Abrupt Temperature Shift Research Articles

Statistical precursor signals for Dansgaard–Oeschger cooling transitions

Abstract. Given growing concerns about climate tipping points and their risks, it is important to investigate the capability of identifying robust precursor signals for the associated transitions. In general, the variance and short-lag autocorrelations of the fluctuations increase in a stochastically forced system approaching a critical or bifurcation-induced transition, making them theoretically suitable indicators to warn of such transitions. Paleoclimate records provide useful test beds if such a warning of a forthcoming transition could work in practice. The Dansgaard–Oeschger (DO) events are characterized by millennial-scale abrupt climate changes during the glacial period, manifesting most clearly as abrupt temperature shifts in the North Atlantic region. Some previous studies have found such statistical precursor signals for the DO warming transitions. On the other hand, statistical precursor signals for the abrupt DO cooling transitions have not been identified. Analyzing Greenland ice core records, we find robust and statistically significant precursor signals of DO cooling transitions in most of the interstadials longer than roughly 1500 years but not in the shorter interstadials. The origin of the statistical precursor signals is mainly related to so-called rebound events, humps in the temperature observed at the end of interstadial, some decades to centuries prior to the actual transition. We discuss several dynamical mechanisms that give rise to such rebound events and statistical precursor signals.

Physiological and perceptual responses to temperature step changes between cold and hot environments

Objectives. This study explores the effects of temperature steps on thermal responses to understand abrupt temperature shifts faced by heat-exposed workers during winter. Methods. Three temperature step changes with three phases (S20: 20–40–20 °C, S30: 10–40–10 °C, S40: 0–40–0 °C) were conducted. Phase 1 took 30 min, phase 2 took 60 min and phase 3 took 40 min. Eleven participants remained sedentary throughout the experiment, and physiological responses, thermal perception and self-reported health symptoms were recorded. Results. In temperature up steps, steady skin temperature and sweating onset were delayed, and heart rate dropped by 10 bpm from S20 to S40. In temperature down steps to cold conditions, individuals transitioned from thermal comfort to discomfort and eventually cold strain. Blood pressure increased in temperature down steps, correlating with temperature step magnitudes. Thermal responses to temperature steps of equal magnitude but opposite directions were asymmetries, which weakened as step magnitude increased. Thermal perceptions responded faster than physiological changes after temperature steps, while self-reported health symptoms lagged behind physiological responses. Conclusions. These findings contribute to expanding basic data to understand the effects of temperature step magnitude and direction.

Life Detection and Microbial Biomarker Profiling with Signs of Life Detector-Life Detector Chip During a Mars Drilling Simulation Campaign in the Hyperarid Core of the Atacama Desert.

The low organic matter content in the hyperarid core of the Atacama Desert, together with abrupt temperature shifts and high ultraviolet radiation at its surface, makes this region one of the best terrestrial analogs of Mars and one of the best scenarios for testing instrumentation devoted to in situ planetary exploration. We have operated remotely and autonomously the SOLID-LDChip (Signs of Life Detector-Life Detector Chip), an antibody microarray-based sensor instrument, as part of a rover payload during the 2019 NASA Atacama Rover Astrobiology Drilling Studies (ARADS) Mars drilling simulation campaign. A robotic arm collected drilled cuttings down to 80 cm depth and loaded SOLID to process and assay them with LDChip for searching for molecular biomarkers. A remote science team received and analyzed telemetry data and LDChip results. The data revealed the presence of microbial markers from Proteobacteria, Acidobacteria, Bacteroidetes, Actinobacteria, Firmicutes, and Cyanobacteria to be relatively more abundant in the middle layer (40-50 cm). In addition, the detection of several proteins from nitrogen metabolism indicates a pivotal role in the system. These findings were corroborated and complemented on "returned samples" to the lab by a comprehensive analysis that included DNA sequencing, metaproteomics, and a metabolic reconstruction of the sampled area. Altogether, the results describe a relatively complex microbial community with members capable of nitrogen fixation and denitrification, sulfur oxidation and reduction, or triggering oxidative stress responses, among other traits. This remote operation demonstrated the high maturity of SOLID-LDChip as a powerful tool for remote in situ life detection for future missions in the Solar System.

