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PubMed2000

Seed germination of six mature neotropical rain forest species in response to dehydration.

We studied effects of dehydration and rehydration on germination of seeds of six mature tropical rain forest species-Cupania glabra Swartz, Cymbopetalum baillonii Fries, Poulsenia armata (Miq.) Standl., Stemmadenia donnell-smithii (Rose) Woodson, Rheedia edulis Triana & Planch. and an understory palm Chamaedorea alternans H. Wendl.-from Veracruz, México. Before the seeds were sown, their water content was reduced by 0 (control), 30, 54 and 72% of their original water content. Dehydration affects the ability of seeds to rehydrate, as well as the rate and final percentage of germination when seeds are subsequently rehydrated. Seed survival and germination behavior showed three patterns: (1) C. baillonii, P. armata and S. donnell-smithii had greater tolerance to seed dehydration than C. glabra, C. alternans and R. edulis; (2) partial dehydration enhanced germinability of C. glabra and C. baillonii seeds; and (3) partial dehydration of C. alternans and R. edulis seeds resulted in delayed or sporadic germination. A relationship was found between the effects of dehydration on germination and the seasonality of seed production.

Journal Article↗
PubMed2002

Rate of dehydration and cumulative desiccation stress interacted to modulate desiccation tolerance of recalcitrant cocoa and ginkgo embryonic tissues.

Rate of dehydration greatly affects desiccation tolerance of recalcitrant seeds. This effect is presumably related to two different stress vectors: direct mechanical or physical stress because of the loss of water and physicochemical damage of tissues as a result of metabolic alterations during drying. The present study proposed a new theoretic approach to represent these two types of stresses and investigated how seed tissues responded differently to two stress vectors, using the models of isolated cocoa (Theobroma cacao) and ginkgo (Ginkgo biloba) embryonic tissues dehydrated under various drying conditions. This approach used the differential change in axis water potential (DeltaPsi/Deltat) to quantify rate of dehydration and the intensity of direct physical stress experienced by embryonic tissues during desiccation. Physicochemical effect of drying was expressed by cumulative desiccation stress [integralf(psi,t)], a function of both the rate and time of dehydration. Rapid dehydration increased the sensitivity of embryonic tissues to desiccation as indicated by high critical water contents, below which desiccation damage occurred. Cumulative desiccation stress increased sharply under slow drying conditions, which was also detrimental to embryonic tissues. This quantitative analysis of the stress-time-response relationship helps to understand the physiological basis for the existence of an optimal dehydration rate, with which maximum desiccation tolerance could be achieved. The established numerical analysis model will prove valuable for the design of experiments that aim to elucidate biochemical and physiological mechanisms of desiccation tolerance.

Adaptation, Physiological↗
PubMed2004

Long term transcript accumulation during the development of dehydration adaptation in Cicer arietinum.

Cool season crops face intermittent drought. Exposure to drought and other abiotic stresses is known to increase tolerance of the plants against subsequent exposure to such stresses. Storage of environmental signals is also proposed. Preexposure to a dehydration shock improved adaptive response during subsequent dehydration treatment in a cool season crop chickpea (Cicer arietinum). We have identified 101 dehydration-inducible transcripts of chickpea by repetitive rounds of cDNA subtraction; differential DNA-array hybridization followed by northern-blot analysis and analyzed their responses to exogenous application of abscisic acid (ABA). Steady-state expression levels of the dehydration-induced transcripts were monitored during the recovery period between 2 consecutive dehydration stresses. Seven of them maintained more than 3-fold of expression after 24 h and more than 2-fold of expression level even at 72 h after the removal of stress. Noticeably, all of them were inducible by exogenous ABA treatment. When the seedlings were subjected to recover similarly after an exposure to exogenous ABA, the steady-state abundances of 6 of them followed totally different kinetics returning to basal level expression within 24 h. This observation indicated a correlation between the longer period of abundance of those transcripts in the recovery period and improved adaptation of the plants to subsequent dehydration stress and suggested that both ABA-dependent and -independent mechanisms are involved in the maintenance of the messages from the previous stress experience.

Abscisic Acid↗
PubMed1996

A Study of the Stationary Volumetric Elastic Modulus during Dehydration and Rehydration of Stems of Pea Seedlings.

