EFFECTS OF ETHYLENEDIUREA AND OZONE IN DETOXIFICANT ASCORBIC-ASCORBATE PEROXIDASE SYSTEM IN TOBACCO PLANTS

The protective effect of the anti-ozonant ethylenediurea (EDU) against O-3 damage is reported. Ascorbate peroxidase (EC 1.11.1.11), guaiacol peroxidase (EC 1.11.1.7) and superoxide dismutase (EC 1.15.1.1) activ ities were measured in O-3-fumigated tobacco plants. The two Nicotiana tabacum cultivars, Havana 425 (O-3-tolerant) and Bel-W3 (O-3-sensitiv e), had noticeably different peroxidase activities even in untreated p lants; the values measured in Havana 425 were double those found in Be l-W3. The peroxidase activities in the two cultivars were also determi ned in successive times following a 2-h ozone treatment (150 ppb). Asc orbate peroxidase (AA-POD) activity increased particularly in the inte rcellular washing fluid (IWF) and this effect was stronger if the plan ts were pre-treated with EDU, 48 h prior to O-3-exposure. The highest activation of AA-POD of IWF was reached 72 h after O-3-treatment in bo th Havana and Bel-W3 pre-treated with EDU. The guaiacol peroxidase and superoxide dismutase activities remained virtually unchanged when the plants were treated with EDU before ozone exposure. The treatment wit h EDU alone did not affect the tested enzymes. The results of the expe riments, conducted on IWF, cellular extract and isolated chloroplasts, show a positive correlation between the increase of AA-POD and EDU pr otection against O-3 damage. This protective effect is demonstrated by the absence of leaf necrosis which is normally induced by ozone, in t he sensitive Bel-W3.