Abstract
Lettuce is an important leafy vegetable that represents a significant dietary source of antioxidants and bioactive compounds. However, the levels of metabolites in different lettuce cultivars are poorly characterized. In this study, we used combined GC × GC-TOF/MS and UPLC-IMS-QTOF/MS to detect and relatively quantify metabolites in 30 lettuce cultivars representing large genetic diversity. Comparison with online databases, the published literature, standards as well using collision cross-section values enabled putative identification of 171 metabolites. Sixteen of these 171 metabolites (including phenolic acid derivatives, glycosylated flavonoids, and one iridoid) were present at significantly different levels in leaf and head type lettuces, which suggested the significant metabolomic variations between the leaf and head types of lettuce are related to secondary metabolism. A combination of the results and metabolic network analysis techniques suggested that leaf and head type lettuces contain not only different levels of metabolites but also have significant variations in the corresponding associated metabolic networks. The novel lettuce metabolite library and novel non-targeted metabolomics strategy devised in this study could be used to further characterize metabolic variations between lettuce cultivars or other plants. Moreover, the findings of this study provide important insight into metabolic adaptations due to natural and human selection, which could stimulate further research to potentially improve lettuce quality, yield, and nutritional value.
Highlights
Lettuce (Lactuca sativa L.), an important vegetable crop that is consumed worldwide, is one of the Asteraceae species, which originated in Ancient Egypt, and was cultivated as early as 2500 BCE1
After pre-processing, 6782 features were extracted from the GC × GC-TOF/MS matrix by LECO Chroma TOF software (Supplemental Figure S2A), and 27,927 features (14,541 in negative mode and 13,386 in positive mode) were extracted from the UPLC-IMSQTOF/MS data by Progenesis QI software (Supplemental Figure S2B)
To the best of our knowledge, a large-scale untargeted metabolomic study based on GC × GC-TOF/MS combined with UPLC-IMS-QTOF/MS has not been reported for any plant species
Summary
Lettuce (Lactuca sativa L.), an important vegetable crop that is consumed worldwide, is one of the Asteraceae species, which originated in Ancient Egypt, and was cultivated as early as 2500 BCE1. Both natural and human selection have generated a variety of lettuce cultivars with huge genetic diversity. As. Yang et al Horticulture Research (2018)5:33 metabolism is strongly affected by genetic factors, different lettuce cultivars are likely to have huge metabolite diversity. In an effort to improve human health, assessment of the metabolic profiles of a variety of leaf and head type lettuces may help to identify the most nutritionally valuable varieties. Metabolomics is a comprehensive metabolic profiling approach that enables analysis of a wide range of metabolite classes simultaneously in a non-biased manner[5]
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