Desiccated State Research Articles

Tripogon loliiformis elicits a rapid physiological and structural response to dehydration for desiccation tolerance.

Resurrection plants can withstand extreme dehydration to an air-dry state and then recover upon receiving water. Tripogon loliiformis (F.Muell.) C.E.Hubb. is a largely uncharacterised native Australian desiccation-tolerant grass that resurrects from the desiccated state within 72h. Using a combination of structural and physiological techniques the structural and physiological features that enable T. loliiformis to tolerate desiccation were investigated. These features include: (i) a myriad of structural changes such as leaf folding, cell wall folding and vacuole fragmentation that mitigate desiccation stress, (ii) potential role of sclerenchymatous tissue within leaf folding and radiation protection, (iii) retention of ~70% chlorophyll in the desiccated state, (iv) early response of photosynthesis to dehydration by 50% reduction and ceasing completely at 80 and 70% relative water content, respectively, (v) a sharp increase in electrolyte leakage during dehydration, and (vi) confirmation of membrane integrity throughout desiccation and rehydration. Taken together, these results demonstrate that T. loliiformis implements a range of structural and physiological mechanisms that minimise mechanical, oxidative and irradiation stress. These results provide powerful insights into tolerance mechanisms for potential utilisation in the enhancement of stress-tolerance in crop plants.

Effect of Drying Temperature on High Quality Functional Processed Products of Chinese Matrimony Vine

Background : Chinese matrimony vine (Lycium chinense Mill.) is a deciduous shrub belonging to the Solanaceae. The leaves are used as an alternative raw material replacing dried fruits associated with high production costs in many industires. The aim of this experiment was to determine the effect of drying temperature on the leaves used in the manufacture of functional products. Methods and Results : The leaves of Chinese matrimony vine were harvested when the plant height reached 60 - 70 ㎝ in the spring and treated at four different temperatures (40℃, 50℃, 60℃ and 70℃). The time to reach the desiccation state of 20% was 63 h at 40℃, 37 h at 50℃, 17 h at 60℃ and 11 h at 70℃. The drying rate per hour was 1.28% at 40℃, 2.25% at 50℃, 4.94% at 60℃ and 7.60% at 70℃. No significant difference were observed in ash, crude fat, polyphenol or rutin content of treated samples. Crude protein and betaine content decreased with higher dry temperatures. Nitrogen free extract of the treated samples increased with higher drying temperatures. Conclusions : Taking into consideration drying time, drying rate, color value, energy consumption and functional ingredients is advantageous to dry the leaves of the Chinese matrimony vine at 60℃ using a hot air agricultural dryer.

The fate of proteins in outer space

It is well established that any properly conducted biophysical studies of proteins must take appropriate account of solvent. For water-soluble proteins it has been an article of faith that water is largely responsible for stabilizing the fold, a notion that has recently come under increasing scrutiny. Further, there are some instances when proteins are studied experimentally in the absence of solvent, as in matrix-assisted laser desorption/ionization or electrospray mass spectrometry, for example, or in organic solvents for protein engineering purposes. Apart from these considerations, there is considerable speculation as to whether there is life on planets other than Earth, where conditions including the presence of water (both in liquid or vapor form and indeed ice), temperature and pressure may be vastly different from those prevailing on Earth. Mars, for example, has only 0.6% of Earth's mean atmospheric pressure which presents profound problems to protein structures, as this paper and a large corpus of experimental work demonstrate. Similar objections will most likely apply in the case of most exoplanets and other bodies such as comets whose chemistry and climate are still largely unknown. This poses the question, how do proteins survive in these different environments? In order to cast some light on these issues we have conducted a series of molecular dynamics simulations on protein dehydration under a variety of conditions. We find that, while proteins undergoing dehydration can retain their integrity for a short duration they ultimately become disordered, and we further show that the disordering can be retarded if superficial water is kept in place on the surface. These findings are compared with other published results on protein solvation in an astrobiological and astrochemical setting. Inter alia, our results suggest that there are limits as to what to expect in terms of the existence of possible extraterrestrial forms as well to what can be achieved in experimental investigations on living systems despatched from Earth. This finding may appear to undermine currently held hopes that life will be found on nearby planets, but it is important to be aware that the presence of ice and water are by themselves not sufficient; there has to be an atmosphere which includes water vapor at a sufficiently high partial pressure for proteins to be active. A possible scenario in which there has been a history of adequate water vapor pressure which allowed organisms to prepare for a future dessicated state by forming suitable protective capsules cannot of course be ruled out.

