Short-Term Changes in Heat Tolerance in the Alpine Cushion Plant Silene acaulis ssp. excapa [All.] J. Braun at Different Altitudes

Abstract: The habit of cushion growth positively affects plant temperature but at the same may increase the risk of occasional overheating. In order to determine the adaptive response to short-term heat stress, we exposed S. acaulis cushions at field sites to controlled heat treatments using infrared lamps. Natural diurnal changes in heat tolerance were monitored at alpine sites and at a site distinctly below the natural distribution boundary, where higher temperatures were expected. The range of heat tolerance limits in summer, 45.5 - 54.5 °C (9 K), exceeded that reported for other alpine species (0.1 - 5 K) and even that for total seasonal changes (5 - 8 K). Heat tolerance either increased or decreased on most days (80 %). The maximum diurnal increase was + 4.7 K. Under the experimental conditions heat hardening started at leaf temperatures around 30 °C and proceeded at mean rates of 1.0 ± 0.5 K/h. The onset of functional disturbances in photosystem II also occurred at 30 °C. Heating rates exceeding those naturally found above 30 °C (> 10 K/h) appeared to retard heat hardening. During summer average leaf temperature maxima were 12.4 K (600 m) and 13.0 K (1945 m) higher than air temperature which corroborates the heat trapping nature of cushion plants. At 600 m, as compared to 1945 m, cushions experienced significantly higher leaf temperature maxima (+ 8.8 K) and exceeded 30 °C on most days (80 %). This resulted in a significantly higher heat tolerance (LT₅₀) at 600 m (51.7 ± 0.2 °C) than at 1945 m (49.8 ± 0.2 °C). The fast short-term changes of heat tolerance in summer help S. acaulis to cope with the occasional diurnal short-term heat stress associated with cushion growth.     

Effect of pre- and post-heat shock temperature on the persistence of thermotolerance and heat shock-induced proteins in Listeria monocytogenes

The effect of incubation temperature, before and after a heat shock, on thermotolerance of Listeria monocytogenes at 58°C was investigated. Exposing cells grown at 10°C and 30°C to a heat shock resulted in similar rises in thermotolerance while the increase was significantly higher when cells were grown at 4°C prior to the heat shock. Cells held at 4°C and 10°C after heat shock maintained heat shock-induced thermotolerance for longer than cells held at 30°C. The growth temperature prior to inactivation had negligible effect on the persistence of heat shock-induced thermotolerance. Concurrent with measurements of thermotolerance were measurements of the levels of heat shock-induced proteins. Major proteins showing increased synthesis upon the heat shock had approximate molecular weights of 84, 74, 63, 25 and 19 kDa. There was little correlation between the loss of thermotolerance after the heat shock and the levels of these proteins. Thermotolerance of heat shocked and non-heat shocked cells was described by traditional log-linear kinetics and a model describing a sigmoidal death curve (logistic model). Employing log-linear kinetics resulted in a poor fit to a major part of the data whereas a good fit was achieved by the use of a logistic model.     

The influence of the rate of temperature change on the activation of dormant seeds of Rumex obtusifolius L.

1. One temperature shift from 20 to 30°C in darkness induces 30–40% germination in Rumex obtusifolius seeds. The same germination percentages are found with heat treatment varying between 1 and 6h duration, indicating that the total heat sum of the temperature shift is not important.
2. Germination is greatly enhanced by three consecutive heat shifts of 1h at 30°C separated by 1h periods at 20°C.
3. The seeds are activated to a small extent after a slow warming (+2°Ch^–1) from 20 to 30°C, followed by incubation for 1h at 30°C. Germination is much higher after rapid heating (+10°Ch^–1) to 30°C, followed by 1h incubation at this temperature. Repeated fast heating treatments on four consecutive days enhances germination. Moderately rapid heatings (+3·3°Ch^–1) give intermediate results.
4. The rate of cooling does not influence the germination percentage. Cooling alone cannot induce germination.
5. Heating alone from 15 to 25°C without cooling also activates germination. In this temperature range the seeds are more activated by rapid warming than by slow warming.
6. The ecological relevance of the response to different warming rate is discussed. The insensitivity of seeds to a slow warming might keep deeply buried seeds in a dormant stage.     

