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CALCIUM MOBILIZATION AND PHOSPHOINOSITIDE PRODUCTION IN RESPONSE TO HYPOXIC STRESS.  J.C. Johnson, J. Torabinejad, and D.B. DeWald. Utah State University, Logan, UT.

     Hypoxia, a lack of oxygen in the plant root-zone, can be caused by several different environmental factors including flooding and microgravity.  Plants have developed mechanisms to survive and acclimate to these conditions through changes in morphology, metabolic pathways, and protein synthesis.  One mechanism used by plants is a signal transduction pathway involving membrane phospholipids that can induce calcium mobilization, or the movement of calcium into the cytosol from extracellular or intracellular stores.  The phosphoinositide phosphatidylinositol 4,5-bisphosphate can be hydrolyzed to diacylglycerol and inositol trisphosphate (InsP₃).  InsP₃ acts as a second messenger to cause calcium mobilization within the cell resulting in protein synthesis and gene expression. However, the signal transduction pathways induced by hypoxia are not fully known.  We have studied the response of Arabidopsis thaliana to hypoxic stress through an examination of calcium mobilization and phosphoinositide production.    HPLC analysis was used to separate and identify changes in membrane phosphoinositides that resulted from hypoxic stress to test the hypothesis that phosphoinositide and inositol phosphate accumulation leads to calcium mobilization.  We have also directly examined calcium mobilization in hypoxia-stressed root and shoot tissues using a ratiometric imaging system in conjunction with transgenic, calcium-indicating A. thaliana.  A better understanding of how the plant responds to hypoxia may potentially allow the development of transgenic plants that can thrive in field and spaceflight-induced hypoxic environments. 

     (Supported by a NASA Rocky Mountain Space Grant Consortium Fellowship, a NASA GSRP, and the U.S.D.A.)