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Carbohydrate metabolism affects cold hardiness in overwintering deciduous fruit trees. In this study, we compared the changes in starch and soluble sugar contents, related enzyme activity, and gene expression in the shoots of 'Soomee' (SM) and 'Odoroki' (OD) peach (Prunus persica) trees during cold acclimation (CA) and deacclimation (DA). SM was cold-hardier than OD from December to March based on the LT50 value, the temperature at which 50% injury occurred. During this period, starch contents were significantly lower in SM than in OD, along with higher total amylase activity and related gene expression. In contrast, total soluble sugar contents were significantly higher in SM than in OD, exhibiting a close relationship to cold hardiness. Of the detected soluble sugars, sucrose was predominant and its content was most significantly correlated with cold hardiness. Sucrose contents were significantly higher in SM than in OD from December to March. Fructose and glucose contents in SM, but not in OD, increased during CA and then decreased during DA concurrently with increased acid invertase activity and related gene expression. Raffinose and stachyose were detectable only from November to April. Their contents and related synthase gene expression were also significantly correlated with cold hardiness, but were not significantly different between the two cultivars. During CA, the activities of the enzymes involved in the synthesis of sucrose, raffinose, and stachyose increased with the up-regulation of their related gene expression. During DA, in contrast, the activities of the enzymes involved in the degradation of starch, sucrose, raffinose, and stachyose increased with the up-regulation of their related gene expression. Furthermore, the differential cold hardiness in the shoots of different peach cultivars was associated with the difference in enzyme activities and gene expression, especially of acid invertase, regulating soluble sugar content during CA and DA. [ABSTRACT FROM AUTHOR]

Significant advances have been made in our understanding of the regulation of cold hardiness. The existence of numerous biophysical and biochemical adaptive mechanisms in perennial woody plants and the complexity their regulation has made the development of methods for managing and improving cold hardiness in perennial woody plants has been very difficult. This may be partially attributed to viewing cold hardiness as a single dimensional response, rather than as a complex phenomenon, involving different mechanisms (avoidance and tolerance), different stages (mid-winter vs. late winter), and having an intimate overlap with the genetic regulation of dormancy. In particular separating the molecular regulation of cold hardiness from growth processes has been challenging. ICE and C-repeat binding factor (CBF), transcription factors (Inducer of CBF expression and CRT-binding factor) have been shown to be an important aspect in the regulation of cold-induced gene expression. Evidence has emerged, however, that they are also intimately involved in the regulation of growth, flowering, dormancy, and stomatal development. This evidence includes the presence of CBF binding motifs in genes regulating these processes, or through cross-talk between the pathways that regulate them. Recent changes in climate that have resulted in erratic episodes of unseasonal warming followed by more seasonal patterns of low temperatures has also highlighted the need to better understand the genetic and molecular regulation of deacclimation, a topic of research that is only more recently being addressed. Environmentally-induced epigenetic regulation of stress responses and seasonal processes such as cold acclimation, deacclimation, and dormancy have been documented but are still poorly understood. Advances in the ability to efficiently generate large DNA and RNA datasets and genetic transformation technologies have greatly increased our ability to explore the regulation of gene expression and explore genetic diversity. Greater knowledge of the interplay between epigenetic and genetic regulation of cold hardiness, along with the application of advanced genetic analyses, such as genome-wide-association-studies (GWAS), are needed to develop strategies for addressing the complex processes associated with cold hardiness in woody plants. A cautionary note is also indicated regarding the time-scale needed to examine and interpret plant response to freezing temperatures if progress is to be made in developing effective approaches for manipulating and improving cold hardiness.

