Sudden Temperature Drop Research Articles

Rapid cold hardening response of the phytoseiid mite Neoseiulus striatus: increased cold tolerance but not reduced predation

The predatory mite Neoseiulus striatus (Wu) (Acari: Phytoseiidae), which has been found on maize plants in Inner Mongolia, is regarded as a promising biological control agent of small sucking pests, especially Tetranychid mites. Temperature is an important abiotic factor, and a sudden drop in temperature may affect its performance when released in areas with big circadian temperature differences. Rapid cold hardening is a type of phenotypic plasticity that allows ectotherms to quickly enhance their cold tolerance in response to a brief chilling exposure. However, it is not clear whether N. striatus possesses such plasticity. To understand how this species of phytoseiid mite copes with short-term low-temperature stress, its rapid cold hardening response was studied in the laboratory by first exploring its critical temperature. Then, the effects of exposure to a series of temperatures (0, 5, 10, 15, and 20°C) for different durations on the survival of N. striatus were investigated to determine the optimal temperature and duration for cold hardening. Moreover, the effect of cold hardening on the consumption of Tetranychus urticae by N. striatus was also investigated, as was the response of immature stages. The critical temperature for N. striatus was - 15°C, at which its survival dropped below 10%. An exposure to 5°C for 2h was optimal for rapid cold hardening, efficiently increasing survival in N. striatus. Rapid cold hardening was found in all developmental stages of N. striatus, and there was no significant effect of exposure on the consumption of spider mites. Our study shows that exposure to low temperatures during a limited period can enhance the cold hardiness but not reduce predation by N. striatus, which will be advantageous to its field applications during a period of large diurnal temperature fluctuations.

Effects of Cold-Surge-Induced Nearshore Seawater Icing on the Eukaryotic Microalgal Community in Aoshan Bay, Qingdao.

Climate change has led to frequent cold surges in mid-latitudes, resulting in sudden temperature drops and icing of nearshore seawater, which may be affecting the eukaryotic microalgal community. In this paper, we investigated the differences between a eukaryotic microalgal community in sea ice and in seawater during the seawater freezing, due to the cold surge in Aoshan Bay, Qingdao, China, in January 2021. The results showed that the eukaryotic microalgal community in the sea ice and in the seawater was similar in composition at the phylum and genus levels, but that its relative abundances differed. In the seawater, the eukaryotic microalgal genera were dominated by Chaetoceros, while its relative abundance was significantly lower in the sea ice, probably because the cold-surge-induced seawater icing existed only for a short period of time, and Chaetoceros had not yet adapted to the rapid environmental changes in the sea ice. The relative abundance of Bathycoccus in the sea ice was higher, and showed a significant positive correlation with nitrite and silicate, while the relative abundance of Micromonas in the sea ice was also significantly higher than in the seawater, which may be related to the elevated CO2 concentration in the sea ice. This study demonstrates that although the seawater icing due to the cold surge was short, it may have affected the seawater eukaryotic microalgal community, to a certain extent.

Study on the Properties and Benefits of a Composite Separator Layer in Airport Cement Concrete Pavement

A composite separator layer in Portland cement concrete pavement, formed by a lower bearing layer and micro surfacing, was seldom used in airport pavement, but it has great application potential. This paper studied the properties of the composite separator layer and its benefits for pavement. The basic properties investigated in the study were resilient modulus and interlayer property between the separator layer and concrete. The resilient modulus of the micro surfacing was tested to calculate the modulus of the whole separation layer. The interlayer shearing test was done on core specimens using a self-developed facility that can apply load in the normal direction. Shearing test results show that temperature affects the shape of the shearing curve and normal stress linearly affects the stable shear force. Additionally, an in-situ erosion test was carried out to prove the anti-scouring property of the separator layer. Furthermore, a finite element model (FEM) model was established to study the influence of the composite separator layer. The FEM employed the modulus test results and the measured interlayer characteristic. The interlayer characteristic was simplified into a two-stage constitutional model. Monitored data on the mechanical response of the pavement structure in an airport validated the FEM model. Results show that the separator layer reduces the chance of contraction crack under the sudden temperature drop in the concrete slab before sawing. FEM results show that though the separator layer slightly increases the tensile stress of concrete, the tensile stress is greatly reduced if the slab develops voids in the future. The most significant benefit of the separation layer is it reduces the chance of void occurrence so that the lifespan of pavement with a separator layer is improved compared to regular pavements which frequently have voids beneath the slab. With the finite element model results and cumulative fatigue life equations, the separator layer was estimated to elongate the pavement service life for years, depending on the time voids appear.

