The molecular signal for the adaptation to cold temperature during early life on Earth

Several lines of evidence such as the basal location of thermophilic lineages in large-scale phylogenetic trees and the ancestral sequence reconstruction of single enzymes or large protein concatenations support the conclusion that the ancestors of the bacterial and archaeal domains were thermophilic organisms which were adapted to hot environments during the early stages of the Earth. A parsimonious reasoning would therefore suggest that the last universal common ancestor (LUCA) was also thermophilic. Various authors have used branch-wise non-homogeneous evolutionary models that better capture the variation of molecular compositions among lineages to accurately reconstruct the ancestral G + C contents of ribosomal RNAs and the ancestral amino acid composition of highly conserved proteins. They confirmed the thermophilic nature of the ancestors of Bacteria and Archaea but concluded that LUCA, their last common ancestor, was a mesophilic organism having a moderate optimal growth temperature. In this letter, we investigate the unknown nature of the phylogenetic signal that informs ancestral sequence reconstruction to support this non-parsimonious scenario. We find that rate variation across sites of molecular sequences provides information at different time scales by recording the oldest adaptation to temperature in slow-evolving regions and subsequent adaptations in fast-evolving ones.     

Evolutionary bursts in Euphorbia (Euphorbiaceae) are linked with photosynthetic pathway

The mid‐Cenozoic decline of atmospheric CO₂ levels that promoted global climate change was critical to shaping contemporary arid ecosystems. Within angiosperms, two CO₂‐concentrating mechanisms (CCMs)—crassulacean acid metabolism (CAM) and C₄—evolved from the C₃ photosynthetic pathway, enabling more efficient whole‐plant function in such environments. Many angiosperm clades with CCMs are thought to have diversified rapidly due to Miocene aridification, but links between this climate change, CCM evolution, and increased net diversification rates (r) remain to be further understood. Euphorbia (～2000 species) includes a diversity of CAM‐using stem succulents, plus a single species‐rich C₄ subclade. We used ancestral state reconstructions with a dated molecular phylogeny to reveal that CCMs independently evolved 17–22 times in Euphorbia, principally from the Miocene onwards. Analyses assessing among‐lineage variation in r identified eight Euphorbia subclades with significantly increased r, six of which have a close temporal relationship with a lineage‐corresponding CCM origin. Our trait‐dependent diversification analysis indicated that r of Euphorbia CCM lineages is approximately threefold greater than C₃ lineages. Overall, these results suggest that CCM evolution in Euphorbia was likely an adaptive strategy that enabled the occupation of increased arid niche space accompanying Miocene expansion of arid ecosystems. These opportunities evidently facilitated recent, replicated bursts of diversification in Euphorbia.     

The First Three-Dimensional Structure of Phosphofructokinase from Saccharomyces cerevisiae Determined by Electron Microscopy of Single Particles

Phosphofructokinaseis a key regulatory enzyme of the glycolytic pathway. We have determined the structure of this enzyme from Saccharomyces cerevisiae to a resolution of 2.0 nm. This is the first structure available for this family of enzymes in eukaryotic organisms. Phosphofructokinase is an octamer composed of 4α and 4β subunits arranged in a dihedral point group symmetry D₂. The enzyme has a very open and elongated structure, with dimensions of 24 nm in length and 17 nm in width. The final structure, calculated from 0° tilt projections of the molecule at random orientations using as reference the volume obtained by the random conical reconstruction technique in ice, has allowed us to discern the shapes of the subunits and their mutual arrangement in the octamer.     

利用孢粉记录定量重建大尺度古植被格局

 古植被定量重建是过去全球变化研究的重点之一, 生物群区化(Biomisation)方法以特征植物功能型来定义生物群区, 通过一种标准化数量方法计算孢粉谱的相似得分, 以此把孢粉谱转变为生物群区类型, 是进行古植被定量重建的一种有效方法。该文在前人综述文章的基础上, 简述了生物群区化方法定量重建古植被格局的发展历史、具体步骤及存在问题, 重点描述了以此方法为基础重建的全新世中期(MH)和末次盛冰期(LGM)的全球古植被分布格局, 以及中国的古植被定量重建工作和古植被格局变化。目前的研究表明, 全新世中期北极森林界线在某些地区有轻微的北移迹象, 北部的温带森林带通常向北远距离迁移, 欧洲的温带落叶林也大范围向地中海地区(向南)和向北扩展, 在北美内陆, 草原侵入到森林生物群区, 但中亚地区却没有此现象, 中国大陆的森林生物群区扩张, 典型撒哈尔植被(如干草原、干旱疏林灌丛和热带干旱森林)进入撒哈拉地区, 而非洲热带雨林却呈减少趋势; 末次盛冰期苔原和草原扩张, 在欧亚大陆北部逐渐混合, 北半球的森林生物群区向南迁移, 北方常绿森林(泰加林)和温带落叶林呈碎片状, 而欧洲和东亚的草原却大范围扩张, 非洲的热带湿润森林(比如热带雨林和热带季雨林)有所减少, 在北美洲的西南地区, 荒漠和草原被开阔针叶疏林所取代。     

