Profiling glucosinolates in vegetative and reproductive tissues of four Brassica species of the U-triangle for their biofumigation potential

Glucosinolates are amino acid derived allelochemicals present in all plants of the order Capparales. These compounds are degraded by myrosinase isoenzymes, releasing a series of biologically active products defined by the parent glucosinolate and the reaction conditions. Species within the Brassicaceae are found to differ in their glucosinolate profile and glucosinolate concentrations. Different tissues within a single plant also show such variations, which are further influenced by the growth stage and environmental conditions. In the experiments described in this paper, four Brassica species of the U-triangle (B. carinata, B. nigra, B. juncea and B. rapa) were compared with respect to their glucosinolate profiles in roots, stems, leaves and reproductive organs at different developmental stages. The glucosinolate profile of corresponding ripe seeds was also determined. Prop-2-enylglucosinolate was identified as the major glucosinolate in the three mustards, where it represented over 90% of the total glucosinolate concentration of ripe seeds and over 50% of green tissues. The relative concentration of this glucosinolate increased in all tissues during plant growth. Brassica rapa showed a different glucosinolate profile than the three mustards, with higher concentrations of but-3-enylglucosinolate, 2-hydroxybut-3-enylglucosinolate and 2-hydroxypent-4-enylglucosinolate. The concentration of indol-3-ylmethylglucosinolates was also higher in B. rapa than in the mustard plants, with 4-hydroxyglucobrassicin representing 30% of the total glucosinolate concentration in ripe seeds. The total glucosinolate concentration of the species studied varied with growth stage and the mustards achieved a maximum towards the end of the period monitored. Glucosinolate concentration decreased in roots and leaves but increased in reproductive tissues. The determined glucosinolate profiles are an initial step in assessing the biofumigation potential of these species of the Brassicaceae family. (c) 2007 Society of Chemical Industry.