variation of glucosinolate concentration during a single day in young plants of Brassica oleracea var acephala and capitata

Changes in the total and individual glucosinolate concentrations of Portuguese leaf type cabbage (Brassica oleracea var acephala cv Galega) and white cabbage (B. oleracea var capitata cv Predena) were monitored throughout the day. In the first experiment (experiment 1) conducted during two hot days, plants of Galega were grown to the four-leaf stage, harvested at 06:00 h, 10:00 h, 14:00 h, 18:00 h and 22:00 h and analysed for glucosinolate concentration. In a second experiment (experiment 2) in milder circumstances, Predena and Galega were grown and harvested similarly. Five glucosinolates were detected using a high-performance liquid chromatography method. In experiment 1 the major compound found in Galega was 3-methylsulphinylpropyl glucosinolate (glucoiberin) followed by allyl- (sinigrin) and indol-3-ylmethyl (glucobrassicin) glucosinolates whilst in experiment 2, indol-3-ylmethyl- was the major compound in both cultivars, followed by allyl- and 4-methoxyindol-3-ylmethyl glucosinolates. A significant decrease in total glucosinolate concentration was noted between 10:00 h and 14:00 h, and the highest concentrations occurred at 18:00 h in experiment 1 and between 06:00 h and 10:00 h in experiment 2. For the total glucosinolate concentration and each of the detected glucosinolates there were very high significant differences (P < 0.001) across the five sampling times in experiment 1. In experiment 2, Galega showed significant differences for total glucosinolate (P < 0.01), allyl glucosinolate (P < 0-05), indol-3-ylmethyl- (P < 0.05) and 1-methoxyindol-3-ylmethyl- (P < 0.05), whilst in Predena only 4-methoxyindol-3-ylmethyl concentrations were significantly different (P < 0.01) across sampling times.