Balancing carboxylation and regeneration of ribulose-1,5- bisphosphate in leaf photosynthesis: temperature acclimation of an evergreen tree, Quercus myrsinaefolia

Changes in the temperature dependence of the photosynthetic rate depending on growth temperature were investigated for a temperate evergreen tree, Quercus myrsinaefolia . Plants were grown at 250 μ mol quanta m^–2 s^–1 under two temperature conditions, 15 and 30 °C. The optimal temperature that maximizes the light-saturated rate of photosynthesis at 350 μ L L^–1 CO₂ was found to be 20–25 and 30–35 °C for leaves grown at 15 and 30 °C, respectively. We focused on two processes, carboxylation and regeneration of ribulose-1,5-bisphosphate (RuBP), which potentially limit photosynthetic rates. Because the former process is known to limit photosynthesis at lower CO₂ concentrations while the latter limits it at higher CO₂ concentrations, we determined the temperature dependence of the photosynthetic rate at 200 and 1000 μ L L^–1 CO₂ under saturated light. It was revealed that the temperature dependence of both processes varied depending on the growth temperature. Using a biochemical model, we estimated the capacity of the two processes at various temperatures under ambient CO₂ concentration. It was suggested that, in leaves grown at low temperature (15 °C), the photosynthetic rate was limited solely by RuBP carboxylation under any temperature. On the other hand, it was suggested that, in leaves grown at high temperature (30 °C), the photosynthetic rate was limited by RuBP regeneration below 22 °C, but limited by RuBP carboxylation above 22 °C. We concluded that: (1) the changes in the temperature dependence of carboxylation and regeneration of RuBP and (2) the changes in the balance of these two processes altered the temperature dependence of the photosynthetic rate.     

Chilling-induced potassium leakage of cultured citrus cells

Callus of 'Marsh' grapefruit ( Citrus paradisi Macf.) albedo tissue was used to investigate the effect of preconditioning temperature on the rate of chilling - stimulated K⁺ leakage. Callus grew most rapidly at 30°C and attained a weight of about 1 g after 30 days. The rate of K.⁺ leakage from nonchilled callus tissue decreased as temperature decreased from 20 to 7.5°C, but no measurable change in rate was observed between 7.5 and 0°C. When calli were held for 40 days at 0¹ 2.5 or 5°C, K⁺ leakage increased 200%, 60% or 0%) respectively. Holding callus for 5 days at 10 or 15°C prior to chilling for 40 days at 0°C prevented the increase in K⁺ leakage observed in callus receiving no preconditioning treatment. Preconditioning at 7.5 and 20°C was less effective in reducing chilling - induced leakage. Preconditioning at 10°C for 5, 2 or 1 day reduced chilling – induced leakage after 40 days at 0°C by 50%, 33% and 15%. respectively.     

Kinetic changes with temperature of phosphoenolpyruvate carboxylase from a CAM plant

Abstract. Purified and crude phosphoenolpyruvate carboxylase from the CAM plant Kalanchoë daigremontiana Hamet et Perrier ( Bryophyllum diagremontianum ) was assayed at temperatures between 10 and 45° C. The optimum temperature of the enzyme activity changed with substrate availability and effector concentration in the assay. l -malate inhibited the enzyme activity and lowered the optimum temperature. Glucose-6-phosphate raised the optimum temperature to 43°C. K _m values for phosphoenolpyruvate increased with assay temperature from 0.12 mol m^-3 at 15° C to 0.36 mol^m−3 at 35° C. Inhibition by malate increased with temperature and acidity of the assay. In the crude enzyme 50% of control activity was inhibited by 1.65 mol m^-3 malate at 15° C and by 0.5 mol m^-3 at 35° C (at pH 7.0). With purification malate sensitivity was lost ( K _i values for malate at least 10 times higher). The shift in optimum temperatures for PEP-carboxylase activity thus results from changes in the kinetic parameters with temperature and allosteric effectors. The often low optimum temperatures for CO₂ fixation observed in nature may thus be the result of substrate and effector concentrations in the cytoplasm and the antagonistic effect of temperature on substrate affinity and effector efficiency on phosphoenolpyruvate carboxylase.     

