Desiccation Process Research Articles

Dissecting the temporal genetic networks programming soybean embryo development from embryonic morphogenesis to post-germination

Key messageDesiccation-stage transcription factors perform similar functions, with early ones focused on desiccation tolerance and later ones on development. Gene networks governing late embryo development diverge between soybean and Arabidopsis.To understand gene activities programming seed embryo development, we profiled the soybean embryo transcriptome across embryonic morphogenesis through post-germination. Transcriptomic landscapes across embryo development feature highly prevalent transcripts, categorized into early and late groups, with shared and distinct functions. During the mid-storage reserve accumulation stage, the upregulated genes are enriched with regulatory tasks at both the transcriptional and chromatin levels, including DNA methylation and chromatin remodeling. The epigenetic-related functions also dominate in the upregulated genes during germination, involving core histone variants and histone chaperones. Gene network analysis reveals both stage-specific modules and modules active across multiple stages. The desiccation-associated gene module integrates diverse transcription factors (TFs) that are sequentially active during different desiccation stages, transitioning from abiotic stress functions early on to developmental functions later. Two TFs, active during the early and mid-desiccation stages were functionally assessed in Arabidopsis overexpression lines to uncover their potential roles in desiccation processes. Interestingly, nearly half of the Arabidopsis orthologs of soybean TFs active in the desiccation-associated module are inactive during Arabidopsis desiccation. Our results reveal that chromatin and transcriptional regulation coordinate during mid-storage reserve accumulation, while distinct epigenetic mechanisms drive germination. Additionally, gene modules either perform stage-specific functions or are required across multiple stages, and gene networks during late embryogenesis diverge between soybean and Arabidopsis. Our studies provide new information on the biological processes and gene networks underlying development from embryonic morphogenesis to post-germination.

Unique Features of Extremely Halophilic Microbiota Inhabiting Solar Saltworks Fields of Vietnam.

The artificial solar saltworks fields of Hon Khoi are important industrial and biodiversity resources in southern Vietnam. Most hypersaline environments in this area are characterized by saturated salinity, nearly neutral pH, intense ultraviolet radiation, elevated temperatures and fast desiccation processes. However, the extremely halophilic prokaryotic communities associated with these stressful environments remain uninvestigated. To fill this gap, a metabarcoding approach was conducted to characterize these communities by comparing them with solar salterns in northern Vietnam as well as with the Italian salterns of Motya and Trapani. Sequencing analyses revealed that the multiple reuses of crystallization ponds apparently create significant perturbations and structural instability in prokaryotic consortia. However, some interesting features were noticed when we examined the diversity of ultra-small prokaryotes belonging to Patescibacteria and DPANN Archaea. Surprisingly, we found at least five deeply branched clades, two from Patescibacteria and three from DPANN Archaea, which seem to be quite specific to the Hon Khoi saltworks field ecosystem and can be considered as a part of biogeographical connotation. Further studies are needed to characterize these uncultivated taxa, to isolate and cultivate them, which will allow us to elucidate their ecological role in these hypersaline habitats and to explore their biotechnological and biomedical potential.

Anisotropic hydraulic conductivity of as-compacted, bare and vegetated soils

Soils are generally considered anisotropic with respect to hydraulic conductivity, while the evolution of the anisotropy condition is unknown for bare and vegetated soils. Therefore, the main goal of this study is to compare the anisotropic hydraulic conductivity of as-compacted, bare and vegetated specimens. Accordingly, a series of 54 hydraulic conductivity tests was conducted in a custom-made cube triaxial permeameter. The as-compacted specimens were revealed as isotropic because the loosely packed preparation procedure resulted in a dominant flocculent structure. However, a five-fold increase in the anisotropy ratio of bare specimens was measured along the isotropic loading path because of the induced surficial degradation zone formed by irrigation and desiccation processes, as evident in preliminary observations and crack network analysis. The variations in anisotropy ratio compared against void ratio function of vegetated soil generally fall below the corresponding function of the bare soil. The function was revealed to have a crossed nature, varying from sub-isotropic to super-isotropic states, corresponding to the lower and upper bounds of 0·3 and 3, respectively. It was postulated that vegetation impacts the flow differently by reducing the potential of desiccation cracks, creating preferential flow through the propagation of primary roots and clogging flow channels by secondary roots.

