Ozone Induced Carbon Dioxide Evolution in Tobacco Callus Cultures

Callus derived from Bel–W3 and Bel–B tobacco plants when exposed to ozone turned brown as a consequence of surface cell destruction. Ozone fumigations above a threshold concentration of 0.10 μl/1 for two hoars caused an increase in the rate of tissue carbon dioxide (CO₂) evolution. The maximum increase in CO₂ evolution was about 65 percent for both the ozone sensitive Bel–W3 and resistant Bel–B callus. However, the ozone dosage required to attain maximum increase in CO₂ evolution was approximately two times greater for the resistant variety. Callus cultures that grew roots were observed to be more resistant to ozone. The addition of the antioxidant N,N'dipnenyl–p–phenylenediamine (DPPD) m the nutrient medium retarded ozone induced CO₂ evolution.