High Rates Of Water Loss Research Articles

Hydraulic segmentation does not protect stems from acute water loss during fire.

The heat plume associated with fire has been hypothesized to cause sufficient water loss from trees to induce embolism and hydraulic failure. However, it is unclear whether the water transport path remains sufficiently intact during scorching or burning of foliage to sustain high water loss. We measured water uptake by branches of Magnolia grandiflora while exposing them to a range of fire intensities and examined factors influencing continued water uptake after fire. Burning caused a 22-fold mean increase in water uptake, with greatest rates of water loss observed at burn intensities that caused complete consumption of leaves. Such rapid uptake is possible only with steep gradients in water potential, which would likely result in substantial cavitation of xylem and loss of conductivity in intact stems. Water uptake continued after burning was complete and was greatest following burn intensities that killed leaves but did not consume them. This post-fire uptake was mostly driven by rehydration of the remaining tissues, rather than evaporation from the tissues. Our results indicate that the fire plume hypothesis can be expanded to include a wide range of burning conditions experienced by plants. High rates of water loss are sustained during burning, even when leaves are killed or completely consumed.

Functional differentiation among 12 dipterocarp species under contrasting water availabilities in Northeast Thailand

Species composition varies greatly dependent on water availability gradients. In Northeast Thailand, dry deciduous forests (DDF) and dry evergreen forests (DEF) show contrasting species composition due to differences in soil structure and moisture. Although plant traits (physiological and morphological characteristics) are known to be involved in species distributions, which traits underpin these distinct distributions (either dry DDF or less-dry DEF) remain unclear. Here, we examined the differentiation of 21 leaf and stem traits between DDF and DEF using 12 dipterocarp species. We found that DDF species showed higher water use efficiency and higher water storage capacity in the lamina and petiole, higher leaf nitrogen content, higher stomatal density, larger leaves, thicker mesophyll layers, and a higher rate of water loss under severe dehydration than DEF species. Leaf osmotic potential at full turgor, wood density, and wood water content were not significantly different between DDF and DEF. We also observed a negative relationship between the potential photosynthetic capacity and the water loss rate during severe dehydration across species. Our results suggest that the differences in leaf traits related to photosynthesis and dehydration avoidance among the tree species produce niche differences along the soil water availability in tropical dry forests.

Constitutive expression of aldose reductase 1 from Zea mays exacerbates salt and drought sensitivity of transgenic Escherichia coli and Arabidopsis

Aldose reductases (ARs) have been considered to play important roles in sorbitol biosynthesis, cellular detoxification and stress response in some plants. ARs from maize are capable of catalyzing the oxidation of sorbitol to glucose. However, little is known how maize ARs response to abiotic stresses. In this work, we cloned one isoform of maize ARs (ZmAR1), and furthermore we analyzed the roles of ZmAR1 in response to salt and drought stresses at both prokaryotic and eukaryotic levels. ZmAR1 encodes a putative 35 kDa protein that contains 310 amino acids. Under normal growth conditions, ZmAR1 was expressed in maize seedlings, and the highest expression level was found in leaves. But when seedlings were subjected to drought or salt treatment, the expression levels of ZmAR1 were significantly reduced. The constitutive expression of ZmAR1 increased the sensitivity of recombinant E. coli cells to drought and salt stresses compared with the control. Under salt and drought stresses, transgenic Arabidopsis lines displayed lower seed germination rate, shorter seedling root length, lower chlorophyll content, lower survival rate and lower antioxidant enzyme activity than wild type (WT) plants, but transgenic Arabidopsis had higher relative conductivity, higher water loss rate, and more MDA content than WT. Meanwhile, the introduction of ZmAR1 into Arabidopsis changed the expression levels of some stress-related genes. Taken together, our results suggested that ZmAR1 might act as a negative regulator in response to salt and drought stresses in Arabidopsis by reducing the sorbitol content and modulating the expression levels of some stress-related genes.

