NO-deficient mutants are altered in the pattern of flavonol accumulation. A, Accumulation of flavonols (kaempferol and quercetin) by DPBA staining in roots of the wild type (Col-0) and noa1 and nia1 nia2 mutants. B, Quantification of flavonols by HPLC-DAD-mass spectrometry analysis in 8-d-old seedlings of the wild type (Col-0) and noa1 and nia1 nia2 mutants. Flavonol concentration is expressed as milligrams per gram of dry weight. Values represent the average of three independent experiments. *, Statistically significant difference from the wild type (P < 0.05). C, F3H, FLS1, FLS3, CHS, and PAL transcription levels in roots of the wild type (Col-0) and noa1 and nia1 nia2 mutants. *, Statistically significant difference from the wild type (P < 0.05). D, Time course (from 5–13 d after sowing) of longitudinal primary root growth of Col-0, Ler, noa1, tt4, and tt4 noa1 seedlings grown vertically under standard conditions. Error bars represent se; n > 40. E, Average cell sizes in the cortical cell layer (cells 1–25 from the QC) of 5-d-old noa1, tt4, and tt4 noa1 mutants and wild-type (Col-0 and Ler) roots.