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As a result of global warming, vegetation suffers from repeated freeze-thaw cycles caused by more frequent short-term low temperatures induced by hail, snow, or night frost. Therefore, short-term freezing stress of plants should be investigated particularly in light of the current climatic conditions. Alcohol dehydrogenase (ADH) plays a central role in the metabolism of alcohols and aldehydes and it is a key enzyme in anaerobic fermentation. ADH1 responds to plant growth and environmental stress; however, the function of ADH1 in the response to short-term freezing stress remains unknown. Using real-time quantitative fluorescence PCR, the expression level of was analyzed at low temperature (4°C). The lethal temperature was calculated based on the electrolyte leakage tests for both deletion mutants ( ) and wild type (WT) plants. To further investigate the relationship between and cold tolerance in plants, low-Mr polar metabolite analyses of and WT were performed at cold temperatures using gas chromatography-mass spectrometry. This investigation focused on freezing treatments (cold acclimation group: -6°C for 2 h with prior 4°C for 7 d, cold shock group: -6°C for 2 h without cold acclimation) and recovery (23°C for 24 h) with respect to seedling growth at optimum temperature. The experimental results revealed a significant increase in expression during low temperature treatment (4°C) and at a higher lethal temperature in compared to that in the WT. Retention time indices and specific mass fragments were used to monitor 263 variables and annotate 78 identified metabolites. From these analyses, differences in the degree of metabolite accumulation between and WT were detected, including soluble sugars (e.g., sucrose) and amino acids (e.g., asparagine). In addition, the correlation-based network analysis highlighted some metabolites, e.g., melibiose, fumaric acid, succinic acid, glycolic acid, and xylose, which enhanced connectedness in network under cold chock. When considered collectively, the results showed that possessed a metabolic response to freezing stress and played an important role in the cold stress response of a plant. These results expands our understanding of the short-term freeze response of in plants.

Alfalfa (Medicago sativa) is a globally distributed economic legume crop used for forage and ecological restoration. We aimed to explore the mechanisms underlying the cold acclimation observed in this species. Our results for fall plant growth showed that non-dormant alfalfa (SD) maintained a vigorous growth rate compared to that of fall-dormant alfalfa (ZD); however, the winter survival rate of ZD was higher than that of SD. Among the ZD samples, the starch content first accumulated and then decreased; the sucrose content was consumed first along with simultaneous raffinose accumulation, which was followed by sucrose content accumulation, with consistent changes in the corresponding related synthase and hydrolase activity. SD exhibited the opposite trend. The transcriptome data showed that most of the differentially expressed genes were involved in carbon metabolism (ko01200), amino acid biosynthesis (ko01230), and starch and sucrose metabolism (ko00500). Our data clearly show that alfalfa’s cold acclimation mechanism is a complex process, with the establishment of stable carbon homeostasis; sucrose is first converted into starch and raffinose, and then, starch is converted into sucrose, which enables alfalfa’s cold resistance. The process is accompanied by CBF/DREB1A TF regulation. This study provides important insights into the cold acclimation mechanisms of alfalfa.

Evergreen ornamental plants can supply year-round aesthetic value and strong ecological benefits in comparison to deciduous species. However, less attention has been paid to the cause of foliar habits, especially in herbaceous perennials. A comparative study on evergreen and deciduous species with close relationships could help to uncover the factors that determine foliar habits when sibling mutants are absent. Three independent experiments were conducted in the present study. Experiment 1 was focused on the changes in the percentage of green leaves (PGL) between evergreen daylilies (Hemerocallis aurantiaca Baker) and the deciduous species (Hemerocallis fulva L.). The results showed that their foliar habits were consistent with those of previous reports but could be influenced dramatically by the air temperature. The leaf freezing tolerance (LFT) and relevant morphological, physiological and biochemical variations in leaf tissues in addition to the shoot growth status were determined during Experiments 2 and 3 when comparing natural cold acclimation to de-acclimation. Correlation analyses between the PGL and other indices indicated that the winter shoot growth probably maintained the green leaves of the evergreen daylilies, while a strong LFT might facilitate the defoliation of deciduous species. Furthermore, the dormant deciduous daylily is more freezing-tolerant than the ever-growing evergreen species. This study also possesses practical value for plants with variant green periods in landscaping.

