OZONE, SULFUR-DIOXIDE, AND ULTRAVIOLET-B HAVE SIMILAR EFFECTS ON MESSENGER-RNA ACCUMULATION OF ANTIOXIDANT GENES IN NICOTIANA-PLUMBAGINIFOLIA L

We have studied the expression of antioxidant genes in response to nea r ambient conditions of O-3, SO2, and ultraviolet B (UV-B) in Nicotian a plumbaginifolia L. The genes analyzed encode four different superoxi de dismutases (SODs), three catalases (Cat1, Cat2, and Cat3), the cyto solic ascorbate peroxidase (cyt APx), and glutathione peroxidase (GPx) . The experimental setup for each treatment was essentially the same a nd caused no visible damage, thus allowing direct comparison of the di fferent stress responses. Our data showed that the effects of O-3, SO2 , and UV-B on the antioxidant genes are very similar, although the res ponse to SO2 is generally less pronounced and delayed. The effects of the different stresses are characterized by a decline in Cat1, a moder ate increase in Cat3, and a strong increase in Cat2 and GPx. Remarkabl y, SODs and cyt APx were not affected. Analysis of SOD and APx express ion in the ozone-sensitive Nicotiana tabacum L. cv PBD6 revealed that induction of the cytosolic copper/zinc SOD and cyt APx occurs only wit h the onset of visible damage. It is proposed that alterations in mRNA levels of catalases and GPx, but not of SODs and cyt APx, form part o f the initial antioxidant response to O-3, SO2, and UV-B in Nicotiana.