Freezing tolerance

Freezing tolerance describes the ability of plants to withstand subzero temperatures through the formation of ice crystals in the xylem and intercellular space, or apoplast, of their cells. Freezing tolerance is enhanced as a gradual adaptation to low temperature through a process known as cold acclimation, which initiates the transition to prepare for subzero temperatures through alterations in rate of metabolism, hormone levels and sugars. Freezing tolerance is rapidly enhanced during the first days of the cold acclimation process when temperature drops. Depending on the plant species, maximum freezing tolerance can be reached after only two weeks of exposure to low temperatures. The ability to control intercellular ice formation during freezing is critical to the survival of freeze-tolerant plants. If intracellular ice forms, it could be lethal to the plant when adhesion between cellular membranes and walls occur. The process of freezing tolerance through cold acclimation is a two-stage mechanism: