Facilitate Water Uptake Research Articles

PIP family-based association studies uncover ZmPIP1;6 involved in Pb accumulation and water absorption in maize roots

Excessive lead (Pb) in the soil affects crop growth and development, thus threatening human beings via food chains. Plasma membrane intrinsic proteins (PIPs) facilitate the transport of substrates across cell membranes. Herein, we characterized maize PIPs and identified eight Pb accumulation-associated PIP genes using association studies. Among these, ZmPIP1;6 was simultaneously correlated with root Pb concentrations under various Pb treatment stages. Significant correlations were observed between the ZmPIP1;6 expression abundance and Pb accumulation in maize roots. Ectopic expression in yeast showed that ZmPIP1;6 conferred Pb accumulation in the cells and affected Pb tolerance in yeast. Overexpression in maize demonstrated that ZmPIP1;6 altered the Pb concentration performance and root moisture content under Pb stress. Meanwhile, protein interaction analyses suggested that ZmPIP1; 6 and three PIP2 members formed isoforms and facilitate water uptake in maize roots. However, ZmPIP1; 6 improved Pb absorption in maize roots probably by interacting with CASP-like protein 2C3 and/or another metal transporter. Moreover, the significant variants in the ZmPIP1;6 promoter caused the variations in ZmPIP1;6 expression level and Pb accumulation among various maize germplasms. Our study will contribute to understanding of PIP family-mediated Pb accumulation in crops and bioremediation of Pb-polluted soils.

Mycorrhization enhances plant growth and stabilizes biomass allocation under drought.

Plants and their symbionts, such as arbuscular mycorrhizal (AM) fungi, are increasingly subjected to various environmental stressors due to climate change, including drought. As a response to drought, plants generally allocate more biomass to roots over shoots, thereby facilitating water uptake. However, whether this biomass allocation shift is modulated by AM fungi remains unknown. Based on 5691 paired observations from 154 plant species, we conducted a meta-analysis to evaluate how AM fungi modulate the responses of plant growth and biomass allocation (e.g., root-to-shoot ratio, R/S) to drought. We found that AM fungi attenuate the negative impact of drought on plant growth, including biomass production, photosynthetic performance and resource (e.g. nutrient and water) uptake. Accordingly, drought significantly increased R/S in non-inoculated plants, but not in plants symbiotic with established AM fungal symbioses. These results suggest that AM fungi promote plant growth and stabilize their R/S through facilitating nutrient and water uptake in plants under drought. Our findings highlight the crucial role of AM fungi in enhancing plant resilience to drought by optimizing resource allocation. This knowledge opens avenues for sustainable agricultural practices that leverage symbiotic relationships for climate adaptation.

Advancing Sustainable Malting Practices: Aquaporins as Potential Breeding Targets for Improved Water Uptake during Controlled Germination of Barley (Hordeum vulgare L.).

The conversion of raw barley (Hordeum vulgare L.) to malt requires a process of controlled germination, where the grain is submerged in water to raise the moisture content to >40%. The transmembrane proteins, aquaporins, influence water uptake during the initial stage of controlled germination, yet little is known of their involvement in malting. With the current focus on sustainability, understanding the mechanisms of water uptake and usage during the initial stages of malting has become vital in improving efficient malting practices. In this study, we used quantitative proteomics analysis of two malting barley genotypes demonstrating differing water-uptake phenotypes in the initial stages of malting. Our study quantified 19 transmembrane proteins from nine families, including seven distinct aquaporin isoforms, including the plasma intrinsic proteins (PIPs) PIP1;1, PIP2;1, and PIP2;4 and the tonoplast intrinsic proteins (TIPs) TIP1;1, TIP2;3, TIP3;1, and TIP3;2. Our findings suggest that the presence of TIP1;1, TIP3;1, and TIP3;2 in the mature barley grain proteome is essential for facilitating water uptake, influencing cell turgor and the formation of large central lytic vacuoles aiding storage reserve hydrolysis and endosperm modification efficiency. This study proposes that TIP3s mediate water uptake in malting barley grain, offering potential breeding targets for improving sustainable malting practices.

Bark water uptake through lenticels increases stem hydration and contributes to stem swelling.