Combining heat treatment and subsequent incubation temperature to prevent growth from spores of non-proteolytic Clostridium botulinum

Refrigerated processed foods of extended durability rely on a mild heat treatment combined with refrigerated storage to ensure microbiological safety and quality. The principal microbiological safety risk in foods of this type is non-proteolytic Clostridium botulinum. In this article the combined effect of mild heat treatment and refrigerated storage on the time to growth and probability of growth from spores of non-proteolytic Cl. botulinum is described. Spores of non-proteolytic Cl. botulinum (two strains each of type B, E and F) were heated at 90°C for between 0 and 60 min and subsequently incubated at 5°, 10° or 30°C in PYGS broth in the presence or absence of lysozyme. The number of spores that resulted in turbidity depended on the combination of heat treatment, incubation time and incubation temperature they received. Heating at 90°C for 1 or more min ensured a 10⁶ reduction when spores were subsequently incubated at 5°C for up to 23 weeks. Heating at 90°C for 60 min ensured a 10⁶ reduction over 23 weeks when subsequent incubation was at 10°C in the presence of added lysozyme. The same treatment did not reduce the spore population by 10⁶ when subsequent incubation was at 30°C.     

Influence of the sporulation temperature upon the heat resistance of Bacillus subtilis

The influence of different sporulation temperatures (30, 37, 44 and 52°C) upon heat resistance of Bacillus subtilis was investigated.
Heat resistance was greater after higher sporulation temperatures. Relation of heat resistance and temperature of sporulation was not linear over all the range of temperatures tested. Heat resistance increased about tenfold in the range of 30–44°C. Sporulation at 52°C did not show any further increase in heat resistance.
This effect was constant over all the range of heating temperatures tested (100–120°C). z value remained constant ( z = 9°C).
Greater heat resistances at higher temperatures of sporulation were not due to selection of more heat resistant cells by a higher sporulation temperature. Spores obtained from cells incubated at 32 or 52°C always possessed heat resistances that corresponded to the sporulation temperature regardless of the incubation temperature of their vegetative cells.     

Synchronization of larval emergence in winter moth (Operophtera brumata L.) and budburst in pedunculate oak (Quercus robur L.) under simulated climate change

1. The hypothesis that a 3 °C elevation in temperature and doubled CO₂ concentration would have no effect on the synchronization of winter moth egg hatch with budburst in oak was tested by comparing the separate and interactive effects of ambient and elevated (+ 3 °C) temperature and ambient and elevated (doubled to 340 p.p.m.) CO₂ in eight experimental Solardomes. In addition, an outdoor control was compared with the ambient temperature/CO₂ treatment combination.
2. Elevated temperature accelerated darkening (preceding egg hatch by about 5–10 days) and hatching of eggs developing off the trees; elevated CO₂ had no effect. The same effects were observed in eggs developing on the trees.
3. Within treatments, date of egg hatch was the same on trees with early or late budburst.
4. Egg darkening and budburst were closely synchronized at both ambient and elevated temperatures.
5. Both eggs and trees required fewer cumulative heat units (day degrees > 4 °C), for hatching and budburst, respectively, at ambient than elevated temperatures. The requirements in the outdoor control treatment were similar to those in the ambient Solardome treatment.
6. Egg hatch between 10 and 25 °C, on a temperature gradient in the laboratory, required a constant number of heat units; fewer were required below 10 °C.
7. Elevated temperatures, in the Solardomes and the field, delayed adult emergence from the pupae.
8. The results suggest that a general increase in temperature with climatic change would not affect the closeness of the synchronization between egg hatch of winter moth and budburst of oak.     

