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PubMed1987

Effect of voluntary dehydration on thermoregulatory responses to heat in men and women.

The effects of dehydration prior to heat exposure on sweating and body temperature were tested in 8 men and 8 women, dehydration being 1.3 and 1.0% of body weight, respectively. The subjects were exposed to 40 degrees C for 60 min. Compared with controls (C), in the dehydrated men (D) there was a longer delay in the onset of sweating (C, 7.8, D, 11.6 min, p less than 0.05), a lower total sweat loss (C, 153, D, 127 g X m-2 X h-1, p less than 0.001), and a greater increase in Tre (C, 0.31, D, 0.43 degree C, p less than 0.002). In women, dehydration did not influence the control time course of sweating significantly, nor were these significant body temperature increases during heat exposure. Delay in the onset of sweating in women (C, 18.1, D, 18.7 min) was generally longer than in men (C, 7.8, D, 11.6 min), [F(1,14) = 7.41, p less than 0.05]. A significant correlation was found between the inertia time of sweating and delta Tre in both control and dehydration conditions in the men (r = 0.81, p less than 0.01). The rectal temperature increases in men were also related to the inertia time of electrical skin resistance (r = 0.83, p less than 0.01). It is concluded that dehydration affects sweating and body temperature in men more severely than in women.

Adult↗
PubMed2003

Exclusion of maltodextrins from phosphatidylcholine multilayers during dehydration: effects on membrane phase behaviour.

The effect of increasing solute size on phosphatidylcholine phase behaviour at a range of hydrations was investigated using differential scanning calorimetry. Dehydration of phospholipid membranes gives rise to a compressive stress within the bilayers that promotes fluid-to-gel phase transitions. According to the Hydration Forces Explanation, sugars in the intermembrane space minimize the compressive stress and limit increases in the fluid-gel transition temperature, T(m), by acting as osmotic and volumetric spacers that hinder the close approach of membranes. However, the sugars must remain between the bilayers in order to limit the rise in T(m). Large polymers are excluded from the interlamellar space during dehydration and do not limit the dehydration-induced rise in T(m). In this study, we used maltodextrins with a range of molecular weights to investigate the size-exclusion limit for polymers between phosphatidylcholine bilayers. Solutes with sizes ranging from glucose to dextran 1000 limited the rise in lipid T(m) during dehydration, suggesting that they remain between dehydrated bilayers. At the lowest hydrations the solutions vitrified, and T(m) was further depressed to about 20 degrees C below the transition temperature for the lipid in excess water, T(o). The depression of T(m) below T(o) occurs when the interlamellar solution vitrifies between fluid phase bilayers. The larger maltodextrins, dextran 5000 and 12,000, had little effect on the T(m) of the PCs at any hydration, nor did vitrification of these larger polymers affect the lipid phase behaviour. This suggests that the larger maltodextrins are excluded from the interlamellar region during dehydration.

Calorimetry, Differential Scanning↗
PubMed2006

Investigation of the multi-step dehydration reaction of theophylline monohydrate using 2-dimensional powder X-ray diffractometry.

PURPOSE: (i) To study the dehydration kinetics of theophylline monohydrate using 2-dimensional (2D) powder X-ray diffractometry (XRD), and (ii) to investigate the effect of polyvinylpyrrolidone (PVP) on the dehydration pathway and kinetics. METHODS: Theophylline monohydrate (C(7)H(8)N(4)O(2).H(2)O; M) was recrystallized from aqueous PVP solutions of different concentrations. Dehydration kinetics was studied isothermally, at several temperatures, from 35 to 130 degrees C. The experimental set-up comprised of a high intensity X-ray source (synchrotron radiation or 8 kW rotating anode), a heating chamber, and a 2D area detector. Diffraction patterns were collected continuously, with a time resolution ranging from 40 ms to 30 s, over the angular range of 3 to 27 degrees 2theta. RESULTS: Dehydration of M resulted in either the stable (C(7)H(8)N(4)O(2); A), or the metastable anhydrate (A*), with the latter having a tendency to transform to A. The XRD technique allowed simultaneous quantification of M, A* and A during the dehydration reaction. The rate constants for individual reaction steps (M-->A*; M-->A and A*-->A) were determined by fitting the data to solid-state reaction models. In presence of PVP, there was a decrease in the magnitude of the rate constant associated with the M-->A transition, resulting in an increased build-up of A* in the product. The inhibitory effect of PVP on M-->A transition was more pronounced at lower dehydration temperatures, and was proportional to the concentration of PVP. CONCLUSIONS: Two dimensional powder X-ray diffractometry, using a high intensity source, is a powerful technique to study kinetics of rapid solid-state reactions. The inhibitory effect of excipients can have profound effect on phases formed during pharmaceutical processing.

