Differential responses of G-protein Arabidopsis thaliana mutants to ozone

Ground-level ozone (O-3) curtails agricultural production in many regions worldwide. However, the etiology of O-3 toxicity remains unclear. Activated oxygen species appear to inflict biochemical lesions and propagate defense responses that compound plant injury. Because some plant defense responses involve membrane-delimited GTPases (G proteins), we evaluated the O-3 sensitivity of Arabidopsis mutants altered in the heterotrimeric G-protein pathway. Eight genotypes were treated with a range of O-3 concentrations (0, 100, 175 and 250 nmol mol(-1)) for 13 d in controlled environment chambers. After treatment with O-3, the epinasty typically observed for wild type leaves did not occur in mutant plants lacking the alpha subunit of the G-protein complex (gpal). O-3-induced suppression of leaf chlorophyll levels and leaf mass per unit leaf area were less for gpal mutants and were not due to differences in O-3 flux. There was a positive correlation between the lack of a G-protein alpha subunit and decreased O-3 sensitivity. Our results suggest that a heterotrimeric G-protein is critically involved in the expression of O-3 effects in plants.