Altered gene expression during cold acclimation of spinach.

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Abstract
Exposure of spinach (Spinacia oleracea L.) plants to a constant 5 degrees C induced a greater tolerance to extracellular freezing. The metabolic basis of this cold acclimation response in plants is not understood. In this study we tested the hypothesis that cold acclimation derives from altered gene transcription. We found that exposure of plants to low temperature resulted in a rapid and stable change in the translatable poly(A)+ RNA populations extracted from leaves, as determined by a cell-free in vitro translation assay. The initial appearance of mRNAs for two high molecular weight translation products correlated with an increase in freezing tolerance. Cold acclimation of plants for 8 days resulted in further qualitative changes in mRNA populations. At least four additional mRNAs increased in concentration upon continued exposure of spinach to 5 degrees C, whereas three other mRNAs present in 20 degrees C-grown leaves decreased. We also tested the possibility that the low temperature-induced mRNAs might encode heat shock proteins. We studied heat shock-induced protein synthesis by in vivo labeling techniques and found that spinach synthesized at least eight distinctive heat shock proteins during exposure to 40 degrees C. Most polypeptides induced by exposure to low temperature, however, appeared not to be heat shock proteins. Thus, the change in mRNAs induced by low temperature is a separate response from that induced by high temperature.