Hyperexpansion of genetic diversity and metabolic capacity of extremophilic bacteria and archaea in ancient Andean lake sediments

BackgroundThe Andean Altiplano hosts a repertoire of high-altitude lakes with harsh conditions for life. These lakes are undergoing a process of desiccation caused by the current climate, leaving terraces exposed to extreme atmospheric conditions and serving as analogs to Martian paleolake basins. Microbiomes in Altiplano lake terraces have been poorly studied, enclosing uncultured lineages and a great opportunity to understand environmental adaptation and the limits of life on Earth. Here we examine the microbial diversity and function in ancient sediments (10.3–11 kyr BP (before present)) from a terrace profile of Laguna Lejía, a sulfur- and metal/metalloid-rich saline lake in the Chilean Altiplano. We also evaluate the physical and chemical changes of the lake over time by studying the mineralogy and geochemistry of the terrace profile.ResultsThe mineralogy and geochemistry of the terrace profile revealed large water level fluctuations in the lake, scarcity of organic carbon, and high concentration of SO42--S, Na, Cl and Mg. Lipid biomarker analysis indicated the presence of aquatic/terrestrial plant remnants preserved in the ancient sediments, and genome-resolved metagenomics unveiled a diverse prokaryotic community with still active microorganisms based on in silico growth predictions. We reconstructed 591 bacterial and archaeal metagenome-assembled genomes (MAGs), of which 98.8% belonged to previously unreported species. The most abundant and widespread metabolisms among MAGs were the reduction and oxidation of S, N, As, and halogenated compounds, as well as aerobic CO oxidation, possibly as a key metabolic trait in the organic carbon-depleted sediments. The broad redox and CO2 fixation pathways among phylogenetically distant bacteria and archaea extended the knowledge of metabolic capacities to previously unknown taxa. For instance, we identified genomic potential for dissimilatory sulfate reduction in Bacteroidota and α- and γ-Proteobacteria, predicted an enzyme for ammonia oxidation in a novel Actinobacteriota, and predicted enzymes of the Calvin–Benson–Bassham cycle in Planctomycetota, Gemmatimonadota, and Nanoarchaeota.ConclusionsThe high number of novel bacterial and archaeal MAGs in the Laguna Lejía indicates the wide prokaryotic diversity discovered. In addition, the detection of genes in unexpected taxonomic groups has significant implications for the expansion of microorganisms involved in the biogeochemical cycles of carbon, nitrogen, and sulfur.EPcqnK6xUD66cr6MUL2q3UVideo

Drying the mystery: a novel electronic sensor to quantify soft-tissue desiccation and natural mummification for forensic taphonomy

This study investigates the desiccation process of soft-tissue in South Africa, analyzing its interaction with environmental parameters and its implications for estimating the post-mortem interval. Through the examination of four decomposing porcine bodies across two summer seasons and one winter season, the research quantifies desiccation patterns using custom-designed and constructed printed circuit boards to measure the moisture content of body tissue over time. Generalized additive models were used to determine the environmental forces driving desiccation. Tissue resistivity was tested against the environmental predictor variables to determine the amount of variation they account for, and predicted values of the region-specific tissue resistivity variables were measured for each decomposing body. Results reveal distinct desiccation trajectories between summer and winter, with summer conditions conducive to precocious natural mummification. Environmental factors, particularly temperature and solar radiation, emerge as significant drivers of desiccation. This study represents the first quantitative analysis of deep tissue desiccation internationally, but also the first quantitative assessment of desiccation and natural precocious mummification in the Western Cape, South Africa. The exploration of desiccation as a potential indicator for estimating PMI opens new avenues for research and the integration of innovative methodologies and technologies promises to revolutionize forensic taphonomy practices.

