ARE EITHER SOD AND CATALASE OR THE POLYAMINES INVOLVED IN THE PARAQUAT RESISTANCE OF CONYZA-CANADENSIS

Paraquat/atrazine coresistant (PqAR) and paraquat resistant (PqR) hors eweed (Conyza canadensis /L./ Cronq.) plants showed - in the first hou r after 0.5 mM paraquat spraying - a decreased catalase activity follo wed by a slight increase. However, the enzyme activity remained always below the initial value. Sensitive plants showed a significant increa se of catalase activity in the first 4 hour after spraying. The transi ent character of paraquat inhibition, the recovery of photosynthetic a ctivity of the PqAR Conyza plants (characterized by variable fluoresce nce) after spraying remained unaffected by the superoxide dismutase (S OD) inhibitor, diethyldithiocarbamate. This indicates that SOD is not involved in the resistance mechanism. Untreated resistant biotypes sho wed about 2.5 times higher total polyamine and putrescine level than t he sensitive one. 100 mu M of exogenously added putrescine was observe d as having a protecting effect against paraquat in floated leaves of the sensitive biotype only. The resistant leaves were unaffected proba bly on account of their higher endogenous polyamine level. It is concl uded that polyamines may play a role in the paraquat resistance of Con yza canadensis.