In addition to the effect of growth temperature, photoperiod
also affected levels of some of the individual glucosinolates. This
effect was not unidirectional, being both higher and lower at
12 h day length. Charron and Sams (2004) found no significant
effect of photoperiod in leafs in rapid-cycling B. oleracea. However,
in a previous study in broccoli we generally found a reduction of
aliphatic glucosinolates due to 24 h photoperiod in combination
high (21/15 C) temperature (Steindal et al., 2013). This was also
observed for the aliphatic glucosinolates, sinigrin and glucoraphanin,
at 15/9 C in the present study as well as for some of the indolic
and the aromatic glucosinolate. A negative effect of a 24 h light
period on glucosinolates may be linked to the lack of circadian
rhythm, which is involved in the regulation of glucosinolates in
Arabidopsis (Huseby et al., 2013). The effect of day length in our