ABSTRACT
Chilling-sensitive plants suffer from metabolic disfunction and structural injuries when exposed to chilling (>0°C) temperature; in contrast, the prolonged exposure of chilling-insensitive herbaceous plants to cold leads to two distinct effects: Improved performance of cells at low temperature and Increased resistance to freezing. Hardening of winter rape plants proceeds in three stages. The first stage is induced by low but above (0°C) temperature and results in increased frost resistance of only a few degrees below its initial level. The second stage of frost hardening of winter rape plants depends on the temporary occurrence of subfreezing temperature, i.e., temperature lower than (0°C) but higher than that of ice initiation in the tissue. The third stage of frost hardening in winter rape plants is related to dehydration of cells by prolonged frosts and may overlap the second one if there are other water stress-provoking factors.
