Cold Acclimation Period Research Articles

Insights into physiological roles of flavonoids in plant coldacclimation.

Flavonoids represent a diverse group of plant specialised metabolites which are also discussed in the context of dietary health and inflammatory response. Numerous studies have revealed that flavonoids play a central role in plant acclimation to abiotic factors like low temperature or high light, but their structural and functional diversity frequently prevents a detailed mechanistic understanding. Further complexity in analysing flavonoid metabolism arises from the different subcellular compartments which are involved in biosynthesis and storage. In the present study, non-aqueous fractionation of Arabidopsis leaf tissue was combined with metabolomics and proteomics analysis to reveal the effects of flavonoid deficiencies on subcellular metabolism during cold acclimation. During the first 3 days of a 2-week cold acclimation period, flavonoid deficiency was observed to affect pyruvate, citrate and glutamate metabolism which indicated a role in stabilising C/N metabolism and photosynthesis. Also, tetrahydrofolate metabolism was found to be affected, which had significant effects on the proteome of the photorespiratory pathway. In the late stage of cold acclimation, flavonoid deficiency was found to affect protein stability, folding and proteasomal degradation, which resulted in a significant decrease in total protein amounts in both mutants. In summary, these findings suggest that flavonoid metabolism plays different roles in the early and late stages of plant cold acclimation and significantly contributes to establishing a new protein homeostasis in a changing environment.

Juniperus virginiana sourced from colder climates maintain higher ratios of soluble sugars to starch during cold acclimation.

Non-structural carbohydrates (NSCs) are carbon compounds that serve a large variety of purposes, which makes it hard to disentangle how their concentrations change in response to environmental stress. Soluble sugars can accumulate in plants as metabolic demand decreases, e.g. in response to drought or as seasonal temperatures decrease. Alternatively, actively allocating to NSCs could be beneficial in cold acclimation or periods of increased aridity because soluble sugars serve non-metabolic functions as cryoprotectants and in osmoregulation. We used Juniperus virginiana, a woody plant currently expanding its range, to investigate whether plants sourced from colder and more arid locations maintained higher concentrations of NSCs. We sourced three populations of J. virginiana from across an environmental gradient, and we compared these with the closely related Juniperus scopulorum. We grew the plants in a common garden in northeast Ohio, part of J. virginiana's historic range. We exposed the plants to a drought treatment during the summer and then measured NSC concentrations and cold hardiness as the plants acclimated to colder temperatures and shorter days. We found that individuals originating from the warmer, more southern, range edge were initially not as cold hardy as plants from the other source populations and only reached similar hardiness after prolonged low temperatures. We did not find an effect of drought on NSCs, although this may be due to other traits conferring a high level of drought tolerance in J. virginiana. Across all plants, the NSCs concentration increased over the cold acclimation period, specifically as sugars. Although the highest concentrations of sugars were found in plants from southern populations, the plants from colder environments maintained higher ratios of sugars to starch. These results highlight the importance of NSCs in cold acclimation, and that plants sourced from different climates showed different physiological responses to shortening days and low temperatures.

Effect of Photoperiod Duration on Efficiency of Low-Temperature Hardening of <i>Arabidopsis thaliana</i> Heynh. (L.)

