Circular Arrangement Research Articles

Introduction to the special topic: a multidisciplinary approach to motor learning and sensorimotor adaptation

Advances in neuroimaging over the past 20 years have provided insight into the dynamic neural processes underlying human motor skill acquisition, focusing primarily on brain networks that are engaged during early versus late stages of learning. What has been challenging for the field is to tightly link these shifting neural processes with what is known about measureable behavioral changes and strategic processes that occur during learning. The complex nature of behavior and strategy in motor learning often result in a trade-off between experimental control and external validity. Researchers in different disciplines have employed varying approaches to understand motor learning but with relatively little crosstalk. Here, we bring together a set of papers which investigate skill learning spanning multiple domains. There are several striking and unique features about the papers assembled for this special issue. One is the broad range of investigative techniques brought to bear on the problem of understanding skill acquisition, including cutting edge analytical approaches (Abe and Sternad, 2013; Sami and Miall, 2013), metrics of brain structure and function (Kam et al., 2012; Steele et al., 2012; Bernard and Seidler, 2013; Gentili et al., 2013; Wadden et al., 2013), behavioral experiments with carefully crafted conditions (Armstrong et al., 2013; Kitago et al., 2013; Leow et al., 2013; Nemeth et al., 2013; Taylor and Ivry, 2013), and comprehensive reviews which put forth new theories and novel viewpoints for interpretation (Abrahamse et al., 2013; Bock, 2013; Heuer and Sulzenbruck, 2013; King et al., 2013; Ruddy and Carson, 2013; Vadakkan, 2013). We expect that motor scientists will find inspiring new ideas, techniques, approaches, and theories in this collection of articles. Another important aspect of these papers is that they report on differing types of skill acquisition including practice of a new skill, adaptation to visuomotor distortions, and acquiring new action sequences. For example, Heuer and Sulzenbruck review their findings evaluating how subjects learn the transformation of a sliding first-order level. This has highly practical implications as this tool type is used in minimal access surgery. The sliding first-order level is a type of tool often used in laproscopic surgery; a fulcrum effect at the skin insertion site results in forward hand movements producing backward tool movements. Moreover, linear hand motions result in curved tool tip paths. Taylor and Ivry leverage comparisons of subjects adapting to visuomotor rotations and to visual translational shifts, and report an interaction between the type of perturbation applied and whether targets are presented in a circular or rectilinear arrangement. Interestingly, they observed that generalization of adaptation across the workspace was linked more to the environmental context than to the perturbation type. Steele and colleagues report findings from a multimodal neuroimaging study using their well-characterized temporal motor sequence task, which requires participants to learn both spatial response locations and a temporal rhythm, similar to playing a musical instrument. They report complementary structural and functional changes with learning; the rate of learning was positively correlated with gray matter volume in cerebellar lobules HV and VI. These same regions exhibit decreases in functional activation with training. Finally, Kitago et al. focus on unlearning in an effort to determine whether it represents forgetting of acquired representations or just reverting back to habitual performance. Their findings support that unlearning is not just forgetting, but is rather an active process. This has important implications for individuals who need to learn new ways of performing everyday skills after suffering from injury or neurological insult. Several of the papers in this special issue also highlight the differing contributions of neurocognitive mechanisms across learning, consolidation and retention. For example, Nemeth et al. assessed skill learning in healthy adults and those with mild cognitive impairment to investigate the role of the hippocampus and medial temporal lobe (MTL) structures in skilled learning. Using the alternating serial response task (ASRT) they report that individuals with MCI, and likely compromised hippocampal/MTL structures, demonstrate a reduced ability to reactivate/recall learned sequences in subsequent blocks of practice. Interestingly, they report that differences in learning disappeared during the second half of a practice block suggesting a differential role for hippocampus/MTL structures across practice even within a block. In a second paper,Wadden et al. evaluated individual variability in the neural networks underlying motor sequence learning in middle aged adults. Comparing initial task performance to that at a delayed retention test following 5 days of continuous tracking practice they report variability in overall measures of implicit sequence specific learning. However, when learning was decomposed into temporal and spatial elements to account for individual variation, improvement in temporal elements were associated with a network of cortical, sub-cortical and

Learning real-life cognitive abilities in a novel 360°-virtual reality supermarket: a neuropsychological study of healthy participants and patients with epilepsy

