Variable thermal stress tolerance of the reef-associated symbiont-bearing foraminifera Amphistegina linked to differences in symbiont type

Coral Reefs - Adaptation, acclimatization and symbiont diversity are known to regulate thermal tolerance in corals, but the role of these mechanisms remains poorly constrained in other...     

Calculation of the standard molal thermodynamic properties of aqueous biomolecules at elevated temperatures and pressures II. Unfolded proteins

Equations of state for completely unfolded proteins have been generated from group additivity algorithms and the revised Helgeson-Kirkham-Flowers (HKF) equations of state to compute the standard molal thermodynamic properties of these molecules at elevated temperatures and pressures. The requisite equations of state parameters were computed from those of groups retrieved by regression of experimental calorimetric and densimetric data reported in the literature. This approach permits calculation of the standard molal thermodynamic properties as a function of temperature and pressure for any completely unfolded protein for which the amino acid sequence is known. Calculations of this kind have been carried out for 11 thermophilic proteins. The thermodynamic properties reported below can be combined with those for protein unfolding to compute the corresponding properties of completely folded (i.e. native) proteins.     

Effect of elevated temperatures on human lymphocyte chromosomes

The influence of elevated temperatures (38-41 degrees C) on chromosomes of human lymphocytes on different phases of the cell cycle was studied. A high thermosensitivity of chromosomes was demonstrated during (S + G2)-phases of the cell cycle. There was a significant increase in the number of aberrant cells at t greater than 38.5%. The main types of chromosome aberrations were chromatid and chromosome deletions. Cells with 3-5 aberrations and induction of chromosome aberrations due to breaks in the centromere region were noticed at high temperatures (40-41 degrees).     

Dynamical seasonal prediction of summer sea surface temperatures in the Great Barrier Reef

Coral bleaching is a serious problem threatening the world coral reef systems, triggered by high sea surface temperatures (SST) which are becoming more prevalent as a result of global warming. Seasonal forecasts from coupled ocean–atmosphere models can be used to predict anomalous SST months in advance. In this study, we assess the ability of the Australian Bureau of Meteorology seasonal forecast model (POAMA) to forecast SST anomalies in the Great Barrier Reef, Australia, with particular focus on the major 1998 and 2002 bleaching events. Advance warning of potential bleaching events allows for the implementation of management strategies to minimise reef damage. This study represents the first attempt to apply a dynamical seasonal model to the problem of coral bleaching and predict SST over a reef system for up to 6 months lead-time, a potentially invaluable tool for reef managers. Communicated by Geology Editor Dr Bernhard Riegl     

Equatorial Pacific sea surface temperatures, faunal patterns, and carbonate burial during the Pliocene

A high-resolution record of radiolarian faunal abundances from the eastern equatorial Pacific is compared to records of carbonate and noncarbonate burial to examine the evolution of eastern tropical Pacific climate processes during the Pliocene. These data provide a means to evaluate the sensitivity of the equatorial Pacific to the onset of Northern Hemisphere glaciation around 2.8−2.5 Ma, to the closure of the Isthmus of Panama around 4.4−3.2 Ma, and to orogeny-related weathering changes before 4.0 Ma. Radiolarian faunal assemblages and sea surface temperature (SST) estimates indicate a gradual cooling from early to late Pliocene, but no significant changes occur near the onset of northern hemisphere glaciation. Records of carbonate and noncarbonate mass accumulation show a long term decrease from the Miocene/Pliocene boundary to the upper Pliocene. Greater carbonate burial in the early Pliocene relative to the late Pliocene parallels a gradual cooling from early to late Pliocene, and may reflect changes related to Isthmus closure or widespread orogeny. No significant time domain changes are seen in the eastern equatorial Pacific that could be related to the onset of Northern Hemisphere glaciation.Evolutive spectral analyses of these equatorial Pacific climate parameters indicate that variance in SST and seasonality commonly concentrate at frequencies not linearly related to orbital variations. Furthermore, cross spectral comparisons with a high resolution benthic δ¹⁸O record indicate that the surface ocean and carbonate flux share little coherent variance with high latitude climate processes during the Pliocene. Given the high degree of chronostratigraphic control in these records, these results suggest that Milankovitch-band surface ocean processes as well as carbonate burial in the equatorial Pacific are decoupled from high latitude climate processes during the Pliocene.     