The effect of photoperiod duration on efficiency of low-temperature hardening was investigated in Arabidopsis thaliana (L.) Heynh. plants, ecotype Col-0. Six-week-old plants were exposed to cold acclimation at a temperature of 2С during 1‒5 days at photoperiods of 0, 8, and 16 h (illuminance of 200 mol/(m2 s)). According to survival data and leakage of electrolytes after test freezing (6C, 24 h), the plants exposed to cold acclimation in the dark did not show frost resistance. The plants hardened in the light (irrespective of the length of photoperiod) considerably improved their frost resistance by the end of the cold-acclimation period. Net photosynthesis/dark respiration ratio in these plants was almost two times greater than in control material (without hardening). The plants exposed to a 16-h-long photoperiod surpassed the type of treatment with 8-h-long illumination both in the highest levels of accumulation of sugars (by almost 40%) and in the rate of reaching these levels in daily dynamics of hardening. It was shown that MDA content transiently rose during the first 24 h of hardening in the light and did not change in the dark, which may point to a signal role of lipid peroxidation products upon cold acclimation. It was discovered that the photoperiod duration affected the formation rate of frost resistance in A. thaliana plants. A more prolonged operation of A. thalianas photosynthetic apparatus at 16-h-long photoperiod considerably accelerated the accumulation of sugars upon cold acclimation and, therefore, hastened development of frost resistance as compared with an 8-h-long photoperiod. It was concluded that rapid formation of frost resistance in A. thaliana requires a combination of low above-zero temperature and 16-h-long photoperiod.

Recruitment of Muscle Genes as an Effect of Brown Adipose Tissue Ablation in Cold-Acclimated Brandt’s Voles (Lasiopodomys brandtii)

Skeletal muscle-based nonshivering thermogenesis (NST) plays an important role in the regulation and maintenance of body temperature in birds and large mammals, which do not contain brown adipose tissue (BAT). However, the relative contribution of muscle-based NST to thermoregulation is not clearly elucidated in wild small mammals, which have evolved an obligate thermogenic organ of BAT. In this study, we investigated whether muscle would become an important site of NST when BAT function is conditionally minimized in Brandt's voles (Lasiopodomys brandtii). We surgically removed interscapular BAT (iBAT, which constitutes 52%~56% of total BAT) and exposed the voles to prolonged cold (4 °C) for 28 days. The iBAT-ablated voles were able to maintain the same levels of NST and body temperature (~37.9 °C) during the entire period of cold acclimation as sham voles. The expression of uncoupling protein 1 (UCP1) and its transcriptional regulators at both protein and mRNA levels in the iBAT of cold-acclimated voles was higher than that in the warm group. However, no difference was observed in the protein or mRNA levels of these thermogenesis-related markers except for PGC-1α in other sites of BAT (including infrascapular region, neck, and axilla) between warm and cold groups either in sham or iBAT-ablated voles. The iBAT-ablated voles showed higher UCP1 expression in white adipose tissue (WAT) than sham voles during cold acclimation. The expression of sarcolipin (SLN) and sarcoplasmic endoplasmic reticulum Ca2+-dependent adenosine triphosphatase (SERCA) in skeletal muscles was higher in cold than in warm, but no alteration in phospholamban (PLB) and phosphorylated-PLB (P-PLB) was observed. Additionally, there was increased in iBAT-ablated voles compared to that in the sham group in cold. Moreover, these iBAT-ablated voles underwent extensive remodeling of mitochondria and genes of key components related with mitochondrial metabolism. These data collectively indicate that recruitment of skeletal muscle-based thermogenesis may compensate for BAT impairment and suggest a functional interaction between the two forms of thermogenic processes of iBAT and skeletal muscle in wild small mammals for coping cold stress.

The Application of Auxin-like Compounds Promotes Cold Acclimation in the Oilseed Rape Plant.

Cold is a major environmental key factor influencing plant growth, development, and productivity. Responses and adaption processes depend on plant physiological and biochemical modifications, first of all via the hormonal system. Indole-3-acetic acid (IAA) plays a critical role in the processes of plant functioning. To assess the influence of the auxin-like compounds 1-[2-chloroethoxycarbonylmethyl]-4-naphthalenesulfonic acid calcium salt (TA-12) and 1-[2-dimethylaminoethoxycarbonylmethyl]naphthalene chloromethylate (TA-14) in the process of cold acclimation, long-term field trials over four years were performed with two rapeseed (Brassica napus L.) plant cultivars with different wintering resistance in temperate-zone countries. In these two rapeseed cultivars, namely ‘Casino’ (less resistant) and ‘Valesca’ (more resistant), investigations were conducted in the terminal buds and root collars. The application of auxin-like compounds revealed a close interlinkage between the composition of dehydrins and the participation of the phytohormone IAA in the adaptation processes. By applying TA-12 and TA-14, the importance of the proteins, especially the composition of the dehydrins, the IAA amount, and the status of the oilseed rape cultivars at the end of the cold acclimation period were confirmed. Following on from this, when introducing oilseed rape cultivars from foreign countries, it may also be of value to assess their suitability for cultivation in temperate-zone countries.