Significant advances have been made in our understanding of the regulation of cold hardiness. The existence of numerous biophysical and biochemical adaptive mechanisms in perennial woody plants and the complexity their regulation has made the development of methods for managing and improving cold hardiness in perennial woody plants has been very difficult. This may be partially attributed to viewing cold hardiness as a single dimensional response, rather than as a complex phenomenon, involving different mechanisms (avoidance and tolerance), different stages (mid-winter vs. late winter), and having an intimate overlap with the genetic regulation of dormancy. In particular separating the molecular regulation of cold hardiness from growth processes has been challenging. ICE and C-repeat binding factor (CBF), transcription factors (Inducer of CBF expression and CRT-binding factor) have been shown to be an important aspect in the regulation of cold-induced gene expression. Evidence has emerged, however, that they are also intimately involved in the regulation of growth, flowering, dormancy, and stomatal development. This evidence includes the presence of CBF binding motifs in genes regulating these processes, or through cross-talk between the pathways that regulate them. Recent changes in climate that have resulted in erratic episodes of unseasonal warming followed by more seasonal patterns of low temperatures has also highlighted the need to better understand the genetic and molecular regulation of deacclimation, a topic of research that is only more recently being addressed. Environmentally-induced epigenetic regulation of stress responses and seasonal processes such as cold acclimation, deacclimation, and dormancy have been documented but are still poorly understood. Advances in the ability to efficiently generate large DNA and RNA datasets and genetic transformation technologies have greatly increased our ability to explore the regulation of gene expression and explore genetic diversity. Greater knowledge of the interplay between epigenetic and genetic regulation of cold hardiness, along with the application of advanced genetic analyses, such as genome-wide-association-studies (GWAS), are needed to develop strategies for addressing the complex processes associated with cold hardiness in woody plants. A cautionary note is also indicated regarding the time-scale needed to examine and interpret plant response to freezing temperatures if progress is to be made in developing effective approaches for manipulating and improving cold hardiness. [ABSTRACT FROM AUTHOR]

The adaptation of St. Augustinegrass (Stenotaphrum secundatum [Walt.] Kuntze) in the transitional climatic zone of the United States is limited due to a lack of sufficient freeze tolerance. Lab-based freeze testing provides plant breeders with a reliable method for evaluating freeze tolerance. However, in developing protocols for freeze testing it is important to account for the underlying mechanisms that affect freeze tolerance. The objective of this research was to evaluate the effects of cold acclimation and deacclimation on nine St. Augustinegrass genotypes ranging in their levels of freeze tolerance. Results indicated that accounting for all levels of acclimation provided excellent genotype separation across freezing temperatures(- 3 and - 4°C) and supports the hypothesis that the inclusion of acclimation response offers the best overall assessment of freeze tolerance. Genotypes with the highest known field winter survival had also the highest improved freeze tolerance upon cold-acclimation. Other genotypes did not respond to cold-acclimation which resulted in poor survival and recovery rates. Conversely, a significant loss of freeze tolerance was identified when plants were subjected to deacclimation events suggesting that St. Augustinegrass can be negatively affected by rapid temperature changes in the transitional climatic zone leading to increased sensitivity to winterkill. Overall, this study provides preliminary information regarding the complex relationships within and between mechanisms affecting freeze tolerance in St. Augustinegrass. Moreover, results presented here should aid in the development of protocols for selection of freeze tolerant breeding materials under controlled environmental conditions. [ABSTRACT FROM AUTHOR]

Two-year-old seedlings of Norway spruce (Picea abies) during spring deacclimation were subjected to controlled reacclimation by exposure to low temperatures of 4/−3°C (day/night) in a cold room. The highest increase in freezing tolerance (by 7°C) was observed after 12 d of low temperature exposure, when shoot water potential (Ψw shoot) decreased to 0.64 MPa. The process of reacclimation was accompanied by an increase in the phospholipid content of needle cell membranes. This increase applied to total (PL) and individual phospholipids: phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and phosphatidic acid (PA). After being exposed to the low temperature for 18 d, the seedlings were moved into the open air. This caused deacclimation, with an increase in Ψw shoot to −0.36 MPa and a decrease in the total phospholipid content and freezing tolerance of the needles. Significant correlations were observed between freezing tolerance, the membrane permeability (MP) of the needles and the phospholipid content, Ψw shoot and water content of the needles. The results show that during spring deacclimation, Norway spruce seedlings can be subjected to reacclimation, which is reflected in the phospholipid content, the biophysical changes of the membranes, and the freezing tolerance of the seedlings. During both spring deacclimation and reacclimation, water content in the needles plays a critical role in the cold tolerance of spruce seedlings.

