Temperature dependence of the photosynthetic activities in the thylakoid membranes from the blue-green alga Anacystis nidulans

The photosynthetic electron transport and phosphorylation reactions were measured in the room temperature region in the thylakoid membranes prepared from the blue-green alga, Anacystis nidulans. The Arrhenius plot of the Hill reaction with 2,6-dichlorophenolindophenol showed a distinct break of straight lines at 21°C in the membranes from cells grown at 38°C, and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the Hill reaction with ferricyanide showed a break at 13°C in the membranes from cells grown at 38°C, and at 7°C in those from cells grown at 28°C. On the other hand, the Arrhenius plot of the System I reaction with methylviologen as an electron acceptor and 2,6-dichlorophenolindophenol and ascorbate as an electron donor system was composed of a straight line in the membranes from cells grown at 28°C as well as at 38°C. The Arrhenius plot of the System II reaction measured by the ferricyanide reduction mediated by silicotungstate in the presence of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea also showed a break at 11°C in the membranes from cells grown at 38°C.The Arrhenius plot of the phosphorylation mediated by N-methylphenazonium methylsulfate showed a break at 21°C in the membranes from cells grown at 38°C and at 12°C in those from cells grown at 28°C. The Arrhenius plot of the phosphorylation mediated by the System I reaction showed a break at 24°C in the membranes from cells grown at 38°C.The characteristic features in the Arrhenius plots of the photosynthetic electron transport and phosphorylation reactions are discussed in terms of the transition of physical phase of the thylakoid membrane lipids.     

Assembly of complex III into newly developing mitochondrial membranes.

Yeast cells grown anaerobically in 0.02% linoleic acid were transferred to air in the presence of 0.02% elaidic acid. At varying times Arrhenius plots were made of QH2-cytochrome c reductase activities in isolated mitochondria. A transition temperature of 8.2 degrees C at 0.5 h was characteristic of linoleate; at 3 h the transition temperature was increased to 24 degrees C characteristic of elaidate. At early times the enzyme was associated with anaerobic promitochondrial membranes; at later states the newly synthesized enzyme was associated with newly developed elaidate membranes.     

Effects of assay and acclimation temperatures on incorporation of amino acids into protein of isolated hepatocytes from the european eel, Anguilla anguilla L.

Hepatocytes of adult eels acclimated to 5° C, 10° C and 20° C, respectively were isolated by perfusion of the liver with collagenase. The liver-somatic index and the protein content of liver cells showed significantly higher values in fish kept at the lower temperatures. However, in the adenine nucleotide content and energy charge no significant differences were observed between the 5° C and the 20° C acclimation groups. The incorporation of radioactivity from a ¹⁴C-labelled amino acid mixture into perchloric acid precipitates was used as an estimate of over-all protein synthesis. When eel hepatocytes were incubated in Hanks' solution containing tracer amounts of amino acids, labelling of perchloric acid precipitates showed linear time courses over at least 60 min at 10° C and 20° C assay temperatures. The total cellular radioactivity, however, exhibited non-linear time courses. In the measurement range from 5° C to 25° C Arrhenius plots of protein labelling exhibited a discontinuity in both groups of fish. Hepatocytes from 10° C-acclimated eel showed almost twice the incorporation rates of amino acids as those from the 20° C-acclimated fish. It is concluded that high temperature dependencies in the low temperature range require an increase in the capacity of the apparatus for protein synthesis during cold acclimation.     