Elevation of the heat resistance of Salmonella typhimurium by sublethal heat shock

The survival of Salmonella typhimurium after a standard heat challenge at 55°C for 25 min increased by several orders of magnitude when cells grown at 37°C were pre-incubated at 42°, 45° or 48°C before heating at the higher temperature. Heat resistance increased rapidly after the temperature shift, reaching near maximum levels within 30 min. Elevated heat resistance persisted for at least 10 h. Preincubation of cells at 48°C for 30 min increased their resistance to subsequent heating at 50°, 52°, 55°, 57° or 59°C. Survival curves of resistant cells were curvilinear. Estimated times for a '7D' inactivation increased by 2.6- to 20-fold compared with cells not pre-incubated before heat challenge.     

The effect of temperature and growth rate on the susceptibility of Listeria monocytogenes to environmental stress conditions

R.A. PATCHETT, N. WATSON, P.S. FERNANDEZ AND R.G. KROLL. 1996. The effect of growth temperature and growth rate on the susceptibility to heat and pH stress were investigated in Listeria monocytogenes grown in continuous culture where these two growth variables could be varied independently of each other, and in batch culture. After growth at 30°C or 10°C at constant growth rate, or at 30°C at different growth rates, cells did not differ in their resistance to heat at 55°C. Cells grown at 30°C were more resistant to acid stress at pH 2.5 than cells grown at the same growth rates at 10°C. Cells grown at low growth rate at 30°C gave greater resistance to acid stress than those grown at high growth rate. Growth temperature and growth rate had independent effects on the susceptibility of L. monocytogenes to acid stress conditions. This may have implications for the survival of L. monocytogenes in acidic foods.     

Responses of poplar to chilling temperatures: proteomic and physiological aspects

Abstract: The effects of cold acclimation on primary metabolism in actively growing poplar ( Populus tremula L. × P. tremuloides Michaux) were studied. Three-month-old poplar plants were exposed to chilling stress (4 °C) and compared to plant material kept at a control temperature (23 °C). This treatment did not affect the survival of the plants but growth was almost stopped. The freezing tolerance of the adult leaves increased from - 5.7 °C for the control plants to - 9.8 °C after 14 days of exposure to 4 °C. During acclimation, the evolution of soluble carbohydrate contents was followed in the leaves. Sucrose, glucose, fructose and trehalose accumulated rapidly under chilling conditions, while raffinose content increased after one week at 4 °C. Proteomic analyses, by bidimensional electrophoresis, performed during this stage revealed that a large number of proteins had higher expression, while much less proteins disappeared or had a lower abundance. MALDI-TOF-MS analyses enabled ca. 30 spots to be proposed for candidate proteins. Among the accumulating or appearing proteins proposed, about a third presented similarities with chaperone-like proteins (heat shock proteins, chaperonins). In addition, dehydrins and other late embryogenesis abundant proteins, i.e., stress-responsive proteins, detoxifying enzymes, proteins involved in stress signalling and transduction pathways were also activated or newly synthesised. Finally, cold exposure induced a decrease in the candidate proteins involved in cell wall or energy production.     

Temperature- and salinity-dependent development of a Nordic strain of Ichthyophthirius multifiliis from rainbow trout

During the twentieth century evidence was presented which suggested the presence of various strains and races of the parasite Ichthyophthirius multifiliis Fouquet. However, ecological profiles of various parasite isolates from different climatic zones are sparse. Such stringent characterizations of parasite development at defined abiotic conditions could provide valuable criteria for the different races; profile comparison from various localities is one way to differentiate these strains. Baseline investigations were therefore performed on the associations between abiotic factors (temperature/salinity) and the development of theronts in tomocysts of I. multifiliis isolated from rainbow trout in a Danish trout farm. It was shown that tomocyst formation and theront development took place between 5 and 30°C. Development rates and sizes of theronts were clearly affected by temperature: theronts escaped tomocysts already after 16–27 h at 25°C and 30°C, whereas this process took 8–9 days at 5°C. Likewise, theront size decreased steadily from a maximum of 57.4 × 28.6 μm at 5°C to 28.6 × 20.0 μm at 30°C. This size variation was only partly associated with the number of theronts that appeared at different temperatures. The lowest number of theronts escaping from one tomocyst was indeed found at 5–7°C (mean 329–413). At 11.6, 17.0 and 21°C, the highest number of theronts appeared (mean 546–642). However, at 25 and 30°C, the number decreased (458 and 424, respectively). Additional studies on the salinity dependent development of the parasite (at 11.6°C) showed that salinities above 5 p.p.t. totally inhibited development. Even at 5 p.p.t. the developmental time significantly increased and the number of theronts produced from one tomocyst decreased.     

