Turnip (Brassica rapa) is an important crop cultivated all over the world. Glucosinolates as the characteristic constituents showed diverse bioactivities, especially for their anti-cancer and hepatoprotective effects. Plenty of investigation has revealed the glucosinolate contents and profiles in various Brassica vegetables (mainly on aerial parts), whereas their detailed comparison between different agroclimatic zones is rarely reported. This study aimed to make a comparison on the total glucosinolate contents (TGCs) and chemical profiles in 59 turnip landraces. The turnip tubers were obtained by collecting the seeds from four agroclimatic zones, Yunnan, Himalayas, Qinghai-Tibetan Plateau (QTP) and Xinjiang, around southwest China and sown in Jianshui County. The TGCs in turnip were high (TGCYunnan = 0.463 ± 0.020 mg g−1 d.w., TGCHimalaya = 0.498 ± 0.019 mg g−1 d.w.) in the middle elevation environments, and decreased in both lower elevation (TGCXinjiang = 0.273 ± 0.014 mg g−1 d.w.) and higher elevation (TGCQTP = 0.346 ± 0.021 mg g−1 d.w.) environments, which followed a hump-shaped pattern along the altitudinal gradient. According to the principal component analysis, the 59 investigated landraces were dissected into two clusters, Yunnan-Himalaya environment and Xinjiang-Qinghai Tibetan Plateau environment. Significant correlation was observed between the aboveground biomass and underground biomass (r = 0.653, p < 0.01), leaf length and tuber diameter (r = 0.448, p < 0.01), whereas the TGCs were neither correlated with the aboveground nor the underground biomass. A total of 18 constituents involving ten glucosinolates, three phenylpropanoids, one lignan and four sulfur compounds were characterized based on their MS/MS fragmentation and UV absorption. Gluconasturtiin (7) and glucobrassicanapin (4) were revealed as the main glucosinolates in turnip. The TGCs in turnip varied significantly (one sample t (297) = 34.859, P = 0.00) with different climatic zones, of which warm and humid climate [e.g. Yunnan and Himalaya areas (TGCwarm and humid = 0.467 ± 0.014 mg g−1 d.w.)] is profitable for the accumulation of glucosinolates, as compared to the arid and stressful environment [e.g. QTP and Xinjiang areas (TGCarid and stressful = 0.329 ± 0.014 mg g−1 d.w.)]. This investigation suggested that the glucosinolate profiles were closely related to the genes involved in regulating glucosinolate biosynthesis, herbivore pressure and vegetative growth.
Agroclimatic zones Brassica rapaChemical profiles Glucosinolates Turnip
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This work was supported by the CAS "Light of West China" Program (Western Youth Scholars "A"), the Program of Yunling Scholarship, the CAS Hundred Talents Program, the Youth Innovation Promotion Association CAS (2013252), and the Applied Basic Research Programs of Yunnan Province (2017FB137).
Swastika Paul performed the experiments and wrote the manuscript. Chang-An Geng, Tong-Hua Yang, Yong-Ping Yang and Ji-Jun Chen helped in supplying samples, technical guidance and writing.