The level of freezing tolerance achieved by perennial grasses and their capacity to remain cold acclimated throughout winter is critical for their winter survival. Research is necessary to better understand the metabolic processes associated with cold acclimation and deacclimation. This study was conducted to assess the response of creeping bentgrass (Agrostis stolonifera L.) (CB) and two ecotypes of annual bluegrass (Poa annua L.), one freezing-tolerant (AB-T) and one freezing-sensitive (AB-S), to cold acclimation and deacclimation. Following cold acclimation, plants were exposed to 8 °C for 0.5, 1, 3, and 5 d to induce deacclimation. Plants were assessed for their freezing tolerance (lethal temperature resulting in 50% mortality, LT50), their concentrations in soluble sugars and amino acids, and for changes in dehydrin-like proteins. Fully acclimated CB achieved higher level of LT50 (−21.5 °C) than AB-T (−19.8 °C), followed by AB-S (−15.3 °C). Total soluble sugars, mainly high molecular weight (HMW) fructans, accumulated in each species/ecotypes during cold acclimation with higher levels measured in CB. Dehydrin-like proteins were present in each species but they were mostly constitutive in AB while they were cold-inducible and linked with the LT50 in CB. Freezing tolerance decreased during deacclimation in each species. However, at each step of deacclimation, CB maintained higher freezing tolerance than AB in which the LT50 reached the low level of non-acclimated plants after five days at 8 °C. The depletion of HMW fructans observed during deacclimation followed a similar trend, with higher levels remaining at the end in CB, followed by AB-T and then by AB-S. The higher susceptibility of AB to winter injury is associated with both its lower cold acclimation capacity and deacclimation sensitivity. [ABSTRACT FROM AUTHOR]

Two-year-old seedlings of Norway spruce (Picea abies) during spring deacclimation were subjected to controlled reacclimation by exposure to low temperatures of 4/-3°C (day/night) in a cold room. he highest increase in freezing tolerance (by 7°C) was observed after 12 d of low temperature exposure, when shoot water potential (Ψw shoot) decreased to 0.64 MPa. he process of reacclimation was accompanied by an increase in the phospholipid content of needle cell membranes. his increase applied to total (PL) and individual phospholipids: phosphatidylcholine (PC), phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and phosphatidic acid (PA). After being exposed to the low temperature for 18 d, the seedlings were moved into the open air. his caused deacclimation, with an increase in Ψw shoot to -0.36 MPa and a decrease in the total phospholipid content and freezing tolerance of the needles. Significant correlations were observed between freezing tolerance, the membrane permeability (MP) of the needles and the phospholipid content, Ψw shoot and water content of the needles. he results show that during spring deacclimation, Norway spruce seedlings can be subjected to reacclimation, which is reflected in the phospholipid content, the biophysical changes of the membranes, and the freezing tolerance of the seedlings. During both spring deacclimation and reacclimation, water content in the needles plays a critical role in the cold tolerance of spruce seedlings. [ABSTRACT FROM AUTHOR]

Changes in cold hardiness, carbohydrate content and β-amylase gene expression were monitored in the shoots of the highbush blueberry (Vaccinium corymbosum L.) cultivars ‘Sharpblue’ and ‘Jersey’ during cold acclimation (CA) and deacclimation (DA). The seasonal patterns were similar in both cultivars, but the levels of cold hardiness determined by electrolyte leakage analysis were significantly different; ‘Jersey’ was hardier than ‘Sharpblue’. Cold hardiness was closely related to total soluble sugar content (r = −0.98** and −0.99** for ‘Sharpblue’ and ‘Jersey’, respectively). In ‘Jersey’, more soluble sugars accumulated during CA. Of the detected soluble sugars, glucose, fructose and raffinose contents were significantly associated with cold hardiness in both cultivars. Sucrose was abundant in both cultivars, and stachyose content changed significantly during CA and DA. However, they were not associated with cold hardiness. A sharp decrease in starch contents in the middle of CA coincided with β-amylase gene (VcBMY) expression, indicating the conversion of starch into soluble sugars. During CA, VcBMY was expressed up to twofold higher in ‘Jersey’ than in ‘Sharpblue’. These results suggest that intraspecies differences in the cold hardiness of highbush blueberries are associated with total soluble sugar content, which is driven partly by differential expression of VcBMY. [ABSTRACT FROM AUTHOR]

