How do vascular plants perform photosynthesis in extreme environments? An integrative ecophysiological and biochemical story

In this work, we review the physiological and molecular mechanisms that allow vascular plants to perform photosynthesis in extreme environments, such as deserts, polar and alpine ecosystems. Specifically, we discuss the morpho/anatomical, photochemical and metabolic adaptive processes that enable a positive carbon balance in photosynthetic tissues under extreme temperatures and/or severe water‐limiting conditions in C₃ species. Nevertheless, only a few studies have described the in situ functioning of photoprotection in plants from extreme environments, given the intrinsic difficulties of fieldwork in remote places. However, they cover a substantial geographical and functional range, which allowed us to describe some general trends. In general, photoprotection relies on the same mechanisms as those operating in the remaining plant species, ranging from enhanced morphological photoprotection to increased scavenging of oxidative products such as reactive oxygen species. Much less information is available about the main physiological and biochemical drivers of photosynthesis: stomatal conductance (g_s), mesophyll conductance (g_m) and carbon fixation, mostly driven by RuBisCO carboxylation. Extreme environments shape adaptations in structures, such as cell wall and membrane composition, the concentration and activation state of Calvin–Benson cycle enzymes, and RuBisCO evolution, optimizing kinetic traits to ensure functionality. Altogether, these species display a combination of rearrangements, from the whole‐plant level to the molecular scale, to sustain a positive carbon balance in some of the most hostile environments on Earth.     

低温微生物的冷适应机理及其应用

低温微生物广泛分布于极地、冰川、永久冻土和深海等寒冷环境,其冷适应能力是多种机理共同作用的结果,包括酶的低温催化活性、低温下膜流动性的保持、冷休克蛋白、抗冻蛋白以及抗冻保护剂等.低温微生物主要应用于催化低温发酵、表达热不稳定蛋白质、生产抗冻保护剂和冬季治理污水等领域.     

Best of Both Worlds: Simultaneous High-Light and Shade-Tolerance Adaptations within Individual Leaves of the Living Stone Lithops aucampiae

“Living stones” (Lithops spp.) display some of the most extreme morphological and physiological adaptations in the plant kingdom to tolerate the xeric environments in which they grow. The physiological mechanisms that optimise the photosynthetic processes of Lithops spp. while minimising transpirational water loss in both above- and below-ground tissues remain unclear. Our experiments have shown unique simultaneous high-light and shade-tolerant adaptations within individual leaves of Lithops aucampiae. Leaf windows on the upper surfaces of the plant allow sunlight to penetrate to photosynthetic tissues within while sunlight-blocking flavonoid accumulation limits incoming solar radiation and aids screening of harmful UV radiation. Increased concentration of chlorophyll a and greater chlorophyll a∶b in above-ground regions of leaves enable maximum photosynthetic use of incoming light, while inverted conical epidermal cells, increased chlorophyll b, and reduced chlorophyll a∶b ensure maximum absorption and use of low light levels within the below-ground region of the leaf. High NPQ capacity affords physiological flexibility under variable natural light conditions. Our findings demonstrate unprecedented physiological flexibility in a xerophyte and further our understanding of plant responses and adaptations to extreme environments.     

Practical insights on enzyme stabilization

Enzymes are efficient catalysts designed by nature to work in physiological environments of living systems. The best operational conditions to access and convert substrates at the industrial level are different from nature and normally extreme. Strategies to isolate enzymes from extremophiles can redefine new operational conditions, however not always solving all industrial requirements. The stability of enzymes is therefore a key issue on the implementation of the catalysts in industrial processes which require the use of extreme environments that can undergo enzyme instability. Strategies for enzyme stabilization have been exhaustively reviewed, however they lack a practical approach. This review intends to compile and describe the most used approaches for enzyme stabilization highlighting case studies in a practical point of view.     