Forecasting decadal changes in sea surface temperatures and coral bleaching within a Caribbean coral reef

Elevated sea surface temperature (SST) caused by global warming is one of the major threats to coral reefs. While increased SST has been shown to negatively affect the health of coral reefs by increasing rates of coral bleaching, how changes to atmospheric heating impact SST distributions, modified by local flow environments, has been less understood. This study aimed to simulate future water flow patterns and water surface heating in response to increased air temperature within a coral reef system in Bocas del Toro, Panama, located within the Caribbean Sea. Water flow and SST were modeled using the Delft3D-FLOW© computer simulation package. Locally measured physical parameters, including bathymetry, astronomic tidal forcing, and coral habitat distribution were input into the model and water flow, and SST was simulated over a four-month period under present day, as well as projected warming scenarios in 2020s, 2050s, and 2080s. Changes in SST, and hence the thermal stress to corals, were quantified by degree heating weeks. Results showed that present-day reported bleaching sites were consistent with localized regions of continuous high SST. Regions with highest SST were located within shallow coastal sites adjacent to the mainland or within the interior of the bay, and characterized by low currents with high water retention times. Under projected increases in SSTs, shallow reef areas in low flow regions were found to be hot spots for future bleaching.     

Gas-phase disproportionation of nitric oxide at elevated pressures

T.P. Melia's chemical kinetics study of the disproportionation of nitric oxide (NO), 3NO →NO₂ + N₂O , (Melia, T.P. (1965) J. Inorg. Nucl. Chem., 27, 95-98), which is the most quoted quantitative investigation presently available, revealed a rather strong dependence of the effective rate constant, Kk ', of Melia's third-order rate law,- d[NO]/d t = Kk'[NO]₃, on the initial pressure of NO. In order to estimate extent of accumulation of NO₂ and N₂O as a function of time by integration of the rate law, we have evaluated the dependence of the effective rate constant as a function of pressure and thus as a function of time on the basis of the non-ideality of NO gas. Although our approach is crude in that the non-idealities of NO₂ and N₂O and other NO_x products and a probable deviation of the gas mixture from the Dalton's law have not been considered, it provides a means for approximately estimating the rate of accumulation of NO₂ and N₂O based on Melia's data. According to these calculations, the extent of the disproportionation is generally negligible at low initial pressures, e.g. 5 atm or less, while at 200 atm, the mole fractions of NO₂ and N₂O can become as high as 12-13% only after 10 days. These values are alarmingly high for handling pressured NO- in N₂-mixture in either research or clinical settings. This information must be borne in mind when compressed NO in commercial cylinders is employed in high precision experiments. Disproportionation of NO under pressure also deserves attention in inhalation of low doses of NO in the treatment of diseases characterized by pulmonary hypertension and hypoxemia.     

Thermogenic responses of high-altitude adapted rats on low temperatures and low pressures

The male rats were raised in two groups, one at Mt. Yatsugatake (2,100 m above sea level, the average ambient temperature 12.5 degrees C) for 30 days, and the other at a laboratory of Matsumoto (610 m above sea level, the average temperature 20 degrees C). The steady-state oxygen consumptions (VO2) and the rectal temperatures (TR) were measured under exposure conditions of various temperatures combined with different simulated altitudes. The values of VO2 and TR for a control group at 610 m-20 degrees C were regarded as 100% and the relative changes to the control values were obtained at various temperatures in the respective low-pressure condition. When measured at a simulated altitude of 2,000 m on the 2nd day after the rats raised at Mt. Yatsugatake were translocated to Matsumoto, the values at 0 degrees C and 10 degrees C room temperatures, VO2 and TR, were still significantly increased as compared with those of rats raised at Matsumoto. On the 40th day after the translocation from Mt. Yatsugatake, however, the values turned out to exhibit no significant difference in both groups. These results indicated that the greater thermogenesis of high-altitude adapted rats had been established by combined stimuli of low temperatures and low pressures as compared with those of Matsumoto-level adapted rats, but the responses returned to the control level by deadaptation process at 40 days after the translocation.     