Characterizing Supply Variability and Operational Challenges in an Intermittent Water Distribution Network

Intermittent piped water supply is common in low- and middle-income countries and is inconvenient for users, particularly when supply schedules are unreliable. In this study, supply schedules and operational challenges were characterized in intermittent areas of the Arraiján, Panama distribution network based on one year of pressure and flow monitoring in four study zones, analysis of three years of pipe break data, and observations of system operation. Service quality was found to vary among users and supply schedules were often irregular and unpredictable. Direct causes of unanticipated supply outages included pump failures, chronic pipe breaks in specific parts of the system, transmission main breaks, irregular valve operations, and treatment plant outages. The extent and duration of these outages were often increased by high rates of water loss, insufficient storage capacity, and difficulty detecting and resolving infrastructure failures. Factors associated with intermittent supply, such as intermittent pumping, appeared to be associated with a higher frequency of pipe breaks. However, the analysis did not indicate a strong general correlation between intermittent supply and pipe breaks. Pressure and flow monitoring in intermittent supply areas, similar to that undertaken in this study, could be a valuable tool to improve regular operations as well as longer-term planning and prioritization of system improvements. Water loss reduction and adequate distribution storage capacity could also mitigate the effects of operational failures. Investments in monitoring and data analysis have the potential to improve the reliability of intermittent supply in cases where continuous supply is not immediately feasible.

A Permeable Cuticle, Not Open Stomata, Is the Primary Source of Water Loss From Expanding Leaves.

High rates of water loss in young, expanding leaves have previously been attributed to open stomata that only develop a capacity to close once exposed to low humidity and high abscisic acid (ABA) levels. To test this model, we quantified water loss through stomata and cuticle in expanding leaves of Quercus rubra. Stomatal anatomy and density were observed using scanning electron microscopy. Leaves of Q. rubra less than 5 days after emergence have no stomata; therefore, water loss from these leaves must be through the cuticle. Once stomata develop, they are initially covered in a cuticle and have no outer cuticular ledge, implying that the majority of water lost from leaves in this phase of expansion is through the cuticle. Foliar ABA levels are high when leaves first expand and decline exponentially as leaves expand. Once leaves have expanded to maximum size, ABA levels are at a minimum, an outer cuticular ledge has formed on most stomata, cuticular conductance has declined, and most water loss is through the stomata. Similar sequences of events leading to stomatal regulation of water loss in expanding leaves may be general across angiosperms.

Genome-Wide Identification of the Physic Nut WUSCHEL-Related Homeobox Gene Family and Functional Analysis of the Abiotic Stress Responsive Gene JcWOX5.

Plant-specific WOX transcription factors have important regulatory functions in plant development and response to abiotic stress. However, the identification and functional analysis of members of the WOX family have rarely been reported in the physic nut plant until now. Our research identified 12 WOX genes (JcWOXs) in physic nut, and these genes were divided into three groups corresponding to the ancient clade, WUS clade, and intermediate clade. Expression analysis based on RNA-seq and qRT-PCR showed that most of the JcWOX genes were expressed in at least one of the tissues tested, whereas five genes were identified as being highly responsive to drought and salt stresses. Subcellular localization analysis in Arabidopsis protoplast cells showed that JcWOX5 encoded a nuclear-localized protein. JcWOX5-overexpression plants increased sensitivity to drought stress, and transgenic plants suggested a lower proline content and CAT activity, higher relative electrolyte leakage, higher MDA content, and higher rate of water loss under drought conditions. Expression of some stress-related genes was obviously lower in the transformed rice lines as compared to their expression in wild-type rice lines under drought stress. Further data on JcWOX5-overexpressing plants reducing drought tolerance verified the potential role of JcWOX genes in responsive to abiotic stress. Collectively, the study provides a foundation for further functional analysis of JcWOX genes and the improvement of physic nut crops.

Exogenous hormones influence Brassica napus leaf cuticular wax deposition and cuticle function.

