Liu Yu, Zhang Hui, Umashankar Shivshankar, Liang Xu, Lee Hui Wen, Swarup Sanjay, Ong Choon Nam
NUS Environment Research Institute, National University of Singapore, Singapore 117411, Singapore.
Saw Swee Hock School of Public Health, National University of Singapore, Singapore 117549, Singapore.
Metabolites. 2018 Dec 14;8(4):94. doi: 10.3390/metabo8040094.
Plants emit characteristic organic volatile compounds (VOCs) with diverse biological/ecological functions. However, the links between plant species/varieties and their phytochemical emission profiles remain elusive. Here, we developed a direct headspace solid-phase microextraction (HS-SPME) technique and combined with non-targeted gas chromatography‒high-resolution mass spectrometry (GC-HRMS) platform to investigate the VOCs profiles of 12 common Brassicaceae vegetables (watercress, rocket, Brussels sprouts, broccoli, kai lan, choy sum, pak choi, cabbage, Chinese cabbage, cauliflower, radish and cherry radish). The direct HS-SPME sampling approach enabled reproducible capture of the rapid-emitting VOCs upon plant tissue disruption. The results revealed extensive variation in VOCs profiles among the 12 Brassicaceae vegetables. Furthermore, principal component analysis (PCA) showed that the VOC profiles could clearly distinguish the 12 Brassicaceae vegetables, and that these profiles well reflected the classical morphological classification. After multivariate statistical analysis, 44 VOCs with significant differences among the Brassicaceae vegetables were identified. Pathway analysis showed that three secondary metabolism pathways, including the fatty acid pathway, methylerythritol phosphate (MEP) pathway and glucosinolate (GLS) pathway, behave distinctively in these vegetables. These three pathways are responsible for the generation and emission of green leaf volatiles (GLVs), terpenes and isothiocyanates (ITCs), respectively. Correlation analysis further showed that volatile metabolites formed via the common pathway had significantly positive correlations, whereas metabolites from different pathways had either non-significant or significantly negative correlations. Genetic influences on these metabolites across various vegetable types were also evaluated. These findings extend our phytochemical knowledge of the 12 edible Brassicaceae vegetables and provide useful information on their secondary metabolism.
植物会释放出具有多种生物学/生态功能的特征性有机挥发性化合物（VOCs）。然而，植物物种/品种与其植物化学物质排放谱之间的联系仍然难以捉摸。在此，我们开发了一种直接顶空固相微萃取（HS-SPME）技术，并结合非靶向气相色谱-高分辨率质谱（GC-HRMS）平台，来研究12种常见十字花科蔬菜（西洋菜、芝麻菜、抱子甘蓝、西兰花、芥蓝、菜心、小白菜、卷心菜、大白菜、花椰菜、萝卜和樱桃萝卜）的挥发性有机化合物谱。直接HS-SPME采样方法能够在植物组织破坏后可重复地捕获快速释放的挥发性有机化合物。结果显示，12种十字花科蔬菜的挥发性有机化合物谱存在广泛差异。此外，主成分分析（PCA）表明，挥发性有机化合物谱能够清晰地区分这12种十字花科蔬菜，并且这些谱很好地反映了经典的形态学分类。经过多变量统计分析，鉴定出十字花科蔬菜中44种具有显著差异的挥发性有机化合物。通路分析表明，包括脂肪酸途径、甲基赤藓糖醇磷酸（MEP）途径和芥子油苷（GLS）途径在内的三条次生代谢途径在这些蔬菜中的表现各不相同。这三条途径分别负责绿叶挥发物（GLVs）、萜类化合物和异硫氰酸盐（ITCs）的生成和排放。相关性分析进一步表明，通过共同途径形成的挥发性代谢产物具有显著的正相关，而来自不同途径的代谢产物要么无显著相关性，要么具有显著的负相关。还评估了不同蔬菜类型对这些代谢产物的遗传影响。这些发现扩展了我们对12种可食用十字花科蔬菜的植物化学知识，并为它们的次生代谢提供了有用信息。
