Abstract
Ice nucleation is considered to be an important mechanism in cold hardy plant tissues to avoid excess supercooling of protoplasm and properly induce extracellular freezing and to accommodate ice crystals in specific tissues. However, there have been only a few studies on ice nucleation activity (INA) associated with wintering plant tissues. We conducted a survey of INA in various plant species using a test tube method and found a high INA associated with stems of blueberry cultivars, much higher than the average of other cold hardy plant stems. We characterized this INA and the results suggest that the high INA in the stem was mainly localized in the bark tissues. This was in agreement with our previous observation using infra-red thermography that blueberry stems initiate freezing from the surface of stems rather than xylem. We determined the effect of exposure time and sample amount of stems on INA. Even 2 mm stem segments had INA of -1. This is probably the highest INA reported with the ice nucleating agents of biological organ. The high INA seemed to be localized in the parenchymal tissues and cavity-rich tissues and not in the xylem, pith, cambium, fiber or phloem tissues.
