Paramagnetic artifact and safety criteria for human brain mapping

Biological effects of magnetic field and their safety criteria, especially effects of gradient magnetic field on the cerebral and pulmonary circulation during functional brain mapping are still unclear. Here we estimated that magnetically induced artifacts for the blood oxygenation level- and flow- based functional magnetic resonance imaging are less than 0.1%, and disturbance in the pulmonary circulation is less than 1.3% even if the field strength of magnetic resonance system is risen up to 10 tesla. These paramagnetic effects are considered to be small and harmless during human brain mapping

Mathematical model studies of the comprehensive generation of major and minor phyllotactic patterns in plants with a predominant focus on orixate phyllotaxis

UTokyo FOCUS Press releases "Mathematics of leaves : Unusual Japanese plant inspires recalculation of equation used to model leaf arrangement patterns" https://www.u-tokyo.ac.jp/focus/en/press/z0508_00047.htm

Analysis of Chromosome Behavior during Meiosis of Arabidopsis Polyploid Mutants

Polyploid lines were constructed from several diploid ecotypes of Arabidopsis thaliana by colchicine treatment. To confirm their ploidy by counting the chromosome number of the respective cells under a microscope, meiotic chromosomes of pollen mother cells were surface-spread on slide glasses and visualized by DAPI staining. It was clearly indicated that the tetraploid lines assumed by flowcytometry had 20 chromosomes, since 10 pairs of bivalents were observed on the metaphase I plate, and 2 sets of 10 chromosomes on metaphase II plates. As far as we analyzed through light microscopic observation, homologous chromosomes normally synapsed at the pachytene stage, congressed on the metaphase plate at metaphase I, and segregated reductionally to daughter cells at the anaphase I, and sister chromatids were separated to produce tetrads during meiosis II. Putting these results together with their fertility, the constructed tetraploid lines were concluded to undergo meiosis as normally as wild-type diploid plants, though the chromosome number was doubled

Mechanical Forces in Floral Development

Mechanical forces acting within the plant body that can mold flower shape throughout development received little attention. The palette of action of these forces ranges from mechanical pressures on organ primordia at the microscopic level up to the twisting of a peduncle that promotes resupination of a flower at the macroscopic level. Here, we argue that without these forces acting during the ontogenetic process, the actual flower phenotype would not be achieved as it is. In this review, we concentrate on mechanical forces that occur at the microscopic level and determine the fate of the flower shape by the physical constraints on meristems at an early stage of development. We thus highlight the generative role of mechanical forces over the floral phenotype and underline our general view of flower development as the sum of interactions of known physiological and genetic processes, together with physical aspects and mechanical events that are entangled towards the shaping of the mature flower.info:eu-repo/semantics/publishedVersio

Effect of Polyploidizing Treatment on Chromosome Behavior during Meiosis of Arabidopsis thaliana

We observed chromosome behavior during meiosis of Arabidopsis thaliana justafter polyploidization. Two strains of A. thaliana, Columbia (Col) and Landsberg erecta(Ler), were treated with colchicine to induce polyploid lines, and the treated generationswere analyzed. Flow cytometric analysis revealed that a tetraploid line was obtained fromthe treated Col and an octoploid line from the treated Ler. Meiotic chromosomes of pollenmother cells of these polyploid lines were visualized by DAPI staining and observed. Bothlines underwent meiosis as normal, as did most of the established tetraploid lines on thewhole. At metaphase I, however, their numbers of bivalent chromosomes were fewer thanexpected and chromosome alignment of the octoploid was occasionally disturbed. Therewas no significant difference between the fertility of diploid and tetraploid, but that ofoctoploid was significantly reduced, which might be correlated with the disturbance ofchromosome configuration

Examination of the Most Suitable Preparation Method for Pollen Observation by Scanning Electron Microscope

