Under non-fatal levels of stress, plants can produce high concentrations of sugars, functional proteins, antioxidants, and other beneficial metabolites. Reactive oxygen species (ROS) are present in all plants as cytotoxic metabolites and as mediators of stress responses. This study investigated the effects on the growth response of hydroponically grown
Lactuca sativa L. ‘Red Fire' seedlings, after treatment with an ROS, hydrogen peroxide (H
2O
2), for 20 days. Treatment with 1.0 mM H
2O
2 significantly decreased growth and increased the anthocyanin content. In contrast, 0.1 mM H
2O
2 treatment significantly increased growth, changed the root morphology, and increased water absorption. H
2O
2 treatment induced endogenous H
2O
2 production within 1 to 3 h, but 0.1 mM H
2O
2 treatment gradually decreased the endogenous H
2O
2 concentration. On the other hand, H
2O
2 was maintained at high concentrations in leaves under 1.0 mM H
2O
2 treatment. These results suggest that a rapid increase in oxidative stress and quick reduction in the H
2O
2 content would be important factors for inducing high growth rate in leaf lettuce via H
2O
2 treatment at an appropriate concentration. Exposure to H
2O
2 or oxidative stress might be a successful strategy for efficient lettuce cultivation.
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