Time and Temperature Interactions in Freezing Tolerance of Winter Wheat

Abstract

1523 RESEARCH C old acclimation, or cold-hardening, occurs in many plant species in response to a period of low, above-freezing temperatures and short daylengths, as occur in the autumn in temperate regions of the world. Cold acclimation is associated with a plethora of metabolic changes that are thought to contribute to the ability to withstand subsequent freezing to potentially damaging tempera-). Specifically with wheat (Triticum aestivum L.), Herman et al. (2006) found that plants that had been cold-acclimated at +3°C for 3 wk, and then exposed to −3°C for 6 h to 3 d, showed an increase in freezing tolerance of more than 2°C, concomitant with changes in the mRNA levels of hundreds of genes, indicating the plants continued to acclimate while in the subzero environment.In a study of five winter wheat lines and their diallel progeny, the minimum temperature significantly impacted survival in 73% of the populations studied, while the length of time the plants were held at the minimum temperature was a significant factor in only 40% of the populations, and those were all progeny populations, not the parent lines (Skinner and Mackey, 2009). This observation suggested that time and temperature in the subzero environment impacted survival in a genotype-specific manner. Because the severity of cold experienced by plants in the field varies greatly from year to year and from place to place within a field (Fowler, 1979), the time and temperature combinations plants experience ABSTRACT To survive the temperature fluctuations that occur during the winter months, winter wheat (Triticum aestivum L.) plants must tolerate episodes of freezing of varying intensity and duration. In this study, the ability of six wheat cultivars to survive exposure to −13.5 to −16.5°C for 2, 3, or 4 h was measured. Tolerance was described as the percentages of plants surviving after time intervals at −10°C or less. The average survival of the six cultivars significantly decreased by about 50% as length of exposure to −10°C or less was increased from 325 to 525 min. Surprisingly, survival then increased with longer exposure times such that the percentages of plants surviving were similar after 675, and after 325 min at −10°C or less. The greater survival after longer exposure times to −10°C or less compared with shorter exposure times suggested that certain freezing tolerance mechanism(s) in wheat are activated only after sufficient exposure to subfreezing temperatures for a sufficient amount of time. Lesser exposure to either temperature or time apparently does not activate this mechanism, leading to greater plant death. Further characterization of this mechanism and its genetic control may lead to development of wheat lines with enhanced ability to survive harsh freezing conditions and thus improved winterhardiness.

Genetic and physiological mechanisms of freezing tolerance in locally adapted populations of a winter annual

“…Both populations experience temperatures that trigger cold acclimation. The range of conditions over which cold acclimation is induced is poorly known and is likely to vary across taxa, but 4°C has been shown to induce cold acclimation in Arabidopsis thaliana (Alonso‐Blanco et al., ; Hannah et al., ; Zhen and Ungerer, ) and winter wheat (Zhu et al., ; Skinner, ). In winter at the SW site, soil temperatures are usually below freezing for more than 80 days, and temperatures can reach as low as −11°C, with air temperatures even colder (Oakley et al., ).…”

Nucleic acid damage and DNA repair are affected by freezing stress in annual wheat (Triticum aestivum) and by plant age and freezing in its perennial relative (Thinopyrum intermedium)

“…While some degree of cold hardening happens at temperatures as high as 10–12°C, for wheat and for other cold‐hardy perennial grasses (e.g., Gay and Eagles, 1991), complete acclimation does not occur until temperatures are well below this induction threshold and typically well below 5°C (Fowler, 2008; Ganeshan et al, 2009). In fact, further cold adaptation requires temperatures well below freezing (Herman et al, 2006; Veisz et al, 1996); individual freezing events even after acclimation have been achieved are associated with further short‐term transcriptional responses (Skinner, 2009); and maximal cold adaptation may require temperatures as low as −10°C (Skinner, 2014; Skinner and Bellinger, 2017). Photoperiod also has a role in achieving or prolonging cold tolerance in some wheat cultivars (Mahfoozi et al, 2001) but not in others (Limin and Fowler, 2006), and in general appears to be much less important than temperature in inducing cold tolerance.…”

Genome‐wide association analysis of freezing tolerance in soft red winter wheat

“…Prior to the hard freeze, we decreased the temperatures to −2 ˚C and added ice chips to the plants to facilitate ice nucleation (Case et al, 2014). The plants were subjected to a period of freezing of −8 ˚C for 24 h. During the freezing period, plants were kept in the dark following other studies to avoid potential confounding effects of temperature and Circadian rhythm (Case et al, 2014;Skinner, 2014;Skinner & Bellinger, 2017). To simulate a freeze-thaw cycle, we then raised the chamber temperature to 4 ˚C for 2 d with 50 PAR with a 4-h photoperiod.…”

“…We then repeated the process of ramping down the temperature and ice chipping and then subjected the plants to another period at −8 ˚C, this time for 48 h. These exposure times and temperatures in this experiment were chosen from among preliminary trials (results not shown) as those that produced the largest relative differences in freezing tolerance between the control line Norstar and select southern accessions. While other studies have assayed freezing tolerance in winter wheat at colder temperatures, typically for shorter durations (Case et al, 2014;Skinner, 2014;Skinner & Bellinger, 2017;Skinner & Garland-Campbell, 2008), here we investigate the effect of slightly warmer temperatures sustained over a longer duration.…”

“…In most temperate herbaceous plants, freezing tolerance requires a period of exposure to low but nonfreezing temperatures (Preston & Sandve, 2013). During this process, termed cold acclimation (Sarhadi et al, 2010;Skinner, 2014;Skinner & Bellinger, 2017), dramatic transcriptional changes, lead to physiological and biochemical changes that enhance tolerance (Case et al, 2014). For instance, proteins and protective substances like soluble sugars and proline are synthetized (Ding et al, 2019).…”