Our system for determining the effect of ice nucleation in plant tissue. This system consists of aluminum chambers, which contain plant tissue samples (e.g., pine seedling shoots, needles, stems, and meristems), that are covered with closed-celled insulation and set on a heating table prior to being placed in a freezer. Because the plant samples are frozen in air, supercooling can occur. Supercooling is one mechanism by which plants can survive short periods of freezing temperatures. Fine gage Type-T thermocouples are connected to each plant sample to measure the exothermic reaction, i.e., the temperature rise that occurs when ice nucleation occurs in plant tissue (the thermocouples are attached to a Campbell Scientific CR-21X datalogger). The freezer is set at a constant temperature of -40°C, while the heated table is maintained at 0°C to equilibrate the samples with the chamber air. A programmable temperature controller subsequently lowers the heat to the heating table so that the aluminum chambers cool at a rate of about 3°C per hour. By removing some of the plant samples just prior to the exothermic reaction, and some plant samples after ice nucleation has occurred, the effect of ice formation in the tissues and the extent of supercooling can be determined. Plant tissues are incubated on moist filter paper in a petri dish in diffuse light for up to five days prior to examination for freezing-induced injury. Measurements of chlorophyll fluorescence, electrical conductivity, and tissue death are used to determine the level of freezing tolerance in the samples tissue.

With:
John D. Marshall, Associate Professor, Department of Forest Resources
Wesley S. Hunt, Research Assistant, Department of Range Resources

Funded by McIntire-Stennis Research Grants Program, USDA.