Cold Acclimation Research Articles

Integrated cellular response of the zebrafish (Danio rerio) heart to temperature change.

A decrease in environmental temperature represents a challenge to the cardiovascular system of ectotherms. To gain insight into the cellular changes that occur during cold exposure and cold acclimation we characterized the cardiac phosphoproteome and proteome of zebrafish following 24 h or one week exposure to 20 oC from 27 oC; or at multiple points during six weeks of acclimation to 20 oC from 27 oC. Our results indicate that cold exposure causes an increase in mitogen-activated protein kinase signaling, the activation of stretch sensitive pathways, cellular remodeling via ubiquitin-dependent pathways, and changes to the phosphorylation state of proteins that regulate myofilament structure and function including desmin and troponin T. Cold acclimation (2-6 weeks) led to a decrease in multiple components of the electron transport chain through time, but an increase in proteins for lipid transport, lipid metabolism, the incorporation of polyunsaturated fatty acids into membranes and protein turnover. For example, there was an increase in the levels of apolipoprotein C, prostaglandin reductase-3, and surfeit locus protein 4, involved in lipid transport, lipid metabolism, and lipid membrane remodeling. Gill opercular movements suggests that oxygen utilization during cold acclimation is reduced. Neither the amount of food consumed relative to body mass nor body condition were affected by acclimation. These results suggest that while oxygen uptake was reduced, energy homeostasis was maintained. This study highlights that the response of zebrafish to a decrease in temperature is dynamic through time and that investment in the proteomic response increases with the duration of exposure.

Physiological and molecular responses of 'Hamlin' sweet orange trees expressing the VvmybA1 gene under cold stress conditions.

Overexpression of VvmybA1 transcription factor in 'Hamlin' citrus enhances cold tolerance by increasing anthocyanin accumulation. This results in improved ROS scavenging, altered gene expression, and stomatal regulation, highlighting anthocyanins' essential role in citrus cold acclimation. Cold stress is a significant threat to citrus cultivation, impacting tree health and productivity. Anthocyanins are known for their role as pigments and have emerged as key mediators of plant defense mechanisms against environmental stressors. This study investigated the potential of anthocyanin overexpression regulated by grape (Vitis vinifera) VvmybA1 transcription factor to enhance cold stress tolerance in citrus trees. Transgenic 'Hamlin' citrus trees overexpressing VvmybA1 were exposed to a 30-day cold stress period at 4°C along with the control wild-type trees. Our findings reveal that anthocyanin accumulation significantly influences chlorophyll content and their fluorescence parameters, affecting leaf responses to cold stress. Additionally, we recorded enhanced ROS scavenging capacity and distinct expression patterns of key transcription factors and antioxidant-related genes inthe transgenic leaves. Furthermore, VvmybA1 overexpression affected stomatal aperture regulation by moderating ABA biosynthesis, resulting in differential responses in a stomatal opening between transgenic and wild-type trees under cold stress. Transgenic trees exhibited reduced hydrogen peroxide levels, enhanced flavonoids, radical scavenging activity, and altered phytohormonal profiles. These findings highlighted the role of VvmybA1-mediated anthocyanin accumulation in enhancing cold tolerance. The current study alsounderlines the potential of anthocyanin overexpression as a critical regulator of the cold acclimation process by scavenging ROS in plant tissues.

Using a thermal gradient table to study plant temperature signalling and response across a temperature spectrum

Plants must cope with ever-changing temperature conditions in their environment. In many plant species, suboptimal high and low temperatures can induce adaptive mechanisms that allow optimal performance. Thermomorphogenesis is the acclimation to high ambient temperature, whereas cold acclimation refers to the acquisition of cold tolerance following a period of low temperatures. The molecular mechanisms underlying thermomorphogenesis and cold acclimation are increasingly well understood but neither signalling components that have an apparent role in acclimation to both cold and warmth, nor factors determining dose-responsiveness, are currently well defined. This can be explained in part by practical limitations, as applying temperature gradients requires the use of multiple growth conditions simultaneously, usually unavailable in research laboratories. Here we demonstrate that commercially available thermal gradient tables can be used to grow and assess plants over a defined and adjustable steep temperature gradient within one experiment. We describe technical and thermodynamic aspects and provide considerations for plant growth and treatment. We show that plants display the expected morphological, physiological, developmental and molecular responses that are typically associated with high temperature and cold acclimation. This includes temperature dose-response effects on seed germination, hypocotyl elongation, leaf development, hyponasty, rosette growth, temperature marker gene expression, stomatal conductance, chlorophyll content, ion leakage and hydrogen peroxide levels. In conclusion, thermal gradient table systems enable standardized and predictable environments to study plant responses to varying temperature regimes and can be swiftly implemented in research on temperature signalling and response.