BackgroundCuticular waxes cover plant surface and play important roles in protecting plants from abiotic and biotic stresses. The variations of wax deposition and chemical compositions under changing environments have been shown to be related to plant adaptations. However, it is still not clear whether the wax depositions could be adjusted to increase plant adaptations to stressed conditions.MethodsIn this study, exogenous methyl jasmonate (MeJA), the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and salicylic acid (SA) were applied to test their effects on cuticular wax deposition in two Brassica napus cultivars, Zhongshuang 9 (ZS9, low wax coverage ) and Yuyou 19 (YY19, high wax coverage). Next, we measured the water loss rate and the transcriptional expression of genes involved in wax biosynthesis as well as genes related to disease defense.ResultsSeven wax compound classes, including fatty acids, aldehydes, alkanes, secondary alcohols, ketones, and unbranched as well as branched primary alcohols, were identified in B. napus leaf wax mixtures. MeJA, SA and ACC treatments had no significant effect on total wax amounts in YY19, whereas ACC reduced total wax amounts in ZS9. Overall, hormone treatments led to an increase in the amounts of aldehydes and ketones, and a decrease of secondary alcohol in ZS9, whereas they led to a decrease of alkane amounts and an increase of secondary alcohol amounts in YY19. Concomitantly, both cultivars also exhibited different changes in cuticle permeability, with leaf water loss rate per 15 min increased from 1.57% (averaged across treatments) at 1.57% (averaged across treatments) at 15 min to 3.12% at 30 min for ZS9 (except for ACC treated plant) and decreased for YY19. MeJA-treated plants of both cultivars relatively had higher water loss rate per 15 min when compared to other treatments. Conclusion. Our findings that B. napus leaf wax composition and cuticle permeability are altered by exogenous SA, MeJA and ACC suggest that the hormone treatments affect wax composition, and that the changes in wax profiles would cause changes in cuticle permeability.

A Simple Method for Simulating Drought Effects on Plants.

Drought is expected to increase in frequency and severity in many regions in the future, so it is important to improve our understanding of how drought affects plant functional traits and ecological interactions. Imposing experimental water deficits is key to gaining this understanding, but has been hindered by logistic difficulties in maintaining consistently low water availability for plants. Here, we describe a simple method for applying soil water deficits to potted plants in glasshouse experiments. We modified an existing method (the “Snow and Tingey system”) in order to apply a gradual, moderate water deficit to 50 plant species of different life forms (grasses, vines, shrubs, trees). The method requires less maintenance and manual handling compared to other water deficit methods, so it can be used for extended periods of time and is relatively inexpensive to implement. With only a few modifications, it is possible to easily establish and maintain soil water deficits of differing intensity and duration, as well as to incorporate interacting stress factors. We tested this method by measuring physiological responses to an applied water deficit in a subset of 11 tree/shrub species with a wide range of drought tolerances and water-use strategies. For this subgroup of species, stomatal conductance was 2–17 times lower in droughted plants than controls, although only half of the species (5 out of 11) experienced midday leaf water potentials that exceeded their turgor loss (i.e., wilting) point. Leaf temperatures were up to 8°C higher in droughted plants than controls, indicating that droughted plants are at greater risk of thermal damage, relative to unstressed plants. The largest leaf temperature differences (between droughted and well-watered plants) were in species with high rates of water loss. Rapid osmotic adjustment was observed in leaves of five species when drought stress was combined with an experimental heatwave. These results highlight the potential value of further ecological and physiological experiments utilizing this simple water deficit method to study plant responses to drought stress.

Hierarchy of hydraulic and energy conservation actions at water supply systems

ABSTRACTWater supply systems (WSS) in developing countries present high water loss and energy consumption rates, thus strategies for conservation of these resources are needed. The challenge is to define which strategies offer better results based on multiple criteria and on the different interests of the stakeholders involved. The objective of this study is to apply the decision support tool, named Water Supply Systems Management (WSSM), which uses the Analytic Hierarchy Process, to establish a hierarchy between the strategies. A case study was carried out in Curitiba, Brazil. Three strategies were selected: leak detection and correction, rational use of water, and the replacement of old water mains. These strategies were evaluated according to implementation cost, flow rate, energy consumption, and population coverage criteria. The leak detection and correction was ranked as the best option. The results of this study show this tool helps to devise guidelines for the efficient use of water and energy in the WSS.

