NPR GENES, WHICH ARE NEGATIVELY REGULATED BY PHYTOCHROME ACTION IN LEMNA-GIBBA L G-3, CAN ALSO BE POSITIVELY REGULATED BY ABSCISIC-ACID

We have found that NPR1 and NPR2, two genes from Lemna gibba L. G-3 th at can be negatively regulated by phytochrome action, can also be posi tively regulated by the plant hormone abscisic acid (ABA). Both genes were responsive to low concentrations of exogenous ABA; an increase in NPR1 RNA could be detected in response to concentrations as low as 10 nM. We have also tested phytochrome responsiveness of 5' promoter-del etion constructs of one of these genes, NPR1, in transient assays util izing particle bombardment. This analysis demonstrated that DNA sequen ces important for phytochrome regulation are present downstream of -19 8 from the transcription start site. A response to ABA treatment could also be observed in the transient assay system. When intact plants we re placed in darkness, there was an increase in ABA levels as well as increased levels of NPR1 and NPR2 RNA.