Estimation of osmotic parameters accompanying zeatin-induced growth of detached cucumber cotyledons

Water potential (ψ), the osmotic potential (ψ_π), and the pressure potential (ψ_p) of detached cotyledons isolated from Cucumis sativus L. cv Marketer seedlings after 0, 1.5, and 3 days growth with and without zeatin were determined. From zero time to 3 days, cotyledons incubated without exogenous zeatin exhibited a slight decrease in ψ (from −0.4 to −1.0 bars), while those grown with zeatin developed even more negative values (about −4 bars). Both groups showed rising ψ_π values (decreases in solutes per unit volume), but this rise was more dramatic in those treated with zeatin. These data indicate that the capacity of zeatin-treated cotyledons to take up water more rapidly than controls and thus expand faster must be due to wall loosening, as reflected in ψ_p values which declined during 3 days from about +11 bars to about +1.4 bars.

It was also found that freshly detached cotyledons or those grown without exogenous zeatin exhibited osmoregulation in polyethylene glycol (PEG) solutions. That is, while cotyledons initially lost H₂O into certain PEG solutions, their ψ values decreased over time and they began absorbing water after 1 to 4 hours. After 3 days growth, zeatin-treated cotyledons had lost most of this capacity of osmoregulate. It seems likely that osmoregulation in cotyledons not treated with zeatin is due to wall loosening rather than changes in ψ_π. Zeatin-treated cotyledons with already loosened walls may not have this option to deal with water stress and thus simply come to equilibrium with external PEG solutions.

     

Limitations of Photosynthesis in Pinus taeda L. (Loblolly Pine) at Low Soil Temperatures

The relative importance of stomatal and nonstomatal limitations to net photosynthesis (A) and possible signals responsible for stomatal limitations were investigated in unhardened Pinus taeda seedlings at low soil temperatures. After 2 days at soil temperatures between 13 and 7°C, A was reduced by 20 to 50%, respectively. The reduction in A at these moderate root-chilling conditions appeared to be the result of stomatal limitations, based on the decrease in intercellular CO₂ concentrations (c_i). This conclusion was supported by A versus c_i analysis and measurements of O₂ evolution at saturating CO₂, which suggested increases in stomatal but not biochemical limitations at these soil temperatures. Nonuniform stomatal apertures, which were demonstrated with abscisic acid, were not apparent 2 days after root chilling, and results of our A versus c_i analysis appear valid. Bulk shoot water potential (ψ) declined as soil temperature dropped below 16°C. When half the root system of seedlings was chilled, shoot ψ and gas-exchange rates did not decline. Thus, nonhydraulic root-shoot signals were not implicated in stomatal limitations. The initial decrease in leaf conductance to water vapor after root chilling appeared to precede any detectable decrease in bulk fascicle ψ, but may be in response to a decrease in turgor of epidermal cells. These reductions in leaf conductance to water vapor, which occurred within 30 minutes of root chilling, could be delayed and temporarily reversed by reducing the leaf-to-air vapor-pressure deficit, suggesting that hydraulic signals may be involved in initiating stomatal closure. By independently manipulating the leaf-to-air vapor-pressure deficit of individual fascicles, we could induce uptake of water vapor through stomata, suggesting that nonsaturated conditions occur in the intercellular airspaces. There was an anomaly in our results on seedlings maintained for 2 days at soil temperatures below 7°C. Lower A appeared primarily the result of nonstomatal limitations, based on large increases in calculated c_i and A versus c_i analysis. In contrast, measurements of O₂ evolution at saturating CO₂ concentrations implied nonstomatal limitations per se did not increase at these temperatures. One explanation for this paradox is that calculations of c_i are unreliable at very low gas-exchange rates because of inadequate measurement resolution, and limitations of A are predominantly stomatal. An alternative interpretation is that increases in c_i are real and the results from O₂-evolution measurements are in error. The high CO₂ concentration used in O₂-evolution measurements (15%) may have overcome nonstomatal limitations by enzymes that were down-regulated by a feedback mechanism. In this scenario, carbohydrate feedback limitations may be responsible for nonstomatal reductions in A after 2 days at soil temperatures below 7°C.     