C4 photosynthesis in Cyperus longus L., a species occurring in temperate climates

Abstract. Cyperus longus L. , which has a widespread but disjunct distribution throughout Europe and extends northwards into Britain, was found to be a C₄ species based upon its Kranz leaf anatomy, low CO₂ compensation point and the labelling of malate as an early product of ¹⁴CO₂ fixation. The photosynthetic characteristics of C. longus are similar to many other C₄ species with a high maximum rate of photosynthesis (> 1.5 mg CO₂ m ⁻² s ⁻¹) and a relatively high temperature optimum (30–35°C), but unlike many C₄ species the rate of photosynthesis does not decline rapidly below the optimum temperature and a substantial rate (0.6 mgCO₂ m⁻²s⁻¹)occursat 15°C. Leaf extension is very slow at 15°C and shows a curvilinear response to temperatures between 15 and 25°C. Leaves extend at a rate of almost 4 cm d⁻¹ at 25°C.     

The interaction of temperature and fish size on growth of juvenile halibut

Growth rate of individually tagged juvenile halibut was influenced significantly by the interaction of temperature and fish size. The results suggest an optimum temperature for growth of juvenile halibut in the size range 5–70 g between 12 and 15° C. Overall growth rate was highest at 13° C (1·62% day ⁻¹). At c. 5 g at the beginning of the experiment, fish at 16° C had the highest growth rate (3·2% day ⁻¹), but reduced this rate as they grew bigger. At 9 and 11°p C, growth rates were equal or only slightly lower during the later stages of the experiment, while the fish at 6° C showed significantly lower overall growth rate (0·87% day⁻¹). Optimal temperature for growth decreased rapidly with increasing size, indicating an ontogenetic reduction in optimum temperature for growth. Moreover, a more flattened parabolic regression curve between growth and temperature as size increased indicated reduced temperature dependence with size. Although individual growth rates varied significantly at all times within the experimental temperatures, significant size rank correlations were maintained during the experiment. This indicated an early establishment of a stable size hierarchy within the fish groups. Haematocrit was highest at the highest temperature while Na⁺/K⁺-ATPase activity was inversely related to temperature. There was no difference in plasma Na⁺, Cl⁻ and K⁺ concentrations among the temperature groups.     

Effects of Temperature and Leaf Weness on the Latent Period of Rbynchosporium Secalis (Leaf Blotch) on Leaves of Winter Barley

Effects of temperature and leaf wetness on the latent period of Rhynchosporium secaits (leaf blotch) on winter barley were examined in controlled environment experiments. At 100% relative humidity (continuous leaf wetness) the mean length of the latent period was c.24 days at 5°C, c. 19 days at 10°C, c. 16 days at l5°C and c. 13 days at 20°C. The mean number of days between the appearance of the first and the last lesions was c. 13 days at 5°C, c. 6 days at 10°C, c. 5 days at 15°C and c. 3 days at 20°C. A negative curvilinear regression of latent period on temperature accounted for 99% of the variance. The mean area of lesions per leaf was 38 mm² at 5°C, 46 mm² at 10°C, 24 mm² at 15°C and 24 mm² at 20°C. At 10°C, after a 48 h wet infection period, the interruption of leaf wetness for 5 or more days at any time during the next 15 days of the latent period did not decrease subsequent lesion area. However, absence of leaf wetness after these 15 days, at the onset of sporuiation, did decrease the area of lesions which developed.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Reappraisal of the effect of temperature on the growth kinetics of Aeromonas salmonicida

The effect of temperature (1–34 °C ) on the maximum specific growth rate of Aeromonas salmonicida could not be described by the classical growth models ; for some strains, two optimal temperatures at 23 °C and 30 °C were observed, as well as an unexpected increase in the pseudolag time above 27 °C. This could be explained by the presence of two subsets, notably S-layer⁺ and S-layer⁻ sub-populations. The A⁻ cells had higher growth parameters (T_opt and μ_opt) than the A⁺ cells and were selected by subcultures above 30 °C. Yet the relative proportion of A⁺ cells did not explain all the variation of μ_max versus temperature, and the growth kinetics of an Aer. salmonicida isolate remained unpredictable.     

