Rectangular arrays of particles on freeze-cleaved plasma membranes are not gap junctions

Freeze-cleave replicas of adult rat diaphragm have revealed the presence of numerous small rectangular arrays of 60 Å particles (respectively pits) on the fracture faces of the sarcolemmas of the myofibers. Since these fibers are separated by thick basal laminae and are not electrically coupled we conclude that the rectangular arrays are not morphological equivalents of gap junctions as suggested by Staehelin [14]. The term “type III gap junctions” for these arrays therefore should be discontinued.     

A modified Bläzka–type respirometer for the study of swimming metabolism in fishes having deep, laterally compressed bodies or unusual locomotor modes

A low volume (8·4 l), rectangular (cross–section) respirometer modified from a Bläzka–type coaxial circuit, which provides rectilinear flow at speeds up to 0·36 m s^–1, is described.     

Convergent evolution of lizard toe fringes

Lizard toe fringes are composed of laterally projecting elongated scales and have arisen independently at least 26 times in seven families of lizards. Four different fringe types are identified: triangular, projectional, conical and rectangular. To determine if variation in fringe morphology can be attributed to environmental differences, each independent evolution of a fringe type is identified; correlation of substrate types with evolutionary independent fringe morphologies are then studied. Variation in fringe morphology shows a strong association with substrate type: triangular, projectional and conical fringes with windblown sand; and rectangular fringes with water. Some aspects of fringe morphology may result from differences in functional requirements, and others may have no adaptive significance. This example of convergent evolution points out difficulties inherent to comparative studies of adaptation and underscores the value of broad comparative surveys which provide an alternative to ad hoc adaptive explanations of similarity.     

The molecular architecture of the extracellular hemoglobin of Ophelia bicornis: Analysis of two-dimensional crystalline arrays

The double-layered hexagonal disks of the extracellular hemoglobin of the annelid worm Ophelia bicornis form two types of two-dimensional crystalline arrays. The hexagonal type exhibited a typical honeycomb pattern of top views with a center-to-center distance of 26.2 nm. Laterally oriented molecules formed rectangular crystals with lattice constants a = 26.7 run and b = 19.8 nm. The three-dimensional structure was determined from both crystal forms by reconstruction from images of tilt series. At the resolutions obtained, 1.8 nm for the hexagonal form and 2.5 nm for the rectangular form, flattening of the hemoglobin molecules against the support was observed. Nevertheless the two independent reconstructions provided information about the mass distribution within the main subunit and the connectivity between different parts of the molecule.     

Three Micmac Pipes Of North Central Saskatchewan

Abstract

Three Micmac type pipes found in the Prince Albert area of Saskatchewan are described for distributional and comparative purposes.

For many years, pipes of the Micmac type have been mentioned in the archeological literature. Usually they are briefly described because of their well-known and distinctive characteristics. Pipes of this type have been carved and ground from relatively soft stone materials such as soapstone, shale, limestone and catlinite. The workmanship is usually of high quality. Diagnostic features include a tulip or inverted acorn-shaped bowl, a short, constricted bowl stem, and a rectangular base.     

中国特有属─—东俄芹属的花粉形态及其分类学意义

利用光学显微镜和扫描电镜观察了伞形科东俄芹属（ＴｏｎｇｏｌｏａＨ．Ｗｏｌｆｆ）７个种的花粉形态,结果表明：除宜昌东俄芹Ｔ．ｄｕｎｎｉｉ（Ｂｏｉｓｓｉｅｕ）Ｈ．Ｗｏｌｆｆ和城口东俄芹Ｔ．ｓｉｌａｉｆｏｌｉａ（Ｂｏｉｓｓｉｅｕ）Ｈ．ｗｏｌｆｆ的花粉为矩形类型外,其它几种的为菱形类型,然而并非都是原始的或典型的菱形,而是处于分化过程中的菱形类型,如纤细东俄芹Ｔ．ｇｒａｃｉｌｉｓＨ．Ｗｏｌｆｆ,大东俄芹Ｔ．ｅｌａｔａＨ．Ｗｏｌｆｆ的花粉形态,表现出近菱形、近椭圆形和近矩形的特征,在我们近期的工作中曾涉及滇芎属ＰｈｙｓｏｓｐｅｒｍｏｐｓｉｓＨ．Ｗｏｌｆｆ类似的花粉形态及分化情况,从花粉资料启示,东俄芹属可能与滇芎属近缘。     

