Cell Tension and Cavitation in Plants During Freezing

Abstract

Freezing behavior of water in plant tissues is often thought to be similar to that of dilute aqueous solutions. Typically, plant tissue water freezes extracellularly which requires cell deformation, specifically, cell contraction. Considering that cells are bound by often rigid cell walls, it is likely that they would offer some resistance to volume changes. This clearly can affect the freezing of water in plant tissues. As cells shrink during extracellular freezing, it allows for cell dehydration to occur (Levitt, 1980). However, when cells offer resistance to deformation during extracellular freezing it can lead to reduced cell dehydration. The impact of cell resistance to deformation during freezing is evident in extreme cases such as supercooling cells which do not dehydrate much, despite the presence of ice in rest of the tissue (George and Burke, 1977). This is remarkable considering the fact that just above the homogeneous nucleation temperature, the water potential of ice surrounding the supercooling cells could be as low as −46 MPa. Also, recent evidence suggests that even non-supercooling woody tissues do not shrink as expected during extracellular freezing (Malone and Ashworth, 1991). Our studies and those of others have shown that even herbaceous tissues such as leaves can resist cell deformation and dehydration during extracellular freezing (Rajashekar and Burke, 1982; Anderson et al., 1983; Hansen and Beck, 1988; Zhu and Beck, 1991; Rajashekar and Lafta, 1996).