Insulation Test of the Nitrogen Blanket Transformer under Sudden Temperature Drop

During the transformer operation, it is a common condition that the oil temperature decreases due to sudden rainstorms. Because the nitrogen layer is set to contact the transformer oil in the nitrogen blanket transformer directly, the influence of nitrogen dissolution and precipitation on the insulation characteristics is very important. In this paper, the effect of nitrogen is analyzed. First, the electrical field under the nitrogen bubble effect is simulated. Second, the sudden temperature drop situation is developed based on the reformed transformer. Last, the insulation changes are analyzed by partial discharge data. According to the analysis, the sudden temperature drop won’t influence the transformer operation.

Analysis of Temperature Sensitivity and Cracking Causes in Suspension Bridge Anchorage Based on Numerical Simulation

Mass concrete, a common structure in bridge engineering, is frequently threatened by cracking. Based on the gravity anchorage of a long-span suspension bridge that has been in operation for more than ten years, the causes of the cracks growing year by year in the anchorage were analyzed in this paper. The refined numerical model of the anchorage was established using the space finite-element software. Taking full account of the environmental characteristics of the bridge site, the temperature sensitivity of the anchorage was simulated and analyzed, as well as the stress distributions on the surface of each side of the anchorage at different temperatures. The calculation results showed that there is little correlation between anchorage cracking and anchorage bolt force. Under condition two, the temperature increased 20°C, the principal tensile stress of anchorage reached to 1.5 times of the allowable stress. Under condition six, the anchorage surface temperature at 40°C suddenly dropped to 20°C, and the principal tensile stress reached 2.4 times the allowable stress. Thus, under the dual effects of internal and external constraints, the cold hit effect of the mass concrete anchorage resulted in the sudden drop of the surface temperature of the anchorage concrete to produce “internal constraint cracks”, and the overall temperature rise caused the expansion of the anchorage concrete to produce “external constraint cracks.” The two types of cracks led to the vertical cracks of the anchorage. Additionally, the environmental and construction factors were the main causes of the cracking in transverse construction joints. Finally, the anchorage was reinforced with high-performance concrete with an anticrack reinforcement mesh, which presented good results in the follow-up observation, providing a certain reference value for similar projects.

Influence of Mine Environmental Factors on the Liquid CO2 Pipeline Transport System with Great Altitude Difference.

To prevent coal spontaneous combustion and store CO2 in the coal mine, it is necessary to establish a fire-prevention pipeline transport system which continuously injects a large amount of liquid CO2 from the ground to the underground area directly. At present, few studies are focused on the law of liquid CO2 transport with great altitude difference. Moreover, the complex transport environment in the coal mine affects the design and application of the pipeline transport system for ground direct injection of liquid CO2. This study explores the influence of environmental factors at different depths in the coal mine on the liquid CO2 transport. Excessive altitude difference, ambient temperature and airflow velocity may lead to the boiling of liquid CO2 during pipeline transport and a sudden drop in CO2 temperature and pressure, which may cause danger in the pipeline transport system. The critical insulation thickness is determined based on the occurrence of the boiling of CO2. In addition, the influence law of adding an insulating layer of different thicknesses to the CO2 pipeline system is obtained. This study is of great significance to the establishment of a pipeline system that safely transports liquid CO2 from the ground to the underground mine.