BackgroundTo increase the ecological validity of neuropsychological instruments the use of virtual reality (VR) applications can be considered as an effective tool in the field of cognitive neurorehabilitation. Despite the growing use of VR programs, only few studies have considered the application of everyday activities like shopping or travelling in VR training devices.MethodsWe developed a novel 360°- VR supermarket, which is displayed on a circular arrangement of 8 touch-screens – the “OctaVis”. In this setting, healthy human adults had to memorize an auditorily presented shopping list (list A) and subsequently buy all remembered products of this list in the VR supermarket. This procedure was accomplished on three consecutive days. On day four, a new shopping list (list B) was introduced and participants had to memorize and buy only products of this list. On day five, participants had to buy all remembered items of list A again, but without new presentation of list A. Additionally, we obtained measures of participants’ presence, immersion and figural-spatial memory abilities. We also tested a sample of patients with focal epilepsy with an extended version of our shopping task, which consisted of eight days of training.ResultsWe observed a comprehensive and stable effect of learning for the number of correct products, the required time for shopping, and the length of movement trajectories in the VR supermarket in the course of the training program. Task performance was significantly correlated with participants’ figural-spatial memory abilities and subjective level of immersion into the VR.ConclusionsLearning effects in our paradigm extend beyond mere verbal learning of the shopping list as the data show evidence for multi-layered learning (at least visual-spatial, strategic, and verbal) on concordant measures. Importantly, learning also correlated with measures of figural-spatial memory and the degree of immersion into the VR. We propose that cognitive training with the VR supermarket program in the OctaVis will be efficient for the assessment and training of real-life cognitive abilities in healthy subjects and patients with epilepsy. It is most likely that our findings will also apply for patients with cognitive disabilities resulting from other neurological and psychiatric syndromes.

An Unusual Distribution of Neuronal Nitric Oxide Synthase (nNOS) Neurons in the Porcine Retina Next to the Ora Serrata

Neuronal nitric oxide synthase (nNOS)-immunoreactive (IR) cells are present in the retina of almost all species. Here we report about an unusual localization of nNOS-IR cells in the porcine retina. While no nNOS-IR amacrine cells were seen in the central porcine retina, a circular arrangement of nNOS-IR cells was observed next to the ora serrata region, particularly in the lower retinal quadrant. The neurons showed co-localization with calretinin. Most of their processes ran parallel to the ora serrata but some were disposed at right angles to the line of the ora serrata, directed either to the epithelial layer of the pars plana or towards the retina. The function of these uniquely located neurons in the porcine retina remains to be determined.

3D-steering and superfocusing of second-harmonic radiation through plasmonic nano antenna arrays

Second-harmonic generation (SHG) of light at nanoparticles provides the possibility to generate light (of a desired frequency) in-situ instead of introducing it by focusing an external light beam. Our theoretical study provides steering SHG light through the superposition of the radiation from a number of nanoparticles which are arranged in a circle. The authors assume cone-shaped or rod-shaped nanoparticles. Their radiation can be modeled as radiating dipoles. The superposition of their fields yields a “hot spot” with a full width at half-maximum of around 100 nm. Even more important, the position of the hot spot within the circular arrangement of nanoantennas can be adjusted in the xy plane simply by changing the incident angle of the exciting beam.

Centrolobium tomentosum: macro-and microscopic diagnosis of the leaf and stem

Centrolobium tomentosum Guillemin ex Benth., Fabaceae, known as "araribá-rosa", is a large tree that is widespread throughout Brazil. The bark of its stem is used in folk medicine as an astringent and the leaves are employed as a poultice for wounds and bruises. The aim of this study was to contribute to the pharmacognostic quality control of this medicinal species through a macro- and microscopic diagnosis of its leaves and stems. Mature leaves and young stems were collected at Embrapa (Colombo, PR) and analyzed using standard microtechniques. The leaves are opposite or alternate, compound, imparipinnate, oblong-lanceolate and hypostomatic with paracytic stomata. The mesophyll is dorsiventral and the midrib is biconvex with a collateral vascular bundle in a circular arrangement. The petiolule is circular and its vascular system is composed of two major vascular bundles in the middle, with smaller bundles between them. The rachis has a structure similar to the petiole, and these parts have a sclerenchymatic sheath shaped in multiple arcs, which surrounds a collateral vascular bundle that is centrally located. The stem has a uniseriate epidermis with peripheral phellogen and a sclerenchymatic sheath composed of many arcs, which surrounds the phloem. The stems and leaves also have non-glandular and glandular trichomes, phenolic compounds and idioblasts made of calcium oxalate crystals. This manuscript has an important role in the morpho-anatomical diagnosis of the Brazilian flora.