A novel approach for the cryodesiccated preservation of tissue-engineered skin substitutes with trehalose

Tissue-engineered skin (TES) holds great promise for wound healing in the clinic. However, optimized preservation methods remain an obstacle for its wide application. In this experimental work, we developed a novel approach to preserve TES in the desiccated state with trehalose. The uptake of trehalose by fibroblasts under various conditions, including the trehalose concentration, incubation temperature and time, was studied. The cell viability was investigated by the MTT assay and CFSE/PI staining after cryodesiccation and rehydration. TES was then prepared and incubated with trehalose, and the wound healing effect was investigated after desiccated preservation. The results showed that the optimized conditions for trehalose uptake by fibroblasts were incubation in 200mM trehalose at 37°C for 8h. Cryodesiccated cells and TES maintained 37.55% and 28.31% viabilities of controls, respectively. Furthermore, cryodesiccated TES exhibited a similar wound healing effect to normal TES. This novel approach enabled the preservation and transportation of TES at ambient temperature with a prolonged shelf time, which provides great advantages for the application of TES.

Evidence for water deficit-induced mass increases of raffinose family oligosaccharides (RFOs) in the leaves of three Craterostigma resurrection plant species.

The leaves of the resurrection plant Craterostigma plantagineum accumulate sucrose during dehydration, via a conversion from the unusual C8 ketose-sugar 2-octulose. However, raffinose family oligosaccharides (RFOs) have been shown to be major photosynthetic products in this plant. The tetrasaccharide stachyose is the major phloem-mobile carbohydrate and is used as a carbon store in roots. It has been suggested that this carbon store is remobilized during rehydration, presumably for cellular repair processes. We examined the effects of water deficit on the leaf water-soluble carbohydrate profiles of three Craterostigma species. Apart from the classical 2-octulose-to-sucrose interconversion, there was a strong water deficit-associated mass increase of RFOs up to the pentasaccharide verbascose. However, the activities of three dedicated RFO biosynthetic enzymes (raffinose, stachyose, and verbascose synthase) was not correlated with RFO accumulation, suggesting that biosynthetic enzyme activities measured in the early stages of water-deficit were sufficient to synthesize enough galactinol and lead to RFO accumulation in the leaves. Our findings are suggestive of RFOs providing additional carbohydrate-based stress protection to the leaves of these plants during the desiccated state.

An easily reversible structural change underlies mechanisms enabling desert crust cyanobacteria to survive desiccation

Biological desert sand crusts are the foundation of desert ecosystems, stabilizing the sands and allowing colonization by higher order organisms. The first colonizers of the desert sands are cyanobacteria. Facing the harsh conditions of the desert, these organisms must withstand frequent desiccation–hydration cycles, combined with high light intensities. Here, we characterize structural and functional modifications to the photosynthetic apparatus that enable a cyanobacterium, Leptolyngbya sp., to thrive under these conditions.Using multiple in vivo spectroscopic and imaging techniques, we identified two complementary mechanisms for dissipating absorbed energy in the desiccated state. The first mechanism involves the reorganization of the phycobilisome antenna system, increasing excitonic coupling between antenna components. This provides better energy dissipation in the antenna rather than directed exciton transfer to the reaction center. The second mechanism is driven by constriction of the thylakoid lumen which limits diffusion of plastocyanin to P700. The accumulation of P700+ not only prevents light-induced charge separation but also efficiently quenches excitation energy.These protection mechanisms employ existing components of the photosynthetic apparatus, forming two distinct functional modes. Small changes in the structure of the thylakoid membranes are sufficient for quenching of all absorbed energy in the desiccated state, protecting the photosynthetic apparatus from photoinhibitory damage. These changes can be easily reversed upon rehydration, returning the system to its high photosynthetic quantum efficiency.