The relationship between cortical-cell turgor pressure (P) and tissue water mass (W) was determined for stem segments of pea (Pisum sativum L.) seedlings subjected to hydration and dehydration. This allowed a test for elastic hysteresis in the cortical cells. The P-W curves for dehydration and hydration were not coincident. In some experiments, the P-W curves exhibited a "roll-off" at high P, similar to the "plateau effect" sometimes observed in pressure-chamber studies. When hydration was followed by a 4-h dehydration, the tissue water mass (W0) at minimum turgor was reduced. This might reflect a reduction in apoplastic water mass and/or a contraction of the symplast during dehydration. Neglecting the decrease in W0 leads to underestimates of the stationary volumetric elastic modulus ([epsilon]stat). The result of an analysis that assumes W0 was constant during hydration suggests that there was no significant difference in [epsilon]stat between dehydration and hydration and, hence, no significant elastic hysteresis. However, a 16-h dehydration increased [epsilon]stat; this might be a response to water stress.

Journal Article↗
PubMed1996

Effects of COR6.6 and COR15am polypeptides encoded by COR (cold-regulated) genes of Arabidopsis thaliana on dehydration-induced phase transitions of phospholipid membranes.

Cold acclimation of Arabidopsis thaliana includes the expression of cold-regulated (COR) genes and the accumulation of COR polypeptides. The hydration characteristics of two COR polypeptides, COR6.6 and COR15am, have been determined and their effects on the dehydration-induced liquid crystalline-to-gel and lamellar-to-hexagonal II phase transitions in phospholipid mixtures have been examined. After dehydration at osmotic pressures between 8 and 150 MPa, the water content of the COR polypeptides was less than that of bovine serum albumin, with COr15am the least hydrated: bovine serum albumin > COR6.6 > COR15am. Neither COR6.6 nor COR15am altered the dehydration-induced gel lamellar --> fluid lamellar phase transition temperature of either dipalmitoylphosphatidylcholine or dioleoylphosphatidylcholine (DOPC). In multilamellar vesicles of dioleoylphosphatidylethanolamine:DOPC (1:1, mol:mol) prepared by either freeze-thaw or reverse-phase evaporation methods, neither COR6.6, COR15am, nor bovine serum albumin altered the incidence of the dehydration-induced formation of the inverted hexagonal phase as a function of osmotic pressure. However, a specific ultrastructural alteration--the formation of a striated surface morphology in the lamellar domains--was observed in mixtures of dioleoylphosphatidylethanolamine:DOPC that were dehydrated in the presence of COR15am. Nevertheless, neither COR6.6 nor COR15am appears to participate in a specific protein-phospholipid interaction that alters the dehydration-induced phase behavior of phospholipid vesicles.

Arabidopsis↗
PubMed2000

Protein dynamics in thylakoids of the desiccation-tolerant plant Boea hygroscopica during dehydration and rehydration.

Plants of Boea hygroscopica F. Muell were dehydrated to 9% relative water content (RWC) by withholding water for 26 d, and afterward the plants were rehydrated. Leaves were taken from control plants after 7, 12, and 26 d from the beginning of dehydration, and after 6 and 48 h from rehydration. The RWC decreased by 80% during dehydration, but the leaves regained RWC with rehydration. Dehydrated plants showed lesser amounts of proteins, lipids, and chlorophyll, all of which increased following rewatering. The lipid-to-protein ratio, which decreased during dehydration, returned to control level after 48 h of rehydration. Thylakoid lipids were more unsaturated when RWC reached the value of 9%. EPR measurements of spin-labeled proteins showed the presence of three different groups of proteins with different mobility in thylakoid membranes. The rotational correlation time of groups 1 and 2 increased with dehydration and decreased upon rehydration, whereas group 3 showed little changes. Desiccation did not cause thylakoid swelling or breakage, but the membrane system assemblage showed changes in thylakoid stacking. After 48 h of rehydration the membrane system recovered completely the organization of the fully hydrated state, showing several well-defined and regularly distributed grana.

Antioxidants↗
PubMed1985

Simulation of dehydration injury to membranes from soybean axes by free radicals.

