Al-Quraan, Nisreen , Locy, Robert , Braam, Janet , Singh, Narendra .
Involvement of Calmodulin in GABA Shunt Regulation and Thermotolerance in Arabidopsis thaliana under Heat Stress.
Plant cells accumulate glutamate, GABA, and alanine (Ala) in response to stressful high temperatures. GABA is synthesized from glutamate (Glu) in a decarboxylation reaction catalyzed by glutamate decarboxylase (GAD), which is modulated by the binding of calcium-activated calmodulin (CAM). GABA aminotransferase the converts GABA and pyruvate into succinate semialdehyde andÂ Ala in plants. Thus, the levels of these amino acids may be regulated by calcium and CAM-dependent activation of GAD. We have investigated this hypothesis by examining the heat-stress-tolerance/sensitivity of seed germination, seedling survival, production of reactive oxygen species (ROS), and GABA shunt metabolite levels in 7 CAM mutants under heat stress at 42oC. Mutations in CAM5 & 6 resulted in significant defects in seed germination and seedling survival, and increased levels of ROS production during heat stress. cam2-3 & cam5-4, but not cam6-1, showed reduced root GABA levels after 2 hours at 42oC. Lower levels of shoot GABA were observed in all the CAM mutants examined, and cam5-4 seedlings showed increased Glu and Ala in roots and increased Glu in shoots. In cam2-3, levels of Glu and Ala in roots were reduced. GABA levels were lowest in cam1 shoots. After 3 hr at 42oC, cam2-3 and cam5-4 seedlings had high levels of Ala and Glu in both roots and shoots. Our results suggest an important role for CAM5 in thermotolerance of seedlings and the GABA shunt pathway. Although cam6-1 had significant phenotypic defects in survival, germination, and accumulation of reactive oxygen species, no significant metabolite level changes were observed. These preliminary mutant characterizations await complementation experiments to confirm causality between phenotype and gene function.
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More Detailed Abstract
1 - Auburn University, Department of Biological Sciences, 101 Life Sciences Building, Auburn, AL, 36849, USA
2 - Rice University, Department of Biochemistry and Cell Biology, MS-140, 6100 Main Street, Houston, Texas, 77251, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM