Freezing Tolerance In Seedlings Research Articles

DIACYLGLYCEROL ACYLTRANSFERASE1 Contributes to Freezing Tolerance.

Freezing limits plant growth and crop productivity, and plant species in temperate zones have the capacity to develop freezing tolerance through complex modulation of gene expression affecting various aspects of metabolism and physiology. While many components of freezing tolerance have been identified in model species under controlled laboratory conditions, little is known about the mechanisms that impart freezing tolerance in natural populations of wild species. Here, we performed a quantitative trait locus (QTL) study of acclimated freezing tolerance in seedlings of Boechera stricta, a highly adapted relative of Arabidopsis (Arabidopsis thaliana) native to the Rocky Mountains. A single QTL was identified that contained the gene encoding ACYL-COENZYME A:DIACYLGLYCEROL ACYLTRANSFERASE1 (BstDGAT1), whose expression is highly cold responsive. The primary metabolic enzyme DGAT1 catalyzes the final step in assembly of triacylglycerol (TAG) by acyl transfer from acyl-CoA to diacylglycerol. Freezing tolerant plants showed higher DGAT1 expression during cold acclimation than more sensitive plants, and this resulted in increased accumulation of TAG in response to subsequent freezing. Levels of oligogalactolipids that are produced by SFR2 (SENSITIVE TO FREEZING2), an indispensable element of freezing tolerance in Arabidopsis, were also higher in freezing-tolerant plants. Furthermore, overexpression of AtDGAT1 led to increased freezing tolerance. We propose that DGAT1 confers freezing tolerance in plants by supporting SFR2-mediated remodeling of chloroplast membranes.

Transgenic Arabidopsis Flowers Overexpressing Acyl-CoA-Binding Protein ACBP6 are Freezing Tolerant

Low temperature stress adversely affects plant growth. It has been shown that the overexpression of ACYL-COENZYME A-BINDING PROTEIN6 (ACBP6) resulted in enhanced freezing tolerance in seedlings and rosettes accompanied by a decrease in phosphatidylcholine (PC), an increase in phosphatidic acid (PA) and an up-regulation of PHOSPHOLIPASE Dδ(PLDδ) in the absence of COLD-RESPONSIVE (COR)-related gene induction. Unlike rosettes, ACBP6-overexpressor (OE) flowers showed elevations in PC and monogalactosyldiacylglycerol (MGDG) accompanied by a decline in PA. The increase in PC species corresponded to a decline in specific PAs. To better understand such differences, the expression of PC-, MGDG-, proline-, ABA- and COR-related genes, and their transcription factors [C-repeat binding factors (CBFs), INDUCER OF CBF EXPRESSION1 (ICE1) and MYB15] was analyzed by quantitative real-time PCR (qRT-PCR). ACBP6-conferred freezing-tolerant flowers showed induction of COR-related genes, CBF genes and ICE1, PC-related genes (PLDδ, CK, CK-LIKE1, CK-LIKE2, CCT1, CCT2, LPCAT1, PLA2α, PAT-PLA-IIβ, PAT-PLA-IIIα, PAT-PLA-IIIδ and PLDζ2), MGDG-related genes (MGD genes and SFR2) and ABA-responsive genes. In contrast, ACBP6-conferred freezing-tolerant rosettes were down-regulated in COR-related genes, CBF1, PC-related genes (PEAMT1, PEAMT2, PEAMT3, CK1, CCT1, CCT2, PLA2α, PAT-PLA-IIIδ and PLDζ2), MGDG-related genes (MGD2, MGD3 and SFR2) and some ABA-responsive genes including KIN1 and KIN2. These results suggest that the mechanism in ACBP6-conferred freezing tolerance varies in different organs.

Effects of cold-hardening on compatible solutes and antioxidant enzyme activities related to freezing tolerance in Ammopiptanthus mongolicus seedlings

Cold acclimation is associated with many metabolic changes that lead to an increase of freezing tolerance. In order to investigate the biochemical process of cold acclimation in Ammopiptanthus mongolicus, seedlings were acclimated at 2°C under 16-h photoperiod (150 µmol·m−2·s−1 photosynthetically active radiation) for 14 d. Freezing tolerance in seedlings increased after 14 d of cold-hardening. Contents of protein, proline and solute carbohydrate in cotyledon increased after cold acclimation. Patterns of isozymes of superoxide dismutase (SOD), peroxidase, catalase and polyphenol oxidase (PPO) were investigated. The activities of SOD, peroxidase and PPO in cold acclimated plants were increased during cold-hardening. We deduced that compatible solutes and antioxidant enzymes play important roles in development of freezing tolerance during cold acclimation in this evergreen woody plant.

Increased freezing tolerance in an ABA-hypersensitive mutant of common wheat

To study role of abscisic acid (ABA) in cold acclimation and cold/freezing tolerance in wheat, we analyzed an ABA-hypersensitive mutant of Triticum aestivum, named ABA27. ABA-hypersensitivity in ABA27 was confirmed by bioassays involving germination and seedling growth and expression analysis of ABA-responsive genes in comparison with the parental cultivar 'Chihoku-komugi' (Chihoku). ABA27 showed significantly increased freezing tolerance in seedlings without cold acclimation. ABA-treated seedlings of ABA27 accumulated more transcripts of ABA-responsive genes Cor/Lea and their putative transcription factor (TF) genes than Chihoku under both normal and low-temperature (LT) conditions. Non-ABA-regulated Cor/Lea transcripts showed higher accumulation in ABA27 also under normal temperature. These results suggest that the elevated ABA sensitivity in ABA27 contributes to the improved freezing tolerance through increased expression of the ABA-regulated LT signal pathway. Based on these and previous results obtained in an ABA-less-sensitive mutant, it is suggested that both positive and negative regulation of ABA response is involved in the basic mechanism of freezing tolerance in wheat.