Metagenomics of microbial and viral life in terrestrial geothermal environments

Geothermally heated regions of Earth, such as terrestrial volcanic areas (fumaroles, hot springs, and geysers) and deep-sea hydrothermal vents, represent a variety of different environments populated by extremophilic archaeal and bacterial microorganisms. Since most of these microbes thriving in such harsh biotopes, they are often recalcitrant to cultivation; therefore, ecological, physiological and phylogenetic studies of these microbial populations have been hampered for a long time. More recently, culture-independent methodologies coupled with the fast development of next generation sequencing technologies as well as with the continuous advances in computational biology, have allowed the production of large amounts of metagenomic data. Specifically, these approaches have assessed the phylogenetic composition and functional potential of microbial consortia thriving within these habitats, shedding light on how extreme physico-chemical conditions and biological interactions have shaped such microbial communities. Metagenomics allowed to better understand that the exposure to an extreme range of selective pressures in such severe environments, accounts for genomic flexibility and metabolic versatility of microbial and viral communities, and makes extreme- and hyper-thermophiles suitable for bioprospecting purposes, representing an interesting source for novel thermostable proteins that can be potentially used in several industrial processes.     

Alternative strategies by thermophilic ants to cope with extreme heat: individual versus colony level traits

Cataglyphis is a fairly homogeneous ant genus which is widespread over the arid regions of the Old World. All Cataglyphis species are thermal specialists which are adapted to extreme environments where they forage at nearly lethal temperatures. This study focusses on two Cataglyphis species which differ considerably in their physical caste systems. These species have developed two alternative mechanisms facing extreme heat. In C. velox , foraging at high surface temperatures is clearly dependent on size: large C. velox workers forage at midday and are able to withstand higher temperatures than small workers. On the other hand, C. rosenhaueri has not developed great physical specialization, but the workers of this species have achieved physiological (such as low cuticular transpiration and metabolic rate), and behavioural adaptations (such as raising their abdomen to protect the vital organs contained in it from high temperatures) to tolerate thermal stress. The result is that small C. rosenhaueri workers may withstand extreme heat conditions in a similar way to large C. velox workers, and much better than small C. velox workers. The different mechanisms used by these two species to withstand extreme heat could reflect fundamental patterns of independent evolution. In some situations, selection may act to promote a relatively narrow size range of adult workers, all of them able to withstand thermal extremes, while in others it may act by producing different worker sizes with different tolerance to environmental conditions.     

Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?

Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory‐based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen‐tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi‐gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.     

Environmental constraints on life histories in Antarctic ecosystems: tempos, timings and predictability

Knowledge of Antarctic biotas and environments has increased dramatically in recent years. There has also been a rapid increase in the use of novel technologies. Despite this, some fundamental aspects of environmental control that structure physiological, ecological and life-history traits in Antarctic organisms have received little attention. Possibly the most important of these is the timing and availability of resources, and the way in which this dictates the tempo or pace of life. The clearest view of this effect comes from comparisons of species living in different habitats. Here, we (i) show that the timing and extent of resource availability, from nutrients to colonisable space, differ across Antarctic marine, intertidal and terrestrial habitats, and (ii) illustrate that these differences affect the rate at which organisms function. Consequently, there are many dramatic biological differences between organisms that live as little as 10 m apart, but have gaping voids between them ecologically.Identifying the effects of environmental timing and predictability requires detailed analysis in a wide context, where Antarctic terrestrial and marine ecosystems are at one extreme of the continuum of available environments for many characteristics including temperature, ice cover and seasonality. Anthropocentrically, Antarctica is harsh and as might be expected terrestrial animal and plant diversity and biomass are restricted. By contrast, Antarctic marine biotas are rich and diverse, and several phyla are represented at levels greater than global averages. There has been much debate on the relative importance of various physical factors that structure the characteristics of Antarctic biotas. This is especially so for temperature and seasonality, and their effects on physiology, life history and biodiversity. More recently, habitat age and persistence through previous ice maxima have been identified as key factors dictating biodiversity and endemism. Modern molecular methods have also recently been incorporated into many traditional areas of polar biology. Environmental predictability dictates many of the biological characters seen in all of these areas of Antarctic research.     

