The dynamics of the DNA hydration shell at gigahertz frequencies

We have used Brillouin scattering to measure the linewidths and frequencies of GHz acoustic phonons in Na- and Li-DNA films as a function of temperature between 300 and 140 K for samples that were dry, lightly, and heavily hydrated. The linewidths decrease with falling temperature and water contents, indicating that coupling to a water relaxation is the main source of phonon damping. The strength of the relaxation was determined using measurements of the phonon linewidth as a function of frequency, and confirmed by comparison of measured and calculated spectral profiles. The relaxation strength is anisotropic, being greater for phonons propagating perpendicular to the helix axis. The hydrated DNA exhibits both a rapid relaxation (≤ 10^?11 s per radian) giving rise to a classical f² damping, and a slower motion with a relaxation time that varies from ～ 4 × 10^?11 s per radian (primary hydration shell) to ～ 2 × 10^?12 s per radian (secondary hydration shell) at room temperature. In the frequency interval that bounds these relaxation times (～ 4 to 80 GHz) we expect degrees of freedom associated with the primary hydration shell to be important. The sample with primary hydration follows a simple Arrhenius behavior with ΔH ～ 5 kcal mole^?1. The effective activation energy for the sample with secondary hydration is somewhat higher (indicating a more cooperative water relaxation) and varies strongly with temperature. The elastic moduli change much more than can be accounted for by relaxation, indicating the importance of water motion in softening interatomic potentials. The extent of the softening caused by the “unfreezing” of water motion is similar to the degree of softening caused by hydrating the sample.     

Dielectric properties of slightly hydrated collagen: time-water content superposition analysis

The frequency dependences of the dielectric constant, ε′, and the loss factor, ε″, in collagen were measured at several water contents from 0.1 to 0.3 g/g collagen over a frequency range of 30 Hz to 100 kHz and at a temperature of 20°C. Remarkable dispersion was observed at the lower frequencies for higher water contents. According to accumulated results on the thermodynamic and structural investigations, the dispersion has some analogy to the surface conduction proposed by B. V. Hamon [(1953) Aust. J. Phys. 6 , 304–315]. An empirical relation bewteen ε″ and frequency, f, ε″ ∝? fⁿ, where 0 < n < 1, suggests that the dielectric and conductive properties of hydrated collagen are related to carrier jumps between neighboring sites. For the polarization mechanism of this dispersion, we supposed a model of the transfer of protons between absorbed water molecules, and found that the time–water content superposition procedure is applicable to slightly hydrated collagen. The results derived from the superposition procedure show that the water content, ?, is related to the conductivity, σ, or the dielectric loss factor by the following equations: σ (?, f) = const. × ?^nm?1f^1?n and ε″ (?, f) = const. ?^nmf^?n, respectively, where m is a constant independent of ? and f. These results agree with that derived by another treatment of the same data. The role of water molecules in the conduction and polarization in slightly hydrated collagen is considered to be not far from that assumed in the model.     

Thermal properties of collagen in helical and random coiled states in the temperature range from 4° to 300°K

The low-temperature heat capacity of collagen (in the hydrated and dehydrated states) and the large entropy of collagen in the coiled state relative to the same protein in the helical state were investigated. The heat capacity for collagen in the solid state in the temperature range 4°–50° K changes proportionally to the square of temperature (C_p ～ T²). Above 50°K there is a linear dependence (C_p ～ T). The differences in the character of temperature dependence of heat capacity for the hydrated and dehydrated collagen show the importance of the specific interaction of water molecules with polypeptide chains of this protein. The peculiarities of the temperature dependence of the heat capacity difference (ΔC_p) of hydrated denatured (random coiled) and hydrated native (helical) collagen are observed at 15°, 120°, and 240°K. These differences are caused by the varying degree of ordering of the hydrate water molecules in native and denatured collagen macromolecules. At all temperatures (4°–300°K) the entropy of the random coiled state is higher than that of collagen in the native state and at 298°K ΔS = ∫ (ΔC_p/T)dT = 0.8 cal/100 g °K.     