Algorithms↗
PubMed1978

Effects of dehydration on reaction centers from Rhodopseudomonas sphaeroides.

Air-dried films of reaction centers from Rhodopseudomonas sphaeroides were found to resemble aqueous suspensions of these reaction centers in their optical and photochemical properties, except that the long wave absorption band of bacteriochlorophyll was shifted from about 860 to 845 nm. The quantum efficiency of the photochemical reaction that produces oxidized bacteriochlorophyll and reduced ubiquinone was greater than 0.75 in the films, using 800-nm actinic light. Dehydration of the films caused further blue shifts of all the absorption bands between 500 and 900 nm, and some loss (about 20%) of intensity of the long wave band, coupled to a gain of absorbance centered at 795 nm. The latter changes were not accompanied by an increase at 1250 nm, ruling out the oxidation of bacteriochlorophyll as a cause of these changes. Dehydration caused about 50% of the reaction centers to become photochemically inactive. For the component that remained active, the photochemical quantum efficiency was about 0.5 at room temperature, rising to 0.7 or more as the temperature was brought below 250 K. The yield of 900 nm fluorescence was approximately the same in air-dried films as in aqueous suspensions; dehydration of a film raised the fluorescence yield about 3-fold. The yield of this fluorescence in a dehydrated film was independent of temperature (+/- 10%) between 300 and 70 K. The back reaction after illumination, return of electrons from reduced ubiquinone to oxidized bacteriochlorophyll, has kinetics in which a most rapid first-order component is mixed with slower components. The fastest component, identified with the return of electrons from 'primary' ubiquinone to oxidized bacteriochlorophyll, was predominant in the materials tested here. Its half time in an aqueous suspension of reaction centers fell from 86 ms at 300 K to 33 MS AT 200 K and declined more gradually to 15 ms at 50 K. An air-dried film showed similar behavior. The dramatic change of half-time between 300 and 200 K can be ascribed to one or more phase transitions involving water; in a dehydrated film the half-time of the fastest decay component was about 22 +/- 5 ms, independent of the temperature between 300 and 70 K. The original properties of an air-dried film were restored fully, after dehydration, by exposure to either H2O or 2H2O vapor. There was no significant difference, in these measurements, between H2O-restored and 2H2O-restored films.

Bacterial Chromatophores↗
PubMed1978

Comparison of firing patterns in oxytocin- and vasopressin-releasing neurones during progressive dehydration.

The electrical activity of neurosecretory cells in the supraoptic nucleus of the urethane-anaesthetized lactating rat was examined after periods of water deprivation ranging from 0-24 h. Supraoptic units were identified by antidromic activation following stimulation of the neurohypophysis, and classified as oxytocin or vasopressin cells according to their response during reflex milk ejection. In 65 vasopressin cells, dehydration increased the mean firing rate from 2.1 spikes/sec at 0 h to 6.8 spikes/sec at 24 h and caused a change from a slow irregular to a phasic firing pattern. Thus, after 6 h or more of dehydration, 84-100% of the vasopressin cells fired phasically, compared to 12% under normal conditions. In phasic vasopressin cells , the intraburst firing rates were closely related to the stages of dehydration, rising from a mean of 6.3 spikes/sec at 6 h to 12.0 spikes/sec at 24 h. However, no systematic relationship was observed between the stages of dehydration and the mean burst or silence durations. In 77 identified oxytocin units, dehydration increased the firing rate from 0.9 spikes/sec to 2.8 spikes/sec after 24 h, but only 3 (4%) of the cells showed phasic firing. Instead, the oxytocin units changed from a slow irregular to a fast continuous discharge. In conclusion, both vasopressin and oxytocin neurones are activated during chronic dehydration, but there is a marked difference in the pattern of their response. The phasic firing of the vasopressin cells may be important in increasing the occurrence of short interspike intervals and thus facilitating hormone release.

