糖蛋白物与发育

糖与蛋白质或脂类共价结合而成的糖蛋白、蛋白聚糖、糖脂以及脂多糖统称糖复合物 ,最近几年人们对糖复合物在生物发育过程中的作用进行了大量的研究 ,已经在许多方面取得了重大进展。1 .糖复合物与配子发生和受精配子发生和受精过程中有大量糖复合物的参与 ,他们在配子发生、精卵识别与受精以及受精完成后防止多精穿入的皮层反应等过程中发挥作用。哺乳动物精子表面有一层几百种糖蛋白组成的糖萼 ,其成熟是精子成熟的标志。射出的精子头部外表面的糖蛋白能阻止顶体酶的释放 ,在获能过程中该糖蛋白被雌性生殖管道分泌物中的酶降解后精子才获…     

被子植物助细胞中钙含量的变化

助细胞是被子植物受精过程中花粉管进入胚囊并释放精子及其内容物的场所,而助细胞中不同时期的钙含量与受精作用的顺利完成密切相关。在大多数植物中,助细胞是成熟胚囊中钙含量最高的细胞。传粉后在花粉管中所产生的信号诱导下,助细胞中钙含量还可能继续增加。花粉管进入退化助细胞后,在超高钙环境中破裂并释放精子,精子沿退化助细胞转移到受精靶区实现双受精。随后助细胞中的钙含量迅速降低。因此钙在吸引花粉管、雄配子释放甚至雄配子转移等过程中都发挥了重要作用。     

受精的生物学及化学

一个多世纪以来科学家们一直对“受精”给予极大的关注。近年来由于扩大了对哺乳动物受精的生物学及化学的认识,因而对受精及节制生育的医学及伦理学方面均有影响。本文将叙述哺乳动物受精的细胞和分子特征,以及从精子与卵的最初相遇到形成受精卵的过程。尽管大多数论述是从体外小鼠配子实验中得出的,但是也适用于大多数哺乳动物(包括人类)体内受精过程。     

香港巨牡蛎与长牡蛎种间配子兼容性

为了评估香港巨牡蛎与长牡蛎的配子兼容性,于2010年7月,以性腺成熟的香港巨牡蛎和长牡蛎为材料,研究了环境因子温度(16、20、24、28、32℃)、盐度(10、15、20、25、30)及内在因子精子浓度(100、101、102、103、104个/μL)、个体差异(240次杂交实验)对其受精率的影响,并计算了以上条件下的F50临界值。结果表明:香港巨牡蛎卵子可以与长牡蛎精子受精,但相反方向不能受精,存在着单向受精现象。温度是影响长牡蛎配子兼容性主要因子,盐度是影响香港巨牡蛎的主要因子,而温度、盐度交互作用是影响种间配子兼容性的最主要因子。种间配子温度、盐度的F50临界值分别为20.90℃、14.7。精子浓度及单对杂交中的个体差异均显著影响配子兼容性,精子浓度的F50临界值为2.40个/μL;在240次杂交实验中,有91次受精率不足50%,说明个体差异比例的F50临界值37.92%。从其内在因子来看,长牡蛎平均受精率最高(96.83%),配子兼容性较好;对于香港巨牡蛎(70.98%)与种间配子(58.70%)而言,受精水平相对较低,且存在着较大的个体差异。     

哺乳动物受精的生物学

哺乳动物的受精(Mammalian Fertilization)是两性配子(精子和卵子)相结合而形成合子的过程,它标志着胚胎发育的开始,也即是一个新生命的起点。受精是生物学家饶有兴味的课题。因为它不仅涉及到一个理论问题,更重要的是当今节育和不育的世界性问题尚未解决,因此,受精的重要性是不言而喻的。当然,受精是一个极其复杂的生命现象,涉及到两性配子的发育和成熟、精子获能、顶体反应、精卵激活、精子     

