Relationship of Deep Supercooling and Dehydration Resistance to Freezing Injury in Dormant Stem Tissues of ‘Starkrimson Delicious’ Apple and ‘Siberian C’ Peach1

Abstract

Abstract Low temperatures (LT) exotherms were found by differential thermal analysis (DTA) at −30°C in ‘Siberian C’ peach (Prunus persica [L.] Batsch) and −39° in ‘Starkrimson Delicious’ apple (Malus domestica Borkh. Nuclear magnetic resonance (NMR) spectrometry of intact stems and isolated bark and wood revealed that the LT exotherm was produced by freezing of deep supercooled water which was detected in the wood but not the bark. Freezing processes of the wood and bark appeared to be independent. In both species, xylem injury occurred at the same temperature as the LT exotherm and was closely, if not causally related to freezing of the supercooled water. Bark injury also occurred at the same temperature as the LT exotherm and may have been caused by dehydration stress or freezing of a small amount of supercooled water which remained undetected by NMR spectrometry. The dehydration resistance of apple wood on desiccation at 70 to 90% relative humidity was greater than that of the peach wood which in turn was greater than that of the bark of both species. The dehydration resistance of apple and peach wood may involve both nonliving and living elements of the wood because pulverizing the tissue destroyed the effect, whereas heat killing only lowered it. Both supercooling and dehydration resistance may be related to microcapillary pore structure which restricts heterogeneous nucleation and sublimation of supercooled water from the ray parenchyma cells.