The primary goal of the contemporary studies on plant acclimation to cold is to understand molecular mechanisms which allow plants to survive freezing stress. However, it has been forgotten that the term "cold acclimation", originally used (in the 1950's) by animal physiologists, describe physiological changes in organisms when exposed to low non-freezing temperature. In the 60's, the term used for plants was defined as "the process of plant adjustment to low temperature (2deg C) which occurs in varying degree in hardy and non hardy varieties" (Kenefick, 1963). The results of further studies led to the conclusion that cold acclimation of biennial plants leads to two distinct effects: (1) improved performance of cells at low temperature and (2) increased resistance to freezing (Kacperska, 1989). Similar opinion was presented by Guy (1990) who stated that" The more precise view of cold acclimation (CA) would include two major functions: the more universal adjustment of metabolism and basic cellular function to the biophysical constraints imposed by low temperature (LT), and the induction of freezing tolerance. The first function of CA differentiates chilling-sensitive from chilling-resistant species. The second function of CA discriminates chilling tolerant but freezing sensitive species from those that are freezing tolerant." In contrast to the above opinions, Palta and Weiss (1993) indicate "cold acclimation per se" as a process which leads to an increase in plant tolerance to freeze-thaw stress. It seems that such a constriction of the term meaning is rather confusing since both cold-induced phenomena, i.e. metabolic adjustment and development of higher resistance to freezing are strongly interrelated.
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