Comparison of thermal variations in post-retrieval graft conditioning on rat livers.

Machine perfusion was found an effective tool to recover organ grafts from ischemic insults during preservation. It could be observed that organ integrity is significantly affected by abrupt temperature shifts during hypothermic storage and implantation periods. Studies showed that a gentle and controlled rise of the temperature during oxygenated machine perfusion prior to implantation can protect the tissue from reperfusion injury. Now, the possible role of temperature kinetics upon retrieval of the graft and prior to later cold storage should be investigated. Rat livers were retrieved after cardiac arrest and subjected to a brief ex situ machine perfusion with either hypothermic resuscitation (HR) at 8°C, near-normothermic resuscitation (NR) at 30°C or progressive resuscitation with lowering the temperature in a controlled fashion from 30°C to 8°C (PR). After cold storage (CS), liver functional parameters were evaluated by an established ex vivo reperfusion system. NR and PR resulted in significantly lower release of hepatic enzymes and less production of tumor necrosis factor upon reperfusion compared to CS while HR had a far less protective effect. An increase in bile production was only observed in the PR group, which also significantly increased the recovery of tissue adenosine triphosphate, the amount of which was, however, nearly paralleled by the NR protocol. Within the limitations of this model, it seems that normothermic recirculation appears to be a superior approach for the restitution of warm-ischemically injured liver grafts than immediate hypothermic machine perfusion.

우리나라 추운 겨울 기온의 체계 변위

The Korean Peninsula has experienced regime shift (RS) in winter temperature since the mid-1980s. After the RS, monthly mean temperature significantly increased by 1.05°C in December with 95% confidence level, 1.36°C in January with 99% confidence level, and 1.60°C in February with 99% confidence level, respectively. Interestingly there is no RS in warm winter with 95% confidence level while there is a clear RS in cold winter with 99% confidence level, especially in December and January (DJ), indicating that the RS of winter temperature is mainly due to an abrupt temperature shift in December and January after the RS. Composite analysis suggests that abrupt shift in January after the RS is related to the reduction in sea level pressure (SLP) between Siberian high and Aleutian low, leading to anomalous southerly. However, abrupt shift in December is closely related to the propagation of Rossby wave spanning from the weakening of Ural high to negative anomaly over the North Pacific via high pressure anomaly over the Korean Peninsula, leading to adiabatic heating. Wave activity flux analysis suggests that the abrupt shift of DJ and the associated high pressure anomaly over the Korean Peninsula is induced by the propagation of Rossby wave spanning from North Atlantic Ocean to the Korean Peninsula via the Arctic, especially in cold winter.

An RNA thermometer dictates production of a secreted bacterial toxin.

Frequent transitions of bacterial pathogens between their warm-blooded host and external reservoirs are accompanied by abrupt temperature shifts. A temperature of 37°C serves as reliable signal for ingestion by a mammalian host, which induces a major reprogramming of bacterial gene expression and metabolism. Enteric Yersiniae are Gram-negative pathogens accountable for self-limiting gastrointestinal infections. Among the temperature-regulated virulence genes of Yersinia pseudotuberculosis is cnfY coding for the cytotoxic necrotizing factor (CNFY), a multifunctional secreted toxin that modulates the host’s innate immune system and contributes to the decision between acute infection and persistence. We report that the major determinant of temperature-regulated cnfY expression is a thermo-labile RNA structure in the 5’-untranslated region (5’-UTR). Various translational gene fusions demonstrated that this region faithfully regulates translation initiation regardless of the transcription start site, promoter or reporter strain. RNA structure probing revealed a labile stem-loop structure, in which the ribosome binding site is partially occluded at 25°C but liberated at 37°C. Consistent with translational control in bacteria, toeprinting (primer extension inhibition) experiments in vitro showed increased ribosome binding at elevated temperature. Point mutations locking the 5’-UTR in its 25°C structure impaired opening of the stem loop, ribosome access and translation initiation at 37°C. To assess the in vivo relevance of temperature control, we used a mouse infection model. Y. pseudotuberculosis strains carrying stabilized RNA thermometer variants upstream of cnfY were avirulent and attenuated in their ability to disseminate into mesenteric lymph nodes and spleen. We conclude with a model, in which the RNA thermometer acts as translational roadblock in a two-layered regulatory cascade that tightly controls provision of the CNFY toxin during acute infection. Similar RNA structures upstream of various cnfY homologs suggest that RNA thermosensors dictate the production of secreted toxins in a wide range of pathogens.

