L-ascorbic acid metabolism in spinach (Spinacia oleracea L.) during postharvest storage in light and dark

L-ascorbic acid metabolism in spinach (Spinacia oleracea L.) leaves during postharvest storage in low intensity white light (20-25 mumol m(-2) s(-1)) and the dark was investigated. The endogenous pool of ascorbic acid (AsA) in both young and mature leaves showed higher values in the light than in the dark. The higher content of AsA in the light could not be explained by the activities of the different redox enzymes involved in AsA metabolism. The enzyme activities did not show marked differences between those stored under light and those in the dark. On the other hand, AsA catabolism as indicated by oxalic acid contents was not indicative of the effects of light and darkness since oxalic acid contents did not quantitatively relate well with AsA contents. Feeding of spinach leaf disks with L-galactono-1,4-lactone showed similar activities of L-galactono-1,4-lactone dehydrogenase during both light and dark incubation; however, production of AsA was higher in the light-incubated than in the dark-incubated leaf disks. Thus it is possible that light could enhance AsA synthesis in spinach leaves. The total soluble carbohydrates and glucose contents of leaves in the light were higher than those in leaves in the dark. These results suggest that continuous illumination of white light effectively supports the photosynthetic capacity of spinach leaves during postharvest storage thereby increasing the availability of soluble carbohydrates, especially glucose, enabling them to contribute to the control of the AsA pool size. (C) 2002 Elsevier Science B.V. All rights reserved.