Effects of temperature shock on the survival of different life stages of large yellow croaker (Larimichthys crocea) by simulated power plant cooling water

Seawater temperatures have increased with global climate change. Coolant water discharged from coastal nuclear power-generating and coal-powered plants, coupled with already increasing seawater temperatures, can adversely affect local fish communities. A sudden drop in temperature caused by the winter shutdown of power plants can also affect fish health and behavior. To assess the effects of temperature change on fish populations, we subjected early life stages of the once commercially important large yellow croaker (Larimichthys crocea) to various water temperature experiments. Fertilized eggs showed the highest hatching rate at 23.4°C and the lowest rate of deformity in hatched larvae at 23.0°C. We determined the incipient lethal temperature for each life stages using derivation models. Ranges between the upper and lower incipient lethal temperatures increased during development from yolk-sac larvae to juveniles, especially in response to cold shock, indicating that later developmental stages in this species are more tolerant of temperature fluctuations. However, thermal tolerance is not solely determined by life stage. Our results suggest that rapid changes in seawater temperature caused by power plant coolant water discharges may significantly affect early developmental stages of fish. Critical thermal maximum tests indicate that the seawater heating rate is significantly negatively correlated with survival time and affects the critical thermal maximum value of L. crocea. On the basis of our determination of incipient lethal temperatures, emergency measures could be taken to avoid adverse economic and ecological impacts due to changes in seawater temperature caused by coolant water discharges.

A coolant supply strategy based on cutting temperature prediction during the 3-axis end-milling of Ti-6Al-4V

Due to serious environmental concerns, the need to reduce energy consumption is emerging in many industries, including manufacturing. In this study, an energy-saving strategy is proposed by controlling the coolant supply in end-milling based on cutting temperature prediction. For cutting temperature prediction, various attempts have been made based on numerical simulation or empirical modeling, both requiring significant efforts. This study aimed to construct a simple but accurate temperature prediction model by analyzing temperature behaviors in end-milling. Here, two sets of experiments were conducted. First, the change in cutting temperature according to the cutting length was observed. Second, Nathan Cook's model, which is the cutting temperature prediction model for orthogonal cutting, was analyzed and applied to the end-milling. The model and experimental results showed that the heat was not accumulated according to the cutting length and the feed was the dominant factor influencing the cutting temperature. The temperature prediction model could be easily constructed with a small number of experiments. As a proof of concept, the coolant supply control based on the temperature prediction was shown. The suggested strategy reduced the energy consumption by 20.9 % without a sudden drop in temperature or surface quality. It is expected that this research can contribute to the development of the coolant supply strategy in industrial fields with ease of temperature prediction and implementation of the strategy.

Insights into Environmental Drivers on the Reproductive Cycle of Diopatra neapolitana (Polychaeta: Onuphidae).

Simple SummaryThe environmental variables that drive the reproductive cycle of Diopatra neapolitana were studied in a population of Ría de Vigo (NW Spain). The identity of the species was corroborated using the six diagnostic morphological characters. A discontinuous reproductive cycle was observed, with a period of proliferation and oocyte maturation from January to September, asynchronous spawning events from July to October and a resting period in November and December. The reproductive cycle seems to be conditioned by the photoperiod and the water temperature. In particular, the sudden drop in water temperature, as a result of coastal upwelling processes that typically occur in the summer months of the study area, was found to induce spawning in this species.The reproductive cycle of Diopatra neapolitana was studied over two years in Redondela (NW Spain), considering both the monthly evolution of the percentage of individuals with oocytes and the variation of the mean oocyte size. Moreover, since three other species of Diopatra have recently been documented in regions geographically close to NW Spain, we first confirmed the identity of this species by carrying out a morphological identification of a representative number of the specimens collected. Our data showed a discontinuous reproductive season, with a period of proliferation and maturation of oocytes from January to September and asynchronous spawning events between July and October. Then, a resting period in the months of November and December was observed. We also explored the influence of some relevant environmental factors (namely, water temperature, photoperiod, salinity, primary production and upwelling index) on the observed reproductive cycle. The results suggest that water temperature is one of the most important drivers of the reproductive cycle for this species. Particularly, in Ría de Vigo, the reproductive cycle seems to be influenced by upwelling events of deep cold water that occur frequently between March and September, and that could act as a spawning-inducing switch.