Waterlogging‐Induced Changes in ABA, Carbohydrates and CBF6 Modify Freezing Tolerance in Prehardened Festuca pratensis

ABSTRACTChanges in precipitation and snow melt during warmer winters can increase low‐temperature waterlogging. Such conditions may bring about different effects when compared with a single stress trigger, such as low‐temperature or water excess. The effects of waterlogging are clearly related to water temperature, and the consequences of water excess might be less severe, as more oxygen is dissolved in colder water. The effect of waterlogging during cold acclimation (CA) is poorly understood; most experiments concerning water excess are performed at relatively high‐temperatures. In this study, we examined the effect of 3 weeks of waterlogging (approx. 2 cm above the soil level) on CA in Festuca pratensis Huds. (Fp), a cool‐season grass. Measurements were taken before CA (after prehardening, before flooding) and after 3 weeks of CA in waterlogged (treated) and non‐waterlogged (control) plants. The work included: (i) freezing tolerance test (regrowth after freezing), (ii) analysis of abscisic acid (ABA) content in the leaf, (iii) leaf stomatal conductance, (iv) leaf water content, (v) carbohydrates analysis, including fructans, and (vi) transcript levels of selected genes involved in freezing tolerance, ABA signalling and fructan biosynthesis. The aim of the study was to test a hypothesis that low‐temperature waterlogging in Fp enhances freezing tolerance (plant regrowth after freezing) related to increased ABA accumulation, increased C‐repeat‐binding transcription factor expression and/or increased carbohydrate accumulation, including fructans. Two out of four genotypes exhibited enhanced regrowth following freezing due to waterlogging relative to control. Principal component analysis (PCA) revealed a positive correlation between ABA levels and freezing tolerance in both treatments, with a more pronounced effect observed in the waterlogged plants. However, the phytohormone played different roles in these two treatments. In the context of low‐temperature waterlogging, ABA may be involved in the dehydration tolerance response in genotypes suffering from physiological drought, as well as the induction of C‐repeat‐binding transcription factors (CBFs) and sucrose, which may improve freezing tolerance. The increased fructan amount and polymerisation degree due to waterlogging may provide a carbohydrate sink to maintain a high photosynthetic efficiency, but are not directly responsible for freezing tolerance changes. The study indicates that tolerance mechanisms of Fp exposed to low‐temperature waterlogging involve maintaining a high photosynthetic rate, as well as oxidative and dehydration stress tolerance.

Does deacclimation reverse the changes in structural/physicochemical properties of the chloroplast membranes that are induced by cold acclimation in oilseed rape?

Winter crops acquire frost tolerance during the process of cold acclimation when plants are exposed to low but non-freezing temperatures that is connected to specific metabolic adjustments. Warm breaks during/after cold acclimation disturb the natural process of acclimation, thereby decreasing frost tolerance and can even result in a resumption of growth. This phenomenon is called deacclimation. In the last few years, studies that are devoted to deacclimation have become more important (due to climate changes) and necessary to be able to understand the mechanisms that occur during this phenomenon. In the acclimation of plants to low temperatures, the importance of plant membranes is indisputable; that is why the main aim of our studies was to answer the question of whether (and to what extent) deacclimation alters the physicochemical properties of the plant membranes. The studies were focused on chloroplast membranes from non-acclimated, cold-acclimated and deacclimated cultivars of winter oilseed rape. The analysis of the membranes (formed from chloroplast lipid fractions) using the Langmuir technique revealed that cold acclimation increased membrane fluidity (expressed as the Alim values), while deacclimation generally decreased the values that were induced by cold. Moreover, because the chloroplast membranes were penetrated by lipophilic molecules such as carotenoids or tocopherols, the relationships between the structure of the lipids and the content of these antioxidants in the chloroplast membranes during the process of the cold acclimation and deacclimation of oilseed rape are discussed.

