Cellular basis for the automorphic curvature of rice coleoptiles on a three-dimensional clinostat: possible involvement of reorientation of cortical microtubules

Coleoptiles of rice (Oryza sativa L.) show a spontaneous (automorphic) curvature toward the caryopsis under microgravity conditions. The possible involvement of the reorientation of cortical microtubules in automorphic curvature was studied in rice coleoptiles grown on a three-dimensional clinostat. When rice seedlings that had been grown in the normal gravitational field were transferred to the clinostat in the dark, cortical microtubules of epidermal cells in the dorsal side of the coleoptiles oriented more transversely than the ventral side within 0.5 h. The rotation on the clinostat also increased the cell wall extensibility in the dorsal side and decreased the extensibility in the ventral side, and induced automorphic curvature. The reorientation of cortical microtubules preceded the changes in the cell wall extensibility and the curvature. The irradiation of rice seedlings with white light from above inhibited microtubule reorientation and changes in the cell wall extensibility, as well as curvature of coleoptiles. Also, colchicine, applied to the bending region of coleoptiles, partially inhibited the automorphic curvature. These results suggest that reorientation of cortical microtubules is involved in causing automorphic curvature in rice coleoptiles on the clinostat.     

Energetics of clathrin basket assembly

A minimal thermodynamic model is used to study the in vitro equilibrium assembly of reconstituted clathrin baskets. The model contains parameters accounting for i) the combined bending and flexing rigidities of triskelion legs and hubs, ii) the intrinsic curvature of an isolated triskelion, and iii) the free energy changes associated with interactions between legs of neighboring triskelions. Analytical expressions for basket size distributions are derived, and published size distribution data (Zaremba S, Keen JH. J Cell Biol 1983;97: 1339–1347) are then used to provide estimates for net total basket assembly energies. Results suggest that energies involved in adding triskelions to partially formed clathrin lattices are small (of the order of kBT), in accord with the notion that lattice remodeling during basket formation occurs as a result of thermodynamic fluctuations. In addition, analysis of data showing the effects of assembly proteins (APs) on basket size indicates that the binding of APs increases the intrinsic curvature of an elemental triskelial subunit, the stabilizing energy of leg interactions, and the effective leg/hub rigidity. Values of effective triskelial rigidity determined in this investigation are similar to those estimated by previous analysis of shape fluctuations of isolated triskelia.     

三核苷酸重复及相关序列宏观弯曲的预测

给出描述３６个四体内三基对平面间相互方位和碱基对间沿长轴方向位移的参数集。考虑到碱基对梯阶间的非紧邻相互作用,提出ＤＮＡ宏观弯曲的经验预测规则。给出ＤＮＡ宏观弯曲的定义,使用联系碱基对梯阶间的变换矩阵计算宏观弯曲。对１８个与人类遗传病有关的三核苷酸重复及相关序列预测了宏观弯曲。理论结果和相应的实验数据作了比较,对结果的理论含义作了讨论。     

Recruitment and distribution of Dreissena polymorpha (Bivalvia) on substrates of different shape and orientation

Dreissena polymorpha recruitment on artificial substrates was studied in the Włocławek Dam Reservoir (the Vistula River, Poland). Densities on downstream and upstream vertical surfaces of plastic plates differed significantly from each other, with the former settled by more individuals. Vertical and horizontal plates, as well as upper and lower horizontal surfaces were settled similarly. In another experiment mussels settled on flat, convex and concave glass surfaces, directed upstream or downstream. Among the upstream surfaces, the concave ones were the most densely settled. No significant differences in mussel recruitment on various downstream surfaces were found. Thus, substrate shape influenced mussels only when they were exposed to water flow. Mussels were aggregated (Lloyd index > 1) along all the edges of the horizontal plates and along the upper edge of the vertical ones. Such distribution was probably caused by the post‐settlement movement of metamorphosed individuals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Is wall-bound calcium redistributed during the gravireaction of stems and coleoptiles?

We have tested the hypothesis that wall-bound calcium is redistributed from the lower to the upper sides of horizontal stems and coleoptiles during the reaction phase of gravicurvature. We used atomic absorption spectrometry to measure wall-bound calcium in the epidermal and internal layers of sunflower (Helianthus annum L.) hypocotyls and pea (Pisum sativum L.) epicotyls, and total calcium in maize (Zea mays L.) coleoptiles at the time of maximal gravireaction. In every case, we found that there was no measurable redistribution of wall-bound calcium either from the lower to the upper sides, or between epidermal and inner tissues in response to the gravistimulus. These results indicate that a redistribution of wall-bound calcium does not play a role during the gravireaction of stems and coleoptiles.     