PHOTOMORPHOGENESIS OF THE GAMETOPHYTES OF LYGODIUM JAPONICUM

Protonemata of Lygodium japonicum turn biplanar in both red and blue light regimes and remain filamentous in far-red light. Biplanar gametophytes formed in red light are longer than broad with long, rectangular cells, whereas in blue light they appear broader than long with short, isodiametric cells. Transfer of protonemata of all ages from far-red regime to red or blue light induces a morphological type of growth characteristic of the new light regime. However, only relatively young biplanar forms transferred from red or blue light are able to resume filamentous type of growth in a subsequent regime of far-red light.     

Plot shape effects on plant species diversity measurements

Abstract. Question: Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies? Location: Grasslands, shrublands and forests in the Mediterranean‐climate region of California, USA. Methods: We compared three 0.1‐ha sampling designs that differed in the shape and dispersion of 1‐m² and 100‐m² nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400‐m² subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire. Results: We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1‐ or 100‐m². Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self‐similarity at the scale of 400 m², but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale. Conclusions: At the 0.1‐ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean‐climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below‐ground niche space outside the sample area.     

Cell shape regulates collagen type I expression in human tendon fibroblasts

Understanding the relationship between cell shape and cellular function is important for study of cell biology in general and for regulation of cell phenotype in tissue engineering in particular. In this study, microcontact printing technique was used to create cell-adhesive rectangular and circular islands. The rectangular islands had three aspect ratios: 19.6, 4.9, and 2.2, respectively, whereas circular islands had a diameter of 50 microm. Both rectangular and circular islands had the same area of 1960 microm(2). In culture, we found that human tendon fibroblasts (HTFs) assumed the shapes of these islands. Quantitative immunofluorescence measurement showed that more elongated cells expressed higher collagen type I than did less stretched cells even though cell spreading area was the same. This suggests that HTFs, which assume an elongated shape in vivo, have optimal morphology in terms of expression of collagen type I, which is a major component of normal tendons. Using immunohistochemistry along with cell traction force microscopy (CTFM), we further found that these HTFs with different shapes exhibited variations in actin cytoskeletal structure, spatial arrangement of focal adhesions, and spatial distribution and magnitude of cell traction forces. The changes in the actin cytoskeletal structure, focal adhesion distributions, and traction forces in cells with different shapes may be responsible for altered collagen expression, as they are known to be involved in cellular mechanotransduction.     

Examination of nanoflow in rectangular slits

This paper presents simulations of 3D nanoscale flow in rectangular channel with molecular dynamics simulation method. Rectangular cross section is a frequently encountered geometric shape for nanoscale flow problems. For a given cross sectional height h, we change the width w of the rectangular cross section and analyze the influence of w/h on the flow characteristics. The distributions of density, temperature, boundary slip and flow velocity inside the rectangular cross section are investigated in detail. Liquid argon material and Lennard-Jones potential are used in the simulations. The simulation results are also compared with Navier–Stokes solutions for rectangular channel flows.     

Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates

Summary Ultrastructure and ontogeny of a new type of eyespot in dinoflagellates is described. A marine tidal poolGymnodinium natalense is found to possess a highly organized eyespot whose structure is unique among dinoflagellates. The eyespot is rectangular in ventral view, C-shaped in apical view, and is located posterior to the sulcus. The eyespot is independent of the chloroplast and consists of several (typically six) layers of hemi-cylindrical walls which are concentrically arranged with narrow spacing between them. Each hemicylindrical wall is enclosed by a single unit membrane and is composed of many regularly arranged rectangular crystalline bricks. These crystalline bricks are produced in small vesicles which are formed in the invaginations of the chloroplast. The vesicles containing newly formed crystalline bricks are then transported to the sulcal area to assemble the eyespot. The crystalline bricks are arranged in a neat row within the vesicle termed “eyespot forming vesicle” (EFV), which is located near the sulcus. The hemi-cylindrical wall is constructed within the EFV. Based on the structure of the eyespot, viz. consisting of concentric multi-layered walls, the eyespot is thought to act as a quarter-wave stack antenna.     

Accounting for tree spatial distribution in a comparison of plot sizes and shapes in dense forest and woodland in Benin (West Africa)

The study examined simultaneously, the effect of tree spatial distribution, inventory plot size and shape on the estimation error of basal area in two contrasting environments. Twenty and fifteen square plots of 1 ha each (divided into 100 quadrats of 0.01 ha) were randomly set in dense forest and woodland, respectively. Thirteen subplots of various shapes and sizes were obtained from the association of adjacent quadrats. Estimation error was calculated using residual mean square of one‐way ANOVA, based on replications of subplot within 1 ha plots. Tree spatial distribution was measured using Green index. Weighted linear regression and mixed effect models were applied to Box & Cox transformed data. In general, the estimation error of basal area decreased with increase in subplot size. However, the effects of tree spatial distribution and plot shape varied with the vegetation type. Where trees tended to be aggregated, estimation error increased with degree of aggregation, and rectangular plots of 0.24 ha produced an acceptable precision. It was concluded that 0.24 ha rectangular plots can be used in tropical environments where the target parameters vary constantly according to one direction, while square plots of the same size are optimal for reliable analysis in case of randomness.     

The Staphylococcus aureus alpha-toxin channel complex and the effect of Ca2+ ions on its interaction with lipid layers.

Using the techniques of two-dimensional crystallization on supported lipid bilayers together with computer image processing, two distinct two-dimensional crystal types of staphylococcal alpha-toxin complex are formed depending on the presence or absence of Ca2+ ions. Without Ca2+, these are hexagonally packed (in A, a = b = 89.5 +/- 2.5 A; theta = 119.7 degrees) With Ca2+ present, rectangular crystal packing is seen (in A, a = 114.8 +/- 1.6 A, b = 140.2 +/- 0.7 A; theta = 89.1 degrees). A third, banded crystal type is also seen which is interpreted as a side-to-side packing of regular tubules. We use these tubular crystals for cross-correlation searches with top and side-on views of the complex from single particle reconstructions, and with the repeating units from the two-dimensional crystal types. The results lead us to propose a model in which the different two-dimensional crystal types are formed as a result of alpha-toxin hexamers packing in different orientations. In the hexagonal crystals the hexamers lie end-on with a 6-fold axis in projection. On the addition of Ca2+, the hexamers reorient to lie tilted with respect to the support, thus giving rise to a rectangular projection.     

光响应曲线的指数改进模型与常用模型比较

光响应曲线的参数是研究植物生理状态的重要指标, 常用的光响应曲线模型无法准确地计算出光饱和点和最大净光合速率。该文利用光响应曲线新模型——指数改进模型、直角双曲线模型、直角双曲线修正模型、非直角双曲线模型和指数模型, 拟合高粱(Sorghum bicolor)、苋(Amaranthus tricolor)、大麦(Hordeum vulgare)和半夏(Pinellia ternata)的光响应曲线, 并随机选取部分数据进行检验, 得到了各模型计算出的主要生理参数, 并对这些数据进行了比较分析, 讨论了各模型之间的优缺点和准确性, 描述了C₃、C₄植物光响应的适宜性。结果表明, 基于C₃植物得到的指数改进模型和直角双曲线修正模型能较准确地计算出C₃、C₄植物饱和光强和最大净光合速率, 并在描述光响应曲线时比另外3个模型具有更高的精确性和适宜性。实验结果可为光响应曲线模型在C₃和C₄光合途径植物中的应用提供参考。     

Investigation on Pollen Morphology of Aconitum L.