A Guide to Establishing Water Potential of Aqueous Two-Phase Solutions (Polyethylene Glycol plus Dextran) by Amendment with Mannitol

A practical guide to calculating the mannitol (MAN) amendment required to achieve the desired water potential (Ψ) of polyethylene glycol/dextran (PEG/DEX) aqueous two-phase systems for protoplast purification is presented. The empirically generated equation Ψ = 305[PEG′]²[MAN] + 0.74[PEG′][MAN]T − 103[PEG′][MAN] + 5.6[PEG′]²T − 623[PEG′]² − 0.25[PEG′]T + 12.7[PEG′] − 0.078[MAN]T − 22.75[MAN]accurately predicts experimental Ψ (in bars). [PEG′] indicates the presence of DEX where [DEX] = [PEG]/(0.6−0.4[PEG]). The equation is applicable for these ranges: [PEG′] from 0.047 to 0.13 gram per gram H₂O; [MAN] from 0 to 0.7 molal; T from 4.5 to 40°C. Actual Ψ should differ from derived Ψ by no more than 8% for the least negative values to 4% for the most negative values. The Ψ for solutions of MAN, of PEG, and of DEX were also determined. Equations to fit data for each were generated. Analyses indicated a significant synergistic effect on Ψ when MAN is added to PEG/DEX and, at certain concentrations, between PEG and DEX.     

Water Relations of Growing Maize Coleoptiles : Comparison between Mannitol and Polyethylene Glycol 6000 as External Osmotica for Adjusting Turgor Pressure

Water relations of growing segments of maize (Zea mays L.) coleoptiles were investigated with osmotic methods using either mannitol (MAN) or polyethylene glycol 6000 (PEG) as external osmotica. Segments were incubated in MAN or PEG solutions at 0 to - 15 bar water potential (Ψ_o) and the effects were compared on elongation growth, osmotic shrinkage, cell sap osmolality (OC), and osmotic pressure (π_i). The nonpenetrating osmoticum PEG affects π_i in agreement with Boyle-Mariotte's law, i.e. the segments behave in principle as ideal osmometers. There is no osmotic adjustment in the Ψ_o range permitting growth (0 to −5 bar) nor in the Ψ_o range inducing osmotic shrinkage (−5 to −10 bar). Promoting growth by auxin (IAA) has no effect on the osmotic behavior of the tissue toward PEG. In contrast to PEG, MAN produces an apparent increase in π_i accompanied by anomalous effects on segment elongation and shrinkage leading to a lower value for Ψ_o which establishes a growth rate of zero and to an apparent recovery from osmotic shrinkage after 2 hours of incubation. These effects can be quantitatively attributed to uptake of MAN into the tissue. MAN is taken up into the apoplastic space and the symplast as revealed by a large temperature-dependent component of MAN uptake. It is concluded that MAN, in contrast to PEG, is unsuitable as an extemal osmoticum for the quantitative determination of water relations of growing maize coleoptiles.     

Characterization of the Resting Axolemma in the Giant Axon of the Squid

Previous electron microscope studies have shown that the Schwann cell layer is traversed by long and tortuous slit-like channels ~60Å wide, which provide the major route of access to the axolemma surface. In the present work the restriction offered by the resting axolemma to the passage of six small non-electrolyte molecules has been determined. The radii of the probing molecules were estimated from constructed molecular models. The ability of the axolemma to discriminate between the solvent (water) and each probing molecule was expressed in terms of the reflection coefficient σ. σ was then used to calculate an effective pore size for the resting axolemma. The value of 4.25 Å found for the pore radius is in excellent agreement with the 1.5 to 8.5 Å limiting values previously calculated from our measurements of water fluxes. The presence of pores with 4.25 Å radius in the resting axolemma is compatible with restricted diffusion of Na. The present paper leads to the conclusion that the axolemma is the only continuous barrier across which the ionic gradient responsible for the normal functioning of the nerve can be maintained. The combined findings of electron microscopy, water permeability, and molecular restricted filtration indicate that in all probability the axolemma is the "excitable membrane" of the physiologists.     

