Acclimation of photosynthesis to temperature in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> and <Emphasis Type="Italic">Brassica oleracea</Emphasis>

Plants differ in how much the response of net photosynthetic rate (P _N) to temperature (T) changes with the T during leaf development, and also in the biochemical basis of such changes in response. The amount of photosynthetic acclimation to T and the components of the photosynthetic system involved were compared in Arabidopsis thaliana and Brassica oleracea to determine how well A. thaliana might serve as a model organism to study the process of photosynthetic acclimation to T. Responses of single-leaf gas exchange and chlorophyll fluorescence to CO₂ concentration measured over the range of 10–35 °C for both species grown at 15, 21, and 27 °C were used to determine the T dependencies of maximum rates of carboxylation (V_Cmax), photosynthetic electron transport (J_max), triose phosphate utilization rate (TPU), and mesophyll conductance to carbon dioxide (g’_m). In A. thaliana, the optimum T of P _N at air concentrations of CO₂ was unaffected by this range of growth T, and the T dependencies of V_Cmax, J_max, and g’_m were also unaffected by growth T. There was no evidence of TPU limitation of P _N in this species over the range of measurement conditions. In contrast, the optimum T of P _N increased with growth T in B. oleracea, and the T dependencies of V_Cmax, J_max, and g’_m, as well as the T at which TPU limited P _N all varied significantly with growth T. Thus B. oleracea had much a larger capacity to acclimate photosynthetically to moderate T than did A. thaliana.     

Shape of leaf photosynthetic electron transport versus temperature response curve is not constant along canopy light gradients in temperate deciduous trees

Responses of foliar light-saturated net assimilation rate (A_max), capacity for photosynthetic electron transport (J_max) and mitochondrial respiration rate (R_d) to long-term canopy light and temperature environment were investigated in a temperate deciduous canopy composed of Populus tremula L. in the upper (17–28 m) and of Tilia cordata Mill. in the lower canopy layer (4–17 m). Climatic measurements indicated that seasonal average daily maximum air temperature (T_max) was 5·5 °C (range 0·7–10·5 °C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between T_max and seasonal average integrated quantum flux density (Q_int), as well as between seasonal average daily mean temperature and Q_int. Because of changes in leaf dry mass and nitrogen per unit area, A_max, J_max, and R_d scaled positively with Q_int in both species at a common leaf temperature (T). According to J_max versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremula with optimum temperature of J_max, T_opt, of 33·5 ± 0·6 °C than in T. cordata with T_opt of 40·7 ± 0·6 °C. This difference was suggested to manifest evolutionary adaptation of photosynthetic electron transport to cooler environments in P. tremula, the range of which extends farther north than that in T. cordata. Possibly because of acclimation to long-term canopy temperature environment, T_opt was positively related to Q_int in P. tremula, foliage of which was also exposed to higher irradiances and temperatures, but not in T. cordata, in the canopy of which quantum flux densities and temperatures were lower, and gradients in the environmental factors less pronounced. Parallel to changes in T_opt, the activation energy for photosynthetic electron transport decreased with increasing Q_int in P. tremula, indicating that J_max of leaves acclimated to colder environment was more responsive to T in lower temperatures than that of high T acclimated leaves. Similar alterations in the activation energy for mitochondrial respiration rate were also observed, indicating that acclimation to temperature of mitochondrial and chloroplastic electron transport proceeds in a co-ordinated manner, and possibly involves long-term changes in membrane fluidity properties. We conclude that, because of correlations between temperature and light, the shapes of J_max versus T, and R_d versus T response curves vary within tree canopies, and this needs to be taken account in modelling whole canopy photosynthesis.     