Electrical properties of hydrated collagen. I. Dielectric properties

The effect of water on the low-frequency (10²-10⁵ H_z) complex permittivitv of native, sold-state collagen has been investigated experimentally. Measurements at ambient temperature show that dry collagen exhibits essentially no frequency or temperature dependence. As water is absorbed, both dielectric constant and loss factor increase simultaneously and rise sharply upward at a hydration level which may be associated with the completion of the primary absorption layer as determined from independent water absorption studies. The behaviour is qualitatively identical to that observed for other proteins and related materials. Temperature-dependent measurements made under vacuum conditions in the range ?196°C to +100°C are characteristic of the dielectric properties of the water in the sample. Dehydration produced by successive temperature recycling to the maximum temperature effectively eliminates any temperature or frequency dependence. A maximum in the temperature-dependent curves is found at about +40°C and is explained as the superposition of two processes: (1) the transition of water molecules from bound to free states, and (2) the difffusion of water molecules out of the system. The dielectric constant of dry collagen, after desorption at ambient temperature, is about 4.5. Desorption at elevated temperatures reduced the room temperature value to about 2.3 and the liquid nitrogen temperature value to a number indistinguishable from the optical value of n² = 2.16.     

A Self‐Doping,O2‐Stable,n‐Type Interfacial Layer for Organic Electronics

Solid films of a water‐soluble dicationic perylene diimide salt, perylene bis(2‐ethyltrimethylammonium hydroxide imide), Petma⁺OH^?, are strongly doped n‐type by dehydration and reversibly de‐doped by hydration. The hydrated films consist almost entirely of the neutral perylene diimide, PDI, while the dehydrated films contain ～50% PDI anions. The conductivity increases by five orders of magnitude upon dehydration, probably limited by film roughness, while the work function decreases by 0.74 V, consistent with an n‐type doping density increase of ～12 orders of magnitude. Remarkably, the PDI anions are stable in dry air up to 120 °C. The work function of the doped film, ? (3.96 V vs. vacuum), is unusually negative for an O₂‐stable contact. Petma⁺OH^? is also characterized as an interfacial layer, IFL, in two different types of organic photovoltaic cells. Results are comparable to state of the art cesium carbonate IFLs, but may improve if film morphology can be better controlled. The films are stable and reversible over many months in air and light. The mechanism of this unusual self‐doping process may involve the change in relative potentials of the ions in the film caused by their deshielding and compaction as water is removed, leading to charge transfer when dry.     

Dielectric properties of hydrated collagen

Dielectric measurements have been carried out on partially hydrated collagen in the frequency ranges 100 kHz–5 MHz, 100 MHz–1 GHz, and 8–23 GHz. In the low-frequency range, a dispersion was observed around 100 kHz which results from inhomogeneous conductivity of the samples. A dielectric relaxation was observed aroud 0.3 GHz using time-domain-spectroscopy techniques. This relaxation can be considered to originate from mobile side chains. Microwave measurements indicate that the water relaxation may extend into the 10-GHz region. An apparent discrepancy between the main water relaxation time and the average rotational correlation time of water as measured by nmr line widths was resolved by the assumption that a fraction of the water molecules is bound to the collagen with residence times on the order of 10^?6 sec, whereas the remainder of the water is only weakly bound and exhibits rotational rates on the order of 10^?10 sec.     

Multinuclear magnetic resonance studies of collagen molecular structure and dynamics

We have measured the percentages of cis and trans Gly-Pro and X-Hyp peptide bonds in thermally unfolded type I collagen. ¹³C-nmr solution spectra show that 16% of the Gly-Pro and 8% of the X-Hyp bonds are cis in unfolded chick calvaria collagen. These results support the hypothesis that cis–trans isomerization is that rate-limiting step in the propagation of the collagen triple helix. We have used multinuclear solid-state nmr to study the molecular dynamics of the collagen backbone in tendon, demineralized bone, and intact bone as a function of temperature, hydration, and pH. These studies show that collagen backbone motions are characterized by a broad distribution of correlation times, τ, covering the range from 10^?4 to 10^?9 s. In the case of nonmineralized collagen, the root-mean-square fluctuations in azimuthal angle, γ_rms, range from ca. 10° when τ ～ 10^?9 s to ca. 30° when τ < 10^?4 s; in the case of bone collagen, γ_rms values are about half as large as those found in nonmineralized collagen. Backbone motions are negligible at temperatures below ?25°C. This is also the case at 22°C when demineralized bone collagen is lyophilized. In contrast, flexibility of hydrated demineralized bone collagen greatly increases as pH is lowered from 7 to 2. The more limited flexibility observed at neutral pH is a consequence of the intermolecular interactions that contribute to fibril organization and strength. However, the fibrils retain significant flexibility at physiological pH, enabling them to distribute stress and dissipate mechanical energy.     