Safety analysis of thermal equipment and piping systems in the CANDU nuclear power plant subjected to thermal shocks

Due to the complexity of nuclear power plants and the risks of damage that may occur during their existence, it is necessary to pay more attention to the safety features. An important influence is the operational temperature of thermal equipment and pipes, especially within the primary circuit, as the coolant is radioactive and in case of damage would cause natural disasters. An assessment of thermal reliability of nuclear power plant equipment and systems is necessary for optimization in the design stage. High thermal shocks with severe and sudden drop in coolant temperature represent a high potential for damage, especially in propagation of existing cracks, under stress due to high pressures. On the other hand, vibrations produced by variable fluid flow conditions or of mechanical origin may induce vibratory fatigue, which combined with thermal fatigue may influence the system’s safety. This study aims to develop computational models for thermal fatigue in pipelines in nuclear power plants, highlighting pressurized thermal shock analysis, temperature distribution diagram along the wall thickness, stress distribution diagram by wall thickness, factor distribution diagram stress intensity, critical crack size diagram, critical reference temperature of nil ductility transition (RTNDT) diagram. Evaluation of these diagrams were performed using the calculation programs Nuclear Piping Integrity Expert System (NPIES) and Reactor Vessel Integrity Evaluation System (RVIES).

Rub-impact behaviors of a multistage bladed drum rotor under high time-varying temperature

In a gas turbine, the multistage bladed drum rotor often operates under high time-varying ambient temperature. Thermal deformations of the thin drum could lead to the rub-impact fault between multistage blade rows and the outer casing, which may cause damage to the blades or even the whole machine. Due to the complexity of the thermoelastic coupling solution, rub-impact characteristics of this kind of rotor system are not clear. This study develops a multistage bladed drum rotor model with the rub-impact fault induced by high time-varying temperature. A solution process for the thermoelastic dynamics analysis of the multistage bladed drum rotor system is proposed, combining experimental, numerical, and analytical methods. According to temperature characteristics in a gas turbine, the effect of the high-temperature environment, heating, fluctuating temperature rise, and cooling on the rub-impact fault is the main emphasis of the study. The high-temperature environment could cause a rub-impact fault for the multistage bladed drum rotor. The sudden increase of the exhaust temperature leads to paroxysmal vibrations, which could induce tip rub or make a slight rub-impact fault into a severe accident. Large fluctuation during temperature rise induces the rub-impact fault and even leads to the continuous aggravation of the rub-impact fault. Fortunately, reducing an appropriate exhaust temperature can eliminate or weaken the rub-impact fault and avoid shock vibrations induced by the sudden drop of the high ambient temperature at the same time. Besides, more blade rows could aggravate this kind of rub-impact phenomenon for the multistage bladed drum rotor.

Formation of Dust Clumps with Sub-Jupiter Mass and Cold Shadowed Region in Gravitationally Unstable Disk around Class 0/I Protostar in L1527 IRS

