Minisymposium 9: Global change

Abs # 22003: Physiological and molecular aspects of chronic ozone impacts on crops

Presenter:	Booker, Fitzgerald L., fbooker@mindspring.com
Authors	Booker, Fitzgerald L. (A) (B)  Burkey, Kent O. (A) (B)  Edwin, Fiscus L. (A) (B)  Michael, Flowers D. (A) (B)  Kirk, Overmyer  (C)   Alan, Jones M. (C)
Affiliations:	(A): USDA-ARS Air Quality - Plant Growth and Development Unit (B): Department of Crop Science, North Carolina State University (C): Department of Biology, University of North Carolina at Chapel Hill

Current ground-level ozone concentrations suppress yield of major agronomic crops such as cotton, soybean and wheat by 5 to 15% annually in the U.S. Tropospheric ozone levels are expected to increase as emissions of ozone precursors – NOx and volatile organic carbon - continue to rise worldwide. A demonstrated effect of ozone on plants is decreased photosynthetic carbon fixation. Chronic ozone exposure lowers net photosynthesis and carboxylation efficiency. The etiology of ozone toxicity, however, remains unclear. Following entry into a leaf via the stomata, ozone reacts to produce activated oxygen species, which may be perpetuated by the plant. If activated oxygen species are not scavenged by extracellular and cytosolic processes, injury such as protein oxidation can result and stress responses such as ethylene production are induced that possibly compound deleterious effects. We hypothesized that membrane-delimited GTPases (G-proteins), which are involved in some plant defense responses, may be involved in ozone-induced responses. Experiments with five G-protein null transcription mutants of Arabidopsis thaliana indicated that the epinasty often found with ozone treatment of Arabidopsis did not occur in gpa1 mutants lacking the alpha subunit of the heterotrimeric G-protein complex. Ozone-induced suppression of leaf mass per unit leaf area was less for gpa1 mutants compared with the other genotypes tested and was not due to differences in ozone flux. These results are consistent with a role for G-proteins as an early signaling link relaying information into the cell from the extracellular site of ozone perception. It is possible that G-proteins modulate ozone responses via their roles in hormone signal transduction. However, our results suggest that a heterotrimeric G-protein is critically involved in the expression of ozone effects in plants.