Involvement of oestrogens in sexual differentiation of gonads as a function of temperature in turtles

Abstract. To investigate the possible involvement of oestrogens in the phenomenon of temperature sex-reversal in the turtle Emys orbicularis , the effects of oestrone, oestradiol and an antioestrogen. tamoxifen, on sexual differentiation of gonads were examined at a male-producing temperature of 25° C and at a female-producing temperature of 30° C. When oestrone or oestradiol were injected into eggs incubated at 25° C just before or at the beginning of the thermosensitive period, the gonads differentiated into ovaries instead of testes. Conversely, when tamoxifen was injected, at the same stages, into eggs incubated at 30° C, epithelial cords or tubes, similar to potential seminiferous cords, differentiated in the interior part of the gonads. However, an ovarian-like cortex persisted at their surface. At 25° C, treatment with tamoxifen or with both tamoxifen and oestradiol also resulted in differentiation of ovotestes. These experiments show that tamoxifen binding to oestrogen receptors prevented the inhibitory action of oestrogens on testicular cord development. Maintenance (at 30° C) or development (at 25° C) of ovarian cortex in the presence of tamoxifen can be expected from an agonistic action of this drug, as already described. Preliminary data on steroid content in the gonads indicate that, during the early stages of the thermosensitive period, the level of estrogens is higher at 30° C than at 25° C. It is proposed that in species displaying temperature sensitivity for the sexual differentiation of gonads, temperature acts on the processes regulating the synthesis or the activity of cyto-chrome-P450 aromatase.     

Influence of food quality and temperature on life history characteristics of the parthenogenetic mayfly, Cloeon triangulifer

SUMMARY. 1. Laboratory and field data indicate that Cloeon triangulifer McDunnough has at least three generations per year in White Clay Creek (Pennsylvania, U.S.A.).
2. The duration of the egg stage ranged from 5 days at 30°C to about 90 days at 10°C.
3. Larvae completed development (i.e. first instar to adult) in 27 days at 25°C, 45 days at 20°C, and 179 days at 10°C on an algal diet dominated by diatoms.
4. Larvae reared on hickory leaves completed development in 30 days at 25°C but died prior to metamorphosis at 10, 15 and 20°C.
5. Adult size (i.e. body length, wing length and dry mass) and fecundity were inversely related to rearing temperature for all laboratory and field experiments.
6. The significant interaction of food quality and temperature suggest that these factors may be important in understanding geographic variation in the life history of C. triangulifer.     

Genetic engineering in rainbow trout, Salmo gairdnerii Richardson, by the suppression of meiotic and mitotic metaphase

Diploid gynogenesis in rainbow trout eggs was induced by a heat shock applied after fertilization with UV irradiated sperm. Survivals were high when the heat treatment was given soon after fertilization at times corresponding to the completion of egg meiosis but were low at all other times. Increases in survival occurred, however, when the heat treatment was given at 4 h 30 min and 5 h after fertilization, with an incubation temperature of 10°C, and at 9 h after fertilization, with an incubation temperature of 5°C. Electrophoretic analysis at three enzyme loci demonstrated a significant increase in homozygous offspring from eggs given these later heat treatments when compared to offspring from eggs treated between 40 and 70 min after fertilization, again with an incubation temperature of 10°C. There was still a significant frequency of heterozygotes in these groups, however, probably of spontaneous origin via diploidization during meiosis. No tetraploid alevins were observed after normal fertilization and attempted suppression of first mitosis.     