Action Potentials↗
PubMed1993

Effects of dehydration and rehydration on plasma vasopressin and aldosterone in horses.

We have investigated the change in plasma vasopressin and aldosterone concentrations in Namib (desert-adapted) and in control horses from a subtropical region, during an acute 12% dehydration and during rehydration, while food was available. During dehydration, vasopressin concentrations increased significantly in both groups of horses, but the increase was significantly greater in Namib horses than in control horses. During rehydration, vasopressin levels fell, but fell significantly less in Namib horses. The change in vasopressin concentration correlated significantly with plasma osmolality (r = 0.88, p < 0.001), and the relationship between these two variables was the same for both groups of horses during the dehydrated and rehydrated states. Aldosterone concentrations fell up to 48-h dehydration in both groups, but decreased significantly more in desert horses. From 48-h dehydration and during rehydration, aldosterone concentrations increased and the increase was sustained longer in Namib than in control horses. Changes in plasma osmolality did not correlate significantly with changes in aldosterone concentration. There were significant correlations between faecal moisture (%) and both vasopressin and aldosterone concentrations (r = -0.72, p < 0.008; r = 0.80, p < 0.002, respectively). During the 12% dehydration, the Namib horses sustained higher plasma osmolalities and consequently vasopressin levels than the control horses. We conclude that plasma osmolality in conjunction with these two hormones plays a significant role in water homeostasis in horses.

Acclimatization↗
PubMed1982

The lipid solubility of fixative, staining and embedding media, and the introduction of LX-112 and poly/bed-812 as dehydrants for epoxy resin embedment.

The manufacture of Shell, Epon-812 (E-812) resin has recently been discontinued. E-812 and two newly introduced E-812 substitutes, and Ladd-112 (LX-112) and the Polysciences, Poly/bed-812 (PB-812) resins, were studied biochemically and morphologically for their effectiveness as polar dehydrants. Their technical properties as general E-812 replacements were also explored. In the biochemical studies, acetone was more effective in retaining lung phospholipid components than ethanol, the resin dehydration was more effective than either acetone or ethanol. There was no appreciable difference in lipid solubility among the three resins. Acetone and uranyl magnesium acetate each had a loosening effect on previously fixed phospholipids. The PB-812 and E-812 resin dehydrated blocks of dense animal tissues, demonstrated serious technical difficulties during sectioning. The L-112 resin substitute, due to its low viscosity and improved infiltration, was found to be technically as effective a dehydrant as ethanol or acetone. None of the three resins was successful as dehydrating agents for the plant tissue. With organic solvent dehydration, both epoxy resin substitutes demonstrated excellent embedment properties with both animal and plant tissues.

Animals↗
PubMed2004

Influence of dehydration temperature on water vapor adsorption, dissolution behavior and surface property of ampicillin.

Several specimens of anhydrous ampicillin were prepared by heating the ampicillin trihydrate at 100, 120, 140 and 160 degrees C. The effects of dehydration temperature on water vapor adsorption, dissolution behavior and surface property were investigated. The water vapor adsorption of anhydrous ampicillin was studied at 89% relative humidity, 40 degrees C and the water vapor adsorption rate was found to decrease with increase of dehydration temperature. Dissolution profiles of the various anhydrous specimens were investigated in 96% ethanol at 35 degrees C by the static disk method. The anhydrous form prepared at higher dehydration temperature exhibited faster dissolution rate. Solid phase transformation from the anhydrous form to the trihydrate form occurred during the dissolution test. The rate of phase transformation during the dissolution test decreased with increasing dehydration temperature. Topographic difference of the anhydrous forms prepared at 100 and 160 degrees C was not observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM); however, difference of the microstructural properties was apparently observed by the AFM phase image. Surface free energy study revealed that when ampicillin was dehydrated at high temperature, the sample surface became more hydrophobic resulting in less interaction force with water and slow water sorption rate. From the results, we concluded that the polarity of sample surface induced by dehydration of ampicillin would affect the phase transformation and dissolution behavior.