Temperature dependence of two parameters in a photosynthesis model

The temperature dependence of the photosynthetic parameters V_cmax, the maximum catalytic rate of the enzyme Rubisco, and J_max, the maximum electron transport rate, were examined using published datasets. An Arrehenius equation, modified to account for decreases in each parameter at high temperatures, satisfactorily described the temperature response for both parameters. There was remarkable conformity in V_cmax and J_max between all plants at T_leaf < 25 °C, when each parameter was normalized by their respective values at 25 °C (V_cmax0 and J_max0), but showed a high degree of variability between and within species at T_leaf > 30 °C. For both normalized V_cmax and J_max, the maximum fractional error introduced by assuming a common temperature response function is < ± 0·1 for most plants and < ± 0·22 for all plants when T_leaf < 25 °C. Fractional errors are typically < ± 0·45 in the temperature range 25–30 °C, but very large errors occur when a common function is used to estimate the photosynthetic parameters at temperatures > 30 °C. The ratio J_max/V_cmax varies with temperature, but analysis of the ratio at T_leaf = 25 °C using the fitted mean temperature response functions results in J_max0/V_cmax0 = 2·00 ± 0·60 (SD, n = 43).     

Photosynthetic capacity and temperature responses of photosynthesis of rubber trees (Hevea brasiliensis Müll. Arg.) acclimate to changes in ambient temperatures

The aim of this study was to assess the temperature response of photosynthesis in rubber trees (Hevea brasiliensis Müll. Arg.) to provide data for process-based growth modeling, and to test whether photosynthetic capacity and temperature response of photosynthesis acclimates to changes in ambient temperature. Net CO₂ assimilation rate (A) was measured in rubber saplings grown in a nursery or in growth chambers at 18 and 28°C. The temperature response of A was measured from 9 to 45°C and the data were fitted to an empirical model. Photosynthetic capacity (maximal carboxylation rate, V _cmax, and maximal light driven electron flux, J _max) of plants acclimated to 18 and 28°C were estimated by fitting a biochemical photosynthesis model to the CO₂ response curves (A–C _i curves) at six temperatures: 15, 22, 28, 32, 36 and 40°C. The optimal temperature for A (T _opt) was much lower in plants grown at 18°C compared to 28°C and nursery. Net CO₂ assimilation rate at optimal temperature (A _opt), V _cmax and J _max at a reference temperature of 25°C (V _cmax25 and J _max25) as well as activation energy of V _cmax and J _max (E _aV and E _aJ) decreased in individuals acclimated to 18°C. The optimal temperature for V _cmax and J _max could not be clearly defined from our response curves, as they always were above 36°C and not far from 40°C. The ratio J _max25/V _cmax25 was larger in plants acclimated to 18°C. Less nitrogen was present and photosynthetic nitrogen use efficiency (V _cmax25/N _a) was smaller in leaves acclimated to 18°C. These results indicate that rubber saplings acclimated their photosynthetic characteristics in response to growth temperature, and that higher temperatures resulted in an enhanced photosynthetic capacity in the leaves, as well as larger activation energy for photosynthesis.     

Response of Photosynthesis to Radiation and Intercellular CO2 Concentration in Sun and Shade Shoots of Norway Spruce

Functional differentiation of assimilation activity of sun versus shade foliage was analysed in a Norway spruce monoculture stand (age 15 years). The investigated stand density (leaf area index 8.6) and crown structure led to variation in the photosynthetically active photon flux density (PPFD) within the crowns of the sampled trees. At the saturating PPFD, the maximum rate of CO₂ uptake (P _Nmax) of exposed shoots (E-shoots) was 1.7 times that of the shaded shoots (S-shoots). The apparent quantum yield (α) of E-shoots was 0.9 times that of the S-shoots. A lower ability to use excess energy at high PPFD in photosynthesis was observed in the S-layer. The CO₂- and PPFD-saturated rate of CO₂ uptake (P _Nsat) of the E-shoots was 1.12 times and the carboxylation efficiency (τ) 1.6 times that of the S-shoots. The CO₂-saturated rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) carboxylation (V_Cmax) and of actual electron transport (J_amax) in the S-needles amounted to 89 and 95 % of V_Cmax and J_amax in the E-needles. Thus, in addition to the irradiation conditions and thus limitation by low J_a, the important limitation of photosynthesis in shade needles is due to carboxylation. This limitation of photosynthesis is accompanied by lower stomatal conductance. This revised version was published online in June 2006 with corrections to the Cover Date.     

