Different responses of transgenic Bt rice and conventional rice to elevated ozone concentration

To assess the different sensitivity to ozone (O₃) between transgenic Bt Shanyou63 (Bt-SY63) and its nontransgenic counterpart Shanyou63 (SY63), the leaf gas exchange, yield, grain elements, and antioxidant enzymes were investigated by performing a pot experiment under ambient O₃ concentration (A-O₃) and elevated O₃ concentration (1.5 × A-O₃, E-O₃). Under A-O₃, the chlorophyll content and yield of Bt-SY63 were significantly lower than those of SY63, whereas the stomatal conductance (Gs), cellular CO₂ concentration (Ci), and Fe, Zn concentration showed the opposite trends. No significant difference was detected for malondialdehyde (MDA) content between two cultivars, although the antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities in Bt-SY63 tended to be higher than those in SY63. Exposure to E-O₃ resulted in significant reduction for photosynthesis (Pn), yield and all grain elements (except for N) concentration in both varieties, and the extents in Bt-SY63 were much greater than those in SY63. Meanwhile, significant increases for MDA content by 30.6 and 23.7% in Bt-SY63 and SY63, respectively, were detected under E-O₃. These results demonstrated that insertion of exogenous gene could induce several unintentional changes of Bt-SY63 in physiology and growth progress, compared with SY63 under ambient O₃ concentration. On the other hand, the injury of Bt-SY63 caused by elevated O₃ concentration was more severe than that of SY63. This study provided valuable baseline information for the commercial release and breeding strategies of Bt-SY63 under the projected future climate.