CLAUSA restricts tomato leaf morphogenesis and GOBLET expression

Leaf morphogenesis and differentiation are highly flexible processes. The development of compound leaves is characterized by an extended morphogenesis stage compared with that of simple leaves. The tomato mutant clausa (clau) possesses extremely elaborate compound leaves. Here we show that this elaboration is generated by further extension of the morphogenetic window, partly via the activity of ectopic meristems present on clau leaves. Further, we propose that CLAU might negatively affect expression of the NAM/CUC gene GOBLET (GOB), an important modulator of compound‐leaf development, as GOB expression is elevated in clau mutants and reducing GOB expression suppresses the clau phenotype. Expression of GOB is also elevated in the compound leaf mutant lyrate (lyr), and the remarkable enhancement of the clau phenotype by lyr suggests that clau and lyr affect leaf development and GOB in different pathways.     

MamA as a Model Protein for Structure-Based Insight into the Evolutionary Origins of Magnetotactic Bacteria

MamA is a highly conserved protein found in magnetotactic bacteria (MTB), a diverse group of prokaryotes capable of navigating according to magnetic fields – an ability known as magnetotaxis. Questions surround the acquisition of this magnetic navigation ability; namely, whether it arose through horizontal or vertical gene transfer. Though its exact function is unknown, MamA surrounds the magnetosome, the magnetic organelle embedding a biomineralised nanoparticle and responsible for magnetotaxis. Several structures for MamA from a variety of species have been determined and show a high degree of structural similarity. By determining the structure of MamA from Desulfovibrio magneticus RS-1 using X-ray crystallography, we have opened up the structure-sequence landscape. As such, this allows us to perform structural- and phylogenetic-based analyses using a variety of previously determined MamA from a diverse range of MTB species across various phylogenetic groups. We found that MamA has remained remarkably constant throughout evolution with minimal change between different taxa despite sequence variations. These findings, coupled with the generation of phylogenetic trees using both amino acid sequences and 16S rRNA, indicate that magnetotaxis likely did not spread via horizontal gene transfer and instead has a significantly earlier, primordial origin.     

Analysis of structure of glycogen in rat hepatocytes using cytochemical and FRET methods

Using cytochemical and Förster resonance energy transfer (FRET) methods, the structure of glycogen was studied in rat hepatocytes during starvation and in some time intervals after the peroral administration of glucose to the animals. Hepatocytes were stained with a fluorescent variant of PAS reaction on object glasses. The staining of preparations for 40 min with ethidium bromide-SO₂ (EtBr-SO₂) revealed the labile fraction (LF) of glycogen, while their subsequent staining with auramine-SO₂ (Au-SO₂) for 50 min revealed the stable fraction (SF) of glycogen in cells. The total glycogen content (LF + SF) in hepatocytes at various stages of rat refeeding was determined using a cytofluorimeter; then, in the same cells, the FRET efficiency was measured. Recording FRET at several sites of cells was performed using a Leica TCS SP5 laser scanning confocal microscope by using the FRET Acceptor Photobleaching (FRET AB) procedure. In this procedure, auramine was used as the donor (D), while ethidium bromide was used as the acceptor (A). The efficiency of FRET in the course of rat refeeding with glucose has been shown to change from 10 to 14%, and the glycogen structure markedly affects the value of this parameter. It is found that, in cells of starved rats and in early terms after the administration of glucose, the FRET efficiency correlates with the A/D ratio, which reflects the degree of filling of external tiers of glycogen molecules with glucose residues. At later terms of refeeding, this correlation is either less pronounced or completely absent. It has been established that, at the same A/D value, the FRET efficiency can change by three to four times. Since the probability of energy transduction from D to A is proportional to 1/R⁶, where R is the distance between D and A. These fluctuations of the FRET efficiency mean that the glycogen molecules have the labile structure, in which chains of glycoside residues can deviate from its axis at a distance of about a half of their diameter.     

Universal Design Principles for Cascade Heterojunction Solar Cells with High Fill Factors and Internal Quantum Efficiencies Approaching 100%

Cascade heterojunction (CHJ) organic solar cells have recently emerged as an alternative to conventional bulk heterojunctions and series‐connected tandems due to their significant promise for high internal quantum efficiency (IQE) and broad spectral coverage. However, CHJ devices thus far have also exhibited poor fill factor (FF), resulting in minimal enhancements (or even decreases) in power conversion efficiency (PCE) when compared with single heterojunction (SHJ) cells. In this study, the major variables controlling the CHJ maximum power point and FF are determined using a combinatorial approach. By matching the maximum power point voltage (V_MPP) of the constituent parallel‐connected heterojunctions (subjunctions) and minimizing the injection barriers intrinsic to CHJs, high FF and PCE can be achieved. Optimized CHJ devices are demonstrated with >99% IQE in the interlayer and a 46% increase in PCE compared to a SHJ reference (4.1% versus 2.8%). Devices with a transparent exciton dissociation layer (EDL)/interlayer/acceptor structure are employed, such that each CHJ has absorption efficiency identical to its interlayer/acceptor SHJ counterpart. Using these results, a clear map of performance as a function of material parameters is developed, providing straightforward, universal design rules to guide future engineering of molecules and layer architectures for CHJ organic photovoltaic devices.     