Uncoupled phytoplankton-bacterioplankton relationship by multiple drivers interacting at different temporal scales in a high-mountain Mediterranean lake

Global-change stressors act under different timing, implying complexity and uncertainty in the study of interactive effects of multiple factors on planktonic communities. We manipulated three types of stressors acting in different time frames in an in situ experiment: ultraviolet radiation (UVR); phosphorus (P) concentration; temperature (T) in an oligotrophic Mediterranean high-mountain lake. The aim was to examine how the sensitivity of phytoplankton and bacterioplankton to UVR and their trophic relationship change under nutrient acclimation and abrupt temperature shifts. Phytoplankton and bacteria showed a common pattern of metabolic response to UVR × P addition interaction, with an increase in their production rates, although evidencing an inhibitory UVR effect on primary production (PP) but stimulatory on bacterial production (HBP). An abrupt T shift in plankton acclimated to UVR and P addition decreased the values of PP, evidencing an inhibitory UVR effect, whereas warming increased HBP and eliminated the UVR effect. The weakening of commensalistic and predatory relationship between phyto- and bacterioplankton under all experimental conditions denotes the negative effects of present and future global-change conditions on planktonic food webs towards impairing C flux within the microbial loop.

Late Quaternary TEX86 paleotemperatures from the world’s largest desert lake, Lake Turkana, Kenya

Wetter climatic conditions prevailed across northern and Equatorial Africa during the terminal Pleistocene until the middle Holocene, a climate event known as the “African Humid Period” (AHP). Although hydrologic changes during this period are well-known, very few records of temperature are available for evaluating the mechanisms and dynamics of climate change during the AHP across tropical Africa. To quantify changes in temperature during the onset and termination of the AHP, the TEX86 temperature proxy was used to generate a 14,000 year record of the surface temperature of Lake Turkana. This biomarker and related measures have been used to reconstruct regional and high-latitude paleotemperatures from the oceans and other continental systems, including other large African lakes. Although Lake Turkana’s climate and hydrology are very different from other large African lakes, our reconstruction exhibits a temperature history that shares a number of climatic trends with previous reconstructions. The TEX86 temperatures from Lake Turkana from 14 to 0.4 ka range from 24.3 to 28.6 °C, with a gradual decrease in temperature from early to late Holocene. This cooling roughly follows northern hemisphere summer insolation, similar to the trend observed in Lake Victoria and other regional records. However, the record from Turkana contains many abrupt temperature shifts not seen in other large lakes in the region. Multi-century-scale fluctuations persist through most of the record, and can be attributed to periods of lake mixing. Larger temperature perturbations are likely associated with changes in evaporation and cloud cover.

Elastic and Mechanical Fatigue at High Temperatures of High-Alumina Castables with Addition of Partially Stabilized Zirconia

This work evaluates the impact of added zirconia on the thermomechanical and thermoelastic fatigue properties of high-alumina refractory castables. Three testing scenarios are presented in the study: 1) Resonant Frequency Damping Analysis (RFDA) after cyclic temperature changes with and without mechanical load, 2) Refractoriness under Load (RuL) tests, and 3) results of abrupt temperature shifts between two high temperatures in a special thermal shock furnace. The tested refractory formulations were a reference castable based on tabular alumina and two castables each containing 13.75 mass-% of zirconia. The formulations of the zirconia castables had an addition of either fully-stabilized zirconia doped with 8 mol-% yttria (Y-FSZ) or partially-stabilized zirconia doped with 3 mol-% calcia (Ca-PSZ). The Y-FSZ castable displayed elastic and mechanical behaviour by means of RFDA and RuL similar to the reference sample and had good recovery after thermal shock testing. The Ca-PSZ formulation showed some beneficial toughening through energy dissipation of progressing cracks, but after cooling exhibited the matrix fracturing influence of the martensitic zirconia phase transformation which would negatively impact service life of the refractory.

