Genetic variation in glucosinolate content within Brassica rapa vegetables

Glucosinolates (GSs) were analyzed in 56 accessions of Brassica rapa grown in the greenhouse. Eight different glucosinolates were identified in the Brassica rapa group. They are the aliphatic glucosinolates progoitrin (PRO), gluconapin (NAP), glucobrassicanapin (GBN), the indolyl glucosinolates 4-hydroxyglucobrassicin (4OH), glucobrassicin (GBC), 4-methoxyglucobrassicin (4ME), neoglucobrassicin (NEO) and the aromatic glucosinolate gluconasturtiin (NAS). Gluconapin, glucobrassicanapin, progoitrin and gluconasturtiin are the most abundant GSs in the Brassica rapa, but there is considerable variation in content among accessions. The total glucosinolate contents in Brassica rapa group varied substantially between the different accessions. The highest amount of GSs (361 µmol/100 g FW) was observed in leaves of vegetable turnip, followed by rapid cycling and yellow sarson, with the amount of 200 and 178 µmol/100 g FW respectively. Whereas the lowest GSs content was found in turnip greens (20.8 µmol/100 g FW) and Wutacai (22.6 µmol/100 g FW). The total aliphatic GSs proportion varied from 50 to 90% of the total GS, while generally the content of indolyl glucosinoloates, especially 4OH glucobrassicin and neoglucobrassicin is low. Gluconasturtiin was found in relatively high concentrations in komastsuna (14.6 µmol/100 g FW), yellow sarson (7.1 µmol/ 100 g FW) and constitutes as much as 24% of the total amount of glucosinolates. Relatively high amounts of gluconapin (281 mmol/100 g FW) and glucobrassicanapin (60.0 mmol/100 g FW) were observed in the leaves of vegetable turnip. Compared with the Brassica oleracea group, Brassica rapa lacks glucoraphanin and sinigrin but contains gluconapin and glucobrassicanapin. Variations in glucosinolate content among genotypes suggest differences in their health-promoting properties and the opportunity for enhancement of their levels through breeding or genetic modification.