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Nitric Oxide and cGMP Signaling and Gravity Dependent Cell Polarity in Ceratopteris richardii. K. E. Morris1, D.M. Porterfield1,2 1Dept. Of Biol. Sciences, 2Dept. of Computer and Elect. Engineering, University of Missouri-Rolla

  Despite the vast amount of information regarding the role of nitric oxide (NO) and cGMP in animal systems, very little is know concerning the role of this signaling pathway in plants. In these experiments we focused on determining if NO signaling plays a role in directing gravity dependent cell polarity in Ceratopteris. Germinating spores were cultured on solid gel medium and exposed to various treatments in order to control for gravimorphogenisis. The role of NO and cGMP were tested using various drugs to either directly modulate NO and cGMP concentrations in the growth medium, or to directly inhibit specific enzymes involved with production of these signaling molecules in vivo. After germination the spores were digitally imaged and analyzed using Scion/Image-J software to measure the morphological angles of emerging rhizoids. All drug treatments were compared to two control treatments. Fixed orientation controls spores orient rhizoid emergence downwards (average angle=179.8o±20.5o; R2=0.4863) whereas slow clinostat rotation (1 RPM) completely disrupted graviorientation (average angle=166.3o±102.9o; R2=0.023). All drugs that released or scavenged NO from the growth medium randomized gravity orientation. Also, all drugs that increased cGMP in the growth medium, or inhibited the breakdown of cGMP in the cytoplasm randomized the graviresponse. For example an inhibitor of the NO modulated enzyme guanylate cyclase (LY 83583) completely randomized the graviresponse (average angle = 103.1o ± 121.1o; R2=0.024) at concentrations as low as 10M.  Viagra (sildenfil citrate), a very specific phosphodiesterse inhibitor, completely disrupted cell polarity at concentrations of 50 M (average angle = 164.9 o ± 22.3 o; R2 = 0.019).  These results suggest a vital role for NO and cGMP signaling during the development gravity directed cellular polarity in the fern spore system. Future work will focus on determining the molecular responses of fern spore to altering these signaling pathways using DNA microarray analysis.

(Supported by NSF: 0316876)