Smooth microsomal membranes were isolated from axes of soybean (Glycine max L. Merr.) seeds at the dehydration-tolerant (6 hours of imbibition) and dehydration-susceptible (36 hours of imbibition) stages of development and were exposed to free radicals in vitro using xanthine-xanthine oxidase as a free radical source. Wide angle x-ray diffraction studies indicated that the lipid phase transition temperature of the microsomal membranes from the dehydration-tolerant axes increased from 7 to 14 degrees C after exposure to free radicals, whereas those from the dehydration-susceptible axes increased from 9 to 40 degrees C by the same free radical dose. The increased phase transition temperature was associated with a decrease in the phospholipid:sterol ratio, and an increase in the free fatty acid:phospholipid ratio. There was no significant change in total fatty acid saturation, which indicated that free radical treatment induced deesterification of membrane phospholipid, and not a change in fatty acid saturation. Similar compositional and structural changes have been previously observed in dehydration-injured soybean axes suggesting that dehydration may induce free radical injury to cellular membranes. Further, these membranes differ in their susceptibility to free radical injury, presumably reflecting compositional differences in the membrane since these membranes were exposed to free radicals in the absence of cytosol.

Journal Article↗
PubMed1986

The effects of osmotic tissue dehydration and air drying on morphology and energy transfer in two species of porphyra.

Studies were conducted to document the effects on morphology and energy transfer in photosynthesis of severe tissue dehydration induced either by air-drying or by immersing the tissues of two Porphyra species in hyperosmotic solutions. These studies showed that the dehydration-tolerant intertidal alga, Porphyra perforata J.Ag., was almost unaffected by either of these treatments, while the dehydration-sensitive Porphyra nereocystis Anders. was damaged similary by both treatments. Damage to that sensitive species was characterized by ruptured organelles as seen by interference microscopy as well as by increased fluorescence emission at 682 nanometers emanating from allophycocyanin. These results suggest that a disruption of energy transfer between allophycocyanin and chlorophyll a occurs because of the damage to membranes following tissue dehydration, and that the increase in the yield of phycobilin fluorescence is a good indicator of these phenomena. Thus, air-drying and osmotic-dehydration appear to have similar physiological consequences in a dehydration-sensitive alga but almost no effect in a tolerant species.

Journal Article↗
PubMed1984

Vasopressin in plasma and cerebrospinal fluid of hydrated and dehydrated steers.

Levels of arginine-vasopressin (AVP), the antidiuretic hormone, have been concurrently measured by radioimmunoassay (RIA) in plasma (p) and cerebrospinal fluid (CSF) from conscious, unrestrained steers. During 4 days of dehydration, plasma osmolarity (posm) rose progressively from control hydrated levels of 301.3 +/- 0.632 mosm/1(mean +/- SE) to 338.5 +/- 3.090 mosm/1(p less than 0.001). Packed cell volume also rose from 39.9 +/- 0.64% to 44.7 +/- 1.24% (p less than 0.001). Associated with these changes was a progressive increase in pAVP from control levels of 1.3 +/- 0.19 microU/ml to 16.9 +/- 1.88 microU/ml(p less than 0.001) after 4 days without water. Log pAVP was linearly related to posm (r = 0.82, p less than 0.001). Mean level of CSF-AVP in control animals was 5.4 +/- 0.97 microU/ml. During dehydration, CSF-AVP levels also rose, becoming significantly greater than control levels (p less than 0.01) after 3 days without water and further increasing to reach 15.2 +/- 1.83 microU/ml after 4 days without water (p less than 0.001). Log CSF-AVP could also be linearly related to posm (r = 0.62, p less than 0.01). Termination of dehydration by restoration of ad libitum water supply was accompanied by return of pAVP and CSF-AVP to pre-dehydration levels. Regression analysis of concurrent levels of pAVP an CSF-AVP indicates that CSF-AVP levels are linearly correlated to pAVP levels in hydrated and dehydrated animals (r = 0.70, p less than 0.001). These experiments suggest that neurosecretory neurons secreting AVP at sites accessible to CSF respond to similar stimuli during dehydration as those neurons secreting AVP into blood.

Animals↗
PubMed1989

Natural dehydration regimes as a prerequisite for the successful induction of anhydrobiosis in the nematode Rotylenchulus reniformis.

