OZONE-INDUCED EXPRESSION OF STRESS-RELATED GENES IN ARABIDOPSIS-THALIANA

Ozone is a major gaseous pollutant that is known to have detrimental effects on plant growth and metabolism. We have investigated the effects of ozone on Arabidopsis thaliana growth and the pattern of expression of several stress-related genes. A. thaliana plants treated with either 150 or 300 parts per billion (ppb) ozone daily for 6 h exhibited reduced growth and leaf curling. Fresh and dry weights of ozone-treated plants were reduced 30 to 48% compared to ambient air controls. RNA blot analyses demonstrated that mRNA levels for glutathione S-transferase (GST), phenylalanine ammonia-lyase (PAL), a neutral peroxidase, and a cytosolic Cu/Zn superoxide dismutase (SOD) were higher in plants treated with 300 ppb ozone than in ambient air-treated controls. The mRNA levels of lipoxygenase and a catalase were not affected by ozone treatment. Of the transcripts examined, GST mRNA levels increased the most, showing a 26-fold induction 3 h after the initiation of ozone treatment. PAL mRNA was also rapidly induced, reaching 3-fold higher levels than controls within 3 h of ozone treatment. The neutral peroxidase and SOD mRNA levels rose more slowly, with both reaching maximum levels corresponding to 5-fold and 3-fold induction, respectively, approximately 12 h after ozone treatment. These studies indicate that ozone-induced expression of stress-related genes in A. thaliana provides an excellent model system for investigating the molecular and genetic basis of ozone-induced responses in plants.