Days Of Rehydration Research Articles

A molecular physiological review of vegetative desiccation tolerance in the resurrection plant Xerophyta viscosa (Baker).

Main conclusionProvides a first comprehensive review of integrated physiological and molecular aspects of desiccation toleranceXerophyta viscosa. A synopsis of biotechnological studies being undertaken to improve drought tolerance in maize is given.Xerophyta viscosa (Baker) is a monocotyledonous resurrection plant from the family Vellociacea that occurs in summer-rainfall areas of South Africa, Lesotho and Swaziland. It inhabits rocky terrain in exposed grasslands and frequently experiences periods of water deficit. Being a resurrection plant it tolerates the loss of 95 % of total cellular water, regaining full metabolic competency within 3 days of rehydration. In this paper, we review some of the molecular and physiological adaptations that occur during various stages of dehydration of X. viscosa, these being functionally grouped into early and late responses, which might be relevant to the attainment of desiccation tolerance. During early drying (to 55 % RWC) photosynthesis is shut down, there is increased presence and activity of housekeeping antioxidants and a redirection of metabolism to the increased formation of sucrose and raffinose family oligosaccharides. Other metabolic shifts suggest water replacement in vacuoles proposed to facilitate mechanical stabilization. Some regulatory processes observed include increased presence of a linker histone H1 variant, a Type 2C protein phosphatase, a calmodulin- and an ERD15-like protein. During the late stages of drying (to 10 % RWC) there was increased expression of several proteins involved in signal transduction, and retroelements speculated to be instrumental in gene silencing. There was induction of antioxidants not typically found in desiccation-sensitive systems, classical stress-associated proteins (HSP and LEAs), proteins involved in structural stabilization and those associated with changes in various metabolite pools during drying. Metabolites accumulated in this stage are proposed, inter alia, to facilitate subcellular stabilization by vitrification process which can include glass- and ionic liquid formation.

Estrogen Effects on Food and Fluid Intake by Ovariectomized Rats During Chronic Dehydration

Intracellular dehydration reduces food intake, and chronic dehydration is often used to study inhibitory signals that control eating. Estrogen influences both vasopressin secretion and water intake in response to dehydration, but it is unknown whether estrogen also influences food intake during dehydration. To determine whether estrogen affects inhibitory signals that control eating during dehydration, we used a protocol in which ovariectomized rats treated with estradiol benzoate (EB) or oil vehicle were given water or 2.5% NaCl for 4 days. On day 5, water was given to all rats. An automated system was used to monitor food and fluid intakes throughout the study. EB reduced feeding, and the inhibitory effect was most pronounced on day 4 of dehydration. However, there were no differences in the number of eating bouts, suggesting that, during dehydration, rats eat less per bout. Decreases in food intake were quickly reversed by rehydration, and EB-treated rats ate amounts comparable to those by oil-treated controls in the same number of bouts, indicating an increase in food intake/bout. EB treated rats drank less, but had more drinking bouts, regardless of hydration status. A decrease in fluid intake in an increased number of bouts suggests an increase in stimulatory signals to rehydrate that may be terminated by the effects of ingesting salt. As expected, both dehydrated groups increased water intake comparably during the first day of rehydration, regardless of EB treatment. Taken together, these results suggest that estrogen influences fluid intake during chronic dehydration, and that decreased feeding during dehydration is attributable to rapidly-occurring inhibitory signals that are enhanced by EB treatment. Supported by OCAST HR12-197

Dehydration Enhances Pain-Evoked Activation in the Human Brain Compared with Rehydration