Induction of anhydrobiosis in the nematode Rotylenchulus reniformis (Linford & Oliveira) was studied using direct exposure to elevated relative humidities and conditions resembling natural dehydration regimes. All larvae and preadults were unable to survive direct short-term exposure to 97% relative humidity. However, dehydration of larvae on model substrates (0.5% agar: 1.0% agarose) that mimic the natural rate of soil moisture loss induced coiling and successful entry into anhydrobiosis. Coiling was maximized at 10-12 days and only coiled larvae survived dehydration, emerging as the preadult form. Larvae could withstand severe dehydration at 80 and 40% relative humidity after the induction of coiling, but were unable to withstand direct exposure to 0% relative humidity. The levels of adaptation utilized by anhydrobiotes to ensure slow dehydration and the adaptive significance of this are discussed in relation to the different environments in which these organisms are found. The results suggest that R. reniformis is well-adapted to its environment and emphasize the importance of natural dehydration regimes for assessing anhydrobiotic potential.

Adaptation, Physiological↗
PubMed2001

Effects of dehydration temperatures on moisture absorption and dissolution behavior of theophylline.

Anhydrous theophylline was prepared by heating theophylline monohydrate at temperatures between 60 degrees C and 140 degrees C. The effects of dehydration temperatures on the moisture absorption and dissolution behavior of anhydrous theophylline were investigated in this study. The hydration rate of anhydrous theophylline at 95% relative humidity and 25 degrees C decreased with increasing dehydration temperatures. From the fitting analysis of solid-state reaction models, the hydration reaction was found to be governed by the phase boundary reaction model for samples prepared at lower dehydration temperatures (<100 degrees C) but the reaction obeyed the growth of nuclei reaction model when samples were dehydrated at higher temperatures. The dissolution rates of various anhydrous theophylline samples were measured by the rotating disk method. The calculated solubility of anhydrous theophylline prepared by heating was about 2.5 times higher than that of theophylline monohydrate. The phase transformation rate from the anhydrous form to the monohydrate during dissolution tests decreased with higher dehydration temperatures. It was found that the anhydrous theophylline prepared at different dehydration temperatures transformed to the monohydrate by way of different growth of hydrate nuclei mechanism.

Absorption↗
PubMed1994

Sulphotransferase-dependent dehydration of atropine and scopolamine in guinea pig.

1. Enzymatic dehydration of atropine and scopolamine was studied in guinea pig. 2. The incubation of these alkaloids with guinea pig liver cytosol in the absence of cofactors gave no dehydrated metabolite. However, when atropine and scopolamine were incubated with cytosol supplemented with ATP and sodium sulphate, dehydrated metabolites, apoatropine and aposcopolamine were formed. The formation of these metabolites was confirmed by gas chromatography-mass spectrometry. 3. The reaction required ATP as well as cytosol as the obligatory factors. Deletion of sodium sulphate from the reaction mixture also resulted in a decrease of the activities, although this treatment showed limited effect when the low concentration of atropine was used. Furthermore, dehydroepiandrosterone, an excellent substrate for hydroxysteroid-sulphotransferase, effectively inhibited the in vitro activity of atropine dehydration. 4. Administration of dehydroepiandrosterone to guinea pig followed by atropine treatment caused decreased urinary excretion of apoatropine. 5. These results strongly suggested that the dehydration of atropine and scopolamine takes place via the sulphate conjugate intermediates produced from the sulphotransferase-catalysed reaction. The present finding is the first example of the sulphotransferase-dependent dehydration of a drug, and its generality in drug metabolism is discussed.

Animals↗
PubMed1999

The on-eye dehydration of proclear compatibles lenses.

PURPOSE: The purpose of the study was to evaluate the on-eye dehydration over time, of molded omafilcon A lenses (Proclear Compatibles) compared to a range of frequent replacement lenses. METHODS: Ten subjects wore a Proclear Compatibles lens in one eye and a control lens in the other eye for 4-, 8- and 12-hours. The control lenses were Acuvue, Soflens 66 and Optima frequent replacement lenses. Each subject wore three different pairs of lenses for each time period in a masked, randomized fashion. A gravimetric technique was used to determine lens water content. RESULTS: The Proclear Compatibles lenses showed significantly less relative dehydration than the Acuvue and Soflens 66 lenses. The Acuvue and Soflens 66 lenses showed a significant increase in relative dehydration with increasing wearing time. Subjective comfort was graded higher with the Proclear Compatibles than with the Acuvue lenses. There was a significant negative correlation between Acuvue dehydration and subjective ratings of comfort. CONCLUSIONS: The study showed that Proclear Compatibles lenses dehydrate significantly less than the other frequent replacement high-water content lenses. The Acuvue and Soflens 66 lenses showed increasing dehydration during the 4-12 hour wearing period.

