The effect of light and temperature on glucosinolate concentration in the leaves and roots of cabbage seedlings

In previous studies it was shown that the concentration of total and individual glucosinolates in brassicaceous plants can vary significantly over a 24-h period grown either in the field or under controlled conditions. The present study shows total and individual glucosinolate variation during a single day. Seedlings of cabbage grown under controlled conditions and at 14 and 15 days after emergence were moved to 20°C (Exp A) and 30°C (Exp B), with a constant photosynthetic photon flux density of 480 μmol m−2 s−1 and 75% relative humidity, over a 2-day period, during which time aerial parts and roots were sampled at regular intervals. Whilst the glucosinolate patterns of the aerial part of the plant and of the roots remained the same, the levels of major glucosinolates in the aerial part, averaged over all sampling times and 2 days, were 233 ± 60 μmol 100 g−1 DW for 3-methylsulphinylpropyl and 72 ± 22 for 2-propenyl; in the roots, 2-phenylethyl and 1-methoxyindol-3-ylmethyl showed the highest average concentrations, with 678 ± 355 μmol 100 g−1 DW and 411 ± 122, respectively. Total and individual glucosinolate levels showed very high significant differences between the two plant parts. Despite the constant temperature, light and relative humidity, glucosinolates varied within a 24-h period, showing ultradian rhythms that are common to several metabolic processes in plants. The results confirm previous observations that at a temperature of 20°C, close to the optimum for growth and development, the diurnal variation in glucosinolate concentration, was smaller than at 30°C. © 1998 Society of Chemical Industry