Plant cold acclimation: The role of abscisic acid

The freezing tolerance or cold acclimation of plants is enhanced over a period of time by temperatures below 10 degrees C and by a short photoperiod in certain species of trees and grasses. During this process, freezing tolerance increases 2-8 degrees C in spring annuals, 10-30 degrees C in winter annuals, and 20-200 degrees C in tree species. Gene upregulation and downregulation have been demonstrated to be involved in response to environmental cues such as low temperature. Evidence suggests ABA can substitute for the low temperature stimulus, provided there is also an adequate supply of sugars. Evidence also suggests there may be ABA-dependent and ABA-independent pathways involved in the acclimation process. This review summarizes the role of ABA in cold acclimation from both a historical and recent perspective. It is concluded that it is highly unlikely that ABA regulates all the genes associated with cold acclimation; however, it definitely regulates many of the genes associated with an increase in freezing tolerance.