Non-equilibrium isotopic compositions of shells of planktonic foraminifera in the Mediterranean sea

The deviation from isotopic equilibrium has been evaluated for eight foraminiferal species from the Mediterranean Basin. A detailed study of some forms presenting an outer calcitic crust in late ontogenetic stages and in sedimented specimens allows us to propose another hypothesis for the biological fractionation: it should be a function of metabolic processes which condition the secretion of the tests.     

Operational stability of copolymerized enzymes at elevated temperatures

The copolymerization method of immobilization was used to obtain preparations of enzymes covalently incorporated in polyacrylamide gel. They possess properties making them suitable for practical use. First, the preparations are hundreds of times more stable against irreversible thermoinactivation than native enzymes. Second, on immobilization, the reversible conformational changes which also lower enzyme activity at elevated temperatures are completely suppressed. As a result, the temperatures of maximum activity for trypsin and alpha-chymotrypsin covalently entrapped in polyacrylamide gel are 75 and 70 degrees C, respectively-25 and 30 degrees C higher than the corresponding values for the native enzymes. Therefore, the copolymerized enzyme preparations have a high operational stability at elevated temperatures.     

Energetics of peptide bond formation at elevated temperatures

Summary The free energies of formation of the peptide bond between carbobenzoxy-glycine and L-phenylalanine amide in aqueous solution at temperatures up to 60°C were calculated from experimentally determined equilibrium constants. The reaction was catalyzed by a thermophylic enzyme. The thermodynamic energy barrier to peptide bond formation was found to decrease with increasing temperature: the standard free energy of peptide bond formation did appear to become negative in the region of 60°C. The possible significance of these results for peptide bond formation under prebiotic conditions is discussed.     

Cytotoxicity of commonly used solvents at elevated temperatures

At 43 degrees C (but not at 41 degrees C), organic solvents used to dissolve water-insoluble chemotherapeutic agents become themselves lethal to cells. This finding is not unique to Chinese hamster cells (HA-1); mouse mammary sarcoma cells (EMT-6) behave similarly. The solvent concentrations involved are in the range of those needed to make drug solutions. Hence experiments measuring drug-cell interactions at elevated temperatures must include controls which independently measure solvent effects.     

Nicotine ingestion reduces elevated blood pressures in rats and squirrel monkeys

Nicotine tartrate (0.002 -5.0 mg/kg/day) was added to the home cage drinking water of albino rat and squirrel monkey subjects for periods from 1 – 10 weeks. Rats received the drug for approximately 10 weeks and were then implanted with a chronic aortic cannula, allowed to recuperate, and blood pressure measured before and following exposure to a mild tail pinch procedure. All subjects receiving nicotine showed reduced blood pressure elevations to noxious stimulation compared to water control subjects, and these reductions were greater at higher drug doses. Squirrel monkeys exhibiting widely differing resting blood pressures were administered chronic dosages of nicotine. Subjects having high blood pressures showed dose-dependent blood pressure decreases, whereas subjects possessing low resting pressures demonstrated little or no pressure change during drug intake. A follow up study with high blood pressure subjects measured effects of progressive increases in drug followed by a return to drug-free water drinking solutions. Here again a dose-dependent decrease in both systolic and diastolic blood pressures were observed. Upon termination of drug intake, pressures rapidly increased to pre-drug levels. The results are concordant with previous studies demonstrating that oral nicotine ingestion causes reductions in aggresive behavior, and suggest that nicotine is selectively influential in altering the biological state of anger, decreasing both its behavioral and somatic components.     

