Variable Temperature Treatments Research Articles

Unraveling the Molecular Mechanisms by Which the miR171b-SCL6 Module Regulates Maturation in Lilium.

Lilium is one of the most widely cultivated ornamental bulbous plants in the world. Although research has shown that variable temperature treatments can accelerate the development process from vegetative to reproductive growth in Lilium, the molecular regulation mechanisms of this development are not clear. In this study, Lbr-miR171b and its target gene, LbrSCL6, were selected and validated using transgenic functional verification, subcellular localization, and transcriptional activation. This study also investigated the differential expression of Lbr-miR171b and LbrSCL6 in two temperature treatment groups (25 °C and 15 °C). Lbr-miR171b expression significantly increased after the temperature change, whereas that of LbrSCL6 exhibited the opposite trend. Through in situ hybridization experiments facilitated by the design of hybridization probes targeting LbrSCL6, a reduction in LbrSCL6 expression was detected following variable temperature treatment at 15 °C. The transgenic overexpression of Lbr-miR171b in plants promoted the phase transition, while LbrSCL6 overexpression induced a delay in the phase transition. In addition, LbrWOX4 interacted with LbrSCL6 in yeast two-hybrid and bimolecular fluorescence complementation assays. In conclusion, these results explain the molecular regulatory mechanisms governing the phase transition in Lilium.

Pre-exposure to a variable temperature treatment improves the response of Acropora cervicornis to acute thermal stress

Given that global warming is the greatest threat to coral reefs, coral restoration projects have expanded worldwide with the goal of replenishing habitats whose reef-building corals succumbed to various stressors. In many cases, however, these efforts will be futile if outplanted corals are unable to withstand warmer oceans and an increased frequency of extreme temperature events. Stress-hardening is one approach proposed to increase the thermal tolerance of coral genotypes currently grown for restoration. Previous studies have shown that corals from environments with natural temperature variability experience less bleaching when exposed to thermal stress, though it remains unclear if this localized acclimatization or adaptation to variable temperatures can be operationalized for enhancing restoration efforts. To evaluate this approach, fragments from six source colonies of nursery-raised Caribbean staghorn coral (Acropora cervicornis) were treated with a variable temperature regime (oscillating twice per day from 28 to 31 °C) or static temperatures (28 °C) in the laboratory for 89 d. Following this, fragments were subjected to a heat-stress assay (32 °C) for 2 weeks. Corals treated with variable temperatures manifested signs of severe thermal stress later than static temperature laboratory controls as well as untreated field controls collected from the nursery. Furthermore, there was a stark contrast in the physiological response to heat stress, whereby the laboratory and field control groups had a significantly higher incidence of rapid tissue sloughing and necrosis, while the variable temperature-treated corals succumbed to bleaching more gradually. Overall, our data show that pre-acclimation to a variable temperature regime improves acroporid thermotolerance. As corals continue to be outplanted back onto Florida’s changing reef scape, understanding the molecular mechanisms underlying this enhanced thermal tolerance and its endurance in situ will be critical for future research and restoration applications.

Distinct Responses of the Nitrogen-Fixing Marine Cyanobacterium Trichodesmium to a Thermally Variable Environment as a Function of Phosphorus Availability.

Surface temperature in the ocean is projected to be elevated and more variable in the future, which will interact with other environmental changes like reduced nutrient supplies. To explore these multiple stressor relationships, we tested the influence of thermal variation on the key marine diazotrophic cyanobacterium Trichodesmium erythraeum GBRTRLI101 as a function of the limiting nutrient phosphorus (P). Two constant temperature treatments represented current winter (22°C) and summer (30°C) mean values. Three variable temperature treatments fluctuated around the constant control values: Mean 22°C, either ± 2°C or ± 4°C; and mean 30°C ± 2°C. Each thermal treatment was grown under both P-replete (10 μmol/L) and P-limiting conditions (0.2 μmol/L). Effects of thermal variability on Trichodesmium were mainly found in the two winter variable temperature treatments (22°C ± 2°C or ± 4°C). P availability affected growth and physiology in all treatments and had significant interactions with temperature. P-replete cultures had higher growth and nitrogen and carbon fixation rates in the 22°C constant control, than in the corresponding variable treatments. However, physiological rates were not different in the P-replete constant and variable treatments at 30°C. In contrast, in P-limited cultures an advantage of constant temperature over variable temperature was not apparent. Phosphorus use efficiencies (PUE, mol N or C fixed h-1 mol cellular P-1) for nitrogen and carbon fixation were significantly elevated under P-limited conditions, and increased with temperature from 22 to 30°C, implying a potential advantage in a future warmer, P-limited environment. Taken together, these results imply that future increasing temperature and greater thermal variability could have significant feedback interactions with the projected intensification of P-limitation of marine N2-fixing cyanobacteria.

