Boundary layer properties of highly dissected leaves: an investigation using an electrochemical fluid tunnel

Abstract. A method for modelling heat and mass transfer by diffusion-controlled electrode reactions in a fluid tunnel is described. In this procedure, a nickelplated leaf functions as a test electrode, and the convective transfer of ions to the leaf cathode in an electrolyte-filled flow tunnel is measured as a function of flow rate. The method permits the simulation of water vapour and heat transfer, and in particular, the determination of boundary layer conductances, by analogy with observed ion transfer. The approach is applicable to many problems in modelling heat and mass transfer between leaves and their surroundings, and is especially useful in examining the properties of leaves in which surface characteristics or overall shape are complex. Using this method, the properties of the highly dissected leaves of Achillea lanulosa with regard to forced convection were investigated. The leaves showed high transfer conductances, indicating that the effective unit of heat transfer was probably the individual leaf subelements. Conductances tended to be greater and effective characteristic dimensions smaller for the larger, more open leaves of a lower altitude population in contrast with leaves from high altitude plants. While the results provide insight into the properties of these complex leaf shapes, difficulties in interpreting the findings are discussed, and a number of exploratory approaches are suggested for data analysis and interpretation.     

Homogentisic acid induces morphological and mechanical aberration of ochronotic cartilage in alkaptonuria

Alkaptonuria (AKU) is a disease caused by a deficient homogentisate 1,2-dioxygenase activity leading to systemic accumulation of homogentisic acid (HGA), that forms a melanin-like polymer that progressively deposits onto connective tissues causing a pigmentation called “ochronosis” and tissue degeneration. The effects of AKU and ochronotic pigment on the biomechanical properties of articular cartilage need further investigation. To this aim, AKU cartilage was studied using thermal (thermogravimetry and differential scanning calorimetry) and rheological analysis. We found that AKU cartilage had a doubled mesopore radius compared to healthy cartilage. Since the mesoporous structure is the main responsible for maintaining a correct hydrostatic pressure and tissue homoeostasis, drastic changes of thermal and rheological parameters were found in AKU. In particular, AKU tissue lost its capability to enhance chondrocytes metabolism (decreased heat capacity) and hence the production of proteoglycans. A drastic increase in stiffness and decrease in dissipative and lubricant role ensued in AKU cartilage. Multiphoton and scanning electron microscopies revealed destruction of cell–matrix microstructure and disruption of the superficial layer. Such observations on AKU specimens were confirmed in HGA-treated healthy cartilage, indicating that HGA is the toxic responsible of morphological and mechanical alterations of cartilage in AKU.     

Oxygen concentration-dependent induction of a 140-kDa protein in magnetic bacterium Magnetospirillum magnetotacticum MS-1

Abstract The magnetic bacterium Magnetospirillum magnetotacticum prefers a microaerobic habitat and should be able to sense oxygen. Therefore, the bacterium was cultured under atmospheres containing 0–5% O₂ and analyzed for oxygen-dependent changes in the levels of its protein components by sodium dodecyl sulfate-polyccrylamide gel electrophoresis (SDS-PAGE). The analysis revealed a marked anaerobic induction of a 140-kDa protein, which was suppressed when M. magnetotacticum was switched from microaerobic (<1% O₂) to aerobic (>1% O₂) growth conditions. Although its function remains to be determined, the 140-kDa protein may serve as a useful tool to gain insight into the physiology of the organism.     

Cryopreservation of heat-shocked canine adipose-derived mesenchymal stromal cells with 10% dimethyl sulfoxide and 40% serum results in better viability,proliferation, anti-oxidation,and in-vitro differentiation

Cryopreserved canine adipose-derived mesenchymal stromal cells (Ad-MSCs) can be used instantly in dogs for clinical uses. However, cryopreservation results in a reduction of the cellular viability, proliferation, and anti-oxidation of post-thawed Ad-MSCs. Therefore, there is a need for in-vitro procedure to improve post-thawed Ad-MSCs’ viability, proliferation, anti-oxidation, and differentiation capacity. In this study, fresh-Ad-MSCs were activated with heat shock, hypoxia (5% O₂), or hypoxia (5% O₂) + heat shock treatments. The results showed that compared to the other treatments, heat shock significantly improved the proliferation rate, anti-oxidation, heat shock proteins and growth factors expressions of canine-fresh-Ad-MSCs. Consequently, fresh-Ad-MSCs were heat-shocked and then cryopreserved with different combinations of dimethyl sulfoxide (Me₂SO) and fetal bovine serum (FBS) to determine the combination that could effectively preserve the cellular viability, proliferation, anti-oxidation and differentiation capacity of Ad-MSCs after cryopreservation. We found that C-HST-Ad-MSCs cryopreserved with 10% Me₂SO + 40% FBS presented significantly (p < 0.05) improved cellular viability, proliferation rate, anti-oxidant capacity, and differentiation potential as compared to C-HST-Ad-MSCs cryopreserved with 1% Me₂SO + 10% FBS or 1% Me₂SO alone or control. We concluded, heat shock treatment is much better to enhance the characteristics of fresh-Ad-MSCs than other treatments, moreover, C-HST-Ad-MSCs in 10% Me₂SO + 40% FBS showed better results compared to other cryopreserved groups. However, future work is required to optimize the expression of heat shock proteins, which would further improve the characteristics of fresh- and cryopreserved-HST-Ad-MSCs and reduce the dependency on Me₂SO and FBS.     