The nervous system of Leptodora kindtii (Branchiopoda, Cladocera) surveyed with confocal scanning microscopy (CLSM), including general remarks on the branchiopod neuromorphological ground pattern

The present study describes the nervous system of Leptodora kindtii Focke, 1844 (Branchiopoda, Cladocera) and compares it with that of other branchiopods, with the aim of determining the characters of the branchiopod neuromorphological ground pattern. L. kindtii shares certain correspondences with all studied branchiopods, including a diffuse deutocerebrum, a separated tritocerebrum and a ventral nerve cord with two commissures in each segment. We document a central complex consisting of central body, a protocerebral bridge and lateral lobes which is homologous to that recently described for the anostracan Artemia salina Linnaeus, 1758 and also known for malacostracans. Other characters in L. kindtii, such as the fused compound eye, are shared with other cladocerans, and some, such as optic fibres, the elongated circumoesophageal connectives and the short ventral nerve cord without ganglia in the thoracal part, are unique to Leptodora. The innervation of the "lateral lobes" of the "lower lip" indicates a correspondence between these lobes and the maxillules. We found evidence that the ganglia of the maxillula and maxilla segments have not been incorporated in other ganglia, as suggested earlier.     

Biotechnological potential of North Sea salt marsh plants—a review of traditional knowledge

Extreme environments are characterised by wide variations in physical factors. Tidal flats and their adjacent salt marshes along the North Sea coast experience this type of variability on a daily, seasonal and annual basis. Plants and animals living in these extreme environments have to adapt to these, at times rapid, changes. This can be done by developing specific physiological responses which often encompass the synthesis of unusual chemicals. A number of salt marsh plants have traditionally been used for medical, nutritional or even industrial purposes. Here, examples are presented for these plants.     

No need for speed: slow development of fungi in extreme environments

Microbial growth under extreme conditions is often slow. This is partly because large amounts of energy are diverted into cellular mechanisms that allow survival under hostile conditions. Because this challenge is universal and diversity in extreme environments is low compared to non-extreme environments, slow-growing microorganisms are not overgrown by other species. In some cases, especially when nutrients are scarce, slow growth was even shown to increase stress tolerance. And in at least some species of extremotolerant and extremophilic fungi, growth rate appears to be coupled with their very unusual morphologies, which in turn may be an adaptation to extreme conditions. However, there is more than one strategy of survival in extreme environments. Fungi that thrive in extremes can be divided into (i) ubiquitous and polyextremotolerant generalists and (ii) rarely isolated specialists with narrow ecological amplitudes. While generalists can compete with mesophilic species, specialists cannot. When adapting to extreme conditions, the risk of an evolutionary trade-off in the form of reduced fitness under mesophilic conditions may limit the maximum stress tolerance achievable by polyextremotolerant generalists. At the same time, specialists are rarely found in mesophilic environments, which allows them to evolve to ever greater extremotolerance, since a reduction of mesophilic fitness is likely to have little impact on their evolutionary success.     

Intraspecific geographic and seasonal physiological variability in an intertidal fish, Girella laevifrons, along a climatic gradient

Metabolic rate and condition factor ( K ) of juvenile Girella laevifrons were highest in southern populations along the Chilean coast. Since adults of G. laevifrons complete their life cycle in subtidal waters, the results suggest a metabolic cold adaptation in juveniles of this species and physiological compensation that enable them to move early to subtidal environments for reproduction     

中国温泉微生物物种多样性及其酶活性研究进展

微生物作为生物群体的重要组成成员,其生长受外界物化条件(如温度、盐度、pH等)影响较大。温泉作为极端水生环境之一,属于相对稳定且较为特殊的生态系统,使生长于其中的微生物可能具有适应高温等特殊生境的独特生存生理机制,具体表现为微生物物种及其活性次级代谢产物呈现出一定的多样性与新颖性。本文从菌株物种多样性分析及其酶活性研究方面,综述了近5年来国内温泉微生物相关研究进展,以期为温泉等极端环境微生物资源开发与保护提供参考。     