Cold Acclimation in Brachypodium Is Accompanied by Changes in Above-Ground Bacterial and Fungal Communities.

Shifts in microbiota undoubtedly support host plants faced with abiotic stress, including low temperatures. Cold-resistant perennials prepare for freeze stress during a period of cold acclimation that can be mimicked by transfer from growing conditions to a reduced photoperiod and a temperature of 4 °C for 2–6 days. After cold acclimation, the model cereal, Brachypodium distachyon, was characterized using metagenomics supplemented with amplicon sequencing (16S ribosomal RNA gene fragments and an internal transcribed spacer region). The bacterial and fungal rhizosphere remained largely unchanged from that of non-acclimated plants. However, leaf samples representing bacterial and fungal communities of the endo- and phyllospheres significantly changed. For example, a plant-beneficial bacterium, Streptomyces sp. M2, increased more than 200-fold in relative abundance in cold-acclimated leaves, and this increase correlated with a striking decrease in the abundance of Pseudomonas syringae (from 8% to zero). This change is of consequence to the host, since P. syringae is a ubiquitous ice-nucleating phytopathogen responsible for devastating frost events in crops. We posit that a responsive above-ground bacterial and fungal community interacts with Brachypodium’s low temperature and anti-pathogen signalling networks to help ensure survival in subsequent freeze events, underscoring the importance of inter-kingdom partnerships in the response to cold stress.

Carbohydrate Accumulation and Differential Transcript Expression in Winter Wheat Lines with Different Levels of Snow Mold and Freezing Tolerance after Cold Treatment.

Winter wheat (Triticum aestivum L.) undergoes a period of cold acclimation in order to survive the ensuing winter, which can bring freezing temperatures and snow mold infection. Tolerance of these stresses is conferred in part by accumulation of carbohydrates in the crown region. This study investigates the contributions of carbohydrate accumulation during a cold treatment among wheat lines that differ in their snow mold tolerance (SMT) or susceptibility (SMS) and freezing tolerance (FrT) or susceptibility (FrS). Two parent varieties and eight recombinant inbred lines (RILs) were analyzed. The selected RILs represent four combinations of tolerance: SMT/FrT, SMT/FrS, SMS/FrT, and SMS/FrS. It is hypothesized that carbohydrate accumulation and transcript expression will differ between sets of RILs. Liquid chromatography with a refractive index detector was used to quantify carbohydrate content at eight time points over the cold treatment period. Polysaccharide and sucrose content differed between SMT and SMS RILs at various time points, although there were no significant differences in glucose or fructose content. Glucose and fructose content differed between FrT and FrS RILs in this study, but no significant differences in polysaccharide or sucrose content. RNAseq was used to investigate differential transcript expression, followed by modular enrichment analysis, to reveal potential candidates for other mechanisms of tolerance, which included expected pathways such as oxidative stress, chitinase activity, and unexpected transcriptional pathways. These differences in carbohydrate accumulation and differential transcript expression begin to give insight into the differences of wheat lines when exposed to cold temperatures.

Involvement of Salicylic Acid and Other Phenolic Compounds in Light-Dependent Cold Acclimation in Maize.

