Scattering spectrum properties and their relationship to biogeochemical parameters: a case study in Taihu Lake

The scattering spectrum properties of highly turbid and eutrophic inland case 2 water from Taihu Lake were studied during three cruises from 2006 to 2007. The scattering [b _p(λ)] and backscattering [b _bp(λ)] coefficients and the backscattering probability (B) for Taihu Lake were found to show a clear spectral dependence, and this dependence was well simulated by a power-law function. This dependence, however, became weak when algae dominated the sample points. The mean values of the power-law index for b _p(λ), v, in Oct 2006, Mar 2007 and Nov 2007 were −0.6712, −0.8129 and −0.7600, respectively. To interpret the spectral characteristics and mechanisms of b _p(λ) and b _bp(λ), water samples were collected simultaneously for the biogeochemical characterization of suspended particles. The average values of the specific scattering coefficients for total suspended matter, inorganic suspended matter (ISPM) and organic suspended matter (OSPM) were 0.634 (550 nm), 1.057 (532 nm), and 0.396 g m⁻² (532 nm), respectively. The power-law index of b _bp(λ) (Y) was significantly related to ISPM/OSPM and b _bp(532 nm), but only weakly related to the particle size distribution index. The mean (spatial and wavelength) values of B in Oct 2006, Mar 2007, and Nov 2007 were 0.0108, 0.0138, and 0.0125, respectively. B decreases with increasing ISPM concentration because of the large contribution of ISPM to b _b(λ) and the strong restraint on b _bp(λ) caused by the multi-scattering effect under high-turbidity conditions.     

Photosystem 2 photochemistry and pigment composition of a yellow mutant of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) under different irradiances

A yellow leaf colouration mutant (named ycm) generated from rice T-DNA insertion lines was identified with less grana lamellae and low thylakoid membrane protein contents. At weak irradiance [50 μmol(photon) m⁻² s⁻¹], chlorophyll (Chl) contents of ycm were ≈20 % of those of WT and Chl a/b ratios were 3-fold that of wild type (WT). The leaf of ycm showed lower values in the actual photosystem 2 (PS2) efficiency (Φ_PS2), photochemical quenching (q_P), and the efficiency of excitation capture by open PS2 centres 1 (F_v′/F_m′) than those of WT, except no difference in the maximal efficiency of PS2 photochemistry (F_v/F_m). With progress in irradiance [100 and 200 μmol(photon) m⁻² s⁻¹], there was a change in the photosynthetic pigment stoichiometry. In ycm, the increase of total Chl contents and the decrease in Chl a/b ratio were observed. Φ_PS2, q_P, and F_v′/F_m′ of ycm increased gradually along with the increase of irradiance but still much less than in WT. The increase of xanthophyll ratio [(Z+A)/(V+A+Z)] associated with non-photochemical quenching (q_N) was found in ycm which suggested that ycm dissipated excess energy through the turnover of xanthophylls. No significant differences in pigment composition were observed in WT under various irradiances, except Chl a/b ratio that gradually decreased. Hence the ycm mutant developed much more tardily than WT, which was caused by low photon energy utilization independent of irradiance.     

Effects of different irradiances on the photosynthetic process during ex-vitro acclimation of Anoectochilus plantlets

