Effects of Oxidative stress on the Growth of Leaf Lettuce upon H₂O₂ Treatment

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    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 (H₂O₂), for 20 days. Treatment with 1.0 mM H₂O₂ significantly decreased growth and increased the anthocyanin content. In contrast, 0.1 mM H₂O₂ treatment significantly increased growth, changed the root morphology, and increased water absorption. H₂O₂ treatment induced endogenous H₂O₂ production within 1 to 3 h, but 0.1 mM H₂O₂ treatment gradually decreased the endogenous H₂O₂ concentration. On the other hand, H₂O₂ was maintained at high concentrations in leaves under 1.0 mM H₂O₂ treatment. These results suggest that a rapid increase in oxidative stress and quick reduction in the H₂O₂ content would be important factors for inducing high growth rate in leaf lettuce via H₂O₂ treatment at an appropriate concentration. Exposure to H₂O₂ or oxidative stress might be a successful strategy for efficient lettuce cultivation.