Poster: Signaling, cell-to-cell

Abs # 436: Is IP₃-Mediated Signal Transduction Required for Synthesis of NO?

Presenter:	Kanter, Diane , dkanter@vt.edu
Authors	Kanter, Diane  (A)   Gillaspy, Glenda  (A)
Affiliations:	(A): Virginia Tech

Inositol 1,4,5-trisphosphate (IP3) is a second messenger that increases transiently and elicits an intracellular calcium release in response to various stimuli, including abscisic acid (ABA) treatment (Burnette et al., 2003; McAinsh et al., 2000). It has been shown that ABA stimulates an increase in nitric oxide (NO), and that synthesis of NO via the nitric oxide synthase (NOS) is required for ABA action (Guo et al., 2003). We wanted to test whether IP3 signaling is required for NO production. Specifically, we hypothesized that ABA acts to increase IP3, which mediates an intracellular calcium release, activating calmodulin and NOS, resulting in new NO production. To test this hypothesis, we are using transgenic plants altered in their expression of the At5PTase1 gene, which encodes an inositol polyphosphate 5-phosphatase (5PTase). The At5PTase1 protein has been shown to hydrolyze IP3 (Berdy et al., 2001), and plants that overexpress At5PTase1 have reduced IP3 levels and altered responses to ABA (Burnette et al., 2003). In contrast, plants containing a knock-out mutation in At5PTase1 contain elevated levels of IP3. Using a fluorescence dye that detects NO, wild type, At5PTase1 overexpressers and At5PTase1 knock-out mutant plants were given an ABA stimulus and then examined for their NO content. Wild type plants have also been pre-treated with a PLC inhibitor, calcium, or EDTA to perturb IP3 and calcium signaling. Preliminary data suggests a relationship between IP3 and NO levels. NOS activity assays are being used to test whether differences in NO levels are attributable to changes in NOS activity. If verified, our hypothesis that IP3-mediated signal transduction is required for NO production, would indicate cross-talk between these two important signaling pathways.