Maximum Low Temperature Tolerance Research Articles

Perspectives on Low Temperature Tolerance and Vernalization Sensitivity in Barley: Prospects for Facultative Growth Habit.

One option to achieving greater resiliency for barley production in the face of climate change is to explore the potential of winter and facultative growth habits: for both types, low temperature tolerance (LTT) and vernalization sensitivity are key traits. Sensitivity to short-day photoperiod is a desirable attribute for facultative types. In order to broaden our understanding of the genetics of these phenotypes, we mapped quantitative trait loci (QTLs) and identified candidate genes using a genome-wide association studies (GWAS) panel composed of 882 barley accessions that was genotyped with the Illumina 9K single-nucleotide polymorphism (SNP) chip. Fifteen loci including 5 known and 10 novel QTL/genes were identified for LTT—assessed as winter survival in 10 field tests and mapped using a GWAS meta-analysis. FR-H1, FR-H2, and FR-H3 were major drivers of LTT, and candidate genes were identified for FR-H3. The principal determinants of vernalization sensitivity were VRN-H1, VRN-H2, and PPD-H1. VRN-H2 deletions conferred insensitive or intermediate sensitivity to vernalization. A subset of accessions with maximum LTT were identified as a resource for allele mining and further characterization. Facultative types comprised a small portion of the GWAS panel but may be useful for developing germplasm with this growth habit.

Developmental regulation of metabolites and low temperature tolerance in lines of crosses between spring and winter wheat

Low temperature (LT) tolerance in cereals needs developmental regulation of metabolites, a process which is associated with vernalization requirement. This study was initiated to investigate the relationships among stage of phenological development, final leaf number (FLN), the activities superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and polyphenol oxidase, the contents of proline, photosynthetic pigments, and hydrogen peroxide (H2O2) during vernalization and LT acclimation in spring and winter wheat. Six genotypes with different vernalization requirements were grown under greenhouse and field conditions. The spring-habit parent, “Pishtaz” and line 4021, rapidly entered the reproductive phase and had a limited capacities to LT acclimate. They also had the lowest antioxidative activities and accumulation of proline among genotypes. Lines 4002 and 4014, with a short vernalization requirement and higher FLN, remained in the early stages of phenological development longer and developed a higher level of LT tolerance and metabolites compared to spring habit genotypes. In contrast, the winter habit “Norstar” and line 4023 spent a longer time in the vegetative stage and accumulated higher levels of metabolites. Maximum LT tolerance and metabolite accumulations occurred near the vegetative/reproductive transition in all genotypes. The longer periods of vernalization and increased FLN that happened along with increased defense mechanisms and decreased damage indices (H2O2 content and LT50) ensured LT tolerance in wheat. These results demonstrate that both genetic and environmental factors via developmental regulation of metabolites play important roles in creating LT tolerance in long mild winters of Iran. Significant correlations coefficients for many of the metabolites considered in this study and Lethal temperature 50 (LT50) also suggest that they could be useful as indirect measures of plant LT tolerance potential in wheat breeding programs.

Dehydrin accumulation and extreme low-temperature tolerance in Siberian spruce (Picea obovata)

To investigate the role of dehydrins (DHNs) in extreme low-temperature (LT) tolerance, we sampled needle tissue of Siberian spruce (Picea obovata Ledeb.) from trees growing in an arboretum in Trondheim, Norway from August 2006 to April 2007 and tracked changes in LT tolerance via relative electrolyte leakage. We used western blotting to estimate relative amounts of proteins binding a DHN K-segment antibody, measured relative amounts of nine transcripts for small (<25 kDa) DHNs by quantitative reverse transcription-polymerase chain reaction (PCR) using primers developed for DHN transcripts in a closely related species, Picea abies (L.) Karsten, and isolated and sequenced PCR products for five P. obovata DHNs. Three protein bands of 53, 35 and 33 kDa were detected on western blots of SDS-PAGE-separated protein extracts. The 53-kDa DHN was already present late in the growing season, but accumulated during acclimation, and levels decreased rapidly during deacclimation. The 33- and 35-kDa proteins, identified as Picg5 class DHNs by mass spectrometry, first appeared in detectable amounts late in the acclimation process and remained at detectable levels throughout the period of maximum LT tolerance. Levels of the 53-kDa DHN correlated with two LT tolerance parameters, while results for the 33- and 35-kDa proteins were equivocal due to limited sample size and variation in LT tolerance during the mid-winter period. Three additional bands of 30, 28 and 26 kDa were detected in extracts from needles collected in November 2010 using an immunity-purified antibody. Immunoblotting of two-dimensional gel electrophoresis gels loaded with proteins extracted from October and November samples corroborated the results obtained by SDS-PAGE western blots. One large spot in the 53 kDa range and two trains of spots in the same size range as the 33 and 35 kDa DHNs were detected using the K-segment antibody. Eight of the nine DHN transcripts closely tracked LT tolerance parameters, whereas the ninth DHN transcripts followed a reverse pattern, decreasing during winter and increasing again during deacclimation. Multiple regression models using principal components of the transcripts to predict two different LT tolerance parameters suggest separate but overlapping functions for different DHNs in establishing and maintaining extreme LT tolerance.