Adsorption↗
PubMedDate not supplied

Cobalt-59 NMR and X-ray diffraction studies of hydrated and dehydrated (+/-)-tris(ethylenediamine) cobalt(III) chloride.

Cobalt-59 NMR experiments have been carried out on single-crystal and polycrystalline (powder) samples of (+/-)-tris(ethylenediamine)cobalt(III) chloride trihydrate, (+/-)-[Co(en)(3)]Cl(3) x 3H(2)O, and of its dehydrate. In addition, the X-ray crystal structure of the dehydrated sample has been determined. X-ray diffraction measurements confirm a long-held assumption that dehydration has only minor effects on the structure of the [Co(en)(3)](3+) cation. Nevertheless, these small differences have a detectable effect on the 59Co nuclear magnetic resonance properties of these compounds; in particular, the nuclear quadrupole coupling constant, C(Q). Straightforward identification of the c-axis for large single crystals of (+/-)-[Co(en)(3)]Cl(3).3H(2)O and of its dehydrate allowed us to obtain single-crystal 59 Co NMR data by orienting the crystals in an MAS rotor. Data collected on single crystals and polycrystalline samples indicate that C(Q)=-3.05+/-0.05 and -2.80+/-0.05 MHz for the hydrated and dehydrated samples, respectively; the signs have been assigned on the basis of a point charge model. The chemical shift tensor principal components were also determined: for the hydrated sample, delta(perpendicular)=7281+/-2 ppm, delta(parallel)=7004+/-4 ppm and delta(iso)=7189 ppm; for the dehydrated sample, delta(perpendicular)=7288+/-2 ppm, delta(parallel)=7008+/-4 ppm and delta(iso)=7195 ppm. The electric field gradient and chemical shift tensors are axially symmetric, as required by crystal symmetry.

Journal Article↗
PubMed1996

Improved immunogold labeling of epoxy sections by the use of propylene oxide as additional agent in dehydration, infiltration and embedding.

The purpose of this study was to examine how the intensity of the immunogold labeling on epoxy sections was affected by the use of propylene oxide as an agent in addition to ethanol in the dehydration and infiltration, and also to examine the effect on the immunogold labeling by adding small amounts of propylene oxide to the embedding mixture. Increased knowledge of the mechanism for antigen detection on resin sections was another aim. Thyroid tissue, kidney tissue, and fibrin were embedded in epoxy resin; some with ethanol as the only dehydration agent and others with propylene oxide as an additional agent in dehydration, infiltration or embedding steps in different ways. Immunogold labeling was performed with anti-thyroglobulin, anti-IgG, and anti-fibrinogen, respectively. A higher degree of immunogold labeling was achieved by increasing the concentration of accelerator during infiltration and embedding (Brorson and Skjørten, 1996a, Micron, 27, 211-217). The immunogold labeling of the sections that were based on additional dehydration and infiltration with propylene oxide showed significantly more intense labeling than the sections of tissues that had only been exposed to ethanol in the dehydration and infiltration steps. The embedding of tissues in a mixture of epoxy resin and 5-10% propylene oxide gave higher yields of immunogold labeling than if pure epoxy resin was used for the embedding. The improved labeling is explained by higher amplitudes of protruding antigens on the surface of the sections because antigens are less tightly incorporated in the polymer network when using propylene oxide as additional agent in dehydration, infiltration or embedding. These results illustrate the advantage of using propylene oxide as an additional agent when preparing specimens for immunoelectron microscopy with epoxy resin embedding.

Animals↗
PubMed2001

Dehydration is catalyzed by glutamate-136 and aspartic acid-135 active site residues in Escherichia coli dTDP-glucose 4,6-dehydratase.

