Tolerance to atmospheric ozone in transgenic tobacco over-expressing glutathione synthetase in plastids

A cross between transgenic tobacco (Nicotiana tabacum L.) plants which over -expressed either gamma-glutamylcysteine synthetase (cpGSHI) or glutathione synthetase (cpGSHII) in their chloroplasts was used to compare the consequ ences of over-expression of components of the glutathione synthetic pathway on tolerance to atmospheric O-3 or paraquat. A high proportion (50%) of th ose progeny which carried the cpGSHII transgene alone showed tolerance to a tmospheric O-3 but not to paraquat. Progeny of an additional two, independe nt, self-pollinated primary transgenic lines, which segregated in a Mendeli an fashion for the presence of the cpGSHII transgene and therefore included both transformed and non-transformed (recessive, wild-type) plants, were a lso challenged by fumigation with O-3. Again, in both cases, about 50% of t he plants expressing the cpGSHII transgene were found to be O-3-tolerant on the basis of reduced ethylene emissions and increased or unchanged total p igment concentrations. However, this tolerance was not due to specific chan ges in stomatal densities.