We have investigated the protostellar disk around a Class 0/I protostar, L1527 IRS, using multiwavelength observations of the dust continuum emission at λ = 0.87, 2.1, 3.3, and 6.8 mm, obtained by the Atacama Large Millimeter/submillimeter Array and the Jansky Very Large Array (VLA). Our observations achieved a spatial resolution of 3–13 au and revealed an edge-on disk structure with a size of ∼80–100 au. The emission at 0.87 and 2.1 mm is found to be optically thick, within a projected disk radius of r proj ≲ 50 au. The emission at 3.3 and 6.8 mm shows that the power-law index of the dust opacity (β) is β ∼ 1.7 around r proj ∼ 50 au, suggesting that grain growth has not yet begun. The dust temperature (T dust) shows a steep decrease with T dust ∝ r proj −2 outside the VLA clumps previously identified at r proj ∼ 20 au. Furthermore, the disk is gravitationally unstable at r proj ∼ 20 au, as indicated by a Toomre Q parameter value of Q ≲ 1.0. These results suggest that the VLA clumps are formed via gravitational instability, which creates a shadow on the outside of the substructure, resulting in the sudden drop in temperature. The derived dust masses for the VLA clumps are ≳0.1 M J. Thus, we suggest that Class 0/I disks can be massive enough to be gravitationally unstable, which may be the origin of gas giant planets in a 20 au radius. Furthermore, the protostellar disks could be cold due to shadowing.

Integrative Proteome and Phosphoproteome Profiling of Early Cold Response in Maize Seedlings.

Cold limits the growth and yield of maize in temperate regions, but the molecular mechanism of cold adaptation remains largely unexplored in maize. To identify early molecular events during cold shock, maize seedlings were treated under 4 °C for 30 min and 2 h, and analyzed at both the proteome and phosphoproteome levels. Over 8500 proteins and 19,300 phosphopeptides were quantified. About 660 and 620 proteins were cold responsive at protein abundance or site-specific phosphorylation levels, but only 65 proteins were shared between them. Functional enrichment analysis of cold-responsive proteins and phosphoproteins revealed that early cold response in maize is associated with photosynthesis light reaction, spliceosome, endocytosis, and defense response, consistent with similar studies in Arabidopsis. Thirty-two photosynthesis proteins were down-regulated at protein levels, and 48 spliceosome proteins were altered at site-specific phosphorylation levels. Thirty-one kinases and 33 transcriptional factors were cold responsive at protein, phosphopeptide, or site-specific phosphorylation levels. Our results showed that maize seedlings respond to cold shock rapidly, at both the proteome and phosphoproteome levels. This study provides a comprehensive landscape at the cold-responsive proteome and phosphoproteome in maize seedlings that can be a significant resource to understand how C4 plants respond to a sudden temperature drop.

A Case Analysis of Dust Weather and Prediction of PM10 Concentration Based on Machine Learning at the Tibetan Plateau

Dust weather is common and disastrous at the Tibetan Plateau. This study selected a typical case of dust weather and analyzed its main development mechanism in the northeast of the Tibetan Plateau, then applied six machine learning methods and a time series regression model to predict PM10 concentration in this area. The results showed that: (1) The 24-h pressure change was positive when the front intruded on the surface; convergence of vector winds with a sudden drop in temperature and humidity led by a trough on 700 hPa; a “two troughs and one ridge” weather situation appeared on 500 hPa while the cold advection behind the trough was strong and a cyclone vorticity was formed in the east of Inner Mongolia. (2) The trajectory of air mass from the Hexi Corridor was the main air mass path influencing Xining City, in this case, since a significant lag in the peak of PM10 concentration appeared in Xining City when compared with Zhangye City. (3) The Multiple Linear Regression was not only timely and effective in predicting the PM10 concentration but had great abilities for anticipating the transition period of particle concentration and the appearance date of maximum values in such dust weather. (4) The MA and MP in the clean period were much lower than that in the dust period; the PM10 of Zhangye City as an eigenvalue played an important role in predicting the PM10 of Xining City even in clean periods. Different from dust periods, the prediction effect of Random Forest Optimized by Bayesian hyperparameter was superior to Multiple Linear Regression in clean periods.

