Photosynthetic electron transport in Hydrilla verticillata (L.) is insensitive to methylviologen (paraquat) inhibition.

Effect of paraquat (methylviologen) was investigated on photosynthetic electron transport activity of a submerged aquatic angiosperm Hydrilla verticillata following polarographic and fluorimetric techniques. The plant showed resistance for electron acceptance by paraquat both in isolated chloroplasts and in intact leaves. The in vitro (isolated chloroplasts) and in vivo (intact leaf) electron transport analysis indicated that the failure of paraquat to intercept electrons from photosynthetic electron transport chain is for the existence of some rate limiting steps at the acceptor side of photosystem I complex. Hydrilla verticillata, as reported here for the first time, is a true paraquat resistant bio-type where the resistance for the herbicide paraquat can be observed both in isolated chloroplasts and also in intact leaf.