Poster Presentation for the Gordon Research Converence on Temperature Stress in Plants - Jan 26-31, 1997, Ventura, CA

R.D. LOCY and J.H. CHERRY, Department of Botany & Microbiology, 101 Life Sciences Building, Auburn University, AL 36849.

Gamma-aminobutyric acid (GABA) is produced in plants in response to a number of environmental stresses, including heat, cold, and anaerobic stresses. In Arabidopsis thaliana heat stress leads to the accumulation of GABA in developing (7 day-old) seedlings. The accumulation of GABA occurs at temperatures above 37 C, the highest temperature at which growth and survival of seedlings is possible. GABA is made from glutamate by the enzyme glutamic acid decarboxlylase (GAD). GAD has been shown by others to be a calmodulin binding protein whose enzyme activity is modulated by Ca2+ and calmodulin (CaM). We have shown that CaM inhibitors, e.g. chloroprimazine and trifluropherazine inhibit the accumulation of GABA in response to growth limiting heat stresses. Thus, the same system for control of GABA synthesis and accumulation that has been shown to operate in other plant systems appears to be operating in Arabidopsis. We have examined the effect of GABA on the growth of Arabidopsis seedlings. GABA supplied in the growth medium inhibits root and hypocotyl growth, promotes root branching, and promotes the formation of leaves by 7-10 day-old seedlings. These effects mimic the morphological effects of sublethal (but near lethal) heat treatments on such seedlings. The role GABA plays in either the development and/or alleviation of such stress symptoms is unclear. In an attempt to better understand this role we have undertaken the selection of Arabidopsis mutants that do not show inhibition of root growth on media containing GABA (putative GABA resistant mutants), and of mutants that are unable to grow as well as wild type on GABA-containing media (putative GABA hypersensitive mutants). At the present time we have optained 15 putative resistant mutants and 42 putative hypersensitive mutants. Plants of these putative mutants are being used for seed production to retest the phenotype on progeny of the original selections.


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