Controlled Oxygenated Rewarming of Cold Stored Livers Prior to Transplantation: First Clinical Application of a New Concept.

Abrupt temperature shift from hypothermia to normothermia incurred on reperfusion of organ grafts has been delineated as a genuine factor contributing to reperfusion injury and graft dysfunction after transplantation. In a first clinical series of 6 patients, cold-stored livers, all allocated by the rescue offer mechanism by Eurotransplant, were subjected to machine-assisted slow controlled oxygenated rewarming (COR) for 90 minutes before engrafting. A historical cohort of 106 patients basically similar in graft (all rescue offer organs) and recipient factors was used for comparison. The clinical benefit of COR was documented by a significant reduction by approximately 50% in peak serum transaminases after transplantation compared to untreated controls (AST 563.5 vs. 1204 U/L, P = 0.023). After 6 months graft survival was 100% in the COR group and 80.9% in the controls (P = 0.24). Respective patient survival was 100% and 84.7% (P = 0.28). Real-time assessment of glucose concentration in the perfusion solution correlated well with postoperative synthetic graft function (r = 0.78; P < 0.02). All treated recipients had normal liver function after a 6-month follow-up and are well and alive. This first clinical application suggests that controlled graft rewarming after cold storage is a feasible and safe method in clinical praxis and might become an adjunct in organ preservation.

North Andean environmental and climatic change at orbital to submillennial time-scales: Vegetation, water-levels and sedimentary regimes from Lake Fúquene between 284 and 130 ka

We present a record of environmental and climatic changes in the northern Andes during the penultimate interglacial–glacial cycle based on integrated information from pollen and grain size distributions (GSDs). The record reflects the 58.33–26.21m interval of a new sediment core from Lake Fúquene (2540m elevation; 5°N) in the Colombian Andes. The age model is mainly based on cyclostyratigraphy and shows that this core interval reflects the period from 284 to 130ka. The 1cm sample increments yield a resolution of ~60yr. In 2553 samples we analyzed 66 selected pollen and spore taxa with the best known ecological ranges. We reconstructed upper forest line (UFL) positions between ~2000 and ~3400m elevation and the most abrupt temperature shifts ranged up to 10°C/100yr at Terminations II and III. Regional vegetation change is mainly driven by eccentricity (100kyr) and obliquity (41kyr) cycles, while changes in local aquatic vegetation show variability in the obliquity and precession (21kyr) bands. Millennial-scale climate variability reflecting Dansgaard–Oeschger (DO) climate cycles in the upper part of the record, continues in this penultimate intergalcial–glacial cycle strongly suggesting that this variability has a persistent character in Pleistocene vegetation and climate dynamics. Short-lived upslope excursions of the UFL reflect 20 DO-style cycles during marine isotope stages (MIS) 7 and 6. Changes in species composition of montane forest are evident, and trees with most pioneer qualities (Alnus, Morella, Quercus and Weinmannia) migrated at the forefront. Other arboreal taxa like Podocarpus, Miconia, and Hedyosmum mostly followed later. Changes in regional vegetation distribution and forest composition, as well as in local aquatic vegetation and GSD of sediments supplied to the lake, allowed the development of an integrated reconstruction of the biotic and abiotic environments in the drainage basin.

Controlled Rewarming after Hypothermia: Adding a New Principle to Renal Preservation.