Water Relations in Pulvini from Samanea saman: I. Intact Pulvini

The movement of Samanea leaflets depends upon changes in the curvature of the pulvinus at the base of each leaflet. Pulvinar bending and straightening, in turn, are driven by the movement of water between opposing (extensor and flexor) sides of the pulvinus. Although water movement depends on water potential (Ψ) and thus on osmotic potential (π) and hydrostatic pressure (P), none of these parameters have been measured in Samanea. In this investigation, Ψ and π were measured and P was calculated for extensor and flexor tissues of excised, whole pulvini that were open in the light and closed in the dark. In fully open pulvini, π in the extensor was generally between 800 and 1000 milliosmol per kilogram and exceeded π in the flexor by 300 to 450 milliosmol per kilogram. In fully closed pulvini the reverse was true, with π in the flexor between 800 and 1000 milliosmol per kilogram, exceeding π in the extensor by 300 to 450 milliosmol per kilogram. To obtain approximate values of Ψ of pulvinar tissues, shallow cuts in extensor and flexor sides of oil-covered pulvini were filled with droplets of polyethylene glycol solutions of known Ψ. Droplets maintaining constant size were assumed to have the same Ψ as the tissue. Extensor and flexor halves of open pulvini had very different Ψ (extensor, about −1.4 MPa; flexor, about −0.3 MPa), but both sides of closed pulvini had similar Ψ (about −0.3 MPa). Measurements of Ψ and π and calculations of P indicate: (a) In open pulvini, P is about the same in extensor and flexor. The large Ψ gradient is caused by a large osmotic gradient. (b) In closed pulvini, P is approximately 50% higher in the flexor than in the extensor. This difference in P compensates for differences in π such that the Ψ gradient is small. (c) Pulvini close as P increases in the flexor and reopen as flexor P decreases; extensor P values are similar in open and closed pulvini.     

The osmotic potential of polyethylene glycol 6000

Osmotic potential (ψ_s) of aqueous solutions of polyethylene glycol 6000 (PEG-6000) was curvilinearly related to concentration. At given concentrations, ψ_s increased linearly with temperature. The effects of concentration and temperature on ψ_s of PEG-6000 solutions differ from those for most salts and sugars and apparently are related to structural changes in the PEG polymer. Measurements of ψ_s with thermocouple psychrometers are more negative than those with a vapor pressure osmometer, with the psychrometer probably giving the more nearly correct ψ_s for bulk solutions. An empirical equation permits calculation of ψ_s from known concentrations of PEG-6000 over a temperature range of 15 to 35 C. Viscometery and gravimetric analysis are convenient methods by which the concentrations of PEG-6000 solutions may be measured.     

Osmotic Adjustment in Leaves of VA Mycorrhizal and Nonmycorrhizal Rose Plants in Response to Drought Stress

Osmotic adjustment in Rosa hybrida L. cv Samantha was characterized by the pressure-volume approach in drought-acclimated and unacclimated plants brought to the same level of drought strain, as assayed by stomatal closure. Plants were colonized by either of the vesicular-arbuscular mycorrhizal fungi Glomus deserticola Trappe, Bloss and Menge or G. intraradices Schenck and Smith, or were nonmycorrhizal. Both the acclimation and the mycorrhizal treatments decreased the osmotic potential (Ψ_π) of leaves at full turgor and at the turgor loss point, with a corresponding increase in pressure potential at full turgor. Mycorrhizae enabled plants to maintain leaf turgor and conductance at greater tissue water deficits, and lower leaf and soil water potentials, when compared with nonmycorrhizal plants. As indicated by the Ψ_π at the turgor loss point, the active Ψ_π depression which attended mycorrhizal colonization alone was 0.4 to 0.6 megapascals, and mycorrhizal colonization and acclimation in concert 0.6 to 0.9 megapascals, relative to unacclimated controls without mycorrhizae. Colonization levels and sporulation were higher in plants subjected to acclimation. In unacclimated hosts, leaf water potential, water saturation deficit, and soil water potential at a particular level of drought strain were affected most by G. intraradices. G. deserticola had the greater effect after drought preconditioning.     

