Molecular Genetics of Plant Responses to Low Temperatures

Abstract

Living organisms are always interacting with their environments. Those that achieve successful adaptations to unfavorable environmental conditions will survive and prevail. During evolution, organisms have developed mechanisms to cope with unfavorable environments. Cold stress is one of the adverse environmental factors that determines ecological habitat of organisms. Being sessile, plants are greatly affected by low temperatures in their geographical distribution and productivity. Therefore, plants are not exempt from developing unique mechanisms to protect themselves from cold stress damage. Some moderately hardy woody plants use supercooling of water to avoid freezing damage. Without ice nucleation, pure water can be supercooled or remain unfrozen until a certain point below 0°C. However, this supercooling is effective only within a narrow temperature window (George et al., 1982). The most common cold stress adaptation is cold acclimation. That is, the process by which plants acquire freezing tolerance after being exposed to cold, but non-freezing temperatures (Guy, 1990). Due to cold acclimation, plants from temperate regions are able to survive winter after experiencing cold, but non-freezing temperatures of the fall. Cold acclimation is correlated with several changes in plants such as changes in leaf ultrastructure (Ristic and Ashworth, 1993), membrane lipid composition (Lynch and Steponkus, 1987 Miquel et al., 1993), enzyme activities, ion channel activities (Knight et al., 1996), levels of sugars and polyamines (Levitt, 1980 Strand et al., 1997) and gene expression (Thomashow, 1994). Attempts to understand cold tolerance mechanisms have long been made because of scientific interest as well as its economic importance in agriculture.