Research of band gap properties based on two-dimensional photonic crystal with mixed shapes of rods

Two new structures of photonic crystals were designed. The band gap properties of photonic crystals with square and circular dielectric rods mixed arrangement are researched. The band gap properties of mixed shapes rods photonic crystal are calculated and compared with the crystals with square rods or round rods by using plane wave expansion method. Simulation results show that for the square lattice, mixed shapes of rods make the higher-order bands of TM modes moving toward the low frequency range. The gap bands’ widths and locations are between the parameters of square and round rods photonic crystal. In triangle lattice, a significant band gap is presented in photonic crystal with mixed shapes of rods in TE mode, while it is almost not presented in square and round rods crystals. The phenomenon of bands moving toward the low frequency range is also found in the triangle lattice mixed shapes rods photonic crystal. The reasons of the results in the vision were analyzed.

ELECTRIC AND MAGNETIC FIELD PROBLEMS WITH PERIODIC CIRCULAR CYLINDRICAL SYMMETRY AND THEIR CONNECTION WITH A NOVEL GEOMETRICAL INTERPRETATION OF THE ALGEBRAIC OPERATION aN±bN

Abstract—This paper deals with the evaluation of the electric and magnetic field generated by a set of N periodically distributed filamentary conductors, in a circular arrangement. The results obtained lead to the computation of a continuous product of distances. In close connection with the computation of such a continuous product, the general problem of the factorization of a sum or difference of two powers, aN ± bN , where a and b are positive real numbers and N a positive integer, is addressed.

CuII Complexes of Isomeric Ligands Derived from 2-Pyridine-carboxaldehyde and m- or p-Xylylenediamine: An Intermolecularly ?-Stacked Dinuclear Species and a Trinuclear Circular Helicate that Encapsulates a Chloride Ion

Di- and trinuclear CuII complexes [Cu2L1(2,2′-bipyridine)2Cl2]Cl2·11H2O and [Cu3(L2)3Cl3]Cl3·1.25MeOH·4H2O incorporating the isomeric Schiff base ligands 1,1′-(1,4-phenylene)bis(N-(pyridin-2-ylmethylene)methanamine) (L1) and 1,1′-(1,4-phenylene)bis(N-(pyridin-2-ylmethylene)methanamine) (L2), each incorporating two separated α-diimine coordination domains, have been synthesised and their X-ray crystal structures and variable temperature magnetic properties determined. The X-ray crystal structure of [Cu2L1(2,2′-bipyridine)2Cl2]Cl2·11H2O shows that each CuII centre is bound to two nitrogen atoms from L1, two from a bipyridine ligand, and a chloride anion. Intramolecular π-stacking interactions are present between the central phenyl ring of L1 and both rings of each bipyridine ligand. The structure of [Cu3(L2)3Cl3]Cl3·1.25MeOH·4H2O shows an unusual trinuclear circular helicate arrangement with approximate C3-symmetry. A chloride anion is encapsulated in the structure being bound by six non-classical hydrogen bond interactions. Variable temperature magnetic susceptibility measurements indicated the presence of weak antiferromagnetic behaviour for [Cu2L1(2,2′-bipyridine)2Cl2]Cl2·11H2O and weak ferromagnetic behaviour for [Cu3(L2)3Cl3]Cl3·1.25MeOH·4H2O.

円形カメラ配置EPIからの補間視点画像生成のための補間対象領域に注目した対応点探索法

This paper proposes a new method of correspondence point search for intermediate viewpoint image generation using Lagrangian interpolation from multi-view images obtained from the circular camera arrangement. Correspondence point search is not performed on the basis of the real camera image but is performed on the basis of interpolation domain. In the conventional method, if the camera interval exceeds 4°, this causes disturbance in the image. However, the proposed method was able to produce an image with fewer disturbances to the intermediate viewpoint with a camera interval up to 6°. In addition, it was able to suppress a significant increase in processing costs by varying the block size to be used for correspondence point search by focusing on the amount of edge that is included in the search range.