Study on the fracture behavior in clayey geomaterials under moisture diffusion by phase field modeling

Clayey geomaterials are prone to cracking under changing moisture conditions, which substantially compromises their engineering properties. When moisture intrusion and boundary constraints act in tandem on geomaterials, the relevance of multi-physics field processes to complex cracking phenomena remains underexplored. To provide deeper insight into the effect of moisture transport on the cracking behavior of clayey geomaterials, a theoretical model for moisture-induced fracture is proposed. The model combines moisture diffusion, volume deformation dependent on moisture conditions, and phase field fracture, and is solved using the finite element method with a user-defined element subroutine. The developed subroutine is applied to simulate soil desiccation experiments and mudstone water absorption tests. The results reveal that moisture gradients induce non-uniform expansion or shrinkage within the clayey geomaterials. The neighboring geomaterial particles mutually constrain these deformations, resulting in an internal stress field that serves as the primary cause of cracking. Stability and sensitivity analyses validate the reliability of the numerical framework. The proposed model can effectively simulate crack initiation, extension, and convergence during humidification or desiccation processes in both two and three dimensions. This study charts a feasible path for numerical simulation and mechanical mechanism exploration of cracking behaviors in clayey geomaterials during water migration.

Shrinkage and desiccation: evaluating the streambed bacterial responses to intermittent water deficit

Hydrological drought, characterized by a significant deficiency in rainfall events, promotes natural desiccation processes. The reduction in water recharge and the loss of freshwater ecosystems pose urgent challenges in the face of increasing global population and the escalating demand for water resources. The variability in the duration of no-flow periods can have profound implications for ecosystem functioning, specifically impacting the microbiota residing in streambed sediments and the vital processes they perform. The streambed serves as an ecotone where microorganisms form biofilms, playing critical roles in in-stream biogeochemical cycles and greenhouse gas emissions. Consequently, prolonged desiccation periods and subsequent rewetting episodes can disrupt, limit, or alter the functions and structure of microbial communities, thereby compromising the overall functioning of aquatic ecosystems. Understanding how streambed microbial communities respond to prolonged desiccation events is crucial. This revision manuscript provides a synthesis of recent empirical and experimental studies that have explored various aspects of streambed microbial communities in the context of diverse drying-rewetting periods. A special focus is placed on highlighting key microbial community structural and functional responses that could be used as endpoints of responses to desiccation. In particular, we showed the greater expression of the phenol-oxidase activity among the intermittent streambeds submitted to long-term drought. This result suggested a potential begin of transition from freshwater to terrestrial systems. Additionally, we observed a tendency of decreasing bacterial diversity in the dry conditions together with a change in the relative abundance of certain microbial taxa and a general shift from Gram-negative to Gram-positive bacteria. All of these evidences strengthened the similarity between the dry streambed systems studied and a (dry)-soil environment, suggesting that prolonged and unusual dry periods could boost the terrestrial transition of the aquatic intermittent ecosystem. By summarizing these findings, we aim to enhance our understanding of the responses exhibited by streambed microbiota in the face of desiccation events. The synthesized results may further provide potential diagnosis and/or management tools for intermittent freshwater ecosystems functioning.

Role of Substrate Roughness in Soil Desiccation Cracking

Soil desiccation crack is ubiquitous in nature, yet the physics of its initiation and propagation remain under debate, as it involves complex interactions across multiple fields of mechanics, hydraulics, and thermals. Here, an experimental attempt is made to uncover the role of substrate roughness on the soil desiccation process. The substrate roughness is deliberately fabricated by 3D printing, whereas the thickness of sample and environmental humidity are controlled to eliminate the effect of large hydraulic gradient. Four types of soils with varying expansibilities were desiccated on substrates with varying roughness. It reveals that: (1) soil desiccation crack evolution can be conceived as a competing process between the shear failure of soil-substrate interface, i.e., slippage of interface, and the tensile failure of soil, i.e., crack initiation, in minimizing the total energy of drying soil; (2) substrate roughness alters the failure mode and shear strength of soil-substrate interface and its sensitivity to moisture, thereby it regulates the pattern of how soil crack propagates upon drying; (3) soil expansibility is recognized as a key factor governing the crack-initiation point in addition to the widely recognized air-entry, and flaws in soil are the sources for the 120° crack angle and bimodal crack angle distribution.

