Freezing Injuries in Plants

Abstract

Two basically different categories of frost-killing mechanisms in plant cells can be distinguished:

• 1. Immediate Injury of Freezing-Sensitive Cells. Plant cells and tissues subject to immediate freezing injury, which in the classical descriptive terminology (Molisch 1897) were called “freezing-sensitive”, are killed as soon as intensive ice formation becomes evident (Fig. 3.1a). Damage may result from freezing following heterogeneous nucleation, or, in cells capable of persistent supercooling, following homogeneous nucleation. Under natural conditions, in most tissues sudden lethal freezing sets in after a considerable deviation from thermodynamic equilibrium (nonequilibrium freezing; Olien 1978, 1981). Appreciable quantities of ice appear in freezing-sensitive tissues only when, under the stress of a large water potential difference between cell solutes and the adjacent ice, the semipermeability of the cell membranes is lost, permitting the efflux of fluid from the cells. In determining the specific temperature limit for lethal nonequilibrium freezing the stability and integrity of the biomembranes play a decisive role (Dowgert and Steponkus 1983; Lindstrom and Carter 1985). The sudden freezing can thus be regarded as a consequence of the preceding disorganization and as the final violent event in the process of freezing.