The exposure of plants to non-lethal low temperatures may increase their tolerance to a subsequent severe chilling stress. To some extent, this is also true for cold-sensitive species, including maize. In the present work, based on our previous microarray experiment, the differentially expressed genes with phenylpropanoid pathways in the focus were further investigated in relation to changes in certain phenolic compounds and other plant growth regulators. Phenylalanine ammonia lyase (PAL) was mainly activated under limited light conditions. However, light-induced anthocyanin accumulation occurred both in the leaves and roots. Chilling stress induced the accumulation of salicylic acid (SA), but this accumulation was moderated in the cold-acclimated plants. Acclimation also reduced the accumulation of jasmonic acid (JA) in the leaves, which was rather induced in the roots. The level of abscisic acid (ABA) is mainly related to the level of the stress, and less indicated the level of the acclimation. The highest glutathione (GSH) amount was observed during the recovery period in the leaves of plants that were cold acclimated at growth light, while their precursors started to accumulate GSH even during the chilling. In conclusion, different light conditions during the cold acclimation period differentially affected certain stress-related mechanisms in young maize plants and changes were also light-dependent in the root, not only in the leaves.

Preferential accumulation of glycosylated cyanidins in winter-hardy rye (Secale cereale L.) genotypes during cold acclimation

Fall-seeded rye improve their frost resistance during a cold acclimation period in the fall, which is often associated with an accumulation of red/purple-colored anthocyanins in plant tissues. The pigments provide antioxidant activity and are proposed to scavenge excess reactive oxygen species (ROS) and mitigate light stress occurring during cold exposure. The relationship between anthocyanin and winter hardiness in rye (Secale cereale L.) was assessed by analyzing 96 genotypes with varying levels of winter survival. HPLC-QTOF MS/MS analyses of tissue extracts prepared from cold-acclimated plants revealed presence of accumulated anthocyanins in leaves of 74 genotypes and 51 of these showed low levels of anthocyanins presence in crown tissues. An overall higher abundance and diversity of anthocyanins was noted for the most cold-hardy as compared to the less hardy genotypes. A total of 18 anthocyanins originating from the pelargonidin, cyanidin, and delphinidin precursors were identified, of which the glycosylated cyanidins were accumulated in 37 of the 39 most winter hardy genotypes, but only detected in six of the 38 most tender genotypes. The link between anthocyanin concentration and profiles with winter-hardiness levels for the 96 rye genotypes suggested a role for cyanidin-derived anthocyanins in mediating enhanced winter hardiness in rye.

Proline content and related gene expression in response to seasonal temperature variation in three Rosaceae fruit trees

Seasonal patterns of proline (Pro) biosynthesis in peach (Prunus persica), plum (Prunus salicina), and apple (Malus × domestica) trees were compared by examining their Pro variation and relative gene expression. Pro levels in the shoots of peach and plum trees increased during spring and Pro level variations were similar during seasonal temperature changes. In apple, Pro content variation differed from that in Prunus species and were accumulated during the cold acclimation period and spring. Furthermore, the Pro contents in peach and plum shoots were positively correlated with the ornithine-δ-aminotransferase (OAT) and pyrroline-5-carboxylate reductase (P5CR) expression. Although the Pro level in apple was not correlated with OAT, it was correlated with P5CR. Our study suggests that, under seasonal temperature variation, the ornithine pathway regulates Pro accumulation in the two Prunus species but not in M. × domestica.

Potential Roles of Fatty Acids and Lipids in Postharvest Needle Abscission Physiology

Our understanding of postharvest needle abscission physiology in conifers has greatly improved in the last decade. Abscission is initially triggered by root detachment, which begins a cascade of changes such as decreased water uptake, water potential, and auxins and increased membrane injury, ethylene, abscisic acid, volatile terpenes, and catalytic enzymes. Needle abscission is also affected by environmental factors. For example, a period of cold acclimation generally delays postharvest abscission. The aforementioned pieces of evidence, along with previous studies, strongly points to a role for plant lipids and fatty acids. Studies from other species have pointed out key roles in abscission and stress responses for a variety of phospholipids and galactolipids, which has not been studied in balsam fir. It is imperative to have an understanding of the role of plant lipids and fatty acids to further our overall understanding of the physiological mechanisms of postharvest abscission and needle abscission resistance. This review is an overview of membrane lipids and fatty acids, changes that occur postharvest and the interaction that lipids may have in the phenomenon of postharvest abscission.