METABOLIC AND ECOLOGICAL CONSTRAINTS IMPOSED BY SIMILAR RATES OF AMMONIUM AND NITRATE UPTAKE PER UNIT SURFACE AREA AT LOW SUBSTRATE CONCENTRATIONS IN MARINE PHYTOPLANKTON AND MACROALGAE1

Marine phytoplankton and macroalgae acquire important resources, such as inorganic nitrogen, from the surrounding seawater by uptake across their entire surface area. Rates of ammonium and nitrate uptake per unit surface area were remarkably similar for both marine phytoplankton and macroalgae at low external concentrations. At an external concentration of 1 μM, the mean rate of nitrogen uptake was 10±2 nmol·cm^?2·h^?1 (n=36). There was a strong negative relationship between log surface area:volume (SA:V) quotient and log nitrogen content per cm² of surface (slope=?0.77), but a positive relationship between log SA:V and log maximum specific growth rate (μ_max; slope=0.46). There was a strong negative relationship between log SA:V and log measured rate of ammonium assimilation per cm² of surface, but the slope (?0.49) was steeper than that required to sustain μ_max (?0.31). Calculated rates of ammonium assimilation required to sustain growth rates measured in natural populations were similar for both marine phytoplankton and macroalgae with an overall mean of 6.2±1.4 nmol·cm^?2·h^?1 (n=15). These values were similar to maximum rates of ammonium assimilation in phytoplankton with high SA:V, but the values for algae with low SA:V were substantially less than the maximum rate of ammonium assimilation. This suggests that the growth rates of both marine phytoplankton and macroalgae in nature are often constrained by rates of uptake and assimilation of nutrients per cm² surface area.     

The function of water channels in Chara: The temperature dependence of water and solute flows provides evidence for composite membrane transport and for a slippage of small organic solutes across water channels

Using the cell pressure probe, the effects of temperature on hydraulic conductivity (Lp; osmotic water permeability), solute permeability (permeability coefficient, P_s), and reflection coefficients (σ_s) were measured on internodes of Chara corallina, Klein ex Willd., em R.D.W.. For the first time, complete sets of transport coefficients were obtained in the range between 10 and 35 °C which provided evidence about pathways of water and solutes as they move across the plasma membrane (water channel and bilayer arrays). Test solutes used to check for the selectivity of water channels were monohydric alcohols of different molecular size and shape (ethanol, n-propanol, iso-propanol, and tert-butanol) and heavy water (HDO). Within the limits of accuracy, Q₁₀ values for Lp and for the diffusive water permeability (P_d) were identical (Q₁₀ for Lp = 1.29 ± 0.17 (± SD; n = 15 cells) and Q₁₀ for P_d = 1.25 ± 0.16 (n = 5 cells)). The Q₁₀ values were equivalent to activation energies of E_a = 16.8 ± 6.4 and 16.6 ± 10.0 kJ · mol⁻¹, respectively, which is similar to that of self-diffusion or of viscous flow of water. The Q₁₀ values and activation energies for P_s of the alcohols were significantly larger (ethanol: Q₁₀ = 1.68 ± 0.16, E_a = 37.1 ± 5.9 kJ · mol⁻¹; n-propanol: Q₁₀ =  1.75 ± 0.40, E_a = 43.1 ± 15.3 kJ · mol⁻¹; iso-propanol: Q₁₀ = 2.12 ± 0.42, E_a =  52.2 ± 14.6 kJ · mol⁻¹; tert-butanol: Q₁₀ = 2.13 ± 0.56, E_a = 51.6 ± 17.1 kJ · mol⁻¹; ±SD; n = 5 to 6 cells). Effects of temperature on reflection coefficients were most pronounced. With increasing temperature, σ_s values of the alcohols decreased and those of HDO increased. The data indicate that water and solutes use different pathways when crossing the membrane. Ordinary and isotopic water use water channels and the other test solutes use the bilayer array (composite transport model of membrane). Changes in σ_s values with temperature were found to be a sensitive measure for the open/closed state of water channels. The decrease of σ_s with temperature was theoretically predicted from the temperature dependence of P_s and Lp. Differences between predicted and measured values of σ_s allowed estimation of the bypass flow (slippage) of solutes through water channels which did not completely exclude test solutes. The permeability of channels depended on the structure and size of test solutes. It is concluded that water channels are much less selective than is usually thought. Since water channels represent single-file or no-pass pores, solutes drag along considerable amounts of water as they diffuse across channels. This results in low overall values of σ_s. The σ_s of HDO was extremely low. Its response to temperature was opposite to that for the σ_s of the alcohols. This suggested a stronger effect of temperature on the hydraulic (osmotic) than on the diffusive water flow across individual water channels, i.e. a differential sensitivity of different mechanisms to temperature. Received: 10 October 1996 / Accepted: 2 December 1996     