Long-term preservation of silica gel-encapsulated bacterial biocatalysts by desiccation

Whole cells encapsulated in silica gels are used in a wide variety of applications in biomedicine, biotechnology and bioremediation. Drying after encapsulation is desirable to enhance the strength of the gel and to make it lighter, facilitating its use, storage and transportation. However, preserving biological activity of the cells in a desiccated state remains a formidable challenge. In this study, different drying conditions for a silica gel-encapsulated bacterial biocatalyst (atrazine biodegrading Escherichia coli) were studied to enhance mechanical properties while sustaining long-term biocatalytic activity of the bacteria. Effects of lyoprotectant solutions containing 0.4 M sucrose, 0.4 M trehalose or 30 % (wt/wt) glycerol on the activity of the encapsulated bacteria during drying were investigated. It was determined that two orders of magnitude increase in the elastic modulus (E) and the compressive stress at failure (σ) of the gel could be achieved by drying, independent of the drying rate. It was shown that partially desiccated silica gels preserved and enhanced the biocatalytic activity of the encapsulated bacteria up to a critical drying level. Atrazine biodegradation activity of encapsulated bacteria suspended with 0.4 M sucrose and PBS increased with increasing water removal, reaching a maximum at 68 % water loss. This enhanced activity was sustained for 3 months, when the gels were stored at 4 °C.

Proteome analysis of dormancy-released seeds of Fraxinus mandshurica Rupr. in response to re-dehydration under different conditions.

Desiccation tolerance is the ability of orthodox seeds to achieve equilibrium with atmospheric relative humidity and to survive in this state. Understanding how orthodox seeds respond to dehydration is important for improving quality and long-term storage of seeds under low temperature and drought stress conditions. Long-term storage of seeds is an artificial situation, because in most natural situations a seed that has been shed may not remain in a desiccated state for very long, and if dormant it may undergo repeated cycles of hydration. Different types of seeds are differentially sensitive to desiccation and this directly affects long-term storage. For these reasons, many researchers are investigating loss of desiccation tolerance during orthodox seed development to understand how it is acquired. In this study, the orthodox seed proteome response of Fraxinus mandshurica Rupr. to dehydration (to a relative water content of 10%, which mimics seed dehydration) was investigated under four different conditions viz. 20 °C; 20 °C with silica gel; 1 °C; and 1 °C after pretreatment with Ca2+. Proteins from seeds dehydrated under different conditions were extracted and separated by two-dimensional difference gel electrophoresis (2D-DIGE). A total of 2919 protein spots were detected, and high-resolution 2D-DIGE indicated there were 27 differentially expressed. Seven of these were identified using MALDI TOF/TOF mass spectrometry. Inferences from bioinformatics annotations of these proteins established the possible involvement of detoxifying enzymes, transport proteins, and nucleotide metabolism enzymes in response to dehydration. Of the seven differentially abundant proteins, the amounts of six were down-regulated and one was up-regulated. Also, a putative acyl-coenzyme A oxidase of the glyoxylate cycle increased in abundance. In particular, the presence of kinesin-1, a protein important for regulation and cargo interaction, was up-regulated in seeds exposed to low temperature dehydration. Kinesin-1 is present in all major lineages, but it is rarely detected in seed desiccation tolerance of woody species. These observations provide new insight into the proteome of seeds in deep dormancy under different desiccation conditions.

‘Weed it out’a Digital Reference Tool for Agricultural Community

India is a rural country with most of its population engaged in agriculture, which is marred by many problems like inclement weather, poor fertile soils, pests and weeds. Weeds cause extensive damage to crops and are often mismanaged due to improper information. The study is an attempt to build a digital collection of Indian weeds using greenstone digital library software. Extensive field trips were made to capture images of weeds with high resolution cameras. Specimens of weeds spotted in desiccated state or not spotted in the fields due to short life span were taken from authentic secondary sources. Each specimen was assigned adequate metadata for easy identification and reference. Through the use of greenstone open source software, a digital library was built. The digital collection is fully text searchable and browsable through scientific name, habitat, season, local name and family. The collection can serve as a digital reference tool for farmers, students, researchers for identification of different weeds.