The Genetics of Winterhardiness in Barley: Perspectives from Genome‐Wide Association Mapping

Winterhardiness is a complex trait that involves low temperature tolerance (LTT), vernalization sensitivity, and photoperiod sensitivity. Quantitative trait loci (QTL) for these traits were first identified using biparental mapping populations; candidate genes for all loci have since been identified and characterized. In this research we used a set of 148 accessions consisting of advanced breeding lines from the Oregon barley (Hordeum vulgare L. subsp vulgare) breeding program and selected cultivars that were extensively phenotyped and genotyped with single nucleotide polymorphisms. Using these data for genome‐wide association mapping we detected the same QTL and genes that have been systematically characterized using biparental populations over nearly two decades of intensive research. In this sample of germplasm, maximum LTT can be achieved with facultative growth habit, which can be predicted using a three‐locus haplotype involving FR‐H1, FR‐H2, and VRN‐H2. The FR‐H1 and FR‐H2 LTT QTL explained 25% of the phenotypic variation, offering the prospect that additional gains from selection can be achieved once favorable alleles are fixed at these loci.

Cold Acclimation Proteome Analysis Reveals Close Link between the Up-Regulation of Low-Temperature Associated Proteins and Vernalization Fulfillment

Low-temperature (LT) stress is one of the major limiting factors in cereal production in cold high-altitude mountainous areas of Iran where cereals are exposed to variable periods of temperatures in the vernalization range during the autumn season. Cereals regulate their development through adaptive mechanisms that are responsive to low but nonfreezing temperatures. We exploited a proteomic approach to determine the interrelationship between vernalization fulfillment and expression of low-temperature (LT)-induced protein in most hardy Norstar and semi-hardy Azar2 wheat (Triticum aestivum L. em. Thell). These cultivars were subjected to 12 h of cold acclimating temperature (2 °C) over a period of 0-89 days. LT tolerance, as measured by LT50, and vernalization fulfillment, as estimated from final leaf number (FLN), was determined at intervals throughout the acclimation period. A significant decrease in FLN associated with LT treatment indicated that Norstar and Azar2 had vernalization responses. Azar2 achieved its vernalization fulfillment and maximum LT tolerance (∼ -8 °C) by 28 days of acclimation. However, Norstar had a longer vernalization requirement (between 35 and 42 days) and reached vernalization fulfillment and maximum LT tolerance (∼ -18.7 °C) about the same time as vernalization fulfillment. We applied a two-dimensional electrophoresis-based proteomics approach to analyze changes in the leaf proteome of two genotypes, Norstar and Azar2, during cold acclimation. Using MALDI-TOF/TOF mass spectrometry, 66 LT-associated proteins could significantly be identified. These proteins were categorized into cold-regulated proteins, antifreezing proteins, oxidative stress defense, photosynthesis, chloroplast post-transcriptional regulation, metabolisms, and protein synthesis. A close association between the vernalization fulfillment and the start of a decline in the protein accumulation of hardy Norstar with a long vernalization requirement and semi-hardy Azar2 with a short vernalization requirement was observed. This finding supported the hypothesis that developmental trait which was regulated by vernalization had a regulatory influence over LT proteome response and highlight a close link between the up-regulation of LT-associated proteins and vernalization fulfillment at the molecular level in wheat.