Raman spectroscopic studies of hen egg-white lysozyme at high temperatures and pressures

In situ high-temperature, high-pressure Raman experiments on 3 mM (pH 5) aqueous solutions of hen egg-white (HEW) lysozyme show a decrease in the relative height of the 505 cm^–1 band associated with S-S stretching vibrations at 72°C (1 bar). The peak height changes are accompanied by significant band broadening, and the integrated band intensity does not change within experimental error. The effect of increased pressure at 72°C was to hinder broadening of the 505 cm^–1 band. HEW lysozyme (2.4 mM,pH 5) was also heated at 76°C, 80°C, and 95°C for different periods of time, and aliquots were quenched to room temperature for Raman and enzymatic activity measurements. After 9 hr at 76°C, the protein exhibits enzyme activity less than 50% of the initial value, and approximately 50% reduction in activity is achieved after 3 hr at 80°C or 1 hr at 95°C. The Raman results suggest that different irreversibly denatured conformations are attained during prolonged exposures at these different temperatures. It is apparent from these studies that the S-S stretch intensity is decreased irreversibly.     

Sensitivity of polyamine-deficient Saccharomyces cerevisiae to elevated temperatures.

Saccharomyces cerevisiae cells that cannot synthesize spermidine or spermine because of a deletion in the gene coding for S-adenosylmethionine decarboxylase are very sensitive to elevated temperatures when incubated in a polyamine-deficient medium; i.e., growth is inhibited and the cells are killed. This sensitivity is very pronounced at 39 degrees C, but a moderate effect is noted even at 33 to 34 degrees C. These findings support findings from other studies from our laboratory on the importance of polyamines in protecting cell components against damage. The sensitivity of spermidine-deficient cells to the temperature 39 degrees C provides a useful method for screening for polyamine auxotrophs.     

Interaction between photon flux density and elevated temperatures on photoinhibition in Alocasia macrorrhiza

The effects of light and elevated temperatures on the efficiency of energy conversion in PSII [?_PSII = (Fm′−Fs)/Fm′], pigment composition and heat tolerance of shade-acclimated Alocasia macrorrhiza were investigated. Leaf discs were exposed for 3 h to high light (HL; 1600 μmol photons · m⁻² · s⁻¹) or low light (LL; 20 μmol photons · m⁻² · s⁻¹) and a series of constant temperatures ranging from 30 to 49 °C. All HL treatments led to rapid and severe decreases in ?_PSII. During the 2-h recovery period (LL, 25 °C) following the HL treatments, fast and slow recovery phases could be distinguished. Leaf discs that had experienced HL and 30 °C recovered completely while no recovery of ?_PSII was seen after a 3-h exposure to HL and 45 °C. A 3-h exposure to 45 °C at LL led to a less severe decrease in ?_PSII and complete recovery was accomplished after less than 1 h. Under LL conditions a temperature of 49 °C was necessary to cause an irreversible decrease in ?_PSII, followed by necrosis the next day. Streptomycin had no effect on the degree of reduction and recovery in ?_PSII discs exposed to HL and 35–45 °C, but partially inhibited recovery in discs exposed to HL and 30 °C. Streptomycin led to a more severe decrease in ?_PSII at LL and 49 °C and completely inhibited recovery. Streptomycin had no effect on the conversion of the xanthophyll-cycle pigments during the treatment or the recovery. The epoxidation state was roughly the same in all leaf discs after a 3-h HL treatment (0.270–0.346) irrespective of the exposure temperature. The back-conversion of zeaxanthin into violaxanthin after a 2-h recovery period was only seen in leaf discs that had been exposed to HL and 30 °C. The thermotolerance of shade A. macrorrhiza leaves of 49.0 ± 0.7 °C (determined by fluorescence) coincided with the temperature at which damage occurred in leaf discs exposed to LL. However, under HL the critical temperature under which necrosis occurred was much lower (42 °C). The thermotolerance of A. macrorrhiza shade leaves could be increased by a short exposure (<20 min) to slightly elevated temperatures. Received: 11 June 1997 / Accepted: 9 September 1997