Synchronization and bundling of anchored bacterial flagella

The synchronization and bundling process of bacterial flagella is investigated by mesoscale hydrodynamic simulations. Systems with two to six flagella are considered, which are anchored at one end, and are driven by a constant torque. A flagellum is modelled as a linear helical structure composed of mass points with their elastic shape maintained by bonds, bending, and torsional potentials. The characteristic times for synchronization and bundling are analyzed in terms of motor torque, separation, and number of flagella. We find that hydrodynamic interactions determine the bundling behavior. The synchronization time is smaller than the bundling time, but their ratio depends strongly on the initial separation. The bundling time decreases with increasing number of flagella at a fixed radius in a circular arrangement due to multi-helix hydrodynamics.

Reappraisal of intergender differences in the urethral striated sphincter explains why a completely circular arrangement is difficult in females: a histological study using human fetuses

To investigate why the development of a completely circular striated sphincter is so rare, we examined histological sections of 11 female and 11 male mid-term human fetuses. In male fetuses, the striated muscle initially extended in the frontal, rather than in the horizontal plane. However, a knee-like portion was absent in the female fetal urethra because, on the inferior side of the vaginal end, a wide groove for the future vestibule opened inferiorly. Accordingly, it was difficult for the developing striated muscle to surround the groove, even though there was not a great difference in width or thickness between the female vestibule and the male urethra. The development of a completely circular striated sphincter seems to be impossible in females because of interruption of the frontal plane by the groove-like vestibule. However, we cannot rule out the possibility that before descent of the vagina, the urethral striated muscle extends posteriorly.

Fast and low-cost structured light pattern sequence projection

We present a high-speed and low-cost approach for structured light pattern sequence projection. Using a fast rotating binary spatial light modulator, our method is potentially capable of projection frequencies in the kHz domain, while enabling pattern rasterization as low as 2 μm pixel size and inherently linear grayscale reproduction quantized at 12 bits/pixel or better. Due to the circular arrangement of the projected fringe patterns, we extend the widely used ray-plane triangulation method to ray-cone triangulation and provide a detailed description of the optical calibration procedure. Using the proposed projection concept in conjunction with the recently published coded phase shift (CPS) pattern sequence, we demonstrate high accuracy 3-D measurement at 200 Hz projection frequency and 20 Hz 3-D reconstruction rate.

Photoelastic Measurement of High Stress Profiles in Ion‐Exchanged Glass

Photoelastic fringes were directly measured to fully characterize high magnitude, steep compressive stress gradients in an ion‐exchanged glass, trade named Ion‐Armor™. Initially, using a thick (9.9 mm) rectangular bar and circular polariscope arrangement the overall residual stress profile in a bulk specimen was determined. However, due to the relatively large thickness of the specimen, the high density of fringes (steep stress gradient) close to the edge of the specimen became too diffused to allow an accurate count of fringe order. A thinner (0.71 mm) specimen was then used along with a polarizing light microscope to enhance the fringe contrast. This arrangement yielded approximately four isochromatic fringes, representing a maximum surface compressive stress of 984 MPa, which rapidly decreased to ~300 MPa within 25 μm depth from the strengthened surface. Also, the case‐depth of the ion‐exchange process was found to be 0.8 mm. Thus, the technique was able to directly capture the extremely high residual compressive stresses generated in an ion‐exchanged glass. The current technique utilized for residual stress measurement is more objective and straightforward to implement than what is specified in ASTM standard C‐1422, particularly for those specimens having steep stress gradients just below the strengthened surface.

Capuchin monkeys (Cebus nigritus) use spatial and visual information during within-patch foraging

Foraging in large-scale (navigation between patches), small-scale (choice of within-patch feeding sites), and micro-scale (close inspection of food items) space presents variable cognitive challenges. The reliability and usefulness of spatial memory and perceptual cues during food search in a forest environment vary among these spatial scales. This research applied an experimental field design to test the ability of a free-ranging group composed of eight black-horned capuchin monkeys, Cebus nigritus, inhabiting a forest fragment in Porto Alegre, State of Rio Grande do Sul, Brazil, to use food-associated spatial, visual, olfactory, and quantitative (amount of food) cues during small-scale foraging decisions. The experimental design involved the establishment of a feeding station composed of eight feeding platforms distributed in a circular arrangement. A series of six experiments, each lasting 20 days, was conducted from March to August 2005. Two feeding platforms in each experimental session contained a food reward (real banana), whereas the remaining six platforms contained either a sham banana or an inaccessible real banana. Data on capuchin monkey foraging behavior at the feeding stations were collected by the "all occurrences" sampling method. The performance of the capuchins in the experiments was analyzed based on the first two platforms inspected in each session. The study group inspected feeding platforms in 571 occasions during 113 sessions. Capuchins used visual cues and spatial information (and adopted a win-return strategy) for finding the platforms baited with real bananas and showed weak evidence of the integration of spatial and quantitative cues, but failed to show evidence of using olfactory cues. In addition, individual differences in social rank and foraging behavior affected opportunities for learning and the performance in the cognitive tasks.