Taxonomic revision of the Taractrocera ilia (Waterhouse) complex (Lepidoptera : Hesperiidae) from north-western Australia and mainland New Guinea based on morphological and molecular data

The taxonomy of the Taractrocera ilia complex is revised based on evidence from multiple sources, including phenotypic characters (wing colour pattern elements, morphology of adult and immature stages), ecology and molecular data. Three species are recognised in the complex: T. psammopetra Braby, sp. nov. is restricted to north-western Australia where it has a disjunct distribution (Kimberley and the central Arnhem Land plateau); T. ilia (Waterhouse, 1932) sensu stricto is endemic to the central Arnhem Land plateau where it is narrowly sympatric with T. psammopetra; while T. beta Evans, 1934, stat. nov. is allopatric and endemic to mainland New Guinea. Each species is illustrated and diagnosed based on comparative morphology of the adult stage, including androconia and male and female genitalia, and information on type material, biology, distribution and habitat is summarised and discussed. A phylogenetic hypothesis of the Australian species of Taractrocera based on combined analysis of molecular data (2.6 kb: mitochondrial COI and nuclear CAD, MDH, wingless) revealed that T. psammopetra is monophyletic and sister to T. ilia, with an overall mean divergence of 3.4% between the two species; the genus Taractrocera, however, emerged as polyphyletic. For T. psammopetra and T. ilia, the life history, including details of larval food plant specialisation and morphology of the immature stages, is described for the first time. Larvae of T. psammopetra and T. ilia specialise on ‘resurrection’ grasses, Micraira spp. (Poaceae), which typically grow as moss-like, mat-forming pioneer plants on shallow rock surfaces comprising open sandstone pavements or on rock ledges and under rock overhangs of sandstone cliffs. These food plants, together with the butterflies that they support, are a characteristic element of the sandstone plateaux of the Kimberley and central Arnhem Land, and they exemplify patterns of diversification, endemism and adaptation to these unique environments within the Australian monsoon tropics. Facultative larval diapause is recorded for both T. psammopetra and T. ilia in which larvae (all instars, but particularly the final instar) may suspend feeding for up to six months during the dry season when the food plants typically dehydrate. It is hypothesised that larval diapause may be the most flexible strategy to ameliorate seasonal adversity of the dry season and the onset, duration and inter-annual cycle of monsoon rainfall during the wet season, which is highly variable and unpredictable, given that Micraira can revive rapidly from a desiccated state after rainfall. http://zoobank.org/urn:lsid:zoobank.org:pub:51438A5E-048C-4C72-AD22-3FD176ECBA55

Micro-morphology, ultrastructure and chemical composition changes ofBryum argenteumfrom a desert biological soil crust following one-year desiccation

Biological soil crusts dominated by mosses are commonly found in arid and semiarid areas, where mosses spend large parts of their time in a state of intense desiccation. The effective recovery of moss crusts after long-term desiccation is vital for their survival. In this study, we analyzed the changes in micromorphology, ultrastructure and chemical composition in Bryum argenteum samples desiccated for 1 week or 1 year. We used non-destructive and anhydrous methods of analysis, including scanning electron microscopy, transmission electron microscopy and Fourier transform infrared analysis. After long-term desiccation (1 year), B. argenteum samples showed a rapid recovery of FV/FM in the light after rehydration. For the 1-year desiccated samples, the thallus remained intact but shrunken. Within the thallus, cell arrangement was disorderly, cell shapes were irregular, and cell walls were thinner. Inside cells, chloroplasts remained intact, but some thylakoids were degraded. In terms of the major cellular components, the lipid and carbohydrate contents increased, the numbers of α helixes and β sheets in protein secondary structures increased, while the number of turn structures in proteins decreased. The changes in protein secondary structure appear to be an important factor in the tolerance of B. argenteum to long-term desiccation. The recovery mechanisms that function after rehydration include processes for the repair of protein conformation and the re-synthesis of thylakoids.

AB5075, a Highly Virulent Isolate of Acinetobacter baumannii, as a Model Strain for the Evaluation of Pathogenesis and Antimicrobial Treatments.

ABSTRACTAcinetobacter baumannii is recognized as an emerging bacterial pathogen because of traits such as prolonged survival in a desiccated state, effective nosocomial transmission, and an inherent ability to acquire antibiotic resistance genes. A pressing need in the field of A. baumannii research is a suitable model strain that is representative of current clinical isolates, is highly virulent in established animal models, and can be genetically manipulated. To identify a suitable strain, a genetically diverse set of recent U.S. military clinical isolates was assessed. Pulsed-field gel electrophoresis and multiplex PCR determined the genetic diversity of 33 A. baumannii isolates. Subsequently, five representative isolates were tested in murine pulmonary and Galleria mellonella models of infection. Infections with one strain, AB5075, were considerably more severe in both animal models than those with other isolates, as there was a significant decrease in survival rates. AB5075 also caused osteomyelitis in a rat open fracture model, while another isolate did not. Additionally, a Tn5 transposon library was successfully generated in AB5075, and the insertion of exogenous genes into the AB5075 chromosome via Tn7 was completed, suggesting that this isolate may be genetically amenable for research purposes. Finally, proof-of-concept experiments with the antibiotic rifampin showed that this strain can be used in animal models to assess therapies under numerous parameters, including survival rates and lung bacterial burden. We propose that AB5075 can serve as a model strain for A. baumannii pathogenesis due to its relatively recent isolation, multidrug resistance, reproducible virulence in animal models, and genetic tractability.