Foliar water uptake can recharge water storage tissue and enable greater hydration than through access to soil water alone; however, few studies have explored the role of the bark in facilitating water uptake. We investigated pathways and dynamics of bark water uptake (BWU) in stems of the mangrove Avicennia marina. We provide novel evidence that specific entry points control dynamics of water uptake through the outer bark surface. Furthermore, using a fluorescent symplastic tracer dye we provide the first evidence that lenticels on the outer bark surface facilitate BWU, thus increasing stem water content by up to 3.7%. X-ray micro-computed tomography showed that BWU was sufficient to cause measurable swelling of stem tissue layers increasing whole stem cross-sectional area by 0.83 mm2 or 2.8%, implicating it as a contributor to the diel patterns of water storage recharge that buffer xylem water potential and maintain hydration of living tissue.

Revealing the Impacts of Chemical Complexity on Submicrometer Sea Spray Aerosol Morphology.

Sea spray aerosol (SSA) ejected through bursting bubbles at the ocean surface is a complex mixture of salts and organic species. Submicrometer SSA particles have long atmospheric lifetimes and play a critical role in the climate system. Composition impacts their ability to form marine clouds, yet their cloud-forming potential is difficult to study due to their small size. Here, we use large-scale molecular dynamics (MD) simulations as a "computational microscope" to provide never-before-seen views of 40 nm model aerosol particles and their molecular morphologies. We investigate how increasing chemical complexity impacts the distribution of organic material throughout individual particles for a range of organic constituents with varying chemical properties. Our simulations show that common organic marine surfactants readily partition between both the surface and interior of the aerosol, indicating that nascent SSA may be more heterogeneous than traditional morphological models suggest. We support our computational observations of SSA surface heterogeneity with Brewster angle microscopy on model interfaces. These observations indicate that increased chemical complexity in submicrometer SSA leads to a reduced surface coverage by marine organics, which may facilitate water uptake in the atmosphere. Our work thus establishes large-scale MD simulations as a novel technique for interrogating aerosols at the single-particle level.

Coronatine promotes maize water uptake by directly binding to the aquaporin ZmPIP2;5 and enhancing its activity.

Water uptake is crucial for crop growth and development and drought stress tolerance. The water channel aquaporins (AQP) play important roles in plant water uptake. Here, we discovered that a jasmonic acid analog, coronatine (COR), enhanced maize (Zea mays) root water uptake capacity under artificial water deficiency conditions. COR treatment induced the expression of the AQP gene Plasma membrane intrinsic protein 2;5 (ZmPIP2;5). In vivo and in vitro experiments indicated that COR also directly acts on ZmPIP2;5 to improve water uptake in maize and Xenopus oocytes. The leaf water potential and hydraulic conductivity of roots growing under hyperosmotic conditions were higher in ZmPIP2;5-overexpression lines and lower in the zmpip2;5 knockout mutant, compared to wild-type plants. Based on a comparison between ZmPIP2;5 and other PIP2s, we predicted that COR may bind to the functional site in loop E of ZmPIP2;5. We confirmed this prediction by surface plasmon resonance technology and a microscale thermophoresis assay, and showed that deleting the binding motif greatly reduced COR binding. We identified the N241 residue as the COR-specific binding site, which may activate the channel of the AQP tetramer and increase water transport activity, which may facilitate water uptake under hyperosmotic stress.

Osmotic characteristics of water retention structures of Bursera microphylla in relation to soil salinity

With a worldwide increase in soil salinity, as well as the climate crisis raising global temperatures, it is important to understand the effects of soil salinity on plant survival. One way to understand how plants may evolve to survive in these xeric desert environments is to gain a further understanding of existing halophytic (live in saline environments) and/or xerophytic (live in dry, arid environments) plants. Bursera microphylla in particular is quite interesting because it is both a halophyte and a xerophyte. One reason it is able to survive in dry environments is due to its bulbs at the base of the trunk and major limbs of the tree, which have been shown to store water during droughts. To facilitate mineral uptake, plants use ATP to transport NaCl ions into the plant, which facilitates water uptake. Because observed field conditions in the Baja California Peninsula were extremely xeric, most plants there have distinct evolutionary traits to facilitate water storage or retention. The Elephant Tree (Bursera microphylla) gets its name from the abnormal proportions of the base of its stem, which is much wider than much of the tree, and studies show that this disproportionately wide stem can store water for use during times of drought, which are common in the Baja California Peninsula. Our hypothesis was that sodium chloride was taken up through the plant’s root structure to facilitate this water transportation, and that this sodium chloride accumulation was directly proportional to the soil salinity. We tested this hypothesis via light microscopy of plant tissues to observe cell tonicity under different concentrations of saline solution. soil salinity was measured using saturated extraction. The results of this experiment show that most cells within the “bulb” structures were isotonic at a concentration approximately twice as high as that of root tissue and ambient soil salinity, therefore supporting the presented hypothesis.

