Dehydration strain avoidance and tolerance in plant cold hardiness

Cell strain during freezing is typically characterized by either a measure of cell volume contraction or a measure of the fraction of cell water frozen. If the measure of strain at the killing temperature increases during cold acclimation, it is concluded that hardiness is controlled by strain tolerance, and if the measure of strain does not increase during cold acclimation it is concluded that hardiness is controlled by strain avoidance. It is demonstrated that the measure of cell volume contraction is not mathematically equivalent to the measure of the fraction of water frozen. Thus the conclusion regarding the relative role of avoidance and tolerance in frost hardiness depends upon the choice of strain measurement. The parameters determining the two measures of strain indicate that if cell injury is related to membrane area contraction or expansion then the measure of cell volume contraction is likely to be the better measure of strain; however, if cell injury is related to solution effects, the measure of the fraction of water frozen is likely to be the better measure of strain. In addition, the temperature dependence of each strain measure is derived to aid in the visualization of the freezing process, and to accommodate calculation of the measures of strain from data obtained at above freezing temperatures.