Cations Affect [3H]Mazindol and [3H]WIN 35,428 Binding to the Human Dopamine Transporter in a Similar Fashion

Abstract: The present study addresses the possibility that there are different cocaine-related and mazindol-related binding domains on the dopamine transporter (DAT) that show differential sensitivity to cations. The effects of Zn²⁺, Mg²⁺, Hg²⁺, Li⁺, K⁺, and Na⁺ were assessed on the binding of [³H]mazindol and [³H]WIN 35,428 to the human (h) DAT expressed in C6 glioma cells under identical conditions for intact cell and membrane assays. The latter were performed at both 0 and 21°C. Zn²⁺ (30–100 µ M ) stimulated binding of both radioligands to membranes, with a relatively smaller effect for [³H]mazindol; Mg²⁺ (0.1–100 µ M ) had no effect; Hg²⁺ at ∼3 µ M stimulated binding to membranes, with a relatively smaller effect for [³H]mazindol than [³H]WIN 35,428 at 0°C, and at 30–100 µ M inhibited both intact cell and membrane binding; Li⁺ and K⁺ substitution (30–100 m M ) inhibited binding to membranes more severely than to intact cells; and Na⁺ substitution was strongly stimulatory. With only a few exceptions, the patterns of ion effects were remarkably similar for both radioligands at both 0 and 21°C, suggesting the involvement of common binding domains on the hDAT impacted similarly by cations. Therefore, if there are different binding domains for WIN 35,428 and mazindol, these are not affected differentially by the cations studied in the present experiments, except for the stimulatory effect of Zn²⁺ at 0 and 21°C and Hg²⁺ at 0°C.     

Effect of temperature on swimming performance of sea bass juveniles

At four temperatures ( T= 15, 20, 25 and 28° C) swimming performance of Dicentrarchus labrax was significantly correlated with total length (23–43 mm L _T); r²=0.623–0.829). The relative critical swimming speed ( RU _crit= U _crit L _T⁻¹), where U _crit is the critical swimming speed, was constant throughout the L _T range studied. The significant effect of temperature on the relative critical swimming speed was described binomially: RU _crit=−0.0323T²+ 1.578 T −10.588 (r²=1). The estimated maximum RU _crit (8.69 L _T s⁻¹) was achieved at 24.4° C, and the 90% performance level was estimated between 19.3 and 29.6° C.     

Photosynthetic response of Eragrostis tef to temperature

Photosynthetic characteristics of leaves of tef, Eragrostis tef (Zucc.) Trotter, plants, grown at 25/15°C (day/night), were measured at temperatures from 18 to 48°C. The highest carbon exchange rates (CER) occurred between 36 and 42°C. and averaged 27 μmol m⁻² s⁻¹. At lower or higher temperatures, CER was reduced, but the availability of CO₂ to the mesophyll, measured as internal CO₂ concentration, was highest when temperatures were above or below the optimum for CER. In addition, CER and stomatal conductance were not correlated, but residual conductance was highly correlated with CER (r = 0.98). In additional experiments, relative ¹³C composition for leaf tissue grown at 25, 35 and 45°C averaged -14.4 per mille, confirming that tef is a C₄ grass species. Dry matter accumulation was higher at 35 than at 25, and lowest at 45°C. Leaf CER rates increased hyperbolically with increased light when measured from 0 to 2000 μmol m⁻² s⁻¹ PPFD. The highest CER, 31.8 μ-mol m_-2 s⁻¹, occurred at 35°C and 2000 μmol m⁻² s⁻¹ PPFR. At high light, CER at 25 and 35°C were nearly equal because of higher stomatal conductance at 25°C. Residual conductance was, however, clearly highest at 35°C compared to 25 and 45°C treatments. Stomatal conductance and residual conductance were not correlated in either set of experiments, yet residual conductance was always highest when temperatures were between 35 and 42°C across experiments, suggesting that internal leaf photosynthetic potential was highest across that temperature range.     

Sensitivity of Bacillus coagulans spores to combinations of high hydrostatic pressure, heat, acidity and nisin

We investigated the combined effects of pressure, temperature, pH, initial spore concentration and the presence of nisin on the survival of spores of Bacillus coagulans. Spores were more sensitive to pressure both at lower pH and at higher treatment temperatures. An additional 1.5-log₁₀ reduction in cfu ml^-1 was observed when pH was lowered from 7.0 to 4.0 during pressurization at 400 Mpa and 45°C. A 4-log₁₀ cfu ml^-1 reduction was observed when the temperature was increased from 25°C to 70°C during pressurization at 400 Mpa. The spores were sensitive to nisin at concentrations as low as 0.2 IU ml^-1. At least a 6-log₁₀ reduction was generally achieved with pressurization at 400 Mpa in pH 4.0 buffer at 70°C for 30 min when plated in nutrient agar containing 0.8 IU ml^-1 nisin.     

