Differential accumulation of maysin and rhamnosylisoorientin in leaves of high‐altitude landraces of maize after UV‐B exposure

Flavonoid induction by UV‐B was investigated in five maize landraces from high altitudes and a W23 inbred line lacking the B1 and Pl1 transcription factors required for anthocyanin synthesis. In their natural habitats these landraces receive much higher UV‐B fluence than plants at lower altitudes at similar latitudes and would be predicted to have UV‐B tolerance by recurrent selection against UV‐B stress. We identified two flavones that are induced by UV‐B in leaves of high‐altitude lines: maysin and its biosynthetic precursor rhamnosylisoorientin. Accumulation is controlled by a p ‐homologous transcription factor expressed in leaves, and this factor is regulated by UV‐B. The levels of either maysin or rhamnosylisoorientin are higher in seedling leaves than in subsequent leaves; the highest flavone concentration was detected in silks. Some landraces have only rhamnosylisoorientin; this likely reflects a mutation in salmon silk1 ( sm1 ) or in a duplicate locus, as genetic crosses with W23 restore the production of maysin in heterozygous F 1 plants. In conclusion, it is demonstrated that maize plants from high altitudes respond to UV‐B radiation by accumulating UV‐absorbing flavones in leaves; in contrast, these compounds are present at only very low levels in inbred lines such as W23 and are not regulated by UV‐B.