Negative effects of dehydration on the human brain and cognitive function have been reported. In this study, we examined the effects of dehydration on pain thresholds and cortical activations in response to pain, compared with rehydration with an oral rehydration solution (ORS) by functional magnetic resonance imaging. Five healthy adult men were subjected to dehydration and rehydration on 2 different days. The condition on the first day was randomly assigned to each subject. They completed a 40-minute exercise protocol using a walking machine after 12 hours of fasting under both conditions. For rehydration, the subjects consumed up to 3000 mL ORS starting from the night before the test day. After exercise, a painful stimulus (cold pressor test) was applied to the subjects' medial forearm in a magnetic resonance imaging scanning gantry, and pain-evoked brain activation was analyzed. On the rehydration day, each of the subjects consumed an average of 2040 mL (range; 1800-2500 mL) ORS. Physiological data revealed that subjects when dehydrated lost more weight from exercise than subjects when rehydrated had a larger heart rate increase, a higher tympanic temperature, and a higher urine osmolality. Subjective data revealed that the subjects reported significantly stronger thirst while dehydrated than while rehydrated with ORS, although the levels of hunger and anxiety and mood did not significantly differ between conditions. The cold pressor test robustly activated the pain-related neural network, notably the anterior cingulate cortex, insula, and thalamus. Such activations in the dehydrated subjects were greater than those in the rehydrated subjects in terms of peak and cluster, accompanied by a decrease in pain threshold (P = 0.001). Our findings suggest that dehydration brings about increased brain activity related to painful stimuli together with enhanced thirst, whereas rehydration with ORS alleviates thirst and decreases brain activity related to painful stimuli.

Pleopeltis pleopeltifolia (Polypodiopsida, Polypodiaceae), a poikilochlorophyllous desiccation-tolerant fern: anatomical, biochemical and physiological responses during water stress

While many ferns have been described as desiccation tolerant (DT), few studies have reported on the mechanisms they use to survive cell desiccation. Among the species belonging to the genus Pleopeltis, P. pleopeltifolia (Raddi) Alston (Polypodiopsida, Polypodiaceae) is a DT species endemic to Brazil. So as to better characterise the mechanisms of desiccation tolerance in ferns, the present study aimed to analyse frond anatomy and physiological changes associated with desiccation and rehydration of P. pleopeltifolia. Fronds are dorsiventral, with uniseriate epidermis. The epidermal cells have various shapes, tending to stretch in the longitudinal direction of the frond. Anticlinal cell walls are sinuous, and periclinal cell walls are convex. Anomocytic stomata are restricted to the abaxial surface. Trichome-type scales are found on both sides of the frond and may play a relevant role in rehydration of this plant when water is available. The mesophyll of the frond consists of palisade parenchyma, tending to a bistratified adaxial surface and spongy parenchyma on abaxial surface. The cuticle on the adaxial surface is conspicuous, ensuring better control of internal water balance. For physiological analyses, sporophytes were subjected to desiccation for 0, 5, 10 and 15 days and rehydration for 1 day. Sporophytes showed a sharp decline in water content when kept without irrigation, reaching 9.6% after 15 days, in addition to wilting and frond rolling. A significant increase in sugar content in fronds was noticeable during desiccation, which may favour a possible osmotic adjustment and vitrification. A notable increase in proline content during rehydration was observed in fronds. During the five initial days of desiccation, the chlorophyll and carotenoid contents decreased abruptly, but after 1 day of rehydration, they had partly recovered. The photosynthetic parameters analysed by fluorescence of chlorophyll a ceased completely after 15 days of desiccation but they had recovered near to pre-desiccation levels after 1 day of rehydration.