Diversity, molecular phylogeny, and metabolic activity of cyanobacteria in biological soil crusts from Santiniketan (India)

The biological soil crusts that appear on the arid soils of Santiniketan, India soon after receiving monsoon rain were studied. The phototrophic organisms in the crusts were principally composed of sheath-forming cyanobacteria belonging to the genera Scytonema and Tolypothrix as the major components along with associated species of 14 different genera. 16S ribosomal RNA (rRNA) sequencing of these organisms showed that they formed a cluster quite different from Leptolyngbya, Microcoleus, and Phormidium, however, were close to Scytonema and Tolypothrix reported from similar biofilms on soils of USA and Costa Rica. All these major cyanobacteria species in soil crust possessed scytonemin in higher proportion than chlorophyll a, suggesting its role in protection from high solar irradiance and UV. Dried crusts started respiring soon after wetting followed by photosynthesis. Nitrogenase activity also revived after 2 to 12 h of wetting and progressed rapidly with longer period of wet conditions coinciding with appearance of heterocysts in the filaments. These results showed that a number of cyanobacteria with distinct sheath layer survived within the soil crusts in desiccated state and revived their metabolic activity soon after receiving monsoon rain thus contributing to carbon as well as nitrogen fixation in the environment and to nutrient mobilization making the soil productive.

Design of novel cell penetrating peptides for the delivery of trehalose into mammalian cells

Stabilization of cells in a desiccated state can significantly simplify the storage and transportation and save expenses for clinical applications. Introduction of the impermeable disaccharide, trehalose, into cells is an important step to improve the desiccation tolerance of cells. In this study, a novel cell penetrating peptide, KRKRWHW, was developed based on molecular simulations. The peptide exhibited little cytotoxicity and high penetrating efficiency into mammalian cells. The cell viability of mouse embryonic fibroblasts (MEFs) after the incubation with various concentrations of KRKRWHW from 0.01mM to 5mM at 37°C for 4h was maintained at around 100%. The peptide was able to penetrate into MEFs within 1h at 37°C with an efficiency of around 90% at 0.1mM. Trehalose, as a cargo coupled with the peptide of KRKRWHW through hydrogen bond and π–π bond, was successfully loaded into the MEFs. This novel peptide provides a novel approach for the delivery of trehalose into mammalian cells.

Physiological history may mask the inherent inducible desiccation tolerance strategy of the desert moss Crossidium crassinerve

Shoots of bryophytes collected in the desiccated state from the field are likely to be hardened to desiccation tolerance (DT) to varying degrees. To account for this, most studies on DT include a relatively short deacclimation period. However, no study has experimentally determined the appropriate deacclimation time for any bryophyte species. Our purposes are to (i) determine if 'field effects' are biologically relevant to DT studies and how long a deacclimation period is required to remove them; and (ii) utilise field versus cultured shoot responses within the context of a deacclimation period to elucidate the ecological strategy of DT. Our hypothesis (based on an extensive literature on DT) is that a deacclimation period from 24 to 72 h should be sufficient to eliminate historical stress effects on the physiology of the shoots and allow an accurate determination of the inherent ecological DT strategy (constitutive or inducible). We determined, however, using chlorophyll fluorescence and visual estimates of shoot damage, that field-collected shoots of the desert moss Crossidium crassinerve required an experimental deacclimation period of >7 days before field effects were removed, and revealed an ecological DT strategy of inducible DT. If the deacclimation period was <6 days, the shoot response conformed to an ecological strategy of constitutive protection. Thus the presence of field effects can obscure the ecological strategy of desiccation tolerance exhibited by the species, and this translates into a need to re-evaluate previous mechanistic and ecological studies of desiccation tolerance in plants.