Broadband Plasmonic Photocurrent Enhancement in Planar Organic Photovoltaics Embedded in a Metallic Nanocavity

A substantial broadband increase in the external quantum efficiency (EQE) of thin‐film organic photovoltaic (OPV) devices using near‐field coupling to surface plasmons is reported, significantly enhancing absorption at surface plasmon resonance (SPR). The devices tested consist of an archetypal boron subpthalocyanine chloride/fullerene (SubPc/C₆₀) donor/acceptor heterojunction embedded within a planar semitransparent metallic nanocavity. The absorption and EQE are modeled in detail and probed by attenuated total internal reflection spectroscopy with excellent agreement. At SPR, the EQE can be enhanced fourfold relative to normal incidence, due to simulated ninefold enhancement in active layer absorption efficiency. The response at SPR is thickness‐independent, down to a few monolayers, suggesting the ability to excite monolayer‐scale junctions with an EQE of ≈6% and a 16‐fold absorption enhancement over normal incidence. These results potentially impact the future design of plasmonically enhanced thin‐film photovoltaics and photodetectors and enable the direct analysis of the dynamics of photocurrent production at OPV heterojunctions.     

DNA image-fluorimetry of individual human chromosomes

A microfluorimetric method has been developed for determination of DNA content in individual human chromosomes. The method is based on a preliminary identification of chromosomes with Hoechst 33258 followed by staining of the chromosomes with Feulgen reaction by using Schiff’s reagent type ethidium bromide-SO₂ and then by measuring the fluorescence intensity of the chromosomes by using an image analyzer. The method allows determining the DNA content of individual chromosomes with an accuracy up to 4.5 fg. The DNA content of individual human chromosomes and their p-and q-arms, as well as homologous chromosomes, were measured by using the developed method. It has been shown that the DNA content in chromosomes of the normal human karyotype is unstable and can fluctuate in some chromosomes within 35–40 fg.     

A Quantitative Study of Regional and Stage Specific Reaction of Xenopus laevisEmbryonic Tissues on Mechanical Load

Residual deformation of fragments of the embryonic tissues preserved after relaxation of the stretching force serve as a criterion of active redistribution of their cells caused by this stretching. We measured residual deformations of the Xenopus laevis ventral and dorsal ectoderm at the early gastrula and lateral ectoderm at the late gastrula-early neurula after stretching of varying time and force. While the samples responded to moderate (up to 40%) short-term stretching as elastic bodies (residual deformations were absent), residual deformation appeared in the early gastrula tissues after 30–60-min stretching, which were more pronounced in the ventral tissues than in the dorsal ones. On the contrary, a contractile reaction developed in the late gastrula-early neurula tissues in response to 60-min stretching, which almost relaxed residual deformation within 20 min after unloading. A conclusion was drawn that gastrulation and neurulation proceed under the conditions of relaxing and nonrelaxing mechanical tensions, respectively. Mechanical bases and morphogenetic role of the described reactions is discussed.     

Corneal Donor Tissue Preparation for Descemet's Membrane Endothelial Keratoplasty

Descemet’s Membrane Endothelial Keratoplasty (DMEK) is a form of corneal transplantation in which only a single cell layer, the corneal endothelium, along with its basement membrane (Descemet''s membrane) is introduced onto the recipient''s posterior stroma³. Unlike Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK), where additional donor stroma is introduced, no unnatural stroma-to-stroma interface is created. As a result, the natural anatomy of the cornea is preserved as much as possible allowing for improved recovery time and visual acuity⁴. Endothelial Keratoplasty (EK) is the procedure of choice for treatment of endothelial dysfunction. The advantages of EK include rapid recovery of vision, preservation of ocular integrity and minimal refractive change due to use of a small, peripheral incision¹. DSAEK utilizes donor tissue prepared with partial thickness stroma and endothelium. The rapid success and utilization of this procedure can be attributed to availability of eye-bank prepared precut tissue. The benefits of eye-bank preparation of donor tissue include elimination of need for specialized equipment in the operating room and availability of back up donor tissue in case of tissue perforation during preparation. In addition, high volume preparation of donor tissue by eye-bank technicians may provide improved quality of donor tissue. DSAEK may have limited best corrected visual acuity due to creation of a stromal interface between the donor and recipient cornea. Elimination of this interface with transplantation of only donor Descemet''s membrane and endothelium in DMEK may improve visual outcomes and reduce complications after EK⁵. Similar to DSAEK, long term success and acceptance of DMEK is dependent on ease of availability of precut, eye-bank prepared donor tissue. Here we present a stepwise approach to donor tissue preparation which may reduce some barriers eye-banks face in providing DMEK grafts.