Dependency on light and vitamin a derivatives of the biogenesis of 3-hydroxyretinal and visual pigment in the compound eyes of Drosophila melanogaster

When the fruitfly, Drosophila rtwlanogaster, was reared on media deficient in carotenoids and retinoids, the level of 3-hydroxyretinal (the chromophore of fly rhodopsin) in the retina decreased to < 1% compared with normal flies. The level of 3-hydroxyretinal increased markedly in flies that were given a diet supplemented with retinoids or carotenoids. The retinas of flies fed on all tram retinoids and maintained in the dark predominantly contained the all-tram form of 3-hydroxyretinal, and showed no increase in the level of either the 11-c/s isomer or the visual pigment. Subsequent illumination of the flies converted substantial amounts of all-tram 3-hydroxyretinal to its 11-c/s isomer. The action spectrum of the conversion by illumination showed the optimum wavelength to be ~420 nm, which is significantly greater than the absorption maximum of free, all-tram 3-hydrox), retinal. Flies that were fed on carotenoids showed a rapid increase of the levels of 11-cis 3-hydroxyretinal and of visual pigment in the absence of light.