Mechanical Behavior and Optimization of Tubing String with Expansion Joint during Fracturing in HTUHP Wells

During the formation testing in high-temperature (HT) and ultra-high-pressure (UHP) wells, one of the major challenges is packer failure in the downhole caused by high-rate fracturing. In such a case, the axial shrinkage trend of the tubing string could be caused by the sudden drop in temperature, but the actual axial length of the tubing string would not change because of the constraints at wellhead and packer. Therefore, this could lead to the upward pull-out of the packer that is due to excessive load from the tubing string. This out-of-control downhole pressure often leads to irreversible consequences, even well abandonment. An expansion joint, as a movable splicer, has the characteristic of mitigating packer load, which can theoretically enhance packer safety. To study the protective effect of an expansion joint on the packer quantitatively, the microscopic characteristics and macroscopic properties of the tubing material (13Cr110) are obtained through experimental tests. Moreover, the mechanical properties of the material at different temperatures are also tested. Then, the testing results are extended to modeling the finite element model (FEM) of the whole section of tubing string with the expansion joint—casing and simulating its internal force changes under fracturing conditions with different injection rates. Our simulation results indicated that an expansion joint can significantly change the distribution of the internal forces in the tubing string, and this change can effectively reduce the load on the packer. Eventually, a tubing string buckling identification plate that considers the injection rate and expansion joint–packer length is obtained to optimize the placement of an expansion joint in the tubing string. Our work can provide a detailed theoretical reference and basis for an expansion joint in field application.

Cold temperature and sudden temperature drop as novel risk factors of asthma exacerbation: a longitudinal study in 18 Chinese cities

BackgroundFew studies have explored the role of ambient temperature in asthma exacerbation. ObjectiveWe aimed to explore the association of temperature with diurnal peak expiratory flow (PEF) variation and asthma exacerbation. MethodWe developed a longitudinal study among asthmatic adults in 18 Chinese cities. Subjects recorded PEF in dynamic pulmonary function monitoring from 2017 to 2020. Linear mixed-effect model and generalized additive model with distributed non-linear models were used to assess the effect of temperature and temperature change between neighboring days (TCN) on diurnal PEF variation and the risk of asthma exacerbation. ResultWe evaluated a total of 79,217 daily PEF monitoring records from 4467 adult asthmatic patients. There were significant increase of diurnal PEF variation and higher risk of asthma exacerbation with cold and sudden temperature drop. Compared with the referent temperature (99th percentile, 32 °C), exposure to moderate cold (25th percentile, 3 °C) and extreme cold (2.5th percentile, −7 °C) was associated with elevations of 1.28% and 1.16% in diurnal PEF variation over lag 0–2 days, respectively. The odds ratios of asthma exacerbation (determined by diurnal PEF variation >20%) at the two temperature cutoffs were 1.68 and 1.73. A sudden temperature drop (2.5th percentile of TCN, −5 °C) was associated with 1.13% elevation in diurnal PEF variation, and with increased risk of asthma exacerbation (odd ratio = 1.50) over lag 0–4 days. ConclusionThis large multicenter study provided the first-hand empirical evidence that cold temperature and a temperature drop may increase the risk of asthma exacerbation.

Nonequilibrium molecular dynamics simulations of mass transfer on transient direct-contact condensation

Direct-contact condensation plays an important role in both natural and engineering sciences. Nonequilibrium molecular dynamics (MD) simulations were conducted in this study to examine the mass transfer during transient direct-contact condensation. We designed an innovative method to construct a nonequilibrium liquid–vapor surface with sudden temperature and pressure drop between the two adjacent sides of the interface. This state was consistent with the initial state of real direct-contact condensation and verified the effectiveness of this method. The MD results indicated that a non-negligible anisotropic region existed near the liquid–vapor interface in the preliminary stage of direct-contact condensation when the nonequilibrium and transient phenomena were obvious. The velocity distributions of the vapor were time- and space-dependent, and the condensation and evaporation coefficients were not equal. Validation of the Schrage relation was conducted to calculate the net condensation rate. The results indicated that the Schrage relation modified by the temperature anisotropy and the evaporation coefficient shows better consistency with the MD results. For engineering applications, the time- and space-dependencies of velocity distributions are regarded having minimal influence on the validity of modified Schrage relation.

