Synthesis of cubic ZnS microspheres exhibiting broad visible emission for bioimaging applications

Biocompatible ZnS microspheres with an average diameter of 3.85 µm were grown by solvo‐hydrothermal (S‐H) method using water–acetonitrile–ethylenediamine (EDA) solution combination. ZnS microspheres were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), Fourier transform (FT)‐Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) techniques. The broad photoluminescence (PL) emissions from 380–580 nm that were seen from the ZnS microspheres attributed to the increase in carrier concentration, as understood from the observed intense Raman band at 257 cm^–1. Cytotoxicity and haemocompatibility investigations of these ZnS microspheres revealed its biocompatibility. ZnS microspheres, along with biological cell lines, were giving visible light emission and could be used for bioimaging applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Changes in thylakoid membrane thickness associated with the reorganization of photosystem II light harvesting complexes during photoprotective energy dissipation

Using freeze-fracture electron microscopy we have recently shown that non-photochemical quenching (NPQ), a mechanism of photoprotective energy dissipation in higher plant chloroplasts, involves a reorganization of the pigment-protein complexes within the stacked grana thylakoids.¹ Photosystem II light harvesting complexes (LHCII) are reorganized in response to the amplitude of the light driven transmembrane proton gradient (ΔpH) leading to their dissociation from photosystem II reaction centers and their aggregation within the membrane.¹ This reorganization of the PSII-LHCII macrostructure was found to be enhanced by the formation of zeaxanthin and was associated with changes in the mobility of the pigment-protein complexes therein.¹ We suspected that the structural changes we observed were linked to the ΔpH-induced changes in thylakoid membrane thickness that were first observed by Murikami and Packer.^2,3 Here using thin-section electron microscopy we show that the changes in thylakoid membrane thickness do not correlate with ΔpH per se but rather the amplitude of NPQ and is thus affected by the de-epoxidation of the LHCII bound xanthophyll violaxanthin to zeaxanthin. We thus suggest that the change in thylakoid membrane thickness occurring during NPQ reflects the conformational change within LHCII proteins brought about by their protonation and aggregation within the membrane.Key words: nonphotochemical quenching, photoprotection, LHCII, photosystem II, thylakoid membrane     