Early graft dysfunction due to preservation/reperfusion injury still represents a notable issue after kidney transplantation, affecting long term prognosis of graft viability. One trigger of postischemic cell dysfunction could be recognized in the abrupt temperature shift from hypo‐ to normothermia, leading to mitochondrial dysfunction and proapoptotic signal transduction.Here we propose a technique to cope with this “rewarming injury” by interposing a period of gentle warming up by hypo‐ to subnormothermic machine perfusion of the isolated graft prior to warm reperfusion. Porcine kidneys were subjected either to 18 hours of hypothermic machine preservation (HMP) or 18 hours static cold storage + 3 hours of gentle, machine controlled oxygenated rewarming (COR). Functional integrity was evaluated in both groups by subsequent normothermic reperfusion in vitro.The functional benefit of COR was documented by an approximately twofold increase in renal clearances of creatinine as well as urea upon warm reperfusion, compared to controls. This was accompanied with a notable mitigation of postischemic mitochondrial dys‐homeostasis. COR significantly improved renal oxygen consumption and maintained total NAD tissue content upon reperfusion. Mitochondrial initiation of cellular apoptosis, as evidenced by activation of caspase 9 was also largely prevented after COR but not in controls.The concept of gentle regenerative graft rewarming could become a valuable adjunct in renal transplantation.

Variations in temperature and extent of Atlantic Water in the northern North Atlantic during the Holocene

We compare six high-resolution Holocene, sediment cores along a S–N transect on the Norwegian–Svalbard continental margin from ca 60°N to 77.4°N, northern North Atlantic. Planktonic foraminifera in the cores were investigated to show the changes in upper surface and subsurface water mass distribution and properties, including summer sea-surface temperatures (SST). The cores are located below the axis of the Norwegian Current and the West Spitsbergen Current, which today transport warm Atlantic Water to the Arctic. Sediment accumulation rates are generally high at all the core sites, allowing for a temporal resolution of 10–102 years. SST is reconstructed using different types of transfer functions, resulting in very similar SST trends, with deviations of no more than ±1.0/1.5°C. A transfer function based on the maximum likelihood statistical approach is found to be most relevant. The reconstruction documents an abrupt change in planktonic foraminiferal faunal composition and an associated warming at the Younger Dryas–Preboreal transition. The earliest part of the Holocene was characterized by large temperature variability, including the Preboreal Oscillations and the 8.2k event. In general, the early Holocene was characterized by SSTs similar to those of today in the south and warmer than today in the north, and a smaller S–N temperature gradient (0.23°C/°N) compared to the present temperature gradient (0.46°C/°N). The southern proxy records (60–69°N) were more strongly influenced by slightly cooler subsurface water probably due to the seasonality of the orbital forcing and increased stratification due to freshening. The northern records (72–77.4°N) display a millennial-scale change associated with reduced insolation and a gradual weakening of the North Atlantic thermohaline circulation (THC). The observed northwards amplification of the early Holocene warming is comparable to the pattern of recent global warming and future climate modelling, which predicts greater warming at higher latitudes. The overall trend during mid and late Holocene was a cooling in the north, stable or weak warming in the south, and a maximum S–N SST gradient of ca 0.7°C/°N at 5000cal. years BP. Superimposed on this trend were several abrupt temperature shifts. Four of these shifts, dated to 9000–8000, 5500–3000 and 1000 and ∼400cal. years BP, appear to be global, as they correlate with periods of global climate change. In general, there is a good correlation between the northern North Atlantic temperature records and climate records from Norway and Svalbard.

Thermophysical Properties of NZP Ceramics (A Review)

Data on the thermophysical properties of NZP ceramics with the NaZr2(PO4)3-type structure are summarized. A system of thermal expansion regularities is proposed making it possible to predict NZP materials with controllable thermal expansion, including ultralow expansion with near-zero anisotropy. The thermodynamic functions of the reactions of synthesis of NZP phosphates are calculated and the applicability of ceramic technology is justified. It is proposed to use NZP ceramics as heat-insulating materials capable of working under abrupt temperature shifts.