The molecular details of collagen hydration

Nuclear magnetic resonance and dielectric data on hydrated collagen are interpreted in terms of Ramachandran's hydration model. It is found that all data are compatible with this model, indicating two specific binding sites per three amino acids in the threefold collagen helix. Sorption data have been interpreted according to the multilayer theory of Guggenheim and used to derive the fraction of bound water in the primary sites. From magnetic resonance anisotropies structural details of the position of the water molecules can be derived under the assumption that both sites are equally occupied. The residence time of a water molecule in one of these sites in moderately hydrated collagen (45 g H₂O/100 g collagen) is 1.2 × 10^?6 sec. The remainder of the water is weakly bound and consists of rapidly exchanging species with rotational correlation time shorter than 10^?10 sec. The sites are 50% occupied at a water content of 10 g/100 g collagen and may contribute significantly to the stability of the collagen threefold helix.     

The nature of the charge carriers in solvated biomacromolecules

Solid state electrolysis experiments were performed on the biomolecules, hemoglobin, cytochromec, collagen, lecithin and melanin at various hydration states; and for hemoglobin at various solvation states with methanol adsorbate. The evolved hydrogen was measured and compared with theoretical (Faraday's Law) expectations for the known amount of charge passed through the adsorbents. The difference between the theoretical and actual is a measure of the contributions of electronic charge carriers to the total current. Thus the protonic/electronic conduction ratios are determined.All biomolecules tested appear to be mixed semiconductors. That is, both electronic and protonic charge carriers make significant contributions to the currents over hydration ranges from 6% to above 50%. The constant temperature conductivity increases exponentially with hydration (solvation) but the ratio of protonic to electronic conduction increases linearly with hydration for the globular proteins, hemoglobin and cytochromec. The fibrous protein, collagen, may be a protonic semiconductor in the dry state, with an electronic component that increases linearly with hydration. The hemoglobin-methanol system shows only electronic conductivity below 2 BET monolayers, with a sharp onset to 70% protonic conductivity above this value. This result is similar to the DNA-water system previously reported. The protonic/electronic ratio in hydrated hemoglobin may be a function of the applied voltage; being predominantly electronic below 30 volts (300 volts/cm), and a constant mixed value above 100 volts (1000 volts/cm). Our results suggest that both electronic and protonic conduction are intrinsic processes in these substances and subject to control by a number of techniques.     

Effect of hydration upon the thermal stability of tropocollagen and its dependence on the presence of neutral salts

The endotherm enthalpy changes ΔH_D and temperatures T_D of thermal denaturation of tropocollagen fibers were measured by DSC calorimetry as functions of water content. The denaturation temperatures decrease with increasing water content. The enthalpy change values increase sharply in the range 0–28% of water content, where a maximum of 14.3 cal g^?1 is reached. The effect of water uptake on the enthalpy term is explained by water bridge formation within the collagen triple helix. Evidence is given for the existence of approximately three intercatenary water bridges per triplet at the enthalpy maximum, their H-bond energy amounting to approximately 4000 kcal/mol of protein. In the 30–60% range of water content, ΔH_D decreases by 2 cal^?1 probably due to interactions between secondary water structures and the stabilizing intrahelical water bonds. The influence of two neutral potassium salts, with a structure-stabilizing and a structure-breaking anion (F^? and I^?), on the hydration dependence of ΔH_D and T_D was also studied. It was shown that the primary hydration is not influenced by these ions, but that T_D and ΔH_D are altered in an ion specific way in the presence of interface and bulk water. Hydrophobic interactions do not explain the experimental results. A reaction mechanism of the effects of ions upon the structural stability of collagen is proposed and discussed in terms of interactions of the medium water molecules with the intrahelical water bonds, and in terms of proton-donor/proton-acceptor equilibria between peptide groups, hydrated ions, and intrahelical water molecules.     

