The health-beneficial effects of Brassica vegetables are mainly attributed to their high contents of glucosinolates and the products of their hydrolysis, especially isothiocyanates. Distribution of glucosinolates across plant organs can strongly vary. Here, we investigated the effect of leaf age on glucosinolate accumulation and hydrolysis in two leafy Brassica vegetables, pak choi and giant red mustard. We also evaluated the activity of the hydrolyzing enzyme myrosinase across the leaves. Finally, we assessed whether glucosinolates are transported from older leaves to younger leaves. Young leaves of both species contained more than 3-fold more glucosinolates than older ones. Accordingly, more isothiocyanates were released in the young leaves. Myrosinases fully hydrolyzed all of the amounts of glucosinolates regardless of the leaf age. Moreover, older leaves were observed to supply younger leaves with glucosinolates. Thus, this study suggests that consumers can improve the nutritional value of food by incorporating young leaves of leafy Brassicas in their diet.
Keywords: Brassica juncea; Brassica rapa; epithiospecifier protein; glucosinolate transport; isothiocyanate; myrosinase.