Water movement across cellular membranes is regulated largely by a family of water channel proteins called aquaporins (AQPs). Since several abiotic stresses such as, drought, salinity and freezing, manifest themselves via altering water status of plant cells and are linked by the fact that they all result in cellular dehydration, we overexpressed an AQP (tonoplast intrinsic protein) from Panax ginseng, PgTIP1, in transgenic Arabidopsis thaliana plants to test its role in plant's response to drought, salinity and cold acclimation (induced freezing tolerance). Under favorable conditions, PgTIP1 overexpression significantly increased plant growth as determined by the biomass production, and leaf and root morphology. PgTIP1 overexpression had beneficial effect on salt-stress tolerance as indicated by superior growth status and seed germination of transgenic plants under salt stress; shoots of salt-stressed transgenic plants also accumulated greater amounts of Na⁺ compared to wild-type plants. Whereas PgTIP1 overexpression diminished the water-deficit tolerance of plants grown in shallow (10 cm deep) pots, the transgenic plants were significantly more tolerant to water stress when grown in 45 cm deep pots. The rationale for this contrasting response, apparently, comes from the differences in the root morphology and leaf water channel activity (speed of dehydration/rehydration) between the transgenic and wild-type plants. Plants overexpressed with PgTIP1 exhibited lower (relative to wild-type control) cold acclimation ability; however, this response was independent of cold-regulated gene expression. Our results demonstrate a significant function of PgTIP1 in growth and development of plant cells, and suggest that the water movement across tonoplast (via AQP) represents a rate-limiting factor for plant vigor under favorable growth conditions and also significantly affect responses of plant to drought, salt and cold stresses.

Evergreen conifers are champions of winter survival, based on their remarkable ability to acclimate to cold and develop cold hardiness. Counterintuitively, autumn cold acclimation is triggered not only by exposure to low temperature, but also by a combination of decreasing temperature, decreasing photoperiod and changes in light quality. These environmental cues control a network of signaling pathways that coordinate cold acclimation and cold hardiness in overwintering conifers, leading to cessation of growth, bud dormancy, freezing tolerance and changes in energy metabolism. Advances in genomic, transcriptomic and metabolomic tools for conifers have improved our understanding of how trees sense and respond to changes in temperature and light during cold acclimation and the development of cold hardiness, but there remain considerable gaps deserving further research in conifers. In the first section of this review, we focus on the physiological mechanisms used by evergreen conifers to adjust metabolism seasonally and to protect overwintering tissues against winter stresses. In the second section, we review how perception of low temperature and photoperiod regulate the induction of cold acclimation. Finally, we explore the evolutionary context of cold acclimation in conifers and evaluate challenges imposed on them by changing climate and discuss emerging areas of research in the field.

Thermal macrophysiology is an established research field that has led to well-described patterns in the global structuring of climate adaptation and risk. However, since it was developed primarily in animals, we lack information on how general these patterns are across organisms. This is alarming if we are to understand how thermal tolerances are distributed globally, improve predictions of climate change, and mitigate effects. We approached this knowledge gap by compiling a geographically and taxonomically extensive database on plant heat and cold tolerances and used this dataset to test for thermal macrophysiological patterns and processes in plants. We found support for several expected patterns: Cold tolerances are more variable and exhibit steeper latitudinal clines and stronger relationships with local environmental temperatures than heat tolerances overall. Next, we disentangled the importance of local environments and evolutionary and biogeographic histories in generating these patterns. We found that all three processes have significantly contributed to variation in both heat and cold tolerances but that their relative importance differs. We also show that failure to simultaneously account for all three effects overestimates the importance of the included variable, challenging previous conclusions drawn from less comprehensive models. Our results are consistent with rare evolutionary innovations in cold acclimation ability structuring plant distributions across biomes. In contrast, plant heat tolerances vary mainly as a result of biogeographical processes and drift. Our results further highlight that all plants, particularly at mid-to-high latitudes and in their nonhardened state, will become increasingly vulnerable to ongoing climate change.

