Abstract
Changes in the physiology of plant leaves are correlated with enhanced freezing tolerance and include accumulation of compatible solutes, changes in membrane composition and behavior, and altered gene expression. Some of these changes are required for enhanced freezing tolerance, whereas others are merely consequences of low temperature. In this study we demonstrated that a combination of cold and light is required for enhanced freezing tolerance in Arabidopsis leaves, and this combination is associated with the accumulation of soluble sugars and proline. Sugar accumulation was evident within 2 h after a shift to low temperature, which preceded measured changes in freezing tolerance. In contrast, significant freezing tolerance was attained before the accumulation of proline or major changes in the percentage of dry weight were detected. Many mRNAs also rapidly accumulated in response to low temperature. All of the cold-induced mRNAs that we examined accumulated at low temperature even in the absence of light, when there was no enhancement of freezing tolerance. Thus, the accumulation of these mRNAs is insufficient for cold-induced freezing tolerance.
Highlights
Tered gene expression, including changes in both mRNA accumulation and enzyme activity (Guy, 1990; Thomashow, 1990; Holaday et al, 1992; Howarth and Ougham, 1993), was observed within a few hours
Arabidopsis acclimates rapidly in response to low temperature; enhanced freezing tolerance has been observed after only 1 d of cold acclimation
Vol 120, 1999 tain different rates and degrees of enhanced freezing tolerance, and we examined the accumulation of soluble sugars, Pro, and several mRNAs that are encoded by COR genes under these different regimes
Summary
Tered gene expression, including changes in both mRNA accumulation (for summary, see Hughes and Dunn, 1996) and enzyme activity (Guy, 1990; Thomashow, 1990; Holaday et al, 1992; Howarth and Ougham, 1993), was observed within a few hours. Decreased water content and structural changes such as increased leaf thickness occurred within days to weeks (Ristic and Ashworth, 1993; Uemura et al, 1995). It is unclear which alterations are necessary for enhanced freezing tolerance or how individual alterations contribute to freezing tolerance. Transgenic plants expressing a transcriptional activator that binds to motifs often found in cold-inducible genes have been constructed These plants display both constitutively enhanced freezing tolerance and overexpression of a set of COR genes (Jaglo-Ottosen et al, 1998; Liu et al, 1998).
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