Dynamics of low-temperature acclimation in temperate and boreal conifer foliage in a mild winter climate

To provide baseline data for physiological studies of extreme low-temperature (LT) tolerance in boreal conifers, we profiled LT stress responses, liquid nitrogen (LN(2))-quench tolerance, and sugar concentrations in foliage of boreal-temperate species pairs in the genera Abies, Picea and Pinus, growing in an arboretum in a temperate oceanic climate from August 2006 through April 2007. The boreal species acclimated more rapidly and deeply than the temperate species, acquiring LN(2)-quench tolerance by late November, despite unusually warm conditions throughout the autumn and early winter. Maximum LT tolerance in the temperate species was in the -25 to -35 degrees C range, and was reached only after a period of freezing temperatures in late January and February. During LT acclimation in the temperate species, sigmoid temperature-relative electrolyte leakage (REL) curves shifted toward lower temperatures, whereas in boreal species there was both a temperature shift and a lowering of the maximum REL until it fell below a threshold associated with irreversible injury. These differences may reflect differences in mechanisms of LT acclimation and LT tolerance. The concentrations of total and individual sugars did not show a clear pattern that could differentiate the boreal and temperate groups. Raffinose and, in three of the six species, stachyose showed the closest association with LT tolerance. Sugar concentrations, principally sucrose, decreased during mild weather, perhaps because of respiratory losses or phloem export, and increased after periods of freezing temperatures. Low-temperature acclimation in boreal species appears to follow a rigid program that may affect their ability to avoid excessive respiratory losses in the event of continued climate warming in boreal regions.

Low-temperature acclimation of barley cultivars used as parents in mapping populations: response to photoperiod, vernalization and phenological development

Six barley (Hordeum vulgare L.) accessions, previously used as parents of mapping populations, were evaluated for characters potentially affecting the location of low-temperature (LT) tolerance QTLs. Three were of winter growth habit (Kompolti Korai, Nure, and Strider), one was facultative (Dicktoo) and two were spring (Morex and Tremois). Final leaf number (FLN) and LT(50 )were determined at weekly intervals from 0 to 98 days of LT acclimation/vernalization under both long day (LD) and short day (SD) photoperiods. The point of vegetative/reproductive transition was determined from measurements of double ridge (DR) formation and FLN. With the exception of Nure, SD delayed development by increasing leaf production. Dicktoo was extremely SD sensitive lengthening its vegetative phase by more than 63 days relative to the LD photoperiod. SD had the opposite effect on Nure, causing an accelerating of flowering exhibiting the characteristic of 'short day vernalization'. All accessions except Dicktoo and Kompolti Korai acclimated rapidly in the first 7 days of LT exposure, approaching their maximum LT tolerance in 14-21 days. Dicktoo and Kompolti Korai continued to slowly acclimate until reproductive transition. The results emphasize two important points: (1) the location of QTLs for LT tolerance, and as a consequence the identification of putative candidate genes, will be a function of the genotypes sampled, the experimental conditions used, and the quality of the phenotypic data and (2) the barley LT tolerance pathway reaches an early impediment relative to closely related more hardy members of the Triticeae such as wheat and rye.

Regulation of low-temperature tolerance in barley under field conditions in northwest Iran

Low-temperature (LT) stress is a major factor limiting the over-winter survival of barley (Hordeum vulgare L.). The objective of this study was to determine the relationship between vegetative/reproductive transition and expression of LT tolerance in barley cultivars acclimated under field conditions. Three cultivars with different vernalization response and photoperiod sensitivity were planted in the field at the Maragheh Dryland Agricultural Research Station (37°15′N, 46°15′E; 1720m) in Iran in the autumns of 2002 and 2003. LT tolerance, as measured by LT50, and stage of phenological development, as estimated from final leaf number (FLN) and shoot apex developmental morphology, were determined during the autumn and winter seasons. The short-day insensitive spring-habit cultivar Rihane-03 had a limited ability to acclimate to LT and it reached its maximum level of LT tolerance very quickly. The winter-habit cultivar Dobrinya reached its maximum LT tolerance at the point of vernalization saturation. The very short-day (SD) sensitive spring-habit cultivar Dicktoo entered the double ridge (DR) stage at about the same time as the winter-habit Dobrinya. The delay in the phenological development of both Dobrinya and Dicktoo was accompanied by increased expression of LT tolerance confirming that the length of the vegetative phase determines a plant’s ability to maintain a high level of cold-tolerance gene expression when temperatures are in the acclimation range. These observations suggest that more detailed studies should be initiated to establish the importance of interactions between photoperiod sensitivity and vernalization requirement with the objective of identifying genetic combinations and management systems that extend the vegetative stage and provide longer-term protection from LT stress in regions with long mild winters like those normally experienced in north-west Iran. Key words: Vernalization, photoperiod, phenological development, freezing resistance, barley