UV-B辐照培养下南极冰藻的形态和超微结构及主要生化组成的变化

对从南极水样中分离到的L-4单细胞绿藻(Chlorophyceae L-4),模拟南极的紫外辐射环境．在人工UV-B辐照下培养绿藻L-4．以滤除UV-B培养的绿藻L-4为对照组。用电镜对绿藻L-4试验组和对照组的形态和超微结构进行观察比较。结果表明：试验组细胞内积累大量的淀粉颗粒,是对照组的10～20倍;脂肪颗粒是对照组的3～4倍;试验组的细胞膜和细胞壁之间充满大量的黑色颗粒物质,而对照组很少。此外,试验组的细胞普遍较对照组大,且细胞外粘附着大量的白色黏性物质。对绿藻L-4试验组和对照组的蛋白质、脂肪、糖、无机元素的总含量进行测定,结果表明．试验组的蛋白质含量低于对照组14．16％;脂肪含量高于对照组46．65％;可溶性总糖含量高于对照组66．34％;灰分和其它物质含量分别低于对照组38．83％和33．31％。UV—B辐照下南极冰藻的细胞超微结构和生化组成的变化,部分反映了南极冰藻在长期的进化过程中对南极强辐射环境的适应。本研究将为从南极冰藻中获取抗紫外辐射活性物质提供科学依据。     

The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss

We discuss the existence of cryospheric “tipping points” in the Earth''s climate system. Such critical thresholds have been suggested to exist for the disappearance of Arctic sea ice and the retreat of ice sheets: Once these ice masses have shrunk below an anticipated critical extent, the ice–albedo feedback might lead to the irreversible and unstoppable loss of the remaining ice. We here give an overview of our current understanding of such threshold behavior. By using conceptual arguments, we review the recent findings that such a tipping point probably does not exist for the loss of Arctic summer sea ice. Hence, in a cooler climate, sea ice could recover rapidly from the loss it has experienced in recent years. In addition, we discuss why this recent rapid retreat of Arctic summer sea ice might largely be a consequence of a slow shift in ice-thickness distribution, which will lead to strongly increased year-to-year variability of the Arctic summer sea-ice extent. This variability will render seasonal forecasts of the Arctic summer sea-ice extent increasingly difficult. We also discuss why, in contrast to Arctic summer sea ice, a tipping point is more likely to exist for the loss of the Greenland ice sheet and the West Antarctic ice sheet.     