Characteristic temperature dependences of respiratory and photosynthetic electron-transport activities in membrane preparations from Anacystis nidulans grown at different temperatures

Electron-transport activities supported by seven different electron donor/acceptor couples in the light and in the dark, respectively, were measured in particle preparations of the cyanobacterium (blue-green alga) Anacystis nidulans after growth at 40, 30 and 25°C. The Arrhenius plots of the photosynthetic electron-transport reactions between ascorbate (plus 2,6-dichlorophenolindophenol (DCIP)) and NADP⁺, diphenylcarbazide and DCIP, diaminodurene and benzyl viologen (O₂), and the plot of the photooxidation of reduced horse heart cytochrome c showed a single discontinuity at approx. 24–25, 15–17 and 10–13°C in membranes derived from cells grown at 40, 30 and 25°C, respectively. By contrast, the dark respiratory electron-transport reactions between NADPH, ascorbate (plus DCIP) or reduced horse heart cytochrome c and oxygen, and the reduction by horse heart cytochrome c of the aa₃-type terminal oxidase as followed directly by dual-wavelength spectrophotometry, all gave Arrhenius plots distinguished by two distinct breaks: The break at the higher temperature corresponded to the break also found in the Arrhenius plots of the photosynthetic reactions while an additional discontinuity was observed at 17–18, 8–9 and 5–6°C in membranes prepared from cells grown at 40, 30 and 25°C, respectively. The temperatures at which the discontinuities in the Arrhenius plots occurred depended on the temperature at which the cells had been grown; they were independent, however, of the specific electron donors and acceptors employed. The characteristic features in the Arrhenius plots of respiratory and photosynthetic electron-transport reactions are discussed in terms of lipid-phase transitions in the cytoplasmic and the intracytoplasmic (thylakoid) membranes of A. nidulans. Implications for possibly distinct sites of the respiratory and photosynthetic electron-transport systems in A. nidulans will be mentioned.     

Temperature and pH dependence of mold α-galactosidase

The effect of temperature and pH on kinetic behavior of α-galactosidase of Mortierella vinacea was investigated on the hydrolysis of p-nitrophenyl-α-D -galactopyranoside (PNPG). A very unusual kinetic behavior was observed for the soluble α-galactosidase i.e., substrate inhibition diminished gradually with increasing temperature or near the neutral pH range, and the kinetics approached the ordinary Michaelis-Menten (MM) type. On the other hand, with decreasing temperature or in acidic pH range, substrate inhibition was accelerated. Therefore, Arrhenius plots based on the initial reaction rate did not give straight lines. Furthermore, the slope in the Arrhenius plot changed with substrate concentration, which would make the determination of a characteristic value using conventional methods meaningless. However, the Arrhenius plots of individual kinetic parameters in the rate equation resulted in straight lines in the temperature range 15 to 50°C. From this, the drastic change in kinetic behavior could be explained in connection with the temperature and pH dependence of kinetic parameters in the model. For mold pellets (whole-cell enzyme), however, the influence of temperature and pH was less apparent than that of soluble enzyme because of the limitation in intraparticle diffusion. By using the rate equation that was determined for soluble enzyme and the theoretically derived effectiveness factor, the overall reaction rate for mold pellets at various temperature and pH could be predicted to some extent.     

Effect of Growth Temperature on the Lipid and Fatty Acid Composition, and the Dependence on Temperature of Light-induced Redox Reactions of Cytochrome f and of Light Energy Redistribution in the Thermophilic Blue-Green Alga Synechococcus lividus

The thermophilic blue-green alga Synechococcus lividus was grown at 55 and 38 C. Arrhenius plots of the transient reduction of cytochrome during actinic illumination with light that excited both pigment systems revealed breaks near 43 and 26 C for cells grown at 55 C. In cells grown at 38 C these breaks occurred near 37 and 28 C, respectively. The shift from pigment state 1 to state 2 measured by fluorescence transients also showed characteristic breaks in the Arrhenius plots at 44 C for cells grown at 55 C and at 37 to 38 C and possibly at 25 C for cells grown at 38 C. The break points in the Arrhenius plots for the state shift as well as for the cytochrome f reduction are discussed in relation to phase transitions of thylakoid membrane lipids as studied by the temperature dependence of chlorophyll a fluorescence.     

