Cytokinins modulate stress response genes in isopentenyl transferase-transfornied Nicotiana plumbaginifolia plants

The effects of transiently elevated cytokinin levels on gene expression following stress were examined in transgenic Nicotiana plumbaginifolia plants. Plants were transformed with a bacterial gene encoding isopentenyl transferase (ipt) cloned behind the heat shock (HS) protein 70 promoter from Drosophila melanogaster. Following a l‐h, 45°C HS of whole plants, the ipt transcript levels in leaves increased 30‐ to 40‐fold. Analysis of in vitro translation products of leaf messenger RNA showed rapid isopentenyl transferase‐dependent changes in gene expression. A subset comprising 1 to 2% of resolvable translation products was specifically up‐regulated in heat shock ipt‐inducible (HS‐ipt) plants. Several cDNA clones were isolated which correspond to mRNAs that are up‐regulated 2‐ to 4‐fold in HS‐ipt plants. Two of the cDNAs encode stress‐related polypeptides. one a member of a class of small heat shock polypeptides (HSP) and the other, a wound‐inducible glycine‐rich protein. Benzylaminopurine feeding experiments show that the HSP transcripts are up‐regulated by other treatments including watering but that cytokinins strongly accelerate or amplify the response. These data are the first to show altered modulation of stress‐induced genes in intact plants transformed with the cytokinin biosynthesis gene ipt.