干旱胁迫下４种常用植物幼苗的光合和荧光特性综合评价

老鸭嘴，山毛豆，假连翘和葛藤是常见的矿山植被恢复植物。采用盆栽控制土壤水分的方法，测定了这 4 种幼苗叶片的光合和荧光指标，以期为矿山植被的恢复植物筛选提供依据。结果表明（1）干旱胁迫处理期间，4 种幼苗叶片的净光合速率（<em>P</em>_n）、气孔导度（<em>G</em>_s）、蒸腾速率（<em>T</em>_r）和胞间CO₂ 浓度（<em>C</em>_i）持续下降，复水8 d后<em>P</em>_n均显著增加，老鸭嘴和山毛豆的<em>G</em>_s和<em>T</em>_r恢复到对照水平，山毛豆和葛藤的<em>C</em>_i恢复到对照水平；假连翘幼苗叶片的气孔限制值（<em>L</em>_s）随干旱胁迫时间的延长而逐渐增加，其他3 种幼苗略降后增加，复水8 d后均恢复到对照水平。（2）干旱胁迫处理期间，4 种幼苗叶片的photosystemⅡ（PSⅡ）光能捕获效率（<em>F</em>_v’/<em>F</em>_m’）、实际光化学量子效率（Yield）和表观电子传递速率（ETR）持续降低，8 d时显著小于对照。复水8 d后，<em>F</em>_v’/<em>F</em>_m’小幅波动，Yield和ETR有所恢复，其中葛藤的Yield和山毛豆的ETR恢复到对照水平；4种幼苗叶片的非化学淬灭（NPQ）持续上升，在第8天显著大于对照，复水8 d后，均持续下降，其中葛藤恢复到对照水平。（3）对光合和荧光指标进行主成分分析表明，干旱胁迫下4 种幼苗的抗旱性能大小顺序为山毛豆 > 老鸭嘴 > 假连翘 > 葛藤。;With global climate change, environmental stresses will become the most important issue for plant growth. Among these environmental factors, drought is the most important factor that limits photosynthesis and growth. As a result, an advancement in the current understanding of the responses of plants to drought stress has became a major target for research. Drought limits stomatal conductance, mesophyll conductance and photosynthetic metabolism, and the possibility of overexcitation of photosystemⅡ increases, and this reduces the photosynthetic rate and lead to an increase in the dissipation of absorbed energy through nonradiative processes. Therefore, photosynthesis and chlorophyll fluorescence can greatly help the differentiation of plants and the physiological understanding of the process under drought conditions. It has been proposed that the choice of a photosynthesis and chlorophyll fluorescence parameters as an indicator of plant performance under drought stress, in order to provide a technique for rapidly screening plants with different drought tolerances. The <em>Thunbergia erecta</em>,<em> Tephrosia candida</em>, <em>Duranta repens</em> and <em>Pueraria lobata</em> are common plant species used for mine vegetation restoration. A test of potting methods with water control was applied to study the photosynthetic and fluorescence characteristics of the seedlings of four plant species for mine vegetation restoration. The results were as follows: (1) The parameters of net photosynthetic rate (<em>P</em>_n), stomatal conductance (<em>G</em>_s), transpiration rate (<em>T</em>_r) and intercellular carbon dioxide concentration(<em>C</em>_i) of the four species decreased gradually with increasing drought time. After 8 days of rehydration, the <em>P</em>_n of the four seedling types greatly increased. The <em>G</em>_s and <em>T</em>_r of <em>T. erecta</em> and <em>T. candida,</em> and the<em> C</em>_i of <em>T. candida </em>and<em> P. lobata </em>returned to the controls level after rehydration with 8 days. The value of stomatal limits (<em>L</em>_s) of<em> D. repens </em>increased gradually with drought time, whereas that of other seedling types slightly decreased followed by an increase, and the <em>L</em>_s of the four seedling types returned to the controls level after 8 days of rehydration. (2) The chlorophyll fluorescence parameters of the excitation capture efficiency of PSⅡ (<em>F</em>_v'/<em>F</em>_m'), photochemical quantum yield of PSⅡ in the light (Yield) and apparent electron transport rate (ETR) of the four seedling types continuously decreased and significantly lower than the controls at 8th days after drought stress. After 8 days of rehydration, the<em> F</em>_v'/<em>F</em>_m' of the four seedling types waved slightly, their Yield and ETR recovered to some extent, but the Yield of <em>P. lobata </em>and the ETR of <em>T. candida</em> returned to the controls level. The non-photochemical quenching (NPQ) of the four seedling types continuously increased and it significantly greater than the control after 8 days of drought stress. The NPQ of <em>P. lobata </em>returned to the controls level, whereas that of the other seedling types decreased continuously after 8 days of rehydration. (4) The photosynthetic characteristics and chlorophyll fluorescence parameter of the four seedling types were evaluated with principal component analysis, indicating that the order of drought resistance of the four seedling types was<em> T. candida</em> > <em>T. erecta</em> > <em>D. repens</em> > <em>P. lobata</em>.