Increase in membrane permeability of electrolytes and betacyanin in beet root disc by fenitrothion

Effect of fenitrothion (phosphorothioic acid, 0,0-dimethyl 0-4-nitro-m-tolyl ester), an organophosphorous insecticide, on membrane permeability employing the leakage of betacyanin and electrolytes as the criteria were studied in beet root(Beta vulgaris) discs. The leakage of both betacyanin and electrolytes increased with increasing concentrations (10–150 ppm) of fenitrothion in the incubation medium. At 0.33 mM the increase in electrolyte leakage was approximately linear for the first 6h, while the increase in betacyanin leakage started with a lag of about 2 h. Long term incubation (24 h) showed a biphasic nature (in the semilog plot) for the increase in betacyanin leakage, while the increase in electrolyte leakage appeared more complex. In the control sample, the Arrhenius plots (25–50°C) of leakage showed a break at 40°C. In treated samples no break was observed, but the slope decreased (for both electrolyte and betacyanin leakage) as compared to the respective slopes in the control in the temperature region greater than 40°C. The results are discussed in terms of the possible effect of the insecticide on the active transport in plant membranes     

Membrane phase transitions and the transport of chlortetracycline.

When chlortetracycline is added to a suspension of respiring Staphylococcus aureus cells, the active transport of the antibiotic may be monitored by its fluorescence enhancement as it moves from a polar aqueous environment into the apolar regions of the membrane. The initial rates of transport are temperature dependent with a maximal rate between 35 and 45 °C. Arrhenius plots of the initial rates are biphasic with a transition temperature of 27 °C for control cells. This transition temperature is sensitive to the fatty acid composition of the S. aureus cells. By culturing the cells in the presence of oleic acid or at 10 °C, the S. aureus cells incorporate a larger percentage of unsaturated and branched chain fatty acids into their membranes, resulting in transition temperatures 8–9 °C lower than the control cells. Studies of depolarization of fluorescence also indicate that the mobility of the bound chlortetracycline is temperature-dependent. Temperature transitions occur at the same temperatures as those measured by Arrhenius plots. The transition temperatures indicated by the Arrhenius plots and the polarization studies are believed to reflect order-disorder phase transitions associated with the melting of the phospholipids in the cell envelope.     

Purification and properties of malate dehydrogenase from the extreme thermophileBacillus caldolyticus

The enzyme malate dehydrogenase (EC 1.1.1.37) from an extreme thermophileB. Caldolyticus was purified to about 91% homogeneity. The molar mass of the enzyme was determined as 73 000 daltons and it is composed of two subunits, each with a molar mass of 37 000. Initial velocity studies with oxaloacetic acid and NADH as substrates at pH 8.1, over a range of temperatures, indicate that the enzyme operates via a sequential type mechanism. Van't Hoff plots of the kinetic parameters displayed sharp changes in slope at characteristic temperatures, whereas the Arrhenius plot exhibited no such breaks over the temperature interval investigated. The enzyme was found to be stable at 41°C and lower temperatures. At 51°C and 59°C an almost immediate 20% reduction in activity was obtained, but no further inactivation occurred during the 60 min of incubation. At 59°C the enzyme lost 50% of its initial activity in about 38 s. High concentration of NADH was observed to greatly stabilize the enzyme at that temperature.It is suggested that the slope changes in the Van't Hoff plots and the stability profies at 51°C and 59°C are representative of a temperature induced conformational change in the enzyme.Proceedings of the Fourth College Park Colloquium on Chemical Evolution:Limits of Life, University of Maryland, College Park, 18–20 October 1978.     