Analysis and Identification of Genes Associated with the Desiccation Sensitivity of Panax notoginseng Seeds.

Panax notoginseng (Burk.) F. H. Chen, a species of the genus Panax, radix has been traditionally used to deal with various hematological diseases and cardiovascular diseases since ancient times in East Asia. P. notoginseng produces recalcitrant seeds which are sensitive to desiccation and difficult to store for a long time. However, few data are available on the mechanism of the desiccation sensitivity of P. notoginseng seeds. To gain a comprehensive perspective of the genes associated with desiccation sensitivity, cDNA libraries from seeds under control and desiccation processes were prepared independently for Illumina sequencing. The data generated a total of 70,189,896 reads that were integrated and assembled into 55,097 unigenes with a mean length of 783 bp. In total, 12,025 differentially expressed genes (DEGs) were identified during the desiccation process. Among these DEGs, a number of central metabolism, hormonal network-, fatty acid-, and ascorbate-glutathione-related genes were included. Our data provide a comprehensive resource for identifying the genes associated with the desiccation sensitivity of P. notoginseng seeds.

Geomicrobiology of the Rincon de Parangueo maar crater: Exploring the link between an evolving extreme environment and its potential metabolic diversity

Abstract Rincon de Parangueo (RP) is a Quaternary maar crater located in the Michoacan‐Guanajuato Volcanic Field in central Mexico. Like other volcanic craters in the region, the central part was occupied by an endorheic lacustrine system. As a consequence of extensive groundwater extraction, the perennial lake started a gradual desiccation process and now the remnant ponds host a highly saline–alkaline ecosystem. The stratigraphic record indicates an exceptional and long‐term sedimentation of carbonate microbialites. Previous studies based on the 16S rRNA gene have shown that microbial communities have a widespread presence in the crater at the microbialites, the remaining saline ponds, superficial soils and below the surface. To understand the possible role of the microbial communities that generate these biogeological structures, novel analytical methods to resolve the amplicon datasets and their microbial metabolic potential were used. We describe in detail the relationship between the microbial communities, the evolution of physicochemical parameters, and carbonate morphology, in four micro‐environments. A 16S rRNA gene sequencing dataset from previous publications was re‐analysed using an ASV‐based bioinformatic pipeline to identify new insights into the microbial assemblage. Finally, a taxon‐based metabolic profile was used to predict the potential metabolic contribution of the prokaryotic community. Results indicated a refinement in terms of community composition using the ASV‐based bioinformatic methods. Functional profiling through 16S rRNA gene‐based analysis suggested metabolisms associated with carbonate precipitation, indicating a broad potential for microbially mediated carbonate precipitation (e.g., carbon fixation and photosynthesis). The possibility of biogenic methane gas production by methanogenic microorganisms was recognised, supporting the estimated flow of methane on the surface soils. The lacustrine evolution over the last years and the extreme physicochemical characteristics of RP have an impact on the microbial community structure. Prokaryotic community and metabolic potential results from RP coincide with the diversity and abundance of microbial communities and functional metabolisms reported from other microbialite‐forming lakes along the Trans Mexican Volcanic Belt. The identification of important possible phylotypes involved in carbonate precipitation might be an important factor in considering RP microbialites as active calcifying entities. These findings provide novel insights into the potential key role of metabolic pathways driving the process of carbonate precipitation inside RP and evidence of its importance as a microbial biodiversity hotspot in Mexico.

Changes in the content of D-chiro-inositol and its α-D-galactosyl derivatives during vegetation and desiccation of common buckwheat (Fagopyrum esculentum Moench)

