Molecular responses in cold-adapted plants

Abstract

Plants differ in their responses and resistance to chilling and freezing temperatures because they originate from different areas and have evolved in different environments. The two mechanisms for freezing resistance are avoidance and tolerance.1 Freezing-avoidant plants may avoid freezing by overwintering as a seed with little freezable water, or they may completely avoid any freezing in the tissues by supercooling. Freezing tolerance is the capacity to withstand extracellular ice formation and to avoid intracellular ice formation.2 Levitt classified plants according to their degree of freezing resistance.1 Tender or completely unhardy plants have no avoidance of freezing and these plants are seriously damaged even at temperatures above freezing point, whereas slightly hardy plants survive freezing at about −5°C. Moderately hardy plants accumulate sugars and other solutes, and are able to survive freezing temperatures within −5 to −10°C. Very hardy plants have developed mechanisms leading to a marked avoidance of both intracellular freezing and extracellular freeze-dehydration resulting from removal of water from the cytoplasm to the growing ice crystals. These plants survive freezing temperatures within −10 to −20°C. Extremely hardy, the most freezing-tolerant plants are able to survive temperatures lower than −20°C by possessing a complete tolerance of freeze-dehydration-induced membrane disruption. The degree of freezing tolerance is different in woody and herbaceous perennials (e.g. conifers and Vaccinium), in overwintering annuals and perennial plants (e.g. winter cereals, winter rape, alfalfa, bromegrass) and in annual plants (e.g. Arabidopsis thaliana, spinach, cabbage).