Drug‐specific cyclodextrins with emphasis on sugammadex, the neuromuscular blocker rocuronium and perioperative anaphylaxis: implications for drug allergy

Cyclodextrins, oligosaccharides linked in a circular arrangement around a central cavity, are used extensively in the pharmaceutical industry to improve drug delivery. Their usefulness depends on their capacity to form a drug inclusion, or host-guest, complex within the cavity. In an attempt to improve the delivery of the widely used neuromuscular blocking drug (NMBD) rocuronium, a rocuronium inclusion complex was formed with a chemically modified γ-cyclodextrin. The high binding affinity and specificity of the modified carrier (named sugammadex) for rocuronium (and other aminosteroid NMBDs) led to its use in anaesthesia as an innovative and useful agent for rapid reversal of rocuronium-induced neuromuscular block by sequestering the drug as an inclusion complex. This, in turn, led to the suggestion that sugammadex might be useful to remove the NMBD from the circulation of patients experiencing rocuronium-induced anaphylaxis, a suggestion subsequently supported in case reports where traditional treatment had failed. Successful resuscitations suggested that sugammadex might be a valuable new treatment for such intractable cases but, given the inappropriateness of clinical trials, confirmation or refutation will have to await the slow accumulation of results of individual case reports. Important questions related to antibody accessibility of drug allergenic structures on the rocuronium-sugammadex inclusion complex, and the competition between sugammadex and IgE antibodies (both free and cell bound) for rocuronium, also remain and can be investigated in vitro. The sugammadex findings indicate that the use of carrier molecules such as the cyclodextrins to improve drug delivery will sometimes give rise to changed immunologic and allergenic behaviour of some drugs and this will have to be taken into account in preclinical drug safety assessments of drug-carrier complexes. The possibility of encapsulating and removing other allergenic drugs, e.g., penicillins and cephalosporins, in cases of difficult-to-reverse anaphylaxis to these drugs is discussed.

Consistent two-dimensional visualization of protein-ligand complex series

BackgroundThe comparative two-dimensional graphical representation of protein-ligand complex series featuring different ligands bound to the same active site offers a quick insight in their binding mode differences. In comparison to arbitrary orientations of the residue molecules in the individual complex depictions a consistent placement improves the legibility and comparability within the series. The automatic generation of such consistent layouts offers the possibility to apply it to large data sets originating from computer-aided drug design methods.ResultsWe developed a new approach, which automatically generates a consistent layout of interacting residues for a given series of complexes. Based on the structural three-dimensional input information, a global two-dimensional layout for all residues of the complex ensemble is computed. The algorithm incorporates the three-dimensional adjacencies of the active site residues in order to find an universally valid circular arrangement of the residues around the ligand. Subsequent to a two-dimensional ligand superimposition step, a global placement for each residue is derived from the set of already placed ligands. The method generates high-quality layouts, showing mostly overlap-free solutions with molecules which are displayed as structure diagrams providing interaction information in atomic detail. Application examples document an improved legibility compared to series of diagrams whose layouts are calculated independently from each other.ConclusionsThe presented method extends the field of complex series visualizations. A series of molecules binding to the same protein active site is drawn in a graphically consistent way. Compared to existing approaches these drawings substantially simplify the visual analysis of large compound series.

Thermal conditioning for urban outdoor spaces through the use of evaporative wind towers

The aim of this paper is to study the thermal comfort levels achieved in open spaces by means of evaporative wind towers. These systems have been installed in an urban area characterized by its hot and dry summer climate. Conventional wind tower designs for enclosed and semi-enclosed spaces have been adapted for this new installation. These systems are usually composed of a few number of wind towers, this one however is composed by a group of sixteen, increasing the total dimensions of the installation. To integrate this construction into the urban public area, it was built in a circular arrangement, creating an activity and meeting point for pedestrians. This passive system was monitored during the summer of 2008. Measurements of temperature, solar radiation, humidity and wind speed were analyzed. During the analyzed period, the average cooling efficiency of the system varied from 38% at the exit of the tower, to 32% at 1 m high. At this last position, the average exceeds the wet bulb temperature up to 8 °C with an increase of moisture around 27%. The shading effect produced by the global installation itself has been modeled theoretically to evaluate the incident solar radiation at the pedestrian area. Two indices have been applied to predict the perception of heat and cold in the south pedestrian zone: Heat index and TS index. In this position, both variables approached the thermal sensation to the comfort levels by the use of these passive strategies when ambient conditions are hot and dry.

