Effect of Ascorbic Acid and Etiolation on Antioxidant Enzyme Activity and Phenylpropanoid Metabolism during Shoot Regeneration from Cut Ends of Tomato Stems

We investigated the effects of ascorbic acid (AsA) or etiolation treatments on the regeneration of shoots from cut ends of tomato stems. For the AsA treatment, AsA solution was applied to leaves of tomato plants immediately after cutting the main stem. The etiolation treatment consisted of covering the cut stem with an aluminum cap. When applied individually, the AsA or etiolation treatments resulted in increased numbers of shoots regenerated from the cut stem. However, application of both treatments simultaneously did not have a synergetic effect on the number of shoots regenerated. To clarify the mechanisms by which these treatments promoted shoot regeneration, we determined the effects of AsA or etiolation treatments on scavenging of reactive oxygen species (ROS) by antioxidant enzymes and phenylpropanoid metabolism in the cut ends of tomato stems during the shoot regeneration process. In this study, activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, catalase) were higher in most of the stems that received AsA or etiolation treatments, compared with those of the control. In addition, compared with the control, plants treated with individual AsA or etiolation had lower levels of hydrogen peroxide, malondialdehyde, and phenols, and lower phenylalanine ammonia-lyase activity. These results indicated that the promotive effects of individual AsA or etiolation treatments on shoot regeneration from cut tomato stems can be attributed to the same mechanism, which involves the high activity of antioxidant enzyme, suppression of oxidative stress and phenol accumulation.