Dark respiration of the stipe of Ecklonia cava (Laminariales, Phaeophyta) in relation to temperature

Sporophytes of Ecklonia cava Kjellman (Laminariales, Phaeophyta) with a stipe length of 22–102 cm were collected at 6–9 m depth in Nabeta Bay, Shimoda, central Japan by scuba diving in February (winter) and in August (summer) 1998. Dark respiration of the intact stipe of E. cava was measured at various water temperatures ranging from 15 to 27.5°C in winter and 15–30°C in summer in a closed system by using a dissolved oxygen meter. The stipe respiration was compared on whole stipe, length, surface area, volume, wet weight and dry weight bases. On each basis, the stipe respiration always increased with a rise in water temperature within the temperature range investigated. The stipes showed similar respiration rates on each basis of length, surface area, volume, wet weight and dry weight at each temperature, irrespective of the stipe length. The mean respiration rates in winter (at 15–27.5°C) were: length, 16.7–32.5 μL O₂ cm^?1 h^?1; surface area, 3.2–6.2 μL O₂ cm^?2 h^?1; volume, 7.6–15.0 μL O₂ cm^?3 h^?1; wet weight, 6.2–12.2 μL O₂ g (wet weight)^?1 h^?1; and dry weight, 43.8–88.0 μL O₂ g (dry weight)^?1 h^?1. Those for summer (at 15–30°C) were: length, 17.1–32.0 μL O₂ cm^?1 h^?1; surface area, 3.6–6.8 μL O₂ cm^?2 h^?1; volume, 9.7–18.7 μL O₂ cm^?3 h^?1; wet weight, 7.6–14.6 μL O₂ g (wet weight)^?1 h^?1; and dry weight, 49.4–95.8 μL O₂ g (dry weight)^?1 h^?1. This is the first report of the intact stipe respiration of E. cava at various temperatures.     

Mass spectrometric monitoring of gases (CO2, CH4, O2) in a mesotrophic peat core from Kopparås Mire, Sweden

Membrane inlet mass spectrometry was used to monitor dissolved gas concentrations (CO₂, CH₄ and O₂) in a mesotrophic peat core from Kopparås, Sweden. 1 A comparison of depth profiles (down to 22 cm) with an ombrotrophic peat core (Ellergower, SW Scotland) investigated previously, revealed major differences in gas concentrations. Thus methane reached concentrations more than twice as high (800 μM) at depths greater than 12 cm in the Kopparås core. As shown previously, the primary determinant of the depth of the oxic zone is the level of the water table. Whereas in the Scottish cores, mass spectrometric detectability of O₂ was confined to the first 3 cm below this level, in the Swedish core penetration of O₂ was greater (7 cm). CO₂ profiles were similar in cores from both locations. 2 A thick layer of Sphagnum mosses dominated the plant cover of the Swedish peat core. A poorly developed deep root system, as distinct from that of the vascular plant cover in Scottish cores, diminished gas exchange rates, and presumably aerobic methane oxidation at depth around roots. These characteristics may contribute to the development of discontinuities in gas profiles at depths greater 15 cm as upward gas transport is established predominantly by diffusion and/or ebullition in the Swedish core. 3 Monitoring gas concentrations at the peat surface and at 2 cm depth after changing water tables showed a delayed response of approximately 4 days as a result of the high water content and moisture‐regulating capacity of mosses. 4 Recovery processes at 2 cm depth after raising the water table revealed final production rates of dissolved CO₂ and CH₄ in the peat pore water between 0.8 and 4.4 μmol h^?1 L^?1 and between 0.1 and 1.7 μmol h^?1 L^?1, respectively. Higher production rates were found during the day, indicating a diurnal rhythm due to plant photosynthetic activity even at the low values of photosynthetically active radiation (PAR: 110 μmol s^?1 m^?2) used in the experimental set‐up. 5 In the water‐logged mesotrophic Kopparås core changes of dissolved gas concentrations (DGC) at 3 and 14 cm depth were surface temperature‐dependent rather than light dependent. This suggests that changes of air temperature alters the covering vegetation to increase the conductivity for dissolved gases through vascular plants and to facilitate gas transport by diffusion and/or ebullition.     

Thermodynamic functions of biopolymer hydration. I. Their determination by vapor pressure studies,discussed in an analysis of the primary hydration process

The primary hydration process of native biopolymers is analyzed in a brief review of the literature, pertaining to various aspects of biopolymer–water systems. Based on this analysis, a hydration model is proposed that implies that the solution conformation of native biopolymers is stable at and above a critical degree of hydration (h_p′ = 0.06–0.1 g H₂O/g polymer). This water content corresponds to the fraction of strongly bound water, and amounts to ～20% of the primary hydration sphere. In order to test this model, detailed sorption–desorption scanning experiments were performed on a globular protein (α-chymotrypsin). The results obtained are consistent with the proposed hydration model. They show that under certain experimental conditions, sorption isotherms can be obtained that do not exhibit hysteresis. These data represent equilibrium conditions and are thus accessible to thermodynamic treatment. Valid thermodynamic functions, pertinent to the interaction of water with biopolymers in their solution state, can be obtained from these sorption experiments.     

