Seasonal development of phloem in scots pine stems

The formation of phloem was studied for two years in stems of 50 to 60 year old trees of Scots pine (Pinus sylvestris L.) growing in nature. The development of phloem of the current year begins 10 to 20 days before the xylem formation and is completed with the termination of shoot growth in the end of June. Observations over the seasonal activity of cambium producing sieve cells of phloem and duration of their differentiation as compared to the xylem derivatives of cambium have shown that the maxima of formation of phloem and xylem cells could coincide or not coincide by season, while the activities of their differentiation were always in antiphase. The sieve cells of early phloem were separated from those of late phloem by a layer of tannin-containing cells, which are formed simultaneously with the formation of late xylem cells by the cambium. Seasonal dynamics of accumulation of starch grain in structural elements of the phloem is related to the xylem development. The content of metabolites in differentiating and mature phloem elements, in the cambium zone, and in the xylem cells growing in the radial direction depended on cell specificity, stage of their development, and type of forming wood, early or late, which differ in the cell wall parameters and, hence, requirement of assimilates. Significant differences were described between the content of low molecular weigh carbohydrates, amino acids, organic acids, and phenol compounds using two methods of calculation: per dry weight and per cell.     

Long‐lived marine species may be resilient to environmental variability through a temporal portfolio effect

Maintenance of genetic variation may provide resilience of populations to natural environmental variability. We used Pacific ocean perch (POP; Sebastes alutus) to test for the maintenance of adaptive variation across overlapping generations. POP are a long‐lived species characterized by widespread larval dispersal in their first year and a longevity of over 100 years. In order to understand how early marine dispersal affects POP survival and population structure, we used restriction site‐associated DNA sequencing (RADseq) to obtain 11,146 single‐nucleotide polymorphisms (SNPs) from 401 young‐of‐the‐year (YOY) POP collected during surveys conducted in 2014 (19 stations) and 2015 (4 stations) in the eastern Gulf of Alaska. Population clustering analysis showed that the POP samples represented four distinct ancestral populations mixed throughout the sampling area. Based on prior work on larval dispersal of POP, these larvae are most likely from distinct parturition locations that are mixing during their pelagic dispersal life stage. Latent factor mixed models revealed that POP larvae face significant selection during their first year at sea, which is specific to the year of their birth. Thus each adult cohort's genetic composition is heavily influenced by the environmental conditions experienced during their first year at sea. Long‐lived species relying on broadcast spawning strategies may therefore be uniquely resilient to environmental variability by maintaining a portfolio of cohort‐specific adaptive genotypes, and age truncation due to overfishing of older cohorts may have detrimental effect on the population viability.     

基于超声射频信号的大鼠脂肪肝分级诊断研究

目的：从分析肝脏超声射频信号的角度,探究一种对脂肪肝进行分级定量诊断的新方法。方法：80只Wistar大鼠,通过喂养高脂饲料建立大鼠脂肪肝模型,其中正常肝的大鼠28只,轻度脂肪肝的大鼠21只,中度脂肪肝的18只,重度脂肪肝的13只。然后采集大鼠左右肝的超声射频信号,选取大鼠肝脏部位感兴趣区域的超声射频信号,分析大鼠肝脏超声射频信号的脂肪肝特征信息,提取了射频信号幅度包络值的均值／标准差（MSR）、偏度（SK）、峰度（Ku）这三个统计特征量,再利用BP神经网络对大鼠脂肪肝进行分类识别。结果：该方法对大鼠正常肝的识别率达92．5％,轻度脂肪肝的识别率达87．5％,中度脂肪肝的识别率达76．7％．重度脂肪肝的识别率达77．3％。结论：本文研究的方法可对大鼠脂肪肝进行分级定量诊断,且证明了超声射频信号在脂肪肝诊断中是有价值的,为对分级诊断脂肪肝疾病的研究提供了新的方向。     

山东半岛滨海沙滩前缘的野生植物

滨海沙滩是以海水影响为基本过程的地貌类型,适应这种环境的植物类群与适生于内陆的沙地植物可能存在巨大差别。在野外调查的基础上,分析了山东半岛滨海沙滩前缘的植物种类及其种间关系。结果表明：（1）滨海沙滩前缘具有独特的优势种库,包括沙钻苔草（Carex kobomugi）、肾叶打碗花（Calystegia soldanella）、粗毛鸭嘴草（Ischaemum bartatum）、单叶蔓荆（Vitex trifolia var.simplicifolia）、矮生苔草（Carex pumila）和沙引草（Messerschmidia sibirica）等;（2）优势种库的成员都是潜在优势种,它们之间主要呈抑制效应,对库外物种几乎没有抑制效应,甚至有互补或互利效应。在进化过程中,这些潜在优势种可能已适应风暴潮的干扰,不会因受风暴潮灾害而灭亡。当植物适应风暴潮后,滨海沙滩不再是灾难环境,反而变为适宜生境。为持续利用这些物种,不仅要保护其赖以生存的天然生境,还要开展引种栽培,消除人们对野生资源的采挖动机。根据物种间的天然联系,栽培时宜将具有互利或互补关系的物种间混种植,不宜将具有抑制关系的物种间混种植。     

拟南芥根原生韧皮部筛管分子的超微结构

运用高压冷冻替代方法固定处理材料,在透射电镜下观察了拟南芥(Arabidopsis thaliana L.)根原生韧皮部筛管分子在发育过程中的超微结构变化.结果表明:在筛管分子发育过程中,细胞核具有细胞程序化死亡的典型特征,出现核膜内陷、核质聚集并边缘化、核膜破毁以及最后核消失.核膜在破毁前一直呈饱满状态,未出现核膜皱缩、核裂瓣和核周腔明显膨大等现象.在成熟筛管分子的细胞质内,具单层膜的淀粉状颗粒.这些淀粉状颗粒常与线粒体在一起,可能为线粒体的产能活动提供基质.小液泡发生于内质网,未见大液泡的形成.     