Six months old in vitro-grown Anoectochilus formosanus plantlets were transferred to ex-vitro acclimation under low irradiance, LI [60 μmol(photon) m⁻² s⁻¹], intermediate irradiance, II [180 μmol(photon) m⁻² s⁻¹], and high irradiance, HI [300 μmol(photon) m⁻² s⁻¹] for 30 d. Imposition of II led to a significant increase of chlorophyll (Chl) b content, rates of net photosynthesis (P _N) and transpiration (E), stomatal conductance (g _s), electron transfer rate (ETR), quantum yield of electron transport from water through photosystem 2 (Φ_PS2), and activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBPCO, EC 4.1.1.39). This indicates that Anoectochilus was better acclimated at II compared to LI treatment. On the other hand, HI acclimation led to a significant reduction of Chl a and b, P _N, E, g _s, photochemical quenching, dark-adapted quantum efficiency of open PS2 centres (F_v/F_m), probability of an absorbed photon reaching an open PS2 reaction centre (F_v′/F_m′), ETR, Φ_PS2, and energy efficiency of CO₂ fixation (Φ_CO2/Φ_PS2). This indicates that HI treatment considerably exceeded the photo-protective capacity and Anoectochilus suffered HI induced damage to the photosynthetic apparatus. Imposition of HI significantly increased the contents of antheraxanthin and zeaxanthin (ZEA), non-photochemical quenching, and conversion of violaxanthin to ZEA. Thus Anoectochilus modifies its system to dissipate excess excitation energy and to protect the photosynthetic machinery.     

Populations ofSitobion avenae andAphidius ervi on spring wheat in the northwestern United States Spatial distribution and sequential sampling plans based on numerical and binomial counts

During a three-year field survey of the English grain aphid,Sitobion avenae (F.) (Homoptera: Aphididae) and the parasitoid,Aphidius ervi Haliday (Hymenoptera: Aphidiidae; represented by aphid mummies) on spring wheat, data sets were generated which consisted of 47 estimates of mean density (m aphids per tiller), variance (s ²), and the proportion of empty tillers (P ₀ forS. avenae and 22 estimates of the same statistics forA. ervi, respectively. Each estimate of the aphid and parasitoid populations was based on counts per individual tiller on each sampling occasion. Taylor's power law was found to fit the data sets better than Iwao'sm ^*−m regression model. Taylor's slope forS. avenae (1.3076) was significantly higher than that forA. ervi (1.1519), indicating thatS. avenae was more aggregated thanA. ervi. Based on temporal changes in spatial aggregation represented by an index, 1/k [wherek was estimated asm ²/(s²−m)],S. avenae was most aggregated at low densities during the early infestation period and tended to be less aggregated as density increased, whereasA. ervi was more likely to be randomly distributed. A commonk was detected for neitherS. avenae norA. ervi because the slopes from the linear regression ofk onm significantly exceeded 0. Sequential sampling plans, based on numerical (complete) and binomial (presence or absence) counts, for the aphid and parasitoid species were developed using Taylor's parameters and those estimated from the linear regression of ln(m) on ln[−ln[P ₀], respectively. Suggestions are made concerning the use of the sampling plans and the levels of precision that may be attained.     

Photosynthetic parameters of young Brazil nut (<Emphasis Type="Italic">Bertholletia excelsa</Emphasis> H. B.) plants subjected to fertilization in a degraded area in Central Amazonia

In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization (branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (P _N) were observed in T1 [13.2±1.0 μmol(CO₂) m⁻² s⁻¹] compared to T2 [8.0±1.8 μmol(CO₂) m⁻² s⁻¹] and T0 [4.8±1.3 μmol(CO₂) m⁻² s⁻¹]. Stomatal conductance (g _s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and 63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (F_v), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants of B. excelsa in young phase.     