Challenges to understand plant responses to wind

Understanding plant response to wind is complicated as this factor entails not only mechanical stress, but also affects leaf microclimate. In a recent study, we found that plant responses to mechanical stress (MS) may be different and even in the opposite direction to those of wind. MS-treated Plantago major plants produced thinner more elongated leaves while those in wind did the opposite. The latter can be associated with the drying effect of wind as is further supported by data on petiole anatomy presented here. These results indicate that plant responses to wind will depend on the extent of water stress. It should also be recognized that the responses to wind may differ between different parts of a plant and between plant species. Physiological research on wind responses should thus focus on the signal sensing and transduction of both the mechanical and drought signals associated with wind, and consider both plant size and architecture.Key words: biomechanics, leaf anatomy, phenotypic plasticity, plant architecture, signal transduction thigmomorphogenesis, windWind is one of the most ubiquitous environmental stresses, and can strongly affect development, growth and reproductive yield in terrestrial plants.^1–3 In spite of more than two centuries of research,⁴ plant responses to wind and their underlying mechanisms remain poorly understood. This is because plant responses to mechanical movement themselves are complicated and also because wind entails not only mechanical effects, but also changes in leaf gas and heat exchange.^5–7 Much research on wind has focused primarily on its mechanical effect. Notably, several studies that determine plant responses to mechanical treatments such as flexing, implicitly extrapolate their results to wind effects.^8–10 Our recent study¹¹ showed that this may lead to errors as responses to wind and mechanical stimuli (in our case brushing) can be different and even in the opposite direction. In this paper, we first separately discuss plant responses to mechanical stimuli, and other wind-associated effects, and then discuss future challenges for the understanding of plant responses to wind.It is often believed that responses to mechanical stress (thigmomorphogenesis) entail the production of thicker and stronger plant structures that resist larger forces. This may be true for continuous unidirectional forces such as gravity, however for variable external forces (such as wind loading or periodic flooding) avoiding such mechanical stress by flexible and easily reconfigurable structures can be an alternative strategy.^12–14 How plants adapt or acclimate to such variable external forces depends on the intensity and frequency of stress and also on plant structures. Reduced height growth is the most common response to mechanical stimuli.^15,16 This is partly because such short stature increases the ability of plants to both resist forces (e.g., real-locating biomass for radial growth rather than elongation growth), and because small plants experience smaller drag forces (Fig. 1). Some plant species show a resistance strategy in response to mechanical stress by increasing stem thickness^1,10 and tissue strength.⁷ But other species show an avoidance strategy by a reduction in stem or petiole thickness and flexural rigidity in response to MS.^11,15–18 These different strategies might be associated with plant size and structure. Stems of larger plants such as trees and tall herbs are restricted in the ability to bend as they carry heavy loads^7,10,19 (Fig. 1). Conversely short plants are less restricted in this respect and may also be prone to trampling for which stress-avoidance would be the only viable strategy.^18,20 Systematic understanding of these various responses to mechanical stress remains to be achieved.Open in a separate windowFigure 1A graphical representation of how wind effects can be considered to entail both a drying and a mechanical effect. Adaptation or acclimation to the latter can be through a force resistance strategy or a force avoidance strategy, the benefit of which may depend on the size and architecture of plants as well as the location of a given structure within a plant.Wind often enhances water stress by reducing leaf boundary layers and reduces plant temperature by transpiration cooling. The latter effect may be minor,¹¹ but the former could significantly affect plant development. Anten et al. (2010) compared phenotypic traits and growth of Plantago major that was grown under mechanical stimuli by brushing (MS) and wind in the factorial design. Both MS and wind treatments reduced growth and influenced allocation in a similar manner. MS plants, however, had more slender petioles and narrower leaf blades while wind exposed plants exhibited the opposite response having shorter and relatively thicker petioles and more round-shaped leaf blades. MS plants appeared to exhibit stress avoidance strategy while such responses could be compensated or overridden by water stress in wind exposure.¹¹ A further analysis of leaf petiole anatomy (Fig. 2) supports this view. The vascular fraction in the petiole cross-section was increased by wind but not by MS, suggesting that higher water transport was required under wind. Our results suggest that drying effect of wind can at least to some extent override its mechanical effect.Open in a separate windowFigure 2Representative images of petiole cross-sections of Plantago major grown in 45 days in continuous wind and/or mechanical stimuli (A–D). Petiole cross-section area (E) and vascular bundle fraction in the cross-section of petiole (F). mean + SD (n = 12) are shown. Significance levels of ANOVA; ***p < 0.001, **p < 0.01, *p < 0.05, ns p > 0.05.Physiological knowledge on plant mechanoreception and signal transduction has been greatly increased during the last decades. Plants sense mechanical stimuli through membrane strain with stretch activated channels²¹ and/or through some linker molecules connecting the cell wall, plasma membrane and cytoskeleton.^4,22,23 This leads to a ubiquitous increase in intracellular Ca²⁺ concentration. The increased Ca²⁺ concentration is sensed by touch induced genes (TCHs),^24,25 which activates downstream transduction machineries including a range of signaling molecules and phytohormones, consequently altering physiological and developmental processes.²⁶ Extending this knowledge to understand plant phenotypic responses to wind however remains a challenge. As responses to wind have been found to differ among parts of a plant (e.g., terminal vs. basal stem) and also across species, physiological studies should be extended to the whole-plant as integrated system rather than focusing on specific tissue level. Furthermore to understand the general mechanism across species, it is required to study different species from different environmental conditions. Advances in bioinformatics, molecular and physiological research will facilitate cross-disciplinary studies to disentangle the complicated responses of plants to wind.     

Synthesis and biological evaluation of nimesulide based new class of triazole derivatives as potential PDE4B inhibitors against cancer cells

A new class of 1,2,3-triazol derivatives derived from nimesulide was designed as potential inhibitors of PDE4B. Synthesis of these compounds was carried out via a multi-step sequence consisting of copper-catalyzed azide–alkyne cycloaddition (CuAAC) as a key step in aqueous media. The required azide was prepared via the reaction of aryl amine (obtained from nimesulide) with α-chloroacetyl chloride followed by displacing the α-chloro group by an azide. Some of the synthesized compounds showed encouraging PDE4B inhibitory properties in vitro that is >50% inhibition at 30 μM that were supported by the docking studies of these compounds at the active site of PDE4B enzyme (dock scores ～ ?28.6 for a representative compound). Two of these PDE4 inhibitors showed promising cytotoxic properties against HCT-15 human colon cancer cells in vitro with IC₅₀ ～ 21–22 μg/mL.     