温度和光照强度对海藻场瓦氏马尾藻碎屑分解的影响

通过气候培养箱在室内模拟不同光照强度及温度条件,测定海藻场瓦氏马尾藻碎屑(简称海藻碎屑)分解速率变化及海藻碎屑对海藻场海域无机营养盐贡献度,旨在为探究大型海藻碎屑的生态服务效能提供科学依据。结果表明:海藻碎屑剩余物质干重和分解速率受温度影响不显著(P0.05),而光照强度影响显著(P0.05);不同温度、光强条件下,海藻碎屑质量损失率在2个月的实验周期内皆大于60%,且温度25.15℃、光强3200 lx条件更有利于海藻碎屑分解;温度对海藻碎屑分解释放氮磷营养盐影响不显著(P0.05);在同一温度(25.15℃)条件下,有无光照条件对水体铵态氮、硝态氮和亚硝态氮营养盐浓度变化影响不显著(P0.05),但对正磷酸盐浓度影响显著(P0.05);光照强度对水体内铵态氮和正磷酸盐浓度变化具有显著影响(P0.05),对硝态氮和亚硝态氮浓度变化影响不显著(P0.05);根据海藻场瓦氏马尾藻碎屑量估算出对现场海域水体溶解无机氮累积贡献量为4.597~17.321 mg·L~(-1),溶解无机磷累积贡献27.989~76.304 mg·L~(-1)。研究表明,不同温度条件下,瓦氏马尾藻碎屑分解释放铵态氮和正磷酸盐的量大于硝态氮和亚硝态氮,温度越高越利于铵态氮释放,而正磷酸盐则更利于在低温下分解释放;随光照强度的升高,氮磷营养盐释放趋势相反,正磷酸盐释放量随光照强度增大而受到抑制。     

大型海藻在珊瑚礁退化过程中的作用

随着全球范围珊瑚礁的退化,大型海藻在珊瑚礁区的覆盖度呈增多的趋势。大型海藻的大量生长,妨碍了珊瑚的生长、繁殖、恢复等过程。概括起来,大型海藻对珊瑚生长、繁殖及恢复过程所产生的不利影响主要包括:(1)大型海藻通过与珊瑚竞争空间和光照而影响珊瑚生长;(2)大型海藻与珊瑚直接接触时,通过摩擦作用及释放化感物质而影响珊瑚生长;(3)大型海藻的大量生长打破了珊瑚与海藻的竞争平衡,珊瑚为应对大型海藻的入侵而把用于生长和繁殖的能量转移到组织修复与防御上,进而造成珊瑚繁殖能量的减少;(4)大型海藻通过影响珊瑚幼虫的附着及附着后的存活率,而阻碍珊瑚群落的发展;(5)海藻还能通过富集沉积物、释放病原体及扰乱珊瑚共生微生物的生长等而间接影响珊瑚生长。明确的竞争机制有利于研究海藻与珊瑚的相互作用过程。在总结前人对海藻与珊瑚的竞争机制研究的基础上,把两者的竞争机制划分成物理机制、化学机制、微生物机制三大类,物理机制是研究得比较透彻的竞争机制,而化学机制与微生物机制则需要更深入的研究,是当前研究的热点。目前,我国对珊瑚礁中底栖海藻与珊瑚的相互作用研究甚少;鉴于此,对底栖海藻功能群的划分类型以及三大类型底栖海藻对珊瑚的作用特点做了简要介绍,并对珊瑚礁退化的现状和退化珊瑚礁区内海藻的表现做了概述。在此基础上,再综述国外关于大型海藻对珊瑚的影响研究进展,指出我国应该加强对南海珊瑚礁区大型海藻的种类分布及丰富度等的调查,评价大型海藻对南海珊瑚礁的影响现状;并结合生理学、分子生物学技术和生态学研究手段,在细胞与分子水平上探索海藻对珊瑚的影响机制,以期为珊瑚礁生态系统的保护提供参考。     

毁灭泰泽球虫小配子形成及受精现象的扫描电镜观察

现今关于球虫超微结构方面的研究资料已相当丰富,其中涉猎最多的是文美耳属(Eimeria)的虫种,同样隶属于孢子虫纲真球虫目艾美耳科的泰泽属球虫(Tyzzeria)尚未见报道。作者以纯种毁灭泰泽球虫(T.Perniciosa)人工感染无球虫北京鸭,定时扑采取小肠组织,利用扫描电镜对虫体小配子的形成过程及其形态进行了描述,并观察了大小配子的受精现象。 小配子形成毁灭泰泽球虫的小配子发育在小肠上皮细胞的带虫泡(Parasito phorous vacuole)内进行,和已报道的肠道艾美耳属球虫相同。在感染严重的样品,一个上皮细胞内往往有几个大、小配子体     