Dynamics of lysozyme and its hydration water under an electric field

The effects of a static electric field on the dynamics of lysozyme and its hydration water are investigated by means of incoherent quasi-elastic neutron scattering (QENS). Measurements were performed on lysozyme samples, hydrated respectively with heavy water (D ₂O) to capture the protein dynamics and with light water (H ₂O), to probe the dynamics of the hydration shell, in the temperature range from 210 < T < 260 K. The hydration fraction in both cases was about ～ 0.38 gram of water per gram of dry protein. The field strengths investigated were respectively 0 kV/mm and 2 kV/mm ( ～2 × 10 ⁶ V/m) for the protein hydrated with D ₂O and 0 kV and 1 kV/mm for the H ₂O-hydrated counterpart. While the overall internal protons dynamics of the protein appears to be unaffected by the application of an electric field up to 2 kV/mm, likely due to the stronger intra-molecular interactions, there is also no appreciable quantitative enhancement of the diffusive dynamics of the hydration water, as would be anticipated based on our recent observations in water confined in silica pores under field values of 2.5 kV/mm. This may be due to the difference in surface interactions between water and the two adsorption hosts (silica and protein), or to the existence of a critical threshold field value E _c ～2–3 kV/mm for increased molecular diffusion, for which electrical breakdown is a limitation for our sample.     

The effects of temperature on swimming performance of juvenile shortnose sturgeon (Acipenser brevirostrum)

The swimming performance of juvenile shortnose sturgeon (～16 cm TL, ～20 g), Acipenser brevirostrum, was quantified with regards to temperature (5 to 25°C) using both increased (U_crit) and fixed velocity (endurance) tests in a laboratory setting. Sturgeons were found to show reduced U_crit values at 5 and 10°C (25.99 and 28.86 cm s^?1 respectively), with performance beginning to plateau at 15°C through 25°C (33.99 cm s^?1). For the endurance protocol, fish were tested at speeds of 35, 40 and 45 cm s^?1 at 5, 15 and 25°C. Performance within a single speed was similar at all temperatures, indicating the usage of anaerobic metabolism to fuel locomotion at these higher velocities. Overall, shortnose sturgeon demonstrated high tolerance towards a wide range of temperatures but showed few differences between performance levels at colder or warmer water conditions.     

Effect of water on piezoelectric,dielectric, and elastic properties of bone

The complex piezoelectric constant (d = d′ ? id″), elastic constant (c = c′ + ic″), and dielectric constant (ε = ε′ ? iε″) were measured at a frequency of 10 Hz over the temperature range from ?150 to 50°C and for a range of hydration up to 0.26 g/g for decalcified bone and up to 0.084 g/g for bone. For decalcified bone, ε′ and ε″ increased with increasing hydration with a deflection at the critical hydration h_c = 0.08 g/g;d′ at ?150°C increased below h_c but decreased above h_c with increasing hydration; c′ increased below ?60°C but decreased above ?60°C with increasing hydration; and the peak temperatures of ε″, d″, and c″ below ?50°C agree with each other and decreased with increasing hydration with a deflection at h_c. For bone, similar hydration and temperature dependences were observed for ε and c. However, the dependence of d on hydration and temperature was different from that of decalcified bone, reflecting a two-phase structure consisting of collagen fibers and mineral hydroxyapatite. The critical hydration for bone was 0.04 g/g.     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Conformation and sweet tastes of L-aspartyl dipeptide methyl esters

In order to investigate the conformational preferences to elicit tastes, conformational free energy calculations using an empirical potential (ECEPP/2) and the hydration shell model were carried out on the L -aspartyl dipeptide methyl esters, L -⁺HAsp^?-L -Xaa-OMe, in the hydrated state, where Xaa includes sweet (Phe, Tyr, Met, and Gly), bitter (Ala, Trp, Val, Leu, and Ile), and tasteless (Ser, Thr, and Abu) residues. The refined preferred conformation of the Phe dipeptide (aspartame) with side chain χ conformation g^? is g^?Fg^? in the hydrated state, which is consistent with the structure deduced from ¹H-nmr experiments. Irrespective of the Xaa and taste, all the dipeptides have the same conformation for the Asp residue, which is attributable to the hydrogen bond between protonated amino hydrogen and carboxylate oxygen and the favored hydration of the carboxylate group. This implies that the L -aspartyl residue is a necessary factor for the dipeptides to be sweet not a sufficient factor. The computed conformational preferences for sweet, bitter, and tasteless dipeptides in the hydrated state indicate to us that the conformation about the N? C^α bond of the Xaa residue, i.e., the orientation of the hydrophobic moiety with respect to the AH/B functionalities in the aspartyl moiety, seems to be crucial to elicit the tastes. In addition, the hydrophobicity and the size of the Xaa residue are found to play a major role in determining the tastes. These well accord with the related works reported previously. © 1994 John Wiley & Sons, Inc.     

