Abstract
Due to global warming, winter hardiness may seem to become less important for plant survival and yield. However, this is a superficial assumption, as probably only the most important factors locally affecting plant overwintering will change. For example, the frequency, degree, and length of extreme winter warming events may increase, leading to de-acclimation of plants. This study aimed to investigate existing variability in de-acclimation tolerance in Polish winter barley breeding materials and European winter and facultative barley cultivars, and to identify accessions with the highest and the lowest tolerance to de-acclimation by means of visual estimation of regrowth after freezing, measurements of electrolyte leakage and chlorophyll fluorescence, and LT50 assessment. The results of this study showed that freezing tolerance and tolerance to de-acclimation are independent traits, and even highly freezing tolerant plants can be susceptible to de-acclimation. Our results highlight the role of photosynthetic apparatus in de-acclimation, proving that chlorophyll fluorescence parameters, especially ET(0)/CS, can be useful indicators of tolerance to de-acclimation. This study also confirmed that although the mechanisms of response to de-acclimation seem to be common for susceptible barley accessions, the mechanisms of tolerance are different, and may be related to the accession's origin.