Deacclimation may be crucial for winter survival of cereals under warming climate.

Climate warming can change the winter weather patterns. Warmer temperatures during winter result in a lower risk of extreme freezing events. On the other hand the predicted warm gaps during winter will decrease their freezing tolerance. Both contradict effects will affect winter survival but their resultant effect is unclear. In this paper, we demonstrate that climate warming may result in a decrease in winter survival of plants. A field study of winterhardiness of common wheat and triticale was established at 11 locations and repeated during three subsequent winters. The freezing tolerance of the plants was studied after controlled cold acclimation and de-acclimation using both plant survival analysis and chlorophyll fluorescence measurements. Cold deacclimation resistance was shown to be independent from cold acclimation ability. Further, cold deacclimation resistance appeared to be crucial for overwintering when deacclimation conditions occurred in the field. The shortening of uninterrupted cold acclimation may increase cold deacclimation efficiency, which could threaten plant survival during warmer winters. Measurements of chlorophyll fluorescence transient showed some differences triggered by freezing before and after deacclimation. We conclude that cold deacclimation resistance should be considered in the breeding of winter cereals and in future models of winter damage risk.

Is the OJIP Test a Reliable Indicator of Winter Hardiness and Freezing Tolerance of Common Wheat and Triticale under Variable Winter Environments?

OJIP analysis, which explores changes in photosystem II (PSII) photochemical performance, has been used as a measure of plant susceptibility to stress. However, in the case of freezing tolerance and winter hardiness, which are highly environmentally variable, the use of this method can give ambiguous results depending on the species as well as the sampling year and time. To clarify this issue, we performed chlorophyll fluorescence measurements over three subsequent winters (2010/11, 2011/12 and 2012/13) on 220 accessions of common winter wheat and 139 accessions of winter triticale. After freezing, leaves were collected from cold-acclimated plants in the laboratory and field-grown plants. Observations of field survival in seven locations across Poland and measurements of freezing tolerance of the studied plants were also recorded. Our results confirm that the OJIP test is a reliable indicator of winter hardiness and freezing tolerance of common wheat and triticale under unstable winter environments. Regardless of species, the testing conditions giving the most reliable results were identical, and the reliability of the test could be easily checked by analysis of some relationships between OJIP-test parameters. We also found that triticale is more winter hardy and freezing tolerant than wheat. In addition, the two species were characterized by different patterns of photosynthetic apparatus acclimation to cold.

The effects of cold, light and time of day during low-temperature shift on the expression of CBF6, FpCor14b and LOS2 in Festuca pratensis.

Strictly controlled and coordinated induction of CBF regulon (a set of genes regulated by CBF proteins) promotes plant freezing tolerance. CBFs regulate the expression of COR genes that confer freezing tolerance. COR14b in barley is one of the effector genes which seems to be important in resistance to combined freezing and photoinhibition of photosynthesis. LOS2 represses the transcription of STS/ZAT10 (a negative regulator of CBF-target genes) and thus acts as a positive regulator of COR genes. In Arabidopis, low temperature induction of CBFs was reported to be gated by the circadian clock. Moreover, light-quality signals have been shown to regulate some plants' freezing tolerance genes. The aim of our study was to determine the effects of combined treatment with light and cold on the transcript levels of CBF6, FpCor14b and LOS2 genes in Festuca pratensis. We have demonstrated that the regulation of CBF6, FpCor14b and LOS2 induction kinetics in F. pratensis occurs through the interaction of temperature and light with time of day during low-temperature shift. The FpCOR14b transcript level was shown to be up-regulated by increasing light intensity. It was also proved that light quality strongly regulates CBF6, FpCor14b and LOS2 transcripts induction kinetics at low temperatures.