Common buckwheat (Fagopyrum esculentum Moench) is the only crop that contains D-chiro-inositol (DCI) in significant contents in vegetative tissues and its α-D-galactosyl derivatives in seeds. Besides DCI, buckwheat tissues contain small contents of D-pinitol (PIN) and myo-inositol (MIN) and their α-D-galactosyl derivatives. D-chiro-inositol is a health-promoting cyclitol of increasing importance in the treatment of some human diseases. However, changes in DCI content in stems, leaves and maturing buckwheat seeds during plant vegetation and under desiccation were not known. The present study analyzed the concentration of cyclitols and their galactosides in the stems, leaves and seeds of plants harvested on 79th, 94th and 123th days after sowing (DAS) and after desiccation at ambient temperature (23° ±2°C). D-chiro-inositol content in stems and leaves increased with vegetation, while the opposite trend was found in developing and maturing seeds. In the seeds, the accumulation of mono-galactosyl DCI derivatives increased, but at the same time, the content of mono-galactosyl PIN and MIN derivatives decreased. The desiccation process drastically increased the content of di-galactosyl derivatives of DCI and MIN in the seeds. The obtained results suggest a protective role of DCI and MIN di-galactosides against desiccation stress in buckwheat tissues.

Effect of extraction conditions on obtaining pectin from agroindustrial coffee by-products

To present a proposal to reduce the waste generated in coffee agroindustrial production and explore potential applications of by-products, this study presents the effects of different physical factors (pH, temperature, and reflux time) on the extraction of pectin from coffee husks Coffea arabica, discarded in coffee farms of San Juan de Rioseco area after the desiccation process. The extraction is carried out by hydrolysis in an acidic medium using hydrochloric acid, precipitation by coagulation with 96% ethanol, filtration, and subsequent drying at 45 °C. Finally, the quality of the pectin obtained is evaluated by infrared spectrophotometry to determine the degree of esterification as well as the yield of the extractions carried out under different conditions. High methoxyl pectins, between 56% and 75% of esterification and yields that do not exceed 1% are obtained from wet material. An inverse temperature-degree of the esterification relationship and a direct time-yield relationship was found, according to an analysis of the main components and surface graphs, finding that the best extraction conditions are pH 2.0, temperature 90 ° C after 1 hour. The results suggest that byproducts from the coffee agro-industrial process are a promising source of pectin.

Finite discrete element modeling of desiccation fracturing in partially saturated porous medium

In this study, a numerical framework is presented for the analysis of desiccation fracturing in variably saturated porous media. The solid phase deformation and fracturing are obtained based on the 2D finite-discrete element method (FDEM), while the fluid flow is characterized by nonlinear Richards’ equation and solved by finite volume discretization. The coupling between phases is realized by Biot’s porous media theory. The capabilities of the model in capturing the unsaturated porous medium flow and coupled hydro-mechanical effects are put to the test against benchmark solutions available in the literature. Furthermore, mechanisms of desiccation cracking in the soil are thoroughly investigated through various numerical test cases. In line with experimental observations, results indicate that the type of mechanical constraints and saturation gradients are two main factors contributing to the generation of cracks in desiccation processes.

Induced polarization of clay-rich materials — Part 1: The effect of desiccation

A petrophysical model describing spectral induced polarization (IP) has been developed for clay rocks accounting for the Maxwell-Wagner polarization. It is also used to connect the complex conductivity to the relative permeability of the material. This model is applied to the Callovo-Oxfordian clay rock of the Paris Basin (France) where the Meuse/Haute-Marne Underground Research Laboratory is located. Laboratory experiments are performed using eight clay-rock cores to study the effect of desiccation on their spectral-IP response. The measurements are performed along the foliation plane. Complex conductivity spectra are measured over a frequency range of 1 mHz to 45 kHz. These spectra are fitted with a double Cole-Cole model to extract the evolution of the Cole-Cole parameters with the saturation during the desiccation process. The low-frequency Cole-Cole model corresponds to IP phenomena, whereas the high-frequency Cole-Cole model corresponds to the Maxwell-Wagner contribution. We obtain the value of the first and second Archie’s exponents and we check the relationship between the surface conductivity and the cation exchange capacity of the clay rocks. We are also able to connect the relative permeability curve to the second (saturation) Archie’s exponent. The monitoring of the complex conductivity can be used to predict how the permeability of the clay-rock formation changes with the water content.