Abscisic Acid Stimulated Osmotic Adjustment and Its Involvement in Adaptation of Tobacco Cells to NaCl

Osmotic adjustment of cultured tobacco (Nicotiana tabacum L. var Wisconsin 38) cells was stimulated by 10 micromolar (±) abscisic acid (ABA) during adaptation to water deficit imposed by various solutes including NaCl, KCl, K₂SO₄, Na₂SO₄, sucrose, mannitol, or glucose. The maximum difference in cell osmotic potential (Ψπ) caused by ABA treatment during adaptation to 171 millimolar NaCl was about 6 to 7 bar. The cell Ψπ differences elicited by ABA were not due to growth inhibition since ABA stimulated growth of cells in the presence of 171 millimolar NaCl. ABA caused a cell Ψπ difference of about 1 to 2 bar in medium without added NaCl. Intracellular concentrations of Na⁺, K⁺, Cl⁻, free amino acids, or organic acids could not account for the Ψπ differences induced by ABA in NaCl treated cells. However, since growth of NaCl treated cells is more rapid in the presence of ABA than in its absence, greater accumulation of Na⁺, K⁺, and Cl⁻ was necessary for ion pool maintenance. Higher intracellular sucrose and reducing sugar concentrations could account for the majority of the greater osmotic adjustment of ABA treated cells. More rapid accumulation of proline associated with ABA treatment was highly correlated with the effects of ABA on cell Ψπ. These and other data indicate that the role of ABA in accelerating salt adaptation is not mediated by simply stimulating osmotic adjustment.     

Root Growth and Oxygen Relations at Low Water Potentials. Impact of Oxygen Availability in Polyethylene Glycol Solutions

Polyethylene glycol (PEG), which is often used to impose low water potentials (ψ_w) in solution culture, decreases O₂ movement by increasing solution viscosity. We investigated whether this property causes O₂ deficiency that affects the elongation or metabolism of maize (Zea mays L.) primary roots. Seedlings grown in vigorously aerated PEG solutions at ambient solution O₂ partial pressure (pO₂) had decreased steady-state root elongation rates, increased root-tip alanine concentrations, and decreased root-tip proline concentrations relative to seedlings grown in PEG solutions of above-ambient pO₂ (alanine and proline accumulation are responses to hypoxia and low ψ_w, respectively). Measurements of root pO₂ were made using an O₂ microsensor to ensure that increased solution pO₂ did not increase root pO₂ above physiological levels. In oxygenated PEG solutions that gave maximal root elongation rates, root pO₂ was similar to or less than (depending on depth in the tissue) pO₂ of roots growing in vermiculite at the same ψ_w. Even without PEG, high solution pO₂ was necessary to raise root pO₂ to the levels found in vermiculite-grown roots. Vermiculite was used for comparison because it has large air spaces that allow free movement of O₂ to the root surface. The results show that supplemental oxygenation is required to avoid hypoxia in PEG solutions. Also, the data suggest that the O₂ demand of the root elongation zone may be greater at low relative to high ψ_w, compounding the effect of PEG on O₂ supply. Under O₂-sufficient conditions root elongation was substantially less sensitive to the low ψ_w imposed by PEG than that imposed by dry vermiculite.     

Evaluation of the water potentials of solutions of polyethylene glycol 8000 both in the absence and presence of other solutes

Published and additional data for polyethylene glycol 8000 (PEG), formerly PEG 6000, solution water potentials (Ψ) are compared. Actual bars Ψ over the concentration range of 0 to 0.8 gram PEG per gram H₂O and temperature (T) range of 5 to 40°C are best predicted (probably within ± 5%) by this equation: Ψ = 1.29[PEG]²T − 140[PEG]² − 4.0[PEG]. Although transformable through division by [PEG] to virial equation form, results indicate that the coefficients are not virial. Mannitol (MAN) interacts with PEG to produce Ψ significantly lower than additive. Vapor pressure osmometer (VPO) data for MAN-PEG synergism compared favorably with those from thermocouple hygrometry; and VPO data showing the interactions between PEG and four salts are presented. The synergism of MAN-PEG and of NaCl-PEG are related linearly to the concentration of solute added with PEG.     