Denoising MAX6675 reading using Kalman filter and factorial design

This paper aims to tune the Kalman filter (KF) input variables, namely measurement error and process noise, based on two-level factorial design. Kalman filter then was applied in inexpensive temperature-acquisition utilizing MAX6675 and K-type thermocouple with Arduino as its microprocessor. Two levels for each input variable, respectively, 0.1 and 0.9, were selected and applied to four K-type thermocouples mounted on MAX6675. Each sensor with a different combination of input variables was used to measure the temperature of ambient-water, boiling water, and sudden temperature drops in the system. The measurement results which consisted of the original and KF readings were evaluated to determine the optimum combination of input variables. It was found that the optimum combination of input variables was highly dependent on the system's dynamics. For systems with relatively constant dynamics, a large value of measurement error and small value of process noise results in higher precision readings. Nevertheless, for fast dynamic systems, the previous input variables' combination is less optimal because it produced a time-gap, which made the KF reading differ from the original measurement. The selection of the optimum input combination using two-level factorial design eased the KF tuning process, resulting in a more precise yet low-cost sensor.

C Group-Mediated Antibiotic Stress Mimics the Cold Shock Response.

A temperature downshift results in stabilized secondary structure formation in mRNA that halts translation to which Escherichia coli responds by synthesizing a set of proteins termed as cold shock proteins (Csps). To cope with the sudden temperature drop, gene expression patterns are reprogrammed to induce Csps at the cost of other proteins. Out of the nine homologous proteins in the CspA family, CspA, CspB, CspG, and CspI have major roles in protecting the cell under a cold shock. Additionally, a subset of Csps has conferred the organism an ability to adapt to various stresses along the lines of nutrient deprivation, oxidative, heat, acid, and antibiotic stresses. Stressors like C group translational inhibitors stall the translational apparatus and produce a response similar to that observed under a temperature downshift. Conditions set by the antibiotic therefore elicit a cold shock response and induce the major Csps, thereby pointing out to a common mechanism existing between the two. In the current review, we briefly describe the induction of E. coli Csps under an antibiotic stress acquired from data published previously and help establish the role of Csps in protecting the cell against the inducing agents and as a participant in the organisms' complex stress response network.

Limited light intensity and low temperature: Can plants survive freezing in light conditions that more accurately replicate the cold season in temperate regions?

Plants in temperate regions have evolved mechanisms that enable them to survive sudden temperature drops. Experiments with plants grown in long-day conditions, in which they are most sensitive to freezing stress, indicate that the cold acclimation mechanism is light-dependent and does not fully operate under low light intensity. However, winter annuals like Arabidopsis thaliana Col-0 germinate in the fall, overwinter as rosettes, and thus must acclimate under short photoperiods and low irradiance. Thus, we have analysed effects of variations in light intensity in plants grown under short-day photoperiod at the 1.14 growth stage (14 rosette leaves). Plants were acclimated at 4 °C for seven days under control and limited-light conditions: 100 and 20 μmol m-2s-1 photosynthetic photon flux density (PPFD), respectively. All cold-acclimated plants accumulated molecular markers reportedly associated with acquired freezing tolerance, including proline, sucrose, cold-responsive gene transcripts, dehydrins and low temperature-induced proteins. Observed changes (and similarity of freezing stress survival rates of plants in both light conditions) indicate that low PPFD did not inhibit the cold acclimation process. The molecular analysis identified distinct PPFD-specific adaptation mechanisms manifested in contrasting contents of anthocyanins, cytokinin conjugates, photosystem proteins, and enzymes involved in protein, energy, and reactive oxygen species metabolism. Finally, the results identify putative proteins and metabolite markers correlating with susceptibility to freezing stress of non-acclimated plants grown under low PPFD. Our data show that Arabidopsis plants grown under short-day photoperiods can be fully cold-acclimated under limited light conditions, employing standard and PPFD-specific pathways.