Cold Acclimation in Plants

Abstract

In zones with a seasonal climate, plants undergo periodic transition from a lower to a higher level of resistance. All categories of frost resistance are affected, the tolerance to equilibrium freezing (Fig. 5.1) as well as the ability to undergo deep supercooling (Fig. 5.2). Two types of seasonal acclimation can be distinguished, each being an expression of the different mechanisms by which they achieve their resistance (see Table 4.3):

• 1. Species Responding Directly to Low Winter Temperatures. Plants growing in regions with a mild winter or in habitats shielded from severe frost acquire greater resistance in the cold season as a direct consequence of the progressive drop in temperature. This enhanced resistance may be due simply to a lowering of T_f and T_sc, or to the acquisition and further development of freezing tolerance. However, if the plants are protected from cold they can remain at a low level of resistance throughout the year. This is the situation in the rhizomes of the cosmopolitan fern Pteris aquilinum, although not in other ferns of the temperate zone (Kappen 1964). A further example is provided by the observation of Larcher (1954) that the leaves of olive trees cultivated in glasshouses exhibit damage at any time of year at −6 °C, whereas under Mediterranean winter conditions they tolerate temperatures down to −10 °C. A similar kind of behaviour is seen in woody plants of the subtropics (e.g. Salix safsaf, S. tetrasperma: Sakai 1978, and Pinus caribaea: Oohata et al. 1981) and in many herbs.