High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated Antarctic lake

Deep Lake in Antarctica is a globally isolated, hypersaline system that remains liquid at temperatures down to −20 °C. By analyzing metagenome data and genomes of four isolates we assessed genome variation and patterns of gene exchange to learn how the lake community evolved. The lake is completely and uniformly dominated by haloarchaea, comprising a hierarchically structured, low-complexity community that differs greatly to temperate and tropical hypersaline environments. The four Deep Lake isolates represent distinct genera (∼85% 16S rRNA gene similarity and ∼73% genome average nucleotide identity) with genomic characteristics indicative of niche adaptation, and collectively account for ∼72% of the cellular community. Network analysis revealed a remarkable level of intergenera gene exchange, including the sharing of long contiguous regions (up to 35 kb) of high identity (∼100%). Although the genomes of closely related Halobacterium, Haloquadratum, and Haloarcula (>90% average nucleotide identity) shared regions of high identity between species or strains, the four Deep Lake isolates were the only distantly related haloarchaea to share long high-identity regions. Moreover, the Deep Lake high-identity regions did not match to any other hypersaline environment metagenome data. The most abundant species, tADL, appears to play a central role in the exchange of insertion sequences, but not the exchange of high-identity regions. The genomic characteristics of the four haloarchaea are consistent with a lake ecosystem that sustains a high level of intergenera gene exchange while selecting for ecotypes that maintain sympatric speciation. The peculiarities of this polar system restrict which species can grow and provide a tempo and mode for accentuating gene exchange.Deep Lake (DL) is an extremely cold and hypersaline environment that has the distinction of being the least productive lake ever recorded (1–3). The lake is a marine-derived system in the Vestfold Hills, East Antarctica, having been isolated from the Southern Ocean by isostatic rebound of the continent ∼3,500 y BP (2, 4, 5) (SI Appendix, Fig. S1). The temperature exceeds 0 °C only in the top few meters for a few summer months per year, and it remains ice-free even in winter when temperatures drop to −40 °C (air) and −20 °C (throughout the lake) (1, 6). Microbial diversity is extremely low, and is dominated by members of the haloarchaea (7). Within this ecosystem, the putative primary producer is the green alga Dunaliella sp., which is found at low biomass concentrations (8–10).From DL, Halorubrum lacusprofundi, the first member of the Archaea domain isolated from a cold environment (11), has been formally described (12). In the laboratory, H. lacusprofundi grows across a wide range of temperatures from −1 °C to 42 °C, with fastest growth rate occurring at ∼33 °C (12, 13). It is capable of using a number of different carbon sources including glucose, mannose, acetate and ethanol, providing it with a seemingly versatile heterotrophic metabolism (12). Aside from studies that have noted the ability of H. lacusprofundi, and a recent isolate, tADL (14), to form aggregates and biofilms at either high or low temperatures (13, 15, 16), the only studies addressing adaptive responses are those linking the production of unsaturated diether membrane lipids to cold adaptation in H. lacusprofundi (3, 17).Various mechanisms that alter genetic composition have been reported in haloarchaea, including archaeal viruses, conjugative plasmids, genome rearrangements mediated by transposons, and significant levels of gene exchange via the formation of heterodiploids followed by homologous recombination (18–25). All these studies have been confined to temperate or tropical systems, not polar environments.For some bacteria, the relationship between recombination frequency and sequence divergence appears to be log-linear (26, 27) but may be as much as two orders of magnitude higher in haloarchaea, such as for Haloferax volcanii and Haloferax mediterranei, which readily undergo cell fusion and DNA exchange (25, 28). Forces driving speciation in microbes include niche adaptation, selective sweeps, genetic drift, recombination, and geographic isolation (29). However, it is unclear how these forces would maintain species homogeneity or bring about lineages when gene flow is high, as is the case in haloarchaea. Although selection is important for speciation, it has been argued that the rate of genomic recombination may be a key determinant when considering sympatric speciation. Modeling has shown that high recombination rates are necessary to generate a new species when an ecological trait inferring increased fitness is controlled by many adaptive loci (30). However, these same high levels of recombination may also increase the number of intermediate (suboptimal) genotypes and reduce “completeness” of speciation. The dynamics of this sympatric evolution hypothesis have not been examined in real populations.The DL system is geographically very isolated, its organismal growth rates are very low, and the combination of cold plus hypersalinity may be expected to promote the physical process of DNA transformation to levels that exceed those of warm hypersaline environments. In this context, we examined the genomes of four recent haloarchaeal isolates and metagenome data from DL to assess genome variation and patterns of gene exchange and derive an understanding of how this unique Antarctic lake community evolves.     

Ascorbic acid status of australian antarctic expeditiones

It is not certain that all personnel active in polar regions receive adequate dietary ascorbic acid. Leucocyte ascorbic acid concentrations were measured during the year of an Australian Antarctic expedition with half the personnel taking a supplement of 1000 mg of the vitamin/day. The results, together with a urinary ascorbic acid excretion study and medical monitoring, indicate that the Australian rations supply adequate dietary ascorbic acid which comes largely from canned fruit juice. Supplemental ascorbic acid is advised for field rations. One man suffered a possible complication of ascorbic acid megadosage.     

