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Drosophila melanogaster was raised on aseptic diets, with and without beta-carotene. The sensitivity of visual receptors in the carotenoid-depleted flies was lowered 3 log units, but the photosensitivity of the circadian rhythm was not affected. This result suggests that the chromophore of the photopigment which mediates light effects on the circadian rhythm is not a carotenoid derivative.
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Zimmerman et al. (1971) studied this question.
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