Small Stomates and Xylem Vessels Associated With Freeze Tolerance in Winter Barley

ABSTRACTFreeze tolerance is a complex agronomic trait that is difficult to evaluate in the field because of year‐to‐year variation in weather. Discovering plant characteristics closely related to freeze tolerance would enable more effective selection for this important trait. To explore possible physiological mechanisms and search for useful characteristics related to freeze tolerance in winter barley, we conducted field and growth chamber experiments with seven freeze‐tolerant and seven freeze‐susceptible genotypes that exhibited contrasting winter survival in preliminary field screenings. In a 2‐year field experiment, malondialdehyde, proline and water‐soluble carbohydrate concentrations were measured during cold acclimation and deacclimation to investigate differences in osmoregulation and membrane stability between freeze‐tolerant and freeze‐sensitive genotypes. All parameters varied by sampling year, and significant differences between freeze tolerance groups were found mainly during cold deacclimation in the spring. In growth chamber experiments, the size of xylem vessels and stomates was measured with and without cold acclimation. Freeze‐tolerant genotypes had smaller xylem vessels and stomates than freeze‐sensitive genotypes with and without cold acclimation, and small stomatal length was associated with a small xylem vessel area. Thus, it may be possible to improve freeze tolerance in winter barley by selecting smaller xylem and stomate cells. This study also validated germplasms of winter barley with differential freeze tolerance for future projects on breeding for improving winter hardiness and on plant physiology and genetics in response to freezing stress.

Changes in protein expression in Acacia mearnsii De Wild (black wattle) as a result of exposure to frost-inducing temperatures

Acacia mearnsii De Wild (black wattle) is one of the most important forestry crops in South Africa. The bark of this species contains high-quality tannins, while its wood is used for wood chips, charcoal and mining timber. One of the main problems faced by black wattle farmers is frost damage, thus there is an urgent need to develop frost-tolerant black wattle varieties. A quick method for the screening of frost tolerance variation would be beneficial for black wattle breeders and would result in the need for fewer families to undergo field trials. Frost tolerance in plants is directly related to their ability to undergo cold acclimation in response to changing weather conditions. During the cold acclimation process, many physiological changes occur, including modifications in protein expression. In this study, two-dimensional gel electrophoresis was used to investigate changes in protein expression among 40 black wattle families with varying levels of frost tolerance before and after a cold-stress treatment. The proteomic data generated from this was analysed using multivariate analysis. Six proteins were observed to be upregulated in frosttolerant black wattle families. The proteins were identified and have been previously shown to contribute to the protection of cellular membranes, maintenance of photosynthetic processes and the prevention of protein misfolding and aggregation.

Immune response to cold exposure: Role of γδ T cells and TLR2-mediated inflammation.

The mammalian body possesses remarkable adaptability to cold exposure, involving intricate adjustments in cellular metabolism, ultimately leading to thermogenesis. However, cold-induced stress can impact immune response, primarily through noradrenaline-mediated pathways. In our study, we utilized a rat model subjected to short-term or long-term mild cold exposure to investigate systemic immune response during the cold acclimation. To provide human relevance, we included a group of regular cold swimmers in our study. Our research revealed complex relationship between cold exposure, neural signaling, immune response, and thermogenic regulation. One-day cold exposure triggered stress response, including cytokine production in white adipose tissue, subsequently activating brown adipose tissue, and inducing thermogenesis. We further studied systemic immune response, including the proportion of leukocytes and cytokines production. Interestingly, γδ T cells emerged as possible regulators in the broader systemic response, suggesting their possible contribution in the dynamic process of cold adaptation. We employed RNA-seq to gain further insights into the mechanisms by which γδ T cells participate in the response to cold. Additionally, we challenged rats exposed to cold with the Toll-like receptor 2 agonist, showing significant modulation of immune response. These findings significantly contribute to understanding of the physiological acclimation that occur in response to cold exposure.