Temperature effect on maintenance and growth respiration coefficients of young, field-grown hinoki cypress (Chamaecyparis obtusa)

Respiration measurements were made on the entire aboveground parts of young, field-grown hinoki cypress (Chamaecyparis obtusa) trees at monthly intervals over a 5-year period, to examine the effect of temperature on maintenance and growth respiration coefficients. The respiration rate of the trees was grouped on a monthly basis and then partitioned into maintenance and growth components. The maintenance respiration coefficient increased exponentially with air temperature. The maintenance respiration coefficient at a temperature of 0°C and itsQ ₁₀ value were 0.205 mmol CO₂ g⁻¹ d.w. month⁻¹ and 1.81, respectively. The growth respiration coefficient, which was virtually independent of temperature, had a mean value of 38.06±1.95 (SE) mmol CO₂g⁻¹ d.w. The growth rate increased exponentially with increasing temperature up to a peak at around 18°C, and thereafter declined, thereby resulting in the growth respiration rate being increasingly less sensitive to increasing air temperature. The reported decreases in theQ ₁₀ value of total respiration with increasing air temperature is due to the way in which the growth component of respiration responds to temperature.     

Growth pattern of <Emphasis Type="Italic">Bidens cernua</Emphasis> L.: relationships between relative growth rate and its physiological and morphological components

Seedlings of Bidens cernua L. emerged when mean air temperature was 17.0±1.3 °C. The highest net photosynthetic rate (P _N), 13.8±0.8 μmol(CO₂) m⁻² s⁻¹, was monitored during the vegetative period (May–August), decreasing on an average by 50 % during flowering (August–September) and during fruiting (September–November) phases. The senescence phase (October–November) was characterised by 79, 58, and 18 % decrease of P _N, chlorophyll content, and leaf area (LA), respectively, from the maximum values. The time span from seedling emergence to the end of fruiting phase was 202 d. The total plant biomass was 1.58±0.05 g of which 81 % was aboveground plant portion. The total dry mass relative growth rate averaged over the assimilation period was 0.0804±0.0002 kg kg⁻¹ d⁻¹, and it was correlated to both the net assimilation rate (NAR) and the leaf area ratio (LAR).     

The response of photosynthetic model parameters to temperature and nitrogen concentration in Pinus radiata D. Don

Responses of photosynthesis (A) to intercellular CO₂ concentration (c_i) in 2-year-old Pinus radiata D. Don seedlings were measured at a range of temperatures in order to parametrize a biophysical model of leaf photosynthesis. Increasing leaf temperature from 8 to 30°C caused a 4-fold increase in V_cmax, the maximum rate of carboxylation (10.7–43.3 μol m^?2 s^?1 and a 3-fold increase in J_max, the maximum electron transport rate (20.5–60.2 μmol m ^?2 s^?1). The temperature optimum for J_max was lower than that for V_cmax, causing a decline in the ratio J_max:V_cmax from 2.0 to 1.4 as leaf temperature increased from 8 to 30°C. To determine the response of photosynthesis to leaf nitrogen concentration, additional measurements were made on seedlings grown under four nitrogen treatments. Foliar N concentrations varied between 0.36 and 1.27 mol kg^?1, and there were linear relationships between N concentration and both V_cmax and J_max. Measurements made throughout the crown of a plantation forest tree, where foliar N concentrations varied from 0.83 mol kg^?1 near the base to 1.54 mol kg^?1 near the leader, yielded similar relationships. These results will be useful in scaling carbon assimilation models from leaves to canopies.     

