Illumination of the dark-grown Euglena gracilis, both the wild-green type and a permanently bleached mutant, for 4 hr at 2, 000 lux caused about 6-fold increase of the cellular content of total L-ascorbic acid. The increase was mainly due to an increase of reduced-form L-ascorbic acid. From the action spectrum only blue light was found to be effective for the increase. Darkening stopped the increase and reillumination started a renewed increase. The activity of L-gulono-ϒ-lactone dehydrogenase, catalyzing the last step of L-ascorbic acid biosynthesis, was also increased two fold by illumination for 2 hr, and was changed in parallel to that of the cellular content of L-ascorbic acid depending on the presence or absence of illumination. The augmentation of L-ascorbic acid formation was markedly inhibited by various inhibitors and uncouplers, but not by dichlorophenyldimethylurea. The results in sum suggest that the light-dependent increase of L-ascorbic acid formation in E. gracilis is not primarily associated with photosynthesis, but is apparently related to the adaptation of the dark-grown cells to the illuminated state.
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Shigeoka et al. (1979) studied this question.