抄録
In this study, changes in the levels of ascorbic acid and dehydroascorbic acid (vitamin C content) in lettuce and spinach by potassium restriction from the middle of the cultivation stage using a water culture medium were examined. It was presumed that the content of glucose, which occurs as an ascorbate matrix, increased in a plant by osmoregulation using potassium restrictions treatment, resulting in an increase in vitamin C content. Vitamin C content in green lettuce, frilly lettuce, and spinach after potassium restriction were 1.9, 1.5, and 1.4 times higher than that in the control, respectively, whereas that in red leaf lettuce did not change. Glucose content in red leaf lettuce, frilly lettuce, and spinach after potassium restriction was 4.0, 1.7, and 2.4 times higher than that in the control, respectively. The activity of L-galactono-γ-lactone dehydrogenase (GLDH), which catalyzes ascorbic acid synthesis, after potassium restriction in frilly lettuce and spinach was 2.2 and 1.8 times higher than that in the control, respectively, whereas that in red leaf lettuce and green lettuce did not change. These results indicate that vitamin C content increased by restricting the levels of potassium in a water culture medium from the middle of the cultivation stage, although responses varied among cultivars.