Polarized NHE1 and SWELL1 regulate migration direction, efficiency and metastasis

Cell migration regulates diverse (patho)physiological processes, including cancer metastasis. According to the Osmotic Engine Model, polarization of NHE1 at the leading edge of confined cells facilitates water uptake, cell protrusion and motility. The physiological relevance of the Osmotic Engine Model and the identity of molecules mediating cell rear shrinkage remain elusive. Here, we demonstrate that NHE1 and SWELL1 preferentially polarize at the cell leading and trailing edges, respectively, mediate cell volume regulation, cell dissemination from spheroids and confined migration. SWELL1 polarization confers migration direction and efficiency, as predicted mathematically and determined experimentally via optogenetic spatiotemporal regulation. Optogenetic RhoA activation at the cell front triggers SWELL1 re-distribution and migration direction reversal in SWELL1-expressing, but not SWELL1-knockdown, cells. Efficient cell reversal also requires Cdc42, which controls NHE1 repolarization. Dual NHE1/SWELL1 knockdown inhibits breast cancer cell extravasation and metastasis in vivo, thereby illustrating the physiological significance of the Osmotic Engine Model.

Crystallographic Mapping and Tuning of Water Adsorption in Metal-Organic Frameworks Featuring Distinct Open Metal Sites.

Crucial steps toward designing water sorption materials and fine-tuning their properties for specific applications include precise identification of adsorption sites and establishment of rigorous molecular-level insight into the water adsorption process. We report stepwise crystallographic mapping and density functional theory computations of adsorbed water molecules in ALP-MOF-1, a metal-organic framework decorated with distinct open metal sites and carbonyl functional groups that serve as water anchoring sites for seeding the nucleation of a complex water network. Identification of an unusual water adsorption step in ALP-MOF-1 motivated the tuning of metal ion composition to adjust water uptake. These studies provide direct evidence that the identity of the open metal sites in MOFs can dramatically affect water adsorption behavior between 0 and ∼20% RH and that multiple proximal water anchoring sites along the MOF skeleton facilitate water uptake which could be potentially useful for applications requiring rapid and energetically facile water sorption.

Potential enhancement in atmospheric new particle formation by amine-assisted nitric acid condensation at room temperature

Atmospheric aerosol plays a critical role in global climate and public health. Recent laboratory experiments showed that new particle formation is significantly enhanced by rapid condensation of nitric acid and ammonia at low temperatures. Amines are derivatives of ammonia with a significant presence in the atmosphere. For example, the wide implementation of amine-based Post-Combustion Carbon Capture (PCCC) units may significantly increase the ambient alkanolamine and polyamine levels. Using thermodynamic simulations, the condensation of alkylamines, alkanolamines and polyamines with nitric acid at various temperatures was systematically evaluated. Alkylamines will condense with nitric acid at temperatures comparable to that of ammonia. However, with additional hydrogen bonding groups, alkanolamines and polyamines may condense with nitric acid at room temperature, suggesting a new potential pathway to remove these amines from the atmosphere. Our results suggest the potentially critical role of amines in the atmospheric new particle formation via condensation with nitric acid to rapidly grow freshly nucleated clusters over their critical size at a higher temperature than ammonia. The condensed amines and nitric acid can also facilitate water uptake by aerosol particles at low relative humidity, which may alter their subsequent atmospheric transformations.

Oligoethylene Glycol Side Chains Increase Charge Generation in Organic Semiconductor Nanoparticles for Enhanced Photocatalytic Hydrogen Evolution.

Organic semiconductor nanoparticles (NPs) composed of an electron donor/acceptor (D/A) semiconductor blend have recently emerged as an efficient class of hydrogen-evolution photocatalysts. It is demonstrated that using conjugated polymers functionalized with (oligo)ethylene glycol side chains in NP photocatalysts can greatly enhance their H2 -evolution efficiency compared to their nonglycolated analogues. The strategy is broadly applicable to a range of structurally diverse conjugated polymers. Transient spectroscopic studies show that glycolation facilitates charge generation even in the absence of a D/A heterojunction, and further suppresses both geminate and nongeminate charge recombination in D/A NPs. This results in a high yield of photogenerated charges with lifetimes long enough to efficiently drive ascorbic acid oxidation, which is correlated with greatly enhanced H2 -evolution rates in the glycolated NPs. Glycolation increases the relative permittivity of the semiconductors and facilitates water uptake. Together, these effects may increase the high-frequency relative permittivity inside the NPs sufficiently, to cause the observed suppression of exciton and charge recombination responsible for the high photocatalytic activities of the glycolated NPs.