Venom on ice: First insights into Antarctic octopus venoms

The venom of Antarctic octopus remains completely unstudied. Here, a preliminary investigation was conducted into the properties of posterior salivary gland (PSG) extracts from four Antarctica eledonine (Incirrata; Octopodidae) species (Adelieledone polymorpha, Megaleledone setebos, Pareledone aequipapillae, and Pareledone turqueti) collected from the coast off George V’s Land, Antarctica. Specimens were assayed for alkaline phosphatase (ALP), acetylcholinesterase (AChE), proteolytic, phospholipase A₂ (PLA₂), and haemolytic activities. For comparison, stomach tissue from Cirroctopus sp. (Cirrata; Cirroctopodidae) was also assayed for ALP, AChE, proteolytic and haemolytic activities. Dietary and morphological data were collected from the literature to explore the ecological importance of venom, taking an adaptive evolutionary approach.Of the incirrate species, three showed activities in all assays, while P. turqueti did not exhibit any haemolytic activity. There was evidence for cold-adaptation of ALP in all incirrates, while proteolytic activity in all except P. turqueti. Cirroctopus sp. stomach tissue extract showed ALP, AChE and some proteolytic activity. It was concluded that the AChE activity seen in the PSG extracts was possibly due to a release of household proteins, and not one of the secreted salivary toxins. Although venom undoubtedly plays an important part in prey capture and processing by Antarctica eledonines, no obvious adaptations to differences in diet or morphology were apparent from the enzymatic and haemolytic assays. However, several morphological features including enlarged PSG, small buccal mass, and small beak suggest such adaptations are present. Future studies should be conducted on several levels: Venomic, providing more detailed information on the venom compositions as well as the venom components themselves; ecological, for example application of serological or genetic methods in identifying stomach contents; and behavioural, including observations on capture of different types of prey.     

Histology of selected tissues of the leopard seal and implications for functional adaptations to an aquatic lifestyle

The microscopic anatomy of the cardio-respiratory system, digestive system, kidney, lymphatic system and integument was investigated in the leopard seal, Hydrurga leptonyx, by examining histological sections of tissues collected from leopard seals in Antarctica and New South Wales, Australia. The majority of the tissues had similar histological features to those described in terrestrial mammals and other pinniped species, particularly phocid seals. Differences noted included readily identifiable Purkinje cells within the endocardium, muscular rather than cartilaginous reinforcement of the smaller airways, a single capillary layer within the alveolar septa, limited and variable keratinization of the oesophageal epithelium, few lymphoid follicles within the lamina propria of the gastrointestinal tract, and an absence of a sporta perimedullaris musculosa described in the kidney of cetaceans and some pinniped species. Adaptations of the lung, spleen and integument, similar to those described in other pinnipeds, including reinforcement of the pulmonary terminal airways, prominent pulmonary interlobular septa, ample smooth muscle in the capsule and trabeculae of the spleen, increased thickness of the epidermis, well-developed dermal sebaceous glands, and a thick blubber layer, appear to confer upon the leopard seal advantages related to its aquatic lifestyle.     

军事孤立封闭环境作业人员标准化神经认知测试的探索

研究军事孤立封闭环境对作业人员认知功能的影响,首先需要一套合格的神经认知测量工具。目前使用的认知测试存在以下问题：不同研究间使用的不一致性;测量的心理过程不明确;存在练习效应;没有针对性的常模数据;灵敏度、难度、全面性不够。据此提出适用于军事孤立封闭环境的神经认知测试应满足如下要求：（1）方便携带,容易开展测试;（2）测试耗时应尽量短（≤30 min）;（3）可重复测量,被试能够较快达到稳定水平;（4）最好是成套测试,检测的认知功能应全面,且必须与完成特定任务密切相关;（5）应有针对军事孤立封闭环境工作人员在一般环境下的常模,以及其随时间变化的测试表现曲线作为对照组数据;（6）认知测试的信效度经过检验;（7）灵敏度较高,测试难度适当;（8）认知测试涉及的心理过程明确且单一,便于解释结果;（9）完成认知测试激活的脑区明确,便于进一步神经心理研究。美国国家航空航天局（NASA）太空飞行认知测试系统Cognition几乎完美契合以上9个要求。未来我军编制神经认知测试时,可在参照Cognition的基础上,着重于提高认知测试装置的便携性、开发计算机自适应认知测验、明确认知测试的纳入标准、开发心理测量学特点一致的平行测验。