Quantitative analysis of animal model lens anatomy: accommodative range is related to fiber structure and organization

Purpose The results of a recent study on accommodation in humans and baboons has revealed that lens fiber structure and organization are key components of the mechanism of accommodation. Dynamic focusing involves the controlled displacement and replacement, or realignment, of cortical fiber-ends at sutures as the mechanism of accommodation at the fiber level. This emended explanation of the mechanism of accommodation raises the following question: as the structure of crystalline lenses are only similar, not identical between species, is accommodative amplitude related to differences in the structure and organization of fibers between species? To address this question, we have quantitatively examined the structure and organization of fibers in a number of the more commonly used animal models (mice, cattle, frogs, rabbits and chickens) for lens research. Materials and methods Lenses (a minimum of 12–18 lenses/species) from mice, cattle, frogs and rabbits were used for this study. Prior to fixation for structural analysis, measurements of the gross shape of the lenses (equatorial diameter, anterior and posterior minor radii [anterior + posterior minor radius = polar axis]) were taken directly through a stereo surgical dissecting microscope equipped with an ocular reticle. Lenses were then prepared for and examined by light (LM), transmission (TEM) and scanning electron microscopy (SEM). Scale computer-assisted drawings (CADs) of lenses and lens fibers were then constructed from quantitative data as described above and from quantitative data contained in micrographs. Results The differences in fiber structure and organization that effect accommodative range arise early in development and are continued throughout lifelong lens growth. In umbilical suture lenses (avian) secondary fibers develop with almost completely tapered anterior ends (85–90% reduction of their measures of width and thickness at the equator). By comparison, in lenses with line sutures (e.g. frogs and rabbits) secondary fibers develop with just a 50–60% reduction in anterior fiber taper. In lenses with Y sutures (mice and cattle), fiber width taper is only 25–40%. However, in all cases, while the taper of the posterior end width of fibers is just slightly less (approx. 15–20%) than that of anterior ends, posterior end thickness is only reduced by one half that of anterior thickness. Conclusions In humans, the mechanism of accommodation at the fiber level involves the controlled realignment of very flattened and flared, rather than tapered fiber-ends at sutures. In this manner, the simultaneous increase in lens thickness and surface curvature in the accommodated state is the result of fiber-ends being overlapped along multiple (9–12) suture branches covering the majority of the anterior and posterior surfaces. The results of this animal study strongly suggest that accommodative range is directly related to quantitative differences in fiber structure and organization in the different suture types. The very broad accommodative range in birds is made possible, at least in part, by the almost complete tapering of fiber-ends at umbilical sutures. In contrast, the essentially negligible accommodative range of animals that have line- and Y-suture lenses is at least partially the result of the fact that these lenses have fibers with very little end taper. Thus, the blunt ends of fibers in line- and Y-suture lenses precludes any significant overlap of end segments to effect accommodation.     

基于春玉米微咸水灌溉的水盐生产函数研究

在石羊河流域开展微咸水灌溉试验,综合考虑水分与盐分因素对春玉米生长的影响,以国际上通用的水分生产函数Blank模型和Jensen模型为基础进行作物水盐模型的构建,通过引入盐分胁迫因子,将水分生产函数转变为水盐生产函数。通过2009年和2010年春玉米不同矿化度微咸水灌溉试验,结合函数求解,探求春玉米各生育阶段的盐分敏感指数,得出春玉米的盐分敏感程度顺序为苗期>拔节期>抽雄灌浆期>成熟期。同时以交替灌溉试验进行验证,结果表明微咸水安排在盐分敏感程度小的生育阶段更有利于作物的生长。     

干旱胁迫下3种岩石边坡生态修复植物的抗旱性

植物的抗旱性直接影响着岩石边坡生态修复的效果。为研究不同植物在持续干旱下的抗旱机理,选择草地早熟禾、狗牙根和红三叶3种常用于岩石边坡生态修复的植物,采用盆栽控水试验和室内分析相结合的方法,研究干旱胁迫下3种植物叶片的相对含水量、相对电导率、丙二醛（MDA）含量、可溶性糖含量、脯氨酸(Pro)含量和叶绿素含量6个生理生化指标的变化情况。结果表明：所有参试植物的生理生化指标都随干旱胁迫的程度而变化,但植物之间和生理生化指标之间存在差异。运用模糊数学隶属函数分析法和灰色关联分析法,综合评价3种植物的抗旱性和各指标对干旱胁迫的敏感性。结果显示：干旱前期和中期,植物的抗旱性为：狗牙根＞红三叶＞草地早熟禾;干旱后期,植物的抗旱性为：草地早熟禾＞狗牙根＞红三叶;各生理生化指标与植物抗旱隶属度的关联度从大到小依次为0.708,0.694,0.638,0.630,0.609和0.607,可作为岩石边坡生态修复抗旱性植物筛选的评价指标,其中,以叶绿素含量和相对含水量对干旱胁迫的反应最为敏感。     