Three cycles of water deficit from seed to young plants of Moringa oleifera woody species improves stress tolerance

The main objective of this study was to assess whether recurring water stress occurring from seed germination to young plants of Moringa oleifera Lam. are able to mitigate the drought stress effects. Germination, gas exchange and biochemical parameters were analysed after three cycles of water deficit. Young plants were used 50 days after germination under three osmotic potentials (0.0, -0.3 and -0.4 MPa). For each germination treatment, control (irrigated) and stressed (10% of water control) plants were compared for a total of six treatments. There were two cycles of drought interspersed with 10 days of rehydration. The young plants of M. oleifera showed increased tolerance to repeated cycles of drought, maintaining high relative water content (RWC), high water use efficiency (WUE), increased photosynthetic pigments and increased activity of antioxidant enzymes. There was rapid recovery of the photosynthetic rate during the rehydration period. The stressed plants from the -0.3 and -0.4 MPa treatments showed higher tolerance compared to the control plants. The results suggest that seeds of M. oleifera subjected to mild water deficit have had increased the ability for drought tolerance when young plant.

Gas-exchange characteristics, leaf water potential and chlorophyll a fluorescence in oil palm (Elaeis guineensis Jacq.) seedlings under water stress and recovery

The gas-exchange characteristics, leaf water potential and chlorophyll (Chl) a fluorescence of oil palm (Elaeis guineensis Jacq.) seedlings subjected to water stress and recovery were investigated in a greenhouse experiment. At 24 days after imposition of stress, leaf water potential in water-stressed seedlings was doubled compared to that of control and there was a drastic decline in gas-exchange parameters viz. photosynthesis, transpiration, and stomatal conductance. Water stress did not irreversibly affect gas-exchange parameters and quantum efficiency of photosystem II, as seedlings exhibited total recovery of photosynthetic apparatus by 12th day of rehydration. These findings indicate that oil palm exhibits physiological plasticity to water stress during the seedling stage.

Soluções conservantes prolongam a vida de vaso de inflorescências cortadas de boca-de-leão

O objetivo deste trabalho foi avaliar o efeito de soluções de vaso na longevidade pós-colheita de inflorescências de boca-de-leão. Hastes de boca-de-leão ('Potomac White'), colhidas com seis a sete flores abertas na inflorescência, foram condicionadas em: (1) água desionizada a 20°C (controle); (2) água quente a 43°C, por uma hora, seguida de água desionizada (20°C) como solução de vaso; (3) solução de Flower® a 20°C; (4) solução de vaso preparada com 200mg L-1 de 8-HQC+20g L-1 sacarose+150mg L-1 ácido cítrico a 20°C; (5) água quente (43°C) por uma hora e Flower® em solução de vaso (20°C); e (6) água quente (43°C) por uma hora e solução contendo 200mg L-1 de 8-HQC+20g L-1 sacarose+150mg L-1 ácido cítrico como solução de vaso (20°C). A vida de vaso das inflorescências de boca-de-leão variou de três a sete dias de acordo com o tratamento utilizado. A maior longevidade foi obtida com a solução contendo 8-HQC, sacarose e ácido cítrico, tratamento que não comprometeu a abertura floral. Além disso, as inflorescências condicionadas nessa solução apresentaram ganho de massa fresca superior à massa daquelas mantidas em água desionizada ou Flower®, a partir de 24 horas, atingindo 24% de aumento no quinto dia da reidratação. Assim, o uso de soluções de vaso adequadas mantém a qualidade e prolonga a longevidade das hastes cortadas de boca-de-leão.

Membrane phase behavior of Escherichia coli during desiccation, rehydration, and growth recovery

The membrane lipid bilayer is one of the primary cellular components affected by variations in hydration level, which cause changes in lipid packing that may have detrimental effects on cell viability. In this study, Fourier transform infrared (FTIR) spectroscopy was used to quantify changes in the membrane phase behavior, as identified by membrane phase transition temperature ( T m), of Escherichia coli during desiccation and rehydration. Extensive cell desiccation (1 week at 20%–40% RH) resulted in an increase in T m from 8.4 ± 1.7 °C (in undried control samples) to 16.5 ± 1.3 °C. Fatty acid methyl ester analysis (FAME) on desiccated samples showed an increase in the percent composition of saturated fatty acids (FAs) and a decrease in unsaturated FAs in comparison to undried control samples. However, rehydration of E. coli resulted in a gradual regression in T m, which began approximately 1 day after initial rehydration and plateaued at 12.5 ± 1.8 °C after approximately 2 days of rehydration. FAME analysis during progressive rehydration revealed an increase in the membrane percent composition of unsaturated FAs and a decrease in saturated FAs. Cell recovery analysis during rehydration supported the previous findings that showed that E. coli enter a viable but non-culturable (VBNC) state during desiccation and recover following prolonged rehydration. In addition, we found that the delay period of approximately 1 day of rehydration prior to membrane reconfiguration (i.e. decrease in T m and increase in membrane percent composition of unsaturated FAs) also preceded cell recovery. These results suggest that changes in membrane structure and state related to greater membrane fluidity may be associated with cell proliferation capabilities.