Effects of Cyclical Temperature Fluctuations on Organic Carbon Mineralization in Purple Soil

In the natural state, the soil temperature changes periodically throughout the day, but there is no unified opinion on whether the daily variation of soil temperature affects the mineralization of soil organic carbon. Therefore, the effect of cyclical temperature fluctuations on organic carbon mineralization of purple soil, widely distributed in southwest China, was studied by an incubation experiment in the laboratory. These soils were incubated at three constant temperatures (15, 20, and 25℃) with cyclically fluctuating temperatures (the range was within 15/25℃) and two moisture levels (70% water holding capacity (WHC) and submerged condition). In the entire incubation period (66 d), aerobic and submerged condition, variable temperature (15/25℃) cultivation of purple soil, SOC cumulative mineralization and the mineralization intensity had no obvious differences with constant temperature of 20℃. This indicated that the periodic variable temperature treatment (15/25℃) of SOC mineralization of purple soil with the same accumulated temperature of constant temperature processing (20℃). In addition, except for constant temperature of 15℃, the temperature processing of submerged condition of purple soil SOC cumulative mineralization was significantly higher than 70% WHC treatment (P<0.05). During the entire incubation period, soil microorganism carbon content could not reflect the SOC mineralization differences under constant temperature and cyclically fluctuating temperature. According to two-pool first-order model, the submerged condition can effectively increase the labile SOC pool size of purple soil, but the cyclically fluctuating temperature cannot effectively affect the labile SOC pool size of purple soil.

Response of Arabidopsis primary metabolism and circadian clock to low night temperature in a natural light environment.

Plants are exposed to varying irradiance and temperature within a day and from day to day. We previously investigated metabolism in a temperature-controlled greenhouse at the spring equinox on both a cloudy and a sunny day [daily light integral (DLI) of 7 mol m-2 d-1 and 12 mol m-2 d-1]. Diel metabolite profiles were largely captured in sinusoidal simulations at similar DLIs in controlled-environment chambers, except that amino acids were lower in natural light regimes. We now extend the DLI12 study by investigating metabolism in a natural light regime with variable temperature including cool nights. Starch was not completely turned over, anthocyanins and proline accumulated, and protein content rose. Instead of decreasing, amino acid content rose. Connectivity in central metabolism, which decreased in variable light, was not further weakened by variable temperature. We propose that diel metabolism operates better when light and temperature are co-varying. We also compared transcript abundance of 10 circadian clock genes in this temperature-variable regime with the temperature-controlled natural and sinusoidal light regimes. Despite temperature compensation, peak timing and abundance for dawn- and day-phased genes and GIGANTEA were slightly modified in the variable temperature treatment. This may delay dawn clock activity until the temperature rises enough to support rapid metabolism and photosynthesis.

Impacto de las variaciones de temperatura diaria en la historia natural de los anuros tropicales