Contact Lenses, Hydrophilic↗
PubMedDate not supplied

Cryopreservation of 'Nabali' olive (Olea europea l.) somatic embryos by encapsulation-dehydration and encapsulation-vitrification.

Olive (Olea europea L.) somatic embryos were successfully cryopreserved using encapsulation-dehydration and encapsulation-vitrification. In the encapsulation-dehydration procedure, a maximum of 48% embryo survival was obtained when bead moisture content was decreased to 21.1% after 4 h dehydration. Preculture of embryos for 4 d in medium containing 0.75 to 1.25 M sucrose produced higher (40 to 34 %, respectively) regrowth after cryopreservation using encapsulation-dehydration procedure. Dehydration of beads for 3 h in PVS2 ensured higher survival (64%) of encapsulated-vitrified and cryopreserved (EVN) somatic embryos. Thermal treatment of embryogenic callus for 1 d at 30 degree C was very effective to increase survival of encapsulated-dehydrated and cryopreserved (EDN) (58%) and EVN (68%) embryos. Plantlets produced from control and cryopreserved embryos were phenotypically similar.

Journal Article↗
PubMedDate not supplied

Core temperature and percentage of dehydration in professional football linemen and backs during preseason practices.

CONTEXT: Thermal responses of average-sized male subjects (mass of approximately 70 kg) may not accurately reflect the rate of heat storage in larger athletes with greater muscle mass. OBJECTIVE: To determine if core temperature (T(c)) is different in National Football League linemen and backs and if T(c) is related to percentage of dehydration or sweat rate. DESIGN: We measured T(c) and sweat rate in professional football players during preseason twice-daily practices. SETTING: Preseason training camp. PATIENTS OR OTHER PARTICIPANTS: Eight linemen (age = 26.6 +/- 2.1 years, height = 191.8 +/- 4.5 cm, mass = 134.8 +/- 10.7 kg, body surface area = 2.61 +/- 0.12 m2) and 6 backs (age = 27.0 +/- 4.2 years, height = 185.0 +/- 6.3 cm, mass = 95.6 +/- 11.1 kg, body surface area = 2.19 +/- 0.16 m2). MAIN OUTCOME MEASURE(S): We measured T(c) using ingestible sensors. Resting T(c) was recorded in the mornings of data collection with players dressed in shorts and then every 15 minutes during 2-hour practices in full pads or shells. Mass was recorded before and after practices for determining the percentage of dehydration. In 8 of the 14 subjects (4 linemen, 4 backs), sweat rate was calculated using the change in mass adjusted for fluid intake and urine production. RESULTS: Height, mass, and body surface area were greater in linemen than in backs. We noted a linear trend over time for T(c) in both groups. Maximal T(c) was higher in linemen (38.65 +/- 0.48 degrees C) than in backs (38.44 +/- 0.32 degrees C), but linemen were less dehydrated than backs (-0.94 +/- 0.6% versus -1.3 +/- 0.7%). Sweat rate was 2.11 +/- 0.77 L/h and correlated significantly with body surface area (r = 0.77, P < .05). Maximal T(c) was not correlated with either percentage of dehydration or sweat rate. CONCLUSIONS: Maximal T(c) was not associated with percentage of dehydration or sweat rate. Linemen were less dehydrated but demonstrated higher T(c) than backs during practice. Maximal T(c) was generally achieved during live scrimmaging.

Journal Article↗
PubMed1982

Exercise-induced hemolysis in sickle cell anemia: shear sensitivity and erythrocyte dehydration.