Comparative transcriptome analysis of coleorhiza development in japonica and Indica rice

BackgroundColeorhiza hairs, are sheath-like outgrowth organs in the seeds of Poaceae family that look like root hair but develop from the coleorhiza epidermal cells during seed imbibition. The major role of coleorhiza hair in seed germination involves facilitating water uptake and nutrient supply for seed germination. However, molecular basis of coleorhiza hair development and underlying genes and metabolic pathways during seed germination are largely unknown and need to be established.ResultsIn this study, a comparative transcriptome analysis of coleorhiza hairs from japonica and indica rice suggested that DEGs in embryo samples from seeds with embryo in air (EIA) as compared to embryo from seeds completely covered by water (CBW) were enriched in water deprivation, abscisic acid (ABA) and auxin metabolism, carbohydrate catabolism and phosphorus metabolism in coleorhiza hairs in both cultivars. Up-regulation of key metabolic genes in ABA, auxin and dehydrin and aquaporin genes may help maintain the basic development of coleorhiza hair in japonica and indica in EIA samples during both early and late stages. Additionally, DEGs involved in glutathione metabolism and carbon metabolism are upregulated while DEGs involved in amino acid and nucleotide sugar metabolism are downregulated in EIA suggesting induction of oxidative stress-alleviating genes and less priority to primary metabolism.ConclusionsTaken together, results in this study could provide novel aspects about the molecular signaling that could be involved in coleorhiza hair development in different types of rice cultivars during seed germination and may give some hints for breeders to improve seed germination efficiency under moderate drought conditions.

Water sorption behavior of phenol formaldehyde resin reinforcing with reduced graphene oxide and ZnO decorated graphene oxide

The effect of two different fillers such as (a) reduced graphene oxide (RGO) produced by the reduction of graphene oxide (GO) using potato starch and (b) zinc oxide decorated graphene oxide (ZnO-RGO) on the water transport properties of phenol formaldehyde (PF) nanocomposites have been investigated at different temperatures. The effect of filler content, nature of filler and temperature on the water sorption of the PF nanocomposites were also studied. The results showed that the RGO content facilitates water uptake while ZnO-RGO filler impedes the water sorption properties of various nanocomposites developed. The diffusion, sorption and permeability coefficient of PF nanocomposites with varying weight percentage of filler at different temperatures were determined. The effect of temperature on the water sorption of PF nanocomposites was studied by determining the activation energy using Arrhenius equation. The thermodynamic studies revealed that the water sorption was spontaneous due to the negative value of ∆Go and the reaction was exothermic because of the negative value of ∆H. The kinetic studies showed that the water sorption of the PF nanocomposites follows a first order reaction.

Dry storage improves the vase quality of cut peony by increasing water uptake efficiency through aquaporins regulation

Proper storage prolongs peony market supply. Here, we determined the changes in fresh weight and expression of four aquaporin genes under dry storage (DS) and wet storage (WS). It has showed that after harvesting, the fresh weight change was accompanied with flower opening. After both short- and long-term of storage, the water uptake efficiency in DS group was greater during the first few vase days, providing a direct material basis of DS improved vase quality. The gene expression results showed that PlPIP1;3 and PlTIP2;1 were mainly expressed in petals, whereas PlNIP1;2-like and PlSIP2;1 were mainly expressed in the green tissues. In addition, the expression of PlTIP2;1 in the petals was consistent with the flower opening process, indicating that it may play a major role in facilitating water uptake. During cold storage, the expression of PlPIP1;3 and PlTIP2;1 was higher or more rapidly induced in the DS group, and thus we deduced that they play important roles in improving the vase quality of DS. Furthermore, the expression of PlNIP1;2-like in the early stage of the DS group was more stable than in WS, which may also be partially responsible for the vase quality improvement. In contrast, PlSIP2;1 may not be involved, since no significant change was observed between the DS and WS group. In short, the expression of PlPIP1;3 and PlTIP2;1 in the DS group during storage may improve water uptake efficiency during the vase period and then improving the vase quality of cut peony.

Developing a buried herbicide method to assess rooting depth of different rice cultivars ( Oryza sativa L.)