Identification of tetratricopeptide repeat domain 9, a hormonally regulated protein

Tetratricopeptide repeat domain 9 (TTC9) mRNA was drastically up-regulated by progesterone in progesterone receptor-transfected breast cancer cells MDA-MB-231. This up-regulation is coupled with progesterone-mediated growth inhibition and induction of focal adhesion. We have generated mouse polyclonal antibody against a predicted 222 aa TTC9 protein and identified a 25 kDa TTC9 protein that is widely expressed in human tissues, with the highest expression in the brain. Immunostaining and cell fractionation studies revealed that TTC9 is predominantly localized to the endoplasmic reticulum. The level of TTC9 protein in MCF-7 cells is regulated by various factors and chemical reagents including estrogen, progesterone, growth factors, ICI182,780, and p38 kinase inhibitor SB203580. Growth factor-induced TTC9 protein expression was inhibited by estrogen and abolished by ERK inhibitor PD98059. Though the function of TTC9 is not yet clear, the susceptibility of its protein level to biological and chemical agents suggests that TTC9 is a biologically significant protein.     

The induction of polyploidy or apoptosis by the Aurora A kinase inhibitor MK8745 is p53-dependent

Aurora kinases are mitotic serine/threonine protein kinases and are attractive novel targets for anticancer therapy. Many small-molecule inhibitors of Aurora kinases are currently undergoing clinical trials. Aurora A kinase is essential for successful mitotic transition. MK8745 is a novel and selective small-molecule inhibitor of Aurora A kinase. MK8745 induced apoptotic cell death in a p53-dependent manner when tested in vitro in cell lines of multiple lineages. Cells expressing wild-type p53 showed a short delay in mitosis followed by cytokinesis, resulting in 2N cells along with apoptosis. However, cells lacking or with mutant p53 resulted in a prolonged arrest in mitosis followed by endoreduplication and polyploidy. Cytokinesis was completely inhibited in p53-deficient cells, as observed by the absence of 2N cell population. The induction of apoptosis in p53-proficient cells was associated with activation of caspase 3 and release of cytochrome c but was independent of p21. Exposure of p53 wild-type cells to MK8745 resulted in the induction of p53 phosphorylation (ser15) and an increase in p53 protein expression. p53-dependent apoptosis by MK8745 was further confirmed in HCT 116 p53^−/− cells transfected with wild-type p53. Transient knockdown of Aurora A by specific siRNA recapitulated these p53-dependent effects, with greater percent induction of apoptosis in p53 wild-type cells. In conclusion, our studies show p53 as a determining factor for induction of apoptosis vs. polyploidy upon inhibition of Aurora A.Key words: Aurora A kinase, polyploidy, apoptosis, p53, cell cycle     

Aurora B Kinase Regulates the Postmitotic Endoreduplication Checkpoint via Phosphorylation of the Retinoblastoma Protein at Serine 780

The phenotypic change characteristic of Aurora B inhibition is the induction of polyploidy. Utilizing specific siRNA duplexes and a selective small molecule inhibitor (AZD1152) to inhibit Aurora B activity in tumor cells, we sought to elucidate the mechanism by which Aurora B inhibition results in polyploidy. Cells treated with AZD1152 progressed through mitosis with misaligned chromosomes and exited without cytokinesis and subsequently underwent endoreduplication of DNA despite activation of a p53-dependent pseudo G1 checkpoint. Concomitant with polyploid cell formation, we observed the appearance of Rb hypophosphorylation, an event that occurred independently of cyclin-dependent kinase inhibition. We went on to discover that Aurora B directly phosphorylates Rb at serine 780 both in vitro and in vivo. This novel interaction plays a critical role in regulating the postmitotic checkpoint to prevent endoreduplication after an aberrant mitosis. Thus, we propose for the first time that Aurora B determines cellular fate after an aberrant mitosis by directly regulating the Rb tumor suppressor protein.     

Purification and characterization of a natural agglutinin in the hemolymph of the prawn Penaeus indicus H. Milne Edwards.

A natural agglutinin in the hemolymph of the marine prawn Penaeus indicus was isolated by gel filtration chromatography, purified using polyacrylamide gel electrophoresis, and characterized. Prawn agglutinin has a native molecular mass of 181 kDa and consists of two monomeric units (97 and 84 kDa), maintains some agglutinating activity over a wide pH range (7-9), and is inactivated at 85 degrees C. The agglutinin was denatured upon mixing with trichloroacetic acid, phenol, chloroform, and 45% ammonium sulfate. It was also sensitive to trypsin digestion. The results indicate that prawn agglutinin is proteinaceous in nature, with agglutinating, hemolytic, and antibacterial properties against marine bacteria and erythrocytes with carbohydrate binding sites.