Poster: Intracellular Signaling

Abs # 816: Rapid induction of NO biosynthesis by cytokinin in wt and nia1/nia2 Arabidopsis: NO is necessary and sufficient to induce the cytokinin-inducible ARR5-GUS

Presenter:	Scherer, Guenther F.E., scherer@zier.uni-hannover.de
Authors	Scherer, Guenther F.E. (A)   Tun, Ni N (A)
Affiliations:	(A): University of Hannover

A fluorescence indicator for NO was applied to detect the release of NO from plant cell cultures (FEBS Lett 509: 174-176 (2001)) and in Arabidopsis. NO production was increased within 3 min in plant cell cultures (Arabidopsis, parsley, and tobacco) treated by cytokinin and was dose-dependent and signal-specific in that other plant hormones and inactive cytokinin analogue were not effective in stimulating NO release. The response was quenched by addition of AET, an inhibitor of the animal nitric oxide synthase (NOS), and by addition of the NO scavenger PTIO. Both wild type and nitrate-reductase-negative nia1/nia2 Arabidopsis seedlings produced NO in response to cytokinin so that nitrate reductase is not the source of cytokinin-induced NO but a separate NO synthase (NOS). NO activity could be visualized by DAF-2. Cytokinin-induced NO was generated mostly in the root, in the bundles of the hypocotyl and the leaves. It was prominent in dividing tissues in young leaves and the shoot meristem and, unexpectedly, in trichomes. We used Arabidopsis transformed by the cytokinin-inducible ARR5-promoter-GUS construct to establish a rapid cytokinin biotest. GUS activity was induced both by the chemical NO donor SNAP and by cytokinin. Cytokinin-induced GUS activity was inhibited by the NOS inhibitors AET and L-NAME and by PTIO, indicating that NO could be necessary and sufficient for the activation of the ARR5 promoter. Additionally, we found that NOS inhibitors also inhibited more complex responses: the cytokinin-induced betalaine synthesis in Amaranthus and the cytokinin-induced hypocotyl growth inhibition. Together, these results implicate that NO may act in cytokinin signal transduction as a potential second messenger.