The pH profile for acid-induced elongation of coleoptile and epicotyl sections is consistent with the acid-growth theory

The acid-growth theory predicts that a solution with a pH identical to that of the apoplast of auxintreated tissues (4.5–5.0) should induce elongation at a rate comparable to that of auxin. Different pH profiles for elongation have been obtained, however, depending on the type of pretreatment between harvest of the sections and the start of the pH-incubations. To determine the acid sensitivity under in vivo conditions, oat (Avena sativa L.) coleoptile, maize (Zea mays L.) coleoptile and pea (Pisum sativum L.) epicotyl sections were abraded so that exogenous buffers could penetrate the free space, and placed in buffered solutions of pH 3.5–6.5 without any preincubation. The extension, without auxin, was measured over the first 3 h. Experiments conducted in three laboratories produced similar results. For all three species, sections placed in buffer without pretreatment elongated at least threefold faster at pH 5.0 than at 6.0 or 6.5, and the rate elongation at pH 5.0 was comparable to that induced by auxin. Pretreatment of abraded sections with pH-6.5 buffer or distilled water adjusted to pH 6.5 or above gave similar results. We conclude that the pH present in the apoplast of auxin-treated coleoptile and stems is sufficiently low to account for the initial growth response to auxin.Abbreviations FS free space - IAA indole-3-acetic acid This research was supported by a grant from the National Adonautics and space Administration (NASA), NAGW 1394 to R.E.C., NASA grant NAGW-297 to M.L.E., and NASA grant NAG 1849 to D.L.R.     

Pivotal role of ADP-ribosylation factor 6 in Toll-like receptor 9-mediated immune signaling

CpG oligodeoxynucleotide (CpG ODN) cellular uptake into endosomes, the rate-limiting step of Toll-like receptor 9 (TLR9) signaling, is critical in eliciting innate immune responses. ADP-ribosylation factor 6 (ARF6) is a member of the Ras superfamily, which is critical to a wide variety of cellular events including endocytosis. Here, we found that inhibition of ARF6 by dominant mutants and siRNA impaired CpG ODN-mediated responses, whereas cells expressing the constitutively active ARF6 mutant enhanced CpG ODN-induced cytokine production. Inhibition of ARF6 impaired TLR9 trafficking into endolysosomes, thereby inhibiting proceed functional cleavage of TLR9. Additional studies showed that CpG ODN uptake was increased in ARF6-activated cells but impaired in ARF6-defective cells. Furthermore, cells pretreated with CpG ODN but not GpC ODN had increased CpG ODN uptake due to CpG ODN-induced ARF6 activity. Further studies with ARF6-defective and ARF6-activated cells demonstrated that class III phosphatidylinositol 3-kinases (PI3K) was required for downstream ARF6 regulation of CpG ODN uptake. Together, our findings demonstrate that a novel class III PI3K-ARF6 axis pathway mediates TLR9 signaling by regulating the cellular uptake of CpG ODN.     

Organization and nucleotide sequence of the genes for ribosomal protein S2 and elongation factor Ts in Spirulina Platensis

A 6.5 kb region from the genome of the cyanobacterium Spirulina platensis was cloned using as a probe the Escherichia coli gene for ribosomal protein S2. Sequence analysis revealed, in this region, the presence of the gene for ribosomal protein S2 and part of the gene for the elongation factor Ts (EF-Ts). The arrangement rpsB-spacer-tsf resembles that reported for E. coli. The deduced amino acid sequences of the platensis S2 and EF-Ts show significant homology with the E. coli counterparts.     

A Mechanism for Localized Dynamics-driven Affinity Regulation of the Binding of von Willebrand Factor to Platelet Glycoprotein Ibα

Binding of the A1 domain of von Willebrand factor (vWF) to glycoprotein Ibα (GPIbα) results in platelet adhesion, activation, and aggregation that initiates primary hemostasis. Both the elevated shear stress and the mutations associated with type 2B von Willebrand disease enhance the interaction between A1 and GPIbα. Through molecular dynamics simulations for wild-type vWF-A1 and its eight gain of function mutants (R543Q, I546V, ΔSS, etc.), we found that the gain of function mutations destabilize the N-terminal arm, increase a clock pendulum-like movement of the α2-helix, and turn a closed A1 conformation into a partially open one favoring binding to GPIbα. The residue Arg⁵⁷⁸ at the α2-helix behaves as a pivot in the destabilization of the N-terminal arm and a consequent dynamic change of the α2-helix. These results suggest a localized dynamics-driven affinity regulation mechanism for vWF-GPIbα interaction. Allosteric drugs controlling this intrinsic protein dynamics may be effective in blocking the GPIb-vWF interaction.     