Effects of chelating agents on the cadmium burden of cells in culture

The effects of some new chelating agents on the cadmium burden of CHO cells in culture were investigated. The chelators were sodium-N-(4-methoxybenzyl)-D-glucamine-dithiocarbamate (MeOBG-DTC), sodium-N-benzyl-D-glucaminedithiocarbamate (BG-DTC) and di-isopropylmeso-2,3-dimercapto succinate (DiP-DMSA). The results were compared with the effect of the well known dimercaptopropanol (BAL).The derivates of dithiocarbamate are much less toxic than DiP-DMSA and BAL. All chelators effectively prevent Cd uptake into the cells. Mobilization of intracellular Cd, however, is more effective by the DTC-derivatives than by DiP-DMSA or BAL. Within the cell the major fraction of Cd after 48 hours incubation is found in the nuclei and cytosol and very little in the peroxisomes. The chelating agents remove the metal mostly from nuclei and cytosol. Incubation of the cells with cadmium leads to the induction of a Cd binding protein of an apparent molecular weight of 12500 Da, presumably metallothionein. MeOBG-DTC is more effective in removing the metal from this protein than BG-DTC.Abbreviations MeOBG-DTC Na-N(4-methoxybenzyl)-D-glucaminedithiocarbamate - BG-DTC Na-N-benzyl-D-glucaminedithiocarbamate - DiP-DMSA di-isopropyl-2,3-dimercaptosuccinate - BAL 2,3-dimercaptopropane-1-o1 - Da dalton - MEM minimum essential medium - IU international units - FBS fetal bovine serum - CD unbroken cells and debris - N nuclei - ML mitochondria, and lysosomes - P peroxisomes - HMW high molecular weight - MT metallothionein     

Time course of color induction in the honeybee

Color induction in the honeybee is investigated in color discrimination experiments. An individual bee walks in a dark arena and is trained to a self-luminant stimulus presented from below. In the dual-choice tests the dark background is replaced by a colored induction stimulus. Choice behavior is recorded by TV camera and analyzed by computer. Successive color induction is separated from simultaneous induction by analysis of the walking paths. Only successive color induction occurs. Simultaneous effects are not observed. That is a stimulus acts as a color inducing stimulus only when the bee crosses this stimulus. Thus, the color perceived by a given eye region is found to be dependent on the viewing history, but not on the stimuli presented simultaneously on neighboring parts of the retina. Color induction in the honeybee described in terms of selective sensitivity decrease (adaptation) does not explain all behavioral effects induced by the stimulus. The time course of successive color induction is calculated from the exposure times to the induction stimulus and from the choice behavior. The data suggest that color induction is complete after a few seconds. Photoreceptor adaptation is sufficient to explain the observed time course.     

Role of fibroblast growth factors as inducing agents in early embryonic development

To assess the potential role of a molecule in development we need to know three things: 1) what are the biological activities of the molecule, 2) what is its expression pattern, and 3) what are the consequences of removing it from the embryo? In the case of the FGF family in Xenopus embryos we have quite a lot of information about all three questions. Most members of the family can induce mesoderm from isolated animal caps, thus mimicking the natural “ventral vegetal” inducing signal operative in the blastula. This activity can be exerted on isolated, disaggregated cells and does not involve a change in division rate. When overexpressed from injected mRNA, the activity of FGFs depends largely on whether or not they possess a signal sequence, showing the importance of secretion in the inductive process. In addition to the mesoderm-inducing activity, there are effects of overexpression on whole embryos which lead to a suppression of anterior structures. Three types of FGF have so far been cloned from Xenopus: direct homologs of each of the mammalian types FGF-2 and FGF-3, and eFGF (“embryonic FGF”), which is equidistant in sequence from mammalian FGF-4 and FGF-6. Attempts to find homologs of mammalian FGF-5 and FGF-7 in Xenopus have proved unsuccessful. All three types of Xenopus FGF are expressed in early development. FGF-2 and eFGF are present in the oocyte and fertilized egg, and are thus both available at the time of mesoderm induction. FGF-3 and eFGF are both expressed from the embryonic genome during gastrulation and concentrated in the forming mesoderm. FGF-2 is expressed from the embryonic genome during neurulation in the brain, and a little later in the branchial arch mesenchyme and in the forming myotomes. These expression patterns suggest that there are several functions for the FGFs. The most successful strategy for inhibition of the FGF system has been the use of a dominant negative receptor construct introduced by Kirschner and colleagues. Overexpression of this construct can abolish the FGF responsiveness of animal caps. In whole embryos, the absence of FGF signaling causes a reduction, although not a total ablation, of mesoderm formation. There is also a severe effect on axis formation in which formation of the posterior parts is reduced consequent on an inhibition of invagination and elongation of the dorsal mesoderm. Thus, the present evidence suggests that the FGF system contributes to, although is not solely responsible for, mesoderm induction in vivo. It is also necessary for normal gastrulation movements, particularly in the dorsal mesoderm, and is likely to have several later functions, particularly in development of the central nervous system and the myotomes. © 1994 Wiley-Liss, Inc.     

HSP70 induction by bleomycin metal core analogs

Induction of heat shock protein 70 (HSP70) is known to be effective against various diseases. We are interested in HSP70 induction capability of an antitumor antibiotic bleomycin which produces oxidative stress by iron chelate formation and oxygen activation in a cell. The HSP70 induction activity of bleomycin and its six metal core analogs was examined, and a compound HPH-1Trt of 10 μM was found to induce this protein in a pheochromocytoma cell line and some T cell and monocytic cell lines. Its mechanism is increase of HSP70 mRNA, but higher concentration of this compound showed toxicity. Two new derivatives were then synthesized, and one of them named DHPH-1Trt was shown to have less toxicity and higher HSP70 induction activity. This study would lead to a clue for new HSP70 inducer clinically used in near future.