Obligatory Nocturnalism in Triassic Archaic Mammals: Preservation of Sperm Quality?

Archaic mammals became exclusively nocturnal by the Late Triassic, and today, the majority of extant mammals remain nocturnal. Although there is ample morphological and physiological evidence supporting Late Mesozoic nocturnalism, a succinct hypothesis for why mammals became nocturnal remains elusive. Here, I propose a hypothesis that, with the onset of body size miniaturization in the Triassic and the concomitant evolution of fur and increased mass-specific metabolic rate and hence body temperature, small mammals became obligatorily nocturnal in order to avoid poor sperm quality, hyperthermia, and high rates of evaporative water loss and to maximize foraging time. The hypothesis hinges heavily on the assumption that, with the absence of externalized testes, the maximum optimum temperature of about 36°C for spermatogenesis was subject to strong stabilizing selection that placed a ceiling on increases in metabolic rate and body temperature. Heat-dissipating capacity during the daytime during the Triassic, Jurassic, and Cretaceous was thereby compromised. The release from the constraint of the optimum temperature of spermatogenesis occurred in placental mammals only with the advent of the externalization of testes in the scrotum in Boreotheria in the Cenozoic or, with the recent claim that the scrotum is plesiomorphic in mammals, as early as the Jurassic with the origin of the marsupials.

Transcriptome analysis in different chieh-qua cultivars provides new insights into drought-stress response

Drought, one of the crucial environmental constraints, seriously threats the quality and yield in chieh-qua. Therefore, cultivating drought-tolerant variety is greatly necessary for its normal growth under water deficiency. However, at present, molecular knowledge on drought resistance is mostly unclear in chieh-qua. In the study, characteristics of two diverse genetic chieh-qua variety, A39 (drought-resistance) and H5 (drought-sensitivity), were analyzed. Under drought stress, H5 exerted high water loss rate, increased malonaldehyde (MDA) content, and decreased enzyme activity of glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) compared with A39. In addition, based on the transcriptome results, we obtained a total of 1821 (511 up-regulated and 1310 down-regulated) and 2114 (1282 up-regulated and 832 down- regulated) differentially expressed genes (DEGs) in the A39 versus H5 under normal and water-deficiency stress, respectively. Several DEGs involved in the cuticle synthesis (cytochrome P450 genes: CYP94A2, CYP86B1, CYP86A7), carbohydrate metabolism, and plant hormone signal transduction (small auxin-up RNA genes: SAUR32, SAUR72; JA-induced genes: TIFY 10A, TIFY 10C; ABA related genes: PYL2, PYL4) were explored and related to drought resistance. These expression patterns observed in the RNA-seq data were further confirmed with quantitative real-time PCR (qRT-PCR). In all, these results not only provided a new insight into analyzing genes of drought response, but also laid a foundation for isolating crucial genes involved in drought stress in chieh-qua.

Desiccation resistance in Central European carabid species: effects of body size and habitat preferences

Water is the limiting factor for all organisms. Due to global climate change, prolonged drought periods are predicted and the importance of drought-related research is increasing. Water, together with temperature, determines the abundance and spatial distribution of animals. In this study, we investigated the effects of body size and habitat preference on desiccation resistance of carabid beetles under controlled laboratory condition. Firstly, we measured the longevity of 641 carabid individuals belonging to 18 species. These beetles were exposed to extremely low relative humidity (ca. 15-20%) using silica gel bags within experimental Petri dishes. Secondly, the rate of water loss was measured for 236 individuals belonging to eight carabid species. Rate of water loss was measured using exposition to the same extremely dry conditions, but only for 12 hours. Body size was represented by elytron length and live weight was also measured to analyse effects of body condition (weight corrected for structural size). Experimental beetles were collected in different habitats ranging from extremely dry to very wet conditions. Carabids were provided with food and water ad libitum for at least 7 days prior to the experiments. All experiments were performed using a climatic chamber set to a long day (16L:8D) and the constant temperature of 20°C. The preliminary results show that species from wet habitats were more sensitive to desiccation and larger species were more resistant (survived for a longer time) compared to smaller species. Species from wet habitats had higher water loss rate compared to species originating from dry habitats. At the intraspecific level, individuals with larger body size (elytron length) survived longer than smaller individuals. Interestingly, the rate of water loss was affected by initial body condition and sex but not by structural body size at the intraspecific level. The most resistant species was Pseudoophonus rufipes. This species was not superior to other species with respect to water loss rate but it had the highest relative water content. It is also possible that P. rufipes has some other physiological or behavioural adaptation enabling a better survival under stressful, dry condition. This issue could be investigated in a future study.