Effects of Temperature and Body Size on the Swimming Speed of Larval and Juvenile Atlantic Cod (Gadus Morhua): Implications for Individual-based Modelling

Synopsis The routine swimming speed (S) of three groups of 4, 9 and 32 cm total length (L_T) juvenile cod (Gadus morhua) was quantified in the laboratory at 6 – 10 different temperatures (T) between 3.2 and 16.7°C. At temperatures between 5 and 15°C, mean group S increased exponentially with increasing T (S=a e^bT) and the effect of temperature (b = 0.082, Q₁₀ = 2.27) was not significantly different among the groups (over the 8-fold difference in fish sizes of early- and post-settlement juveniles). Differences in mean S among individuals within each group were quite large (coefficient of variation = 40 – 80%). Swimming data for juveniles and those collected for groups of 0.4, 0.7 and 0.9 cm standard length (L_S) larvae were combined to assess the effect of body size on S. At 8°C, S (mm s⁻¹) increased with L_S (mm) according to: S = 0.26L_S^Φ−5.28L_S⁻¹, where Φ = 1.55L_S^−0.08. Relative S (body lengths s⁻¹) was related to L_S by a dome-shaped relationship having a maximum value (0.49 body lengths s⁻¹) at 18.5 – 19 mm L_S corresponding to the sizes of fish at the end of larval-juvenile metamorphosis. Previous larval cod IBM’s using a cruise-predator mode likely overestimated rates of foraging (prey searching and encounters) by a factor of ~2, whereas foraging rates in pause-travel models are closer to estimates of swimming velocities obtained in this and other laboratory studies.     

Membrane permeability of formate in human erythrocytes: NMR measurements

The rate of the rapid exchange of formate mediated by band 3 in human erythrocytes, under equilibrium exchange conditions, was measured by using a T ₁ relaxation method with ¹³C-labelled formate and ¹³C NMR, and a pulsed field-gradient spin-echo (PFGSE) method using ¹H NMR. The former analysis was based on large differences in T ₁ between the inside and the outside of the cells brought about by added Mn²⁺; the latter was based on large differences in the apparent diffusion coefficient inside and outside the cells. There was close agreement in the estimates of the membrane permeabilities made using both methods, suggesting a lack of interference of the exchange process by Mn²⁺. Regression analysis yielded estimates (under the specified conditions, including 37°C) of V _max of 3.5±0.3×10^–9 and 3.8±0.4×10^–9 mol cm^–2 s^–1, and K _m of 9.8±0.2 and 8.1±0.2 mM, for the T ₁ and the PFGSE methods, respectively. These are new estimates made using methodology that has not previously been applied to measuring rapid (sub-second time scale) formate exchange in cells. Received: 8 May 1998 / Accepted: 16 July 1998     

Optimization of dilution rate for the production of value added product and simultaneous reduction of organic load from pineapple cannery waste

Candida utiilis NRRL Y-900 was grown on pineapple cannery waste as the sole carbon and energy source in a chemostat at dilution rates ranging between 0.05 and 0.65 h⁻¹ to determine the growth kinetics. The cell yield coefficient varied with dilution rate and a maximum value of 0.662 ± 0.002 g_x/g_carb was obtained at a dilution rate of 0.4 h⁻¹. At steady state, the concentrations of carbohydrate, reducing sugar, and chemical oxygen demand (COD) appeared to follow Monod kinetics. At maximum specific growth rate (μ_max) 0.65 h⁻¹, the saturation constants for carbohydrate, reducing sugar and COD were 0.51 ± 0.02 g_carb/1, 0.046 ± 0.003 g_rs/1, and 1.036 ± 0.001 g_COD/1, respectively. Maximum biomass productivity (Q _{x max}) 2.8 ± 0.03 g_x/1 h was obtained at a dilution rate of 0.5 h⁻¹. At this dilution rate, only 71.0 ± 0.41% COD was removed whereas at a dilution rate of 0.1 h⁻¹, 98.2 ± 0.35% reduction in COD was achieved. At a dilution rate of 0.4 h⁻¹, the optimal yeast productivity and reduction in COD were 2.7 ± 0.13 g_p/1 h, and 84.2 ± 0.42%, respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Age,growth, maturity and extinction risk of an exploited and endangered skate,Atlantoraja castelnaui,from off Uruguay and northern Argentina