被子植物雌雄配子及早期胚胎的分离与研究应用

被子植物的有性生殖过程复杂精巧并深藏于母体组织内进行,一直以来难以对该过程进行直接的细胞学和分子生物学研究。如今在多种植物中获得了有活力而无污染的配子细胞和早期胚胎,结合少量细胞m RNA提取技术、基因组深度测序以及离体授精系统等技术,人们已能对被子植物受精过程中的配子识别、配子融合、合子激活等重要发育事件进行深入分析。本文对有代表性的被子植物配子和早期胚胎的分离技术及其在受精作用研究中的应用、存在的问题和前景进行了总结,旨在为植物生殖发育研究提供帮助。     

自花传粉和异花传粉的界说

在农业实践中,经常可以看到自花传粉作物品种退化的现象,自花传粉作物的品种经过一定年代栽培后,优良的特性逐渐变劣,降低了对不良条件的抵抗力和引起产量的下降。李森科认为自花传粉作物品种退化的一个基本原因是长期的自花传粉。因此他提出自花传粉作物进行品种内杂交,可以克服品种退化,提高作物的生活力和产量。达尔文根据自己对自花传粉作用和异花传粉作用多年来的研究,得出结论:连续的自花受精在生物学上是有害的,而异花受精则是有利的;同时指出异花受精的益处在于通过受精作用结合了某种程度差异的两性配子的结果,而两性配子的差异是由于不同个体处于不同的生活条件下引起的。经多年的研究,自花传粉有害性与异花传粉有利性是进行有性繁殖的植物的共同规律。A.N.阿夫托诺莫夫在棉花方面的研究中,指出只要经过3—4年代的连续强制自交就会引起棉花产量质量的退化。自花传粉     

53 A Seaweed's perspective on marine reserves

In response to major changes in coastal ecosystems in recent decades, a number of governmental agencies around the world are establishing marine reserves – areas where removal of animals or plants is prohibited. Although marine reserves are touted as an ecosystem based approach to management of marine resources, the vast majority of attention on reserve design and impact focuses solely on fish. Although a few species of algae are commercially harvested, most are not. As a result, they will receive little direct benefit from protection by reserves aside from habitat protection. From the perspective of a seaweed, the primary impacts of marine reserves will therefore be indirect through species interactions. We examine the rapidly growing theoretical and empirical literature on marine reserves to anticipate the likely responses of seaweeds to exclusion of fishing. The key issues that emerge are: the trophic level of prior fishing and the dispersal scales of seaweeds relative to their competitors and consumers. The latter issue is poorly understood and poses a key challenge to phycologists if we are to effectively incorporate seaweeds into future marine reserve design.     

Life strategy, ecophysiology and ecology of seaweeds in polar waters

Polar seaweeds are strongly adapted to the low temperatures of their environment, Antarctic species more strongly than Arctic species due to the longer cold water history of the Antarctic region. By reason of the strong isolation of the Southern Ocean the Antarctic marine flora is characterized by a high degree of endemism, whereas in the Arctic only few endemic species have been found so far. All polar species are strongly shade adapted and their phenology is finely tuned to the strong seasonal changes of the light conditions. The paper summarises the present knowledge of seaweeds from both polar regions with regard to the following topics: the history of seaweed research in polar regions; the environment of seaweeds in polar waters; biodiversity, biogeographical relationships and vertical distribution of Arctic and Antarctic seaweeds; life histories and physiological thallus anatomy; temperature demands and geographical distribution; light demands and depth zonation; the effect of salinity, temperature and desiccation on supra-and eulittoral seaweeds; seasonality of reproduction and the physiological characteristics of microscopic developmental stages; seasonal growth and photosynthesis; elemental and nutritional contents and chemical and physical defences against herbivory. We present evidence to show that specific characteristics and adaptations in polar seaweeds help to explain their ecological success under environmentally extreme conditions. In conclusion, as a perspective and guide for future research we draw attention to many remaining gaps in knowledge. Dedicated to Prof. Dr. Gunter O. Kirst and to Prof. Dr. Klaus Lüning on occasion of their retirement 28. Februar 2006 and 31. March 2006, respectively.     

Crowding in clonal seaweeds: Does self-thinning occur in Mastocarpus papillatus shortly before stand biomass peaks?