Modulation of the activity of 5′-nucleotidase by the transfer of non-esterified cholesterol to rat-liver microsomal fraction and evidence for regulation of the concentration of non-esterified cholesterol in plasma membranes in vivo

The transfer of non-esterified cholesterol to rat-liver microsomal fraction resulted in a considerable decrease in the activity of 5′-nucleotidase and in changes in the characteristics of the Arrhenius plots of the enzyme. The decrease in the activity of 5′-nucleotidase and the increase in the concentration of non-esterified cholesterol in the serum-treated preparations were serum-concentration-dependent and incubation-time-dependent. The enzyme in serum-treated preparations with high non-esterified cholesterol content showed Arrhenius plots with a constant activation energy between 37 and 19°C, whereas the enzyme in the non-treated microsomal fraction or the lipoprotein-deficient serum-treated preparations showed a break at about 28°C, with activation energies higher below and lower above the break. These changes in the temperature-induced kinetics are consistent with an increase in the concentration of non-esterified cholesterol in the plasma membrane vesicles of the serum-treated preparations. The Arrhenius plots of 5′-nucleotidase in liver microsomal fraction from rats fed cholesterol-supplemented diet showed constant activation energy between 37 and 19°C and had similar characteristics with the plots for 5′-nucleotidase in serum-treated preparations. Since the changes in the characteristics of Arrhenius plots of the enzyme in microsomal fraction from rats that had been denied food for 36 h were in the opposite direction to those produced by feeding cholesterol, these results are consistent with a lower concentration of non-esterified cholesterol in hepatic plasma membranes from fasted rats relative to that in plasma membranes from fed rats. The isolation of a plasma membrane preparation with negligible contamination of endoplasmic reticular membranes from rats fed the standard or cholesterol-supplemented diet and from fasted rats showed that the ratio of cholesterol to phospholipid has increased in the preparation from rats fed cholesterol and decreased in that from rats that had been denied food relative to the ratio in the preparation from rats fed the standard diet. The Arrhenius plots of 5′-nucleotidase in these preparations showed characteristics similar to the corresponding plots of the enzyme in the microsomal fraction from the rats in the three experimental conditions.     

Regulation of protein synthesis in mammalian cells. V. Further studies on the effect of actinomycin D on translation control in HeLa cells

The rate of protein synthesis in HeLa cells appears to be regulated, in part, by a factor which promotes the association of ribosomes with messenger RNA and whose production is inhibited by actinomycin. The decline in protein synthesis after the administration of actinomycin is not primarily due to a decay of available messenger RNA but, rather, is a result of a decrease in the rate of ribosomal association with message.The decay of protein synthesis in actinomycin can be varied over a wide range by altering the temperature of cell incubation. Thus the half-life of protein synthesis decay ranges from eight hours at 34 °C to two hours at 41°C. The rapid decline of protein synthesis at 41 °C is not accompanied by a corresponding decay of the messenger RNA. Polyribosomes decrease in size, but they can be restored to normal sedimentation distributions by low levels of cycloheximide, suggesting that messenger RNA remains functional. The translation rate at 41 °C is unaltered. The dose-response of protein synthesis inhibition by actinomycin was measured and a half-maximum inhibition was found to be effected by 0·1 μg of the drug/ml.Another important aspect of the regulation of translation in HeLa cells is the response of cells to depressed rates of protein synthesis. At 42 °C, protein synthesis is severely inhibited, due to a failure in the association of ribosomes with messenger RNA. Prolonged incubation at the elevated temperature results in a significant repair of the lesion. This repair is inhibited by actinomycin. The half-maximum inhibition is achieved at levels of from 0·05 to 0·1 μg of the drug/ml.The cell response to depressed rates of protein synthesis can also be demonstrated using the drug cycloheximide. Prolonged incubation in the drug results in a response which then can promote protein synthesis at 42 °C. Here again, the half-maximum inhibition of the response to cyclohemixide is achieved by 0·1 μg of actinomycin/ml. These experiments suggest, but do not prove, that the cellular response may be mediated through the synthesis of RNA that promotes the initiation of translation and does not involve the subsequent production of protein.     

