Abscisic acid levels and anti-oxidant activity are affected by an inhibitor of cytochrome P450 in apple seedlings

SummaryThe effects of an inhibitor of cytochrome P450 (uniconazole) on the levels of abscisic acid (ABA) and on anti-oxidant activity were investigated in apple seedlings. In uniconazole-treated seedlings, ABA reached its highest concentrations 24 h after the beginning of a dehydration treatment, and remained at high concentrations compared to levels in well-watered, uniconazole-untreated seedlings. Uniconazole decreased stomatal aperture up to 9 h after its application, and stomatal aperture remained constant for 72 h. Although the EC50 values of the 1,1-diphenyl-2-picrylhydrazyl hydrate (DPPH) and superoxide (O2.−) radical-scavenging activities were decreased by dehydration treatment, those in uniconazole-treated seedlings were higher than those in untreated seedlings. Superoxide dismutase (SOD) activity in uniconazole-untreated seedlings increased at the start of the dehydration treatment, but SOD activity in uniconazole-treated and well-watered seedlings did not increase. These facts suggest that application of the cytochrome P450 inhibitor induced stomatal closure earlier by increasing ABA concentrations, increased anti-oxidant activities, and may induce tolerance against water-stress damage.