Chlorophyll Proteins and Lipids in Paraquat Treated Sensitive and Resistant Cony za Canadensis Leaves

Photosynthetic activity and molecular composition o f thylakoid membranes o f sensitive and atrazine/paraquat coresistant biotypes o f Conyza canadensis (L.) Cronq was compared before and after 5 x 10~4 molar paraquat spraying. In contrast to the irreversibly damaged sensitive plants the Rfd values (vitality indices) calculated from parameters o f fluorescence induction curves, and the in vivo C 0 2 fixation in resistant plants showed after a transitory inhibition a recovery. Resistant thylakoids contained higher amount o f PS II and LHC II, (i.e. lower relative amount o f CP I) which can be the result o f an adaptation process. Fatty acid composition o f total leaf extract was almost the same in both biotype even after spraying. The amount o f the oligomeric form o f LHCP II decreased in paraquat treated sensitive thylakoids, which was in correlation with the reduction o f A3-transhexadecanoic acid content. Decrease in oligomeric LHCP II and/or special lipids (PG) in sensitive thylakoids may change the association o f LHCP II and photosystem II core as it is evidenced from lowering o f the Mg2+ induced changes o f the short wavelength fluorescence intensity and increase in the relative quantum requirement values. The results are discussed in connection with a possible effect o f paraquat on PS II.