ABSTRACT
Many plants respond to environmental cues, such as prolonged expo sure to low temperature, and acquire increased tolerance to sub-zero temperatures (Weiser, 1970; Guy, 1990). This process, which is termed cold acclimation, is accompanied by changes in gene expression and the accumulation of stress induced proteins (Guy, 1990; Thomashow, 1990; 1999; Pearce, 1999). Many of the genes expressed during cold acclima tion are also induced in response to drought stress. This is not surpris ing, as both drought and freeze-stress lead to cellular desiccation (Burke et al., 1976; Levitt, 1980; Guy, 1990). The first desiccation related pro teins were identified in studies on cotton seed development. Several proteins were found to be induced during late stages of seed develop ment and were termed Late Embryogenesis Abundant (LEA) proteins (Dure et al., 1981; Dure, 1993). LEA proteins have been divided into 6 unique groups based upon sequence characteristics (Baker et al., 1988; Wood, 1994). These classes of proteins, with the exception of group 6,
share common characteristics such as boiling stability, hydrophilicity, deficiency in cysteine and tryptophan residues and the presence of puta tive amphipathic a-helices or random coils (Wood, 1994). Group 2 (D-l 1) dehydrin proteins have been identified in numerous plants ex posed to desiccation stresses such as salinity, drought and freezing (re viewed by Close et al., 1993a; 1993b; Close,1996; 1997; Campbell and Close, 1997). Dehydrin-like proteins have also been shown to accumu late in several woody plant species during cold acclimation (Muthalif and Rowland, 1994; Arora and Wisniewski, 1994; 1996; Arora et al., 1996; Salzman et al., 1996; Wisniewski et al., 1996; Welling et al., 1997; Rinne et al., 1998; 1999; Lim et al., 1999).