Kinetic properties and regulation of glycerol-3-phosphate dehydrogenase from the overwintering, freezing-tolerant gall fly larva, Eurosta solidagenis

The kinetic properties of cytoplasmic glycerol-3-P dehydrogenase from the third instar larva of the gall fly, Eurosta solidaginis, were studied with emphasis on temperature effects on the enzyme and the regulation of enzyme activity during the synthesis of the cryoprotectant, glycerol. Isoelectrofocusing revealed one major and two minor forms of the enzyme with no alteration in the pI's or relative activities of the forms in larvae acclimated to 24 versus ?30 °C. Kinetic properties of the enzyme were also the same in larvae acclimated to high and low temperatures. Arrhenius plots were linear over a 30 to 0 °C range with an activation energy of 12,630 ± 185 cal/mol and a Q₁₀ of 2.16. The K_m for dihydroxyacetone-P was constant, at 50 μM, between 30 and 10 °C but increased by 75% at 0 °C; this increase may be a factor in the cessation of glycerol synthesis which occurs below 5 °C in this species. The K_m(NADH), by contrast, was higher (5–6 μM) at 30 °C but decreased (3 μM) at lower temperatures. In the reverse direction, K_m's were 340 μM for glycerol-3-P and 12 μM for NAD⁺. Effects of most inhibitors (of the forward reaction), glycerol-3-P (K_i = 2.4 mM), NAD⁺ (K_i = 0.2 mM), ATP, Mg·ATP, and P_i, were unaltered by assay temperature but ADP effects were potentiated by low temperature while citrate inhibition was greatest at high temperatures. Glycerol and sorbitol, which accumulate as cryoprotectants in E. solidaginis, had no significant effects on kinetic constants at any temperature but decreased the V_max activity of the enzyme. Thermal inactivation studies showed an increased thermal stability of the larval enzyme compared to the homologous enzyme from rabbit muscle while added polyols stabilized enzyme activity, decreasing the rate of enzyme inactivation at 50 °C.     

Suboptimal temperature-dependent changes in the brain development and activity in Galleria mellonella larvae

The development of Galleria mellonella larvae is strongly affected by suboptimal temperature (18°C). One-day-old last-instar larvae react to 18°C with the arrest of further development for several months described as facultative larval diapause. The aim of this study was to find what type of changes, if any, in the brain correlate with the larval diapause induced by suboptimal temperature. Morphological analysis demonstrated the gradual inhibition of brain development. Paraldehyde-fuchsin (PAF) staining revealed cyclicity in the activity of the medial neurosecretory cells (M-NSC) in the larval brain. SDS-PAGE was used to examine the brain proteins of larvae reared at 30°C and at 18°C. The rate of protein synthesis in the brain of the last instar larvae kept at 18°C, measured as l -[³⁵S]methionine incorporation during 2-h incubation in vitro, was only about 40% of the value characteristic for this tissue during normal development (at 30°C). Despite decrease in the rate of total protein synthesis, suboptimal temperature induced an increase in the level of two major brain proteins: 112 and 84 kDa. In SDS-PAGE analysis, these two proteins appear 21–28 days after transfer to the lower temperature. Whether these proteins are specific for induction of larval diapause of Galleria mellonella remains to be further investigated. Arch. Insect Biochem. Physiol. 38:66–73, 1998. © 1998 Wiley-Liss, Inc.     

Heat-Resistance and Heat-Shock Response in the Nosocomial Pathogen <Emphasis Type="Italic">Enterococcus faecium</Emphasis>

We have characterized the heat-shock response of the nosocomial pathogen Enterococcus faecium. The growth of E. faecium cells was analyzed at different temperatures; little growth was observed at 50°C, and no growth at 52°C or 55°C. In agreement, a marked decrease of general protein synthesis was observed at 52°C, and very light synthesis was detected at 55°C. The heat resistance of E. faecium cells was analyzed by measuring the survival at temperatures higher than 52°C and, after 2 h of incubation, viable cells were still observed at 70°C. By Western blot analysis, two heat-induced proteins were identified as GroEL (65 kDa) and DnaK (75 kDa). Only one isoform for either GroEL or DnaK was found. The gene expression of these heat-shock proteins was also analyzed by pulsed-labeled experiments. The heat-induced proteins showed an increased rate of synthesis during the first 5 min, reaching the highest level of induction after 10 min and returning to the steady-state level after 20 min of heat treatment. Received: 29 March 2002 / Accepted: 5 July 2002     

