes faces des cristaux élaborés. Les variations thermiques de la permittivité et de la biréfringence ont permis de mettre en évidence deux maxima l'un à $T_{1}\cong 100$ K selon [100], l'autre à $T_{\rm C}\cong 680$ K selon [001] ; ce dernier correspond à al température de Curie ferroélectrique