Energetics of swimming at maximal speeds in humans

The energy cost per unit of distance (C _s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (v), C _s was measured dividing steady-state oxygen consumption (V˙O₂) by the speed (v, metres per second). At supra-maximal v, C _s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E _an+V˙O_2max t _p−V˙O_2max(1−e^{−( t p/)}), where E _an was the amount of energy (kilojoules) derived from anaerobic sources, V˙O_2max litres per second was the maximal oxygen uptake, α (=20.9 kJ · l O₂ ⁻¹) was the energy equivalent of O₂, τ (24 s) was the time constant assumed for the attainment of V˙O_2max at muscle level at the onset of exercise, and t _p (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t _p to an asymptotic value of 0.418 kJ · kg⁻¹ of body mass for t _p ≥ 120 s. The lactic acid component of E _an was obtained from the net increase of lactate concentration after exercise (Δ[La]_b) assuming that, when Δ[La]_b = 1 mmol · l⁻¹ the net amount of metabolic energy released by lactate formation was 0.069 kJ · kg⁻¹. Over the entire range of v, front crawl was the least costly stroke. For example at 1 m · s⁻¹, C _s amounted, on average, to 0.70, 0.84, 0.82 and 0.124 kJ · m⁻¹ in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m · s⁻¹, C _s was 1.23, 1.47, 1.55 and 1.87 kJ · m⁻¹ in the four strokes, respectively. The C _s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly C _s attained a minimum at the two lowest v to increase exponentially at higher v. The C _s in breaststroke was a linear function of the v, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of v occurring in the non-propulsive phase. Accepted: 14 April 1998     

Photosynthesis performance in sweet almond [<Emphasis Type="Italic">Prunus dulcis</Emphasis> (Mill) D. Webb] exposed to supplemental UV-B radiation

Due to anthropogenic influences, solar UV-B irradiance at the earth’s surface is increasing. To determine the effects of enhanced UV-B radiation on photosynthetic characteristics of Prunus dulcis, two-year-old seedlings of the species were submitted to four levels of UV-B stress, namely 0 (UV-B_c), 4.42 (UV-B₁), 7.32 (UV-B₂) and 9.36 (UV-B₃) kJ m⁻² d⁻¹. Effects of UV-B stress on a range of chlorophyll (Chl) fluorescence parameters (FPs), Chl contents and photosynthetic gas-exchange parameters were investigated. UV-B stress promoted an increase in minimal fluorescence of dark-adapted state (F₀) and F₀/F_m, and a decrease in variable fluorescence (F_v, F_v/F_m, F_v/F₀ and F₀/F_m) due to its adverse effects on photosystem II (PSII) activity. No significant change was observed for maximal fluorescence of dark-adapted state (F_m). Enhanced UV-B radiation caused a significant inhibition of net photosynthetic rate (P _N) at UV-B₂ and UV-B₃ levels and this was accompanied by a reduction in stomatal conductance (g _s) and transpiration rate (E). The contents of Chl a, b, and total Chl content (a+b) were also significantly reduced at increased UV-B stress. In general, adverse UV-B effects became significant at the highest tested radiation dose 9.36 kJ m⁻² d⁻¹. The most sensitive indicators for UV-B stress were F_v/F₀, Chl a content and P _N. Significant P<0.05 alteration in these parameters was found indicating the drastic effect of UV-B radiation on P. dulcis.     

Application of oscillation for efficiency improvement of continuous ethanol fermentation with Saccharomyces cerevisiae under very-high-gravity conditions

Compared with steady state, oscillation in continuous very-high-gravity ethanol fermentation with Saccharomyces cerevisiae improved process productivity, which was thus introduced for the fermentation system composed of a tank fermentor followed by four-stage packed tubular bioreactors. When the very-high-gravity medium containing 280 g l⁻¹ glucose was fed at the dilution rate of 0.04 h⁻¹, the average ethanol of 15.8% (v/v) and residual glucose of 1.5 g l⁻¹ were achieved under the oscillatory state, with an average ethanol productivity of 2.14 g h⁻¹ l⁻¹. By contrast, only 14.8% (v/v) ethanol was achieved under the steady state at the same dilution rate, and the residual glucose was as high as 17.1 g l⁻¹, with an ethanol productivity of 2.00 g h⁻¹ l⁻¹, indicating a 7% improvement under the oscillatory state. When the fermentation system was operated under the steady state at the dilution rate of 0.027 h⁻¹ to extend the average fermentation time to 88 h from 59 h, the ethanol concentration increased slightly to 15.4% (v/v) and residual glucose decreased to 7.3 g l⁻¹, correspondingly, but the ethanol productivity was decreased drastically to 1.43 g h⁻¹ l⁻¹, indicating a 48% improvement under the oscillatory state at the dilution rate of 0.04 h⁻¹.     

