Are either SOD and catalase or the polyamines involved in the paraquat resistance of Conyza canadensis?

Paraquat/atrazine coresistant (PqAR) and paraquat resistant (PqR) horseweed (Conyza canadensis /L./ Cronq.) plants showed - in the first hour after 0.5 mM paraquat spraying - a decreased catalase activity followed by a slight increase. However, the enzyme activity remained always below the initial value. Sensitive plants showed a significant increase of catalase activity in the first 4 hour after spraying. The transient character of paraquat inhibition, the recovery of photosynthetic activity of the PqAR Conyza plants (characterized by variable fluorescence) after spraying remained unaffected by the superoxide dismutase (SOD) inhibitor, diethyldithiocarbamate. This indicates that SOD is not involved in the resistance mechanism. Untreated resistant biotypes showed about 2.5 times higher total polyamine and putrescine level than the sensitive one. 100 mu M of exogenously added putrescine was observed as having a protecting effect against paraquat in floated leaves of the sensitive biotype only. The resistant leaves were unaffected probably on account of their higher endogenous polyamine level. It is concluded that polyamines may play a role in the paraquat resistance of Conyza canadensis.