The spotback skate Atlantoraja castelnaui (Arhynchobatidae) is a large and threatened skate species subjected to fishing pressure, endemic to the Southwest Atlantic that occurs from Rio de Janeiro, Brazil, to San Jorge Gulf, Argentina. The age, growth, age at maturity and the maximum intrinsic rate of population increase r_max of A. castelnaui were studied using 152 specimens collected from off Uruguay and north Argentina (35°–42° S), between June 2013 and February 2020. Vertebrae from 143 individuals were used for ageing (females: n = 83, size range 404–1300 mm total length, TL; males: n = 60, size range 400–1270 mm TL). Maximum ages determined for females and males were 30 and 28 years, respectively. To fit growth models, non-linear and Bayesian estimation approaches were considered. For the first approach, a set of four candidate growth (size-at-age) models were fitted: three-parameter von Bertalanffy, two-parameter von Bertalanffy with fixed L₀, Gompertz and Logistic. In the second approach, von Bertalanffy, Gompertz and Logistic were fitted. For non-linear estimation, model selection indicated that the entire set of candidate growth models were supported by the data. The von Bertalanffy was selected as the best model for Bayesian estimation. There were no differences in growth between sexes. For the sexes combined, the von Bertalanffy growth model by Bayesian method was considered the most adequate to describe the growth of A. castelnaui (growth mean parameters ± S.D. : L_∞ = 1210.29 ± 40.68 mm; k = 0.12 ± 0.01 years⁻¹; L₀ = 179.20 ± 11.62 mm). The age at maturity was estimated at 16.21 and 14.04 years for females and males, respectively. The maximum intrinsic rate of population increase r_max was estimated as 0.252 years⁻¹. Life-history traits and r_max provided in the present study suggest that this species has a relatively low productivity and may be vulnerable to an intense fishing pressure.     

Maximum sustainable speed, energetics and swimming kinematics of a tropical carangid fish, the green jack Caranx caballus

Maximum sustained swimming speeds, swimming energetics and swimming kinematics were measured in the green jack Caranx caballus (Teleostei: Carangidae) using a 41 l temperature‐controlled, Brett‐type swimming‐tunnel respirometer. In individual C. caballus [mean ±s.d. of 22·1 ± 2·2 cm fork length (L_F), 190 ± 61 g, n = 11] at 27·2 ± 0·7° C, mean critical speed (U_crit) was 102·5 ± 13·7 cm s^?1 or 4·6 ± 0·9 L_F s^?1. The maximum speed that was maintained for a 30 min period while swimming steadily using the slow, oxidative locomotor muscle (U_max,c) was 99·4 ± 14·4 cm s^?1 or 4·5 ± 0·9 L_F s^?1. Oxygen consumption rate (M in mg O₂ min^?1) increased with swimming speed and with fish mass, but mass‐specific M (mg O₂ kg^?1 h^?1) as a function of relative speed (L_F s^?1) did not vary significantly with fish size. Mean standard metabolic rate (R_S) was 170 ± 38 mg O₂ kg^?1 h^?1, and the mean ratio of M at U_max,c to R_S, an estimate of factorial aerobic scope, was 3·6 ± 1·0. The optimal speed (U_opt), at which the gross cost of transport was a minimum of 2·14 J kg^?1 m^?1, was 3·8 L_F s^?1. In a subset of the fish studied (19·7–22·7 cm L_F, 106–164 g, n = 5), the swimming kinematic variables of tailbeat frequency, yaw and stride length all increased significantly with swimming speed but not fish size, whereas tailbeat amplitude varied significantly with speed, fish mass and L_F. The mean propulsive wavelength was 86·7 ± 5·6 %L_F or 73·7 ± 5·2 %L_T. Mean ±s.d . yaw and tailbeat amplitude values, calculated from lateral displacement of each intervertebral joint during a complete tailbeat cycle in three C. caballus (19·7, 21·6 and 22·7 cm L_F; 23·4, 25·3 and 26·4 cm L_T), were 4·6 ± 0·1 and 17·1 ± 2·2 %L_T, respectively. Overall, the sustained swimming performance, energetics, kinematics, lateral displacement and intervertebral bending angles measured in C. caballus were similar to those of other active ectothermic fishes that have been studied, and C. caballus was more similar to the chub mackerel Scomber japonicus than to the kawakawa tuna Euthynnus affinis.     