Involvement of Membrane Lipids in Cold Shock-induced Autolysis of Bacillus subtilis Cells

Exponentially growing Bacillus subtilis cells autolysed when exposed to cold shock treatment in minimal medium followed by incubation at 37°C. From characteristics of the lysis, it was suggested that the cold-shock-induced cell lysis resulted from the perturbation of membrane organization that is initiated by rapid changes in temperature, lipid phase transitions. For maximum lysis induction to occur, in addition to rapid cooling to 5°C or lower, retention at temperatures lower than 10°C for at least 20 min is required. The cell sensitivity to the autolysis induction by cold shock was different between cells grown at 25°C and cells grown at 37°C. Analyses of the fatty acid composition and the phase transition temperature of membrane lipids suggested that the membrane fluidity may affect the autolysis induction. Experiments to discover the effects of cerulenin treatment and lipid addition on autolysis induction and the autolysin activity level support the hypothesis that membrane lipids are involved in cold-shock-induced cell autolysis.     

In vitro synthesis of peritrophic membranes of the blowfly, Calliphora erythrocephala.

Tyrode solution containing added glutamine and Leloup's medium 1 has been used as a basic medium for the in vitro culture of the so-called proventriculus of adult Calliphora erythrocephala to elucidate some of the factors controlling the synthesis of peritrophic membranes (PM) in vitro. The formation rate was chosen as a quantitative criterion for the evaluation of the modifications of the incubation media.After systematic variation of osmolarity, pH, and temperature optimal formation rates were obtained in media with an osmolarity of 320 to 360 mOsmol, a pH of 6·8, and an incubation temperature of 27°C. Under these conditions the average rate of formation was in the modified Tyrode solution 3·0±1·1 mm PM/hr, and in Leloup's medium 3·6±0·8 mm PM/hr. In the modified Tyrode solution the formation of PM was complete after 5 to 7 hr, whereas in Leloup's medium it continued up to 24 hr. The addition of β-ecdysone caused an increase of the formation rate of PM to 4·5 to 5·5 mm PM/hr.The results obtained led to the hypothesis that an osmotically regulated enzyme system could be the limiting factor of the formation rate of peritrophic membranes, i.e. a system which could regulate the internal osmolarity of the formative cells by the interconversion of a bulk polymer and its monomer which are needed for the synthesis of PM.     

Independence of deoxyribonucleic acid replication and initiation from membrane fluidity and the supply of unsaturated fatty acids in Escherichia coli.

Mutant derivatives of the unsaturated fatty acid auxotroph K1062 were employed to investigate whether the supposedly membrane-bound bacterial replication machinery requires for its replicatory functions a fluid membrane environment as is known for several membrane-associated protein functions. Temperatures Tt for fluid reversible nonfluid phase transitions of membrane phospholipids are raised from below 18 to 38 degrees C when mutant cells are supplemented with elaidate instead of with oleate. In this experimental system current or synchroneously initiated new rounds of DNA replication are shown in vivo to continue 8 degrees below Tt, provided appropriate corrections for the concurrent cellular metabolic breakdown are considered. Temperature rate profiles for in vitro deoxyribonucleic acid replication rates measured in lysates of either oleate- or elaidate-supplemented cells yield congruent Arrhenius plots without discontinuities at corresponding Tt positions. We conclude that neither the start nor the propagation of replication forks depends on a fluid membrane. The capacity for the assembly of new replication complexes was studied in replication-aligned cells either shifted from oleate to elaidate (at temperatures below Tt for newly synthesized phospholipids) or starved for oleate. Regardless of whether unsaturated fatty acids are exchanged or completely withheld, new replication complexes can be normally assembled and initiated. These results do not support the conclusions reached by Fralick and Lark (1973) that the availability of unsaturated fatty acids is a prerequisite for the assembly of a functional replication complex.     