The relationship between vegetation and soil moisture reveals the vegetation carrying capacity threshold—A case study of a Haloxylon ammodendron plantation in the Alxa desert, China

Afforestation is an important and effective way to curb wind-sand hazards in the Alxa Desert. However, over-afforestation makes soil drying occur frequently. The formation of a soil drying layer is seriously restricting the effectiveness of vegetation construction and regional ecological stability. To clarify the process of soil desiccation inHaloxylon ammodendronplantations and determine the suitable planting years, a typicalH. ammodendronplantation in this area was selected as the research object, and the soil moisture variation characteristics of this sand-fixing vegetation region with vegetation age were analyzed. The analysis results on soil water supply, consumption, and balance showed that the soil water storage in 0–400 cm soil layer ofH. ammodendronplantation varies significantly in different ages. The soil water storage in 0–11 years old was the largest, and the soil water supply was greater than the soil water consumption. The soil water storage in profile increased with the increase of precipitation, the soil water storage ofH. ammodendronat 11–22 years old increased first and then decreased with precipitation, and the inflexion existed in 16.5 years old. The soil water consumption ofH. ammodendronplantation at 22–46 years old was greater than that of soil water supplement, and the soil moisture appeared negative balance continuously. Therefore, to prevent further deterioration of soil moisture ecological environment in theH. ammodendronplantation and to promote the sustainable development of afforestation in desert areas, thinning measures are suggested when the growth period reaches 16.5 years. The research results could provide scientific basis for afforestation and soil dry layer regulation in the Alxa desert.

Effect of oil exposure stages on the heat resistance of Salmonella enterica serovar Enteritidis phage type 30 in peanut flour

The oil in low-moisture foods (LMFs) shows protective effects on bacteria during thermal processing. However, the circumstances under which this protective effect strengthens remain unclear. This study aimed to understand which step of the oil exposure to bacterial cells (inoculation, isothermal inactivation, or recovery and enumeration step) in LMFs can enhance their heat resistance. Peanut flour (PF) and defatted PF (DPF) were selected as the oil-rich and oil-free LMF models. Salmonella enterica Enteritidis Phage Type 30 (S. Enteritidis) was inoculated into four designated PF groups representing different oil exposure stages. It was isothermally treated to obtain heat resistance parameters. At a constant moisture content (aw,25°C = 0.32 ± 0.02) and controlled aw,85°C (0.32 ± 0.02), S. Enteritidis exhibited significantly high (p < 0.05) D values in oil-rich sample groups. For instance, the heat resistance values of S. Enteritidis in the PF-DPF and DPF-PF groups were D80°C of 138.22 ± 7.45 min and 101.89 ± 7.82 min; however, the D80°C in the DPF-DPF group was 34.54 ± 2.07 min. The oil addition after the thermal treatment also helped injured bacterial recovery in the enumeration. For instance, the D80°C, D85°C, and D90°C values in the DFF-DPF oil groups were 36.86 ± 2.30, 20.65 ± 1.23, and 7.91 ± 0.52 min, respectively, which were higher than those in the DPF-DPF group at 34.54 ± 2.07, 17.87 ± 0.78, and 7.10 ± 0.52 min. We confirmed that the oil protected S. Enteritidis in PF in all three stages: desiccation process, heat treatment, and recovery of bacterial cells in plates.

Quantitative characterization of drying-induced cracks and permeability of granite residual soil using micron-sized X-ray computed tomography

Drying-induced cracks negatively impacts the performance of soils in the context of global warming. Traditional testing approaches used for the cracking characterization of soils are mainly based on surface observation and qualitative inspections. In this study, a temporal investigation of micron-sized X-ray computed tomography (Micro-CT) tests was performed on the granite residual soil (GRS) during desiccation for the first time. Through three-dimensional (3D) reconstructions and seepage simulations, the dynamic evolution of drying-induced cracks and permeability that evolved (0 to 120 h) was visually characterized and intensively quantified. Experimental results show that the averaged area-porosity ratio varies as an increasing trend, appearing fast at first and slowly thereafter during desiccation.. Observed by 3D reconstruction models, connected cracks rapidly propagated through the samples while isolated cracks occupied small volumes and remained almost unchanged. The pore-diameter distribution of GRS reveals that the propagation of connected cracks is essential in influencing soil cracking. The simulated permeability is generally comparable with measuring ones with an acceptable error margin, demonstrating the accuracy of seepage models. The increasing permeability from both experiments and numerical simulations indicates the desiccation process severely impacts the hydraulic properties of soils. This study provides an adamant evidence that the Micro-CT is an effective and feasible tool for the elucidation of drying-induced crack evolutions and in building numerical models for permeability validation.

