Transcript levels of knockdown and overexpressing OPR lines. A, Quantitative RT-PCR expression analysis on 14-d-old wild-type (WT) plants and knockdown OPR1,2 lines. Results are means of three independent RNA isolations measured in triplicate ± se. B, Representative semiquantitative RT-PCR on 14-d-old wild-type plants, overexpressing (oxOPR) lines, and pentaerythritol tetranitrate reductase-expressing (onr) lines. The experiment was repeated twice with similar results.