Abstract
Blueberry stems (ca. 20cm long) were placed at -8〜-10℃ without ice inoculation and freezing process was observed using infra-red video thermography. Differential images obtained by subtraction of the initial image clearly visualized where the first freezing events occurred and how the freezing propagated in the stems. The results maybe summarized as follows: 1) freezing pattern was different from one experiment to another even when the same stems was repeatedly used; 2) in many cases, freezing was initiated from multiple sites (not like the ones reported by other researchers); 3) the speed of ice spread was faster when the stem was supercooled more; 4) freezing was sometimes arrested or slow-downed at stem nodes. These things allow us to speculate that the ice nucleation activity should occur throughout the stems. To test this hypothesis, we determined ice nucleation activity of blueberry stems using a test tube method. The results showed that every stem segment (7.5mm long) had a high ice nucleation activity. The thermography data and test tube ice nucleation assays were in agreement and supported an idea that high intrinsic ice nucleation activities occur throughout the blueberry stems that allow the stems to readily initiate freezing upon exposure to subzero temperatures.