Physiological changes and DREB1s expression profiles of tall fescue in response to freezing stress

Tall fescue is a widely used cool season turfgrass. In this study, we screened freezing tolerance of six tall fescue cultivars based on TEL50 (temperature causing 50% electrolyte leakage). We observed that freezing tolerant tall fescue cultivar exhibited lower EL, accumulated higher soluble sugar and proline, and showed higher CAT and SOD activities when compared with freezing intolerant cultivar. Based on bioinformatics analysis, 6 FaDREB1 unigenes were identified from publicly available transcriptomic data. Expression profiles showed that freezing tolerant cultivar only activated specific FaDREB1 unigenes, while freezing intolerant cultivar activated all six FaDREB1s during cold acclimation period. These findings indicated that cold stress modulated diverse physiological process in different tall fescue cultivars and activated various gene networks through regulating different subsets of FaDREB1s.

Janus-Faced Nature of Light in the Cold Acclimation Processes of Maize.

Exposure of plants to low temperature in the light may induce photoinhibitory stress symptoms, including oxidative damage. However, it is also known that light is a critical factor for the development of frost hardiness in cold tolerant plants. In the present work the effects of light during the cold acclimation period were studied in chilling-sensitive maize plants. Before exposure to chilling temperature at 5°C, plants were cold acclimated at non-lethal temperature (15°C) under different light conditions. Although exposure to relatively high light intensities during cold acclimation caused various stress symptoms, it also enhanced the effectiveness of acclimation processes to a subsequent severe cold stress. It seems that the photoinhibition induced by low temperature is a necessary evil for cold acclimation processes in plants. Greater accumulations of soluble sugars were also detected during hardening at relatively high light intensity. Certain stress responses were light-dependent not only in the leaves, but also in the roots. The comparison of the gene expression profiles based on a microarray study demonstrated that the light intensity is at least as important a factor as the temperature during the cold acclimation period. Differentially expressed genes were mainly involved in most of assimilation and metabolic pathways, namely photosynthetic light capture via the modification of chlorophyll biosynthesis and the dark reactions, carboxylic acid metabolism, cellular amino acid, porphyrin or glutathione metabolic processes, ribosome biogenesis and translation. Results revealed complex regulation mechanisms and interactions between cold and light signalling processes.

Freeze Tolerance and Cryoprotection of Erythrocytes from Warm and Cold Acclimated D. chrysoscelis

