CYTOKININS MODULATE STRESS-RESPONSE GENES IN ISOPENTENYL TRANSFERASE-TRANSFORMED NICOTIANA-PLUMBAGINIFOLIA PLANTS

The effects of transiently elevated cytokinin levels on gene expressio n following stress were examined in transgenic Nicotiana plumbaginifol ia plants. Plants were transformed with a bacterial gene encoding isop entenyl transferase (ipt) cloned behind the heat shock (HS) protein 70 promoter from Drosophila melanogaster. Following a 1-h, 45-degrees-C HS of whole plants, the ipt transcript levels in leaves increased 30- to 40-fold. Analysis of in vitro translation products of leaf messenge r RNA showed rapid isopentenyl transferase-dependent changes in gene e xpression. A subset comprising 1 to 2% of resolvable translation produ cts was specifically up-regulated in heat shock ipt-inducible (HS-ipt) plants. Several cDNA clones were isolated which correspond to mRNAs t hat are up-regulated 2- to 4-fold in HS-ipt plants. Two of the cDNAs e ncode stress-related polypeptides, one a member of a class of small he at shock polypeptides (HSP) and the other, a wound-inducible glycine-r ich protein. Benzylaminopurine feeding experiments show that the HSP t ranscripts are up-regulated by other treatments including watering but that cytokinins strongly accelerate or amplify the response. These da ta are the first to show altered modulation of stress-induced genes in intact plants transformed with the cytokinin biosynthesis gene ipt.