Global stability in consumer-resource cascades

 Models of population growth in consumer-resource cascades (serially arranged containers with a dynamic consumer population, v, receiving a flow of resource, u, from the previous container) with a functional response of the form h(u/v ^b ) are investigated. For b∈[0, 1], it is shown that these models have a globally stable equilibrium. As a result, two conclusions can be drawn: (1) Consumer density dependence in the functional or in the per-capita numerical response can result in persistence of the consumer population in all containers. (2) In the absence of consumer density dependence, the consumer goes extinct in all containers except possibly the first. Several variations of this model are discussed including replacing discrete containers by a spatial continuum and introducing a dynamic resource. Received 25 February 1995 / received in revised form 27 July 1995     

Autotrophic and heterotrophic respiration in needle fir and Quercus-dominated stands in a cool-temperate forest, central Korea

To investigate annual variation in soil respiration (R _S) and its components [autotrophic (R _A) and heterotrophic (R _H)] in relation to seasonal changes in soil temperature (ST) and soil water content (SWC) in an Abies holophylla stand (stand A) and a Quercus-dominated stand (stand Q), we set up trenched plots and measured R _S, ST and SWC for 2 years. The mean annual rate of R _S was 436 mg CO₂ m⁻² h⁻¹, ranging from 76 to 1,170 mg CO₂ m⁻² h⁻¹, in stand A and 376 mg CO₂ m⁻² h⁻¹, ranging from 82 to 1,133 mg CO₂ m⁻² h⁻¹, in stand Q. A significant relationship between R _S and its components and ST was observed over the 2 years in both stands, whereas a significant correlation between R _A and SWC was detected only in stand Q. On average over the 2 years, R _A accounted for approximately 34% (range 17–67%) and 31% (15–82%) of the variation in R _S in stands A and Q, respectively. Our results suggested that vegetation type did not significantly affect the annual mean contributions of R _A or R _H, but did affect the pattern of seasonal change in the contribution of R _A to R _S.     

Large Conductance Ca2+-activated K+ Channels in the Soma of Rat Motoneurones

Properties of large conductance Ca²⁺-activated K⁺ channels were studied in the soma of motoneurones visually identified in thin slices of neonatal rat spinal cord. The channels had a conductance of 82 ± 5 pS in external Ringer solution (5.6 mm K⁺ _o //155 mm K⁺ _i ) and 231 ± 4 pS in external high-K _o solution (155 mm K⁺ _o //155 mm K⁺ _i ). The channels were activated by depolarization and by an increase in internal Ca²⁺ concentration. Potentials of half-maximum channel activation (E₅₀) were −13, −34, −64 and −85 mV in the presence of 10⁻⁶, 10⁻⁵, 10⁻⁴ and 10⁻³ m internal Ca²⁺, respectively. Using an internal solution containing 10⁻⁴ m Ca²⁺, averaged K_Ca currents showed fast activation within 2–3 msec after a voltage step to +50 mV. Averaged K_Ca currents did not inactivate during 400 msec voltage pulses. External TEA reduced the apparent single-channel amplitude with a 50% blocking concentration (IC₅₀) of 0.17 ± 0.02 mm. K_Ca channels were completely suppressed by externally applied 100 mm charybdotoxin. It is concluded that K_Ca channels activated by Ca²⁺ entry during the action potential play an important role in the excitability of motoneurones. Received: 7 November 1996/Revised: 29 October 1997     

Effect of high temperature on photosynthesis and transpiration of sweet corn (<Emphasis Type="Italic">Zea mays</Emphasis> L. var. <Emphasis Type="Italic">rugosa</Emphasis>)