Dryophytes chrysoscelis (Cope's gray treefrog) is a freeze tolerant frog that survives the freezing of extracellular fluids throughout winter. Prior to freezing, D. chrysoscelis goes through a cold acclimation period during which the temperature, hours of daylight, and food intake decrease. Cold‐acclimated frogs have elevated plasma levels of glycerol and urea, solutes that function as cryoprotectants by minimizing osmotically induced cell damage during freezing and thawing. To minimize damage, urea and glycerol must be taken up by erythrocytes. Erythrocytes from cold‐acclimated frogs have enhanced abundance and membrane localization of an aquaglyceroporin, HC‐3, through which the intra‐ and extracellular flux of glycerol and urea occur. It is hypothesized that erythrocytes frozen in solution containing glycerol/urea would have greater post‐freeze (PF) viability than cells frozen without glycerol or urea. It is further hypothesized that cells frozen with naturally accumulating, and HC‐3 permeating, solutes (glycerol and urea) would have enhanced PF viability compared to cells frozen with solutes that do not accumulate during cold acclimation (glucose, NaCl, sorbitol). In this study, erythrocytes were obtained from warm‐acclimated (22°C) or cold‐acclimated (4°C) frogs, suspended in phosphate buffered saline (PBS) ± solutes, then incubated at 0 or −8°C for 30 minutes. A separate aliquot of cells was frozen in liquid nitrogen for a 100% hemolysis control. Hemolysis was determined by a colorimetric assay. The percentage of free hemoglobin from the total hemoglobin in the erythrocyte sample was calculated and was normalized to the 100% hemolysis control. Viability of the liquid nitrogen sample was taken as 0%. Viability of cells from warm‐acclimated frogs was reduced by 85% when cells were incubated at −8°C in PBS as oppose to 0°C (p<0.001). Cell viability was reduced approximately 50%, when cells from cold‐acclimated frogs were incubated at −8°C compared to 0°C (p<0.001). Erythrocytes from cold‐acclimated frogs have a 2.6‐fold increase in PF viability compared to cells from warm‐acclimated frogs. Cells from warm‐acclimated frogs had a 2.8‐fold increase in PF viability with the addition of urea in the PBS (p<0.005). Cells from cold‐acclimated frogs had a 0.6‐fold increase in PF viability with the addition of urea or glycerol to the PBS (p<0.001 or p<0.005, respectively). The addition of glucose, NaCl, or sorbitol to PBS did not significantly alter PF viability of cells from warm‐ or cold‐acclimated frogs (p>0.05). Enhanced PF viability of cells from cold‐acclimated frogs, compared to cells from warm‐acclimated frogs suggests cold acclimation aids in the freeze tolerance of D. chrysoscelis by mechanisms other than glycerol/urea accumulation. The results of the cryoprotection assay support the involvement of glycerol and urea in the complex cryoprotectant system of D. chrysoscelis.Support or Funding InformationThis research was supported by NSF IOS‐1121457 (CMK and DLG), Schuellein Chair in the Biological Sciences to CMK, and Schuellein Graduate Research Fellowship to LG.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Impairment of exercise performance following cold water immersion is not attenuated after 7days of cold acclimation.

It is well-documented that severe cold stress impairs exercise performance. Repeated immersion in cold water induces an insulative type of cold acclimation, wherein enhanced vasoconstriction leads to greater body heat retention, which may attenuate cold-induced exercise impairments. The purpose of this study, therefore, was to investigate changes in exercise performance during a 7-day insulative type of cold acclimation. Twelve healthy participants consisting of eight males and four females (mean ± SD age: 25.6 ± 5.2years, height: 174.0 ± 8.9cm, weight: 75.6 ± 13.1kg) performed a 20min self-paced cycling test in 23°C, 40% humidity without prior cold exposure. Twenty-four hours later they began a 7-day cold acclimation protocol (daily 90min immersion in 10°C water). On days one, four, and seven of cold acclimation, participants completed the same cycling test. Measurements of work completed, core and skin temperatures, heart rate, skin blood flow, perceived exertion, and thermal sensation were measured during each cycling test. Successful insulative cold acclimation was observed. Work produced during the baseline cycling test (220 ± 70kJ) was greater (p < 0.001) than all three tests that were performed following immersions (195 ± 58, 197 ± 60, and 194 ± 62kJ) despite similar ratings of perceived exertion during each test, suggesting that cold exposure impaired cycling performance. This impairment, however, was not attenuated over the cold acclimation period. Results suggest that insulative cold acclimation does not attenuate impairments in exercise performance that were observed following acute cold water immersion.

