Photosynthetic abilities of spinach (Spinacia oleracea L.) leaves during postharvest storage under light and dark conditions

Changes in the photosynthetic abilities of mature leaves of stored spinach were studied under light (45 mumole m(-2) s(-1), popular strength in market showcases) or dark storage conditions at 8degreesC. Abilities of carbon dioxide fixation and oxygen release measured in dark-stored leaves, which were subsequently light-adapted prior to analysis, were still retained even after 14 d. However, changes in carbon dioxide fixation of leaves during the course of storage and senescence did not provide a realistic pattern of photosynthetic performance since this was influenced by the stomatal aperture of both light-stored and dark-stored leaves. Meanwhile, the photochemical quenching and energy-quenching values of the leaves seemed to be maintained under both light and dark conditions but decreased greatly soon after the onset of leaf yellowing. On the other hand, the maximal variable fluorescence of leaves decreased in both light and dark but was kept higher in the light than in the dark before the onset of yellowing. This could indicate that a part of the photosystems in the chloroplasts may have already been denatured even before leaf yellowing of the dark-stored leaves becomes visually apparent and that functional or structural disorder in the leaf tissues may have occurred during dark storage. This could further imply that the photosynthetic structure of spinach leaves during postharvest storage is ably supported by low intensity light until the onset of leaf yellowing.