Analysis of desiccation‐induced candidate phosphoproteins from Craterostigma plantagineum isolated with a modified metal oxide affinity chromatography procedure

Reversible protein phosphorylation/dephosphorylation is crucial for regulation of many cellular events, and increasing evidence indicates that this post-translational modification is also involved in the complex process of acquisition of desiccation tolerance. To analyze the phosphoproteome of the desiccation tolerant resurrection plant Craterostigma plantagineum, MOAC-enriched proteins from leaves at different stages of a de-/rehydration cycle were separated by 2-D PAGE and detected by phosphoprotein-specific staining. Using this strategy 20 putative phosphoproteins were identified by MALDI-TOF MS and MS/MS, which were not detected when total proteins were analyzed. The characterized desiccation-related phosphoproteins CDeT11-24 and CDeT6-19 were used as internal markers to validate the specificity of the analyses. For 16 of the identified proteins published evidence suggests that they are phosphoproteins. Comparative analysis of the 2-D gels showed that spot intensities of most identified putative phosphoproteins change during the de-/rehydration cycle. This suggests an involvement of these proteins in desiccation tolerance. Nearly all changes in the phosphoproteome of C. plantagineum, which are triggered by dehydration, are reversed within 4 days of rehydration, which is in agreement with physiological observations. Possible functions of selected proteins are discussed in the context of the de-/rehydration cycle.

Desiccation tolerance of the introduced marine green alga Codium fragile ssp. tomentosoides – clues for likely transport vectors?

The invasive marine green macroalga Codium fragile ssp. tomentosoides is now considered to be an introduced marine pest along the northwest Atlantic and southern Australian coasts. International or domestic translocation of C. fragile ssp. tomentosoides is usually attributed to the fouling of ship hulls or shellfish, particularly oysters. A likely domestic vector is shipboard transport, involving the translocation of whole thalli or fragments entangled in fishing nets, ropes, etc. that are then released in a previously unaffected area. Here we investigated the survival of C. fragile ssp. tomentosoides under emersed conditions, simulating shipboard transport. C. fragile ssp. tomentosoides was able to survive periods of emersion of up to 90 days in high relative air humidity. Net photosynthesis remained positive at about 50% of the rates of submersed control thalli. After 2 days of emersion and 4 days of rehydration under submersed conditions thalli recover to their initial net photosynthesis rates. Hence, C. fragile ssp. tomentosoides is likely to survive long shipboard journeys entrapped in fishing nets, anchor wells or other protected, high-humidity areas of a vessel. Furthermore, C. fragile ssp. tomentosoides may survive emersion on an exposed deck during short trips, especially in cooler conditions such as at night. The incursion sites of C. fragile ssp. tomentosoides in Australia are generally in modified environments, often associated with shipping-related infrastructure such as wharves, jetties, rip rap, and moorings.

The protective role of the spore matrix ofColletotrichum musaeduring rehydration and exposure to extreme temperatures and UV radiation

Although an inhibitory role of the spore matrix on germination of Colletotrichum musae is well established, its role in protecting spores from adverse environmental conditions remains to be proven. The possible role of the spore matrix in the survival of spores of C. musae was investigated by germinating unwashed spores of four isolates after storage at 18°C, washed and unwashed spores of three isolates after storage at -4°C and 37°C, and one isolate after exposure to UV (∼290 nm) radiation. Unwashed spores with the matrix intact consistently survived better than washed spores. The rate of germination of matrix containing stored spores was greater following 1–2 days of rehydration than when immersed directly into water. Removing the matrix was fatal to spores exposed to UV radiation. This study suggests that the spore matrix of gloeosporoid fungi, such as C. musae, is critical to their survival.