Fronds from crowded stands of clonal seaweeds, particularly those in which holdfasts are mostly perennial and are the major source of new fronds every year, are thought not to undergo self-thinning during the growth season, unlike those from crowded stands of unitary seaweeds. For clonal seaweeds, it is not known, however, what happens at the very end of the growth season, when crowding is highest for the year. By sampling twice more frequently than previously done for similar species, the possible occurrence of frond self-thinning was tested for Mastocarpus papillatus (Rhodophyta, Gigartinales, Petrocelidaceae) from western Canada during the growth season (spring) of 2003. Initially, stand biomass increased together with frond density, as found previously for similar clonal seaweeds. Shortly before stand biomass peaked for the year (June), frond density remained statistically unchanged. Thus, the increased sampling precision of this study confirms that fronds of these clonal seaweeds do not undergo self-thinning, not even shortly before crowding is highest. Frond size inequality for M. papillatus remained statistically similar during the growth season, which is also consistent with a model of no self-thinning. There are similarities in biomass–density dynamics and in size inequality dynamics between clonal seaweeds and clonal vascular plants.     

A meta-analysis of seaweed impacts on seagrasses: generalities and knowledge gaps

Seagrasses are important habitat-formers and ecosystem engineers that are under threat from bloom-forming seaweeds. These seaweeds have been suggested to outcompete the seagrasses, particularly when facilitated by eutrophication, causing regime shifts where green meadows and clear waters are replaced with unstable sediments, turbid waters, hypoxia, and poor habitat conditions for fishes and invertebrates. Understanding the situations under which seaweeds impact seagrasses on local patch scales can help proactive management and prevent losses at greater scales. Here, we provide a quantitative review of available published manipulative experiments (all conducted at the patch-scale), to test which attributes of seaweeds and seagrasses (e.g., their abundances, sizes, morphology, taxonomy, attachment type, or origin) influence impacts. Weighted and unweighted meta-analyses (Hedges d metric) of 59 experiments showed generally high variability in attribute-impact relationships. Our main significant findings were that (a) abundant seaweeds had stronger negative impacts on seagrasses than sparse seaweeds, (b) unattached and epiphytic seaweeds had stronger impacts than 'rooted' seaweeds, and (c) small seagrass species were more susceptible than larger species. Findings (a) and (c) were rather intuitive. It was more surprising that 'rooted' seaweeds had comparatively small impacts, particularly given that this category included the infamous invasive Caulerpa species. This result may reflect that seaweed biomass and/or shading and metabolic by-products like anoxia and sulphides could be lower for rooted seaweeds. In conclusion, our results represent simple and robust first-order generalities about seaweed impacts on seagrasses. This review also documented a limited number of primary studies. We therefore identified major knowledge gaps that need to be addressed before general predictive models on seaweed-seagrass interactions can be build, in order to effectively protect seagrass habitats from detrimental competition from seaweeds.     

Simulation of drifting seaweeds in East China Sea

Drifting seaweeds plays a major role in areas where they are present. We describe a computer model, JeoSim that clarifies the roles of those seaweeds in relation to their transport using particle-tracking algorithm. The Euler rule with trapezoidal approximation, used to calculate drifting paths, is implemented in JeoSim in discrete events fashion in order to simulate the path and movement of seaweeds. Pre-processing of the ocean currents is done with the Princeton Ocean circulation Model (POM). Simulated current constitutes the data that provides force and directions for the calculations of drifting paths. Along with the implementation of the particle-tracking algorithm in discrete event fashion, the originality of the JeoSim software lies in its Object Oriented architecture which makes it especially suited to perform simulation of living, cross scale systems with complex behavior. Behavior of drifting seaweeds of the Sargasso family has been implemented in JeoSim, and experimented in East China Sea following a drifting seaweed collection campaign in May 2002. Despite a relatively low resolution ocean currents data, simulated results compare well with the observed distribution.     

Seaweed cultivation: Methods and problems

This paper presents an overview of the state of the art in global seaweed cultivation. It describes methodological approaches and main cultivation methods and discusses different problems arising during the application of these methods. One of the major problems is the negative effect of large-scale monoculture of seaweeds on natural benthic biocenoses. We express our views on how to tackle the most acute problems of macroalgal farming on the basis of our own data and data from other authors. The sustainable use of natural monodominant seaweed communities is shown to be preferable to mariculture. A detailed analysis is given of various mariculture models and the latest achievements in the integrated farming of seaweeds, fish, crustaceans, and mollusks.     