Acclimation of photosynthesis to temperature in eight cool and warm climate herbaceous C3 species: Temperature dependence of parameters of a biochemical photosynthesis model

To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 °C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 – 35 °C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (C_i), A at high C_i, and stomatal conductance. The first two measurements allow calculation of V_Cmax, the maximum rate of carboxylation of ribulose bisphosphate carboxylase and J_max, the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 – 35 °C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 ×) than in the cool climate species (2.5 ×). The initial slope of A vs. C_i exhibited an optimum temperature which ranged from 20 to 30 °C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high C_i ranged from 25 to 30 °C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. C_i and A at high C_i were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of J_max — V_Cmax normalized to 20 °C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of J_max and V_Cmax than to the ratio of their normalized values.This revised version was published online in October 2005 with corrections to the Cover Date.     

Ethidium bromide binding to native and denatured poly(dA)poly(dT)

Isotherms of the EtBr adsorption on native and denatured poly(dA)poly(dT) in the temperature interval 20–70°C were obtained. The EtBr binding constants and the number of binding sites were determined. The thermodynamic parameters of the EtBr intercalation complex upon changes of solution temperature 20–48°C were calculated: 1.0·10⁶ M⁻¹≤K≤1.4·10⁶ M⁻¹, free energy ΔG ^o=−8.7±0.3 kcal/mol, enthalpy ΔH ^o≅0, and entropy ΔS ^o=28±0.5 cal/(mol deg). UV melting has shown that the melting temperature (T _m) of EtBr-poly(dA)poly(dT) complexes (μ=0.022,4.16·10⁻⁵ M EtBr) increased by 17°C as compared with the ΔT _m of free homopolymer, whereas the half-width of the transition (T _m) is not changed. It was shown for the first time that EtBr forms complexes of two types on single-stranded regions of poly(dA)poly(dT) denatured at 70°C: strong (K ₁=1.7·10⁵ M⁻¹; ΔG ^o=−8.10±0.03 kcal/mol) and weak (K ₂=2.9·10³ M⁻¹; ΔG ^o=−6.0±0.3 kcal/mol).The ΔG ^o of the strong and weak complexes was independent of the solution ionic strength, 0.0022≤μ≤0.022. A model of EtBr binding with single-stranded regions of poly(dA)poly(dT) is discussed.     

Upper thermal limits of cardiac function for Arctic cod Boreogadus saida,a key food web fish species in the Arctic Ocean

The objective of this study was to determine the upper thermal limits of Arctic cod Boreogadus saida by measuring the response of maximum heart rate (f_Hmax) to acute warming. One set of fish were tested in a field laboratory in Cambridge Bay (CB), Nunavut (north of the Arctic Circle), and a second set were tested after air transport to and 6 month temperature acclimation at the Vancouver Aquarium (VA) laboratory. In both sets of tests, with B. saida acclimated to 0° C, f_Hmax increased during acute warming up to temperatures considerably higher than the acclimation temperature and the near‐freezing Arctic temperatures in which they are routinely found. Indeed, f_Hmax increased steadily between 0·5 and 5·5° C, with no significant difference between the CB and VA tests (P > 0·05) and with an overall mean ± s.e. Q₁₀ of 2·4 ± 0·5. The first Arrhenius breakpoint temperature (T_AB) for f_Hmax was also statistically indistinguishable for the two sets of tests (mean ± s.e. 3·2 ± 0·3 and 3·6 ± 0·3° C), suggesting that the temperature optimum for B. saida could be reliably measured after live transport to a more southerly laboratory location. Continued warming above 5·5° C revealed a large variability among individuals in the upper thermal limits that triggered cardiac arrhythmia (T_arr), ranging from 10·2 to 15·2° C with mean ± s.e. 12·4 ± 0·4° C (n = 11) for the field study. A difference did exist between the CB and VA breakpoint temperatures when the Q₁₀ value decreased below 2 (the Q₁₀ breakpoint temperature; T_QB) at 8·0 and 5·5° C, respectively. These results suggest that factors, other than thermal tolerance and associated cardiac performance, may influence the realized distribution of B. saida within the Arctic Circle.     