Resistance of Escherichia coli grown at different temperatures to various environmental stresses

Aims:  To study the influence of growth temperature on the resistance of Escherichia coli to three agents of different nature: heat, pulsed electric field (PEF) and hydrogen peroxide.
Methods and Results:  Escherichia coli cells were grown to stationary phase at 10°C, 20°C, 30°C, 37°C and 42°C. Survival curves to a heat treatment at 57·5°C, to a PEF treatment at 22 kV cm⁻¹ and to 40 mmol l⁻¹ hydrogen peroxide were obtained and fitted to a model based on the Weibull distribution to describe and compare the inactivation. Time to inactivate the first log cycle of the population at 57·5°C of cells grown at 42°C was sixfold higher than that corresponding to cells grown at 10°C. On the contrary, cells grown at 10°C and 20°C were more resistant to PEF and hydrogen peroxide treatments.
Conclusions:  The influence of growth temperature on bacterial resistance depends on the stress applied. Cells grown at higher temperatures were more heat resistant, but more sensitive to PEF and hydrogen peroxide.
Significance and Impact of the Study:  Results obtained in this investigation help in understanding the physiology of bacterial resistance and the inactivation mechanisms of different technologies.     

Influence of the incubation temperature after heat treatment upon the estimated heat resistance values of spores of Bacillus subtilis

S. CONDÓN, A. PALOP, J. RASO AND F.J. SALA. 1996. The influence of the incubation temperature on the estimated heat resistance for survivors after heat treatment was investigated. The survival curves and the D _t values of spores of Bacillus subtilis heated at different temperatures in pH 7 buffer, obtained after incubating survivors at different temperatures (30, 37, 44 or 51°C), were compared. The incubation temperature influenced the profile of survival curves. Lower incubation temperatures led to bigger D _t values and longer shoulders. D _t values obtained after incubating at 30°C were higher (x3 approx.) than those obtained by incubating at 51°C. The incubation temperature did not modify z values ( z = 9.1). These results show that shoulders are not only due to the activation of dormant spores but also to heat damage repair mechanisms. From the profile of survival curves at different incubation temperatures it would seem that heat damage is accumulative. Cells can repair the initial heat injury, but the accumulation of injuries would eventually make the damage irreversible.     

Respiratory Q10 of marigold (Tagetes patula) in response to long-term temperature differences and its relationship to growth and maintenance respiration

Acclimation of respiration to temperature is not well understood. To determine whether whole plant respiration responses to long-term temperature treatments can be described using the Q₁₀ concept, the CO₂ exchange rate of marigolds ( Tagetes patula L. 'Queen Sophia'), grown at 20°C or 30°C, was measured for 62 days. When plants of the same age were compared, plants grown at 20°C consistently had a higher specific respiration (R_spc) than plants grown at 30°C (long-term Q₁₀= 0.71–0.97). This was due to a combination of greater dry mass at 30°C and a decrease in R_spc with increasing mass. When plants of the same dry mass were compared, the long-term Q₁₀ was 1.35–1.55; i.e. R_spc was higher at 30°C than at 20°C. Whole plant respiration could be accurately described by dividing respiration into growth and maintenance components. The maintenance respiration coefficient was higher at 30°C than at 20°C, while the growth respiration coefficient was lower at 30°C, partly because of temperature-dependent changes in plant composition. These results suggest difficulties with interpreting temperature effects on whole plant respiration, because conclusions depend greatly on whether plants of the same age or mass are compared. These difficulties can be minimized by describing whole plant respiration on the basis of growth and maintenance components.     

Enhancing effects of heat shock and gibberellic acid on the thermotolerance in etiolated Vigna radiata. I. Physiological aspects on thermotolerance

The effect of heat shock on the thermotolerance of etiolated mung bean seedlings ( Vigna radiata L. cv. Wilczek) and the effects of gibberellic acid (GA) were studied. The potentially lethal temperature of etiolated mung bean seedlings was 45°C. But, when seedlings were pretreated with a heat-shock period at 40°C for 1 h before incubation at 45°C, they become thermotolerant and survived the 45°C treatment. The addition of actinomycin D or cycloheximide during the heat-shock period decreased the subsequent thermotolerance of the seedlings. Depending upon the time of its application, GA appeared to have multiple effects: (1) when applied during the 40°C heat-shock period, GA enhanced the heat-shock effect; (2) when applied during the 45°C potentially lethal temperature period, GA enhanced the subsequent growth of hypocotyls. This suggests that GA makes the seedlings tolerant to the potentially lethal temperature; (3) when GA was applied during a following 25°C growth period to seedlings which had been exposed first to 40°C and then 45°C, it promoted growth, suggesting that GA enhanced the restoration of the seedlings from high temperature damage. The role of GA and heat shock in the acquisition of thermotolerance in etiolated mung bean seedlings are discussed.     

