Effect of light intensity and wavelengths on ascorbic acid content and the antioxidant system in tomato fruit grown in vitro

The ascorbic acid (ASA) content of tomatoes is regulated by culture practices and environmental conditions such as light. However, in tomatoes, little is known about the direct effect of lighting conditions on ASA content in the absence of natural environmental fluctuations. The aim of this study was to determine the direct light regulation of ASA and dehydroascorbic acid (DHA) contents and the antioxidant system in tomato fruits grown in vitro using two different cultivars (high- and low-ASA cultivars), different light intensities [darkness, low light (similar to 249 mu mol m(-2) s(-1)), and high light (similar to 961 mu mol m(-2) s(-1))], and different light spectra light emitting diodes (LEDs) under the same light intensity (226-249 mu mol m(-2) s(-1)): control (eight-peak LED), red LED light (peaks at 625 and 660 nm), and blue LED light (peaks at 420 and 450 nm). Results indicate that the effect of light on ASA and DHA content may be universal regardless of whether the cultivar is designated as a high- or low-ASA cultivar. ASA content was enhanced by an increase in light intensity and by blue (but not red) LED light. Our results also indicate that stimulation of the antioxidant system (ascorbate peroxidase and dehydmascorbate reductase activity) enhances ASA content under high light intensity, and underlying differences in mechanisms in response to blue and red LED light were observed. Therefore, we conclude that the direct light regulation of ASA content and the antioxidant system occurs in tomato fruits grown in vitro. In addition, our findings provide useful information for improving agricultural techniques to develop high-ASA tomatoes by controlling lighting conditions and by applying LED light.