Sites of microtubule reorganization in tobacco BY-2 cells during cell-cycle progression

Summary The sites of microtubule (MT) reorganization were examined in synchronized tobacco BY-2 cells. The MTs of these cells were completely destroyed by a combined cold and drug treatment at 0 °C with 100 M propyzamide for 3 h. After the cells were washed and cultured at 30 °C, the reorganization of MTs was observed in detail. Sites for MT reorganization at each stage of the cell cycle were identified on the cell cortex and nuclei, the mitotic apparatus, the nuclei (or the nuclei and cell cortex), and the cell cortex in the S-G₂ phase, M phase, M/G₁ interface, and g₁ phase, respectively. The polypeptide synthesis elongation factor (EF)-1 is co-localized with these sites of MT reorganization. At some stages, microfilaments (MFs) were found to be involved in the reorganization of MTs. Based on these results, the mode of MT reorganization during cell cycle progression is discussed.Abbreviations EF-1 elongation factor 1 - MAP microtubule-associated protein - MF microfilament - MIs mitotic indices - MT microtubule     

Versican Facilitates Chondrocyte Differentiation and Regulates Joint Morphogenesis

Versican/PG-M is a large chondroitin sulfate proteoglycan in the extracellular matrix, which is transiently expressed in mesenchymal condensation areas during tissue morphogenesis. Here, we generated versican conditional knock-out mice Prx1-Cre/Vcan^flox/flox, in which Vcan is pruned out by site-specific Cre recombinase driven by the Prx1 promoter. Although Prx1-Cre/Vcan^flox/flox mice are viable and fertile, they develop distorted digits. Histological analysis of newborn mice reveals hypertrophic chondrocytic nodules in cartilage, tilting of the joint, and a slight delay of chondrocyte differentiation in digits. By immunostaining, whereas the joint interzone of Prx1-Cre/Vcan^+/+ shows an accumulation of TGF-β, concomitant with versican, that of Prx1-Cre/Vcan^flox/flox without versican expression exhibits a decreased incorporation of TGF-β. In a micromass culture system of mesenchymal cells from limb bud, whereas TGF-β and versican are co-localized in the perinodular regions of developing cartilage in Prx1-Cre/Vcan^+/+, TGF-β is widely distributed in Prx1-Cre/Vcan^flox/flox. These results suggest that versican facilitates chondrogenesis and joint morphogenesis, by localizing TGF-β in the extracellular matrix and regulating its signaling.     

大兴安岭北坡火烧迹地森林景观恢复及其影响因子——以郁闭度指标为例

1987年发生在大兴安岭北坡的特大火灾造成了森林资源的巨大损失,森林景观恢复一直是人们关注的热点.本研究选取与森林生产力密切相关的郁闭度因子作为研究对象,以ArcView、ArcGIS等地理信息系统软件为研究平台,采用1987年和2000年两期森林资源二类调查数据,对郁闭度、火烧强度、抚育类型和地形因子等进行分级,利用Kendall等级相关分析、相似性分析等方法,探讨了森林郁闭度格局的恢复状况以及火烧强度、更新类型、地形因子对郁闭度恢复的影响.结果表明,2000年郁闭度等级构成与1987年火前相比发生了明显变化,无林地以及高郁闭度等级比重明显下降,较低郁闭度等级比重显著上升;火烧强度对火后恢复的影响最为关键,火烧强度与郁闭度等级呈负相关;更新措施短期内对郁闭度恢复影响不显著,但可以缩短森林演替的周期,对未来针叶林群落生产力恢复具有重要的促进作用;地形因子中坡度对郁闭度恢复影响最为明显,其次为坡位,坡向影响最弱.