Regulatory mechanism of cold-inducible diapause in Caenorhabditis elegans

Temperature is a critical environmental cue that controls the development and lifespan of many animal species; however, mechanisms underlying low-temperature adaptation are poorly understood. Here, we describe cold-inducible diapause (CID), another type of diapause induced by low temperatures in Caenorhabditis elegans. A premature stop codon in heat shock factor 1 (hsf-1) triggers entry into CID at 9 °C, whereas wild-type animals enter CID at 4 °C. Furthermore, both wild-type and hsf-1(sy441) mutant animals undergoing CID can survive for weeks, and resume growth at 20 °C. Using epistasis analysis, we demonstrate that neural signalling pathways, namely tyraminergic and neuromedin U signalling, regulate entry into CID of the hsf-1 mutant. Overexpression of anti-ageing genes, such as hsf-1, XBP1/xbp-1, FOXO/daf-16, Nrf2/skn-1, and TFEB/hlh-30, also inhibits CID entry of the hsf-1 mutant. Based on these findings, we hypothesise that regulators of the hsf-1 mutant CID may impact longevity, and successfully isolate 16 long-lived mutants among 49 non-CID mutants via genetic screening. Furthermore, we demonstrate that the nonsense mutation of MED23/sur-2 prevents CID entry of the hsf-1(sy441) mutant and extends lifespan. Thus, CID is a powerful model to investigate neural networks involving cold acclimation and to explore new ageing mechanisms.

ATBS1-INTERACTING FACTOR 2 Positively Regulates Freezing Tolerance via INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR-Induced Cold Acclimation Pathway.

The INDUCER OF CBF EXPRESSION 1/C-REPEAT BINDING FACTOR (ICE1/CBF) pathway plays a crucial role in plant responses to cold stress, impacting growth and development. Here, we demonstrated that ATBS1-INTERACTING FACTOR 2 (AIF2), a non-DNA-binding basic helix-loop-helix transcription factor, positively regulates freezing tolerance through the ICE1/CBF-induced cold tolerance pathway in Arabidopsis. Cold stress transcriptionally upregulated AIF2 expression and induced AIF2 phosphorylation, thereby stabilizing the AIF2 protein during early stages of cold acclimation. The AIF2 loss-of-function mutant, aif2-1, exhibited heightened sensitivity to freezing before and after cold acclimation. In contrast, ectopic expression of AIF2, but not the C-terminal-deleted AIF2 variant, restored freezing tolerance. AIF2 enhanced ICE1 stability during cold acclimation and promoted the transcriptional expression of CBFs and downstream cold-responsive genes, ultimately enhancing plant tolerance to freezing stress. MITOGEN-ACTIVATED PROTEIN KINASES 3 and 6 (MPK3/6), known negative regulators of freezing tolerance, interacted with and phosphorylated AIF2, subjecting it to protein degradation. Furthermore, transient co-expression of MPK3/6 with AIF2 and ICE1 downregulated AIF2/ICE1-induced transactivation of CBF2 expression. AIF2 interacted preferentially with BRASSINOSTEROID-INSENSITIVE 2 (BIN2) and MPK3/6 during the early and later stages of cold acclimation, respectively, thereby differentially regulating AIF2 activity in a cold acclimation time-dependent manner. Moreover, AIF2 acted additively in a gain-of-function mutant of BRASSINAZOLE-RESISTANT 1 (BZR1; bzr1-1D) and a triple knockout mutant of BIN2 and its homologs (bin2bil1bil2) to induce CBFs-mediated freezing tolerance. This suggests that cold-induced AIF2 coordinates freezing tolerance along with BZR1 and BIN2, key positive and negative components, respectively, of brassinosteroid signaling pathways.

HOS15-mediated turnover of PRR7 enhances freezing tolerance.

Arabidopsis PSEUDO RESPONSE REGULATOR7 (PRR7) is a core component of the circadian oscillator which also plays a crucial role in freezing tolerance. PRR7 undergoes proteasome-dependent degradation to discretely phase maximal expression in early evening. While its transcriptional repressive activity on downstream genes is integral to cold regulation, the mechanism of the conditional regulation of the PRR7 protein activity is unknown. We used double mutant analysis, protein interaction and ubiquitylation assays to establish that the ubiquitin ligase adaptor, HIGH EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 15 (HOS15), controls the protein accumulation pattern of PRR7 through direct protein-protein interactions. Freezing tolerance and electrolyte leakage assays show that PRR7 enhances cold temperature sensitivity, supported by ChIP-qPCR at C-REPEAT BINDING FACTOR (CBF) and COLD REGULATED 15A (COR15A) promoters where PRR7 levels were higher in hos15 mutants. We establish that HOS15 mediates PRR7 protein turnover through enhanced ubiquitylation at low temperature in the dark. Under the same conditions, increased PRR7 association with the promoter regions of CBFs and COR15A in hos15 correlates with decreased CBF1 and COR15A transcription and enhanced freezing sensitivity. We propose a novel mechanism whereby HOS15-mediated regulation of PRR7 provides an intersection between the circadian system and other cold acclimation pathways leading to freezing tolerance through upregulation of CBF1 and COR15A.