To examine the most suitable method to prepare pollen for scanning electronmicroscope observation, several fixation methods and dehydration (or drying) methods wereapplied to Arabidopsis and lily pollen obtained from flowers before and after flowering.Light and confocal laser microscope observations revealed that, in both plants, pollenobtained before flowering was swollen and wet, while that obtained after flowering wasshrunken and dry. For scanning electron microscopy, pollen was unfixed or fixed with 50%(eventually 100%) acetone, FAA (5% formalin with 50% ethanol and 5% acetic acid) or 6%glutaraldehyde solutions. It was then dried naturally in air or artificially by either criticalpoint-dry or freeze-dry machines, respectively. The results indicated that, for scanningelectron microscope observation of dry pollen, the most suitable treatment is natural dryingwithout fixation. On the other hand, to observe wet pollen, the combination of FAA orglutaraldehyde fixation with artificial drying using either machines is preferable, andfixation with acetone is unsuitable.テクニカルノー

Transcriptional repression by MYB3R proteins regulates plant organ growth

In multicellular organisms, temporal and spatial regulation of cell proliferation is central for generating organs with defined sizes and morphologies. For establishing and maintaining the post-mitotic quiescent state during cell differentiation, it is important to repress genes with mitotic functions. We found that three of the Arabidopsis MYB3R transcription factors synergistically maintain G2/M-specific genes repressed in post-mitotic cells and restrict the time window of mitotic gene expression in proliferating cells. The combined mutants of the three repressor-type MYB3R genes displayed long roots, enlarged leaves, embryos, and seeds. Genome-wide chromatin immunoprecipitation revealed that MYB3R3 binds to the promoters of G2/M-specific genes and to E2F target genes. MYB3R3 associates with the repressor-type E2F, E2FC, and the RETINOBLASTOMA RELATED proteins. In contrast, the activator MYB3R4 was in complex with E2FB in proliferating cells. With mass spectrometry and pairwise interaction assays, we identified some of the other conserved components of the multiprotein complexes, known as DREAM/dREAM in human and flies. In plants, these repressor complexes are important for periodic expression during cell cycle and to establish a post-mitotic quiescent state determining organ size

Mathematical model studies of the comprehensive generation of major and minor phyllotactic patterns in plants with a predominant focus on orixate phyllotaxis.

Plant leaves are arranged around the stem in a beautiful geometry that is called phyllotaxis. In the majority of plants, phyllotaxis exhibits a distichous, Fibonacci spiral, decussate, or tricussate pattern. To explain the regularity and limited variety of phyllotactic patterns, many theoretical models have been proposed, mostly based on the notion that a repulsive interaction between leaf primordia determines the position of primordium initiation. Among them, particularly notable are the two models of Douady and Couder (alternate-specific form, DC1; more generalized form, DC2), the key assumptions of which are that each leaf primordium emits a constant power that inhibits new primordium formation and that this inhibitory effect decreases with distance. It was previously demonstrated by computer simulations that any major type of phyllotaxis can occur as a self-organizing stable pattern in the framework of DC models. However, several phyllotactic types remain unaddressed. An interesting example is orixate phyllotaxis, which has a tetrastichous alternate pattern with periodic repetition of a sequence of different divergence angles: 180°, 90°, -180°, and -90°. Although the term orixate phyllotaxis was derived from Orixa japonica, this type is observed in several distant taxa, suggesting that it may reflect some aspects of a common mechanism of phyllotactic patterning. Here we examined DC models regarding the ability to produce orixate phyllotaxis and found that model expansion via the introduction of primordial age-dependent changes of the inhibitory power is absolutely necessary for the establishment of orixate phyllotaxis. The orixate patterns generated by the expanded version of DC2 (EDC2) were shown to share morphological details with real orixate phyllotaxis. Furthermore, the simulation results obtained using EDC2 fitted better the natural distribution of phyllotactic patterns than did those obtained using the previous models. Our findings imply that changing the inhibitory power is generally an important component of the phyllotactic patterning mechanism