Аннотация:Summary The steady‐state level of transcripts coding for the pyrroline‐5‐carboxylate reductase of Arabidopsis ( At‐P5R ) increased under salt and heat stress, mainly because of an enhanced mRNA stability. However, the At‐P5R protein level was not induced, and its translation was inhibited at initiation stage and probably also at later stages. Replacement of the 5′ untranslated region (5′UTR) and β‐glucuronidase ( gus ) fusion analysis revealed that the first 92 bp region of the At‐P5R 5′UTR was sufficient to mediate transcript stabilization and translation inhibition during salt and heat stresses. Furthermore, the first 92 bp region of the At‐P5R 5′UTR was also involved in transcription efficiency in a promoter‐dependent manner. The results demonstrated that the stress regulation of At‐P5R is complex and involves the 5′UTR which acts at three levels, partly in opposing directions.