“土地换社保”背景下土地承包经营权价格研究

从资源经济学、产权角度探讨"土地换社保"背景下土地承包经营权价格内涵,并以江苏省为例进行了实证研究。研究表明:(1)"土地换社保"虽然始于对征地制度改革的探索,但在农用地产权转移、农用地用途改变程度及政策实施的出发点方面与土地征用有本质上的区别;(2)"土地换社保"背景下,土地承包经营权价格应包括农用地经济价格中属于农民的部分和农用地对农民所具有的就业保障、医疗保障、养老等基本生活保障的功能价值,而不包括农用地的生态价值和粮食安全价值。研究提出,要真正实现农民土地承包经营权的"资本化",并使得农民通过土地流转提高其土地收益和财产性收益,应加快土地承包经营权市场化流转机制建设。     

北方6种绿化灌木水分胁迫的生理响应

以红瑞木(Cornus alba)、红王子锦带(Weigela florida)、麦李(Prunus glandulosa)、辽东水蜡(Ligustrumobtusifolium)、杞柳(Salix integra)、忍冬(Lonicera maackii)6种绿化灌木幼苗为试验材料。采用盆栽控水法研究水分胁迫对6树种叶绿素相对含量值(DSPA)、相对电导率、丙二醛摩尔质量浓度、游离态脯氨酸质量分数、可溶性糖质量分数的影响,并采用模糊隶属函数法对6树种的抗旱能力进行综合评定。结果表明:6树种的抗旱能力均较强,只是适应干旱的方式不同,其抗旱能力由强到弱依次为彩叶杞柳>辽东水蜡>红瑞木>红王子锦带>麦李>金银忍冬。     

重要生态功能保护区农户土地利用受限及补偿研究综述

分析农户土地利用受限补偿在理论和技术两个方面存在的问题。并对该项研究提出理清补偿相关概念,构建补偿标准的测算和评价体系,加强补偿监督和评价体系等建议。     

输气站场自控系统夜间无人值守功能的实现

基于西气东输管道系统的实际运行情况,给出了实现夜间无人值守功能所需的功能逻辑。根据西气东输站场自动化控制系统的构架,对现有系统程序进行编辑与修改,加入了流量计算机的故障报警逻辑、压力调节自动分输逻辑和流量调节自动分输逻辑,提出了实现夜间无人值守功能的自动化控制系统改造方法,包括:PLC逻辑设置、RCI文件修改、增加站控画面及数据库建点。西气东输分输站夜间无人值守功能的实现,在保证管道安全生产的同时,提高了自动控制水平和管理水平。     

多效唑对马铃薯会-2光合效应及生长的影响

为弄清多效唑在晚熟马铃薯上的作用机理,采用田间试验,研究了不同浓度多效唑对马铃薯晚熟品种会2的叶绿素相对含量、净光合速率及其生长的影响.结果表明:在马铃薯开花期对叶片喷施适宜浓度的多效唑能促进马铃薯叶片叶绿素相对含量和光合色素含量的提高,进而促进净光合速率及产量的提高.本试验条件下,以100 mg/L的多效唑溶液效果最好.其产量最高(3309.8kg/667m2),比CK高859.2 kg/667m2,增幅为35.1％,与其他处理间差异显著.     

茅台酒生态功能保护区的种子植物区系特征

为了摸清茅台酒生态功能保护区的种子植物种类及区系特征,采取实地考察、标本采集、分类鉴定等方法对该地区的种子植物进行了调查。结果表明:1)茅台酒生态功能保护区共有种子植物101科279属411种,仅含1种的属或科较多,优势科、属不明显,区系具有明显的亚热带性质,温带成分有减少趋势。2)该区有国家级保护植物3种、中国特有属植物5种,该植物区系在区划上属于贵州高原亚地区,与黔北的其他6个保护区相比,热带成分所占比例最大,原因可能是该区年均气温较高。