Correlating gene expression to physiological parameters and environmental conditions during cold acclimation of Pinus sylvestris, identification of molecular markers using cDNA microarrays

Scots pine (Pinus sylvestris L.) seedlings were grown under different conditions (three field locations, two seasons and two climate room regimes), and then analyzed for freezing tolerance of shoots and roots and for transcript abundance in apical buds based on a cDNA microarray containing about 1500 expressed sequence tags (ESTs) from buds of cold-treated Scots pine seedlings. In a climate room providing long daily photoperiods and high temperatures, seedlings did not develop freezing tolerance, whereas seedlings in a climate room set to provide declining temperatures and day lengths developed moderate freezing tolerance. Control seedlings grown outside under field conditions developed full freezing tolerance. Differences in physiological behavior of the different seedling groups, combined with molecular analysis, allowed identification of a large group of genes, expression of which changed during the development of freezing tolerance. Transcript abundance of several of these genes was highly correlated with freezing tolerance in seedlings differing in provenance, field location or age, making them excellent candidate marker genes for molecular tests for freezing tolerance.

Different responses of northern and southern ecotypes of Betula pendula to exogenous ABA application

We investigated responses of northern and southern ecotypes of silver birch (Betula pendula Roth) to exogenous abscisic acid (ABA) under controlled environmental conditions to determine the role of ABA in cold acclimation and dormancy development. Abscisic acid was sprayed on the leaves and changes in freezing tolerance, determined by the electrolyte leakage test, and bud dormancy were monitored. Applied ABA induced cold acclimation but had no effect on growth cessation in seedlings grown in long day conditions (LD, 24-h photoperiod at 18 degrees C). It enhanced freezing tolerance and accelerated growth cessation in seedlings grown in short day conditions (SD, 12-h photoperiod at 18 degrees C), and slightly enhanced freezing tolerance in seedlings grown at low temperature (LT, 24-h photoperiod at 4 degrees C) in both ecotypes. There were distinct ecotypic differences in ABA-induced cold acclimation and dormancy development. The northern ecotype was more responsive to applied ABA than the southern ecotype, resulting in more rapid development of freezing tolerance in all treatments, and earlier dormancy development in SD. When plants were grown in a photoperiod just above the critical photoperiod for the ecotype (defined as the longest photoperiod that induces growth cessation), applied ABA caused growth cessation and dormancy development. Compared with ABA-treated seedlings grown in SD, dormancy development was delayed in ABA-treated seedlings exposed to a near-critical photoperiod, but even in this treatment dormancy developed faster in the northern ecotype than in the southern ecotype.

Phosphorus and nitrogen effects on the freezing tolerance of Norstar winter wheat

To increase the probability of winter survival, it is recommended that winter wheat (Triticum aestivum L.) be sown into standing stubble from a previous crop, which acts to trap an insulating layer of snow. Therefore, to replenish nutrients used by the previous crop and to obtain optimum yields of winter wheat, these soils have to be fertilized with N and P. The objective of this study was to determine the effect of N and P, alone and in combination, on the freezing tolerance of Norstar winter-wheat seedlings in the fall and in early spring and during storage at −4 °C throughout the winter months. None of the fertilizer treatments had an effect on the freezing tolerance of the seedlings in late fall, however, P in combination with N decreased freezing tolerance in March and April, with the effects being more pronounced at high rates of P. Seedlings sampled from the field in early May were similar in freezing tolerance, irrespective of the level of fall-applied N and P. Both shoot and root growth of seedlings collected in the spring were enhanced by P fertilization in combination with N. Fall-applied P increased the level of tissue N and P, while applications of N increased the level of tissue N of seedlings sampled in late fall. Key words: Winter wheat, nitrogen, phosphorous, freezing tolerance

Growth and Freezing Tolerance of Winterfat Seedlings

Tolerance to freezing temperatures may be an important factor in the regeneration ecology of winterfat (Ceratoides lanata (Pursh) J.T. Howell). Therefore, growth and freezing tolerance of winterfat seedlings were determined after being grown under different controlled temperatures for 7, 14, 21, or 28 days. Growth of seedlings was greater under day temperatures of 15 and 20 degrees C relative to 5 and 10 degrees C. Freezing tolerance of seedlings was dependent on seedling age and growth conditions. Younger seedlings were more freezing tolerant than older ones grown under the same environmental conditions. Seedlings grown under lower temperatures were more freezing tolerant than those grown under higher temperatures. The lowest observed lethal temperature for 50% mortality (LT50) was -11.8 degrees C for 7-day old seedlings grown under 10/0 degrees C alternating temperatures, and the highest LT50 was about -5 degrees C for seedlings 28 days of age when grown under 29/1 degrees C. Based on seedbed temperatures in the field, the results suggest that freezing temperatures may indeed limit the establishment of winterfat seedlings on Northern Mixed Prairie. Seedbeds with litter accumulations or standing dead plant material may ameliorate low temperature extremes and reduce mortality of winterfat seedlings.