The effect of abrupt shifts in temperature on the lag phase duration of Escherichia coli and Klebsiella oxytoca

The effect of temperature of incubation on lag times of two gram-negative foodborne bacteria was investigated. Bacteria were instantaneously transferred between temperatures within and beyond the normal physiological temperature range (NPTR). Abrupt temperature shifts induced lag phases, but the degree of the response was dependent on the direction and magnitude of the shift. Temperature downshifts induced larger relative lag times (RLT; the ratio of lag time to generation time), than equivalent upshifts. The hypothesis of Robinson et al. [Int. J. Food Microbiol. 44 (1998) 83] that lag time can be understood in terms of the amount of work to be done to adjust to new environmental conditions and the rate at which that work is done was supported. Deviation of the reported proportionality between lag time and generation time was observed when late-exponential phase cells were subjected to abrupt temperature shifts from beyond the normal physiological range.

Timing of parr-smolt transformation in Atlantic salmon ( Salmo salar): effects of changes in temperature and photoperiod

Water temperature modified the development of smolt characteristics and their duration after an abrupt increase in daylength. A temperature change alone was not a sufficient environmental cue to induce a similar development. To complete parr-smolt transformation after an abrupt increase in daylength, a thermal sum of approximately 400 degree-days (°d) seemed to be necessary. Three groups of Atlantic salmon (1 +) were reared under continuous light (LL) from hatching and then exposed to a 7-week period of short days (LD 8.15:15.45) which ended April 2. In parallel, three groups were exposed to continuous light alone. All six groups were then split into two subgroups of equal numbers. A subgroup from the short-day regime were then mixed with a subgroup from the continuous light regime, to make it possible to continue the experiment with only six tanks and still use duplicates in each combination of light and temperature regime. Thereafter, three temperature regimes were applied: 7.7°C (mean) (4.5–10.8) (range), 10.7°C (7.6–13.7) or 13.7°C (10.5–17.3). Mean temperature from January 31 to April 2 was 9.1°C. The medium temperature regime included no abrupt temperature shift. The short-day regime caused a lower thermal-growth coefficient (TGC) than the continuous regime until the increase in daylength. After this increase and in the rest of the experiment, the TGC was still lowest ( P<0.05) in the groups previously exposed to short days. The short-day regime caused a reduction in the condition factor ( P<0.001) and an increase in gill Na–K-ATPase ( P<0.001) after the increase in daylength in contrast to the continuous light regime. Silvery colour and the ability to regulate plasma Cl − level in a 24-h seawater challenge test developed under both light regimes. The decrease in condition factor was not significantly affected by temperature. Silvering and Na–K-ATPase activity developed more rapidly at the high temperature regime ( P<0.001), but no difference was found between the medium and low temperatures. An elevated gill Na–K-ATPase activity and low plasma Cl − levels in the 24-h seawater challenge test were found for a shorter period at higher temperatures. Plasma Cl − levels below 150 mM were found for approximately 1, 2 or 6 weeks in the high, medium and low temperature regime, respectively. In the continuous light regime, the temperature regime had no significant effect on the development of silvering, condition factor or gill Na–K-ATPase activity, but the ability to regulate plasma Cl − was affected by temperature ( P<0.05).

Acquired Thermotolerance and Stressed-Phase Growth of the Extremely Thermoacidophilic Archaeon Metallosphaera sedula in Continuous Culture

The response of an extremely thermoacidophilic archaeon, Metallosphaera sedula (growth temperature range, 50 to 79(deg)C; optimum temperature, 74(deg)C; optimum pH, 2.0), to thermal stress was investigated by using a 10-liter continuous cultivation system. M. sedula, growing at 74(deg)C, pH 2.0, and a dilution rate of 0.04 hr(sup-1), was subjected to both abrupt and gradual temperature shifts in continuous culture to determine the responses of cell density levels and protein synthesis patterns. An abrupt temperature shift from 74 to 79(deg)C resulted in little, if any, changes in cell density and a small increase in total protein per cell. When the culture temperature was shifted further to 80.5(deg)C, cell density dropped to below 5 x 10(sup6) cells/ml from 10(sup8) cells/ml, leading to washout of the culture. Operation at this temperature and slightly higher temperatures, however, could be achieved by exposing the culture to thermal stress more gradually (0.5(deg)C increments). As a result, stable operation could be maintained at temperatures of up to 81(deg)C, and the washout temperature could be increased to 82.5(deg)C. Continuous culture operation at 81(deg)C for 100 h (stressed phase) led to an approximately sevenfold lower steady-state cell density than that observed for operation at or below 79(deg)C. However, sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis (both one and two dimensional) revealed significantly higher levels (sixfold increase) of a 66-kDa stress response protein (MseHSP60), immunologically related to Thermophilic Factor 55 from Sulfolobus shibatae (J. D. Trent, J. Osipiuk, and T. Pinkau, J. Bacteriol. 172:1478-1484, 1990). If the acclimated culture was returned to a lower temperature (i.e., 74(deg)C), the amount of MseHSP60 returned to levels observed prior to thermal acclimation. Furthermore, when the previously acclimated culture (at 81(deg)C) was shifted back from 74 to 81(deg)C, without going through gradual acclimation steps, the result was the immediate onset of washout, suggesting no residual thermotolerance. This study shows that gradual thermal acclimation of M. sedula could only extend the temperature range of stable growth for this organism by 2(deg)C above its maximal growth temperature, albeit at reduced cell densities. Also, this investigation illustrates the utility of continuous culture for characterizing heat shock response and assessing maximum growth temperatures for extremely thermophilic microorganisms.