Light acclimation at the end of the growing season in two broadleaved oak species

The ability of plants to increase their net CO₂ assimilation rate in response to increased irradiance is due to morphological and physiological changes, which might be related to their shade tolerance and leaf ontogeny, but few studies have considered morphology and physiology. Two sympatric oak species (the shade-tolerant Q. petraea and the comparatively shade-intolerant Q. pyrenaica) were grown in hydroponic solution in low-light (LL) and high-light (HL) conditions. 5 months after leaf expansion under these conditions, half of the LL plants were transferred to high light (TLH). Transfer of Q. pyrenaica, from low- to high light led to photoinhibition and after 21 days in higher light there was little acclimation of the maximum rate of carboxylation (V_Cmax) or the maximum rate of electron transport (J_max). Q. pyrenaica TLH plants showed lower stomatal conductance at all times compared to plants growing in LL. Stomatal closure was the main limitation to photosynthesis after transfer in Q. pyrenaica. The increase in evaporative demand upon TLH did not affect hydraulic conductivity of Q. pyrenaica. In contrast, the more shade-tolerant Q. petraea showed a greater degree of acclimation of gas exchange in TLH than Q. pyrenaica and two weeks after transfer gas-exchange rates were as high as in LL plants. In Q. petraea, the most important changes occurred at the level of leaf biochemistry with significant increase in V_Cmax that decreased the J_max/V_Cmax ratio below values recorded in HL plants. However, this potential increase in photosynthesis was at least partially hamstrung by a decrease in internal conductance, which highlights the importance of internal conductance in acclimation to higher light in mature leaves. Neither oak species reached the photosynthetic rates of HL plants; however a trend towards leaf acclimation was observed in Q. petraea while the transfer was harmful to the leaves of Q. pyrenaica developed in the shade.     

Temperature response of parameters of a biochemically based model of photosynthesis. I. Seasonal changes in mature maritime pine (Pinus pinaster Ait.)

Responses of plant processes to temperature may vary according to the time scale on which they are measured. In this study, both short‐term and seasonal responses of photosynthesis to temperature were examined. A field study of seasonal changes in the temperature response of photosynthesis was conducted on two provenances, French and Moroccan, of mature maritime pine (Pinus pinaster Ait.). Measurements were made every 2 months over a 1‐year period and used to parameterize a mechanistic model of photosynthesis. Temperature responses of maximum Rubisco activity, V_cmax, and potential electron transport rate, J_max, were obtained for each measurement period, as was the response of stomatal conductance, g_s, to water vapour pressure deficit (VPD). Absolute values of V_cmax and J_max at 25 °C were related to needle nitrogen content, N_area.N_area, and thus V_cmax and J_max, were negatively correlated with the mean minimum temperature in the month preceding measurements. The ratio of J_max : V_cmax at 25 °C varied between 1 and 1·7 but did not show any seasonal trend. Nor was there any seasonal trend in the relative temperature response of V_cmax, which had an activation energy H_a of approximately 57 kJ mol^?1 throughout the experiment. The activation energy of J_max was also close to constant throughout the experiment, averaging 39 kJ mol^?1. For the French provenance, the optimal temperature of J_max was positively correlated with the maximum temperature of the previous day, but no such correlation was found for the Moroccan provenance. The response of g_s to VPD also varied seasonally, with much stronger stomatal closure in winter months. Taken together, these results implied a translational shift downwards of the photosynthetic temperature response curve with increasing T_prev, and a shift in the temperature optimum of photosynthesis of 5–10 °C between summer and winter. These results illustrate that the short‐term temperature response of photosynthesis varies significantly on a seasonal basis.