Proteins affecting thylakoid morphology – the key to understanding vesicle transport in chloroplasts?

We recently showed that a Rab protein, CPRabA5e (CP = chloroplast localized), is located in chloroplasts of Arabidopsis thaliana where it is involved in various processes, such as thylakoid biogenesis and vesicle transport. Using a yeast two-hybrid method, CPRabA5e was shown to interact with a number of chloroplast proteins, including the CURVATURE THYLAKOID 1A (CURT1A) protein and the light-harvesting chlorophyll a/b binding protein (LHCB1.5). CURT1A has recently been shown to modify thylakoid architecture by inducing membrane curvature in grana, whereas LHCB1.5 is a protein of PSII (Photosystem II) facilitating light capture. LHCB1.5 is imported to chloroplasts and transported to thylakoid membranes using the post-translational Signal Recognition Particle (SRP) pathway. With this information as starting point, we here discuss their subsequent protein-protein interactions, given by the literature and Interactome 3D. CURT1A itself and several of the proteins interacting with CURT1A and LHCB1.5 have relations to vesicle transport and thylakoid morphology, which are also characteristics of cprabA5e mutants. This highlights the previous hypothesis of an alternative thylakoid targeting pathway for LHC proteins using vesicles, in addition to the SRP pathway.     

青年颈椎生理曲度变直全节段有限元建模与分析

目的建立青年颈椎生理曲度变直和正常的全节段有限元模型,进行对比与分析。方法采集青年颈椎曲度变直志愿者CT数据,利用生物力学有限元软件构建高质量颈椎全节段模型,然后采用基于离散微分属性的体网格变形技术,将变直模型映射生成曲度正常模型,在相同边界条件进行下进行对比分析。结果在前屈、后伸、侧弯、和旋转工况下,生理曲度变直模型的活动度范围比正常值要小,并且出现再分配。在应力分布方面,C3-C4,C4-C5之间的小关节、钩突关节,和C3-C4之间的椎间盘出现应力集中。结论通过使用新型建模软件和体网格变形技术,能方便构建颈椎生理曲度变直和正常模型,分析结果对青年颈椎病的临床诊治有指导意义。     

The effect of local bending on gating of MscL using a representative volume element and finite element simulation

Many physiological processes such as cell division, endocytosis and exocytosis cause severe local curvature of the cell membrane. Local curvature has been shown experimentally to modulate numerous mechanosensitive (MS) ion channels. In order to quantify the effects of local curvature we introduced a coarse grain representative volume element for the bacterial mechanosensitive ion channel of large conductance (MscL) using continuum elasticity. Our model is designed to be consistent with the channel conformation in the closed and open states to capture its major continuum rheological behavior in response to the local membrane curvature. Herein we show that change in the local curvature of the lipid bilayer can modulate MscL activity considerably by changing both bilayer thickness and lateral pressure profile. Intriguingly, although bending in any direction results in almost the same free-energy cost, inward (cytoplasmic) bending favors channel opening, whereas outward (periplasmic) bending facilitates closing of the narrowest part of the MscL pore. This quantitative study using MscL as a model channel may have wide reaching consequences for the effect of local curvature on the physiological function of other types of prokaryotic and eukaryotic membrane proteins.     

Ecomorphology reveals Euler spiral of mammalian whiskers

Whiskers are present in many species of mammals. They are specialised vibrotactile sensors that sit within strongly innervated follicles. Whisker size and shape will affect the mechanical signals that reach the follicle, and hence the information that reaches the brain. However, whisker size and shape have not been quantified across mammals before. Using a novel method for describing whisker curvature, this study quantifies whisker size and shape across 19 mammalian species. We find that gross two-dimensional whisker shape is relatively conserved across mammals. Indeed, whiskers are all curved, tapered rods that can be summarised by Euler spiral models of curvature and linear models of taper, which has implications for whisker growth and function. We also observe that aquatic and semi-aquatic mammals have relatively thicker, stiffer, and more highly tapered whiskers than arboreal and terrestrial species. In addition, smaller mammals tend to have relatively long, slender, flexible whiskers compared to larger species. Therefore, we propose that whisker morphology varies between larger aquatic species, and smaller scansorial species. These two whisker morphotypes are likely to induce quite different mechanical signals in the follicle, which has implications for follicle anatomy as well as whisker function.