Four temperature treatments were studied in the climate controlled growth chambers of the Georgia Envirotron: 25/20, 30/25, 35/30, and 40/35 °C during 14/10 h light/dark cycle. For the first growth stage (V3-5), the highest net photosynthetic rate (P _N) of sweet corn was found for the lowest temperature of 28–34 μmol m⁻² s⁻¹ while the P _N for the highest temperature treatment was 50–60 % lower. We detected a gradual decline of about 1 P _N unit per 1 °C increase in temperature. Maximum transpiration rate (E) fluctuated between 0.36 and 0.54 mm h⁻¹ (≈5.0–6.5 mm d⁻¹) for the high temperature treatment and the minimum E fluctuated between 0.25 and 0.36 mm h⁻¹ (≈3.5–5.0 mm d⁻¹) for the low temperature treatment. Cumulative CO₂ fixation of the 40/35 °C treatment was 33.7 g m⁻² d⁻¹ and it increased by about 50 % as temperature declined. The corresponding water use efficiency (WUE) decreased from 14 to 5 g(CO₂) kg⁻¹(H₂O) for the lowest and highest temperature treatments, respectively. Three main factors affected WUE, P _N, and E of Zea: the high temperature which reduced P _N, vapor pressure deficit (VPD) that was directly related to E but did not affect P _N, and quasi stem conductance (QC) that was directly related to P _N but did not affect E. As a result, WUE of the 25/20 °C temperature treatment was almost three times larger than that of 40/35 °C temperature treatment.     

Kinetics of K-Cl Cotransport in Frog Erythrocyte Membrane: Effect of External Sodium

In frog red blood cells, K-Cl cotransport (i.e., the difference between ouabain-resistant K fluxes in Cl and NO₃) has been shown to mediate a large fraction of the total K⁺ transport. In the present study, Cl⁻-dependent and Cl⁻-independent K⁺ fluxes via frog erythrocyte membranes were investigated as a function of external and internal K⁺ ([K⁺] _e and [K⁺] _i ) concentration. The dependence of ouabain-resistant Cl⁻-dependent K⁺ (⁸⁶Rb) influx on [K⁺] _e over the range 0–20 mm fitted the Michaelis-Menten equation, with an apparent affinity (K _m ) of 8.2 ± 1.3 mm and maximal velocity (V _max ) of 10.4 ± 1.6 mmol/l cells/hr under isotonic conditions. Hypotonic stimulation of the Cl⁻-dependent K⁺ influx increased both K _m (12.8 ± 1.7 mm, P < 0.05) and V _max (20.2 ± 2.9 mmol/l/hr, P < 0.001). Raising [K⁺] _e above 20 mm in isotonic media significantly reduced the Cl⁻-dependent K⁺ influx due to a reciprocal decrease of the external Na⁺ ([Na⁺] _e ) concentration below 50 mm. Replacing [Na⁺] _e by NMDG⁺ markedly decreased V _max (3.2 ± 0.7 mmol/l/hr, P < 0.001) and increased K _m (15.7 ± 2.1 mm, P < 0.03) of Cl⁻-dependent K⁺ influx. Moreover, NMDG⁺ Cl substitution for NaCl in isotonic and hypotonic media containing 10 mm RbCl significantly reduced both Rb⁺ uptake and K⁺ loss from red cells. Cell swelling did not affect the Na⁺-dependent changes in Rb⁺ uptake and K⁺ loss. In a nominally K⁺(Rb⁺)-free medium, net K⁺ loss was reduced after lowering [Na⁺] _e below 50 mm. These results indicate that over 50 mm [Na⁺] _e is required for complete activation of the K-Cl cotransporter. In nystatin-pretreated cells with various intracellular K⁺, Cl⁻-dependent K⁺ loss in K⁺-free media was a linear function of [K⁺] _i , with a rate constant of 0.11 ± 0.01 and 0.18 ± 0.008 hr⁻¹ (P < 0.001) in isotonic and hypotonic media, respectively. Thus K-Cl cotransport in frog erythrocytes exhibits a strong asymmetry with respect to transported K⁺ ions. The residual, ouabain-resistant K⁺ fluxes in NO₃ were only 5–10% of the total and were well fitted to linear regressions. The rate constants for the residual influxes were not different from those for K⁺ effluxes in isotonic (∼0.014 hr⁻¹) and hypotonic (∼0.022 hr⁻¹) media, but cell swelling resulted in a significant increase in the rate constants. Received: 19 November 1998/Revised: 23 August 1999     

