Abstract
Selenium (Se) is an essential mineral in multiple human metabolic pathways with immune modulatory effects on viral diseases including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and HIV. Plant-based foods contain Se metabolites with unique functionalities for the human metabolism. In order to assess the value of common salad greens as Se source, we conducted a survey of lettuce commercially grown in 15 locations across the USA and Canada and found a tendency for Se to accumulate higher (up to 10 times) in lettuce grown along the Colorado river basin region, where the highest amount of annual solar radiation of the country is recorded. In the same area, we evaluated the effect of sunlight reduction on the Se content of two species of arugula [Eruca sativa (E. sativa) cv. “Astro” and Diplotaxis tenuifolia (D. tenuifolia) cv. “Sylvetta”]. A 90% light reduction during the 7 days before harvest resulted in over one-third Se decline in D. tenuifolia. The effect of light intensity on yield and Se uptake of arugula microgreens was also examined under indoor controlled conditions. This included high intensity (HI) (160 μ mol−2 s−1 for 12 h/12 h light/dark); low intensity (LI) (70 μ mol m−2 s−1 for 12 h/12 h light/dark); and HI-UVA (12 h light of 160 μ mol m−2 s−1, 2 h UVA of 40 μ mol m−2 s−1, and 10 h dark) treatments in a factorial design with 0, 1, 5, and 10 ppm Se in the growing medium. HI and HI-UVA produced D. tenuifolia plants with 25–100% higher Se content than LI, particularly with the two higher Se doses. The addition of Se produced a marked increase in fresh matter (>35% in E. sativa and >45% in D. tenuifolia). This study (i) identifies evidence to suggest the revision of food composition databases to account for large Se variability, (ii) demonstrates the potential of introducing preharvest Se to optimize microgreen yields, and (iii) provides the controlled environment industry with key information to deliver salad greens with targeted Se contents.
Highlights
The micronutrient selenium (Se) has attracted much attention of medical researchers during the last several decades
In the survey of commercially grown lettuce, our results showed that the plants grown along the Colorado river basin have significantly higher Se content than lettuce plants grown elsewhere (Figure 1)
These results suggested the critical effect of light intensity given that this region continuously shows the highest recorded solar radiance [36], whereas temperature and soil Se content (Supplementary Table 2) are variable across all the locations
Summary
The micronutrient selenium (Se) has attracted much attention of medical researchers during the last several decades. Over 30 mammalian selenoproteins [1, 2] have been identified, many of which provide biochemical disease resistance for mammalian health [3,4,5]. It has been suggested that the intake of Se reduces the risk of chronic health problems and skeletal deformities [6, 7] and metastasis of diverse cancer tumors [8, 9] including those associated to esophageal and gastric cancer [10]. Se deficiency has been shown to increase RNA replication of various viruses [12], which has elicited attention of the scientific community due to the emergence of coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A recent report suggested the biofortification of plants to produce a broad impact on COVID-19, arguing that plant-derived Se compounds can be a significant supplementary treatment for prevention and disease control and can be an effective way to reduce massive viral load and subsequent mutation of the virus [15]
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