Autophagy is suppressed by low temperatures and is dispensable for cold acclimation in Arabidopsis.

Plants have evolved various mechanisms to adapt to the ever-changing external environment. Autophagy is one such mechanism and has been suggested to play a key role in responding to and adapting to abiotic stresses in plants. However, the role of autophagy in adaptation to cold and freezing stresses remains to be characterized in detail. Here, we investigated the role of autophagy in the low-temperature response of Arabidopsis using atg mutants. Both the atg5-1 and atg10-1 mutants exhibited normal freezing tolerance, regardless of cold acclimation. A comparison of fresh weights indicated that the difference in growth between the wild-type and atg plants under cold conditions was rather small compared with that under normal conditions. Analysis of COLD-REGULATED gene expression showed no significant differences between the atg mutants and wild type. Treatment with 3-methyladenine, an inhibitor of autophagy, did not impair the induction of COR15Apro::LUC expression upon exposure to low temperature. Evaluation of autophagic activity using transgenic plants expressing RBCS-mRFP demonstrated that autophagy was rarely induced by cold exposure, even in the dark. Taken together, these data suggest that autophagy is suppressed by low temperatures and is dispensable for cold acclimation and freezing tolerance in Arabidopsis.

Context-dependent effects of thermal acclimation on physiological correlates of animal personality in Asiatic toads.

Persistent individual variation in behaviour, or 'personality', is a widespread phenomenon in animals, and understanding the evolution of animal personality is a key task of current biology. Natural selection has been proposed to promote the integration of personality with animal 'intrinsic states', such as metabolic or endocrine traits, and this integration varies with ecological conditions. However, these external ecological modulatory effects have rarely been examined. Here, we investigate the effects of thermal acclimation on between-individual covariations between physiology and behaviour in Asiatic toads (Bufo gargarizans) along an altitudinal gradient. Our results reveal that the thermal modulatory effects on the covariations depend on the altitudinal population. Specifically, at low altitudes, between-individual covariations are highly plastic, with risk-taking behaviour covarying with baseline glucocorticoids (GCs) under warm acclimation, but risk-taking and exploration behaviour covarying with resting metabolic rate (RMR) under cold acclimation. In contrast, between-individual covariations are relatively fixed at high altitudes, with risk-taking behaviour consistently covarying with baseline GCs. Furthermore, at low altitudes, changes in covariations between RMR and personality are associated with adjustment of energy management models. Evidently, animal physiological states that determine or covary with personality can adapt according to the seasonal thermal environment and the thermal evolutionary background of populations. Our findings highlight the importance of a multi-system physiological approach to understand the evolution of animal personality.

Cold hardiness-informed budbreak reveals role of freezing temperatures and daily fluctuation in a chill accumulation model.

Fundamental questions in bud dormancy remain, including what temperatures fulfill dormancy requirements (i.e. chill accumulation). Recent studies demonstrate freezing temperatures promote chill accumulation and cold hardiness influences time to budbreak-the phenotype used for dormancy evaluations. Here we evaluated bud cold hardiness and budbreak responses of grapevines (Vitis hybrids) throughout chill accumulation under three treatments: constant (5 °C), fluctuating (-3.5 to 6.5 °C daily), and field conditions (Madison, WI, USA). Chill treatments experiencing lower temperatures promoted greater gains in cold hardiness (field>fluctuating>constant). All treatments decreased observed time to budbreak with increased chill accumulation. However, perceived treatment effectiveness changed when time to budbreak was adjusted to remove cold acclimation effects. Among three classic chill models (North Carolina, Utah, and Dynamic), none was able to correctly describe adjusted time to budbreak responses to chill accumulation. Thus, a new model is proposed that expands the range of chill accumulation temperatures to include freezing temperatures and enhances chill accumulation under fluctuating temperature conditions. Most importantly, our analysis demonstrates that adjustments for uneven acclimation change the perceived effectiveness of chill treatments. Therefore, future work in bud dormancy would benefit from simultaneously evaluating cold hardiness.

Biosynthesis and differential spatial distribution of the 3-deoxyanthocyanidins apigenidin and luteolinidin at the interface of a plant-cyanobacteria symbiosis exposed to cold.