Climate change will increase autumn air temperature, while photoperiod decrease will remain unaffected. We assessed the effect of increased autumn air temperature on timing and development of cold acclimation and freezing resistance in Eastern white pine (EWP, Pinus strobus) under field conditions. For this purpose we simulated projected warmer temperatures for southern Ontario in a Temperature Free-Air-Controlled Enhancement (T-FACE) experiment and exposed EWP seedlings to ambient (Control) or elevated temperature (ET, +1.5°C/+3°C during day/night). Photosynthetic gas exchange, chlorophyll fluorescence, photoprotective pigments, leaf non-structural carbohydrates (NSC), and cold hardiness were assessed over two consecutive autumns. Nighttime temperature below 10°C and photoperiod below 12 h initiated downregulation of assimilation in both treatments. When temperature further decreased to 0°C and photoperiod became shorter than 10 h, downregulation of the light reactions and upregulation of photoprotective mechanisms occurred in both treatments. While ET seedlings did not delay the timing of the downregulation of assimilation, stomatal conductance in ET seedlings was decreased by 20-30% between August and early October. In both treatments leaf NSC composition changed considerably during autumn but differences between Control and ET seedlings were not significant. Similarly, development of freezing resistance was induced by exposure to low temperature during autumn, but the timing was not delayed in ET seedlings compared to Control seedlings. Our results indicate that EWP is most sensitive to temperature changes during October and November when downregulation of photosynthesis, enhancement of photoprotection, synthesis of cold-associated NSCs and development of freezing resistance occur. However, we also conclude that the timing of the development of freezing resistance in EWP seedlings is not affected by moderate temperature increases used in our field experiments.

During autumn, evergreen conifers utilize the decrease in daylength and temperature as environmental signals to trigger cold acclimation, a process that involves the downregulation of photosynthesis, upregulation of photoprotection, and development of cold hardiness. Global warming will delay the occurrence of autumn low temperatures while daylength remains unaffected. The impact of autumn warming on cold acclimation and the length of the carbon uptake period of species with ranges that encompass diverse climates, such as Douglas-fir ( Pseudotsuga menziesii ), remains unclear. Our study investigated intraspecific variation in the effects of autumn warming on photosynthetic activity, photosynthetic pigments, and freezing tolerance in two interior (var. glauca ) and two coastal (var. menziesii ) Douglas-fir provenances. Following growth under simulated summer conditions with long days (16 h photoperiod) and summer temperatures (22/13°C day/night), Douglas-fir seedlings were acclimated to simulated autumn conditions with short days (8 h photoperiod) and either low temperatures (cool autumn, CA; 4/−4°C day/night) or elevated temperatures (warm autumn, WA; 19/11°C day/night). Exposure to low temperatures in the CA treatment induced the downregulation of photosynthetic carbon assimilation and photosystem II efficiency, increased the size and de-epoxidation of the xanthophyll cycle pigment pool, and caused the development of sustained nonphotochemical quenching (NPQ). Seedlings in the WA treatment exhibited no downregulation of photosynthesis, no change in xanthophyll cycle pigment de-epoxidation, and no development of sustained NPQ. Albeit these changes, freezing tolerance was not impaired under WA conditions compared with CA conditions. Interior Douglas-fir seedlings developed greater freezing tolerance than coastal seedlings. Our findings suggest that autumn warming, i.e., short photoperiod alone, does not induce the downregulation of photosynthesis in Douglas-fir. Although autumn warming delays the downregulation of photosynthesis, the prolonged period of photosynthetic activity does not bear a trade-off of impaired freezing tolerance.

Unpredicted variability in temperature is associated with frequent extreme low-temperature events. Wheat is a leading crop in fulfilling global food requirements. Climate-driven temperature extremes influence the vegetative and reproductive growth of wheat, followed by a decrease in yield. This review describes how low temperature induces a series of modifications in the morphophysiological, biochemical, and molecular makeup of wheat and how it is perceived. To cope with these modifications, crop plants turn on their cold-tolerance mechanisms, characterized by accumulating soluble carbohydrates, signaling molecules, and cold tolerance gene expressions. The review also discusses the integrated management approaches to enhance the performance of wheat plants against cold stress. In this review, we propose strategies for improving the adaptive capacity of wheat besides alleviating risks of cold anticipated with climate change.