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.

82 melon NAC (CmNAC) genes were identified in melon. We putatively identified the function of CmNAC gene in melon under salt stress. NAC transcription factor proteins play important roles in many biological processes, including plant development and stress responses. To date, few full-length melon NAC proteins have been identified. In this study, 82 melon NAC (CmNAC) genes were identified in the Cucumis melo L. genome. By interrogating our cDNA libraries and transcriptome data from melon under salt stress, and comparison of their phylogenetic relationship with Arabidopsis NAC salt stress-related genes, we putatively identified that the fourth clade of CmNAC genes were involved in the salt stress response, especially the second clade of the group IV of the phylogenetic tree. Expression analysis confirmed that eleven of the twelve CmNAC genes from the group IV were induced in melon seedling roots by salt stress; the other gene was down regulated by salt stress. The expression of CmNAC14 continually increased in 12 h under salt stress, and was selected for transformation into Arabidopsis for functional verification. Overexpression of CmNAC14 increased the sensitivity of transgenic Arabidopsis lines to salt stress, which were simultaneously demonstrated by reduced expression of abiotic stress-response genes and variation in several physiological indices. This study increases our knowledge and may enable further characterization of the roles of CmNAC family in the response to salt stress.

Temperature strongly influences lettuce (Lactuca sativa L.) seed germination. Different lettuce genotypes respond differently to higher temperatures or thermal stress. In this study, we evaluated the germination performance of 304 lettuce accessions incubated at three temperature settings, 21 °C, 28 °C and 35 °C, respectively, for 40 h. At 21 °C, seeds of all 304 accessions germinated with very well an average germination percentage of 87.72%; at 28 °C, the average germination percentage dropped to 42.84% and at 35 °C, the germination decreased to 1.01%. Then, we investigated changes in metabolic profiles of lettuce seed response to thermal stress using an untargeted metabolomics approach. Results suggested that seeds of thermal-sensitive and thermal-tolerant cultivars employed different metabolic strategies in response to thermal stress during germination. Thermal-sensitive buds accumulated more significant amounts of organic acids, amino acids, sugars, sterols, phenolic compounds and terpenoids compared to thermal-tolerant buds at 21 °C. Thermal-tolerant lettuce cultivar accumulated higher concentrations of amino acids, organic acids, sugars, sesquiterpene lactones, sterols, and fatty acids derivatives during the germination at 35 °C compared to germinated at 21 °C. This investigation paves the way to link the metabolomics to other external and internal factors affecting lettuce seed germination under thermal stress.

The development of highly active and efficient nonprecious‐metal electrocatalysts for the oxygen evolution reaction is important for the design of renewable energy production and storage devices. In this work, highly dense, ultrathin Co–Ni boride nanoflakes supported on a 3 D CoNi skeleton are fabricated in situ by a simple one‐step, high‐temperature, solid‐state boronation process. As a result of the induced high electroactive surface area and low charge transfer resistance, CoNiB‐700 exhibits high catalytic activity at an overpotential of 262 (η10) and 284 mV (η20) to deliver current densities of 10 and 20 mA cm−2, respectively, with a Tafel slope of 58 mV dec−1 in an alkaline medium towards the oxygen evolution reaction. DFT calculations show that the Ni‐regulated Co–B compound has a lower rate‐determining energy barrier for the *OOH intermediate than the mono‐Co–B compound, which facilitates the production of more active catalytic sites for an accelerated surface charge‐transfer process for the oxygen evolution reaction.

Glycine, the simplest amino acid in nature and one of the most abundant free amino acids in soil, is regarded as a model nutrient in organic nitrogen studies. To date, many studies have focused on the uptake, metabolism and distribution of organic nitrogen in plants, but few have investigated the nutritional performance of plants supplied with organic nitrogen. Lettuce (Lactuca sativa L.), one of the most widely consumed leafy vegetables worldwide, is a significant source of antioxidants and bioactive compounds such as polyphenols, ascorbic acid and tocopherols. In this study, two lettuce cultivars, Shenxuan 1 and Lollo Rossa, were hydroponically cultured in media containing 4.5, 9, or 18 mM glycine or 9 mM nitrate (control) for 4 weeks, and the levels of health-promoting compounds and antioxidant activity of the lettuce leaf extracts were evaluated. Glycine significantly reduced fresh weight compared to control lettuce, while 9 mM glycine significantly increased fresh weight compared to 4.5 or 18 mM glycine. Compared to controls, glycine (18 mM for Shenxuan 1; 9 mM for Lollo Rossa) significantly increased the levels of most antioxidants (including total polyphenols, α-tocopherol) and antioxidant activity, suggesting appropriate glycine supply promotes antioxidant accumulation and activity. Glycine induced most glycosylated quercetin derivatives and luteolin derivatives detected and decreased some phenolic acids compared to nitrate treatment. This study indicates exogenous glycine supplementation could be used strategically to promote the accumulation of health-promoting compounds and antioxidant activity of hydroponically grown lettuce, which could potentially improve human nutrition.