Detecting cellular damages in freezing plants: are acoustic emissions useful?

Ultrasonic acoustic emission analysis has often been used to detect hydraulic failures in xylem conducting elements under drought and/or frost stress. However, other sources can generate acoustic signals. In this study, we hypothesized that frost stress generates acoustic signals in living cells in relation to frost-induced dehydration. Living cells are able to transiently increase their frost resistance through the process of frost acclimation / deacclimation. The temperature at which freeze-induced acoustic signals would be recorded should therefore show seasonal changes. Well-hydrated lavender plants were frozen in three different seasons: winter (January and February), spring (April) and summer (June and July). The acoustic activity as a function of temperature showed seasonal changes. The temperature inducing 50% acoustic emissions was recorded at -25°C in winter and spring while it occurred at -15°C in summer. This temperature was very similar and strongly correlated to the temperature inducing 50% damages, detected by the electrolyte leakage method. Although further studies are needed to identify the exact acoustic source, these results represent a promising avenue for monitoring frost stress in a constrained environment and an alternative technique for measuring plant frost hardiness.