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.     

Tracer Determinations of Human Red Cell Membrane Permeability to Small Nonelectrolytes

A flow system has been used to determine the permeability of human red cell membranes to four small nonelectrolytes labeled with ¹⁴C. The permeability coefficients, ω, in units of mol dyne^-1 sec^-1 x 10¹⁵, are: ethylene glycol, 6; urea, 13; formamide, 22; and methanol, 131. The values for urea and formamide are in good agreement with values obtained by Sha'afi, Gary-Bobo, and Solomon by the minimum method. The unusually high value for ω for methanol is ascribed to its solubility in the red cell membrane since its ether: water partition coefficient is 0.14, higher by more than an order of magnitude than the ether: water partition coefficient for water. The other three solutes are hydrophilic and are characterized by values of ω which behave consistently with those of other hydrophilic amides and ureas. The values of ω for the three hydrophilic solutes measured are also consistent with an equivalent pore radius of about 3.5 A in agreement with previous estimates made on the basis of other types of studies.     

Salinity Effects on Water Potential Components and Bulk Elastic Modulus of Alternanthera philoxeroides (Mart.) Griseb

Pressure volume curves for Alternanthera philoxeroides (Mart.) Griseb. (alligator weed) grown in 0 to 400 millimolar NaCl were used to determine water potential (Ψ), osmotic potential (ψ_s), turgor potential (ψ_p) and the bulk elastic modulus (ε) of shoots at different tissue water contents. Values of ψ_s decreased with increasing salinity and tissue Ψ was always lower than rhizosphere Ψ. The relationship between ψ_p and tissue water content changed because ε increased with salinity. As a result, salt-stressed plants had larger ranges of positive turgor but smaller ranges of tissue water content over which ψ_p was positive. To our knowledge, this is the first report of such a salinity effect on ε in higher plants. These increases in ε with salinity provided a mechanism by which a large difference between plant Ψ and rhizosphere Ψ, the driving force for water uptake, could be produced with relatively little water loss by the plant. A time-course study of response after salinization to 400 millimolar NaCl showed Ψ was constant within 1 day, ψ_s and ψ_p continued to change for 2 to 4 days, and ε continued to change for 4 to 12 days. Changes in ε modified the capacity of alligator weed to maintain a positive water balance and consideration of such changes in other species of higher plants should improve our understanding of salt stress.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : V. Water Relations of Imbibition and Germination

The initiation of radicle growth during seed germination may be driven by solute accumulation and increased turgor pressure, by cell wall relaxation, or by weakening of tissues surrounding the embryo. To investigate these possibilities, imbibition kinetics, water contents, and water (Ψ) and solute (ψ_s) potentials of intact muskmelon (Cucumis melo L.) seeds, decoated seeds (testa removed, but a thin perisperm/endosperm envelope remains around the embryo), and isolated cotyledons and embryonic axes were measured. Cotyledons and embryonic axes excised and imbibed as isolated tissues attained water contents 25 and 50% greater, respectively, than the same tissues hydrated within intact seeds. The effect of the testa and perisperm on embryo water content was due to mechanical restriction of embryo swelling and not to impermeability to water. The Ψ and ψ_s of embryo tissues were measured by psychrometry after excision from imbibed intact seeds. For intact or decoated seeds and excised cotyledons, Ψ values were >−0.2 MPa just prior to radicle emergence. The Ψ of excised embryonic axes, however, averaged only −0.6 MPa over the same period. The embryonic axis apparently is mechanically constrained within the testa/perisperm, increasing its total pressure potential until axis Ψ is in equilibrium with cotyledon Ψ, but reducing its water content and resulting in a low Ψ when the constraint is removed. There was no evidence of decreasing ψ_s or increasing turgor pressure (Ψ-ψ_s) prior to radicle growth for either intact seeds or excised tissues. Given the low relative water content of the axes within intact seeds, cell wall relaxation would be ineffective in creating a Ψ gradient for water uptake. Rather, axis growth may be initiated by weakening of the perisperm, thus releasing the external pressure and creating a Ψ gradient for water uptake into the axis. The perisperm envelope contains a cap of small, thin-walled endosperm cells adjacent to the radicle tip. We hypothesize that weakening or separation of cells in this region could initiate radicle expansion.     