Temperature Dependence of Muscarinic Acetylcholine Receptor Activation, Desensitization, and Resensitization

Abstract: The effects of temperature on muscarinic acetylcholine receptor activation, desensitization, and resensitization were studied with the use of intact mouse neuroblastoma cells (clone N1E-115), which have muscarinic receptors that mediate cyclic GMP synthesis. Below 15-20°C, activation or desensitization of muscarinic receptors by carbamylcholine and recovery from desensitization (caused by carbamylcholine at 37°C) did not occur. Above these temperatures, the apparent rates of receptor-mediated cyclic GMP synthesis, desensitization, and recovery of sensitivity increased as the incubation temperature was increased. Arrhenius plots of the data yielded activation energies of 25, 14, and 23 kcal.mol⁻¹ for activation, desensitization, and resensitization, respectively. These data suggest that a certain degree of membrane phospholipid fluidity is required for these processes to occur.     

Temperature-dependent conformational changes in a voltage-gated potassium channel

Temperature was used as a biophysical tool to investigate the energy changes associated with conformational change during the gating of a non-inactivating voltage-gated K⁺ channel present in the membrane of αT3-1 cells, a gonadotroph cell line. The time course of the current activation was described by a single exponential function at three temperatures: 15, 25 and 35 °C. The Q ₁₀ values were between 1.5 to 1.9 and in agreement with the activation energy determined from Arrhenius plots of the forward and backward rate constants associated with channel opening. The Gibb's free energy change associated with channel opening and closing at various membrane potentials estimated by two approaches yield similar values. The changes in Gibb's free energy (ΔG°) with depolarization potential is a quadratic and more prominent at 15 than at 25 or 35 °C. The results suggest that increase in temperature favours movement of voltage sensing segments, and reduces the restraint on them brought about by other parts of the channel molecule. Received: 2 September 1998 / Revised version: 27 October 1998 / Accepted: 21 January 1999     

How incubation temperature influences the physiology and growth of embryonic lizards

Eggs of two small Australian lizards, Lampropholis guichenoti and Bassiana duperreyi, were incubated to hatching at 25 °C and 30 °C. Incubation periods were significantly longer at 25 °C in both species, and temperature had a greater effect on the incubation period of B. duperreyi (41.0 days at 25 °C; 23.1 days at 30 °C) than L. guichenoti (40.1 days at 25 °C; 27.7 days at 30 °C). Patterns of oxygen consumption were similar in both species at both temperatures, being sigmoidal in shape with a fall in the rate of oxygen consumption just prior to hatching. The higher incubation temperature resulted in higher peak and higher pre-hatch rates of oxygen consumption in both species. Total amount of oxygen consumed during incubation was independent of temperature in B. duperreyi, in which approximately 50 ml oxygen was consumed at both temperatures, but eggs of L. guichenoti incubated at 30 °C consumed significantly more (32.6 ml) than eggs incubated at 25 °C (28.5 ml). Hatchling mass was unaffected by either incubation temperature or the amount of water absorbed by eggs during incubation in both species. The energetic production cost of hatchling B. duperreyi (3.52 kJ · g⁻¹) was independent of incubation temperature, whereas in L. guichenoti the production cost was greater at 30 °C (4.00 kJ · g⁻¹) than at 25 °C (3.47 kJ · g⁻¹). Snout-vent lengths and mass of hatchlings were unaffected by incubation temperature in both species, but hatchling B. duperreyi incubated at 30 °C had longer tails (29.3 mm) than those from eggs incubated at 25 °C (26.2 mm). These results indicate that incubation temperature can affect the quality of hatchling lizards in terms of embryonic energy consumption and hatchling morphology. Accepted: 27 January 2000