Reversible cellular and metabolic changes induced by dehydration in desiccation‐tolerant wheat seedling shoots

Wheat seedlings obtained after 2 or 3 days of seed germination in darkness at 20°C (i.e. with a 0.5–0.7 cm long coleoptile) were still viable after drying in darkness in ambient conditions which reduced the shoot moisture content to about 0.30 g H2O g−1 dry mass (DM). Coleoptile and primary leaf growth resumed upon rehydration, but primary roots died and new roots regenerated. In the present work we have investigated whether desiccation tolerance of the shoot (coleoptile and primary leaf combined) was related to some reversible cellular or metabolic changes induced by dehydration. Non‐dehydrated shoots were high in moisture content (4.0–5.0 g H2O g−1 DM) and exhibited an active metabolism as indicated by a high energy charge (EC = 0.85) and cells with well developed mitochondria, endoplasmic reticulum, polysomes and Golgi bodies. Dehydration induced changes in cell membrane properties since it reduced in vivo capacity of the shoot to convert 1‐aminocyclopropane 1‐carboxylic acid (ACC) to ethylene (i.e. ACC oxidase activity). This effect was already observed at 4–5 h of dehydration, namely when shoot moisture content dropped down below about 3.0 g H2O g−1 DM, and ACC‐dependent ethylene production became almost nil when shoot moisture content reached 1.0 g H2O g−1 DM. Dehydration also resulted in decreases in ATP and non‐adenylic triphosphate nucleotide (NTP) contents down to 1–2% of their initial values, and in EC value to 0.20. Concomitant with water loss, sucrose content of the shoot increased and was maximal (about 330 mg g−1 DM, namely three‐fold that of non‐dehydrated organs) after 2 days of drying. Upon rehydration, shoots regained their original moisture content within 3 days, during which they progressively recovered apparent normal metabolism. Reversal of extensive dehydration‐associated cell wall folding occurred between 2 and 3 days of rehydration, when the ultrastructure of coleoptile and primary leaf cells also provided evidence of intensive autophagic activity, indicative of the removal of damaged cell components. Concomitantly, apparently undamaged organelles and endomembranes persisted in the cytoplasm. Restoration of 60–70% of ACC oxidase activity and 80–90% of EC value occurred within 48 and 18 h, respectively. However, the values of the ATP/ADP and NTP/ATP ratios remained lower than in control non‐dehydrated shoots, indicating that not all metabolic deterioration induced by dehydration was completely repaired. Differences in relationships between shoot moisture content and ACC‐oxidase activity or energy metabolism during dehydration and upon rehydration, and cell ultrastruture analyses suggest that desiccation tolerance of wheat seedling shoot is related to mechanisms involved in the maintenance of cell structure during water loss and the cell capacity to repair the dehydration damage.

Drought Adaptation in Fraxinus excelsior L.: Physiological Basis of the Elastic Adjustment

This study examines the drought-induced mechanisms in Fraxinus excelsior L., a species that exhibits a great tolerance with respect to severe water shortage. Pressure-volume curves obtained from seedlings submitted to an artificially induced drought showed a decrease in the osmotic potential at full turgor and at zero turgor. This osmotic adjustment was also demonstrated in stressed plants by the increase in the level of the main organic compounds, malate and mannitol. By calculating the elastic modulus (ε) of the foliar tissues, it was also shown that the cell walls of the stressed plants became less extensible. This adaptative response to water deficit was easily reversed after only 1 day of rehydration. A similar increase in ε could be induced in short term experiments by the application of 20 μmol/L ABA to detached well-watered leaves, and counteracted in detached leaves from water-stressed seedlings by treatment with acidic pH buffer. From these data, it is suggested that bonding rearrangements rather than structural modifications of the cell wall are involved in the elastic adjustment. The advantages of the elastic adjustment procedure are discussed in relation to plants water availability.

A patch coating method for preparing biocatalytic films of Escherichia coli.