Anuran embryos and tadpoles are daily exposed to wide thermal variations in their ponds, with maximum temperatures at midday. The aim of this research was to study the impact of three daily variable thermal environments (with maximum experimental temperatures between 10:00 and 16:00 hours), on the survival, developmental time and body size of metamorphs of four tropical anuran species from lowland habitats in Colombia. A total of 50 embryos (Gosner stage ten) to metamorphosis (Gosner stage 46) of Rhinella humboldti, Hypsiboas crepitans and Engystomops pustulosus were exposed to each one of the three daily variable temperature treatments: high temperature (mean = 27.5 °C; maximum temperature = 34 ± 1 °C; range = 23-35 °C), medium temperature (25.5 °C; 29 ± 1 °C; 23-30 °C), and low temperature (24 °C; 24 ± 1 °C; 23-25 °C). For the other species, Espadarana prosoblepon, 40 embryos to metamorphosis were exposed to each one of the following thermal treatments: high temperature (mean = 22 °C; maximum temperature = 25 ± 1 °C; range = 18-26 °C), medium temperature (20.5 °C; 22 ± 1 °C; 18-23 °C), and low temperature (19 °C; 19 ± 1 °C; 18-20 °C). For all species, the thermal variable environment with the highest temperature showed the greatest accumulated survival, reduced significantly the developmental time from embryos to metamorphs, and the snout-vent-length of metamorphs. Therefore, under field conditions where ponds are exposed to thermally variable environments, the highest temperatures may promote a decrease in the period of time to metamorphosis, and a positive increase for the anuran survival; nevertheless, extreme temperatures were also found in the microhabitat of the species studied, higher than their upper thermal limits reported, which suggest a vulnerable situation for them and other tropical anurans from similar habitats.

Sex‐specific variation in the onset of reproduction and reproductive trade‐offs in a boreal small mammal

In seasonal environments, the optimal onset of reproduction plays a major role in defining the reproductive success of an individual. Environmental cues, like day length, weather conditions, and food, regulate the initiation and termination of the breeding season. Besides the interspecific variation in response to environmental cues, it has been suggested that due to different selection pressures, females and males can have different responses to environmental stimuli. However, this phenomenon has gained relatively little consideration, and the physiological mechanism behind these differences is not well known. Here, we report how two different environmental cues, variability of temperature and nutritional conditions in spring, affect the onset of breeding in a boreal small rodent, the bank vole, Myodes glareolus. We exposed wild‐trapped individuals to four different treatments manipulating temperature (stable vs. variable) and food quality (high vs. low protein content) over five weeks in the laboratory. We monitored body‐mass development, food consumption, and initiation of breeding. We found sex‐specific responses to temperature variability, as males achieved their breeding condition faster in variable temperature treatments, whereas female maturation was delayed. Food quality had no effect on the onset of breeding. To test for possible reproductive trade‐offs caused by reproductive decisions made in early spring, the experiment was continued in large outdoor enclosures. There seemed to be no significant long‐term effects on reproduction, but early summer survival was affected by climate conditions experienced in spring. Our results show clear sex differences in the response to environmental cues regulating the onset of reproduction in bank voles. Hence, our study suggests that when an organism experiences rapid environmental changes, as are occurring on a global scale, divergent cues may lead to a reproductive mismatch between the sexes. This could noticeably decrease the fitness of many seasonally breeding species.

The Effect of Diel Temperature and Light Cycles on the Growth of Nannochloropsis oculata in a Photobioreactor Matrix

A matrix of photobioreactors integrated with metabolic sensors was used to examine the combined impact of light and temperature variations on the growth and physiology of the biofuel candidate microalgal species Nannochloropsis oculata. The experiments were performed with algal cultures maintained at a constant 20°C versus a 15°C to 25°C diel temperature cycle, where light intensity also followed a diel cycle with a maximum irradiance of 1920 µmol photons m−2 s−1. No differences in algal growth (Chlorophyll a) were found between the two environmental regimes; however, the metabolic processes responded differently throughout the day to the change in environmental conditions. The variable temperature treatment resulted in greater damage to photosystem II due to the combined effect of strong light and high temperature. Cellular functions responded differently to conditions before midday as opposed to the afternoon, leading to strong hysteresis in dissolved oxygen concentration, quantum yield of photosystem II and net photosynthesis. Overnight metabolism performed differently, probably as a result of the temperature impact on respiration. Our photobioreactor matrix has produced novel insights into the physiological response of Nannochloropsis oculata to simulated environmental conditions. This information can be used to predict the effectiveness of deploying Nannochloropsis oculata in similar field conditions for commercial biofuel production.