Hypometabolism in torpid goldsinny wrasse subjected to rapid reductions in seawater temperature

Goldsinny Ctenolabrus rupestris were subjected to rapid, environmentally realistic, reductions in temperature at 2° C increments from 10 to 4° C over a 3-day period in full-strength sea water. In separate experiments, oxygen uptake measurements and ultrasound recordings of heart rate and opercular motion were carried out at regular intervals over the same temperature regime. Mean oxygen uptake rates fell from 0.042 to 0.028 ml O₂ g⁻¹ h⁻¹ between 10 and 6° C respectively (Q₁₀=2.71). Between 6 and 4° C mean rates decreased from 0.028 to 0.008 ml O₂ g⁻¹ h⁻¹ (Q₁₀=542). Mean opercular motion and heart beat rates decreased from 49.5 and 60.3 beats min⁻¹ respectively at 10° C to 18.7 and 18.0 beats min⁻¹ respectively at 4° C. Most goldsinny subjected to 4° C were observed in a torpid state and would not react to external stimulation. Opercular motion was erratic at 4° C and would at times cease altogether for periods up to 1.3 min duration. Heart movement was diffcult to detect at 4° C and may also have ceased for prolonged periods. Q₁₀ values for opercular motion and heart beat rates recorded between 6 and 4° C were 6.39 and 24.52 respectively compared with values of 2.42 and 2.93 respectively recorded between 10 and 8° C. Such large depressions in metabolism appear not to have been reported previously for a marine fish species. No goldsinny mortalities were recorded at any temperature. The possibility that hypometabolic torpor is an adaptive strategy for goldsinny survival at low environmental temperatures is discussed.     

Behaviour of Staphylococcus aureus strains, producers of enterotoxins C1 or C2, during the manufacture and storage of Burgos cheese

Burgos cheese was manufactured from pasteurized ewes milk inoculated with Staphylococcus aureus strains FRI 137 and FRI 361, at levels of ca 10³ and 10⁵ cfu/ml and stored at 4°, 10° and 15°C and at room temperature (10°-15°C). Populations of Staph. aureus and mesophilic aerobes, pH, and production of thermonuclease and enterotoxins C₁ and C₂ were investigated. Aerobic counts increased during cheese-making and storage. With both test strains, important growth was observed only during the storage period, the larger levels corresponding to the higher temperatures. Although Staph. aureus strains attained populations of over 10⁸ cfu/g, no enterotoxin was detected. Strain FRI 361 reached 10⁷ cfu/g without production of a detectable amount of thermonuclease. With strain FRI 137, the minimal population associated with enzyme activity was influenced by the inoculum size. Staphylococcus aureus counts are better indicators of staphylococcal growth in Burgos cheese than the thermonuclease test.     

Effects of temperature, hypoxia and activity on the metabolism of juvenile Atlantic cod

Standard metabolic rate (SMR), active metabolic rate (AMR) and critical oxygen saturation ( S_crit ) were measured in Atlantic cod Gadus morhua at 5, 10 and 15° C. The SMR was 35.5, 57.0 and 78.2 mg O₂ kg⁻¹ h⁻¹ and S_crit was 16.5, 23.2 and 30.3%, at 5, 10 and 15° C, respectively. Previously reported SMR for Atlantic cod from arctic waters at 4° C was twice that measured at 5° C in the present study. A possible intraspecific latitudinal difference in the SMR is discussed. The AMR was 146.6, 197.9 and 200.4 mg O₂ kg⁻¹ h⁻¹ and the critical swimming speed ( U_crit ) was 1 6, 1.7 and 1.9 at 5, 10 and 15° C, respectively. The maximum oxygen consumption was found to be associated with exercise, rather than recovery from exercise as previously reported in another Study of Cod metabolism.     

