THE INFLUENCE OF WATER DEFICITS ON MESSENGER-RNA LEVELS IN TOMATO

The levels of particular mRNAs in tomato leaves are altered in response to water stress. Certain transcripts appear as a consequence of the stress whereas others diminish in abundance. These changes were analysed by cell-free translation of leaf RNA followed by two-dimensional polyacrylamide gel electrophoresis of the translation products. Within 20 min of the onset of reduced leaf water potential in detached leaflets, stress-induced mRNAs appear in the transcript population. Other mRNAs accumulate more slowly and include among their in vitro translation products a prominently labelled group of polypeptides of about 18-19 kD. These transcripts are recovered from detached leaflets incubated for 2 and 8h at low water potential and from leaflets of intact plants that were stressed in situ for 10d. An additional water stress-induced mRNA that encodes a 64-kD polypeptide is detected in the transcript population from detached leaflets when [H-3]glycine is used in place of [S-35]methionine in the cell-free translations. Among the transcripts that decline in abundance as a consequence of water stress is an mRNA that encodes the small subunit of ribulose-1,5-bisphosphate carboxylase. Within 2h of rewatering stressed plants, certain mRNAs that were lost from the population return and those in the 18-19kD range that are associated with the stress are not detectable.