The rate of allelism of lethal genes in a geographically structured population

The expected rate of allelism, E[I(x)], of lethal genes between two colonies with distance x in a structured population is studied by using one- and two-dimensional stepping-stone models. It is shown that E[I(x)] depends on the magnitude of selection in heterozygous condition (h), the rate of migration among adjacent colonies (m), the number of loci which produce lethal mutations (n) and the effective population size of each colony (N).——E[I(x)] always decreases with distance x. The rate of decrease is affected strongly by the magnitude of m. The rate of decrease is faster when m is small. E[I(x)] also decreases with increasing N and n. The effect of h on E[I(x)] is somewhat complicated. However, E[I(0)] is always smaller when h is small than when it is large.——For large x, the following approximate formulae may be obtained: (see PDF) where q and Var (q) are the mean and the variance of gene frequencies in each colony, t is approximated as t=h, (see PDF), -h for the partially recessive, completely recessive, and overdominant lethals, respectively, and C₀ is a function of m and t. It is clear that E[I(x)] declines exponentially with x in a one-dimensional habitat. The decrease E[I(x)] is faster in a two-dimensional habitat than in a one-dimensional habitat. The present result is applied to some of the existing data and the estimation of population parameters is also discussed.     

Small scale vertical gradients of Arctic ice algal photophysiological properties

Photosynthetic parameters of phytoplankton and sea ice algae from landfast sea ice of the Chukchi Sea off Point Barrow, Alaska, were assessed in spring 2005 and winter through spring 2006 using Pulse Amplitude Modulated (PAM) fluorometry including estimates of maximum quantum efficiency (F _v/F _m), maximum relative electron transport rate (rETR_max), photosynthetic efficiency (α), and the photoadaptive index (E _k). The use of centrifuged brine samples allowed to document vertical gradients in ice algal acclimation with 5 cm vertical resolution for the first time. Bottom ice algae (0–5 cm from ice–water interface) expressed low F _v/F _m (0.331–0.426) and low α (0.098–0.130 (μmol photons m⁻²s⁻¹)⁻¹) in December. F _v/F _m and α increased in March and May (0.468–0.588 and 0.141–0.438 (μmol photons m⁻²s⁻¹)⁻¹, respectively) indicating increased photosynthetic activity. In addition, increases in rETR_max (3.3–16.4 a.u.) and E _k (20–88 μmol photons m⁻² s⁻¹) from December to May illustrates a higher potential for primary productivity as communities become better acclimated to under-ice light conditions. In conclusion, photosynthetic performance by ice algae (as assessed by PAM fluorometry) was tightly linked to sea ice salinity, temperature, and inorganic nutrient concentrations (mainly nitrogen).     

Sex-related differences in thermoregulatory responses while wearing protective clothing

This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m² · kg⁻¹ · 10⁻², Dubois surface area 2.01 (0.16) m², %body fatness 14.6 (3.9)%, V˙O_2peak 49.0 (4.8) ml · kg⁻¹ · min⁻¹] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m² · kg⁻¹ · 10⁻², 1.68 (0.13) m², 20.2 (4.8)%, 43.2 (6.6) ml · kg⁻¹ · min⁻¹, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h⁻¹ followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical protective clothing (0.29 m² ·°C · W⁻¹ or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i _m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min⁻¹ at 105 min (n = 13) compared with 145.1 (14.4) beats · min⁻¹ for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T _re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m⁻² for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg⁻¹] compared with M [9.45 (1.26) kJ · kg⁻¹]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg⁻¹ for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness. Accepted: 31 October 1997     