Aquatic ferns of the genus Azolla (Azolla) form highly productive symbioses with filamentous cyanobacteria fixing N2 in their leaf cavities, Nostoc azollae. Stressed symbioses characteristically turn red due to 3-deoxyanthocyanidin (DA) accumulation, rare in angiosperms and of unknown function. To understand DA accumulation upon cold acclimation and recovery, we integrated laser-desorption-ionization mass-spectrometry-imaging (LDI-MSI), a new Azolla filiculoides genome-assembly and annotation, and dual RNA-sequencing into phenotypic analyses of the symbioses. Azolla sp. Anzali recovered even when cold-induced DA-accumulation was inhibited by abscisic acid. Cyanobacterial filaments generally disappeared upon cold acclimation and Nostoc azollae transcript profiles were unlike those of resting stages formed in cold-resistant sporocarps, yet filaments re-appeared in leaf cavities of newly formed green fronds upon cold-recovery. The high transcript accumulation upon cold acclimation of AfDFR1 encoding a flavanone 4-reductase active in vitro suggested that the enzyme of the first step in the DA-pathway may regulate accumulation of DAs in different tissues. However, LDI-MSI highlighted the necessity to describe metabolite accumulation beyond class assignments as individual DA and caffeoylquinic acid metabolites accumulated differentially. For example, luteolinidin accumulated in epithelial cells, including those lining the leaf cavity, supporting a role for the former in the symbiotic interaction during cold acclimation.

Transgenerational cross‐susceptibility to heat stress following cold and desiccation acclimation in the Angoumois grain moth

AbstractThe Angoumois grain moth, Sitotroga cerealella (Olivier), is a significant cosmopolitan primary pest of cereals worldwide and has thrived in divergent environments. However, the mechanisms underlying its survival in multiple contrasting environments are poorly understood. Here, we hypothesised that when facing diverse environmental stress, F1 generation exhibits transgenerational cross‐protection as a mechanism to persist under divergent stressful environments. Notably, F1 acclimation to cold or desiccation conditions could either enhance or lower heat tolerance in the F2 generation. Specifically, we tested whether typical diurnal fluctuations and/or winter rapid or chronic cold temperatures (18–22°C) as well as desiccation acclimation of F1 parental population yields transgenerational cross‐protection/susceptibility to heat stress on F2 offspring. F1 moths were exposed to cold hardening (2 h), chronic (72 h) and variable (fluctuating between 18 and 22°C for 72 h) temperature treatment groups. Desiccation treatment included incubation at 0%–1% relative humidity (24 h). F2 generation moths were then assessed for heat tolerance using critical thermal maxima (CTmax) at three different ramping rates (0.06, 0.25 and 0.5°C/min) as well as heat knockdown time (HKDT). Findings indicated that (i) desiccation, cold hardening and chronic low‐temperature acclimations in F1 reduced heat tolerance in F2 populations and (ii) ramping rate was crucial to decipher differences between treatment groups, with lower ramping rates associated with lower CTmax. Transgenerational cross‐susceptibility to heat stress indicates possible fitness costs of exposure to multiple contrasting stressors in the Angoumois grain moth and can be used in designing physical pest management strategies.

Autumn cold acclimation and freezing tolerance of three oak species in semi-Mediterranean Zagros forests

Aim of study: To identify and compare the early frost resistance mechanisms in three oak species (Quercus brantii, Quercus libani and Quercus infectoria). Area of study: Zagros forests of Iran. Material and methods: The physiological and biochemical variables such as chlorophyll fluorescence, relative water content (RWC), electrolyte leakage, and osmotic metabolite content, such as proline, glucose, and potassium of three oak species seedlings with varying altitudinal and latitudinal ranges were measured under various treatments, including cold treatments (4°C: control, -20°C (1 hour) and -20°C (2 hours)) and four levels of hardening steps with decreasing temperature and photoperiod. Main results: Results showed that decreasing photoperiod and temperature during cold hardening was associated with decreasing Fv/Fm, ΦPSII and electron transport rate, increasing (NPQ) measured from chlorophyll fluorescence, as well as increasing osmotic metabolite content and decline of RWC, except the glucose content decreased in Q. brantii from lower altitudes and south aspect. On the other hand, Q. libanii, which originates from higher altitudes and north aspect showed the strongest cold-resistance and faster developing cold-acclimation capacity using earlier accumulation of osmotic metabolites, diminishing RWC and subsequently lowest EL compared to the other oak species. Research highlights: The physiological and biochemical responses of oak species differed based on origin and there was a positive relation between osmotic metabolite content, NPQ, altitude, and cold stress resistance. These physiological responses, especially NPQ (as a fast and non-invasive tool) provide a quantitative assessment of the risks associated with autumn freezing in different oak species and ecotypes relevant to conservation and reforestation projects of the Zagros forests under changing climatic conditions.

