Photoreceptor cells in animal eyes contain light-absorbing pigments derived from compounds called chromophores. These pigments are localized on densely packed layers of membrane within the photoreceptors. Assembly and ongoing turnover of the membranes and their photopigments may be crucial to features of vision such as light adaptation, but the role of turnover is not yet well understood. This project exploits special properties of the visual system of insects for attacking this problem. The hawkmoth Manduca develops from a larval caterpillar into an adult moth; if the larva has a diet deficient in chromophores (vitamin A-related compounds), the adult has severely impaired vision. Remarkably, simply "painting" the adult eyes with the compounds in a special solution has been found to partially restore visual sensitivity. This system now will be used to assess how the chromophore is synthesized into photopigment, how the chromophore and membranes interact, and how the photopigment is inserted into the membrane. Anatomical and biochemical methods will be used to examine the membrane ultrastructure, the localization of the photopigments, and the metabolism of chromophores. This preparation provides a novel approach to address a central issue in vision, and will yield useful information on nocturnal vision in an ecologically important group of insects.