Effect of culture age, pre-incubation at low temperature and pH on the thermal resistance of Aeromonas hydrophila

S. CONDON, M.L. GARCIA, A. OTERO AND F.J. SALA. 1992. The thermal resistance of Aeromonas hydrophila strain NCTC 8049 was determined within the range 48°-65°C with a thermoresistometer TR-SC and McIlvaine buffer. The effects of culture age, pre-incubation at 7°C and the pH of the heating menstruum were evaluated. The pattern of thermal death was dependent on culture age. Cells heated in the late logarithmic growth phase (15 h at 30°C) were twice as resistant as those in the early stage (5 h at 30°C), and the maximum D -value was obtained after 72 h incubation (5.5 total increase). The age of the cells did not affect z -values significantly. The heat resistance of cells incubated for 48 h at 30°C increased (twice) after holding at 7°C for 72 h. Pre-incubation at low temperature of older cultures (72 h, 30°C) did not influence their D -values. Maximum heat resistance was found at pH 6.0 and minimal at pH 4.0. Decreasing the pH from 6.0 4.0 reduced D -values by a factor of 5. Although the strain studied was heat-sensitive ( D _55°C= 0.17 min; z = 5.11°C), survivor curves of cultures older than 50 h showed a significant tailing. Organisms surviving in the tails were only slightly more resistant than were the original population.     

The effect of temperature on the ability of Tilapia mossambica Peters to enter deep water

The ability of adult Tilapia mossambica Peters to enter deep water was determined at 15, 22 and 30°C. At 30°C adults compensate to about 20m depth but at 15°C to only 7 m. Compensation is more rapid at high than at low temperatures. T. mossambica haemoglobin has a marked Root effect which is the same at 22 and 30°C. The oxygen affinity of the haemoglobin is higher at 15°C than at 30°C. There was no measurable difference in the rate of passive oxygen diffusion across the swimbladder wall in the temperature range 15–30°C. It is concluded that the ability to enter deeper water at higher temperatures is related to decreased oxygen affinity of the haemoglobin and higher rates of oxygen secretion and blood circulation.     

The relative importance of temperature and diet to larval development and adult size of the winter stonefly, Soyedina carolinensis (Piecoptera: Nemouridae)

SUMMARY. 1. Soyedina carolinensis Claassen, a leaf shredding stonefly, was reared in a series of three laboratory experiments from early instar to adult on different species of deciduous leaves and at various constant and fluctuating temperature regimes.
2. Experiment 1, which involved rearing larvae on fourteen different leaf diets at ambient stream temperatures, showed that diet significantly affected larval growth and adult size but did not affect overall developmental time.
3. Experiment 2, which involved rearing larvae on five different leaf diets at each of three fluctuating temperature regimes (viz ambient White Clay Creek (WCC), ambient WCC+3°C, and ambient WCC+6°C), showed that: (i) adding 6°C to the normal temperature regime of WCC was lethal to 99% of the larvae regardless of diet; and (ii) warming WCC by 3°C did not affect developmental time but did significantly reduce adult size relative to adults reared at WCC temperatures on certain diets.
4. Experiment 3, which involved rearing larvae on five different leaf diets at each of five constant temperatures (viz 5, 10, 15, 20, 25°C), showed that: (i) temperature significantly affected the mortality, growth, and development time of larvae whereas diet only affected larval growth and mortality; (ii) temperatures at or near 10°C yielded maximum larval growth and survival for most diets; (iii) at 5°C, larval mortality was high and growth was low resulting in a few small adults for most diets; (iv) larval mortality was at or near 100% at 15°C regardless of diet; and (v) no larvae survived at 20 and 25°C.