The dTDP-glucose 4,6-dehydratase catalyzed conversion of dTDP-glucose to dTDP-4-keto-6-deoxyglucose occurs in three sequential chemical steps: dehydrogenation, dehydration, and rereduction. The enzyme contains the tightly bound coenzyme NAD(+), which mediates the dehydrogenation and rereduction steps of the reaction mechanism. In this study, we have determined that Asp135 and Glu136 are the acid and base catalysts, respectively, of the dehydration step. Identification of the acid catalyst was performed using an alternative substrate, dTDP-6-fluoro-6-deoxyglucose (dTDP-6FGlc), which undergoes fluoride ion elimination instead of dehydration, and thus does not require protonation of the leaving group. The steady-state rate of conversion of dTDP-6FGlc to dTDP-4-keto-6-deoxyglucose by each Asp135 variant was identical to that of wt, in contrast to turnover using dTDP-glucose where differences in rates of up to 2 orders of magnitude were observed. These results demonstrate Asp135's role in protonating the glucosyl-C6(OH) during dehydration. The base catalyst was identified using a previously uncharacterized, enzyme-catalyzed glucosyl-C5 hydrogen-solvent exchange reaction of product, dTDP-4-keto-6-deoxyglucose. Base catalysis of this exchange reaction is analogous to that occurring at C5 during the dehydration step of net catalysis. Thus, the decrease in the rate of catalysis ( approximately 2 orders of magnitude) of the exchange reaction observed with Glu136 variants demonstrates this residue's importance in base catalysis of dehydration.

Aspartic Acid↗
PubMed2002

Concerted and stepwise dehydration mechanisms observed in wild-type and mutated Escherichia coli dTDP-glucose 4,6-dehydratase.

The conversion of dTDP-glucose into dTDP-4-keto-6-deoxyglucose by Escherichia coli dTDP-glucose 4,6-dehydratase (4,6-dehydratase) takes place in the active site in three steps: dehydrogenation to dTDP-4-ketoglucose, dehydration to dTDP-4-ketoglucose-5,6-ene, and rereduction of C6 to the methyl group. The 4,6-dehydratase makes use of tightly bound NAD(+) as the coenzyme for transiently oxidizing the substrate, activating it for the dehydration step. Dehydration may occur by either of two mechanisms, enolization of the dTDP-4-ketoglucose intermediate, followed by elimination [as proposed for beta-eliminations by Gerlt, J. A., and Gassman, P. G. (1992) J. Am. Chem. Soc. 114, 5928-5934], or a concerted 5,6-elimination of water from the intermediate. To assign one of these two mechanisms, a simultaneous kinetic characterization of glucosyl C5((1)H/(2)H) solvent hydrogen and C6((16)OH/(18)OH) solvent oxygen exchange was performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The reaction of the wild-type enzyme is shown to proceed through a concerted dehydration mechanism. Interestingly, mutation of Asp135, the acid catalyst, to Asn or Ala alters the mechanism, allowing enolization to occur to varying extents. While aspartic acid 135 is the acid catalyst for dehydration in the wild-type enzyme, the differential enolization capabilities of D135N and D135A dehydratases suggest an additional role for this residue. We postulate that the switch from a concerted to stepwise dehydration mechanism observed in the aspartic acid variants is due to the loss of control over the glucosyl C5-C6 bond rotation in the active site.

Escherichia coli↗
PubMed2005

Crystal structure of an ethylene sorption complex of fully vacuum-dehydrated fully Ag+-exchanged zeolite X (FAU). Silver atoms have reduced ethylene to give CH2 2- carbanions at framework oxide vacancies.