A method has been developed for immobilizing viable but nongrowing Escherichia coli in highly uniform patches. The patches consist of a thin layer of bacteria in acrylate vinyl acetate covered with a thin layer of the same polymer devoid of bacteria and sealed by the edges. This method permits study of immobilized cell physiology in biocatalytic films by the assay methods used for suspended cells. Large numbers of patches of immobilized E. coli can be generated on metal or polyester sheets. Those described here are 12.7 mm in diameter; in them the cell layer is 30 microm thick and contains more than 5 x 10(8) viable cells. The method allows the cell-plus-polymer layer and the polymer sealant to be varied in thickness from 5 to 60 microm and from 7 to 80 microm, respectively. No leakage of cells was detected from 87% of the patches during 15 days of rehydration. Culturability of the immobilized cells, released by shaking the cells out of the porous polymer layer, was 80% of pre coating culturability. E. coli beta-galactosidase activity and measurements of total RNA and DNA from immobilized and suspended cells indicated that cells immobilized in the thin polymer layer have higher specific beta-galactosidase activity and a slower total RNA degradation rate than suspended cells over 15 days.

Dehydration and rehydration selectively and reversibly alter glial fibrillary acidic protein immunoreactivity in the rat supraoptic nucleus and subjacent glial limitans

Ultrastructural studies of the supraoptic nucleus (SON) of the hypothalamus suggest that an active retraction and extension of astrocytic processes (structural plasticity) from between magnocellular neuroendocrine neurons plays a role in the release of oxytocin, vasopressin, or both peptides that accompanies parturition, lactation, and dehydration. In support of this, Salm et al. (1985) previously demonstrated a lactation-associated reduction in immunoreactive glial fibrillary acidic protein (GFAP), an astrocyte-specific cytoskeletal constituent. To determine if similar changes occur in response to dehydration, and if they are reversible, the present study examined GFAP-immunoreactivity (IR) in the SON under various hydration states. Rats were dehydrated for 7 days by substitution of drinking water with 2% saline (n = 3), or dehydrated for 7 days followed by 7 days of rehydration (n = 3). A control group (n = 3) with free access to tap water was used for comparisons. The optical density of GFAP-IR was obtained from the SON, globus pallidus, and lateral hypothalamic regions. The areas of the ventral glial limitans subjacent to the SON (SON-VGL) and of linearly equivalent segments of glial limitans more distant from the SON were also determined. Dehydration resulted in a significant reduction in GFAP-IR in the SON compared to control and rehydrated levels. We also found that the area of the SON-VGL was significantly larger than that of linearly equivalent segments of glial limitans elsewhere and that it was significantly reduced in dehydrated rats, returning to control levels with rehydration. GFAP-IR and glial limitans thickness in regions unrelated to body fluid homeostasis lateral to the SON, overlying to dorsal cortex, and subjacent to the optic chiasm were not significantly changed by hydration state. These results are similar to the changes of GFAP-IR reported for lactating rats and provide further evidence for a role of structural plasticity of astrocytes in events surrounding the selective functional activation of local neurons.

Structural dynamics of neural plasticity in the supraoptic nucleus of the rat hypothalamus during dehydration and rehydration

It has been known that magnocellular neuroendocrine cells (MNCs) of mammalian hypothalamus show structural plasticity in response to chronic osmotic stimulation. In this study, we investigated the relationships among plasma osmolarity and several structural changes such as alterations of soma size, juxtaposition, and synapses of the supraoptic nucleus (SON) in the rat hypothalamus during dehydration and rehydration. Male rats were osmotically stimulated by supplying with 2% Nad solution instead of tap water for 10 days, and then they were rehydrated with tap water. Plasma osmolarity was gradually elevated with progress of salt loading and returned to control level on the seventh day of rehydration. Both the percentage of membrane contact (juxtaposition) and the soma size of MNCs were increased in response to the rise of plasma osmolarity, and decreased to control level on the seventh day of rehydration. The number of synapses including both single synapses and multiple synapses per 100 μm soma membrane was lower than control on the fifth day of dehydration, but it was not different from controls on the tenth day of dehydration, and on the seventh and fourteenth day of rehydration. The total number of synapses per 100 μm soma membrane, the synaptic density, was maintained relatively constant, although soma size was progressively changed during dehydration or rehydration. This synaptic reorganization seems to be mainly regulated by synaptic sprouting during dehydration and by degradation of synapses during rehydration. The number of multiple synapses per 100 μm soma membrane and the percentage of multiple synapses to total synapses were significantly higher than those of controls on the fifth and tenth day of dehydration and on the seventh day of rehydration, and they returned to control level on the fourteenth day of rehydration. Furthermore, most of the multiple synapses was observed to contact preferentially with soma and dendrites at increased stages of multiple synapses, indicating the special interaction of multiple synapses to soma by acting via adjacent dendrite.