黄瓜韧皮部的类血影蛋白

以黄瓜 (CucumissativusL .)叶柄为实验材料 ,应用胶体金免疫电镜技术证明类血影蛋白存在于韧皮部的筛管_伴胞复合体中 ,广泛分布于筛分子中的韧皮蛋白纤丝以及筛分子网络结构上 ,并且分布在伴胞的细胞质和线粒体膜以及筛分子与伴胞之间的分支状胞间连丝上 ,表明该蛋白可能由伴胞合成并经由二者之间的胞间连丝运输到筛分子中。用免疫印迹技术证明 ,黄瓜韧皮部汁液蛋白中存在类血影蛋白 ,其分子量约为 2 6 0kD ,与动物细胞中血影蛋白的分子量接近     

Profiles of light absorption and chlorophyll within spinach leaves from chlorophyll fluorescence

Chlorophyll fluorescence was used to estimate profiles of absorbed light within chlorophyll solutions and leaves. For chlorophyll solutions, the intensity of the emitted fluorescence declined in a log–linear manner with the distance from the irradiated surface as predicted by Beer's law. The amount of fluorescence was proportional to chlorophyll concentration for chlorophyll solutions given epi‐illumination on a microscope slide. These relationships appeared to hold for more optically complex spinach leaves. The profile of chlorophyll fluorescence emitted by leaf cross sections given epi‐illumination corresponded to chlorophyll content measured in extracts of leaf paradermal sections. Thus epifluorescence was used to estimate relative chlorophyll content through leaf tissues. Fluorescence profiles across leaves depended on wavelength and orientation, reaching a peak at 50–70 µm depth. By infiltrating leaves with water, the pathlengthening due to scattering at the airspace : cell wall interfaces was calculated. Surprisingly, the palisade and spongy mesophyll had similar values for pathlengthening with the value being greatest for green light (550 > 650 > 450 nm). By combining fluorescence profiles with chlorophyll distribution across the leaf, the profile of the apparent extinction coefficient was calculated. The light profiles within spinach leaves could be well approximated by an apparent extinction coefficient and the Beer–Lambert/Bouguer laws. Light was absorbed at greater depths than predicted from fibre optic measurements, with 50% of blue and green light reaching 125 and 240 µm deep, respectively.     

Ciliary sieving and active ciliary response in capture of particles by suspension-feeding brachiopod larvae

Larvae of a brachiopod, Glottidia pyramidata, used at least two ciliary mechanisms to capture algal cells upstream from the lateral band of cilia that produces a feeding/swimming current. (1) Filtration: the larvae retained algal cells on the upstream (frontal) side of a sieve composed of a row of stationary laterofrontal cilia. Movement of the laterofrontal cilia could not be observed during capture or rejection of particles, but the laterofrontal cilia can bend toward the beating lateral cilia, a possible mechanism for releasing rejected particles from the ciliary sieve. (2) Localized changes of ciliary beat: the larvae may also concentrate particles by a local change in beat of lateral cilia in response to particles. The evidence is that the beat of lateral cilia changed coincident with captures of algal cells and that captured particles moved on paths consistent with a current redirected toward the frontal side of the tentacle by an induced local reversal of the lateral cilia. The change of beat of lateral cilia could have been an arrest rather than a reversal of ciliary beat, however. The similar ciliary bands in adult and larval lophophorates (brachiopods, phoronids, and bryozoans) suggest that these animals share a range of ciliary behaviours. The divergent accounts of ciliary feeding of lophophorates could be mostly the result of different authors observing different aspects of ciliary feeding.     

Actin in Pumpkin Phloem Exudate

When analyzing cytoskeletal proteins in Cucurbita pepo phloem exudate by immunoblotting, we detected actin in an amount comparable to that in some plant tissues and a small amount of -tubulin. Electron-microscopic examination of the exudate permitted us to observe filaments that were capable of interacting with the myosin subfragment S1 from rabbit skeletal muscle and with phalloidin conjugated with colloidal gold. The addition of 0.5 mM phalloidin to the exudate in the medium containing 20 mM dithiothreitol (DTT) resulted in an increased number of filaments. Since high DTT concentrations induce a breakdown of filaments of the phloem protein PP1, it seems likely that the produced filaments were composed of actin. The addition of 50 mM MgCl₂ to the exudate resulted in the formation of dense bundles and paracrystals, which resembled those produced by muscle actin under similar conditions. Our results demonstrated that actin in phloem sap was capable of polymerization with filament formation.     

Fluid Dynamics Simulating Experiment of Pressure Gradient for Assimilate Translocation in Sieve Tubes

According to the similitude theory of fluid mechanics, a pressure-driven experiment in a sieve tube model has been performed. The relationships between the pressure gradient and the transport velocities at the various diameters of sieve pore have been obtained. The experimental data were compared with the theoretical prediction based on the poiseuille equation. The result shows that the pressure gradient required for translating the assimilate is directly proportional to the translating velocity, which agrees with Poiseuille equation. However, the resistance of the sieve plate to flow is much more than that estimated by the previous theory. Even though the translating velocity is a normal level and the diameter of the sieve tube is a typical size, the pressure gradient required for flow is about 1 bar/m. It will increase sharply with the decrease of the diameter of sieve pore. The ratios of the pressure gradients measured in the test to that predicted by Poiseuille equation are about 2–4 for the five kinds of diameters of Sieve pore. Additionally, a simulating test of the pores being partly plugged has been performed. The result shows that the pressure gradients measured are greatly beyond the range that may be kept in plants. This study will be helpful to assess Munch hypothesis.