Transcriptome Changes in Response to Cold Acclimation in Perennial Ryegrass as Revealed by a Cross‐Species Microarray Analysis

Freezing tolerance in perennial ryegrass (Lolium perenne L.) can be dramatically increased by a period of cold acclimation. To understand the mechanisms of cold acclimation and freezing tolerance in L. perenne, a cross‐species microarray study was conducted by using total RNA from cold‐acclimated and nonacclimated L. perenne to hybridize with Affymetrix Barley1 GeneChips from barley (Hordeum vulgare L.). Our results indicate that selection of proper background correction and normalization method is critical for the success of a barley–perennial ryegrass cross‐species microarray study. By using a specific three‐step normalization method, a total of 2870 (12.6%) genes out of approximately 22,000 genes on the barley gene chip were identified as differentially regulated by either 1 or 7 d of cold acclimation. Quantitative reverse transcriptase polymerase chain reaction (qRT‐PCR) analysis confirmed that the expression patterns of 14 selected genes are consistent with the signal intensity patterns observed in the microarray study, supporting the validity of using a cross‐species microarray in studying gene expression in species for which genomic resources remain scarce. Gene ontology analysis of differentially regulated genes indicates that different biological processes, cellular components, and molecular functions responded differently to cold acclimation in observable temporal patterns, suggesting that perennial ryegrass gradually acquires freezing tolerance by systematically regulating gene expression in an orderly manner.

NMR-based Metabolomics to Study the Cold-acclimation Strategy of Two Miscanthus Genotypes.

Abiotic stress is a major cause of yield loss in plant culture. Miscanthus, a perennial C4 grass, is now considered a major source of renewable energy, especially for biofuel production. During the first year of planting in Northern Europe, Miscanthus was exposed to frost temperature, which generated high mortality in young plants and large loss of yield. One strategy to avoid such loss is to apply cold-acclimation, which confers on plants a better resistance to low temperature. The aim of this study is to describe the effect of a cold-acclimation period on the metabolome of two Miscanthus genotypes that vary in their frost sensitivity at the juvenile stage. Miscanthus × giganteus (GIG) is particularly sensitive to frost, whereas Miscanthus sinensis August Feder (AUG) is tolerant. Polar metabolite extraction was performed on Miscanthus, grown in non-acclimated or cold-acclimated conditions. Extracts were analysed by 1 H-NMR followed by multivariate statistical analysis. Discriminant metabolites were identified. More than 40 metabolites were identified in the two Miscanthus genotypes. GIG and AUG showed a different metabolic background before cold treatment, probably related to their genetic background. After cold-acclimation, GIG and AUG metabolomes remained different. The tolerant genotype showed notably higher levels of accumulation in proline, sucrose and maltose when subjected to cold. These two genotypes seem to have a different adaptation strategy in cold conditions. The studied change in the metabolome concerns different types of molecules related to the cold-tolerant behaviour of Miscanthus. Copyright © 2016 John Wiley & Sons, Ltd.

De novo Synthesis and Assembly of rRNA into Ribosomal Subunits during Cold Acclimation in Escherichia coli

During the cold adaptation that follows a cold stress, bacterial cells undergo many physiological changes and extensive reprogramming of their gene expression pattern. Bulk gene expression is drastically reduced, while a set of cold shock genes is selectively and transiently expressed. The initial stage of cold acclimation is characterized by the establishment of a stoichiometric imbalance of the translation initiation factors (IFs)/ribosomes ratio that contributes to the preferential translation of cold shock transcripts. Whereas de novo synthesis of the IFs following cold stress has been documented, nothing was known concerning the activity of the rrn operons during the cold acclimation period. In this work, we focus on the expression of the rrn operons and the fate of rRNA after temperature downshift. We demonstrate that in Escherichia coli, rRNA synthesis does not stop during the cold acclimation phase, but continues with greater contribution of the P2 compared to the P1 promoter and all seven rrn operons are active, although their expression levels change with respect to pre-stress conditions. Eight hours after the 37°→10°C temperature downshift, the newly transcribed rRNA represents up to 20% of total rRNA and is preferentially found in the polysomes. However, with respect to the de novo synthesis of the IFs, both rRNA transcription and maturation are slowed down drastically by cold stress, thereby accounting in part for the stoichiometric imbalance of the IFs/ribosomes. Overall, our data indicate that new ribosomes, which are possibly suitable to function at low temperature, are slowly assembled during cold acclimation.