Growth of Sesbania rostrata (Brem) with stem nodules under controlled conditions

A series of experiments was carried out in an attempt to produce nodulated plants of Sesbania rostrata with qualities more closely resembling those in the wild than has been achieved to date. When groups of five plants were grown in a controlled climate chamber in pipes containing ～12dm³ modified Jensen's medium with 6mol m^?3 nitrate, the daily growth in height reached 5 cm and at 30 d the plants were ～40cm high. At this time, the stems were inoculated with Azorhizobium caulinodans ORS 571 and the medium replaced with Jensen's medium without nitrate. In the subsequent 19-d period ～300 nodules (representing >50% of the potential infection sites) developed on each stem. The nodules increased linearly in size over this time to ～15mg. Specific acetylene reduction activity, ARA ((μmol C₂H₄ mg^?1 h^?1) rose to 45 between days 5 and 10 after inoculation and plateaued; total ARA rose to ～200 μmol C₂H₄ plant^?1 h^?1. Under the conditions described the plants grew vigorously, and reproducibly uniform yields of nodules with high ARA activities were obtained. As outlined, the procedure offers a standard system in which, within a 2-week period after inoculation, individual strains of bacteria can be quantitatively compared in their ability to induce nodulation and N₂-fixation. Physiological and biochemical aspects of the nodulated system can be much more readily approached than with plants producing only root nodules. The inhibitory effects of stem nodules induced by wild type and two mutant strains of Azorhizobium on the development and activity of root nodules are described.     

Heart rate as an indicator of metabolic rate and activity in adult Atlantic salmon, Salmo salar

Telemetered heart rate (f_H) was examined as an indicator of activity and oxygen consumption rate (VO₂) in adult, cultivated, Atlantic salmon, Salmo salar L. Heart rate was measured during sustained swimming in a flume for six fish at 10° C [mean weight, 1114 g; mean fork length (f. l.), 50·6 cm] and seven fish at 15° C (mean weight, 1119 g; mean f. l., 50·7 cm) at speeds of up to 2·2 body lengths/s. Semi–logarithmic relationships between heart rate and swimming speed were obtained at both temperatures. Spontaneously swimming fish in still water exhibited characteristic heart rate increases associated with activity. Heart rate and Vo₂ were monitored simultaneously in a 575–1 circular respirometer for six fish (three male, three female) at 4° C (mean weight, 1804 g; mean F. L., 62· cm) and six fish (three male, three female) at 10° C (mean weight, 2045 g; mean f. l., 63·2 cm) during spontaneous but unquantified activity. Linear regressions were obtained by transforming data for both f_H and Vo₂ to log values. At each temperature, slopes of the regressions between f_H and Vo₂ for individual fishes were not significantly different, but in some cases elevations were. All differences in elevation were between male and female fish. There were no significant differences in regression slope or elevation for fish of the same sex at the two temperatures and so regressions were calculated for the sexes, pooling data from 4 and 10° C. There was no significant difference in the mean ± S. D. Vo₂ between the sexes at 4° C (male, 66·0 ± 59·6 mgO₂ kg^?1 h^?1; female, 88·0 ± 60·1 mgO₂ kg^?1 h^?1) or 10° C (male, 166·2 ± 115·4 mgO₂ kg^?1 h^?1; female, 169·2 ± 111–1 mgO₂ kg^?1h^?1). Resting Vo₂ (x?± s. d.) at 4°C was 36·7 ± 8.4 mgO₂ kg^?1 h^?1, and 10° C was 72·8 ± 11·9 mgO₂ kg^?1 h^?1. Maximum Vo₂ (x?± S. D.) at 4° C was 250·6 ± 40·2 mgO₂ kg^?1 h^?1, and at 10° C was 423·6 ± 25·2 mgO₂ kg^?1 h^?1. Heart rate appears to be a useful indicator of metabolic rate over the temperature range examined, for the cultivated fish studied, but it is possible that the relationship for wild fish may differ.