Naming the Nation: A Poetic Retrospect

The work of conjuring settler nationhood for literary space was a self-conscious, colonial, and then nationalist task for both and New Zealand, and as literary space becomes increasingly global or, as Wai-Chee Dimock and Lawrence Buell would put it, planetary, that conjuring must be repeated for broader (and usually more powerful) reading formations and in ways that can guarantee no singular literary tradition for either nation. This conjuring project is powerfully present in poems bearing the name of the country in which they were written, apostrophizing that national/colonial entity and bringing it into a literary reading space. The Australian colonial poets, from the first half of the nineteenth century onward, sought to trope the in global and imperial terms: in 1859, just before John Brown's raid on Harpers Ferry, for instance, Caroline Carlton's Song of Australia took pains to declare that No shackled slave can breathe the air / Fairest of Britain's daughters' fair-Australia! Repeated in the national anthem Advance Fair, which was penned by Peter Dodds McCormick in 1878 but did not replace God Save the Queen until 1984, the fairness of settler mained at for poetry, as it did for the non-white and Indigenous populations through Federation in 1900 and beyond. Bernard O'Dowd's poem from the year of Federation conjures Australia as the Last sea-thing dredged by sailor Time from Space-imperial cartography and European temporalities write Australian literary space as already belated even as it is inaugurated.A 1932 poem titled Australia from the long-lived feminist and socialist Mary Gilmore begins by lamenting the censured, absented Aboriginal names for country replaced by Australia. It is sensitive and typically elegiac in pondering the differing gaps between the land and its perceivers' apprehension of it: between landscape and language, place and speech.There was great beauty in the names her people called her,Shaping to patterns of sounds the form of their words;They wove to measure of speech the cry of the bird,And the voices that rose from the reeds of the cowal.All these Australia poems address the classically postcolonial question of how to leverage a sense of cultural difference that would speak back to British colonial sway, yet find credibility within the Anglophile canon that, as Leigh Dale has has pointed out in The English Men, came along with Anglo-Celtic settlement. ( AngloCeltic was often used both to acknowledge the Irish element in the nineteenth-century diaspora and to recognize that migrants from other European countries had a different status within Australia.) Cultural nationalism is the logical response. Settler Australians sought their own sense of identity, to repudiate the stigma of inferior belatedness that Anglocentric discourse can propagate. But the search for identity not only effaced the tear in the national fabric represented by excluding Indigenous people from that identity, it also had the potential to lead to the facile, rousing optimism appropriate only to national songs.This optimism is precisely the target of A. D. Hope's satiric, yet deeply felt, 1939 poem Australia.They call her a young country, but they lie:She is the last of lands, the emptiest,A woman beyond her change of life, a breastStill tender but within the womb is dry.Hope undoes the Austral trope, exposing its gendered elements, too; the virtues that an optimistic brand of settler nationalism would claim for Australia-that it is fresh, virginal, and untainted by or tragedy-are not there. Geologically the continent is old, and culturally it is barren: Without songs, architecture, and history echoes the charges of antipodean cultural failure familiar from European first encounters. Yet it is precisely the state of Australia's cultural desiccation that lends it some promise for Hope-hoping, if still from the desert the prophets come // Such savage and scarlet as no green hills dare / Springs in that waste [. …

Dry up and survive: the role of antioxidant defences in anhydrobiotic organisms

Although the evolution of life has turned oxygen into a vital chemical for aerobic organisms, this element can also have deleterious effects on living systems through the production of oxidative stress. This is a process resulting from an imbalance between the excessive production of Reactive Oxygen Species (ROS) and the limited action of antioxidant defences. It is a particularly harmful health risk factor, involved in the development of several chronic human pathologies and believed to play a major role in the ageing process. Consequently aerobic metabolism needs a stringent control of ROS. Water too is essential for life, but some organisms widespread throughout nature have the ability to survive complete desiccation by entering an anhydrobiotic state. The loss of water induces changes in metabolism, cell membrane organization, and molecular composition. In the anhydrobiotic state, high temperatures, high humidity, light exposure, and high oxygen partial pressure negatively affect organism survival and directly influence the time required to reactivate the metabolism after a period of desiccation. These abiotic factors induce damages that are accumulated in proportion to the time spent in the desiccated state, potentially leading to organism death. Oxidative stress seems to be one of the most deleterious damages due to water depletion, therefore anhydrobiosis also needs a stringent control of ROS production. Anhydrobiotic organisms seem to apply two main strategies to cope with the danger of oxygen toxicity, namely an increased efficiency of antioxidant defences and a metabolic control of both energy-production and energy-consuming processes. Experimental studies provide evidence that antioxidant defences such as ROS scavenging enzymes ( e.g. peroxidases, catalases, superoxide dismutase, glutathione peroxidases) and other molecules ( e.g. glutathione, carotenoids, vitamins C and E) represent a key group of molecules required for desiccation tolerance in anhydrobiotic organisms. The action of these molecules emphasises the need for redox balancing in anhydrobiotic organisms including tardigrades and chironomid larvae.