Diapause, a potent force in the evolution of freshwater crustaceans

After a brief historical review of the discovery of diapause in freshwater crustaceans, its dramatic nature in certain cyclopoid copepods, in which diapausing individuals may occur at densities of > 10⁶ per m², is used to illustrate the enormous ecological significance of the phenomenon. Some of the problems presented by dispause in cyclopoid copepods are noted, including the different behaviour in different lakes of what appears to be a single species. Different physiological cues or different genetic endowments are clearly involved.The wider incidence of diapause in freshwater copepods and ostracods is noted.Among freshwater crustaceans it it the Branchiopoda that have universally adopted diapause, always at the egg stage. Even such an ancient order as the Anostraca, perhaps the most primitive of all crustaceans, produces elaborately constructed resting eggs that are capable of cryptobiosis, can remain viable in a dry state for long periods, and can tolerate extreme conditions. The nature of branchiopod resting eggs is briefly reviewed. Of these, only those of the Anomopoda are protected by containers derived from the parental carapace. These are mechanically complex in the most advanced species but, as shown by fossils, are extremely ancient structures.Factors initiating the onset and termination of diapause in branchiopods are briefly noted, and the process of hatching of resting eggs is outlined.     

极端环境下嗜热酸甲烷营养细菌研究进展

甲烷营养细菌能够将温室气体甲烷(CH4)转化为CO2或生物质,在碳生物地球化学循环及缓解由温室气体导致的全球气候变化方面发挥着重要的作用.甲烷营养细菌生存的条件范围较为广泛,但在中性pH (5～8)和中温(20～35℃)范围内生长最佳.系统进化分析认为,它们均属于γ-或α-变形菌门(Proteobacteria).最近3项独立完成的研究从极端热酸(pH接近1,温度高于50℃)环境中分离获得了具有甲烷氧化(营养)功能的微生物,经鉴定均属于疣微菌门(Verrucomicrobia).这些全新的、不同于以往的研究结果不仅是对现有关于甲烷营养细菌生态学认知的进一步拓展,同时也暗示着可能存在着新型的、由微生物介导的CH4氧化途径与机制. 因此,特就极端环境中嗜热嗜酸甲烷营养细菌的最新研究进展作一概述.     

Perspectives on environmental adaptability and physiological polymorphism in thermoregulation

The environmental adaptability of human beings has progressed according to various environments experienced in the course of evolution. Therefore, various phenotypes for environmental adaptability exist and are considered to be physiological polymorphism. Physiological polymorphism in thermoregulation is influenced by genotype, individual characteristics, environmental factors, cultural factors, etc. Moreover, it is thought that physiological polymorphism is evidenced more clearly in physiological responses to extreme situations and/or changing conditions than in environments where homeostasis is easily maintained. In the field of physiological anthropology, I think that it is important not only to discover the physiological responses that demonstrate polymorphism, but also to hypothesize about the mechanisms and the processes by which such polymorphisms were formed, and their meaning for human beings. Such discussions may be supposed to lead to an evaluation of the environmental adaptability of humans from the viewpoint of physiological anthropology.     

Life in the extreme: thermoacidophilic methanotrophy

Aerobic methane-oxidizing bacteria (methanotrophs) have a key role in the global carbon cycle, converting methane to biomass and carbon dioxide. Although these bacteria have been isolated from many environments, until recently, it was not known if they survived, much less thrived in thermoacidic environments, that is, locations with pH values of approximately 1 and temperatures greater than 50 degrees C. Recently, three independent studies have isolated unusual methanotrophs from such extreme environments, expanding the known functional and phylogenetic diversity of methanotrophs.