The on‐ground feasibility of a waterless barrier to stop the spread of invasive cane toads in Western Australia

AbstractModeling suggests that excluding invasive cane toads from artificial water points (e.g., pastoral dams) along an arid coastal corridor in Western Australia would create a “waterless barrier” halting their spread. In this study, we explored one critical assumption of these models: that toads cannot persist in the corridor during the dry season without access to artificial water points. We explicitly tested this assumption by translocating and radio‐tracking 78 male cane toads in the proposed barrier region during the dry season. Telemetered toads moved substantial distances (maximum distance >2.5 km/night) and were adept at finding shelter. Nonetheless, toads experienced high water loss rates (1.89%/hr) and rapid mortality in both desert (mean ± SD = 43.6 hr ±1.4) and coastal (24.5 hr ±1.2) habitats. Survival analysis suggested that toads could survive a maximum of 5 days without access to surface water and would move a maximum of 5.35 km in this time. Our results confirm that artificial water points are a critical resource for toads in the proposed barrier region and provide further evidence that the waterless barrier could successfully halt toad expansion in Western Australia.

Phenotypic variation in egg survival in the predatory mite Phytoseiulus persimilis under dry conditions

The predatory mite Phytoseiulus persimilis is widely used for augmentative biological control, as an effective predator of the spider mite Tetranychus urticae. However, the biocontrol efficacy of P. persimilis decreases under dry conditions. One of the reasons for this decline concerns P. persimilis’ eggs, which are sensitive to low humidity. In this study, we investigated the possibility to select for a strain of P. persimilis adapted to dry conditions. To understand the potential sources of phenotypic variation in egg survival under dry conditions, we tested the effects of genetic and environmental factors on variation in this trait. We compared egg hatching of five P. persimilis strains, under constant as well as variable humidity conditions, at 25 °C. The results show no intraspecific genetic variation among the five tested strains in egg hatching under constant and variable humidity conditions. In all five strains, less than 20% of the eggs hatched when they were exposed to constant low (60% RH) humidity conditions. However, when eggs were exposed to successive cycles of low and high humidity, a common pattern observed in the field, significantly higher hatching rates were observed. Under variable humidity conditions, more than 73% of the eggs hatched successfully, even when exposure to high humidity was limited to only 13% of the egg developmental time. Although P. persimilis eggs suffered from a high rate of water loss under constant dry conditions, they were able to compensate for this water loss when exposed to high humidity conditions for a few hours during their development. A decreased biocontrol efficacy of P. persimilis under dry conditions may be explained by a higher egg mortality when relative humidity is constantly low. Yet, when relative humidity exhibits diurnal variation, periods of high humidity may mitigate the effects of periods of low humidity during development of P. persimilis eggs.

Dehydration during egg production alters egg composition and yolk immune function