The crystal structure of an ethylene sorption complex of fully vacuum-dehydrated fully Ag(+)-exchanged zeolite X (FAU), a = 24.865(2) A, has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd at 21 degrees C. It is very different from the ethylene complex of Ag(92)-X that had been dehydrated at 400 degrees C in flowing oxygen, as were the two dehydrated structures. The crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M AgNO(3) for 3 days, followed by dehydration at 400 degrees C and 2 x 10(-6) Torr for 2 days, followed by exposure to 300 Torr of zeolitically dry ethylene gas for 2 h at 21 degrees C. The structure was determined in this atmosphere and was refined using all data to the final error indices (based upon the 534 reflections for which F(o) > 4sigma(F(o))) R(1) = 0.062 and wR(2) = 0.135. In this structure, per unit cell, 14 Ag(+) ions were found at the octahedral site I (Ag-O = 2.611(9) A), and 32 partially reduced Ag(+) ions fill two different site I' positions deep in the sodalite cavities (Ag-O = 2.601(13) and 2.618(12) A). The sodalite cavities host two different cationic silver clusters. In about 47% of sodalite units, eight silver atoms form interpenetrating tetrahedra, Ag(8)(n+) (n = 4 is suggested), with T(d)() symmetry. The other 53% of the sodalite units host cyclo-Ag(4)(m+) (m = 2 is suggested) cations with near S(4) symmetry. These clusters are very similar to those in vacuum-dehydrated Ag(92)-X. Thirty-two Ag(+) ions fill the single 6-rings, 15 at site II' (Ag-O = 2.492(10) A), and 17 at site II (Ag-O = 2.460(9) A). The latter 17 lie in supercages where each forms a lateral pi-complex with an ethylene molecule. In turn, each C(2)H(4) molecule forms two cis electrostatic hydrogen bonds to framework oxygens. The remaining 14 Ag+ ions occupy three different II' sites. Vacuum dehydration had caused substantial decomposition: per unit cell, 30 of the 92 Ag(+) ions were reduced and 15 of the 384 framework oxide ions were oxidized to O2(g), leaving lattice vacancies. The sorption of C(2)H(4) at 21 degrees C reoxidized about 7 of the 30 Ag(0) atoms to Ag(+) and reduced 1.75 ethylene molecules to give CH(2)(2-) groups which refilled 3.5 of these 15 lattice vacancies. The remaining vacancies may have been filled with H(2)C=C(2-) ions. The unit cell formula, which originally contained 384 oxygen atoms, may be |Ag(92)(C2H4)17|[Si(100)Al(92)O(369)(CH2)3.5] or |Ag(92)H(23)(C2H4)17|[Si(100)Al(92)O(369)(CH2)3.5(C2H2)11.5].

Adsorption↗
PubMed2006

Mechanisms of glycerol dehydration.

Dehydration of neutral and protonated glycerol was investigated using quantum mechanical calculations (CBS-QB3). Calculations on neutral glycerol show that there is a high barrier for simple 1,2-dehydration, E(a)=70.9 kcal mol(-1), which is lowered to 65.2 kcal mol(-1) for pericyclic 1,3-dehydration. In contrast, the barriers for dehydration of protonated glycerol are much lower. Dehydration mechanisms involving hydride transfer, pinacol rearrangement, or substitution reactions have barriers between 20 and 25 kcal mol(-1). Loss of water from glycerol via substitution results in either oxirane or oxetane intermediates, which can inter-convert over a low barrier. Subsequent decomposition of these intermediates proceeds via either a second dehydration step or loss of formaldehyde. The computed mechanisms for decomposition of protonated glycerol are supported by the gas-phase fragmentation of protonated glycerol observed using a triple--quadrupole mass spectrometer.

Desiccation↗
PubMed2004

Intermediate-depth earthquake faulting by dehydration embrittlement with negative volume change.

Earthquakes are observed to occur in subduction zones to depths of approximately 680 km, even though unassisted brittle failure is inhibited at depths greater than about 50 km, owing to the high pressures and temperatures. It is thought that such earthquakes (particularly those at intermediate depths of 50-300 km) may instead be triggered by embrittlement accompanying dehydration of hydrous minerals, principally serpentine. A problem with failure by serpentine dehydration is that the volume change accompanying dehydration becomes negative at pressures of 2-4 GPa (60-120 km depth), above which brittle fracture mechanics predicts that the instability should be quenched. Here we show that dehydration of antigorite serpentinite under stress results in faults delineated by ultrafine-grained solid reaction products formed during dehydration. This phenomenon was observed under all conditions tested (pressures of 1-6 GPa; temperatures of 650-820 degrees C), independent of the sign of the volume change of reaction. Although this result contradicts expectations from fracture mechanics, it can be explained by separation of fluid from solid residue before and during faulting, a hypothesis supported by our observations. These observations confirm that dehydration embrittlement is a viable mechanism for nucleating earthquakes independent of depth, as long as there are hydrous minerals breaking down under a differential stress.