We describe a steady-state patient with sickle cell anemia (SS disease) who developed sporadic hemoglobinuria, historically related to vigorous exercise. We studied him and four other patients with SS disease and demonstrated exercise-induced hemoglobinemia. To see if SS erythrocytes were abnormally fragile when exposed to shear forces that could be generated in small vessels of exercising muscles, we exposed them to physiologic shear rates in a cone-plate viscometer. We show that SS erythrocytes are more shear sensitive than normal erythrocytes. This phenomenon is directly related to the presence of dehydrated cells as demonstrated by the increasing shear sensitivity of increasingly dehydrated cells separated on Stractan density gradients. Normal shear sensitivity could be restored to dehydrated layers by restoring normal hydration. Restoration of shear stability was complete in all layers except for the most dense ISC layer. A control group of patients with SC disease exhibited no exercise-induced hemoglobinemia, no abnormal shear sensitivity of whole blood, and only rare dehydrated ISCs. These studies suggest that the exercise-induced hemolysis in SS patients is related to the lysis of dehydrated, shear-sensitive cells. This same process may also contribute to the chronic hemolysis of SS disease--a phenomenon known to correlate with the numbers of dehydrated ISCs.

Adult↗
PubMed1997

Peculiarities of the osmotic response in dehydrated erythrocytes.

Human erythrocytes were dehydrated in concentrated sucrose solutions and rehydrated in isotonic NaCl solution. The osmotic responses of erythrocytes dehydrated in media with osmolarities over 1 M corresponded to the ideal osmotic behaviour. This was also true of the ghosts formed during rehydration of dehydrated erythrocytes irrespective of the initial osmolarity. Fresh erythrocytes as well as erythrocytes dehydrated in sucrose media with osmolarity of 0.5-0.6 M displayed nonideal responses (volume changes were lower than predicted). In contrast to the cells dehydrated at 0 degree C, the peculiarities of the osmotic response of the cells dehydrated within the osmolarity range of 0.7-0.8 M at 37 degrees C can be detected spectrophotometrically. The data obtained suggest that the nonideal osmotic response of human erythrocytes is probably due to a specific state of hemoglobin.

Cell Size↗
PubMed1999

How commonly are children hospitalized for dehydration eligible for care in alternative settings?

BACKGROUND: Avoiding unnecessary hospitalization has long been a goal of child health care providers. Managed care practice environments increasingly pressure the practicing pediatrician to avoid hospitalization. OBJECTIVES: To estimate the proportion of childhood dehydration hospitalizations eligible for care in alternative settings (eg, short-stay treatment and triage units, home nursing) and to assess the type and duration of services that might be required for alternative setting care of children with these illness episodes. DESIGN: All dehydration hospitalizations for the 198 593 children (aged > 1 month and < 19 years) dwelling in Rochester, NY (Monroe County), between 1991 and 1995 were identified in county-wide hospital discharge computer files. Medical records were reviewed for a random sample of 380 of the hospitalizations. Children with major underlying conditions were excluded from analysis because of higher risk for deterioration, and greater complexity of medical care might render alternative settings inappropriate. Measures included a 4-item score estimating level of dehydration, serum bicarbonate level at presentation, and time to rehydration. Rehydration was defined as a drop in urine-specific gravity to 1.010 or less or reduction of fluid administration to the maintenance rate. RESULTS: Altogether, 1121 dehydration hospitalizations occurred during the study period. Based on medical record review for a random sample of 380 of these 1121, major underlying problems were present in 27.4% (104) of hospitalizations sampled. Simple, acute gastroenteritis accounted for 75.4% (208) of 276 hospitalizations remaining in the sample. Levels of dehydration for these children were estimated as at least 5% for 51.0% (106) and at least 10% for 16.3% (34) of hospital admissions, and serum bicarbonate levels were 12 mmol/L or less for 26.0% (54). Time from hospital admission to rehydration was no greater than 12 hours for 79.3% (165) and no greater than 24 hours for 94.7% (197). However, hospital stay was generally substantially longer. The time hospitalized following rehydration represented 85.8% of the average inpatient stay. Hospital discharge was heavily concentrated in daytime hours, although the children achieved rehydration at all hours of the day. No deterioration occurred during hospitalizations studied. CONCLUSION: Nearly all children hospitalized for simple, acute gastroenteritis in Rochester might be eligible for care in alternative settings designed to provide hospital-level care for short periods.

Adolescent↗