OXIDATIVE STRESS RESPONSES IN TRANSGENIC TOBACCO CONTAINING ALTERED LEVELS OF GLUTATHIONE-REDUCTASE ACTIVITY

A pea glutathione reductase cDNA was expressed in tobacco. Three class es of construct were used which gave a range of elevated levels of glu tathione reductase (GR) activity in the cytosol (GR32), chloroplasts ( GR36), or in both chloroplasts and mitochondria (GR46). In some transg enic progeny (T-2) from self-fertilized GR32 and GR36 primary transfor mants, having approximately twofold elevation of GR activity as compar ed with recessive siblings, there was an amelioration of the effect on leaf discs of up to 15 mu M paraquat. However, lines with similarly e levated levels of GR activity showed no decreased sensitivity to the h erbicide. None of the GR32 and GR36 lines was less sensitive to ozone. Conversely, T-2 progeny of GR46 lines, with greater than 4.5-fold ele vations of GR activity, showed no reduced sensitivity to paraquat but two out of four of these lines were less sensitive to ozone fumigation . The differential response to stress cosegregated with the presence o f the transgene but there was no relationship between the degree of st ress response and the level of GR activity. There was an elevation in the total glutathione pool in all lines showing increased GR activity but there was no change in the ratio of oxidized to reduced glutathion e. These results demonstrate that the mechanisms of protection against ozone and paraquat are different although both can be mediated by ele vated GR activity.