Multi-scale characterisation of cold response reveals immediate and long-term impacts on cell physiology up to seed composition in sunflower.

Early sowing can help summer crops escape drought and can mitigate the impacts of climate change on them. However, it exposes them to cold stress during initial developmental stages, which has both immediate and long-term effects on development and physiology. To understand how early night-chilling stress impacts plant development and yield, we studied the reference sunflower line XRQ under controlled, semi-controlled and field conditions. We performed high-throughput imaging of the whole plant parts and obtained physiological and transcriptomic data from leaves, hypocotyls and roots. We observed morphological reductions in early stages under field and controlled conditions, with a decrease in root development, an increase in reactive oxygen species content in leaves and changes in lipid composition in hypocotyls. A long-term increase in leaf chlorophyll suggests a stress memory mechanism that was supported by transcriptomic induction of histone coding genes. We highlighted DEGs related to cold acclimation such as chaperone, heat shock and late embryogenesis abundant proteins. We identified genes in hypocotyls involved in lipid, cutin, suberin and phenylalanine ammonia lyase biosynthesis and ROS scavenging. This comprehensive study describes new phenotyping methods and candidate genes to understand phenotypic plasticity better in response to chilling and study stress memory in sunflower.

Effects of cold acclimation on serum biochemical parameters and metabolite profiles in Schizothorax prenanti

BackgroundEnvironmental temperature is critical in regulating biological functions in fish. S. prenanti is a kind of cold-water fish, but of which we have little knowledge about the metabolic adaptation and physiological responses to long-term cold acclimation.ResultsIn this study, we determined the physiological responses of S. prenanti serum after 30 days of exposure to 6℃. Compared with the control group, the levels of TC, TG, and LDL-C in the serum were significantly (P < 0.05) increased, and the level of glucose was significantly (P < 0.05) decreased under cold acclimation. Cold acclimation had no effect on the gene expression of pro-inflammatory factors and anti-inflammatory factors of S. prenanti. Metabolomics analysis by LC-MS showed that a total of 60 differential expressed metabolites were identified after cold acclimation, which involved in biosynthesis of amino acids, biosynthesis of unsaturated fatty acids, steroid degradation, purine metabolism, and citrate cycle pathways.ConclusionThe results indicate that cold acclimation can alter serum metabolites and metabolic pathways to alter energy metabolism and provide insights for the physiological regulation of cold-water fish in response to cold acclimation.

Genomic and Phenotypic Adaptations of Rattus tanezumi to Cold Limit Its Further Northward Expansion and Range Overlap with R. norvegicus.

Global climate change has led to shifts in the distribution ranges of many terrestrial species, promoting their migration from lower altitudes or latitudes to higher ones. Meanwhile, successful invaders have developed genetic adaptations enabling the colonization of new environments. Over the past 40 years, Rattus tanezumi (RT) has expanded into northern China (Northwest and North China) from its southern origins. We studied the cold adaptation of RT and its potential for northward expansion by comparing it with sympatric Rattus norvegicus (RN), which is well adapted to cold regions. Through population genomic analysis, we revealed that the invading RT rats have split into three distinct populations: the North, Northwest, and Tibetan populations. The first two populations exhibited high genetic diversity, while the latter population showed remarkably low genetic diversity. These rats have developed various genetic adaptations to cold, arid, hypoxic, and high-UV conditions. Cold acclimation tests revealed divergent thermoregulation between RT and RN. Specifically, RT exhibited higher brown adipose tissue activity and metabolic rates than did RN. Transcriptome analysis highlighted changes in genes regulating triglyceride catabolic processes in RT, including Apoa1 and Apoa4, which were upregulated, under selection and associated with local adaptation. In contrast, RN showed changes in carbohydrate metabolism genes. Despite the cold adaptation of RT, we observed genotypic and phenotypic constraints that may limit its ability to cope with severe low temperatures farther north. Consequently, it is less likely that RT rats will invade and overlap with RN rats in farther northern regions.