INCREASED WATER STORAGE CAPACITY IN CACTUS WOOD: A STUDY IN THE TRIBE CEREEAE (CACTOIDEAE, CACTACEAE)

Secondary xylem of fibrous cactus wood is characterized by short narrow vessel elements with both simple perforation plates and large intervessel pits, libriform septate fibers, and large rays. These are present in basal cactus taxa, as well as in many other groups of the family. In Cactoideae, the most diversified and most derived subfamily, there are remarkable variations found in the secondary xylem, with the more highly derived taxa containing the greatest water storage capacity. Unlignified parenchyma is one specialization found in the fibrous wood of cacti. We observed this tissue in the secondary xylem at the base of the sterns of several Brazilian endemic species of Arrojadoa, Melocactus, and Stephanocereus, all members of the tribe Cereeae. In Arrojadoa and Melocactus the unlignified parenchyma occurs in lines and bands amongst the axial and radial xylem elements, while in Stephanocereus it is mainly restricted to the rays and does not form bands. We address the adaptive importance of the unlignified parenchyma in the fibrous wood in tribe Cereeae and the family Cactaceae as a whole.

Specific leaf areas of the tank bromeliad Guzmania monostachia perform distinct functions in response to water shortage

Leaves comprise most of the vegetative body of tank bromeliads and are usually subjected to strong longitudinal gradients. For instance, while the leaf base is in contact with the water accumulated in the tank, the more light-exposed middle and upper leaf sections have no direct access to this water reservoir. Therefore, the present study attempted to investigate whether different leaf portions of Guzmania monostachia, a tank-forming C(3)-CAM bromeliad, play distinct physiological roles in response to water shortage, which is a major abiotic constraint in the epiphytic habitat. Internal and external morphological features, relative water content, pigment composition and the degree of CAM expression were evaluated in basal, middle and apical leaf portions in order to allow the establishment of correlations between the structure and the functional importance of each leaf region. Results indicated that besides marked structural differences, a high level of functional specialization is also present along the leaves of this bromeliad. When the tank water was depleted, the abundant hydrenchyma of basal leaf portions was the main reservoir for maintaining a stable water status in the photosynthetic tissues of the apical region. In contrast, the CAM pathway was intensified specifically in the upper leaf section, which is in agreement with the presence of features more suitable for the occurrence of photosynthesis at this portion. Gas exchange data indicated that internal recycling of respiratory CO(2) accounted for virtually all nighttime acid accumulation, characterizing a typical CAM-idling pathway in the drought-exposed plants. Altogether, these data reveal a remarkable physiological complexity along the leaves of G. monostachia, which might be a key adaptation to the intermittent water supply of the epiphytic niche. (C) 2009 Elsevier GmbH. All rights reserved.

Optical energy storage properties of Sr(2)MgSi(2)O(7):Eu(2+),R(3+) persistent luminescence materials

The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr(2)MgSi(2)O(7):Eu(2+),R(3+) materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr(2)MgSi(2)O(7):Eu(2+),R(3+) material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 A degrees C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr(2)MgSi(2)O(7):Eu(2+),R(3+) materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R(3+) co-dopants.

Effect of cold storage on culture viability and some rheological properties of fermented milk prepared with yogurt and probiotic bacteria

We examined the effect of storage time on culture viability and some rheological properties (yield stress, storage modulus, loss modulus, linear viscoelastic region, structural recuperation and firmness) of fermented milk made with Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus acidophilus (LA) and Bifidobacterium animalis ssp. lactis in coculture with Streptococcus thermophilus (ST). Acidification profiles and factors that affect viability (postfermentation acidification, acidity and dissolved oxygen) were also studied during 35 days at 4C. Fermented milk prepared with a coculture of ST and Bifidobacterium lactis gave the most constant rheological behavior and the best cell viability during cold storage; it was superior to ST plus LA for probiotic fermented milk production.

Evaluation of Postpolymerization as a Function of the Storage Time of Triethylene Glycol Dimethacrylate/2,2-Bis[4-(2-Hydroxy-3-Methacryloxy-Prop-1-Oxy)-Phenyl]-propane Bisphenyl-alpha-Glycidyl Ether Dimethacrylate Copolymers Used in Dental Resins by Differential Scanning Calorimetry and Dynamic Mechanical Analysis

The aim of this work was to evaluate the effect of the storage time on the thermal properties of triethylene glycol dimethacrylate/2,2-bis[4-(2-hydroxy-3-methacryloxy-prop-1-oxy)-phenyl]propane bisphenyl-alpha-glycidyl ether dimethacrylate (TB) copolymers used in formulations of dental resins after photopolymerization. The TB copolymers were prepared by photopolymerization with an Ultrablue IS light-emitting diode, stored in the dark for 160 days at 37 degrees C, and characterized with differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and Fourier transform infrared spectroscopy with attenuated total reflection. DSC curves indicated the presence of an exothermic peak, confirming that the reaction was not completed during the photopolymerization process. This exothermic peak became smaller as a function of the storage time and was shifted at higher temperatures. In DMA studies, a plot of the loss tangent versus the temperature initially showed the presence of two well-defined peaks. The presence of both peaks confirmed the presence of residual monomers that were not converted during the photopolymerization process. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 679-684, 2009