Enhanced iturin A production by <Emphasis Type="Italic">Bacillus subtilis</Emphasis> and its effect on suppression of the plant pathogen <Emphasis Type="Italic">Rhizoctonia solani</Emphasis>

The behavior of Streptomyces peucetius var. caesius N47 was studied in a glucose limited chemostat with a complex cultivation medium. The steady-state study yielded the characteristic constants μ _max over 0.10 h⁻¹, Y _XS 0.536 g g⁻¹, and m_S 0.54 mg g⁻¹ h⁻¹. The product of secondary metabolism, ɛ-rhodomycinone, was produced with characteristics Y _PX 12.99 mg g⁻¹ and m _P 1.20 mg g⁻¹ h⁻¹. Significant correlations were found for phosphate and glucose consumption with biomass and ɛ-rhodomycinone production. Metabolic flux analysis was conducted to estimate intracellular fluxes at different dilution rates. TCA, PPP, and shikimate pathway fluxes exhibited bigger values with production than with growth. Environmental perturbation experiments with temperature, airflow, and pH changes on a steady-state chemostat implied that an elevation of pH could be the most effective way to shift the cells from growing to producing, as the pH change induced the biggest transient increase to the calculated ɛ-rhodomycinone flux.     

Single-Channel Analysis of a Delayed Rectifier K+ Channel in Xenopus Myelinated Nerve

Single-channel properties of a delayed rectifier voltage-gated K⁺ channel (I-type) were investigated in peripheral myelinated axons from Xenopus laevis. Channels activated between −60 and −40 mV with a potential of half-maximal activation, E₅₀, at −47.5 mV. Averaged single-channel currents activated with a time delay at all membrane potentials tested. Time to half-maximal activation decreased from 80 to 1.6 msec between −60 and +40 mV. The channel inactivated monoexponentially with a time constant of 10.9 sec at −40 mV. The time constant of deactivation was 126 msec at −80 mV and 16.9 msec at −110 mV. In symmetrical 105 mm K⁺, the single-channel conductance (γ) was 22 and 13 pS at negative and positive membrane potentials, respectively, at 13–15°C. In Na⁺-rich solution with 2.5 mm extracellular K⁺γ was 7 pS and the reversal potential was negative to −80 mV, indicating a high selectivity for K⁺ over Na⁺. γ depended on extracellular K⁺ concentration (K _D = 19.6 mm) and temperature (Q ₁₀= 1.45). External tetraethylammonium (TEA) reduced the apparent single-channel current amplitude at all potentials tested with a half-maximal inhibiting concentration (IC₅₀) of 0.6 mm. Open probability of the channel, but not single-channel current amplitude was decreased by extracellular dendrotoxin (DTX, IC₅₀= 6.8 nm) and mast cell degranulating peptide (MCDP, IC₅₀= 41.9 nm). In Ringer solution the membrane potential of macroscopic I-channel patches was about −65 mV and depolarized under TEA and DTX. It is concluded that besides their activation during action potentials, I-channels may also stabilize the resting membrane potential. Received: 2 June 1995/Revised: 13 October 1995     

Variation of chromophoric dissolved organic matter and possible attenuation depth of ultraviolet radiation in Yunnan Plateau lakes