Hydrangea macrophylla is a popular and commercially important flowering shrub, but frost injury of buds and current-year shoots is a common problem in some of its cultivars. As a result of climate warming, temperate winters are becoming progressively milder, and temperature patterns are becoming increasingly irregular with an increased frequency of warm spells. Warm spells may induce premature dehardening, increasing the risk of subsequent freezing injuries. This study investigated cold-hardiness of stems and buds of Hydrangea macrophylla ssp. macrophylla (Thunb.) Ser. 'Alma' during dehardening in response to simulated warm spells and subsequent rehardening in January and early March. Plants were acclimated in the field and dehardened in the greenhouse at controlled warm temperatures for various durations. Dehardened plants were rehardened for up to 12 days in an unheated greenhouse (January) or in the field (March). Buds of H. macrophylla were slightly less cold-hardy than stems. In both stems and buds, the dehardening resistance and the rate of dehardening were influenced by temperature, but buds appeared to be less resistant to dehardening and dehardened faster than stems, in stems, dehardening proceeded faster in March than in January, and the capacity of the stems to reharden seemed reduced, indicating that both dehardening and rehardening were influenced by the progression of winter. Results of this study indicate that buds of H. macrophylla are more sensitive to frost injury than stems and the vulnerability of stems to frost injuries, caused by an unstable temperature regime, changes during the winter season. [ABSTRACT FROM AUTHOR]

Twelve southern-adapted blueberry genotypes, both southern highbush ( Vaccinium corymbosum L. introgressed with 2x V. darrowi Camp) and rabbiteye ( V. ashei Reade), were evaluated for bud development using a morphological scale and for mid-winter cold hardiness using a shoot freezing assay. The winter of 2006–2007 was particularly warm producing higher bud development scores for several of the genotypes and an apparent decrease of cold hardiness. Significant differences in LT50 values (treatments causing 50% bud mortality) were observed among the genotypes in both years, with a significant clone × year interaction. The greatest range in LT50 values occurred in 2007, when values ranged from −11.9°C for ‘Millennia’ to −25.5°C for ‘Reveille’, two southern highbush cultivars. Results suggest that germplasm selected in North Carolina might typically have sufficient cold hardiness to be used without concern as parental material in the development of blueberry germplasm with northern adaptation. Other more southern germplasm was generally less hardy and, if utilized as parental material, the resulting progeny would require greater scrutiny with regard to cold hardiness. [ABSTRACT FROM AUTHOR]

From 2004 to 2006, cold hardiness assays were performed to evaluate the relative winterhardiness of flower buds in selections of pure Vaccinium ashei Reade and V. constablaei Gray as well as in selections/families composed of various combinations of V. ashei and V. constablaei germplasm. Significant differences were observed among entries with LT50 values ranging from -17.2 to -28.4 °C. An analysis of LT50 versus percent V. constablaei yielded a regression of LT50 (°C) = (-0.08 x V. constablaei percentage) - 21.57. Families or selections with 50% (or greater) V. constablaei and some with 25% V. constablaei had LT50 values equivalent to or better than 'Bluecrop'. Based on this information, a 25% V. constablaei constitution appears suitable to develop northern-adapted rabbiteye types if proper parents are selected and if sufficient selection pressure for winterhardiness is exercised. [ABSTRACT FROM AUTHOR]

Information concerning genes and signals regulating cold acclimation processes in plants is abundant; however, less is known about genes and signals regulating the deacclimation process. A population of primarily winter B. napus varieties was used to conduct a genome-wide association study and to compare the transcriptomes from two winter B. napus varieties showing time-dependent differences in response to cold acclimation and deacclimation treatments. These studies helped to identify loci, candidate genes, and signaling processes impacting deacclimation in B. napus. GWAS identified polymorphisms at five different loci associated with freezing tolerance following deacclimation. Local linkage decay rates near these polymorphisms identified 38 possible candidate genes. Several of these genes have been reported as differentially regulated by cold stress in arabidopsis (Arabidopsis thaliana), including a calcium-binding EF-hand family protein (encoded by BnaCnng10250D) that was also differentially expressed during deacclimation in this study. Thousands of other genes differentially expressed during the acclimation and deacclimation treatments implicated processes involving oxidative stress, photosynthesis, light-regulated diurnal responses, and growth regulation. Generally, responses observed during acclimation were reversed within one week of deacclimation. The primary differences between the two winter B. napus varieties with differential deacclimation responses involved protection from oxidative stress and the ability to maintain photosynthesis. [ABSTRACT FROM AUTHOR]