Parent-offspring conflicts occur when resources are limited for allocation, and, historically, energy has been the primary currency of focus when examining these trade-offs. Water is a fundamental resource that has received far less consideration for parent-offspring conflicts. Previous research suggests that, when water is limited, reproductive females are compromised in favor of developing embryos. However, these studies limited their assessments to standard metrics such as clutch size and mass. We tested the hypothesis that the mother-offspring conflict over limited water resources leads to finer scale morphological and physiological impacts on the eggs in Children's pythons (Antaresia childreni). We predicted that water deprivation during gravidity alters female investment into her eggs, impacting egg water content and shell development. Additionally, we predicted that the yolk in these dehydrated eggs would have enhanced immune performance metrics, as has been documented in dehydrated adults. We found that eggs from water-deprived females were dehydrated as indicated by reduced percent water and greater yolk osmolality compared to eggs from females that received ad libitum water. We also found that eggs from dehydrated mothers had thinner shells and higher water loss rates. The impacts were not entirely negative as dehydrated eggs had higher antimicrobial capabilities. Also, thinner and more permeability eggshells might allow for elevated rates of rehydration from nest substrate. Overall, by examining an array of egg traits, we demonstrated that dehydration of gravid females impacts the eggs, not just the females as previously reported. As a result, the mother-offspring conflicts are indeed two-sided.

Overexpression of BoNAC019, a NAC transcription factor from Brassica oleracea, negatively regulates the dehydration response and anthocyanin biosynthesis in Arabidopsis

NACs are one of the largest transcription factor families in plants and are involved in the response to abiotic stress. BoNAC019, a homologue of AtNAC019, was isolated from cabbage (Brassica oleracea). BoNAC019 was localized in the nucleus and functioned as a transcriptional activator. The expression of BoNAC019 was induced by dehydration, salt, abscisic acid (ABA), and H2O2 treatments. BoNAC019 overexpressing plants were generated to explore the function of BoNAC019 in response to drought stress. Overexpression (OE) of BoNAC019 reduced drought tolerance with lower survival rate, higher water loss rate, lower proline content and ABA content. The seed germination and root length assays of BoNAC019-OE plants showed decreased sensitivity to ABA. Under drought condition, antioxidant enzymes and anthocyanin content decreased in BoNAC019 -OE plants, resulting in the accumulation of more reactive oxygen species (ROS), which cause damage to plants. Several stress-responsive genes, antioxidant enzymatic genes, anthocyanin biosynthetic genes and ABA signaling genes were down-regulated under drought condition while the ABA catabolism genes were induced in BoNAC019-OE plants under both normal and drought conditions. Our results demonstrated that BoNAC019 might participated in regulating drought tolerance by inducing ABA catabolism genes and decreasing ABA content.

Estimating isotherm parameters of drying clay for the ceramic industry of Sergipe, Brazil

Abstract The drying process is one of the main stages of production phase of ceramics. Drying without (previous) knowledge of the technological characteristics of clay and the drying parameters may create cracks and deformations in the products. In this study, the models of Page, Henderson & Pabis, Lewis and Midilli were used to evaluate the drying process conditions of five clays used in the ceramic industry in the state of Sergipe, Brazil. The samples in this study were identified as: 1-PIN, 2-IN, 3-PIR, 4-MA and 5-VER, which come from four different deposits in Sergipe and from a deposit in Alagoas. The clays were first characterized through particle size analysis, chemical composition, organic matter content, plasticity index and X-ray diffractometry. Specimens were prepared by axial pressure with 8% moisture and subjected to drying where moisture loss over time was evaluated. The drying parameters were estimated using non-linear adjustments with the GAMS (General Algebraic Modeling System) application. The sum of squared errors (SSE) was used as the objective function and the root mean square error (RMSE) was used as the models performance function. According to the results found, we observed that the Midilli model best described the drying of the five clays, with 5-VER clay presenting drying coefficient of k = 1.442 h−1 and clay 3-PIR presenting k = −0.125 h−1. Thus, 5-VER and 3-PIR clays showed high and low rates of water loss, respectively. These results are consistent with the data obtained through the physical, chemical and structural characterization of clays.

Variation and repeatability of cutaneous water loss and skin resistance in relation to temperature and diel variation in the lizard Sceloporus consobrinus.