Estimation of the volumetric elastic modulus and membrane hydraulic conductivity of willow sieve tubes

Severed aphid stylets were used to follow the kinetics of sieve tube turgor and osmotic pressure (π) responses following step changes in water potential applied to the cambial surface of willow (Salix exigua Nutt.) bark strips. The kinetics of the turgor response were monitored with a pressure transducer. In separate experiments, the kinetics of the π response were followed by freezing point determinations on stylet exudate. The sieve tube volumetric elastic modulus in the bark strips was about 21 bars, but may be higher in intact stems. The membrane hydraulic conductivity was about 5 × 10⁻³ centimeters per second per bar; several factors make it difficult to estimate its value accurately. Differences in the turgor pressure (P) and π responses, as well as the relatively more rapid initial turgor response to a water potential (ψ) change, suggested a time-dependent component in sieve tube wall elasticity.

Our observations were generally not supportive of the idea that sieve tubes might osmoregulate. However, the bark strip system may not be suitable for addressing that question.

Separate measurements of ψ, P, and π demonstrate that the relationship predicted by the fundamental cell water potential equation, ψ = P − π, is applicable within experimental error (± 0.4 bar) to sieve tube water relations.

     

The Psychometric Properties of the Center for Epidemiologic Studies Depression Scale in Chinese Primary Care Patients: Factor Structure,Construct Validity,Reliability, Sensitivity and Responsiveness

Background

The Center for Epidemiologic Studies Depression Scale (CES-D) is a commonly used instrument to measure depressive symptomatology. Despite this, the evidence for its psychometric properties remains poorly established in Chinese populations. The aim of this study was to validate the use of the CES-D in Chinese primary care patients by examining factor structure, construct validity, reliability, sensitivity and responsiveness.

Methods and Results

The psychometric properties were assessed amongst a sample of 3686 Chinese adult primary care patients in Hong Kong. Three competing factor structure models were examined using confirmatory factor analysis. The original CES-D four-structure model had adequate fit, however the data was better fit into a bi-factor model. For the internal construct validity, corrected item-total correlations were 0.4 for most items. The convergent validity was assessed by examining the correlations between the CES-D, the Patient Health Questionnaire 9 (PHQ-9) and the Short Form-12 Health Survey (version 2) Mental Component Summary (SF-12 v2 MCS). The CES-D had a strong correlation with the PHQ-9 (coefficient: 0.78) and SF-12 v2 MCS (coefficient: -0.75). Internal consistency was assessed by McDonald’s omega hierarchical (ωH). The ωH value for the general depression factor was 0.855. The ωH values for “somatic”, “depressed affect”, “positive affect” and “interpersonal problems” were 0.434, 0.038, 0.738 and 0.730, respectively. For the two-week test-retest reliability, the intraclass correlation coefficient was 0.91. The CES-D was sensitive in detecting differences between known groups, with the AUC >0.7. Internal responsiveness of the CES-D to detect positive and negative changes was satisfactory (with p value <0.01 and all effect size statistics >0.2). The CES-D was externally responsive, with the AUC>0.7.