Pollen morphology of 62 species in Aconitum L. was investigated with light and scanning electron microscopies. The pollen grains in this genus are 3-colpate and exhibit spinulate surface pattern in all the species. According to the shape of pollen grains in equatorial view Aconiturn L. may be divided into three types. Type Ⅰ pollen grains are wide elliptic; Type Ⅱ are narrow-elliptic and type Ⅲ are rectangular or close to square in shape. The pollen characteristics among species are very similar. The morphological information of the pollen grains shows that species of Aconiturn L. are a natural taxon.     

不同土壤水分下山杏光合作用CO2响应过程及其模拟

在半干旱黄土丘陵区,以2年生盆栽山杏为材料,应用CIRAS-2型光合作用系统,测定了8个土壤水分梯度下山杏光合作用的CO₂响应过程,并采用直角双曲线模型、指数方程和直角双曲线修正模型对其CO₂响应数据进行拟合,分析了山杏光合作用与土壤水分的定量关系.结果表明: 山杏CO₂响应过程对土壤水分有明显的阈值响应特征.维持山杏叶片较高的光合速率(P_n)和羧化效率(CE)的土壤相对含水量(RWC)在46.3%～81.9%,在此水分范围内,光合作用没有发生明显的CO₂饱和抑制现象;当RWC超出此范围,土壤水分升高或降低均明显降低山杏叶片的光合能力(P_{n max})、CE和CO₂饱和点(CSP).在不同土壤水分条件下,3个模型对山杏CO₂响应数据的模拟效果有明显差别.在46.3%～81.9%土壤水分范围内,3个模型均能较好地拟合山杏CO₂响应过程及其特征参数CE、CO₂补偿点(Γ)和光呼吸速率(R_p),其拟合精度均表现为直角双曲线修正模型＞指数方程＞直角双曲线模型;当土壤水分含量过高(RWC＞81.9%)或过低(RWC＜46.3%)时,只有直角双曲线修正模型能较好地拟合山杏CO₂响应过程及其特征参数.RWC在46.3%～81.9%范围内,山杏具有较高的光合作用效率;与传统直角双曲线模型和指数方程相比,直角双曲线修正模型具有更好的适用性.     

Polymorphism of Crystals of Salmonella minnesota Re and Ra Lipopolysaccharides

Salmonella minnesota Re and Ra lipopolysaccharides (LPSs) formed three-dimensional crystals when they were precipitated by the addition of 2 volumes of 95% ethanol containing 375 mM MgCl₂ and incubated in 70% ethanol containing 250 mM MgCl₂ at 4 C. Besides typical shapes of crystals, hexagonal plates and solid columns, which were already reported (J. Bacteriol. 172: 1516–1528 (1990)), the LPSs thus treated formed crystals possessing various shapes such as square or rectangular plate, lozenge plate, discoid, and truncated hexangular pyramid forms. Electron diffraction patterns from all these crystals except square or rectangular plate crystals obtained by electron irradiation from the direction perpendicular to the basal plane were essentially the same as those from hexagonal plate crystals, indicating that they consist of hexagonal lattices with the lattice constant of 4.62 Å. From these results as well as the results of electron microscopic observations of these crystals, it was concluded that all these crystals except square or rectangular plate crystals are composed of hexagonal plate sheets as the basic structural units. Square or rectangular crystals were assumed to correspond to the {1011} planes of solid hexagonal column crystals.     