Adaptation of Autumn‐Sown Faba Bean Germplasm to Southeastern Washington

Information regarding the suitability of autumn‐sown faba bean (Vicia faba L.) in southeastern Washington is lacking. Therefore, a variety trial testing the effects of two sowing dates was conducted for two seasons (2011–2012 and 2012–2013) at three locations: Central Ferry Research Farm (CF), Pomeroy, WA; Spillman Agronomy Farm (SF), Pullman, WA; Whitlow Farm (WF), Pullman, WA, with 20 northern European breeding lines, or cultivars, and U.S. Department of Agriculture‐Agricultural Research Service National Plant Germplasm System (USDA‐ARS NPGS) sourced germplasm accessions with predetermined winter‐hardiness. Winter‐hardiness and yield varied depending on location, timing of sowing, and genotype effects. Survival was greatest at CF where the extreme low air temperature was –6°C, yet multiple entries tolerated an extreme low of –14°C in Pullman. In both years, the second sowing at the CF location improved survival, whereas the first sowing was only beneficial at the Pullman locations when seedlings were established before the first hard frost. Providing a longer establishment and cold acclimation period was expected to optimize hardiness and yield potential. However, achieving two to three nodes before the first hard frost was difficult at dryland managed SF and WF locations where soil moisture was limiting. Across entries and site‐years, the mean survival was 65% with a yield of 2800 kg ha−1. To realize the potential of autumn‐sown faba bean in southeastern Washington, genotypes with earlier maturity than the northern European materials tested herein will be needed.

Integrative molecular profiling indicates a central role of transitory starch breakdown in establishing a stable C/N homeostasis during cold acclimation in two natural accessions of Arabidopsis thaliana.

BackgroundThe variation of growth and cold tolerance of two natural Arabidopsis accessions, Cvi (cold sensitive) and Rschew (cold tolerant), was analysed on a proteomic, phosphoproteomic and metabolomic level to derive characteristic information about genotypically distinct strategies of metabolic reprogramming and growth maintenance during cold acclimation.ResultsGrowth regulation before and after a cold acclimation period was monitored by recording fresh weight of leaf rosettes. Significant differences in the shoot fresh weight of Cvi and Rschew were detected both before and after acclimation to low temperature. During cold acclimation, starch levels were found to accumulate to a significantly higher level in Cvi compared to Rschew. Concomitantly, statistical analysis revealed a cold-induced decrease of beta-amylase 3 (BAM3; AT4G17090) in Cvi but not in Rschew. Further, only in Rschew we observed an increase of the protein level of the debranching enzyme isoamylase 3 (ISA3; AT4G09020). Additionally, the cold response of both accessions was observed to severely affect ribosomal complexes, but only Rschew showed a pronounced accumulation of carbon and nitrogen compounds. The abundance of the Cold Regulated (COR) protein COR78 (AT5G52310) as well as its phosphorylation was observed to be positively correlated with the acclimation state of both accessions. In addition, transcription factors being involved in growth and developmental regulation were found to characteristically separate the cold sensitive from the cold tolerant accession. Predicted protein-protein interaction networks (PPIN) of significantly changed proteins during cold acclimation allowed for a differentiation between both accessions. The PPIN revealed the central role of carbon/nitrogen allocation and ribosomal complex formation to establish a new cold-induced metabolic homeostasis as also observed on the level of the metabolome and proteome.ConclusionOur results provide evidence for a comprehensive multi-functional molecular interaction network orchestrating growth regulation and cold acclimation in two natural accessions of Arabidopsis thaliana. The differential abundance of beta-amylase 3 and isoamylase 3 indicates a central role of transitory starch degradation in the coordination of growth regulation and the development of stress tolerance. Finally, our study indicates naturally occurring differential patterns of C/N balance and protein synthesis during cold acclimation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0668-1) contains supplementary material, which is available to authorized users.