Journal Article↗
PubMed1998

Two dehydration-inducible transcripts from the resurrection plant Craterostigma plantagineum encode interacting homeodomain-leucine zipper proteins.

The molecular dissection of desiccation tolerance in the resurrection plant Craterostigma plantagineum led to the isolation of two dehydration-stress inducible homeo-domain-leucine zipper genes (CPHB-1 and -2). When the coding region of CPHB-1 was used as bait in the yeast two-hybrid system, the ability of CPHB-1 to form homodimers was demonstrated. The two-hybrid system was also used to isolate CPHB-2, which heterodimerises with CPHB-1. Both transcripts are inducible by dehydration in leaves and roots, but steady state levels vary in response to exogenously applied ABA. Although expression of CPHB-1 is not inducible by ABA, the transcript level of CPHB-2 increases during ABA-treatment. Both genes are expressed at very early stages of dehydration and thus may be involved in the regulation of gene expression during dehydration. CPHB-1 and -2 differential expression in response to ABA suggests that they act in different branches of the dehydration-induced signalling network. In vitro binding studies revealed that CPHB-1 specifically binds to the pseudopalindromic sequence CAAT(C/G)ATTG. Using this element for in vitro binding studies with nuclear proteins from dehydrated leaves, an inducible DNA-protein complex was identified.

Abscisic Acid↗
PubMed2001

Involvement of a novel Arabidopsis phospholipase D, AtPLDdelta, in dehydration-inducible accumulation of phosphatidic acid in stress signalling.

Phospholipid metabolism is involved in plant responses to drought and salinity stress. To investigate the role of phospholipase D (PLD) and its product phosphatidic acid (PtdOH) in stress signalling, we isolated a novel PLD cDNA, designated AtPLDdelta, by screening a cDNA library prepared from dehydrated Arabidopsis thaliana. The AtPLDdelta protein, of 868 amino acids, has a putative catalytic domain and a C2 domain that is involved in Ca2+/phospholipid binding. The AtPLDdelta mRNA accumulated in response to dehydration and high salt stress. Histochemical analysis showed that the AtPLDdelta gene is strongly expressed in the vascular tissues of cotyledons and leaves under dehydration stress conditions. Under normal growth conditions, AtPLDdelta was expressed in roots, leaves, stems and flowers but not in siliques. We showed that dehydration stimulates the accumulation of PtdOH. The accumulation of PtdOH in response to dehydration was significantly suppressed in AtPLDdelta antisense transgenic plants. These results suggest that AtPLDdelta may be involved in PtdOH accumulation in the dehydration stress response.

Amino Acid Sequence↗
PubMed1978

Discrete length classes of DNA depend on mode of dehydration.

The length of double-stranded coliphage lambda DNA, as determined by electron microscopy using the benzyldimethylalkyl ammonium chloride technique, depends on the mode of dehydration. The freeze-dried DNA form is the longest (16.5 micron), whereas dehydration in methanol (15.9 micron) or in ethanol (three forms: 15.2 micron, 13.9 micron, and 12.4 micron) results in progressively shorter molecules. These measured lengths of the freeze-dried, methanol-dehydrated, and shortest ethanol-dehydrated forms correspond to the axial rise per nucleotide pair in the B, C, and A forms of DNA, respectively. The remaining forms of ethanol-dehydrated DNA seem to represent novel intermediary conformations of DNA. In agreement with the predicted increment, DNA exposed to ethidium bromide and freeze-dried is elongated by 39% (22.9 micron). All size classes show the same relative distribution pattern of bound Escherichia coli RNA polymerase molecules (nucleoside triphosphate:RNA nucleotidyltransferase, EC2.7.7.6), used as intramolecular markers, indicating that the dehydration-caused transitions are uniform.

Benzyl Compounds↗