Characterization of cyanobacteria isolated from biofilms on stone monuments at Santiniketan, India

Cyanobacterial biofilms occurring on the exterior of three stone monuments at Santiniketan, India were analyzed. Species of Scytonema and Tolypothrix were the major components of these biofilms. Identification was obtained by morphometric procedures and 16S rRNA gene sequencing. Biofilms cultured for prolonged periods revealed the presence of several other cyanobacteria belonging to 14 different genera. Cyanobacteria on stone in the tropical environment of India formed a distinct cluster that was quite different from that of cyanobacteria reported for a similar substratum in temperate regions. Absorption spectra of the organisms from Santiniketan showed a high quantity of scytonemin, mycosporine-like amino acids, and carotenoids. All of the organisms survived in a desiccated state and rapidly revived after wetting. The organisms were heterocystous and nitrogenase activity was reactivated within 24 h of wetting by which time heterocysts in their filaments had also appeared.

The response of Asterochloris erici (Ahmadjian) Skaloud et Peksa to desiccation: a proteomic approach

The study of desiccation tolerance of lichens, and of their chlorobionts in particular, has frequently focused on the antioxidant system that protects the cell against photo-oxidative stress during dehydration/rehydration cycles. In this study, we used proteomic and transcript analyses to assess the changes associated with desiccation in the isolated phycobiont Asterochloris erici. Algae were dried either slowly (5-6 h) or rapidly (<60 min), and rehydrated after 24 h in the desiccated state. To identify proteins that accumulated during the drying or rehydration processes, we employed two-dimensional (2D) difference gel electrophoresis (DIGE) coupled with individual protein identification using trypsin digestion and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Proteomic analyses revealed that desiccation caused an increase in relative abundance of only 11-13 proteins, regardless of drying rate, involved in glycolysis, cellular protection, cytoskeleton, cell cycle, and targeting and degradation. Transcripts of five Hsp90 and two β-tubulin genes accumulated primarily at the end of the dehydration process. In addition, transmission electron microscopy (TEM) images indicate that ultrastructural cell injuries, perhaps resulting from physical or mechanical stress rather than metabolic damage, were more intense after rapid dehydration. This occurred with no major change in the proteome. These results suggest that desiccation tolerance of A. erici is achieved by constitutive mechanisms.

Understanding desiccation tolerance using the resurrection plant Boea hygrometrica as a model system.

Vegetative tissues of Boea hygrometrica, a member of the Gesneriaceae family, can tolerate severe water loss to desiccated state and fully recover upon rehydration. Unlike many other so called “resurrection plants,” the detached leaves of B. hygrometrica also possess the same level of capacity for desiccation tolerance (DT) as that of whole plant. B. hygrometrica is distributed widely from the tropics to northern temperate regions in East Asia and grows vigorously in areas around limestone rocks, where dehydration occurs frequently, rapidly, and profoundly. The properties of detached B. hygrometrica leaves and relative ease of culture have made it a useful system to study the adaptive mechanisms of DT. Extensive studies have been conducted to identify the physiological, cellular, and molecular mechanisms underlying DT in the last decade, including specific responses to water stress, such as cell wall folding and pigment-protein complex stabilizing in desiccated leaves. In this review, the insight into the structural, physiological, and biochemical, and molecular alterations that accompany the acquisition of DT in B. hygrometrica is described. Finally a future perspective is proposed, with an emphasis on the emerging regulatory roles of retroelements and histone modifications in the acquisition of DT, and the need of establishment of genome sequence database and high throughput techniques to identify novel regulators for fully understanding of the matrix of DT.