Contemporary Gathering Practice and Antioxidant Benefit of Wild Seaweeds in Hawai’i

Contemporary Gathering Practice and Antioxidant Benefit of Wild Seaweeds in Hawai’i. Wild-gathered seaweeds (limu) are a prominent component of Native Hawaiian diet and culture, but are understudied for their nutritional benefits and contemporary cultural use. This study uses a combination of ethnographic, pharmacological, and ecological approaches to document contemporary levels of wild seaweed gathering and consumption, and it explores the impact of cultivation and eutrophication on the disease-preventive benefits wild seaweeds may provide. Levels of gathering and consumption of seaweed were assessed with surveys of high school students and interviews with adult limu gatherers on O’ahu island, Hawai’i. Antioxidant activity was assessed with laboratory-based assays. Almost all students surveyed reported consuming cultivated seaweeds, one-third reported having consumed wild seaweeds, and one-fifth had gathered them, confirming that gathering practice and traditional diet have persisted in Hawai’i despite major social and environmental change. Wild gathering was three times as high and consumption 60% more prevalent among Native Hawaiians compared to non-Hawaiian students. Further, students with a parent who gathered limu were six times more likely to have gathered limu themselves, asserting the importance of within-family transmission to cultural continuity. A larger proportion of male than female Hawaiian students reported gathering wild seaweeds, indicating a cultural shift from pre-Contact Hawai’i, when women were the predominant gatherers and consumers of limu. The wild seaweeds assessed demonstrated higher levels of antioxidant activity than did cultivated seaweeds. Eutrophication was correlated with a decline in antioxidant activity, indicating that changing ocean conditions may alter the nutritional quality of this traditional food. Today, nearly all students are receiving some antioxidant benefits from seaweed, with Native Hawaiian youth from families that gather seaweed most likely to receive this health benefit. Conservation and restoration of near-shore environments to promote native edible seaweeds in pollution-free areas would provide greater opportunities for Native Hawaiian gathering practice and would support Native Hawaiian health.     

Activation of chemical defenses in the tropical green algae Halimeda spp.

Halimeda spp. are among the most common seaweeds on tropical reefs where herbivory is intense. These calcified seaweeds produce diterpenoid feeding deterrents; the major metabolites are halimedatetraacetate and halimedatrial. We found that most species of Halimeda on Guam immediately convert the less-deterrent secondary metabolite halimedatetraacetate to the more potent feeding deterrent halimedatrial when plants are injured by grinding or crushing. This conversion would therefore occur when fishes bite or chew Halimeda plants. We term this process of rapid conversion “activation”. Extracts from injured plants contained higher amounts of halimedatrial and were more deterrent toward herbivorous fishes than extracts from control plants. Herbivore-activated defenses are common in many families of terrestrial plants: however, this is the first example of an activated defense in a marine plant.     

Rapid determination of nucleosides,nucleobases and free amino acids in brown seaweeds using ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry

In this study the contents of nucleosides, nucleobases and free amino acids (FAAs) in common brown seaweeds Saccharina japonica, Sargassum pallidum, S. fusiforme, S. thunbergii and S. muticum from major production areas in China were determined by ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-TQ-MS). The total contents of nucleosides and nucleobases varied from 48.46 to 4,105.00 μg g^?1. Among the five seaweeds, levels of nucleosides and nucleobases in S. japonica were higher than the other species. The contents of ribonucleosides in these brown seaweeds were higher than those of deoxynucleosides. Uridine was the predominant constituent in all samples while 2′-deoxycytidine was the least in most samples. FAAs contents ranged from 0.14 to 22.76 mg g^?1. Among the five seaweeds, levels of FAAs in S. muticum were higher than the other species. Essential amino acids accounted for 3.26–51.49 % of total FAAs contents in different species. Glutamic acid was the major constituent in most samples. Four non-protein amino acids, γ-aminobutyric acid, taurine, hydroxyproline and citrulline, were found in the seaweed samples. Furthermore, principal component analysis (PCA) showed that chemical profiles of nucleosides, nucleobases and FAAs in S. pallidum and S. fusiforme were different from S. muticum, S. thunbergii and S. japonica. Common brown seaweeds could be promising natural sources for future industrial research into nucleosides, nucleobases and FAAs with potential benefits for human health.