Elicitation with hydrogen peroxide promotes growth, phenolic-enrichment, antioxidant activity and nutritional values of two hydroponic lettuce genotypes.

Dietary vegetables rich in bioactive compounds are major responsible for promoting human health. Herein, the effect of hydrogen peroxide (H2O2), an important signaling compound, on growth and quality of two hydroponic lettuce genotypes was investigated. The maximum enhancement of growth traits was shown in lettuce elicited with 10 mmol/L H2O2, while 40 mmol/L H2O2 significantly reduced above growth traits. H2O2 elicitation increased pigment contents and photosynthetic process, which consequently caused enhancements of phenolic compounds, ascorbic acid, glutathione, carotenoids, soluble sugars, free amino acids, soluble protein, minerals, and antioxidant capacity, while above alterations appeared in a genotype-dependent manner. The phenolic accumulation was correlated with improved activity of phenylalanine ammonia lyase (PAL) and expression levels of genes related to phenolic biosynthesis, including PAL, chalcone synthase, flavanone 3-hydroxylase, dihydroflavonol-4 reductase, and UDP-glucose: flavonoid 3-O-glucosyltransferase. Therefore, elicitation with H2O2 is a promising strategy to develop lettuce with high bioactive compounds and biomass.

Hydrogen peroxide regulates the biosynthesis of phenolic compounds and antioxidant quality enhancement in lettuce under low nitrogen condition.

Reduced nitrogen availability is an efficient strategy for increasing the accumulation of phenolic compounds in vegetables, but related mechanisms remain unknown. Here, the production of hydrogen peroxide (H2O2) and its potential roles in regulating phenolic biosynthesis and enhancing the antioxidant quality of lettuce under low nitrogen (LN) conditions were investigated. The LN treatment caused a rapid production of H2O2, which effectively increased lettuce quality by enhancing the levels of phenolic compounds and other nutrients such as ascorbic acid, glutathione, soluble sugar, and soluble protein. The increased phenolic content was related to the higher expression levels of phenolic biosynthesis genes, including PAL, CHS, DFR, F35H, and UFGT, and higher photosynthetic capacity after H2O2 addition under LN conditions. However, these positive effects were suppressed by dimethylthiourea (DMTU), a scavenger of H2O2. These results suggest that H2O2 as an important signal molecular mediates the LN-caused phenolic accumulation and antioxidant quality enhancement in lettuce.