Variation in rates of water loss has been proposed to be an important mechanism in the survival of terrestrial organisms, as high rates of water loss in desiccating environments may lead to hydric stress and death. Vapor density deficit, the driving force for evaporative water loss, increases exponentially as temperature increases. Acute temperature changes may be the result of daily behavioral thermoregulation of ectotherms, which may influence the among individual variation rates of water loss. The goals of this study were to determine (1) how rates of cutaneous water loss (CWL) and skin resistance (Rs) are affected by acute temperature acclimation, (2) how rates of CWL and Rs vary throughout the day allowing behavioral thermoregulation and (3) the repeatability of CWL and Rs within and among sampling periods. We measured CWL and calculated skin resistance (Rs) of 30 male Sceloporus consobrinus lizards across three summers. We measured CWL on the dorsal and ventral surface of each lizard at 23°C followed by measurements at 35°C, and three separate times throughout the day. We found a significant increase in Rs and decrease in CWL at increased acclimation temperatures (35°C), a significant difference in CWL and Rs throughout the day allowing behavioral thermoregulation, and support for the repeatability of CWL and Rs. Our results demonstrate variability in CWL and Rs in relation to temperature acclimation and thermoregulation, but mixed evidence for repeatability across treatments. Our results suggest other factors, such as peripheral blood flow, may be influencing the inter-individual variation in CWL and Rs.

The Arabidopsis Mediator Complex Subunit MED19a is Involved in ABI5-mediated ABA Responses

Arabidopsis Mediator complex subunit 19a (MED19a), which mediates interactions between transcriptional regulators and RNA polymerase II, plays a critical role in plant response to infection by pathogens. However, the roles of MED19a in other signaling pathways are unknown. Here, we report that MED19a plays an important role in regulation of abscisic acid (ABA)-mediated transcriptional regulation in Arabidopsis. Plants deficient in MED19a showed reduced sensitivity to ABA inhibition of seed germination, cotyledon greening, root growth, and stomatal opening. MED19a-deficient mutants also had reduced resistance to drought stress, evidenced by high water-loss rates and low survival rates. Molecular genetic analysis revealed that MED19a mutants had down-regulated ABA-induced genes, including Em1, Em6, and RD29B, and MED19a could occupy the promoters of Em1 and Em6 in an ABA-dependent manner. Furthermore, MED19a interacted with the transcription factor ABA-insensitive 5 (ABI5) in split-luciferase complementation assays and co-immunoprecipitation assays. An analysis of double mutants (med19a-2 and abi5-7) suggested that the action of MED19a in ABA signaling was dependent upon ABI5. Furthermore, MED19a and ABI5 influenced each other in recruiting the promoters of the target genes Em1 and Em6, which are involved in embryonic development. Altogether, these results indicate that MED19a acts as a positive regulator in ABI5-mediated ABA responses.

Differential effects of water loss and temperature increase on the physiology of fiddler crabs from distinct habitats

Temperature is one of the main environmental constraints to organism distribution, affecting physiology and survival. Organisms that inhabit the intertidal zone are exposed to temperature variation and, with climate change, they should face different conditions which include higher temperatures, leading to higher rates of water loss through evaporation and then fitness reduction or mortality. Here we tested the effects of desiccation and increased temperature in two fiddler crabs species that occupy distinct habitats in regard to vegetation cover and position on the intertidal zone and thus may respond differently to these stressors. Leptuca thayeri, which is restricted to the mid-tide zone and vegetated areas, had higher desiccation and mortality rates than Minuca rapax, a generalist species, when exposed to desiccation for 120 min. Also, compared to M. rapax, L. thayeri had a more permeable carapace. Temperature elevation of 10 °C and 20 °C for 72 h caused no mortality in either species. However, there were changes in hemolymph osmolality and muscle hydration in both species. Leptuca thayeri osmolality was low in the intermediate temperature, suggesting that at this temperature this species has a better salt secretion capability. Minuca rapax, however, had an increase in hemolymph osmolality at the highest temperatures with no LDH increase, which indicates that osmotic control in this species is more sensitive to temperature increase. Our results show that L. thayeri suffers more from desiccation, due to a more permeable carapace. However, because of this higher permeability L. thayeri is capable of lowering its temperature more than M. rapax. As temperature elevation produces great physiological changes in M. rapax, a reduced ability to keep a low temperature can be an issue for this species if temperature increases. However, higher water loss to keep body temperature low may decrease L. thayeri survivability in the same scenario.