Gefriervorgänge in lebendem Pflanzengewebe: der Beginn des intrazellulären Gefrierens

Highly sensitive temperature measurements by means of a thermistor made it possible to directly record individual crystallization processes in petiolar tissue of Saintpaulia ionantha during fast cooling. Supercooling to deep temperatures increases the freezing velocity in the region of the so-called first freezing point. Extensive supercooling produces an increased amount of ice at the first freezing point, compared with less supercooling of the same tissue. With the onset of intracellular freezing, ice formation in individual cells or cell complexes shows up as characteristic sharp peaks superimposed on the curves. These peaks begin immediately after the first freezing point; intracellular freezing is thus indicated to start at temperatures higher than the so-called second freezing point. The temperatures recorded by a probe are not equal to the actual freezing temperatures of extracellular liquid or living cells. They are influenced by loss of heat from samples into the surrounding air and by different supercooling of individual cells.