Effect of Growth Temperature and Temperature Shifts on Spinach Leaf Morphology and Photosynthesis

The growth kinetics of spinach plants (Spinacia oleracea L. cv Savoy) grown at 5 degrees C or 16 degrees C were determined to allow us to compare leaf tissues of the same developmental stage rather than chronological age. The second leaf pairs reached full expansion at a plant age of 32 and 92 days for the 16 degrees C and 5 degrees C plants, respectively. Growth at 5 degrees C resulted in an increased leaf area, dry weight, dry weight per area, and leaf thickness. Despite these changes, pigment content and composition, room temperature in vivo fluorescence, and apparent quantum yield and light-saturated rates of CO(2) exchange or O(2) evolution were not affected by the growth temperature. Furthermore, 5 degrees C expanded leaves were found to be more resistant to photoinhibition at 5 degrees C than were 16 degrees C expanded leaves. Thus, it is concluded that spinach grown at low temperature is not stressed. However, shifting spinach leaves from 5 degrees C to 16 degrees C or from 16 degrees C to 5 degrees C for 12 days after full leaf expansion had occurred resulted in a 20 to 25% reduction in apparent quantum yields and 50 to 60% reduction in light saturated rates of both CO(2) exchange and O(2) evolution. This was not accompanied by a change in the pigment content or composition or in the room temperature in vivo fluorescence. It appears that leaf aging during the temperature shift period can account for the reduction in photosynthesis. Comparison of cold-hardened and non-hardened winter rye (Secale cereale L. cv Muskateer) with spinach by in vivo fluorescence indicated that rye is more sensitive to both short term and longer duration temperature shifts than is spinach. Thus, susceptibility to an abrupt temperature shift appears to be species dependent.

Effect of Abrupt Temperature Shift on the Growth of Mesophilic and Psychrophilic Yeasts

Effect of Abrupt Temperature Shift on the Growth of Mesophilic and Psychrophilic Yeasts

Effect of abrupt temperature shift on the growth of mesophilic and psychrophilic yeasts.

Exponentially growing cultures of mesophilic and psychrophilic yeasts were subjected to abrupt changes in temperature. Temperature shifts made within the range in which the temperature characteristic, mu, is relatively constant (moderate temperatures) immediately induced growth at the normal exponential rate for the new temperature. Prior incubation at temperatures defined as moderate enabled some yeasts to grow for a few generations at temperatures higher than their normal maximal temperature for growth. Shifts made to or from temperatures above or below those in the moderate temperature range resulted in growth rates that were intermediate between the normal steady-state rates for the initial and final temperatures. A period of transient growth rate at the new temperature outside the moderate temperature range seems to be required before normal steady-state growth rates can be attained after such temperature shifts. The psychrophiles gave transient growth rates only below 10 C, whereas the mesophiles gave transient rates below 20 C. However, the psychrophiles cannot be distinguished from the mesophiles on the basis of the temperature characteristic, mu, which was found to be about 12,000 cal/mole for both types.