Alterations in vasopressin and oxytocin messenger RNA in the rat supraoptic nucleus during dehydration-rehydration evaluated by in situ hybridization and Northern blotting

Male rats were deprived of water for 5 days, and then given water ad libitum for 3, 7, 10 or 14 days. Plasma osmolarity returned to normal in less than 3 days, while pituitary vasopressin (AVP) and oxytocin (OXT) only returned to control levels after 14 days. Sections of the supraoptic nucleus (SON) were hybridized with 35S-labelled cDNA (OXT) or oligonucleotide (AVP) probes. Relative AVP and OXT mRNA contents were quantitated by counting the number of silver grains on a large standard area of the SON, then extrapolating this value to the volume of the whole SON (deduced from surface areas of all the sections). Dehydration significantly enlarged the volume of the SON (×1.54) and increased the AVP and OXT mRNAcontent (×2). During rehydration, both SON volume and density of silver grains were higher than normal for at least 7–10 days, although levels started to fall by day 3. The distribution of individual cells according to their silver grain densities remained unimodal during the dehydration-rehydration sequence with an extension, then a return to normal of the distribution range. Maximum sizes of AVP and OXT mRNAs on Northern blots of RNAs extracted from 5 pooled SONs were observed on dehydration day 5. The size of these species fell progressively, reaching control values by rehydration day 14. We conclude that during rehydration, at a time when most of the putative inducers of gene transcription are no longer activated, the peptidergic deficit was accompanied by an increased level of AVP and OXT mRNAs. However, both the amount and the size of these mRNAs started to fall as soon as the osmotic stimulus was removed.

Fluid absorption from the rumen during rehydration in sheep

Water movements across the rumen wall were studied during rehydration in four fistulated sheep. The animals were dehydrated for 48 h which increased total plasma protein, plasma osmolality, plasma Na+, arginine vasopressin and plasma renin activity. Two series of experiments were performed: Expt I with no food available during rehydration, and Expt II where the animals were fed hay. On the rehydration day, a fluid marker (cobalt-EDTA) was administered into the rumen. To avoid water outflow from the rumen a stopper was inserted into the reticulo-omasal orifice. When the animals were provided with water they immediately drank 9 l. The water offered contained the same marker concentration (Co2+) as in the rumen liquid. In Expt I, Co2+ concentration increased after drinking, and remained elevated until the stopper was removed. The highest value was obtained after 20 min, and this corresponded to at least a 11 water absorption in individual animals. In Expt II, the sheep immediately started to eat following drinking and the inflow of saliva caused a dilution of the marker. Plasma osmolality and Na+ concentration decreased in both experiments indicating that water absorption occurred in both experiments. Removal of the stopper did not cause any significant changes in the parameters measured. Vasopressin concentration fell immediately on the sight of water, and then continued to decrease. It is concluded that in the sheep, voluntary drinking is followed by an immediate and substantial absorption of water from the rumen.

Avian epidermal differentiation II. Adaptive response of permeability barrier to water deprivation and replenishment

Zebra Finches are the epitome of desert-adapted avian species; i.e. they are able to survive without drinking water for over a year. Whereas transepidermal water loss (TEWL) in naked Zebra Finch nestlings is lower than in adults, and desert adaptation is accompanied by intercellular deposition of epidermal multigranular body (MGB) contents, MGB secretion is reduced as nestlings mature into feathered adults, indicative of less stringent barrier requirements. Here, removal of drinking water resulted in increased intercellular deposition of MGB contents, and TEWL progressively decreased. In contrast, MGB intercellular deposition decreased when birds were rehydrated, with TEWL returning towards normal within 5 days of rehydration. Finally, water-deprivation caused significant changes in epidermal lipid composition that returned toward control levels with rehydration. These studies show that adult Zebra Finches adapt to xeric stress by increased secretion of multigranular bodies resulting in reduced TEWL.