Conclusions

The CES-D appears to be a valid, reliable, sensitive and responsive instrument for screening and monitoring depressive symptoms in adult Chinese primary care patients. In its original four-factor and bi-factor structure, the CES-D is supported for cross-cultural comparisons of depression in multi-center studies.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : I. Water Relations of Seed and Fruit Development

Total water potential (ψ), solute potential, and turgor potential of field-grown muskmelon (Cucumis melo L.) fruit tissue (pericarp) and seeds were determined by thermocouple psychrometry at 5-day intervals from 10 to 65 days after anthesis (DAA). Fruit maturity occurred between 44 and 49 DAA, and seed germination ability developed between 35 and 45 DAA. Pericarp ψ was essentially constant at approximately −0.75 megapascal (MPa) from 10 to 25 DAA, then decreased to a minimum value of −1.89 MPa at 50 DAA before increasing to −1.58 MPa at 65 DAA. Seed ψ remained relatively constant at approximately −0.5 MPa from 10 to 30 DAA then decreased to −2.26 MPa at 50 to 60 DAA before increasing to −2.01 MPa at 65 DAA. After a rapid increase to 20 DAA, seed fresh weight declined until 30 DAA due to net water loss, despite continuing dry weight gain. As fruit and seed growth rates decreased, turgor potential initially increased, then declined to small values when growth ceased. A disequilibrium in ψ was measured between seeds and pericarp both early and late in development. From 20 to 40 DAA, the ψ gradient was from the seed to the tissue, coinciding with water loss from the seeds. From 50 to 65 DAA, seed ψ decreased, causing a reversal of the ψ gradient and a slight increase in seed water content. The partitioning of solutes between symplast and apoplast may create and maintain ψ gradients between the pericarp and seed. The low solute potential within the pericarp due to solute accumulation and loss of cellular compartmentation during ripening and sensecence may be involved in prevention of precocious germination of mature seeds.     

Role of Hydrogen-Bonding in Nonelectrolyte Diffusion through Dense Artificial Membranes

The diffusion of two series of alcohols and amides through complex cellulose acetate membranes was studied. The thin dense part of these membranes behaves as a nonporous layer of low water content. In this layer, called the skin, the solute diffusion coefficients, ω, depend upon size, steric configuration, and the partition coefficient, K₈, between membrane and bathing solution. From the experimental values of ω and K₈, the over-all friction, f, experienced by the solutes in the membrane was computed. It was found that f depends upon the chemical nature of the solute and is related to hydrogen-bonding ability. In the coarse, porous layer of the cellulose acetate membrane, diffusion occurs mainly through aqueous channels. In this instance also the hydrogen-bonding ability of the solute seems to exercise a smaller but significant influence.     

Osmotic adjustment in sorghum: I. Mechanisms of diurnal osmotic potential changes

Osmotic adjustment, defined as a lowering of osmotic potential (ψ_π) due to net solute accumulation in response to water stress, has been considered to be a beneficial drought tolerance mechanism in some crop species. The objective of this experiment was to determine the relative contribution of passive versus active mechanisms involved in diurnal ψ_π changes in sorghum (Sorghum bicolor L. Moench) leaf tissue in response to water stress. A single sorghum hybrid (cv AT×623 × RT×430) was grown in the field under variable water supplies. Water potential, ψ_π, and relative water content were measured diurnally on expanding and the uppermost fully expanded leaves before flowering and on fully expanded leaves during the grain-filling period. Diurnal changes in total osmotic potential (Δψ_π) in response to water stress was 1.1 megapascals before flowering and 1.4 megapascals during grain filling in comparison with 0.53 megapascal under well-watered conditions. Under water-stressed conditions, passive concentration of solutes associated with dehydration accounted for 50% (0.55 megapascal) of the diurnal Δψ_π before flowering and 47% (0.66 megapascal) of the change during grain filling. Net solute accumulation accounted for 42% (0.46 megapascal) of the diurnal Δψ_π before flowering and 45% (0.63 megapascal) of the change during grain filling in water-stressed leaves. The relative contribution of changes in nonosmotic volume (decreased turgid weight/dry weight) to diurnal Δψ_π was less than 8% at either growth stages. Water stress did not affect leaf tissue elasticity or partitioning of water between the symplasm and apoplasm.