电子断层成像技术及其在细胞生物学中的应用

电子断层成像技术（electrontomography）是近年来发展起来一项三维成像技术,可以在纳米分辨率（2-10nm）水平上获得生物大分子及其复合物或聚集体、细胞器、细胞以及组织的三维结构,而且可以用于研究生物大分子在细胞中的定位、排列、分布以及相互作用,已逐渐成为细胞生物学领域中的一项重要技术手段。该文针对这项技术及其在细胞生物学中的应用作一简要介绍。     

常规肌力康复训练联合血流限制训练对前交叉韧带重建术后患者膝关节功能、股四头肌功能和平衡功能的影响

摘要 目的：探讨常规肌力康复训练联合血流限制训练对前交叉韧带（ACL）重建术后患者膝关节功能、股四头肌功能和平衡功能的影响。方法：选取2020年9月-2022年7月期间我院收治的ACL重建术患者82例。根据随机数字表法分为对照组（n=41,接受常规肌力康复训练）和研究组（n=41,接受常规肌力康复训练联合血流限制训练）。比较两组膝关节功能、股四头肌功能、平衡功能和并发症发生率。结果：治疗6周后,研究组膝关节Lysholm评分高于对照组,膝关节肿胀程度、大腿周径差值小于对照组,膝关节最大屈曲角度大于对照组（P<0.05）。治疗6周后,研究组股四头肌厚度薄于对照组,平均功率、峰力矩大于对照组（P<0.05）。治疗6周后,研究组站立平衡平均压力峰值差、缓慢弯膝平均压力峰值差、向下蹲位平均压力峰值差小于对照组（P<0.05）。研究组（4.88%）的并发症发生率低于对照组（24.39%）（P<0.05）。结论：ACL重建术后患者应用血流限制训练联合常规肌力康复训练进行干预,可有效改善患者膝关节功能、股四头肌功能和平衡功能,降低并发症发生率。     

江西省不同类型退化荒山生态系统植被恢复与重建措施

对江西省 5种不同类型退化荒山生态系统进行综合治理 ,开展植被恢复与重建技术及理论研究。研究结果表明 :优选的植物组合及合理的配置并辅以工程措施是快速启动植被恢复进程 ,控制水土流失、重建退化荒山生态系统的有效措施。一林多用的树种组合 ,合理的生物体系设计和针、阔叶树种混交是改良地力 ,改善环境 ,促进退化荒山生态系统进展演替的优良途径。先进造林技术的应用和林农牧业结合的复合经营方式是提高综合治理效益 ,促进并维持生态恢复过程稳定的先决条件     

人类胚胎三叉神经节细胞的局在性分布

目的:应用三维重建方法对人类胚胎三叉神经节细胞的局在性分布进行研究。方法:本研究选用非疾病死亡的引产胚胎标本8例,胎龄20-26周,在获取标本1-4小时内,对标本进行灌流固定。其中2例标本在手术显微镜下开颅取出三叉圣经节,石蜡包埋、冰冻切片、HE染色、光学显微镜下观察、照相,用三位重建技术制作三维立体图片。其余6例标本在手术显微镜下开颅、找出三叉神经三大分支眼神经、上颌神经及下颌神经,各选2例分别注入DiI结晶体、在37℃恒温箱内保存3个月,取出标本、明胶包埋、冰冻切片,在荧光显微镜下观察、照相,用三位重建技术制作三维立体图片。结果:(1)眼神经的节细胞分布于神经节的前内侧、下颌神经的节细胞在神经节的后外侧、上颌神经的节细胞位于眼神经和下颌神经节细胞之间。(2)上颌神经和下颌神经节细胞之间存在少量的重叠。结论:三叉神经节细胞在神经节内由前内侧向后外侧分别为眼神经、上颌神经、下颌神经的顺序排列;上颌神经和下颌神经的起始细胞之间存在少量的重叠现象;三维重建图片结果显示人胚胎三叉神经节细胞即眼神经、上颌神经及下颌神经的起始细胞存在明显的局在性分布特征。     

激光共聚焦显微镜与光学显微镜之比较

激光扫描共聚焦显微镜在活细胞的动态检测、光学切片和三维结构重建等方面较光学显微镜有质的飞跃。本文对激光扫描共聚焦显微镜和光学显微镜进行了比较和讨论,并简单介绍多光子激光扫描显微镜。     

恢复力视角下的乡村空间演变与重构

乡村生产、生活、生态空间重构是中国乡村发展转型的重要途径。恢复力是指系统吸收干扰、经历变化和重组后,仍然保持原有功能、结构、特性和反馈的能力。梳理社会-生态系统恢复力、乡村社区恢复力、空间恢复力相应概念,借助宏观生态学领域中的恢复力相关概念阐释乡村空间演变过程,可以在深化乡村空间演变与重构理论内涵的同时更有效的理解乡村空间的演变过程和重构目标。乡村空间重构并不只是国土或规划层面的景观空间优化,而需要站在强化社会-生态系统恢复力的角度,从乡村空间演化机制入手,提升乡村空间演化动力从而驱动空间重构。将乡村空间的演变阶段嵌入社会-生态系统适应性循环过程中,将作为当前国际研究热点的社会-生态系统恢复力研究引入乡村地理学研究领域,从而进一步扩展了学科研究视角,完成乡村空间演变与重构的理论抽象。