Temporal variation in temperature determines disease spread and maintenance inParameciummicrocosm populations

The environment is rarely constant and organisms are exposed to temporal and spatial variations that impact their life histories and inter-species interactions. It is important to understand how such variations affect epidemiological dynamics in host-parasite systems. We explored effects of temporal variation in temperature on experimental microcosm populations of the ciliate Paramecium caudatum and its bacterial parasite Holospora undulata. Infected and uninfected populations of two P. caudatum genotypes were created and four constant temperature treatments (26°C, 28°C, 30°C and 32°C) compared with four variable treatments with the same mean temperatures. Variable temperature treatments were achieved by alternating populations between permissive (23°C) and restrictive (35°C) conditions daily over 30 days. Variable conditions and high temperatures caused greater declines in Paramecium populations, greater fluctuations in population size and higher incidence of extinction. The additional effect of parasite infection was additive and enhanced the negative effects of the variable environment and higher temperatures by up to 50 per cent. The variable environment and high temperatures also caused a decrease in parasite prevalence (up to 40%) and an increase in extinction (absence of detection) (up to 30%). The host genotypes responded similarly to the different environmental stresses and their effect on parasite traits were generally in the same direction. This work provides, to our knowledge, the first experimental demonstration that epidemiological dynamics are influenced by environmental variation. We also emphasize the need to consider environmental variance, as well as means, when trying to understand, or predict population dynamics or range.

Growth and carbon relations of tree line forming conifers at constant vs. variable low temperatures

1 Natural climatic driven tree line positions follow a mean growing season temperature of around 6 °C in seasonal as well as non-seasonal climates. The influence of constant vs. variable temperature regimes on growth was explored by experimentally exposing 2-year-old seedlings of two montane conifer species (Larix decidua and Pinus mugo) to either constant temperatures of 6 °C or 12 °C, or seasonally and diurnally changing temperatures that varied around the same means (covering a 13-K amplitude across the season). 2 In both species, exposure to 6 °C during a 20-week growing season reduced growth dramatically in constant as well as variable temperature treatments. Nevertheless, new biomass production was still measurable at 6 °C, indicating that a complete cessation of growth occurs at a lower temperature. 3 The biomass increment by the end of the season was hardly influenced by the presence or absence of temperature variation for both, the 6 °C and 12 °C mean treatments. While seasonal and diurnal variable temperatures had a slightly positive effect on growth compared to a full season at constant temperatures in the deciduous Larix, biomass increments of the evergreen Pinus were the same at constant and variable temperature treatments. 4 End of season sugar and starch concentrations in different tissues revealed higher concentrations in cold treated seedlings at constant and varying temperatures. In line with previous field data, low temperatures did not lead to carbon depletion (carbon limitation). We thus assume a stronger impact of cool temperatures on meristematic processes (sink activity) than on photosynthesis (source activity). 5 Synthesis. The similar growth rates of trees in experimentally constant vs. variable growing season temperatures match field observations. Although metabolic responses to temperature are nonlinear, this implies an overall ‘quasi-linear’ response of growth to temperature in trees at their lower temperature limit, which awaits further explanation. The higher concentrations of non-structural carbohydrates in cold treated seedlings support the sink-limitation hypothesis of plant growth in cold climates.

A quick method for thermal diffusivity estimation: Application to several foods

A reliable, quick and userfriendly method for thermal diffusivity estimation has been developed. An appropriate software tool, based on least square optimization of a finite difference solution of Fourier’s equation , has been created and an appropriate measuring cell has been designed and made in order to decrease the systematic error in probe positioning. The method has been experimentally validated and its results have been compared with those obtained by three other available methods. Several foods (tomato products, low-acid pasta sauces, olive pate, confectioner’s custard and apricot jam) were tested and in every case the method proved to be effective. The developed software also allowed estimation of thermal diffusivity via heat penetration curves obtained by variable temperature treatments. So it has been also possible to exclude the contribution of container material from the estimation of thermal diffusivity of liquid packed foods. The proposed method turns out to be a useful tool for scientific design of several processes, such as sterilization and pasteurization, and for correct control of transport, storage and distribution of foods.