The increase of ultraviolet radiation (UVR, 280–400 nm) caused by stratospheric ozone depletion has profound effects on aquatic ecosystems. High-altitude lakes in the Yunnan Plateau are exposed to high intensities of UVR and contain low concentrations of chromophoric dissolved organic matter (CDOM). Thirty-eight lakes in the Yunnan Plateau with elevations from 1291 to 3809 m above sea level were investigated to study CDOM concentrations and possible effects of UVR on the lake ecosystem. The attenuation of UVR in the Yunnan Plateau lakes was calculated from the absorption coefficient of CDOM based on an empirical relationship from lakes in the Alps and Pyrenees mountains. Absorption coefficients [α(λ)] at 320 nm [α(320)] ranged from 0.52 to 14.05 m⁻¹ (mean ± standard deviation, 4.40 ± 3.85 m⁻¹) and at 380 nm [α(380)] from 0.05 to 4.51 m⁻¹ (1.40 ± 1.30 m⁻¹). The exponential slope coefficient for the relationship of wavelength to α(λ) ranged from 16.2 to 41.4 μm⁻¹ (21.74 ± 4.93 μm⁻¹) over the 280–400 nm interval. Normalized fluorescence emission (NFLU) at 450 nm from an excitation wavelength of 355 nm, F _n(355), averaged 7.93 ± 3.22 NFLU. A significant positive relationship was found between α(355) and F _n(355). The estimated diffuse attenuation coefficients of UV-B (320 nm) and UV-A (380 nm) ranged from 0.55 to 15.77 m⁻¹ and from 0.24 to 6.73 m⁻¹; the corresponding 1% attenuation depths ranged from 0.29 to 8.44 m and from 0.68 to 19.12 m. Twenty-five of 38 lakes had 1% UV-B attenuation depths of 1.5 m or more. The median 1% attenuation depth was 28.8% of the sampling depth for UV-B radiation and 60% for UV-A. In addition to CDOM, chlorophyll α (Chla) and total suspended matter (TSM) also may contribute to attenuation of UVR.     

Effects of 3 days of carbohydrate supplementation on muscle glycogen content and utilisation during a 1-h cycling performance

This study compared the effects of supplementing the normal diets of six trained cyclists [maximal oxygen uptake O_2max) 4.5 (0.36)l · min⁻¹; values are mean (SD)] with additional carbohydrate (CHO) on muscle glycogen utilisation during a 1-h cycle time-trial (TT). Using a randomised crossover design, subjects consumed either their normal diet (NORM) for 3 days, which consisted of 426 (137) g · day⁻¹ CHO [5.9 (1.4) g · kg⁻¹ body mass (BM)], or additional CHO (SUPP) to increase their intake to 661 (76) g · day⁻¹ [9.3 (0.7) g · kg⁻¹ BM]. The SUPP diet elevated muscle glycogen content from 459 (83) to 565 (62) mmol · kg⁻¹ dry weight (d.w.) (P < 0.05). However, despite the increased pre-exercise muscle glycogen stores, there was no difference in the distance cycled during the TT [40.41 (1.44) vs 40.18 (1.76) km for NORM and SUPP, respectively]. With NORM, muscle glycogen declined from 459 (83) to 175 (64) mmol · kg⁻¹ d.w., whereas with SUPP the corresponding values were 565 (62) and 292 (113) mmol · kg⁻¹ d.w. Accordingly, both muscle glycogen utilisation [277 (64) vs 273 (114) mmol · kg⁻¹ d.w.] and total CHO oxidation [169 (20) vs 165 (30) g · h⁻¹ for NORM and SUPP, respectively] were similar. Neither were there any differences in plasma glucose or lactate concentrations during the two experimental trials. Plasma glucose concentration averaged 5.5 (0.5) and 5.6 (0.6) mmol · l⁻¹, while plasma lactate concentration averaged 4.4 (1.9) and 4.4 (2.3) mmol · l⁻¹ for NORM and SUPP, respectively. The results of this study show that when well-trained subjects increase the CHO content of their diet for 3 days from 6 to 9 g · kg⁻¹ BM there is only a modest increase in muscle glycogen content. Since supplementary CHO did not improve TT performance, we conclude that additional CHO provides no benefit to performance for athletes who compete in intense, continuous events lasting 1 h. Furthermore, the substantial muscle CHO reserves observed at the termination of exercise indicate that whole-muscle glycogen depletion does not determine fatigue at this exercise intensity and duration. Accepted: 25 November 1996