Abstract
Efficient cultivation methods were investigated to promote the branding of products in plant factories. Moderate stress can enhance plant constituents that are beneficial for human health, without reducing yield. Dehydration stress in lettuce rhizospheres increased some antioxidants, including L-ascorbic acid (AsA) and polyphenols. In this study, the major factors contributing to the augmentation of antioxidant constituents were investigated. The drought treatment resulted in increased hydrophilic oxygen radical absorbance capacity (ORAC) values but not hydrophobic ORAC values. Both activities of antioxidant enzymes (superoxide dismutase, SOD, and ascorbate peroxidase, APX) were elevated under drought conditions. RNA-seq analysis revealed 33 upregulated and 115 downregulated differentially expressed genes, and 40 gene ontology enrichment categories. A dehydrin gene was the most significant among the upregulated genes in response to drought stress. Dehydrin protects plant cells from dryness through multiple functions, such as radical scavenging and protection of enzymes. Real-time PCR validated the substantial increase in some dehydrin paralogs with root desiccation. In conclusion, the enhancement of antioxidant levels by drought stress is likely not due to the induction of antioxidant enzyme genes, but due to increased enzymic activities. These activities might be protected by dehydrins encoded by the upregulated paralogs under drought stress.
Highlights
Plant factories have become common in several countries
The upper part of the root area began browning in all the treatments, except the control. From these results we confirmed that the drought stress was given to the lettuce by exposing the roots to the air
Under optimized drought conditions (7 days of drought treatment with 4 cm of air space), both ascorbic acid (AsA) and polyphenols were increased without a significant yield reduction [14]
Summary
Plant factories have become common in several countries. They produce many vegetables at a time and year-round; for example, 10,000 heads of lettuce in a day. Severe environmental stresses inhibit the growth of plants, whereas moderate stresses can increase the various components expressing tolerance mechanisms Some salubrious antioxidants, such as L-ascorbic acid (AsA), glutathione, alpha-tocopherol (vitamin E), and polyphenols, were enriched in response to oxidative stress brought about by environmental stimuli [2,3,4,5]. We found that the fresh weight of hydroponic lettuce remained steady for the first 7 days with 4 cm of airspace, but decreased significantly beyond 7 days [14] This method could increase the AsA, polyphenol, and sugar content of leaf lettuce Functions other than antioxidants were discussed, based on the genes differentially expressed under dehydration stress
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