Recovery of Phytophthora ramorum Following Exposure to Temperature Extremes

We examined the impact of exposure to high and low temperature extremes on recovery of Phytophthora ramorum both as free chlamydospores and within infected rhododendron tissue over a 7-day period. Chlamydospores held in moistened sand were incubated at 30, 35, 40, 0, -10, and -20°C for up to 7 days. Infected Rhododendron 'Cunningham's White' leaf disks held in sandy loam, loam, or sand at two different soil moisture levels also were subjected to these temperatures for up to 7 days, and to a variable temperature regimen for 12 weeks. Recovery was characterized by growth of P. ramorum on selective agar medium following exposures to temperature treatments. Chlamydospores held in moistened sand showed a high rate of recovery at 30°C, steadily declining recovery at 35°C, and no recovery at 40°C over the 7-day period. Chlamydospores were recovered from 0°C after 7 days, with little or no recovery observed at -10 or -20°C. In infected rhododendron tissue, P. ramorum was recovered at 20 and 30°C after 7 days but, at 35°C, the pathogen showed a decline within 2 days and no recovery by 4 days. A 40°C treatment allowed no recovery of P. ramorum from infected tissue after 2 days. For cold treatments, P. ramorum was recovered from infected leaf disks at 0 and -10°C after 7 days. At -20°C, recovery declined rapidly after 1 to 3 days and no recovery was obtained after 4 days. P. ramorum showed nearly 100% recovery from leaf disks subjected to a 12-week variable temperature treatment based on ambient summer temperatures in Lewisburg, TN. The results suggest that P. ramorum is capable of surviving some highly adverse temperature conditions for at least 7 days both as free chlamydospores in sand and within infected host tissue. Thus, P. ramorum present as free chlamydospores or within tissue of infected plants shipped to the eastern United States has the potential to survive some of the adverse conditions encountered in summer and winter in many eastern states.

Development and Emergence of the Alfalfa Pollinator &lt;I&gt;Megachile rotundata&lt;/I&gt; (Hymenoptera: Megachilidae)

Megachile rotundata (F.), a gregarious, cavity-nesting, leaf-cutting bee, is used throughout North America for the pollination of alfalfa, Medicago sativa L., seed crops. We examined the influence of various temperature regimes on development, survival, emergence, and longevity in both nondiapausing and diapausing forms of this species. In general, development rates increased with increasing constant temperatures used in this study (18, 22, 26, and 29°C), but the 26 and 29°C treatments were clearly superior as rearing temperatures for immatures. In diapausing individuals, a variable temperature treatment 14:27°C (8:16 h daily cycle, mean 22°C) reduced the length of prepupal and pupal development stages following incubation in the early summer when compared with individuals reared under the constant 22°C treatment. We discuss the importance of differing temperature regimes on M. rotundata development, survival, and longevity over the entire life cycle. We also discuss the importance of making a connection between immature development and sufficient wintering conditions to postdiapause development, a topic that has received much more attention in the literature.

Effect of temperature fluctuations and food supply on the growth and metabolism of juvenile sea scallops ( Placopecten magellanicus )

On the eastern shore of Nova Scotia late summer atmospheric systems cause upwelling of shelf water; the associated temperature variations of 10 °C with a 6 to 8 d period are comparable in magnitude to the seasonal variation. A laboratory study was undertaken to assess the effects of these temperature fluctuations on sea scallop (Placopecten magellanicus) growth and metabolism. In a factorial design, scallops were subjected to constant (10 °C) or a variable (6 to 15 °C) 8 d temperature cycle, and either a low (seston in filtered seawater) or high (seston supplemented with cultured phytoplankton) food diet. During the 48 d experiment scallop mortality was low and growth positive in all treatments. Shell and total tissue growth rate did not differ between temperature treatments, but growth in the high food treatments was 40 to 50% higher than in the low food treatments. However, soft tissue (excluding adductor) growth did show a temperature treatment effect; growth rates were significantly higher in the fluctuating temperature treatment, due in part to greater gonad development. Weight-standardized rates of scallop oxygen consumption (V sO2 , μmol O2 g−1 h−1) were 20 to 25% higher in high food than in low food treatments, consistent with the expected increase in respiration due to the higher growth rates. Scallop metabolism did not acclimate to the fluctuating temperature cycle; V sO2 and ammonium excretion (V sNH+ 4, μmol O2 g−1 h−1) remained dependent on ambient temperature throughout the experiment. V sNH+ 4 Q10 (2.77) was higher than V sO2 Q10 (2.01) which was reflected in a decrease in the O:N ratio at 15 °C, indicating a shift toward increased protein catabolism and a stressed state. At 10 °C, V sO2 and V sNH+ 4 in the variable temperature treatments were 15 to 18% lower than in the constant temperature treatments, a difference that was not detected in growth measurements. Results demonstrate that the metabolism of Placopecten magellanicus, unlike some bivalve species, is tightly coupled to fluctuations in ambient temperature. Although an absence of compensatory acclimation had a minimal effect on growth in this study, if high temperatures were combined with low food conditions a reduction in scallop production could result.

Application of Time‐Temperature Indicators in Monitoring Changes in Quality Attributes of Perishable and Semiperishable Foods

ABSTRACTThe response of full‐history time‐temperature indicators attached to different packages containing five perishable and semiperishable foods (tomatoes, naked and wrapped lettuce, canned fruitcake, and UHT sterilized milk) was studied. The products were stored at constant and variable temperature treatments simulating commercial storage and handling practices. Changes in specific quality attributes were periodically evaluated by means of sensory analysis, and the monitored attributes were correlated with indicator response. Statistical analysis showed significant correlations (p &lt; 0.05) between the indicators studied and quality changes in tomatoes and UHT sterilized milk.

Monitoring quality changes in stored frozen strawberries with time-temperature indicators

Commercially available time-temperature indicators were examined as quality change monitors for frozen strawberries during storage. Strawberries were stored under constant (−12, −18 and −35°C) and variable temperature treatments, and quality changes were evaluated at three-week intervals by sensory and chemical analysis methods. Indicator response was strongly correlated with firmness and ascorbic acid change in strawberries stored at −12°C.

Performance Evaluation of Time‐Temperature Indicators for Frozen Food Transport

ABSTRACTTime‐temperature indicators from four different manufacturers were evaluated on the basis of their response to constant and variable storage temperature treatments. Several time‐temperature indicators of each type were exposed to constant temperatures of ‐18°C and +5°C, and a variable temperature treatment which could simulate the conditions encountered in a frozen food transport. The discussion presents the time‐temperature response of the indicators tested, the average endpoint response recorded, and comments on the characteristic assets and limitation of the indicators investigated.

Effects of light and temperature on leaf anatomy and photosynthesis in Fragaria vesca.

Fragaria vesca, the woodland strawberry, was grown under a series of controlled environments including variations in light intensity, average temperatures, and temperature amplitude around a constant mean. Observations on CO2 exchange capacities, leaf anatomy, and cell ultrastructure were made for each treatment to determine relationships between these variables. With increasing light intensity, leaf thickness, leaf density, and mesophyll cell surface area and volume per leaf surface area increased. Net photosynthesis (NPS) per leaf weight decreased with increasing light pretreatment while NPS per area increased from low to medium intensity, then decreased at the highest intensity. Depression of photosynthesis at the highest light pretreatment may have been due to massive starch accumulation in the chloroplasts associated with the sodium vapor lamps used. Correlation of all anatomical variables was highly significant with dark respiration and NPS per dry weight but insignificant for NPS per leaf area. In the variable temperature treatments, photosynthetic acclimation occurred with a shift in optimum temperature for NPS in the direction of prevailing growth temperature. Absolute rates were highest at moderate pretreatment temperatures and were reduced by extreme growth temperatures. Thick leaves with low density mesophyll became thinner and more dense with increasing growth temperature corresponding to an increase in maximum net photosynthetic rates. Leaves became thicker and more dense at the highest temperatures, but with an increase in cell damage and indications of changes in metabolic pathways. Highest correlations for gas exchange rates were with specific leaf weight (weight per area). Correlation with other anatomical variables were scattered or insignificant. It was concluded that adaptation to a range of environmental conditions cannot be consistently attributed to changes in mesophyll cell volume or surface area.