Membrane Topology of the Colicin E1 Channel Using Genetically Encoded Fluorescence

The membrane topology of the colicin E1 channel domain was studied by fluorescence resonance energy transfer (FRET). The FRET involved a genetically encoded fluorescent amino acid (coumarin) as the donor and a selectively labeled cysteine residue tethered with DABMI (4-(dimethylamino)phenylazophenyl-4'-maleimide) as the FRET acceptor. The fluorescent coumarin residue was incorporated into the protein via an orthogonal tRNA/aminoacyl-tRNA synthetase pair that allowed selective incorporation into any site within the colicin channel domain. Each variant harbored a stop (TAG) mutation for coumarin incorporation and a cysteine (TGT) mutation for DABMI attachment. Six interhelical distances within helices 1-6 were determined using FRET analysis for both the soluble and membrane-bound states. The FRET data showed large changes in the interhelical distances among helices 3-6 upon membrane association providing new insight into the membrane-bound structure of the channel domain. In general, the coumarin-DABMI FRET interhelical efficiencies decreased upon membrane binding, building upon the umbrella model for the colicin channel. A tentative model for the closed state of the channel domain was developed based on current and previously published FRET data. The model suggests circular arrangement of helices 1-7 in a clockwise direction from the extracellular side and membrane interfacial association of helices 1, 6, 7, and 10 around the central transmembrane hairpin formed by helices 8 and 9.

Clinical evaluation of three toothbrush models tested by schoolchildren

The aim of this single-blind cross-over study was to compare the performance of three different toothbrush models in the control of dental biofilm and maintaining a healthy gingival condition. Twenty-seven schoolchildren (aged 9-10 years) participated in the study. Three toothbrushes with different bristle arrangements were used: T1 - bristles on the same plane, straight arrangement; T2 - bristles on different planes, straight arrangement; T3 - bristles on different planes, straight and circular arrangement. The participants were then randomly divided into three groups for brushing with one of the three toothbrushes. Each experimental period lasted 15 days each, with three daily brushings and a 7-day washout interval was used between periods. The oral hygiene and gingival bleeding indices were recorded by a single, calibrated examiner blind to the brush used. Bristle wear was measured with a digital calliper at the end of each period. The data were analysed using parametric (anova and Student's t-test) and non-parametric (Cochran's Q and McNemar) tests. The toothbrushes achieved similar results (P>0.05) for the clinical parameters investigated. The three models exhibited a similar degree of bristle wear (P>0.05). The arrangement of the bristles had little influence over the removal of biofilm and gingival conditions. Thus, there is no clinical justification for replacing conventional toothbrushes with more expensive models.

Abiotic Stress and Induced DNA Hypomethylation Cause Interphase Chromatin Structural Changes in Rice rDNA Loci

Global climate change, i.e. higher and more variable temperatures, and a gain in soil salinity are increasing plant stress with direct consequences on crop yield and quality levels. Rice productivity is strongly affected by abiotic stress conditions. The regulation of chromatin structure in response to environmental stress is poorly understood. We investigated the interphase chromatin organization from rice plants in non-stress versus stress conditions. We have used a cytogenetic approach, based on fluorescence in situ hybridization (FISH) with 45S, 5S rDNA and centromeric probes on rice tissue sections. The abiotic stress conditions included cold, heat and mild salinity and were applied during seed germination. In contrast to cold, saline and heat stresses caused extensive decondensation of 45S rDNA chromatin and also an increase in the distance between the 2 homologous 5S rDNA loci. 5-Azacytidine (5-AC), a DNA hypomethylating drug, greatly increased 45S rDNA chromatin decondensation and interestingly was able to induce polarization of centromeres in rice interphase nuclei. The abiotic stresses tested did not perturb the spatial position of centromeres, typically with circular arrangement around the nucleolus. The results suggest a role for chromatin plasticity in a world of climate changes.