Rice (Oryza sativa L.) is one of the main staple foods of the world. With the increase of population and the deficit of irrigated water, the increase in rice production that is predicted will be dependent on areas prone to drought. Root depth is important for plant growth and survival during drought because of its role in facilitating water uptake from deep soil layers. By advances in genomics, the plant root systems can be linked to quantitative trait locus (QTL) information to achieve a most beneficial design of root system architecture. There is a demand to develop and validate techniques that permit estimation of the root system. Therefore, one technique (a buried TRIK and Diuron herbicide method at depth 30 cm) was used in this study to assess root traits in a total of 32 rice cultivars. The results from these screens was assessed with root traits measured on the same cultivars in the rhizotrons, hydroponic and non-woven fabric experiments. Correlations between these methods showed that herbicide score at day 35 was most strongly related to traits of the rhizotron experiment, especially number of roots passed 50 cm at 35 days, root angle at day 21, root thickness, water use and % root mass. Using all of these traits obtained in the rhizotron in a best subset regression suggests that up to 71% of the variation in herbicide score can be explained. These data strongly imply that symptoms are related to root development and transpiration demand and are therefore ideal for assessing water extraction by roots at depth. Therefore, developing a cost effective high-throughput system that can measure traits related to drought avoidance on a large number of plants would aid genetic studies in breeding.

Photosynthetic and enzymatic metabolism of Schinus terebinthifolius Raddi seedlings under water deficit

ABSTRACT Schinus terebinthifolius Raddi is a tree species that can be used in the recovery of degraded areas, as it exhibits rapid growth and has a very expansive root system, facilitating water uptake from the deeper layers of the soil. The objective of this study was to evaluate photosynthesis and enzymatic activity in S. terebinthifolius seedlings under conditions of water deficit and their potential to recover following re-irrigation. The experiment was conducted in a greenhouse under a plastic covering where plants were distributed into two groups: Group 1 - control plants, where irrigation was maintained at 70% of the water retention capacity, and Group 2 - stressed plants, where irrigation was suspended until the photosynthetic rate neared zero, followed by rehydration for 12 days, then a further suspension of irrigation. At the beginning of the experiment and during the suspension of irrigation and rehydration, plants were evaluated for gas and antioxidant enzyme exchanges. Hydric stress significantly reduced photosynthesis, stomatal transpiration conductance, carboxylation efficiency of Rubisco, and the chlorophyll content of the S. terebinthifolius plants. Following rehydration, plants recovered the carboxylation efficiency of Rubisco, but not the photosynthetic rate. Antioxidant enzyme activity increased in both the aerial part and the root in response to water deficit.

Fetal Membrane Ultrastructure and Development in the Oviparous Milksnake Lampropeltis triangulum (Colubridae) with Reference to Function and Evolution in Snakes.

In eggs of oviparous reptiles, fetal membranes maintain developing embryos through the exchange of respiratory gases and provision of water and calcium. As part of a survey of reptilian fetal membranes, we used scanning electron microscopy to study fetal membrane morphology in the oviparous Pueblan milksnake, Lampropeltis triangulum campbelli. The chorioallantois initially is an avascular structure lined by enlarged chorionic and allantoic epithelia. Upon vascularization, the chorionic epithelium becomes greatly attenuated, enhancing the potential for gas exchange; the allantoic epithelium also flattens. The bilaminar omphalopleure of the yolk sac lacks blood vessels, but it becomes vascularized by allantoic capillaries and transformed into an omphalallantois. Upon regression of the isolated yolk mass, this membrane is converted to chorioallantois, equipping it for gas exchange. Allantoic fluid serves as a water reservoir, and we postulate that it facilitates water uptake by establishing an osmotic gradient. Early in development, epithelia of both the chorion and the omphalopleure show apical microvilli that greatly increase the cell surface area available for water uptake. However, these features are incompatible with gas exchange and are lost as oxygen needs take precedence. A comparison of the fetal membranes to those of other squamate species (both oviparous and viviparous) reveals characteristics that are probably ancestral for snakes, some of which are plesiomorphic for Squamata. The widespread phylogenetic distribution of these features reflects their utility as adaptations that serve functional requirements of squamate embryos.