Seasonal changes in vertical distribution, biomass and faecal production of tubificids in the profundal region of a shallow Japanese lake

Two tubificid species Limnodrilus hoffmeisteri and L. claparedeianus formed more than 93% of the total number of oligochaetes in the profundal. Limnodrilus spp. worms were found down to 33 cm in the sediment but in great numbers in the upper zone in June and October. Worms confined to the top 15 cm of sediment accounted for 53-92% of the total number. There were two annual maxima in population density and biomass, one in late spring (66000 inds m⁻², 17 g wet wt m⁻²) and the other in mid autumn (97000 inds m⁻², 176 g wet wt m⁻²). Two regression lines describing the effect of temperature on faecal production rate were obtained; Log F = 0.0604 T (°C) −0.7660 (below 15°C), Log F = 0.0266 T – 0.2170 (above 15°C). In total 26.8 kg dry wt m⁻² of sediment was defecated annually by Limnodrilus spp. The sediment in the 0–10 cm stratum may pass through the guts of the worms 2.3 times a year. Sedimentation rates in profundal region were very low with respect to the faecal production rates of the tubificids.     

Stimulation of biomethanation by Clostridium sp. PXYL1 in coculture with a Methanosarcina strain PMET1 at psychrophilic temperatures

Aim:  Bioaugumentation of low temperature biogas production was attempted by addition of cold-adapted Clostridium and a methanogen.
Methods and Results:  A psychrotrophic xylanolytic acetogenic strain Clostridium sp. PXYL1 growing optimally at 20°C and pH 5·3 and a Methanosarcina strain, PMET1, growing optimally on acetate and producing methane at 15°C were isolated from a cattle manure digester. Anaerobic conversion of xylose at 15°C with the coculture of the two strains was performed, and batch culture methane production characteristics indicated that methanogenesis occurred via acetate through 'acetoclastic' pathway. Stimulation studies were also undertaken to evaluate the effect of exogenous addition of the coculture on biogas yields at 15°C. Addition of 3 ml of PXYL1 at the rate of 12 × 10² CFU ml⁻¹ increased the biogas 1·7-fold (33 l per kg cowdung) when compared to control (19·3 l per kg cowdung) as well as increased the volatile fatty acid (VFA) levels to 3210 mg l⁻¹ when compared to 1140 mg l⁻¹ in controls. Exogenous of addition of 10 ml PMET1 inoculum at the rate of 6·8 ± 10² CFU ml⁻¹ in addition to PXYL1 served to further improve the biogas yields to 46 l kg⁻¹ as well as significantly brought down the VFA levels to 1350 mg l⁻¹.
Conclusions:  Our results suggest that the rate-limiting methanogenic step at low temperatures could be overcome and that biogas yields improved by manipulating the population of the acetoclastic methanogens.
Significance and Impact of the Study:  Stimulation of biomethanation at low temperature by coculture.     

Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures

Abstract. Germination responses of redroot pigweed ( Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log-linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm³ m⁻³ were observed after 32 d, compared to 0.18−1.6 cm³ m⁻³ after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose-response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.     

Growth rate and physiology of Yersinia enterocolitica; influence of temperature and presence of the virulence plasmid

The effect of temperature on the growth rate, protein pattern and fatty acid composition of Yersinia enterocolitica strain W22703 pYV⁺, its plasmidless isogenic derivative W22703 pYV^- and four recent field isolates was examined.
The growth rate was clearly influenced by presence or absence of the virulence plasmid: pYV^- strains grew consistently faster than pYV⁺ strains. This difference in growth rate was high at 30–35°C, moderate at 1–10°C and 25°C, but hardly significant at 15–20°C.
Increasing the growth temperature above 25°C resulted in the induction of the 220 kDa virulence plasmid-encoded Yop1 protein. In the 1–20°C range no obvious temperature- or plasmid-related differences in protein patterns could be detected.
The fatty acid composition showed a clear temperature-dependent change: with all strains the degree of saturation was low at 1°C and gradually increased with raising temperatures. All strains had similar fatty acid patterns, except one of the field isolates which showed aberrant C16 : 1 and cyclic fatty acid contents in the 5–25°C and 15°C ranges respectively. With strain W22703, the presence or absence of the virulence plasmid did not significantly alter the fatty acid pattern.