Epidermal micromorphology of the genus Festuca L. subgenus Festuca (Poaceae)

Qualitative and some quantitative micromorphological characters of leaf blades, lemmas and paleas were examined using scanning electron microscopy for 29 species of Festuca subgenus Festuca, including the first observations on members of sections Amphigenes, Dimorphae and Cataphyllophorae. The aim of this study was to survey these features in the subgenus Festuca, to assess their taxonomical value. The observed patterns are compared with current taxonomic proposals based on molecular studies. The characters show important taxonomic value, mainly of the abaxial lemma. Characters showing the greatest variation are shape of long cells, shape of the periclinal walls, thickness of anticlinal walls, presence of prickles and abundance of silica bodies. The principal characters of the leaf-blade surfaces include the type and shape of short cells. Two different surface patterns were observed on the lemma, one, long cells rectangular to elongated, with flat to slightly convex periclinal walls and thickened anticlinal walls, for the sections Amphigenes and Dimorphae, and another, long cells rectangular to square, with concave periclinal walls and unthickened anticlinal walls, for the remaining sections. This study confirms the taxonomic value of micromorphological characters in the subgenus Festuca, and that abaxial lemma surface appears to be the most useful.     

Incisor Schmelzmuster Diversity in South America's Oldest Rodent Fauna and Early Caviomorph History

Investigation of the enamel microstructure of 20 isolated rodent incisors from the ?Eocene Santa Rosa local fauna (Peru) yielded exclusively schmelzmuster with multiserial Hunter–Schreger bands (HSB). All three subtypes of multiserialHSB with parallel, acute angular, and rectangular interprismatic matrix (IPM) that were previously reported for caviomorph rodents are present. Two lower incisors with rectangular IPM can be attributed to the Octodontoidea, a caviomorph superfamily exhibiting this highly derived enamel type. The plesiomorphic pauciserial condition that characterizes early Paleogene rodents such as North American Ischyromyoidea (including “Franimorpha”) has not been detected. It is therefore probable that the founder populations of South American Caviomorpha already possessed a derived incisor schmelzmuster with multiserial HSB that is shared with African Thryonomyoidea. Because on the North American continent a possible stem-lineage representative of Caviomorpha with multiserial HSB has never been detected, incisor enamel microstructure supports the hypothesis of an African origin of Caviomorpha from a common ancestor shared with Thryonomyoidea.     

贝壳砂生境干旱胁迫下杠柳叶片光合光响应模型比较

以黄河三角洲贝壳堤岛3年生杠柳(Periploca sepium)苗木为试验材料, 模拟设置贝壳砂生境下的4种水分梯度, 利用CIRAS-2型光合作用系统测定杠柳叶片在不同干旱胁迫下的光合作用光响应过程, 采用4种光响应模型进行拟合分析, 以比较贝壳砂生境干旱胁迫下适宜的光响应模型, 探讨最佳光响应模型参数对干旱胁迫的适应规律。结果表明: 4种模型对杠柳叶片光合作用光响应过程拟合效果的优劣顺序为: 直角双曲线修正模型>非直角双曲线模型>指数模型>直角双曲线模型, 后3种模型均为没有极值的函数, 故不能很好地拟合光响应曲线光抑制过程, 并不能直接求解最大净光合速率(P_nmax)和光饱和点(LSP)。光响应参数拟合效果最佳表现为: 非直角双曲线模型的暗呼吸速率(R_d), 直角双曲线模型的光补偿点(LCP), 直角双曲线修正模型的P_nmax和LSP。4种光响应模型对干旱胁迫具有不同的适应性, 直角双曲线修正模型适应各种水分条件, 直角双曲线模型和指数模型较适合轻度干旱胁迫条件, 非直角双曲线模型较适合重度干旱胁迫条件。随干旱胁迫的加剧, 光响应参数表观量子效率(AQY)、R_d和LCP先升高后下降, 净光合速率(P_n)、P_nmax和LSP逐渐下降。轻度、中度和重度干旱胁迫下, LSP分别比对照下降5.2%、16.3%和34.5%, P_nmax分别比对照下降17.8%、39.0%和59.0%。水分充足条件下, 杠柳叶片光能利用最强, 光照生态幅最宽; 重度干旱胁迫下, 杠柳叶片表现出明显的光饱和、光抑制现象, 光能利用减弱, 光合能力受到较大限制。