Using a novel CLEM system to localize lipid droplets and membranes in desiccated embryonic axis cells of soybean seeds.

Lipid droplets and membranes in radicle cells from desiccated embryonic axes of soybean (Glycine max) seeds were examined by a recently developed correlative light and electron microscopy system, which has been designed to facilitate the observation of identical locations using an upright reflected light microscope and compact SEM successively with minimum time lapse. Lipids are major components of membranes and are also stored in numerous lipid droplets lining plasma membranes in many seed cells. Fluorescently stained lipid droplets and membranes in the desiccated radicle cells were mainly located along the surface of shrunk protoplasm and around presumptive protein bodies, which will turn into vacuoles and increase their volume for radicle protrusion. Co-localization of lipid droplets and membranes suggests the presence of a membrane protection mechanism during desiccation and rehydration processes that ensures prompt elongation of radicle cells during germination.

Ecological successions throughout the desiccation of Tirez lagoon (Spain) as an astrobiological time-analog for wet-to-dry transitions on Mars

Tirez was a small and seasonal endorheic athalassohaline lagoon that was located in central Spain. In recent years, the lagoon has totally dried out, offering for the first time the opportunity to analyze its desiccation process as a “time-analog” to similar events occurred in paleolakes with varying salinity during the wet-to-dry transition on early Mars. On the martian cratered highlands, an early period of water ponding within enclosed basins evolved to a complete desiccation of the lakes, leading to deposition of evaporitic sequences during the Noachian and into the Late Hesperian. As Tirez also underwent a process of desiccation, here we describe (i) the microbial ecology of Tirez when the lagoon was still active 20 years ago, with prokaryotes adapted to extreme saline conditions; (ii) the composition of the microbial community in the dried lake sediments today, in many case groups that thrive in sediments of extreme environments; and (iii) the molecular and isotopic analysis of the lipid biomarkers that can be recovered from the sediments today. We discuss the implications of these results to better understanding the ecology of possible Martian microbial communities during the wet-to-dry transition at the end of the Hesperian, and how they may inform about research strategies to search for possible biomarkers in Mars after all the water was lost.

The mechanism underlying the response of Agarophyton vermiculophyllum to desiccation–rehydration stress

Agarophyton vermiculophyllum is a macroalga that inhabits the intertidal zone, which is a dynamic environment that undergoes rapid changes in physical conditions associated with turning tides. One of the main factors affecting the growth and vertical distribution of macroalgae in the intertidal zone is desiccation stress. To clarify the mechanism underlying the response of A. vermiculophyllum to desiccation stress, changes in the content of photosynthetic pigments, antioxidant enzyme activity, and the expression of stress-responsive genes were characterized under different desiccation (0 h, 2 h, 4 h, and 6 h) and rehydration (2 h, 4 h, and 6 h) times. The increased photosynthetic pigments content of the thalli could effectively reduce oxidative damage during desiccation. The level of lipid peroxidation in the cell membrane changed slightly during the desiccation process, which further confirmed that A. vermiculophyllum is highly tolerant of desiccation stress. The expression of stress-responsive genes of A. vermiculophyllum were characterized. The expression of respiratory burst oxidase homologs (Rboh) gene was rapidly up-regulated early during desiccation, which indicated that ROS produced by NADPH oxidases served as key signals of desiccation stress. Proton gradient regulation 5 (PGR5)-dependent cycle electron flow protected photosystem I from photodamage under desiccation stress. Changes in the expression of heat shock protein (HSP) genes mediated the folding and unfolding of proteins during the desiccation and rehydration process. Overall, our findings indicate that high tolerance of desiccation stress in A. vermiculophyllum is mediated by diverse physiological responses.