Ultrastructure of the fetal membranes of the oviparous kingsnake, Lampropeltis getula (Colubridae) as revealed by scanning electron microscopy

ABSTRACTIn reptilian sauropsids, fetal (extraembryonic) membranes that line the eggshell sustain developing embryos by providing for gas exchange and uptake of water and eggshell calcium. However, a scarcity of morphological studies hinders an understanding of functional specializations and their evolution. In kingsnakes (Lampropeltis getula), scanning electron microscopy reveals two major fetal membranes: the chorioallantois and yolk sac omphalopleure. In early development, the chorioallantois contains tall chorionic epithelial cells, avascular connective tissue, and enlarged allantoic epithelial cells. During its maturation, the chorionic and allantoic epithelia thin dramatically and become underlain by a rich network of allantoic capillaries, yielding a membrane ideally suited for respiratory gas exchange. Yolk sac development initially is like that of typical lizards and snakes, forming an avascular omphalopleure, isolated yolk mass (IYM), and yolk cleft. However, unlike the situation in most squamates studied, the omphalopleure becomes transformed into a “secondary chorioallantois” via three asynchronous events: flattening of the epithelium, regression of the IYM, and vascularization by the allantois. Progressive expansion of chorioallantois parallels growing embryonic needs for gas exchange. In early through mid‐development, external surfaces of both the chorionic and omphalopleure epithelium show an abundance of irregular surface protrusions that possibly increase surface area for water absorption. We postulate that the hypertrophied allantoic epithelial cells produce allantoic fluid, a viscous substance that facilitates water uptake and storage. Our findings are consistent with a previous study on the corn snake Pantherophis guttatus, but include new observations and novel functional hypotheses relevant to a reconstruction of basal squamate patterns. J. Morphol. 276:1467–1481, 2015. © 2015 Wiley Periodicals, Inc.

Germination and early-stage development in the seagrass, Zostera muelleri Irmisch ex Asch. in response to multiple stressors

Episodic freshwater events within coastal environments may influence germination and early-stage seedling development within the seagrass Zostera muelleri. Hypocotyl hairs have the potential to provide anchorage to sediments, initiate geotropism and facilitate water uptake. To this point, production of these structures in seagrasses has received little attention in the literature though they may significantly influence their ability to maintain populations within estuarine environments. Early-stage development of Z. muelleri was examined under various salinity, temperature and light conditions using a fully factorial design. We found that germination rates declined significantly with increasing salinity, with the greatest germination occurring in treatments subjected to 24-h darkness at either 15 or 20°C. Hypocotyl hair initiation was influenced by both temperature and salinity. Seeds which germinated at 20°C in 24-h darkness had significantly more germinants developing hypocotyl hairs than the other treatments. Although the initiation of hypocotyl hairs was generally greater under higher salinity concentrations, germinants subjected to lower salinity conditions had a greater likelihood of developing fully extended hypocotyl hairs. Based on our results, freshwater pulses that occur shortly after seed maturation could initiate year round germination in temperate regions. Furthermore, germinants stored at salinities of less than 16ppt showed greater elongation of hypocotyl hairs, indicating such pulses would also aid in the development of these structures. The timing of freshwater pulses may exert control over the recruitment and long-term survival of the species.

Ultrastructure of the fetal membranes of the oviparous kingsnake, Lampropeltis getula (Colubridae) as revealed by scanning electron microscopy

In reptilian sauropsids, fetal (extraembryonic) membranes that line the eggshell sustain developing embryos by providing for gas exchange and uptake of water and eggshell calcium. However, a scarcity of morphological studies hinders an understanding of functional specializations and their evolution. In kingsnakes (Lampropeltis getula), scanning electron microscopy reveals two major fetal membranes: the chorioallantois and yolk sac omphalopleure. In early development, the chorioallantois contains tall chorionic epithelial cells, avascular connective tissue, and enlarged allantoic epithelial cells. During its maturation, the chorionic and allantoic epithelia thin dramatically and become underlain by a rich network of allantoic capillaries, yielding a membrane ideally suited for respiratory gas exchange. Yolk sac development initially is like that of typical lizards and snakes, forming an avascular omphalopleure, isolated yolk mass (IYM), and yolk cleft. However, unlike the situation in most squamates studied, the omphalopleure becomes transformed into a "secondary chorioallantois" via three asynchronous events: flattening of the epithelium, regression of the IYM, and vascularization by the allantois. Progressive expansion of chorioallantois parallels growing embryonic needs for gas exchange. In early through mid-development, external surfaces of both the chorionic and omphalopleure epithelium show an abundance of irregular surface protrusions that possibly increase surface area for water absorption. We postulate that the hypertrophied allantoic epithelial cells produce allantoic fluid, a viscous substance that facilitates water uptake and storage. Our findings are consistent with a previous study on the corn snake Pantherophis guttatus, but include new observations and novel functional hypotheses relevant to a reconstruction of basal squamate patterns.